Saturday 30 January 2021

Chapter 13 Organisms and Populations








All organisms including plants depend on some sort of surrounding medium known as Environment. It is derived from the word “Environia” which means fo surround.

Environment is the sum total of all the physical and biotic conditions which

influence the responses of organism.


HABITAT: It is a specific place or locality occupied by an organism, population or



ECOLOGICAL NICHE: It is animals place in environment and its functional role in



ECOLOGY: It studies the interaction among organisms and between the organism

and its abiotic environment.


BIOLOGICAL ORGANISATION:It is the arrangement of smaller components into larger ones and so on ina hierarchy in which components of each level coordinate with one another.Ecology is concerned with 4 levels of biological organisation:

1. Organisms

2. Population

3. Community

4. Biomes


ORGANISM: It is the smallest level of Ecological hierarchy. Organisms show interdependence with biotic and abiotic factors of the environment.


COMMUNITY: It is the group of organism that lives together and interacts with each other within an environment. e.g. Pond, Forest, Lake.


BIOME: It is large Biosystem characterized by major vegetation and wildlife. It is

wide integrated natural units of living organisms. It also possesses the stages in

the development of the community.


There are five major types of biomes:

1. Aquatic

eg. Coral reefs, Estuaries, lakes etc.

 2. Grassland

eg. Eurasian steppes, North American prairies etc.

3. Forest

eg. Tiaga, Boreal forests etc.


4. Desert

eg. Sahara desert, Thar desert efc.


5. Tundra

eg. Alpine tundra, Arctic tundra etc.




1. Biological Organisation starts with:

a) Atomic level

b) Submicroscopic level

c) Cellular level

d) Organismic level


2. Large Biosystem characterized by wildlife and vegetation is:

a) Community

b) Population

c) Biome

d) Species


3. Functional role of species with reference to place of occurrence is called:

a) Habitat

b) Biome

c) Niche

d) Environment


4. Smallest level of Ecological Hierarchy is:

a) Population

b) Biome

c) Community

d) Organism


5. The interaction and interdependence of different populations in a biotic community is called:

a) Biome

b) Biocoenosis

c) Biota

d) Biosphere



1. The Natural home of an organism is ----------—.

2. Group of individuals in a geographical area is called ----—-----—-.

3. Arrangement of smaller components to a larger one is called----—--—-.



1. Sum of abiotic and biotic components of a geographical area is called biotic


2. Animals place in environment and functional role in an area is called Habitat.









1. Habitat

2. Population

3. Organisation


1. False (Environment)


2. False (Ecological niche)



Q.1 Define Population and Community.

Q.2 Name the physical components of a habitat.



Q.1 Explain the various levels of Biological Organisation.





Each of the major terrestrial ecosystems or distinctive terrestrial areas with their

group of climax plants and associated animals constitutes biomes.A TE is the largest terrestrial community. Rainfall, temperature range, nature of 

soil, barriers, latitude and altitude determine the nature and extent of biomes.


CLASSIFICATION: Biomes can be classified into two types, namely TERRESTRIAL and AQUATIC BIOMES.


Terrestrial biomes include grasslands, deserts, and tropical forests. Freshwater

biomes include polar freshwaters, large lakes, tropical and sub-tropical coastal

rivers, temperate coastal rivers and much more. Marine biomes include continental

shelves, tropical coral, and kelp forests.


MAJOR BIOMES OF WORLD: Biomes are often classified into following categories:


These tropical rain forests occur in Central America, around Amazon basin in

South America, in Africa and in South-East Asia including India. In India tropical

rain forests occur in Western Ghats, Assam and Andamans.Ps The tropical rain forest, a biome occurs in regions of high temperature (average 25°C) and high rainfall (200-450cm per year). This biome is characterized by multistoried vegetation (upto five distinct

layers or storeys of vegetation). Further maximum biodiversity on land is shown

by this biome and itis estimated that one half to two-thirds of all species of

terrestrial plants and insects live in tropical forests.

a: Life is abundant in this biome. It has different varieties and number of

plants and animals. 

Lianas (vascular plants rooted in soil and they only get support of trees for climbing to top) and epiphytes (air plants) are common in this biome due to

excess of moisture. The trees of this biome possess buttressed trunks and phenomenon of cauliflory (presence of flowers and fruits on main trunk and main branches) is common in this biome.


Each storey has different fauna. Giant trees of the tropical forest support a rich and diverse community of animals on their branches. (Upper storeys have birds, insects, bats, monkeys, lemurs, tree frogs, lizards and anteaters. Ground fauna includes many snakes, some lizards, deer, forest goat,

antelope, tapir, elephant, leopard, jaguar, etc.


 Like tropical forests, savannahs are found near the equator but in areas having

less annual rainfall (90-150 cm/year). Some areas near the equator experience

prolonged dry seasons. Savanna occurs in North Australia, India, Central and

Southem Africa including east- central S. Africa


a. The heat, periodic dryness and poor soils

cannot support a forest but have led to evolution of tropical open grasslands

with scattered shrubs and trees.


a. Savannah is named after dominant tree like Acacia, Phoenix,Eucalyptus. Availability of soil moisture determines composition and

productivity. Root system of grasses is present in upper 30cm of soil while

woody species penetrate to deeper horizons.


The vegetation of this biome support large grazing herbivores like buffalo, zebra, etc., which are food for carnivores like lions, tigers, etc. The savannah also supports a large number of plant eating invertebrates like mites,grasshoppers, ants, beetles and termites. The termites are one of the most

important soil organisms in savannahs.

Indian tropical grasslands are not true savannahs but these are the result of

destruction and modification of tropical deciduous forests by cutting, grazing

and fire.


It occupies about 1/5 of land. These are the biomes that have 25 cm (10 inches)

or less of precipitation annually .Most of these lie around tropic of Capricorn and

tropic of Cancer between 15°-35° latitude in both hemispheres. Sahara of North

Africa, Thar of West Asia and Gobi of Asia are most important deserts. Deserts

can be cold (Tibet, Gobi) and hot (Thar and Sahara). Deserts show poor biodiversity and their productivity is minimum.

a Annual plants are abundant in deserts and tide over unfavorable dry season in the form of seeds. Succulent plants are characteristics of deserts.Trees and shrubs present in deserts have deep roots. Desert plants show

phenomenon of Allelopathy, i.e., they secret some chemical substances which inhibit the growth of plants growing in their near vicinity.)f | Desert animals have also fascinating adaptations that enable them to

adjust with limited water supply.


BIOME 4 TEMPERATE GRASSLANDS:Temperate grasslands experience a greater amount of rainfall than deserts but a lesser amount than savannahs.Temperate grasslands have different names in different parts of the world, e.g.,Prairies of North America, Steppes of Russia, Veldts of South Africa, Pampas of South America, Pusztas of Hungary and Tussocks of New Zealand.Physical Characteristics: They occur at higher latitudes than savannahs but like

savannahs are characterized by perennial grasses and herbs of grazing mammals. There is hot summer, cold winter, seasonal 25-75cm rainfall.


grasses are dominant with non graminaceous herbs mostly leguminous (maintain nitrogen fertility of soil), scattered bushes and occasional trees.


Consists of Deer, Elk, Bison, Wolf, Prairie Dog, Bear, Bighom Sheep,Rabbit, Mice, Budges, Coyote, and Burrowing Owl.


It is found in both the northern hemisphere (Canada, eastern U.S.A. , north

central Europe, eastern Asia) and southern hemisphere ( New Zealand, eastern

Australia).Temperate deciduous forests occur in areas having warm summers, cold winters

and moderate amount of precipitation (75-150cm annually). The trees of this

forest loose their leaves during autumn and remain dormant throughout winter

(term ‘deciduous’ derived from Latin word meaning ‘to fall’).


temperate forest biome, there is an upper canopy of dominant trees like beech, oak, birch, maple, etc. followed by lower tree canopy and then a layer of shrubs beneath.


BE Animal life in this biome is abundant on the ground as well as on the trees. Animals include frogs, salamander, turtles, snakes, lizards, rabbits, hares,squirrels, opossums, foxes, raccoons, deer, bear,owls, sparrows and several song birds. In winter some animals undergo hibernation or migrate to warmer places.



The taiga or northern coniferous forests or boreal forests consist of evergreen,

cone bearing trees like spruce, hemlock and fir and extend across vast areas of

Eurasia, and North America.The taiga is characterized by long, cold winters with little precipitation. The harsh climate limits productivity of the taiga community. The cold temperatures,very wet soil during the growing season and acids produced by fallen conifers needles and Sphagnum inhibit full decay of organic matter, due to which thick layers of semi decayed organic material called peat is formed, which acts as

energy source. Life is fairly rich in this biome.


a: Dominant vegetation consists of evergreen conifers which are able to tolerate wide fluctuations of temperate, light and soil. They are Pine, fir,Hemlock, Spruce, Juniper, Yew, Larch, deodar. The ground flora consists

herbs, ferns, mosses and lichens. Vines and wild flowers are common.


Animal community of the biome is represented by mouse, wolves,otters, beavers, elks, deer, raven, rabbit hare squirrels, pumas, lynx, grouse and many species of insects, etc.


The Biome occurs in Mediterranean area, Pacific coast of North America,Chile, South Africa and South Australia.It is a broad leaved ever green shrub forest of hard and thick leaved small trees and shrubs which usually contain resin but are resistant to fire. It receives humid air from nearby oceans which also keeps the temperature moderate.The rainfall is during winter only.

GE = Both plants and animals are adopted to frequent and long periods of drought. The common plants of Chaparral are Arctostaphylos,Sage, Oak and Eucalyptus. Animals include Rabbits, Rats, Chipmunks,

deer, snakes, lizards, birds, tiger etc.


It lies north of timber line or 60° N Latitude below the polar ice. Tundra occupies

some 8 million km 2 area of land mass extending North America, Europe and Asia.

It occurs only in the Artic region therefore called as Artic tundra. It's absent in

southem hemisphere.


The area receives very little precipitation around 25 cm per year in the form of snow. The climate is therefore extremely cold. Strong winds and snow storms are frequent. Summer is for short duration of 45-75 days.

The highest summer tempura is 10°C. It is unable to melt snow except for the

upper 10-20 cm. The remaining part of the soil is in permanently frozen condition



Life: Both vegetation and animal life exist in this biome, though very scarce.

BE Vegetation is thin plants are shallow rooted. Mosses and Lichens show best development in the area. The other plants growing are grasses, sedges,heaths, a few shrubs, draft willows and draft birches. The plants posses xerophytic character.


WE Arthropods appear in summer. Common animals of tundra are warm-blooded and have protective covering like feathers and hairy skins. Main birds of tundra are snow owl and snow grouse. Important mammals of the areas are polar bear, arctic hare, arctic fox, musk ox, caribou, reindeer, arctic wolf and weasels.


INDIAN BIOMES: Indian forest are classified into three major types based on

temperature - tropical, temperate and alpine.



Marine Biome:Marine biomes incorporate the seas of the world, the biggest oceanic biomes,described by saltwater. Furthermore, seas have different layers identified with

daylight’s entrance.


Wet land Biome:Wetlands are shallow waterways, for example, lowlands, bogs, swamps, and mudflats. Also, they give the environment to numerous plants and creatures.

The water stream is enduring in freshwater wetlands. Example; The Bolsa Chica Ecological Reserve in Orange County, California.


Coral Reef Biome:Coral reefs exist in shallow pieces of some tropical seas. Made of calcified stays from coral creatures, these reefs develop after some time and give living space to numerous submerged species. For example, the Great Barrier Reef of Australia is an enormous case of a coral reef biome.


1. Which out of the following are the major biomes in India?

(i) Desert,

(ii) grassland,

(iii) tropical rain forest,

(iv) temperate forest,

(v) coniferous forest,

(vi) deciduous forest,

(vii) sea coast,

(viii) tundra

a. (ii), (iv), (vi), (vii)

b. (i), (ii), (v), (viii)

c. (i), (iii), (vi), (vii)

d. (ii), (iii), (vi), (viii)


2. Important key elements that bring about variations in the habitat are ?

a. Temperature, water, light and soil

b. Salinity, pollutants and water

c. Modern developmental parameters in the region.

d. Scientific progress and technological innovations.


3. Which of the following ability is present in the desert animals?

a. Ability to concentrate urine

b. Ability to remain inside the shelter and escape need of water

c. Ability to derive water from all the fruits.

d. Ability to absorb water from the air.


4. Which land biome is extremely cold and dry?

a. desert

b. tundra

c. grass land

d. mountains


5. Ponds and rivers are two types of:

a. Marine biomes

b. Rain forest biomes

c. Fresh water biomes

d. Estuary biomes


1. Coniferous trees are found in biome.

2. Grass is the primary vegetation of biome.

3. and are cold deserts.


1. Desert plant show phenomenon of allelopathy.

2. Termites are one of the most important soil organisms in savannahs.



1. (c) (i), (iii), (vi), (vii)

2. (a) Temperature, water, light and soil.

3. (a) Ability to concentrate urine.

4. (b) Tundra

5. (c) Fresh water biomes.


1. Taiga

2. Savannah

3. Tibet, Gobi.


1. True

2. True



1. Define Biome?

2. Whatis Allelopathy?



1. Classify terrestrial biomes along with their characteristic feature also mention

flora and fauna found in them.





ABIOTIC FACTORS are essentially what nature provides, including the Physical Geography of a place — Climate, Soils, and Water quantity determine the availability of nutrients, and the potential for food production.


DEFINITION:Abiotic factor is non-living part of an ecosystem that shapes its environment.

In Tarraoaetrial Eenevetam avamniac minht inclhiida Tamneratira | inht and \Alator





1. The average temperature on land varies seasonally, decreases progressively from the equator towards the poles and from the plains to the mountains tops.


2. Thermal springs and deep-sea hydrothermal vents are unique habitats where average temperatures exceed 1000° Celsius.


3. Temperature affects the kinetics of enzymes and through it the basal metabolic activity and other physiological functions of the organism.


4. Organisms which can tolerate and thrive in a wide range of temperatures, they are called Eurythermal Organisms.Example- cat, dog etc.


5. Organisms which can tolerate a narrow range of temperatures such organisms are called Stenothermal Organisms. Example- fish, reptile etc.



1. Life on earth originated in water and is unsustainable without water.


2. For aquatic organisms the chemical composition, pH of water is important.


3. The salt concentration varies in aquatic environment.


4. The salt concentration (measured as salinity in parts per thousand), is less

than 5 per cent in inland waters, 30-35 per cent the sea and more than 100 per cent in some hyper saline lagoons.


5. The organisms which can tolerate a wide range of salinities, they are called

Euryhaline Organisms. Example- the green crab.


6. The organisms which tolerate a narrow range of salinities, they are called

Stenohaline Organisms. Example- goldfish.



1. Plants are dependent on light to produce food through the process of photosynthesis.


2. Many plants are dependent on sunlight to meet their photoperiodic requirement for flowering.


3. Animals use the diurnal and seasonal variations in light intensity and duration

(photoperiod) as cues for timing their foraging, reproductive and migratory




1. Soil composition, grain size and aggregation determine the percolation and

water holding capacity of the soils, which along with parameters such as pH,mineral composition and topography determine the vegetation in any area.


2. In the aquatic environment, the sediment-characteristics often determine the type of benthic animals that can thrive there.




A. Multiple Choice Questions:


1. The natural habitat of tuna fish is:

a) Temperate ocean

b) Polar region

c) Sub temperate ocean

d) Tropical ocean


2. A majority of organisms are restricted to narrow range of temperature are called:

a) Stenothermal

b) Endothermal

c) Exothermal

d) Aerothermal


3. Some organisms that are tolerate to wide range of salinity are:

a) Stenohaline

b) Euryhaline

c) Osmoregulatory

d) Moonflower


4. The algae of following type inhibit the deepest ocean:

a) Brown

b) Green

c) Red

d) Blue green


5. Small animals are rarely found in:

a) Desert

b) Polar region

c) Air

d) Water


8. Fill in the Blanks:

1. Species that can tolerate narrow range of temperature are called .

2. The animals require sunlight for their and seasonal activities.

3. Species that can tolerate a high range of salinity are called .


c. True/False:

1. Most important ecological factor is light. ( )

2. Autotrophs require sunlight for photosynthesis. ( )



A. Multiple Choice Questions:






B. Fill in the blanks: -

1. Stenothermal

2. Euryhaline

3. Diverse


C. True/False: -

1. True

2. True



1. What are stenothermal animals?

2. What do you mean by abiotic factors?

3. What are the two categories of abiotic factors?



1. What are abiotic factors? Explain any 2 of them.





Our ecosystem is made of two components or factors. These are called Abiotic Components or Factors and Biotic Components or Factors.

Abiotic factors are nonliving factors, substances and conditions of the environment which influence survival, form function, behaviour and reproduction of organisms.

There are many abiotic factors. Out of them the four major abiotic factors are Temperature, Water, Light and Soil.

Here we will study two Abiotic Factors:

1. Temperature

2. Soil


1. TEMPERATURE:Temperature is a major ecological factor which influences the various vital activities of organisms. It is the degree of hotness and coldness. Factors

like latitude, altitude topography, slope and vegetation cause variation in temperature. There are large temperature variations in the biosphere.It ranges from sub-zero levels in polar areas and high altitudes to more

than 50°C in tropical deserts in summer.

Temperature gradient over earth's surface or lapse rate is 6.4 — 6.5 °C per 10° latitude or 1000m altitude.Animals have classified on the basis of their tolerance towards

tem perature.

Eurythermal organisms

Stenothermal organisms


Every organism has a specific range of temperature tolerance.The vertical temperature gradient over the surface of earth is known as Lapse Gradient.


Three different zones can be differentiated on the basis of temperature in each hemisphere:


Hot and torrid zones near the equator.

Moderate temperate zones in the middle.

Cold zones at the pole.

Each of these zones has specific populations of plants and animals.



There is a decrease in temperature with the increase in altitude which is mainly because of the convection currents in the troposphere.


2. SOIL:It is a very important ecological factor which is a natural medium for

growth of plants. It is an essential environmental component for the

existence of organisms including human beings.Pedology, the science of study of soil. The word Soil has been derived

from Latin word “Solum” which means earthy material for the growth and sustenance of plants.It not only provides a substratum for the attachment of plants but also supplies water and mineral nutrition to them.

Formation of soil takes place by the following processes:

Physical weathering

Chemical weathering


B. Mineralization and Humification:

Types of soil

Residual soil — Red soil and black soil

Transported soil — Alluvial soil, glacial soil, eolian soil, colluvial soil.

Soil water

Runway water

Gravitational water

Hygroscopic water

Capillary water


Water holding capacity:It is amount of percentage water retained by unit weight of dry soil.


Field capacity:It is the amount of water that remains in the soil after down drainage of

gravitational water.


Soil profile:The vertical section of a soil from its surface to unweathered rock exhibits

the presence if successive horizontal layers one after the other. These are as follows:


O01 region

O2 region






Soil temperature :Soil temperature in summer noons may go up between 50 to 67°C. Root

growth is healthier at temperature below 30°C and above 10°C.


Chemical properties of Soil:The colloidal particles of soil possess electronegative charge due to adsorption of excess of the charges. These particles have a tendency to

adsorb Cations on their surface to balance their negative charge.


Soil erosion:It is wearing away of fertile soil surface from its original place and its

deposition at some other place. Water and wind are two main climatic factors causing soil erosion:

Water erosion

Wind erosion


Soil conservation: means its judicious use and protection from erosion to maintain its productivity.


Following steps and practices help in conservation of soil:

Crop rotation and mixed cropping


Strip cropping

Contour farming in hills

Checking of overgrazing

Afforestation and reforestation




1. Multiple choice questions:


1. Removal of soil by action of wind and water is known as:

(a) Soil erosion

(b) Soil conservation

(c) Salination

(d) All the above


2. The pH of a fertile soil is usually around:

(a) 2-3

(b) 6 -7

(c) 8-10

(d) 11 -— 12


3. A soil is a mixture of:

(a) Sand and clay

(b) Sand and humus

(c) Clay and humus

(d) Sand, clay and humus


4. What is cold blood animals called?

(a) Homeotherm

(b) Poikilotherm

(c) Littoral

(d) Stenohaline


5. Organism that can tolerate a wide range of temperature is called:

(a) Eurythermal

(b) Mesotherms

(c) Stenothermal

(d) Stenohaline


2. Fill in blanks:

(a) Plants growing at very low temperature are called ..................

(b) The best soil for healthy and vigorous growth of the plant is................


3. True/False

(a) The incomplete decomposed organic matter left after mineralization is called humus.

(b) Red soils are poor in calcium, magnesium, nitrogen and phosphorus.

(c) Black soil is also called as black cotton soil.



a) Multiple choice questions:


1. (a)

2. (b)

3. (d)

4. (b)

5. (a)


b) Fill in blanks:

1. Hekistotherms

2. Loamy soil



c) True/False:

1. True

2. True

3. True



1. What are the important features of well aerated soil?

2. What harms are caused by soil erosion?

3. What is the main reason for temperature decrease with increasing altitude?



1. Describe the soil profile and composition of its various horizons.





BIOTIC FACTORS:Dear students, you know that our ecosystem is made of two components

or factors. These are called Abiotic Components or Factors and Biotic Components or Factors .Here we will study BIOTIC FACTORS.


Living organisms present in an ecosystem are called BIOTIC FACTORS.These are Bacteria, Fungi, Protists, Plants and Animals. So there are different types of living organisms present in an ecosystem.They are linked with each other through food and web of other relations.Food provides energy for body functioning and materials for building the

body.So on the basis of mode of taking food Biotic Factors are of three types:-




4. Some other HETEROTROPHS


1. PRODUCERS:-Those organisms which are able to prepare their food from inorganic raw

material for themselves and also for other biotic components of ecosystem are

called producers.

They are also called Autotrophs.

Autotrophs obtain energy from solar radiations for photosynthesis and are also

called Photoautotrphs.


Photoautotrophs convert solar energy into chemical energy therefore, they are

also called Transducers.


Solar energy is used in converting inorganic raw material into organic compounds like carbohydrates, proteins, lipids ete.


The producers also maintain COz and O2 balance in ecosystem.


6CO2 +6H20 ---—--> CsHi206 +602

Green plants, algae, algal protists, cyanobacteria, phytoplanktons etc. are

examples of biotic components.


2. CONSUMERS:Those organisms which obtain their food from other organisms are called



They are also called Phagotrophs because their mode of obtaining food is



Animals, insects, protists, fish,snakes, birds etc.are consumers.


Consumers are of following types:-

|. Primary or First order consumers

ll. Secondary or second order consumers

lll. Tertiary or Third order consumers

IV. Top carnivores


|. Primary or First order consumers:- These animals directly feed on producers are also called HERBIVORES.E.g. Protozoan protists, mosquito larvae,tadpoles,caterpillars, rat, hare,cattle, insects,butterflies etc.


ll. Secondary or second order consumers:- Those animals which feed upon (prey on) herbivores are called secondary consumers.

They are also called Primary Carnivores. E.g. water insects,Hydra,frog, spiders, insectivorous birds,snakes, fox,wild cats etc.


lll.Tertiary or Third order Consumers: - Those animals that feed upon primary carnivores are called Tertiary Consumers.

E.g. larger fishes feeding on small fish,wolf feeding on fox, snakes feeding on

frog etc.


IV.TOP CARNIVORES: - The carnivores which are not eaten by any other organisms are called top carnivores. They may belong to the category of primary, secondary or tertiary carnivores.E.g. tiger,lion,falcon, panther etc.


They are saprotrophic micro-organisms which obtain nourishment from organic remains.


They pour their digestive enzymes on organic remains.


Extracellular digestion takes place and organic remains are degraded or dispossed off completely.


During this process inorganic minerals are liberated, therefore decomposers are also called mineralisers.


4. Some other HETEROTROPHS:-

Scavengers or Detrivores:-They feed on corpses (dead bodies),e.g.Vultures, Carrions beetle.


Parasites :- They get their nourishment

from other living host that may be all

categories of organisms.Parasites are Bacteria, Fungi, Protozoa,Round worms,Flat worms,some insects etc.



Multiple choice questions:


1. Those organisms which are able to produce their food themselves are called-

(a) Producers

(b) Autotrophs

(c) Photoautotrophs

(d) All the above


2. The organisms that obtain their nourishment from organic remains are


(a) Carnivores

(b) Detritivores

(c) Decomposers

(d) Producers


3. Photoautotrophs convert solar energy in-

(a) Chemical energy

(b) Electrical energy

(c) Mechanical energy

(d) None of the above


4. Falcon belongs to the category of-

(a) Primary carnivore

(b) Secondary carnivore

(c) Tertiary carnivore

(d) Top carnivore


5. In deep aquatic ecosystems, main producers are floating minute autotrophs called-

(a) Phytoplanktons

(b) Herbivores

(c) Zooplanktons

(d) Carnivores


Fill in blanks

(a) Transducers convert solar energy into ................during photosynthesis.

(b) ...............0btain their nourishment from HOST (living organisms)and

harmful to HOST also.



(a) Biotic factors are living components of ecosystem.

(b) Scavengers or Detritivores feed on corpses.

(c) Decomposers degrade organic remains into inorganic nutrients.



Multiple choice questions-


1. (a) Green plants are autotrophs.

2. (c) Detrivores convert organic remains into inorganic nutrients.

3. (a) Chemical energy is stored in organic molecules.

4. (d) Falcon is top carnivore

5. (a) These are aquatic microorganisms.


Fill in blanks:

1. Chemical energy

2. Parasites



1. True

2. True

3. True



1. What is difference between Decomposers and Detritivores ?

2. What are Parasites?

3. What are Photoautotrophs?



1. Explain different types of Consumers with two examples each ?








POPULATION:Dear students, we rarely find isolated individuals of any species in nature,but majority of them live in groups in a well-defined geographical area, share or

compete for similar resources which can potentially interbreed. Such groups

make population.


A number of populations of different species are present in a biotic community. All of them do not interbreed with one another. Breeding occurs only among the individuals of same population. Also breeding term implies the sexual reproduction but the organisms resulting from asexual reproduction are also

considered population for ecological studies.



Cormorants in a wetland

Rats in an abandoned dwelling

Teakwood trees in a forest tract

Lotus plants in a pond


POPULATION ATTRIBUTES:A population has certain attributes (characteristics) which an_ individual organism does not have. An individual can be male or female, but the population has sex ratio. An individual may have birth or death, but the population as whole has birth rate and death rate. So, population has group Attributes such as

Natality, Mortality, sex ratio, density, dispersal, age distribution and growth forms etc.


1.NATALITY RATE (BIRTH RATE) :It is defined as the number of individuals added in a unit of population due to births of new young ones. In case of humans, it is expressed as the number of births per 1000 persons per year in the population. The birth rate is expressed as change in numbers with respect to actual population.For example, in a pond there were 20 lotus plants last year and 8 new plants are added by birth of new plants. So, birth rate will be 8/20=0.4 new plants or

40% per lotus plant per year.


2. MORTALITY RATE (DEATH RATE) :The number of natural deaths in a unit of population per unit time is called mortality rate. In animals the death rate is counted per 100 individuals where as In case of humans, it is expressed as the number of deaths per 1000 individuals per year in the population. The death rate is also expressed as change in numbers with respect to actual population.

For example, If four individuals in a Laboratory population of 40 fruit

flies died during a specified period say a week, So, the death rate in the population

will be will 04/40=0.1 individuals per fruit fly per week.


3. SEX RATIO:The sex ratio of a population is the ratio of males to females per thousand

individuals in a population. In case of humans Generally the sex ratio is depicted as

number of females per thousand males. In case of Animals, males and females are usually equal in numbers but the ratio is greatly disturbed in case of humans due to

human intervention in natural process of reproduction.According to 2011 census the sex ratio of Punjab is 895 females with respect to 1000 males and that of Haryana was 879 females w.r.t.1000 males which was much

less in comparison to national sex ratio of 940 females w.r.t 1000 males


4. AGE DISTRIBUTION:The age distribution is also an important feature of population A population at any given time is composed of individuals of different ages. If the age distribution (percent individuals of a given age or age group) is plotted for the population the resulting structure is called an AGE PYRAMID. Following pyramids show the age distribution of males and females for human population. —


The ratio of various age groups in a population determines the current reproductive status of the population. In 1958 the ecologist Bodenheimer divided these age groups as pre -reproductive, reproductive and post -reproductive age groups.Pre-Reproductive Individuals: - These are young individuals who will enter the reproductive age after some time. Generally, a rapidly expanding population contains a large number of pre-reproductive (young) individuals.


Reproductive Individuals: - These individuals are those which add new individuals to the population. In a stable population the number is equal to pre reproductive individuals. A stable population has a small number of

pre -reproductive individuals and shows zero growth.


Post-Reproductive Individuals: - These are the older individuals who do not take part in reproduction. A declining population has larger number of older individuals to the population.


5. POPULATION DISPERSAL:It is defined as the movement of individuals into and out of an area during their life this results in the change in the size of population. The dispersal in population helps in far distribution of organisms, protection from extreme hot and cold seasons, protection from predators and invaders. Dispersal occurs by three ways: -





MIGRATION: - It is a process of regular and usually seasonal movement of a part

or whole population to and from an area. Many birds, fishes, reptiles, amphibians, and

insects migrate from their native area to other parts. It is done to escape from

unfavourable conditions


EMIGRATION: - It is the permanent departure of individuals from a population for

settlement into new area. Emigration occurs in animals to save them from natural

calamities. Emigration also occurs to cope with scarcity of food and shelter.In case of human beings, we see Many Indians go to western countries to settle there, that is emigration.


IMMIGRATION: - It is the permanent entry of individuals from outside into an existing population. In animals’ immigration occurs due to availability of better food and shelter facilities.In case of human beings, we experience of a number of examples

of natives of Uttar, Pradesh Bihar and Nepal which immigrate to Punjab and other

states of India.


6. POPULATION DENSITY:The number of individuals of a population present per unit area is called density. If the total number of individuals is represented by letter ‘N’ and space is represented letter ‘S’ then population density D=N/S.


The term Population size is technically known as population density


The size of population tells about its status in the habitat.


The action of predator or the effect of pesticide application can be viewed by

the poplation size.


Absolute density or total counting can be one by countig of all individuals of a



Counting can be indirect as the tiger census in our national parks is based on pug marks and faecal pellets.


Number of fish caught per trap is used as a mearure for estimating ththe population density of fish in a lake


Population density is never static, rather it is dynamic and always changing


Environment resistance, ,food availability, predationpressure,weather and group properties have a direct impact on population density




The size of a population for any species is not static parameter


It keeps on changing with time, depending on various factors such as food availability, predation, pressure and adverse weather conditions.


The changes in population density give us an idea that whether the population is flourishing or declining


The increase in the size of a population over a period of time is called Population Growth


Population density in a given habitat fluctuates due to changes in four basic



Two processes (Natality and immigration) contribute to an increase in population density


Two processes (Mortality and Emigration) contribute to a decrease in population density


If Nis the population density at time t, its population density at time t+1 is Ne =Net+[(B+1)-(D+E)Where Natality----B, Immigration-—-I, Mortality—-D, Emigration---E




Let’s know what we have learnt!


A. Multiple choice questions:

1. The average number of new individuals added per unit population due to birth of new young ones is called as:

(a) Natality rate

(b) Birth rate

(c) Mortality rate

(d) Both (a) and (b)


2. The diagrammatic representation of age distribution is called as:

(a) Bar graphs

(b) Pie chart

(c) Age Pyramids

(d) None of the above


3. The population with older (post reproductive individuals)

(a) Stable population

(b) Expanding population

(c) Declining population

(d) Static population


4. The seasonal movement of Siberian Cranes to a suitable habitat is:

(a) Immigration

(b) Migration

(c) Emigration

(d) Mitigation


5. The tiger census in our national parks and tiger reserves is based upon:

(a) Actual counting

(b) Counting of pug marks

(c) Counting of faecal pellets

(d) Both (b) and (c)


B. Fill in blanks:

(a) Generally, sex ratio in case of human beings is expressed as number of

females per ................ males.

(b) The poplation size can be viewed by -------------- or the effect of pesticide

application .


C. True/False:

(a) A single population lives in a biotic community.

(b) Expanding population has more number of pre- reproductive Individuals.

(c) Immigration decreases the population density whereas Emigration increases the population density.



A. Multiple choice questions:

1. (d) Natality rate and Birth rate

2. (c) Age Pyramids.

3. (c) The population in which a greater number of post reproductive

individuals is called Declining population

4. (b) Migration

5. (d) counting of pug marks and faecal pellets


B. Fill in blanks:

1. 1000 males

2. Action of predator


C. True/False:

1. False

2. True

3. True



1. Define population?

2. What are Population attributes?

3. Define natality rate and mortality rate.

4. Name ecological ages. What are age pyramids?

5. Define immigration, emigration, and migration.

6. What is population density?

7. Write the formula for population density or population growth.




1. Explain different population attributes?

2. With diagrammatic representation explain; population density, natality,mortality, immigration, emigration. Also write formula for population density.






Population is a group of individuals living in a well-defined geographical area,

share or compete for similar or compete for similar resources and potentially

interbreed, constitute a population e.g. All cormorants in a wetland, rats in an

abandoned dwelling, teakwood trees in a forest, bacteria in a culture plate and

lotus plants in a pond. Although the term interbreeding means sexual reproduction

but a group of individual resulting from even asexual reproduction is also considered population for the purpose of ecology. Although an individual organism is the one that has to cope with a changed environment but natural selaction operates at population level to evolve the desired traits.


Population Growth: Density of population in a given habitat during a given period, fluctuates due to changes in following four basic processes :


(i)Natality (B):It is the number of births during a given period in the population

that are added to initial desnsity.


(ii)Mortality (D):It is the number of deaths in the population during a given period.


(ii) Immigration (I): It is the number of individuals of the samespecies that

have come into the habitat fromi elsewhere in a given period


(iv) Emigration (E) =it is the number of individuals of the population who left

the habitat and gone elsewhere during a given time period.

Natality and immigration cause increase in population density.Mortality and emigration cause decrease in population density.If N, is the population density at time t, then its density at time t+1 is Nui = Nit {{B+ 1)-(D+E)]From the above equation it is clear that population density will increase it number of births plus the number of immigrants.(B+1) is more than the number of deaths plus the number of emigrants (D+E),

otherwise it will decrease.Under normal conditions, births and deaths are the most important factors which influence population density.Other two factors become important only under special conditions e.g. if a new

habitat is just being colonized, the population is growing more by immigration

than by birth rates.


Growth Models: Growth of a population with time show specific predictable


pattern:Exponential growth:When resources (food and space) in the habitat are

unlimited, each species has the ability to realize fully innate potential to grow in

number (Biotic potential), Darwin observed this while developing theory of natural selection. Then population grows in an exponential of geometric fashion.If in a population of size N, the birth rates are represented as b and death rate as d, then the increase or decrease in N during a unit time period t will be = dN= (b-d) x N, Let (b-d) = r then dN= rN.dt dt The r in the equation is called ‘intrinsic rate of natural increase’. It is very important parameter chosen for assessing the impacts of any biotic or abiotic factor on population growth. Magnitude of r value for Norway rat is 0.015, for flour beetle=0.12. In 1981, the r value for human population in India was

0.0205. The above equation describes the exponential or geometric growth pattern of a population. It results in a J-shaped curve when we plot N in relation to time. The integral form of exponential growth equation is as follows:

N= Noe™

N: = population density after time t

No = population density at time zero.

r = intrinsic rate of natural increase.

e = the base of natural logarithms (2.71828)


The equation describes the exponential or geometric growth pattern of a population and result in a J- shaped curve of exponential growth is characteristic of some population that are introduced into a new or unfilled

environment or whose numbers have been drastically reduced by a catastrophic

event and are rebounding.Any species growing exponentially under unlimited resource conditions can reach enormous population densities in a short time.


Logistic qrowth: No population of any species. in nature has at its disposal unlimited resources to permit exponential growth. A population growing in a habitat with a unlimited resources show initially a lag phase, followed by phases of acceleration and deceleration and finally an asymptote, when the population density reaches the carrying capacity. A plot of N in relation to time


(t) results in a sigmoid curve. This type of population growth is called Ver hulst -

Pearl Logistic Growth . It is described by following equation:dN/dt = rN (K-N/K), Population density at time t. r = Intrinsic rate of natural increase, K= Carrying capacity.


Resources for growth for most animal population are finite and become limiting

sooner or later. So logistic growth model is considered more realistic one.


Biotic Potential : Biotic potential is the natural capacity of a population to

increase at its maximum rate (It is not dependent on environmental factors).

Environmental Resistance: The sum of the factors which prevent a population from reproducing at its maximum rate.


Carrying Capacity : Carrying capacity is the environment's ability to provide necessary resources to support a population.Exponential model does not have carrying capacity because responses are not limiting the growth plot.






1. Which of the following parameter is not a part of population growth?

(a) Natality

(b) Mortality

(c) Metapopulation

(d) Emigration


2. In growth pattern, (1-N/K) is:

(a) Carrying capacity

(b) Intrinsic rate of natural increase

(c) Environmental resistance

(d) Biotic potencial


3. Exponential population growth is

(a) dn/dt = rN

(b) dt/dN = rN

(c) dN/rN = at

(d) rN/dN = dt


4. The density of a population in a given habitat during a given period,fluctuates due to changes in four basic processes On this basis choose the correct option to fill up A and B boxes in the given diagram.

(a) A = Natality +lmmigration. B = Mortality+ Emigration

(b) A=Natality + Mortality, B= Immigration +Emigration

(c) (c) A= Birth rate+ Death rate, B= Mortality + Emigration

(d) A=Natality +Emigration, B =Mortality + Immigration


5. Identify Ito 1V which affect the population density:




1. is the number of individuals of the population who left the habitat and gone elsewhere during the time period under consideration.

2. The formula for Logistic Growth are.

3. The two basic processes which contribute a increase in population density are




1.The integral form of the exponential growth equation is N; = No e*. (T/F)

2. Organisms with very high intrinsic growth rates have long generation times.(T/F)

3. In exponential growth, the increase or decrease in population size during a unit

period is N x (b-d). (T/F)




1. c Metapopulation

HINT : Population growth is the increase in the number of individuals in a population.

Natality, Immigration, Mortality and Emigration are the process which effects the

density of population in a given habitat during a given period of time. The former two

processes contribute an increase in population density whereas the latter two

processes toward decrease.


2. c Environmental Resistance

HINT: In growth pattern, environmental resistance (1-N/K) is the action of limiting

abiotic and biotic factors that prohibit the growth of a population as it would grow

according to its biotic potencial.


3. a dN/dt = rN

HINT:The population grows in an exponential of geometric fashion. If in a population of

size N, the birth rates are represented as b and death rate as d, then the increase or

decrease in N during a unit time period t will be:= dN= (b-d) x N, Let (b-d) =r then dN= rN.dt dt


4. (a) A= Natality +Immigration. B = Mortality+ Emigration HINT: It is the number of births during a given period in the population that are added to initial desnsity.


It is the number of deaths in the population during a given period.


Itis the number of individuals of the samespecies that have come into the habitat fromi elsewhere in a given period.


It is the number of individuals of the population who left the habitat and gone

elsewhere during a given time period.


5. (c) Increase Increase Decrease Decrease

HINT: According to the given figure, |. Il. Ill. And IV (which affects the basic process of population density) are respectively Increase. Increase. Decrease and Decrease.




1 Emigration HINT: It is the number of individuals of the population who left the habitat and gone elsewhere during a given time period.


2. dN/dt = rN [ kw/«] HINT: A population growing in a habitat with an unlimited

resources show initially a lag phase, followed by phases of acceleration and

deceleration and finally an asymptote, when the population density reaches the

carrying capacity. A plot of N in relation to time (t) results in a sigmoid curve. This

type of population growth is called Ver hulst - Pearl Logistic Growth . It is described

by following equation: dN/dt =r N (K-N/K), Population density at time t. r = Intrinsic

rate of natural dt increace capacity.


3. Natality and immigration. HINT: — . It is the number of births during a given period in the population that are added to initial desnsity.It is the number of individuals of the samespecies that have come into

the habitat fromi elsewhere in a given period.



1.TRUE HINT: The integral form of exponential growth equation is as follows:

Ni = Noe™

N: = population density after time t

No= population density at time zero.

r = intrinsic rate of natural increase.

e = the base of natural logarithms (2.71828)


The equation describes the exponential or geometric growth pattern of a population and result in a J- shaped curve of exponential growth is characteristic of some population that are introduced into a new or unfilled environment or whose numbers have been drastically reduced by a catastrophic event and are rebounding.


2. FALSE HINT: The intrinsic rate of increase is inversely related to generation time, T. Therefore, organisms with very high intrinsic growth rates have short generation times.


3. TRUE HINT: In exponential growth, the increase or decrease in population size

during a unit period is N x (b-d).



1. What is “carrying capacity” of a species in a habitat? Why logistic growth model is

considered more realistic?

2. Write difference between population size and population density.

3. Explain Natality and Mortality.



1. Draw and explain a Logistic curve for a population of density (N) at a time (t)

whose intrinsic rate of natural increase is (r) and carrying capacity (K).





Adaptation is a quality of the organism that enables them to become better suited to the changing environment. Plants adapt or adjust to their surroundings. This helps them to live and grow.


You would not see a cactus growing in Iceland nor would you see tall trees in

grasslands. A tree that lives in the rainforest would die in a desert area. A cactus that lives in the deserts would not survive in a water lily pad. Thus plants adapt to their surroundings and climates. If the habitat changes drastically the plant species must adapt, otherwise they would not survive.


There is different ecological adaptation of plants like morphological,physiological or behavioural.



The following are the ecological adaptation of hydrophytes:

1. They have extensive air spaces in their leaves stems and roots.

2. Epidermis usually lacks cuticle

3. They have reduced vascular elements

4. Mucilage prevent the decays of plants in the water

5. Water is absorbed by the entire plant surface



Mesophytes do not have any specific morphological adaptation

1. They usually have broad ,flat and green leaves

2. They have a extensive fibrous roots system to absorb water

3. They have ability to develop perennating organs such as corns ,rhizoms and water for use during drought.



1. Root system is well-developed

2. Stem is usually green and is covered with thick cuticles, wax and it is covered with dense hairs.

3. Leaves usually absent and are modified into spines or scales

4. Sunken stomata are present

5. Many xerophytes show CAM ( crassulacean acid metabolism) cycle

6. Seeds are with thick and coat for protection




a) MCQs

1. Waxy coating on the surface of floating leaves prevents :-

a) Respiration

b) Photosynthesis

c) Clogging of stomata

d) Transpiration


2. Air spaces are present in leaves stem and roots is characteristic feature of

a) Hydrophytes.

b) Mesophytes

c) Xerophytes.

d) Heliophytes


3. Which one are xerophytes?

a) Rose.

b) Lotus

c) Casuarina

d) China rice


4. Xerophytes are mostly:

a) Succulents.

b) water-related

c) Mesophytes

d) None of these


5. Plants that prefer area with high moisture content:

a) Hydrophytes.

b) Mesophytes

c) Xerophytes.

d) Halophytes


b) Fill ups

1. The plants protects themselves from extremes of temperature

2. prevents the decay of plant body in water.

3. Rhizoms and bulbs are adaptation of plant.


c) True/False

1. Sunken stomata are present in mesophytes.

2. In xerophytes CAM cycle is present.










b)Fill ups:

1. Xerophytes

2. Mucilage

3. Mesophytes



1. False (It present in mesophytes)

2. True



1. What are the adaptations of plants to water scarcity?

2. What are adaptations?

3. What is significance of adaptations?



1. Compare the differences of mesophytes, hydrophytes and xerophytes?






The adaptations are the useful morphological, physiological or behavioural changes developed in living organisms over a long period of time to adjust, itself according to a particular environment. The adaptations make the organisms more fit to its environment and increase their chances of survival and reproduction for the continuation of race.Following adaptations occur in animals:




Some animals brings changes in their morphology or anatomy for thermo regulation as evident from following rules -

a-Jorden’s rule — The fish found in water of low temperature tend to have more vertebrae than those of warmer waters

b-Gloger’s rule- The mammals, birds and insects of tropical region are more darker in colour and heavily pigmented than those of arctic region.

c-Resch’s rule — The birds of colder regions tend to have relatively narrow wings than the birds found in warmer areas

.d-Bergaman‘s rule — The birds and mammals of cold regions are large sized than those of warmer region.


Allen’s rule — The tail snout, pinnae of ears and legs of mammals are relatively shorter in colder part than in the warmer parts. The pinnae of desert fox are largest sized while those of red fox are small sized and those of arctic fox are the smallest in size.


2- Polar bear and polar sea animals like seals have a thick layer of fat called

blubber in their subcutaneous zone of skin. The blubber acts as insulator and reduces the loss of body heat.


B- ADAPTATIONS FOR OSMOREGULATION:The desert animals face the problem of scarcity of water they develop different methods for either moisture getting or moisture conversation. Camel has water cells in wall of its stomach to store metabolic water formed during the biological breakdown of fats stored in its hump. Kangaroo rat depends on metabolic water

produced during its fat oxidation.


C- PHYSIOLOGICAL ADAPTATIONS-These are those adaptations which enable the organisms to respond quickly to a stressful situation .The person living in planes have ever gone to hilly area, start suffering from high attitude sickness characterized by nausea, fatigue, heart palpitation due to less availability of oxygen.


D- BEHAVIOURAL ADAPTATION -These are those adaptations which are shown by certain organisms in their behaviour to protect themselves from a stressful situation. Desert lizards bask in sun to absorb heat radiations and increase its body temperature in cold conditions


BIOCHEMICAL ADAPTATIONS —These are those adaptations in the biochemical reactions and the enzymes controlling such reactions which enable them to live in the extreme environment .Marine invertebrates and fishes live at great depths in ocean where pressure could be hundred times than normal conditions.




A- Multiple choice questions:


1) According to Allen’s rule, the mammals from colder climates have

(a) Shorter eras and longer limbs

(b) Longer ears and shorter limbs

(c) Longer ears and longer limbs

(d) Shorter ears and shorter limbs


2) According to Gloger’s rule mammals, birds and insects of tropical region

(a) More darker in colour

(b) More lighter in colour

(c) Sometimes darker and sometimes lighter

(d) All of theses


3) Which of following animal depends on metabolic water produced during its fat oxidation?

(a) Kangaroo rat

(b) Snail

(c) Fish

(d) Polar bear


4) Choose the correct option:

(a)Adaptations increase the chances of survival

(b)Adaptations decrease the chances of survival

(c)Adaptations do not affect chances of survival

(d) Adaptations rarely affect chances of survival


5) Which of following animal bask in the sun to absorb heat radiations?


(b) Desert lizard

(c) Camel

(d) Kangaroo rat


B — True / False:

a) Adaptations make the organisms more fit to its environment.

b) According to Jorden’s rule fishes found in water of low temperature tend to have less vertebrae than those of warmer water.

c) Desert animals face the problem of scarcity of water.


C -Fill in the blanks:

a) Polar bear have a thick lair of fat called -------- in their subcutaneous zone of skin.

b) ---------- has water cells in wall of its stomach to store metabolic water.



A) Multiple choice questions:

1- (d) Shorter ears and shorter limbs

2- (a) More darker in colour

3- (a) Kangaroo rat

4- (a) Adaptation increase the chances of survival

5- (b) Desert Lizard


B) True / false:

a) True

b) False

c) True


C) Fill in the blanks:

a) Blubber

b) Water





1) Write a short note on biochemical adaptation?

2) Give examples of osmoregulation adaptation?

3) What are physiological adapation?



1)Describe Allen’s rule with example?





Species interactions refers to direct and indirect interrelationship or association between different organisms, which could be between different organisms, which could be between:

Plants and plants,

Plants and animals and

Animals and animals as well as micro-organisms like bacteria, fungi and the like



Among different species there is a struggle for living ,|nabitat food, for survival in nature. Animals,plants and microbes cannot live in isolation but interact in various ways to form a biological community. Even in minimal communities many interactive linkages exist although all may not be readily



Even a plant species which makes its own food cannot survive alone, it needs soil microbes to break down the organic matter in soil and return the in organic nutrients for absorption.Pollination also need agents for dispersal.Interspecific interactions arise from the interaction of populations of two

different species. They could be beneficial, detrimental or neutral( neither harm nor benefit) to one of the species or both, assigning’ +' sign for beneficial interaction and '_' for detrimental and’ 0' for neutral interaction.Let us look at all the possible outcomes of interspecific interactions.




In mutualistic relationship, two organisms of of different species work together for the benefit of each other.

1) The ox pecker(a bird) sits on back of rhinoceros and feeds on its skin ectoparasites. Bird gets the food and rhinoceros is relieved of the parasites


2) Pollination of flowers by insects. Insects gets nectar and pollens as food while for plants its important for continuity of race


3) Lichens involve the symbiotic association between a green algae (phycobiont) and a fungus (mycobiont). algal cells photosynthesize and make food, while fungal hyphae provide moisture and minerals to algal cells.


4) Mycorrhizae involves symbiotic association between a fungus (mycobiont)and higher plant (phycobiont). The roots provide carbohydrates and shelter while fungus helps in absorption of water and minerals.



Simplest interspecific positive interaction, in which small member called commensal is benefitted and larger member called host is niether benefitted nor harmed.


Example: Epiphytes, also called space parasites, grow perched on other plants, use host for support and ‘not’ for water or food supply.


Fig:-3 Example of Commensalism: Epihytic roots of Vanda

In epiphytes, there is a special tissue called velamen,over the root surface

which can take up water from the atmosphere. Money plant grow as epiphyes and orchids also.



In predation, larger species called predator, attacks, kills and feeds on the smaller species called prey.Example; Insectivorous plants, lion eating a deer, cat attacking a mouse.



In a parasitic relationship smaller partner, called parasite, derives food and

shelter from the body of larger partner called host and inhibits survival of the



Example tapeworms fleas and branches.

The fleas harm their hosts such as dogs by biting their skin sucking their blood and causing them to itch.


Tapeworms attach themselves to the inside of the intestine of animals such as cows pigs and humans.



In this interaction, two or more members of same species or different species of same trophic level compete for a common resource like light, moisture,nutrients etc, which are in short supply.


So, both the interacting species are harmed.

The example of competition is a colony of bees birds and protect a Hive together or microbes compared for chemical substrate.



It is biological interaction among two species where one is destroyed or inhibited and other remains unaffected.

Example: Formation of antibiotics that are antagonistic to microbes. Mould Penicillium secretes penicillin that ultimately kills bacteria.


Part A) Very short answer type questions :-

Multiple choice questions.


Q-1) interspecific competition is also known as

a) allelopathy

b) interference competition

c) scramble competition

d) none of these


Q-2) In commensalism

a)Both partners harmed

b)Both partners are benefited

c)None of the partner benefited

d)Weaker partner is benefited


Q-3) The relationship between climber and host it is an example of

a) Mutualism

b) commensalism

c) parasitism

d) neutralism


Q-4) When food is obtained by killing of host in which the stronger partner is benefited and host is damaged it is

a) competition

b) antibiosis

c )predation

d) Parasitism


Q-5) Bread mould penicillium secretes penicillin that kills

a) Bacteria

b) virus

c) fungi

d) algae



Q-6)Animals and plants can live in isolation.

Q-7) In mutualism both organisms are beneficial for each other.

Q-8) in commensalism one organism is  benefited and other is neither harmed not benefited.


Fill inthe blanks: -

Q-9) Pollination needs ........ for dispersal of seeds.

Q-10) in amensalism one species is destroyed and other remains.........


Part B) short answer type questions.-

Q-1) write two examples of parasitism.

Q-2) write a note on predation.

Q-3) define competition.


Part-C) Long answer type questions:-

Q-4) what are interspecific interactions? Write main types of




Multiple choice questions


ANS 1} — (b) Interference competition

ANS 2} = (d)weaker partner is benefited : while the other one is niether harmed nor benefitted

ANS 3} —_(b) Commensalism : As climbers are space parasites and do not derive food and water from the host.

ANS 4} — (c) predation :The stronger partner is the predator and weaker one is prey.

ANS 5} = (a) bacteria : The fungus secretes antibiotic that kills bacteria and the interaction is called ammensalism.



ANS 6)- ‘False : They can not live in isolation because they interact with each other is one or other way.

ANS 7)- True

ANS 8)- True


Fillinthe blanks

ANS 9) agents

ANS 10) Unaffected.






In nature animals, plants and microbes cannot live in isolation. They interact with each other in various ways.Positive interactions are those interspecific interactions in which either one or both the interacting species are benefitted but neither is harmed.

these are assigned '+' sign.Positive interactions are of following types:


1. Mutualism (obligatory)

2. protocooperation (facultative)

3. commensalism


MUTUALISM (+/+,obligatory)It is the interaction in which both the members favour the growth and survival of each other.

The examples are:

Lichens - an intimate relationship between fungus and algae.fungus absorbs nutrients for algae which prepares food for fungus.


Mycorrhizae- association of fungus with roots of higher plants.The fungus help the plants in absorption of nutrients which in turn

provide the fungus with energy rich compounds.


Pollination of flower by insects - the insect gets nectar and pollen as food while the plant gets pollinated.


Trichonympha (protozoan) is a symbiont in the intestine of white ant (termite). The ant provides food and shelter to the protozoan

which in turn secretes cellulase enzyme the cellulose of wood ingested by the ant.

It is a Kind of positive interspecific interaction in which both species

are benefitted but the association is optional.


Crocodile and bird association:

The crocodile bird enters the opened mouth of crocodile and eats the leeches. So the bird gets the food while the crocodile is relieved of sanguivorous parasites.

 Hermit crab and Sea anemone association


Tick bird — Rhinoceros


The tick birds sits on the back of rhinoceros and feeds on its skin ectoparasites such as lice, ticks , mite, etc. The bird gets food and rhinoceros gets relief from sanguivorous parasites.



It is the interaction in which one species is benefitted and the other is neither harmed nor benefitted.The species which gets benefit is assigned a ‘+’ sign.The species which is neither harmed nor benefitted is assigned ‘o’ sign.The examples are:


Epiphytes, also called space parasites, grow perched on other plants,use host for support and ‘not’ for water or food supply. Eg: Orchids growing on mango tree, Money plant is also a space parasite


Barnacle growing on the back of a whale.


Sea anemone and clown fish. The clown fish gets protection from predators by tentacles of sea anemone but the sea anemone gets no





Part A: Very Short Type Question Answer:



1. Which sign is assigned to interacting species in mutualism?

(a) A(+) B(+) =

(b) A(+) B(-)—

(€) A(-) B(+)—

(d) A(-) B(-)


2. Which type of interaction occurs in lichen?

(a) protocooperation

(b) commensalism

(c) mutualism

(d) predation


3. Association of clown fish and sea anemone is an example of

(a) mutualism

(b) predation

(c) protocooperation

(d) commensalism


4. Which of the following in an example of commensalism?

(a) tick bird-rhinoceros

(b) epiphyte-mango


(d) lichen


5. In protocooperation the association between interacting species

(a) is obligatory

(b) is facultative

(c) none of these

(d) both of these



1. The living organisms can live in isolation.

2. The association between species is always beneficial to both

3. The species which is benefitted is assigned (+) sign.



1. The interactions in which both members are benefitted are called interactions.

2. The member which is neither benefitted nor harmed is assigned a sign.



1. What do you mean by positive interactions?

2. What is relationship of fig and wasp?

3. What are (+) and (0) signs used for?



1. Explain protocooperation with examples.





1. (a) A(+) B(+) : in mutualism both species are benefitted.

2. (c) mutualism in lichen algae and fungus coexist benefitting from each other

3. (d) commensalism clown fish gets protection and sea anemone is unaffected.

4. (b) epiphyte and mango tree epiphyte is benefitted by getting shelter from the mango tree, whereas the mango tree is neither harmed nor benefitted.

5. (b) is facultative in protocooperation association is optional not compulsory.



1. False : they interact through one or other means

2. False : there are positive as well as negative interactions

3. True



1. Positive

2. (0)








“Population interaction is the interaction between different populations. !t refers to

the effects that the organism in a community have on one another.”Dear students, we have discussed about positive interactions in our previous assignment. In this assignment we will discuss about negative interactions.

Negative interactions:-In these interactions members of either one or both the

interacting species are harmed.These are called antagonistic relationships.

Inhibited or harmed species is symbolised as(-).


Negative interactions are of following different ty pes:-







Parasitism:-It is a type of antagonistic interspecific interaction in which smaller

partner, called parasite, derives food and shelter from in or on the body of larger partner, called host, and inhibits the survival of the host. So the parasitic species is benefitted while host species is harmed.Species A(Parasite)=(+)

Species B(Host) =(-)


On the basis of host-parasite relationship parasitism is of two types:-

(a) Temporary or partial parasitism:-In this, the parasite spends most of their life cycle as free- living organism and only a part of life is spent as parasite e.g

Glochidium larva of Unio(fresh-water mussel)undergoes metamorphosis as

ectoparasite on a freshwater fish.


(b) Permanent or Holoparasitic parasitism:-

In this, the organism spend their whole life cycle as parasites. It is of two types:-

(1) Ectoparasitism:-In this, the parasites live outside the host's body e.g bugs, fleas,ticks,lice, numerous crustaceans. The most important example of ectoparasitism are the lice on humans and ticks on dogs.Many marine fishes are infested with ectoparasitic copepods.Cuscutta a parasitic plant that is

commonly found growing on hedge plant .


(2) Endoparasitism:-In this,the parasites live inside the host body e.g Jaenia

Ascaris and Entamoeba in the intestine of man and cause Taeniasis,Ascariasis and Amoebic dysentery respectively.

Plasmodium (matarial parasite) in the liver cells and RBCs of man causes malaria.The life - cycle of some parasites involves one or two intermediate hosts or vectors to facilitate parasitism of its primary hosts.


The human liver fluke depends on two intermediate hosts ( a snail and a fish) to

complete its life- cycle. The malarial parasite needs a vector ( mosquito) to spread to other host.

Brood parasitism, also called social parasitism, is the exploitation by one individual (the brood parasite) of the parental care of another (thehost). Brood parasites can deposit eggs in the nests or broods of another individual of the same (conspecific brood parasitism) or of a different (interspecific brood parasitism) species. Hosts often raise

young of the brood parasite, typically at the expense of their own young.

It is found in members of certain species of birds e.g black headed ducks and about 50% of species of cuckoos .The female koel does not prepare its own nest and lays its eggs in the crow’s nest.Brood parasitism relieves the parasitic parents from the investment of rearing young or building nests for the young, enabling them to spend more time on other activities such as foraging and producing further offspring. Bird parasite species mitigate the risk of egg loss by distributing eggs amongst a number of different hosts.



A type of negative interaction in which larger species called predator attacks and

kills and feeds on the smaller species is called prey.


Biocontrol: Predation also helps in biological control in which members of

harmful species are regulated by the members of useful Predator species Example

1) control of opuntia by Australian cochineal insects

2) control of mosquito larvae by gambusia fish



Competition occurs when an individuals attempt to obtain a resource that is

inadequate to support all the individuals seeking itor even if the resource is

adequate, individuals harm one another in trying to obtain it.In this type of interaction both species are harmed.

Species A=(-)

Species B=(-)

The resources competed for can be divided into two types.


(1) Raw material such as light, inorganic nutrients, and water in autotrophs and

organic food and water in heterotrophs.


(2) Space to grow,nest,hide from predators.

The competition may be:-

Intraspecific:-occuring between two or more members of the same species of the population.


Interspecific:-occuring between two or more members of different species of the

same trophic level. So both the interacting species are harmed.


Gause's "Competition exclusion principle" which states that :

“when two closely related species with similar requirements occur in the

same environment,they use different food or become active at different periods or occupy different niches to avoid competition, otherwise,one of them will be eliminated as no two species can occupy exactly the same

ecological niche”.



Amensalism is an antagonistic interspecific interaction in which one species is

inhibited while other species is neither benefited nor harmed.

Species A=(-) called Amensal

Species B=(0) called inhibitor.


Most common e.g of Amensalism is formation of antibiotics that are antagonistic to the microbes e.g Penicillium notatum releasing Penicillin to Inhibit the growth of variety of bacteria especially Staphylococcus bacterium.





1.Amensalism is an association between two species where

(a) one species is harmed and other is benefitted.

(b) one species is harmed and other is unaffected.

(c) one species is benefitted and other is unaffected

(d) both the species are harmed


2. Cuscuta is an example of

(a) Mutualism

(b) Commensalism

(c) Parasitism

(d) Competition


3.Which one of the following population interactions is widely used in medical science for the production of antibiotics?

(a) Commensalism

(b) Parasitism

(c) Mutualism

(d) Amensalism


4. In which of the following interactions, both partners are adversely affected?

(a) Competition


(c) Parasitism

(d) Mutualism


5. Parasitism can be represented by:

(a) Species A(-); Species B(-)

(b) Species A(+); Species B(0)

(c) Species A(-); Species B(0)

(d) Species A(+); Species B(-)


( B) True/False:-

1. Cuscuta is an example of brood parasitism.

2. In endoparasitism the parasities live outside the body of the host.

3. Taeniasis is caused by Taenia


(C) Fill in the blanks:-

1. When two or more species compete for limited resources,itis knownas__..

2. In parasitism the smaller partner which drives food and shelter

from the body of larger partner is called__.



(A) Multiple Choice Type Question:-


1. (b) Explanation:- Amensalism is the association in which one species is harmed and other is unaffected.


2. (c) Explanation:- Cuscuta is an example of Parasitism.


3. (d) Explanation:- Most common phenomenon of amensalism is formation of antibiotics that are antagonistic to the microbes.


4. (a) Explanation:tn competition both the interacting species are harmed.


5. (d) Explanation :- In parasitism the parasite(Species A)is benefitted while the host (Species B) is harmed.


(B) True/False

1-False:-Brood Parasitism is found in member of certain species of birds e.g Koel.

2- False:- In endoparasitism the parasites live inside the body of the host. e.g Taenia, Ascaris etc.

3-True:- Taeniasis is caused by Taenia.


(c) Fill in the Blanks

1 - Interspecific competition

2 - Parasite


Q-1 State Gause’s Competitive Exclusion Principle.

Q-2 Define parasitism.Give one example.

Q-3 What is Brood parasitism? Give one example.


Q-1 Describe the negative interactions amongst different species.

Q-2 Differentiate between:-

(a) Intraspecific and interspecific competition.

(b) Ectoparasitism and endoparasitism




1. How is diapause different from hibernation?

Ans: Diapause is a period of suspended growth or development occuring in many insects and other invertebrates during which metabolic activities are greatly reduced.On the other hand, hibernation is a sieep like state in which a few animals, such as fishes and amphibians, pass the winter season as a way of surviving food scarcity and cold weather. While diapause can occur anytime in the year, hibernation occurs only in winter months.


2. If a marine fish is placed in a fresh water aquarium, will the fish be able to survive? Why or why not?

Ans: When a marine fish is placed in a fresh water aquarium, the fish will not be able

to survive because marine fish is adapted to live in saline seawater. In fresh water,

it will not be able to cope with the outside hypotonic environment because of

osmoregulation problem. In fresh water, the concentration of water, the difference

between the concentration of the water and inside of the fish are increased and

therefore, the osmotic pressure is also increased.The fish has to take more water

into the body to be able to survive and to get rid of the excess salt present in its



3. Most living organisms cannot survive at temperature above 45°C. How are some microbes able to live in habitats with temperatures exceeding 100°C?

Ans: Micro-organisms of hot.springs and vents (mouth of sea bed volcanoes) are able to survive at the high temperature due to

(i) occurrence of branched chain lipids in their cell membrane that reduce fluidity of

cell membranes.

(ii) having minimum amount of free water in their bodies. Removal of water provides

resistance to high temperature.


4. Last the attributes that populations but not individuals possess.

Ans: Some significant attributes that populations but not individual possess are — (i)Natality (ii) Mortality (iii) Growth forms (iv) Population density (v) Population

dispersion (vi) Population age distribution (vii) Sex ratio


5. If a population growing exponentially double in size in 3 years, what is the intrinsic rate of increase (r) of the population?



6. Name important defence mechanisms in plants against herbivory.

Ans: There are various defence measures for animals against predators. But plants,

as they cannot move away, have certain defence mechanisms against herbivory.

Their main defences are chemical toxins, such as strychnine, a poison produced by

tropical vine, morphine by opium poppy, nicotine produced by tobacco plant. Apart

from these chemicals, the common defence measure is presence of spines (modified leaves) on the leaves, stems of the plant, modifications of leaves into thorns, development of sharp silicated edges in leaves which prevent them against damage caused by herbivores.


7. An orchid plant is growing on the branch of mango tree. How do you describe this interaction between the orchid and the mango tree?

Ans: An orchid plant is growing on the branch of a mango tree is called epiphyte,

i.e., plants growing on other plants or trees. This type of interaction is known as

commensalism, where in orchid / derives benefit of interaction whereas mango tree

is not affected. The orchid growing on the branch of mango tree get more light to

grow and also, the mango is not harmed in any way. Commensalism can be defined as an interaction between two animal or plant species that habitually live together in which one species benefits from the association while the other is not

significantly affected.



8. What is the ecological principle behind the biological control method of

managing with pest insects?

Ans: The ecological principle behind the biological control method of managing with

pest insects is predator — prey relationship. It is based on the ability of the predator

to regulate prey population.


9. Distinguish between the following: (a) Hibernation and Aestivation



10. Write a short note on (a) Adaptations of desert plants and animals (b) Adaptations of plants to water scarcity (c) Behavioural adaptations in animals (d) Importance of light to plants (e) Effect of temperature or water scarcity and the adaptations of animals.

Ans: (a) Desert plants have very small leaves or no leaves at all, and carrying out photosynthesis through the stems. Their stem could become succulent, and can store and retain water. Animals living in hot climatic region tend to be smaller than those living in cold climates. This can be explained by the fact that the amount of heat gained from the environment is approximately

proportional to the body surface area. The majority of animals living in desert are small, like, kangaroo rat. It feed on dry seeds and other dry plant material and does not drink,


(b) The evergreen trees such as Rhododendron, show water scarcity by an inward curling of the leaves. A more significant response is the closure of stomata, which reduces transpiration, but raises the internal temperature of die leaf affecting the rate of synthesis of proteins and photosynthesis.

Deciduous trees of the temperature region drop their leaves in autumn, avoiding winter drought.Some water stressed plant's accumulate excessive amounts of inorganic ions.

(c)Migrating temporarily to a less stressful habitat forms a more stressful habitat is a kind of behavioural adaptation in animals which enables them to survive in better environmental conditions. Desert lizards regulate their body temperature constant by behavioural means. They bask in the sun and absorb heat when their body temperature decreases below the optimum, but move into shady or underground places when the temperature of the surrounding area starts



(d) Light affects plants through its quality, intensity and duration. Duration of light affects phenology, photosynthesis, growth, reproduction, flowering. Quality of light influences flowering,seed germination and movements. Light is required for the production of chlorophyll in chloroplasts. Plants germinated under insufficient illumination causes the destruction of



(e) Animals mainly are of two types as they are adapted to controlling their body temperature.Poikilothermous are the animals whose temperature fluctuates with that of the environment, e.g.,invertebrates and vertebrates, other than birds and animals. In contrast, homeotherms are the animals which can maintain their body temperature at a constant level, e.g., birds and mammals.


11. List the various abiotic environmental factors.

Ans: Abiotic factors are non living factors

and conditions of the environment which influence survival, function and behaviour of

organisms. Various abiotic factors are :


(i) Temperature — Temperature is one of the most important environmental factors. The average temperature varies seasonally. It ranges from subzero level in polar areas and high altitudes to more than 50°C in tropical deserts in summer and exceeds 100°C in thermal springs and deep-sea hydrothermal vents.


(ii) Water — Next to temperature, water is the most important factor which influences the life of organisms. The productivity and distribution ofland plants are dependent upon availability of water.Animals are adapted according to the water availability. E.g., aquatic animals are ammonotelic while xerophytic animals excrete dry feces and concentrated urine.


(iii) Light — Plants produce food through photosynthesis for which sunlight is essential source of energy. Light intensity, light duration and light quality influences the number of life processes in organisms, such as — photosynthesis, growth, trans-piration, germination, pigmentation,

movement and photoperiodism.


(iv) Humidity — Humidity refers to the moisture (water vapour) content of the air. It determines the formation of clouds, dew and fog. It affects the land organisms by regulating the loss of water as vapour from their bodies through evaporation, perspiration and transpiration. (v) Precipitation —Precipitation means rainfall, snow, sleet or dew. Total annual rainfall, seasonal distribution humidity of the air and amount of water retained in the soil are the main criteria that limit the distribution of plants and animals on land.


{vi) Soil — The soil is one of the most important ecological factor called the edaphic factor. It comprises of different layers called horizons. The upper weathered humus containing part of soil sustains terrestrial plant life.




12. Give an example for:

(a) An endothermic animal

(b) An ectothermic animal

(c)An organism of the benthic zone

Ans: (a) Man, (Homo sapiens) (b) Black bear (c) Corals


13. Define population and community.

Ans: Population can be defined as the total number of individuals of a species or any other class of an organism in a defined area or habitat or a group of individuals of the same species within a commnity. Community can be defined as a naturally octurring assemblage of species living within a defined area or habitat.


14. Define the following terms and give one example for each: (a) Commensalism (b)

Parasitism (c) Camouflage (d)Mutualism (e) Interspecific competition

Ans: (a) Commensalism is the association between organisms of different species in which one species benefits but does not apparent harm to the other. For example, in the large intestine of human being, bacteria Escherichia coli are present which helps in digestion.


(b) Parasitism is an association in which one organism lives on or in the body of another, from which it obtains its food. For example, the parasites of humans include fleas and lice, various bacteria, protozoans and fungi.


(c) Camouflage is a high degree of similarity between an animal and its visual environment, which enables it be disguished or concealed. For example, birds with necks and heads of contrasting colours are not easily recognised by their enemies under certain conditions.


(d) Mutualism is an association between two organisms of different species in which each partner benefits. For example, the cross fertilization or pollination of plant flowers by insects (sometimes by birds) is a mutual relation of wide occurrence and great importance, because many plants are

self- sterile.


(e) Inter-specific competition can be defined as an interaction occurs between different species that share some environmental resource when this is in short supply. Inter-specific competition often results in the dominance of one species over another. For example, when two species of

Paramoecium,Paramoecium caudatum and P.aurelia are confined in a closed containers with fixed amount of food, out of them one species always died out.


15. With the help of suitable diagram describe the . ; logistic population growth curve.

Ans: The S-shaped growth curve is also called a logistic growth curve. It describes a situation in which (in a new environmental condition) the population density of an organism increases slowly establishing itself then increasing rapidly, approaching an exponential growth rate. Later, when the

resources become limited, growth slows and eventually stops.Many population of micro-

organisms broadly follow this basic sigmoidal pattern. For example, when a fresh culture medium is inoculated with bacteria, sigmoidal or S-shaped growth curve is observed. The S-shaped curve is generated when a population approaches the environmental’s carrying capacity.Carrying capacity is the maximum number of individuals of a population that can be supported in a given time.



16. Select the statement which explains best parasitism.

(a) One organism is benefited.

(b) Both the organisms are benefited.

(c) One organism is benefited,

other is not affected.

(d) One organism is benefited, other is affected.

Ans:(d) One organism is benefited, other is affected.


17.List any three important characteristics of a population and explain.

Ans: The three important characteristics of a population are:

(a) Density: The number of individuals per unit area or volume. For example, the number of frogs per meter cube of forest region.


(b) Natality or Birth rate: The birth rate is determined by the number of individuals born to a given population during a given period of time.


(c) Mortality or Death rate: The death rate or mortality represents a decrease in a given population during a given period of time. Generally, the death of individuals in a population are expressed by specific mortality which is described as the mortality population are expressed by specific mortality which is described as the mortality for given age group.





Ecology is the branch of biology that deals with the interactions among organisms

and between the organism and its physical (abiotic) environment. Study of

ecology is important to strike a balance between development and maintenance

of natural environmental and biotic communities, use and conservation of

resources, solve local, regional and global environmental problems.It is basically concerned with four levels of biological organization —organisms, populations, communities, and biomes.


Ecological hierarchy or ecological level of organization connected with ecological

grouping of organisms.



Ecological factors are environmental variables that impact organisms and contribute to their characteristic modes of behavior. These factors cause dynamic

changes in a population or species in a particular geographical region.


Major Abiotic Factors are:

a) Temperature- is the most important ecological factor to determine the bio-mass

of a place. Average temperature on land varies seasonally and decreases progressively from the equator towards the poles and from plains to mountain tops.Temperature affects the kinetics of enzymes and basal metabolism along with physiological functions of the organisms.


The organisms that can tolerate wide range of temperature are called eurythermal, for example cat, dogs, tigers etc.


The organisms which have the ability to tolerate only a narrow range of temperature are called stenothermal, for example Penguin, fishes, and crocodile.etc.


b) Water- life on earth is unsustainable without water. Productivity and distribution

of plants is heavily dependent on water. For aquatic organisms the quality (chemical composition, pH) of water becomes important. The salt concentration (measured as salinity in parts per thousand), is less than 5 in inland waters, 30-35 in the sea and > 100 in some hypersaline lagoons.


The organisms that can tolerate wide range of salinities are called euryhaline,for example salmon, herring etc.


The organisms which have the ability to tolerate only a narrow range of salinities are called stenohaline, for example goldfish (fresnwater) and haddock (marine water) etc.


c) Light- plants produce food through photosynthesis in presence of sunlight.

Some plants are adapted to low light conditions because they are overshadowed

by tall canopied trees. Flowering in some plants occurs only in presence of critical

day light called Photoperiodism. The availability of lignt and land is closely linked that of temperature as the sun is the source of both. UV component of sunlight is

harmful to plants and animals.


d) Soil: Types of soil depends upon climate, weathering process, whether soil is

transported or sedimentary and how soil development occurred. Soil composition,

grain size and aggregation determine the percolation and water holding capacity of

the soils along with pH, mineral, composition and topography determine the vegetation in any area.


Responses to Abiotic Factor: In the course of evolution, many species have evolved constant internal environment to permits all biochemical reactions and physiological functions to work with maximum efficiency to have over all fitness of species. Organisms try to maintain the constancy of its internal environment (homeostasis) in spite of varying external environment.There are various ways to establish homeostasis-


Regulate- all birds and animals are capable of maintaining homeostasis by physiological means which ensures constant body temperature, constant osmotic concentration etc. Thermoregulation and osmoregulation are the source of success of mammals in all the environmental conditions. In summer, when

outside temperature is more than our body temperature, we sweat often, resulting

evaporative cooling, which brings down the body temperature. In winter we start

to shiver, a kind of exercise which produces heat and raises the body temperature.


Conform- Most of animals and plants, their body temperature change with ambient temperature. In aquatic animals, osmotic concentration of the body fluid change with that of the ambient water osmotic concentration. These animals are called conformer. Conformers are not able to bear the energetic expenses to maintain the constant body temperature. Heat loss or heat gain is a function of surface area. Since small animals have a larger surface area relative to their volume, they tend to lose body heat very fast when it is cold outside; then they have to expend much energy to generate body heat through metabolism.


Migrate- The organisms move away for time being from the stressful unfavorable habitat to more suitable habitat and return back when stressful period is over. Many birds undertake long-distance to migrate to more hospitable areas.Siberia birds migrate to Keolado National Park, Bharatpur, India.


Suspend- In microorganisms like bacteria, fungi and lower plants thick-walled

spores are formed which help them to survive unfavorable conditions. These spores germinate on return of suitable conditions. In higher plants, seeds and some other vegetative reproductive structures serves the means to tide over periods of stress and help them in dispersal also. The metabolic activities are reduced to minimum during this dormant period.


a) Hibernation — the condition or

period of an animal or plant spending the winter in a dormant state e.g., bear


Aestivation — the condition or period of an animal or plant spending the summer to avoid heat and desiccation in a dormant state e.g., snails.


Diapause- A stage of suspended development in zooplankton species in

lakes and ponds.



“Adaptation” is the attribute of organism morphological, physiological and behavioral changes that enables the organism to survive and reproduce in its habitat.


Kangaroo rat in North American deserts fulfills the water requirement by

internal oxidation of fat in absence of water. It also has the ability to concentrate its urine so that minimal volume of water is used to remove excretory products.


Thick cuticle in many plants also prevents loss of water. CAM plants open their stomata during night to reduce the loss of water during photosynthesis.


Mammals from colder climates have shorter ears and limbs to minimize heat loss. This is called Allen's Rule.- In polar seas aquatic mammals like seals have a thick layer of fat called blubber, below their skin that acts as an insulator.


Altitude sickness is observed at higher altitude that includes symptoms like nausea, fatigue, heart palpitations due to less oxygen and atmospheric pressure. The person gradually gets acclimatized and stops experiencing altitude sickness. This is type of physiological adaptation.


Anumber of marine invertebrate and fish live in temperature always less than zero and some lives in great depth in ocean where pressure is very high by array of biochemical adaptations.Some organisms like desert lizard lack the physiological ability that mammals have but deal with high temperature of

their habitat by behavioral means. They bask in the sun and absorb heat and when their body temperature drops below the comfort zone, but moves in shade when the ambient temperature starts increasing.


Major Biotic Factors

Any of the living organisms that make up, build, and shape the environment are

called Biotic Factors. These are the important and major parts of the ecosystem.

Biotic Factors comprise living organisms that depend on others for survival such

as animals, plants, and microorganisms.

Population and its attributes Populations: Individuals of any species live in groups in well-defined geographical area, share or compete for similar resources, potentially interbreed and constitute a population.


Population Attributes: A population has certain attributes that an individual

organism does not such as an individual may have births and deaths, but a population has birth rates and death rates.


The birth and death rates: are referred as per capita births or deaths respectively, which is increase and decrease with respect to members of the population.


Sex ratio: is another attribute of population. An individual may be male or

female but population has sex ratio.


Age distribution: A population at given time composed of different individual of

different ages. If the age distribution is plotted for the population, the resulting

structure is called age pyramids. The shape of pyramids reflects the shape of growth status of population. Which may be

(i) Expanding

(ii) Stable

(iii) Declining


Population size or population density (N) is measured in terms of number but it may sometime not appropriate.


Population Growth: The size of population is not static. It keeps changing with time, depending upon food availability, predation pressure and reduces weather. The main factors that determine the population growth are-


Natality (number of births during a given period in the population)


Mortality (number of deaths during a given period in the population)


Immigration (individual of same species that have come into the habitat)


Emigration (individual of population that have left the habitat)


If ‘N’ is the population density at a time't’, then its density at time t+1 is

Nt+1Nt+[(B +1)-(D+E)]Population density will increase if the number of births plus the number of immigrants (B + |) is more than the number of deaths plus the number of

emigrants (D + E), otherwise it will decrease.


Growth models or curves

Growth of population takes place according to availability of food, habit condition

and presence of other biotic and abiotic factors. There are two main types of



i. Exponential Growth- in this kind of growth occurs when food and space is

available in sufficient amount. When resources in the habitat are unlimited,

each species has the ability to realize fully its innate potential to grow in number.

The population grows in an exponential or geometric fashion. If in a population of

size N, the birth rates as represented as ‘b’ and death rate as ‘d’. Then increase

and decrease in N during unit period time ‘t’ will be


Let (b —d) =r, then

dN / dt =rN

Then, the rin this equation is called ‘intrinsic rate of natural increase’.


ii. Logistic Growth- there is a competition between the individuals of a

population for food and space. The fittest organism survives and reproduces. In

this types of growth initially snows a leg phase followed by phases of acceleration

and de-acceleration.

dN/dt =rN (4)

Where N = Population density at time t

R = Intrinsic rate of natural increase

K = Carrying capacity


Since resources for growth for populations are finite and become limiting,

the logistic growth model is considered a more realistic one.


All animals, plants and microbes in a biological community interact with each

other. These interactions may be beneficial, detrimental or neutral to one of

species or both. Following types of interaction is seen-

a. Predation

b. Competition

c. Parasitism

d. Commensalism

e. Mutualism

f. Amensalism


a) Predation: It is an Interspecific Interaction where one animal kills and

consumes the other weaker animal.


Roles of Predators

Transfer energy from plants to higher trophic levels (position of organism in food chain)

Control Prey population — Prickly pear cactus- moth Biological control of Agricultural pest Maintain species diversity by reducing intensity of competition among competing prey species Over exploitation of prey by the predators results in extinction of prey and predator.

Defense to lessen impact of predation

a) Insects and frog — camouflage

b) Monarch butterfly — poisonous


b) Competition: Interaction either among individuals of same species or between

individuals of different species occurs among closely related species but not always true


1. Unrelated species also compete- flamingo & fish compete for Zooplankton


2. Feeding efficiency of a species reduce due to other species even if resources are plenty Abingdon tortoise.Evidence for competition

Competitive release species distribution restricted to small areas due to

competitively superior species.


c) Parasitism: It is the interaction where one species (parasite) depends on the

other species (host) for food and shelter, host is harmed.

Parasites and host self-evolve.

- Adaptations of parasites

1. Loss of unnecessary sense organs

2. Hooks and sucker

3. Loss of digestive system

4. High Reproductive capacity



(i) Reduce the survival of host

(ii) Growth and reproductive rate are reduced

(iii) Render the host vulnerable to its predators by making them weak


Types of parasites:

Ectoparasites— depend on external surface of host Example — head lice on humans, ticks on dogs


Endoparasites— take shelter within the body of the host organism

Example — Liver fluke, Plasmodium


d) Commensalism: Commensalism is the term used to describe a relationship

between individuals of two species. In this one species obtains food or other may

get benefits from the first species without either harming or benefiting the latter.

For example: Epiphytic plants.


e) Mutualism: It is interaction in which both the interacting species are benefited


1. Lichen — fungi and algae

2. Mycorrhizae — fungi and roots of higher plants

3. Pollination of plants by insects

4. Mediterranean orchid- sexual deceit for pollination- appears as female bee

f) Amensalism: Interaction between two different species, in which one

species is harmed and the other species is neither harmed nor benefited. Example. Bacterial culture, after few days, fungus growth will be there on it like Penicillium, and its secretions of chemical will kill bacteria, but no benefits to fungi.




(a) Multiple choice questions:

1. Exponential growth occurs when there is

(a) a great environmental resistance

(b) no environmental resistance

(c) no biotic potential

(d) a fixed carrying capacity


2. ACszplant is one that is able to grow

(a) In all climates

(b) In arid climates

(c) In wet climates

(d) In moderate climates


3. Winter sleep is also called as

(a) Hibernation

(b) Suspend

(c) Migrate

(d) Aestivation


4. Whatis a biological interaction between organisms of different species in which each individual receives benefit known?

(a) Parasitism

(b) Competition

(C) Commensalism

(d) Mutualism


5. Astage of suspended development is called

(a) Diapause

(b) Suspend

(c) Migrate

(d) Retardation


6. The interaction where one species is benefitted and the other is neither benefitted nor harmed is called

(a) Amensalism

(b) commensalism

(c) Mutualism

(d) None of the above


7. The interdependent evolution of flowering plants and pollinating insects together is known as

(a) Mutualism

(b) Co-evolution

(c) Commensalism

(d) Co-operation




8. Penicillium notatum, a mould, produces an antibiotic, penicillin, which inhibits the growth of many bacteria and apparently does not get gain by their death. This is an example of

(a) Commensalism

(b) Competition

(c) Parasitism

(d) Amensalism


9. Cuscuta is an example of

(a) Ectoparasitism

(b) Brood parasitism

(c) Predation

(d) Endoparasitism


10. ‘When two species of Paramecium (P. caudatum and P. aurelia) are kept together, one is eliminated’, this is a case of

(a) Adaptation

(b) Amensalism

(c) Competition

(d) Protocooperation


(b) Fillin the blanks:

a) Community refers to groups of organisms belonging to several different -------------- that live together in same area or habitat and interact.

b) The phenomenon of spending cold period in an inactive stage by an animal is called —-—-

c) Mutualism is an interspecific interaction between individuals of two species where both

the interacting species are ---—---------—---in an obligatory way.

d) Ocimum sanctum checks the growth of plants near it which is an example of the

phenomenon ----—-------------.

(e) --—------------—---- is the interaction between two species, one of which captures, kills and eats up the other



(i). Write one common feature among predation, parasitism and amensalism.

(ii). Define natality.

(iii). How do spines help the cactus plants survive in the desert?



1. Describe the different kinds of interactions that take place between different species.



a) Multiple choice questions


1. (b) No environmental resistance: When resources are limited, populations

exhibit logistic growth. In logistic growth, population expansion decreases as

resources become scarce. It levels off when the carrying capacity of the environment is reached, resulting in an S-shaped curve.


2. (c) In wet climates: C3 plants are the most common and the most efficient

at photosynthesis in cool, wet climates.


3. (a) Hibernation: Hibernation is a way of coping to cold winters, without having

to forage for food. It's also known as winter sleep.


4. (d) Mutualism is a long-term, close association between two species in which

both partners benefit.


5. (a) Diapause: Under unfavourable conditions, many zooplankton (free floating

aquatic microbes) species in lakes and ponds are known to enter diapause, a stage of suspended development.


6. (b) Commensalism is a class of relationships between two organisms where one

organism benefits from the other without affecting it.


7. (b) Co-evolution:The evolution of complementary adaptations in two species

caused by the selection pressures that each exerts on the other is called co-evolution.


8. (d) Commensalism: It is defined as in which members of one species gain benefits while the second species neither gets benefited nor gets harmed.


9. (a) Ectoparasite: Cuscuta is a total snoot parasite of many plants lives on body of

plant, so it is a ectoparasite (a parasite that lives on the surface of a host organism).


10. (c) Competition: Microbial population competes for any growth-limiting resources such as carbon source, nitrogen source, phosphorus, vitamins,growth factors etc.



a) Species: An ecological community consists of all the populations of all the

different species that live together in a particular area.

b) Hibernation: Hibernation is a way animals conserve energy to survive adverse weather conditions or lack of food.

c) Benefitted: Mutualism is a long-term, close association between two species in which both partners benefit.

d) Amensalism: In this type of interaction, when one population finds itself in

danger the other population is not majorly affected.

e) Predation: in animal_behaviour, the pursuit, capture, and killing of animals

for food. Predatory animals may be solitary hunters, like the leopard, or they may be group hunters, like wolves.

Chapter 13 Organisms and Populations