Navodaya Vidyalaya Samiti – Bhopal Region.
Chapter 13
ORGANISMS AND POPULATION
Salient features :1. Temperature, light, water and soil are the major abiotic factors to which organisms are
adopted in various ways. The maintenance of constancy of its internal environment of an
organism is homeostasis.
2. Population is a group of individuals of the same species inhabiting the same area. A
population is characterised by parameter like density, natality, mortality, age distribution,
biotic potential, growth from etc.
3. Population growth curve may be J-shaped or S-shaped. J-shaped growth curve is obtained
when the environment resistance does not exert any influence. S-shaped (sigmoid) is
attained when the population first grows slowly, then more rapidly and finally it shows
down gradually due to environmental resistance.
4. Population or individuals in a community interact with each other for obtaining food and
shelter and also on the habits of the species.
5. Predation is the direct food relation where one animal (predator) captures and feeds on
another (prey). In scavenging, animal feed on other animals which have died naturally or
have been killed by another animal.
6. Parasitism, commensalism, symbiosis, competition and mimicry are the other interactions
which the different animals undergo for their survival.
7. Desert plants possess deep roots, sunken stomata, deciduous small leaves and waxy
cuticle in order to reduce transpiration for adapting to desert conditions. Plants adapt to
high concentration of salt in soil or water by salt excretion, salt exclusion or by
accumulating organic solutions in stems and roots.
8. Adaptation in animals occurs through migration, camouflages, hibernation and
aestivation, mimicry, warning coloration. In case of Mullerian mimicry, the mimic shares
the same defensive mechanisms as the model. In cold environment, organisms adapt by
lowering the freezing point proteins or by super cooling their body fluids.
Some important definitions and terms
(1) Adaptation. Special characteristics of plants and animals that enable them to be
successful under prevailing set of environmental conditions.
(2) Aestivation. Spending the dry hot period in an inactive state.
(3) Biome. Comprises of the major regional, ecological community of plants and animals
extending over a large natural areas.
(4)Camouflage. The capacity of an organism to blend with surroundings.
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(5)Climate. Average weather of an area including general patterns of atmospheric
conditions, seasonal variations and weather extremes averaged over a long period.
(6)Coomensalism. Relationship between two organisms where one is benefited and the
other remains unaffected.
(7)Community. A localized association of several population of different species.
(8)Competition. A type of interaction in which each population is adversely affected by
other in search for food, shelter and mate etc.
(9)Diapause. A stage of suspended development.
(10)Ecology. Study of interactions, functions and factors in the biosphere.
(11)Ectotherm. Cold blooded animals whose body temperature tends to match with the
environmental temperature in which they live.
(12)Ecosystem. All communities of plants and animals in an area together with their
abiotic environment.
(13)Endotherm. Warm blooded animals who regulate their body temperature by
physiological means and maintain more or less constant internal temperature.
(14)Ephemerals. The plants which evade dry condition.
(15)Habitat. Place where an organism lives.
(16)Heliophytes. Plants of saline environments which are adapted to grow in high
concentration of salt in soil or water.
(17)Hibernation. Spending winter in dormant conditions.
(18)Homeostasis. Inheritant capacity of an individual to maintain its internal
environment instant inspite of changes in the external environment.
(19)Landscape. A unit of land with a natural boundary having a mosaic of patchs.
(20)Microclimate. Climatic condition that prevails at a local scale or in areas of limited
size.
(21)Migration. Long distance or short distance movements of animals from one region
to another.
(22)Mimicry. A special form of adaptive colouration in animals serving as protective
mechanism to ensure the better survival of the species.
(23)Morality. Death rate.
(24)Mutualism. A relationship between two organisms where both obtain some benefit.
(25)Mycorrhiza. Symbiotic association of roots of higher plants with fungi.
(26)Natality. Birth rate.
(27)Niche. Functional role of an organism in the ecological system.
(28)Osmoconformer. Organism which change the osmolarity of the body fluids
according to the external medium.
(29)Parasitism. An interaction where one species lives in or on the body of the second
(host), adversely affecting it but cannot live without it.
(30)Phenology. Refers to the timing of seasonal activities of plants in relation to change
in environmental conditions.
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(31)Population. Group of organisms of the same kind at a particular time and occupies a
particular space.
(32)Population density. Total number of individuals present per unit area or volume at a
given time.
(33)Predation. One species catches, kills and feeds upon the second.
(34)Stenothermal. Organisms restricted to narrow range of temperature.
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ORGANISMS AND POPULATION
VERY SHORT TYPE QUESTIONS (1 MARKS)
1. What are the two factors that cause annual variations in the
intensity and duration
of temperature leading to distinct seasons?
ANS:- (i) The rotation of earth around the sun and
(ii) The tilt of the axis of earth, are the two factors that cause annual variation in the
intensity and duration of temperature.
2. Name the factors that account for the formation of major biomes?
ANS:- (i)The annual variations in the intensity and duration of
temperature and
(ii)The annual variation in precipitation, account for the formation of major biomes.
3. Name the major factor that determines the geographical distribution of organisms?
ANS:- The level of thermal tolerance of different species.
4. Most living organisms cannot survive at temperature above 45˚C. How are some microbes
able to live in habitats with temperature exceeding 100˚C?
ANS:- They possess some heat-resistant or thermostable proteins/enzymes and an array of
biochemical adaption.
5. Which one of the two, stenothermal or eurythermals, shows wide range of distribution, on
earth and why?
ANS:- Eurythermals show a wide range of distribution as they can tolerate and thrive in a
wide range of temperatures.
6. Cows and dogs are eurythermal animals. Why are polar bears categorized as stenothermal
animals? Give one reason?
ANS:- Cows and dogs can tolerate and thrive in a wide range of temperatures while polar
bears are restricted only to a narrow range of temperatures in very cold regions; so polar
bears are stenothermals.
7. Between amphibians and birds, which will be stable to cope with global warming? Give
reason.
ANS:- Birds will be stable; they are eurythermal animals, which can tolerate a wide range
of temperatures.
8. What do the evolutionary biologists believe to be the reason for success of mammals?
ANS:- Eolutionary biologists believe that the success of mammals is the due to their
ability to maintain a constant body temperature.
9. Why many fresh water animals cannot live for long in sea water or vice versa?
ANS:-it is because of the osmotic problems they would face.
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SHORT ANSWER TYPE QUESTIONS(2 MARKS)
1. Name the four major biomes found in india?
ANS:-the major biomes of india includes :
(i)Tropical rain forest
(ii)Tropical deciduous forest
(iii) Desert &
(iv) Sea coast
2. Differentiate between eurythermal and stenothermal animals/organisms?
ANS:eurythermal organisms
Stenothermal organisms
-eurythermal organisms are those which -stenothermal organisms are those which
can tolerate a wide range of temperatures.
thrive only in a narrow range of
temperature.
3. If a marine fish is placed in a fresh water aquarium, will the fish be able to survive? Why
are why not.
ANS:-the fish will not be able to survive.
-there will be passive entry of water into its body cells, since the osmolarity of its
body fluids is stronger than that of freshwater.
4. How does light influence the life of animals?
ANS:--animals take cues from the intensity & duration of light for their following
activities:
(i)foraging
(ii) migratory activities &
(iii) reproduction.
5. How does human being maintain a constant body temperature despite changes in the
surroundings?
ANS:-human beings maintain a constant body temperature in the following two ways:
(i)in summer, we sweat profusely; the evaporation of the sweat causes cooling & brings
down the body temperature.
(ii) in winter, we shiver & that produces more heat, to raise the body temperature.
6. Why are very small animals generally not found in polar/arctic regions?
ANS:--Heat loss/gains a function of the surface area; small animals have a larger surface
area relative to their volume.
-so they tend to lose body heat very fast when it is cold outside; consequently they have
to spend more energy to generate body heat.
-considering the cost & benefits of energy expenditure, very small animals are generally
not found in polar regions.
7. Distinguish between ectotherms and endotherms?
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ectotherms
-ectotherms are those animals whose body
temperature changes to match with that of
the environment in which they are living.
endotherms
-endotherms are those animals whose body
temperature is maintained relatively
constant by physiological regulations.
8. Distinguish between hibernation and aestivation. Give an example of each.
ANS:hibernation
aestivation
-hibernation is the process in which animals -it is the process in which animals spend
spend the winter in an inactive/dorminant the dry, hot(summer) period in an inactive
state.
states.
e.g. frogs
e.g. snails
SHORT ANSWER TYPE QUESTIONS(3 MARKS)
1. Discuss the importance of light on plants and animals life?
ANS:-light on plant life:
-plant needs light for photosynthesis.
-photoperiods determine the flowering & fruiting in plants.
-light is necessary for germination of seeds is certain plants.
Light on animal life:
-diurnal animals are active only during light period.
-seasonal variations in the light intensity & photoperiods are the cues for animal activities
like migration, foraging & reproduction.
2. List the various abiotic environmental factors?
ANS:-the environmental factors include:
(i)
light
(ii)
water
(iii) temperature
(iv)
humidity
(v)
wind
(vi)
salinity of soil
(vii) type of soil etc.
3. What are conformers? Why have they not evolved mechanisms for temperature regulation
or osmoregulation?
ANS:-conformers are those organisms, which change their body temperature, osmolarity,
etc. according to the external environmental conditions.
-during the course of evolution of the costs & benefits of maintaining a constant internal
environment are taken into consideration; when it is not advantageous , the organisms have not
evolved mechanisms to maintain homeostasis.
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-heat loss or gain is function of surface area & hence very small animals are not found in polar
regions, i.e. they have become distributed according to the external conditions.
-similarly aquatic animals, that are conformers can change the osmolarity of their body fluid
according to the surroundings.
4. How do organisms manage with stress conditions existing in their habitats for short
duration? Explain with the help of one example each?
ANS:-under such conditions, the organisms follow one of the following alternatives:(i)
The organism moves away from the stressful habitat to a more hospitable area &
return to their habitat when the stressful period is over, e.g. Birds from Siberia &
other cold countries migrate to Bharatpur sanctuary in Rajasthan.
(ii)
Animals which cannot migrate show hibernation during winter (e.g. frog), or
aestivation in summer(e.g. snails) or enter disuse.
(iii)
In, bacteria, fungi & lower groups of plants, various types of thick walled spores are
formed; they germinate under suitable conditions.
(iv)
In higher plants & seeds & some other vegetative reproductive structures serves as
means to tide over stress conditions.
5. Describe any three productive strategies that organisms have evolved in relation to a
particular set of selective pressures.
ANS:- under a particular set of selective pressures, organisms evolve towards the most
efficient reproductive strategy:
(i)
Some organisms breed only once in their life time e.g., Pacific Salmon fish &
bamboo.
(ii)
Many organisms breed many times during their life e.g. Birds, mammals.
(iii) Some produce a large no. of small sized offspring e.g. oysters, pelagic fishes.
(iv)
Some organisms produce a small no. of large sized offspring e.g. mammals &
birds.
6. Explain the three basic types of interspecific interactions?
ANS:-(i) beneficial interaction:
-the inter specific interaction is beneficial to both the interacting species is mutation.
- Commensalism, is beneficial to one, but neutral to the another.
(ii) Detrimental interactions;
-competition is the type of interaction, that is detrimental to both the interacting species.
-parasitism is beneficial to one & detrimental to the other.
-Amensalism is detrimental to one & neutral to the another.
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(iii) Neutral interactions:
-Commensalism is the type of interaction that is neutral to one but beneficial to the other.
7. Competition does not occur between closely related species related species for the same
limiting resources. Substantiate the statements with an examples.
ANS:i.
totally unrelated species can compete for the same resources, e.g., The visiting
compete for their common food, zooplanktons.
ii.
In interference competition, the feeding efficiency of one species decrease by the
inhibitory & interfering presence of the other species.
e.g. Abington tortoise in Galapagos islands became extinct within a decade after
introducing goats into the islands; the goats are more efficient in grazing than
tortoise.
8. Differentiate between ectoparasites and endoparasiteds. Give an example of each.
ANS:ectoparasite
Endoparasite
-those organisms which live on the surface -those organisms which live inside the body
of other living organisms & derived food of the other living organisms & derived food
from it, are called ectoparasite.
from it, are called endoparasites.
e.g., Ticks on dogs, lice on humans.
e.g. plasmodium, & liver fluke in man.
9. What is brood parasitism? Give an example. What adaptation has evolved in this
phenomenon?
ANS:--brood parasitism is a phenomenon in which one parasite species lays eggs in the
nest of the another species of bird & lets the host incubate them e.g. Cuckoo bird lays eggs
in the nest of the crow.
-the eggs of the parasitic bird have evolved resemblances with the eggs of the host in colour, size
etc. to reduce the chances of the host bird detecting the host bird detecting the foreign eggs &
ejecting them from the nest.
10. Mutualism often involves co-evolution of the mutualists. Describing taking the example of
animal-plant (wasp-fig) relationship?
ANS:--evolution of the flower characteristics & its pollinator species in highly linked with
each other.
-a given species of fig is pollinated by a specific wasp species.
- the wasp pollinates the fig inflorescence while searching for a suitable place for oviposition.
-the female wasp uses the ovary of flowers for ovipositions & the developing seeds provide
nourishment to the developing young ones of the wasp. -later the young ones emerge from the
fruits of fig.
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LONG ANSWER QUESTIONS (5 MARKS)
1. List any exibit the following characterstics of a population & explain?
ANS:- (i)Birth rate/natality
-natality refers to the no of individuals added to a population by birth, at a given period of time,
-it increases the population size
(ii) Death rate/mortality
-mortality refers to the no. of individuals removed by death from a population, at a given period
of time.
-it decreases the population size.
- birth rate & death rate are expressed change in the no. with respect to the no. of members in a
population.
(iii) Sex ratio;
-it refers to the ratio between the no. of males & females in a given population at a given period
of time.
(iv)Age ratio:
-age ratio of a population refers to the no. of individuals in different ages/age groups in a
population.
-the age groups are pre-reproductive & post-reproductive ages.
-a population with more individuals in the pre-reproductive & reproductive age group will be an
expanding one.
-A population with less individuals in the pre-reproductive age group & more in the postreproductive age group will be a decline one.
2. What is an pyramid? what do they show about human population? Represent
diagrammatically the different shapes of age pyramids & mention what each type
represents?
ANS:- Age pyramid is the graphic representation of the age distribution, i.e. per cent
individuals in different age groups of a population.
For human population, the age pyramids generally show age distribution of males &
females in a combined diagram.
-the shape of the age pyramids reflects the growth status of the population.
-the size of the population tells us a lot about its status in the habitat.
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-any ecological process is investigated in terms of a change in the population size.
3. Define the following terms & give an example for each.
(a)Commensalism
(b)Parasitism
(c)Camouflage
(d)Mutualism
(e)Interspecific competition
ANS:-(i) Commensalisms:-it is the inter specific interactions, where one species is benefited by the association, while the
other is neither benefited nor harmed, e.g. a clown fish living among sea anemones.
(ii) Parasitism:-it is the inter specific interactions, where one species takes food & shelter from another living
species & damages the host in due course of time; the parasite is benefited & the host is harmed.
e.g. liver fluke in human beings.
(iii)Camouflage:-it is an adaptation where the animal blends with the surroundings to escape detection by the
predator e.g. Frogs have olive green skin with patches of chromatophores to camouflage with the
grasses.
(iv)Mutalism:-it is the inter specific interactions where individuals of two different species are mutually
benefited. e.g. An algae & a fungus in a lichen.
(v) Interspecific competition:- it is an inter specific interactions where individuals of two different species compete with eavh
other for certain resources & both are formed.
e.g. Flamingoes & fishes in a lake competing for the same zooplankton.
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