CBSE Class 12 Biology Organisms And Populations Notes

 ORGANISMS AND POPULATIONS

Ecology: It is a branch of biology which studies the interactions i) among organisms and ii) between the organism and its physical ( abiotic) environment.

Organism: Individual of a species.

Population: Population is a group of individuals of the same species which can interbreed among themselves and live in a localized area.

Biome: The largest ecological regions distinguishable by characteristic plants and animals. Eg. tundra, conifer, deciduous forest, grassland, tropical, and desert.

Alpine tundra: Alpine tundra is located on mountains throughout the world at high altitude where trees cannot grow. The growing season is approximately 180 days. The night time temperature is usually below freezing. Unlike the arctic tundra, the soil in the alpine is well drained.

Group of animals that live in Alpine tundra:

Mammals: mountain goats, sheep

Insects: beetles, grasshoppers, butterflies

Coniferous forests: Coniferous forests are made up mainly of cone-bearing or coniferous trees, such as spruces, hemlocks, pines and firs. The leaves of these trees are either small and needle-like or scale-like and most stay green all year around (evergreen). All are softwoods able to survive cold temperatures and acidic soil.

Temperate Forests: The term ‘temperate forest’ is very broad. It covers the forests found between the tropical and subtropical regions and the barren, treeless lands of the far north and extreme south.

Tropical forest: "Tropical forests" encompass the idyllic rainforest, the remote cloud forest, and the lesser-known but equally endangered dry forest, pine savanna and much, much more. They are not one ecosystem, but millions of unique ecosystems.

Deciduous forest: The average annual temperature in a deciduous forest is 50° F. The average rainfall is 30 to 60 inches a year. The deciduous forest has four distinct seasons, spring, summer, autumn, and winter. In the autumn the leaves change color. During the winter months the trees lose their leaves. 

Temperature, water, light, soil.

• Temperature

• Average temperature varies seasonally

•  Organisms may be Eurythermal or Stenothermal

•  Eurythermal- wide range of temperature tolerence

• Stenothermal-Narrow range of temperature tolerance 

Water

• Influences life of organisms. No life without water.

• Productivity and distribution of plants are water dependent.

• Organisms may be Euryhaline or Stenohaline.

•  Euryhaline:Wide range of salinity tolerance

•  Stenohaline:Narrow range of salinity tolerance. 

Light

•  Photosynthesis and release of oxygen light dependent.

•  Sciophytes need to use diurnal and seasonal light intensity of forage, migration and reproduction. 

Soil

•  Nature and proportion of soil in a place depends on climate, weathering process and types of soil.

•  Soil composition, grain size and aggregation determine percolation and water holding capacity of soil.

• Physical and chemical properties determine type of plants and Animals that survive in a habitat. 

Response of organisms to environmental condition 

Regulation
• Organisms maintain homeostasis achieved by physiological and behavioral means
• Thermo regulation and osmoregulation.

Conformation
• Cannot maintain constant internal Environment
• Body temperature and osmotic concentration of body changes with ambient temperature and concentration of medium.-Thermo confirmer and osmo-confirmer

Migration
• Organism moves away temporarily to another habitat in stressful condition. e.g.- Migratory birds like Siberian crane

Suspension
• Organisms suspend their metabolic activities during stressful condition
• Resume their function at the return of favorable conditions.

E.g. Hibernation (winter sleep) of Frog, Reptiles, Polar Bear etc
• Aestivation (summer sleep) in Snail and Fish.
• Seed dormancy.

Adaptation
• Morphological, physiological and behavioral changes that enable organisms to adjust to the ever changing environment .

E.g. Kangaroo rat survives in desert conditions through internal oxidation of fat, removing concentrated urine of limited quantity.
• Allen‗s rule-cold climate mammals have shorter ears and limbs to minimize heat loss.
• Polar mammals like seals have blubber to prevent heat loss.
• Burrowing habit to escape from heat
• Higher count of RBC, Hb (haemoglobin) at high altitudes.

Population attributes
• Birth Rate – Number of individuals born per thousand per year.
• Death Rate – Number of individuals die per thousand per year.
• Sex Ratio – Ratio of male-female in the population.
• Population density. - the number of individual organisms per unit area (appropriate measure – total number-sometimes difficult to determine or meaningless because 4
factors N+I-M+E are concerned w.r.t habitat concerned )

Age pyramids
• If the age distribution (per cent individuals of a given age or age group) is plotted for the population, the resulting structure is called an age pyramid.
• Three ecological ages:
• Pre-reproductive, Reproductive and Post-Reproductive
• High proportion pre-reproductive individuals occur in Expanding population
• Pre-reproductive individuals are uniform in Stable population.
• Pre-reproductive individuals are less in Declining population.

Population growth

Factors that affect the size of population
Food
availability
Weather
Predation pressure
Competition
Density of population at any time at a given
place depends on Natality, Mortality, Emigration
Immigration

• MEASURING DENSITY
• Population Density – Number of individuals per unit of area.
• Population will grow if B+I > D+E
• Population will shrink if B+I < D+E
• Population will be in equilibrium if B+I=D+E

POPULATION GROWTH MODELS
I. Exponential Growth( geometric growth) : Applicable when the resources are unlimited.
Mathematical expression: dN/dt= rN Where ‘r’ is called the ‘intrinsic rate of natural increase’.
• The value of ‘r’ for the Norway rat = 0.015
• The value of ‘r’ for the floor beetle=0.0205
• Population density(N) and Time graph result in a J-shaped curvre.
• Integral form of the exponential equation: Nt = N0ert

II. Logistic Growth ( Verhulst-Pearl Logistic Growth): Applicable when the resources are limited. In nature, a given habitat has enough resources to support a maximum possible number, beyond which no further growth is possible.This limit is called as nature’s ‘Carrying capacity’(K) for that species in that habitat.
• A plot of N in relation to time (t) resuls in a sigmoid curve.
• Mathematical expression: dN/dt=rN(K-N/K) where (K-N/K) is environmental resistance.

Types of population interactions

Mutualism: Both species are benefited.

Lichens: Relationship between Non-photosynthetic Fungi and photosynthetic Algae or Cyanobacteria.

Mycorrhiza: Association between Fungi and Higher Plants like Pinus. Plants and insects for pollination Orchid ophrys and male bee a good example for co-evolution of plants and animals.

PREDATION
One species gets benefited and the other harmed.
Tiger and Deer
Snake and Frog Herbivores and plants

Competition
Both the species are harmed.
Flammingoes and resident fishes compete for the common food zooplankton in South American lakes.
Abington Tortoise and goats in Galapagos Islands for food.
Gause’s Competitive Exclusion Principle -Two closely related species competing for the same resource cannot co-exist indefinitely and the competitively inferior one will be eventually eliminated.

Parasitism
One species gets benefit and the other is harmed.
Parasites

Adaptations of parasites
• Loss of sense organs
• Presence of adhesive organs or suckers
• Loss of digestive system
• High reproductive capacity.

Ammensalism
One species hurts the other but the other is not affected.
Penicillium secretes Penicillin and kill Bacteria but by this Penicillium does not benefit. Algal bloom leads to death of fishes, but the death of fishes is of no use to the algal bloom.

Commensalism
One species benefits and the other neither harmed nor benefited.
The cattle egret catches the insects disturbed by moving cattle, but the cattle neither harmed nor benefited.

Another example
Clown fish gets protection from predators by close association with sea anemone, but the sea anemone is not effected.

Question. If b = 65 and d is = 45, N =100 then find out dN /dt
(a) 2000
(b) 1000
(c) 200
(d) 100
Answer : A

Question. When does the growth rate of a population following the logistic model equal zero? The logistic model is given as dN/dt = rN(l-N/K) NEET 2016
(a) when N nears the carrying capacity of the habitat
(b) when N/K equals zero
(c) when death rate is greater than birth rate
(d) when N/K is exactly one
Answer : D

Question. Which model is considered a more realistic one?
(a) Logistic model
(b) Exponential model
(c) Geometric model
(d) J-shaped model
Answer : A

Question. Asymptote in a logistic growth curve is obtained, when
(a) The value of ‘r’ approaches zero
(b) K = N
(c) K > N
(d) K < N
Answer : B

Question. Populations evolve to maximise their reproductive fitness are also called
(a) Mendel’s fitness
(b) Darwinian fitness
(c) Lamarck’s fitness
(d) Individual fitness
Answer : B

Question. Life history traits of organisms have evolved in relation to the constraints imposed by which components of habitat?
(a) Organic components
(b) Abiotic components
(c) Biotic components
(d) Both (b) and (c)
Answer : D

Question. Choose the incorrect match for life history variations in various organisms.
(a) Breeds only once in their life – Pacific salmon fish, bamboo
(b) Breeds many times during lifetime – Most birds, mammals
(c) Produces large number of small-sized offspring – Birds
(d) Produces large number of large-sized offspring –
Answer : C

Question. Even a plant species, which makes its own food, cannot survive alone, it needs soil microbes to breakdown the …A… matter in soil and return the …B… nutrients for absorption. And then, how will the plant manage pollination without an animal agent? It is obvious that in nature, animals, plants and microbes cannot live in …C… but interact in various ways to form a biological community.
Choose the correct option for A, B and C.
(a) A–inorganic, B–organic, C–isolation
(b) A–organic, B–inorganic, C–isolation
(c) A–organic, B–inorganic, C–community
(d) A–inorganic, B–organic, C–community
Answer : B

Question. Interspecific interactions arise from the interaction of
(a) population of two different species
(b) population of same species
(c) two individuals of same species
(d) two individuals of different area
Answer : A

Question. Interspecific interaction could be
(a) beneficial
(b) detrimental
(c) neutral
(d) All of these
Answer : D

Question. If ‘+’ sign is assigned to beneficial interaction, ‘–’sign to detrimental and ‘0’ sign to neutral interaction,then the population interaction represented by ‘+’ ‘–’refers to
(a) mutualism
(b) amensalism
(c) commensalism
(d) parasitism
Answer : D

Question. The population interaction in which free-living organism that catches, kills and devours individuals of other species called prey is called
(a) parasitism
(b) predation
(c) amensalism
(d) commensalism
Answer : B

Question. Predation is
(a) an unnatural way of transferring of energy to higher trophic level
(b) a natural way of transferring of energy to higher trophic level
(c) harmful to the natural balance
(d) All of the above
Answer : B

Question. Animals eating plants are categorised separately as …A…, they are in a broad ecological context, not very different from …B… .
Choose the correct option A and B.
(a) A–herbivores; B–predator
(b) A–herbivores; B–omnivores
(c) A–omnivores; B–herbivores
(d) A–omnivores; B–predator
Answer : A

Question. Exotic species are also called
I. introduced species
II. alien species
III. non-indigenous species
IV. non-native species
Choose the correct combination.
(a) I, II and III
(b) II, III and IV
(c) I, III and IV
(d) I, II, III and IV
Answer : D

Question. Exotic species sometimes become invasive and starts spreading fast because of
(a) natural predators
(b) abundant natural competitor
(c) invaded land not having its natural predators
(d) mutation in their genome
Answer : C

Question. The prickly pear cactus becomes unusually abundant after its introduction in Australia because it
(a) does not have its predator
(b) formed new mycorrhizal association
(c) lost its thorns
(d) All of the above
Answer : A

Question. Prickly pear cactus (an exotic species) can be brought under control (in Australia) by using
(a) babul eating predators
(b) kikar eating predators
(c) cactus feeding predators
(d) intensive herbicides
Answer : D

Question. Predators also help in …A… species diversity in a community, by …B… the intensity of competition among competing prey species. Here, A and B can be
(a) A–exceeding; B–increasing
(b) A–maintaining; B–reducing
(c) A–reducing; B–maintaining
(d) A–maintaining; B–increasing
Answer : B

Question. Starfish pisaster is the important predator in intertidal communities of
(a) American pacific coast
(b) Indian pacific coast
(c) Middle pacific coast
(d) East Indian lakes
Answer : A

Question. ‘Cryptically-coloured’ (camouflaged) is a technique through which prey can
(a) feed abundantly
(b) lessen the impact of predator
(c) increase their number
(d) increase their reproductive fitness
Answer : B

Question. Monarch butterflies are highly distasteful to predator due to
(a) its ugly look
(b) a special chemical present in his body
(c) Both (a) and (b)
(d) a poison secreted by their special glands
Answer : B

Question. You never see any cattle or goat browsing on Calotropis due to
(a) its appearance
(b) production of foul odour
(c) production of cardiac glycosides
(d) distastefulness of its leaves
Answer : C

Question. Which of the following is not an example of a defence used by plants against herbivores?
(a) Production of caffeine, tannins and quinine
(b) More production of non-woody tissues
(c) Production of hairs, thorns, spines
(d) Production of hormone-like chemicals that interfere with insect metamorphosis
Answer : B

Question. Which of the following is not an example of prey-predator relationship?
(a) Tiger eating deer
(b) Plant Nepenthes trapping an insect
(c) Bacteria decomposing organic matter
(d) Crocodile killing a man
Answer : C

Question. In which of the following interactions both partners are adversely affected?
(a) Competition
(b) Predation
(c) Parasitism
(d) Mutualism
Answer : A

Question. On the rocky sea coasts of Scotland, the larger and competitively superior barnacle Balanus dominates the intertidal areas and excludes the smaller barnacle Chathamalus from that zone.
Which kind of interaction is being depicted by this example?
(a) Predator
(b) Parasitism
(c) Commensalism
(d) Competition
Answer : D

Question. Level of competition between species depends on
(a) availability of resources
(b) population density
(c) group interaction of organism
(d) All of the above
Answer : D

Question. When Darwin spoke of the struggle for the existence and survival of the fittest in the nature, he was convinced that
(a) intraspecific competition is a potent force in organic evolution
(b) interspecific competition is a potent force in organic evolution
(c) intensive reproduction is the potent force in organic evolution
(d) intensive predation is the potent force in organic evolution
Answer : B

Question. Competition is best defined as a process in which the fitness of one species (measured in terms of its ‘r’ the intrinsic rate of increase) is significantly
(a) lower in the presence of another superior species
(b) higher in the presence of another superior species
(c) equal in the presence of another superior species
(d) equal in the presence of their own species
Answer : A

Question. A species whose distribution is restricted to a small geographical area because of the presence of a competitively superior species is found to expand its distributional range dramatically when the competing species is experimentally removed. This is called as
(a) competitive exclusion
(b) competitive release
(c) predation
(d) mutualism
Answer : A

Question. The principle of competitive exclusion was stated by
(a) C Darwin
(b) GF Gause 
(c) MacArthur
(d) Verhulst and Pearl
Answer : B

Question. Gause’s principle of competitive exclusion states that
(a) competition for the same resources excludes species having different food preferences
(b) no two species can occupy the same niche indefinitely for the same limiting resources
(c) larger organisms exclude smaller ones through competition
(d) more abundant species will exclude the less abundant species through competition
Answer : B

Question. Species facing competition might evolve mechanism that promotes coexistence rather than exclusion. One such mechanism is
(a) competitive release
(b) resource partitioning
(c) coevolution
(d) None of the above
Answer : B

Question. Read the following reasons for the adaptation in parasites.
I. loss of unnecessary organs.
II. presence of adhesive organs.
III. origin of suckers to cling to host.
IV. loss of digestive system.
V. high reproductive capacity.
Choose the correct option.
(a) I, III and IV
(b) II, IV and V
(c) I, IV and V
(d) I, II, III, IV and V
Answer : D

Question. Parasite that feed on the external surface of the host organism is called
(a) endoparasite
(b) ectoparasite
(c) brood parasite
(d) None of these
Answer : B

Question. ....A... parasite have simple life cycle and ....B....parasite have complex life cycle.
(a) A–Ecto, B–endo
(b) A–Endo, B–brood
(c) A–Brood, B–endo
(d) A–Brood, B–ecto
Answer : A

Question. An interaction in which one organism is benefitted and other is unaffected
(a) predation
(b) commensalism
(c) mutualism
(d) parasitism
Answer : B

Important Questions for NCERT Class 12 Biology Organisms and Populations

Ques. Gause’s principle of competitive exclusion states that
(a) no two species can occupy the same niche indefinitely for the same limiting resources
(b) larger organisms exclude smaller ones through competition
(c) more abundant species will exclude the less abundant species through competition
(d) competition for the same resources exclude species having different food preferences. 

Answer: A

Ques. In which of the following interactions both partners are adversely affected?
(a) Parasitism (b) Mutualism
(c) Competition (d) Predation

Answer: C

Ques. According to Darwin, the organic evolution is due to
(a) competition within closely related species
(b) reduced feeding efficiency in one species due to the presence of interfering species
(c) intraspecific competition
(d) interspecific competition. 

Answer: C

Ques. Besides paddy fields, cyanobacteria are also found inside vegetative part of
(a) Equisetum (b) Psilotum
(c) Pinus (d) Cycas. 

Answer: D

Ques. A sedentary sea anemone gets attached to the shell lining of hermit crab. The association is
(a) commensalism
(b) amensalism
(c) ectoparasitism
(d) symbiosis. 

Answer: A

Ques. A biologist studied the population of rats in a barn. He found that the average natality was 250, average mortality 240, immigration 20 and emigration 30. The net increase in population is
(a) 05 (b) zero
(c) 10 (d) 15. 

Answer: B

Ques. The age pyramid with broad base indicates
(a) high percentage of old individuals
(b) low percentage of young individuals
(c) a stable population
(d) high percentage of young individuals.

Answer: D

Ques. Cuscuta is an example of
(a) ectoparasitism (b) brood parasitism
(c) predation (d) endoparasitism.

Answer: A

Ques. Which one of the following is categorised as a parasite in true sense?
(a) The female Anopheles bites and sucks blood from humans.
(b) Human fetus developing inside the uterus draws nourishment from the mother.
(c) Head louse living on the human scalp as well as laying eggs on human hair.
(d) The cuckoo (koel) lays its eggs in crow’s nest.

Answer: C

Ques. Which one of the following is most appropriately defined?
(a) Host is an organism which provides food to another organism.
(b) Amensalism is a relationship in which one species is benefitted whereas the other is unaffected.
(c) Predator is an organism that catches and kills other organism for food.
(d) Parasite is an organism which always lives inside the body of other organism and may kill it.

Answer: C

Ques. Geometric representation of age structure is a characteristic of
(a) population (b) landscape
(c) ecosystem (d) biotic community.

Answer: A

Ques. The population of an insect species shows an explosive increase in numbers during rainy season followed by its disappearance at the end of the season. What does this show?
(a) The food plants mature and die at the end of the rainy season.
(b) Its population growth curve is of J-type.
(c) The population of its predators increases enormously.
(d) S-shaped or sigmoid growth of this insect.

Answer: B

Ques. If the mean and the median pertaining to a certain character of a population are of the same value, the following is most likely to occur
(a) a bi-modal distribution
(b) a T-shaped curve
(c) a skewed curve
(d) a normal distribution. 

Answer: D

Ques. A high density of elephant population in an area can result in
(a) intraspecific competition
(b) interspecific competition
(c) predation on one another
(d) mutualism. 

Answer: A

Questions for Self Evaluation

1. A four years old girl suffered from ADA deficiency. She was cured by inserting a correct gene into her.a) what is this process called? b) In which cells are the genes introduced ?

2. What is the other name of mobile genetic elements?

3. Differentiate between insulin and pro insulin?

4. Explain down stream processes?

5. Differentiate exonuclease and endonuclease.

6. Expand the term PCR.

7. What is its importance in genetic engineering?

AMENSALISM :- Interaction in which one species is harmed whereas the other one is unaffected.

CARRYING CAPACITY :- Maximum size of population that can be sustained by the Environment

COMMENSALISM :- Interaction in which one species gets benefits and other is neither harmed nor benefited.

CONFORMERS :- Majority of animals and nearly all plants which cannot maintain constant internal environment.

EURYTHERMAL :- the organisms that can tolerate and thrive in a wider range of temperature.

EXPONENTIAL GROWTH :- Unimpeded growth of a population in an environment with abundant resources.

LOGISTIC GROWTH :- Growth of a population in an environment with limited resources (initial lag phase, phase of acceleration and finally stationary phase).

MORTALITY :- The number of deaths in a population during a given period.

NATAILITY :- The number of births in a population during a given period.

POPULATION DENSITY :-The number of individuals of a species present in per unit area at given time.

REGULATORS :- The organisms which maintain homeostasis (constant body temperature and osmotic concentration) by physiological means.

STENOTHERMAL :- The organisms that area restricted to narrow range of temperature.

ASSIGNMENTS

LEVEL 1

1 Why is thermoregulation more effectively achieved in larger animals than smaller ones?

2 What are osmoconformers?

3.What are the 2 forms of population growth?

4.What type of interaction is shown by sparrow eating the seeds?

5.How are eurythermal animals differ from stenothermal?

6.Name the four levels of organization that are studied in ecology.

7.Give any one example of brood parasitism.

8.Write an expression, which gives the change in population size after a given time.

LEVEL2

1.Mention the adaptations the mammals of colder areas have.

2.When does a population growth curve assume J-shape?

3.What is Gause‘s Compitition Exclusion Principle? Give 1 example.

4. How is cactus adapted to survive?

5. Lichen and mycorrhiza are very important examples of mutualism.

(i) Define mutualism.

(ii) Write the names of components of both.

(iii) What is the benefit of mutualism to both of them.

6. What type of morphological and physiological defences have been evolved by plants.

LEVEL3

1. Mr. Ram on a trip to Rohtang Pass Suddenly experienced heart Palpitations, Nausea, fatigue etc

on reaching the destination. Suggest the reasons for his sudden deterioration of health and also state whether his body will withstand this problem if he stays there for long and how? 

2. Observe the following equation :

i) Name the population growth curve.
ii)What does N, r and K represent?
iii).What type of growth status the following pyramid represents.

3. .Anand on a visit through an under the ocean aquarium found that many sea anemones are attached to hermit crab shells, sucker fisher attached to the ventral surface of sharks and clown fish living among the sea anemones. He wondered whether all these associations are of the same type; can you help him to arrive at the correct conclusion.

4. Abingdon tortoise in Galapagos Island became extinct with in a decade after goats were introduced on the island. Why? What could be principle behind this situation?

5. An orchid plant is growing on the branch of a mango tree. How do we describe this interaction b/w orchid and mango tree?

6. Observe this diagram and answer the following question

a. What is the terminology for B& E.?
b. If B + I is more then D + E then what will happen to population density.

(c) What are the most important factors which influence a population density of an area under normal condition ?
(d) If a habitat is being colonised recently then which factor contribute more to the population growth

QUESTIONS FOR SELF EVALUATION

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

2. The population of tigers in a forest becomes zero, due to uncontrolled hunting. What would be the long term effects of this situation in the forest?

3. Identify the biome distribution with respect to annual temperature and Precipitation from the following graph. Answer A, B, C & D.

4. The following graph represents the organismic0 response to certain environmental condition.

(i) which one of these, A , B , C depicts conformers?
(ii) How do A , B differ from each other with reference to homeostasis?
(iii) What does C of graph depict?
(iv) Mention the category to which man belongs.

(i) Men Study the given age profiles related to human population and answer the following questions
(ii) tion the names given to A , B , C kinds of age profiles.
(iii) Which one of these is ideal for a population?(iv) How do such age profile studies help policy makers prepare for future planning?

5. Why small animals are rarely found in polar region?

6. How does the special photosynthetic pathway like CAM support desert plants? 

7. Why do animals migrate from one region to the other region in the cold season?

8. What type of population interaction in A, B, C, D between the species A and B as per the tabular column given below.
(i) Men Study the given age profiles related to human population and answer the following questions.
(ii) tion the names given to A , B , C kinds of age profiles.
(iii) Which one of these is ideal for a population?
(iv) How do such age profile studies help policy makers prepare for future planning?