Organisms and Populations Exam Questions Class 12 Biology

Exam Questions Class 12

Please see Chapter 13 Organisms and Populations Exam Questions Class 12 Biology below. These important questions with solutions have been prepared based on the latest examination guidelines and syllabus issued by CBSE, NCERT, and KVS. We have provided Class 12 Biology Questions and answers for all chapters in your NCERT Book for Class 12 Biology. These solved problems for Organisms and Populations in Class 12 Biology will help you to score more marks in upcoming examinations.

Exam Questions Chapter 13 Organisms and Populations Class 12 Biology

Objective Questions

Question. The term ‘precipitation’ includes
(a) rain
(b) snow
(c) hails
(d) all forms of water that fall to the ground.

Answer

D

Question. A majority of organisms which are restricted to narrow range of temperature are called as
(a) stenothermal
(b) endothermal
(c) ectothermal
(d) eurythermal

Answer

A

Question. The salinity in sea water in parts per thousand (ppt) ranges between
(a) 5-15%
(b) 30-35%
(c) 50-75%
(d) more than 100%

Answer

B

Question. Deep (>500m) in the oceans, the environment is perpetually dark and its inhabitants are not aware of the existence of a celestial source of energy called_________.
(a) ATP
(b) photosynthesis
(c) sun
(d) light

Answer

C

Question. The benthic organisms
(a) live near the sea bottom.
(b) found in open water.
(c) always live at the depth of 50-100 m.
(d) live outside water.

Answer

C

Question. Which of the following is the stage of suspended development?
(a) Dormancy
(b) Hibernation
(c) Aestivation
(d) Diapause

Answer

A

Question. _____ is any attribute of the organism (morphological physiological, behavioural) that enables the organisms to survive and reproduce in its habitat.
(a) Exponential growth
(b) Acclimatization
(c) Adaptation
(d) Mutualism

Answer

C

Question. Microbes present in hydrothermal vents where the temperature far exceed 100°C is
(a) cyanobacteria
(b) archaebacteria
(c) eubacteria
(d) none of these

Answer

D

Question. The age of pyramid with narrow base indicates
(a) high number of young individuals.
(b) low number of young individuals.
(c) high number of old individuals.
(d) low number of old individuals.

Answer

D

Question. _______________ is the number of individuals of the population who left the habitat and have gone elsewhere during the time period under consideration.
(a) Natality
(b) Mortality
(c) Immigration
(d) Emigration

Answer

A

Question. Thorns of Acacia and cactus are the most common morphological means of
(a) reproduction
(b) competition
(c) defence
(d) economical importance

Answer

D

Question. Connell’s elegant field experiments are related to barnacle, in which superior barnacle Balanus dominates the inter tidal area, and excludes the smaller barnacle Chathamalus from that zone. This phenomenon is called
(a) competitive exclusion principle
(b) competitive release
(c) interspecific competition
(d) none of the above

Answer

D

Question. _____________ in birds is an interesting example of parasitism in which the parasitic bird lays its eggs in the nest of its host and the host incubates them.
(a) Bird parasitism
(b) Breed parasitism
(c) Brood parasitism
(d) Ectoparasites

Answer

D

Question. The interaction is detrimental to both the species, in
(a) predation
(b) commensalism
(c) amensalism
(d) competition

Answer

D

Question. An interaction where one species is harmed while the other is unaffected is called
(a) commensalism
(b) competition
(c) amensalism
(d) parasitism

Answer

A

Very Short Answer Questions

Question. Why are cattle and goats not seen browsing on Calotropis growing in the fields?
Ans. Calotropis produces highly poisonous cardiac glycosides. Therefore, cattle and goats do not browse on them.

Question. When and why do some animals like snails go into aestivation?
Ans. Snails undergo aestivation if they are unable to migrate in order to avoid stressful condition of high temperature.

Question. What is mycorrhiza?
Ans. Mycorrhiza is a symbiotic association between a fungus and the roots of higher plants.

Question. Why are mammals the most successful animals on earth?
Ans. The mammals are most successful animals on earth because they can maintain a constant body temperature with high range of tolerance whether in Antarctica or in Sahara desert.

Question. Give an example of an organism that enters ‘diapause’ and why. 
Ans. Many species of Zooplankton under unfavourable conditions enters diapause which delay overall development and hence they can pass unfavourable conditions.

Question. What is a tree line? 
Ans. When we go up the altitude, beyond a particular height no tree are found and the vegetation comprise only of shrubs and herbs. The altitude beyond which no tree is seen is known as tree line.

Question. Why are green algae not likely to be found in the deepest strata of the ocean?
Ans. The wavelength of light at the deepest strata is unsuitable for growth of green algae.

Question. Why has life history of variation evolved? 
Ans. (a) Life history of variation has evolved.
(b) In order to maximise reproductive fitness of individual.

Question. What is the ecological principle behind the biological control method of managing with pest insects?
Ans. The ecological principle operating in the biological control method of managing with pest insect is through their natural enemies, i.e., predators and parasites.

Question. Name the interaction between sea anemone and the hermit crab that grows on it.
Ans. Commensalism

Question. State Gause’s Competitive Exclusion principle. 
Ans. Gause’s Competitive Exclusion Principle states that two closely related species competing for same resources, cannot coexist indefinitely, (the inferior will be eliminated) by the superior one.

Short Answer Questions

Question. In certain seasons we sweat profusely while in some other season we shiver. Explain.
Ans. Human beings maintain a constant body temperature of 37°C. OU In summers: The outside temperature is much higher than our body temperature. Therefore, we sweat profusely. This results in evaporative cooling and our body temperature is brought down to normal (37°C). OU In winters: The outside temperature is much lower than our body temperature. Therefore, we start to shiver; this action (of shivering) is a kind of exercise (work) that produces heat and raises the body temperature.

Question. Explain Verhulst-Pearl Logistic Growth of a population. 
Ans. According to Verhulst–Pearl Logistic growth, a population growing in a habitat with limited resources initially shows a lag phase, followed by phases of acceleration and deceleration and finally an asymptote when the population density reaches the carrying capacity. It is given by the following equation:

dN /dt = rN [K-N/K]

where, N = population density at time t, r = intrinsic rate of natural increase, K = carrying capacity.

Question. Why are small animals rarely found in the polar regions? Explain.
OR 
Why are small birds like humming birds not found in polar regions? Explain. 
Ans. Small animals like humming birds have a large surface area relative to their volume. So they tend to lose body heat very fast when it is cold outside. Then, these animals have to use their energy (generated by metabolic reactions) to generate body heat. That is the reason why small sized animals are rarely found in the polar regions.

Question. Co-evolution is a spectacular example of mutualism between an animal and a plant. Describe co-evolution with the help of an example. 
OR
Describe the mutual relationship between fig tree and wasp and comment on the phenomenon that operates in their relationship. 
Ans. Co-evolution can be observed in Fig (plant) and wasp (animal). The female wasp uses the fruit for oviposition or egg laying. It also uses developing seeds within the fruit for nourishing its larvae.
The wasp in turn pollinates the fig inflorescence. The given Fig species can be pollinated by its ‘partner’ wasp species and no other species.

Question. Many fresh water animals cannot survive in marine environment. Explain.
Ans. Marine environment has high salt concentration. These fresh water animals in such hypertonic surroundings suffer from osmotic problems. Their bodies start losing water by exosmosis.

Question. How do seals adapt to their natural habitat? Explain. 
Ans. Seals adapt to the cold climate by developing a thick layer of fat (blubber) below their skin that acts as an insulator and reduce excess loss of body heat.

Question. Some organisms suspend their metabolic activities to survive in unfavourable conditions. Explain with the help of any four examples. 
Ans. (i) Polar bear: They hibernate during winter to escape the cold weather.
(ii) Snails/fishes: They go into aestivation during summer to avoid heat related problems and desiccation.
(iii) Seeds of higher plants/spores of bacteria/fungi: They become dormant in unfavourable conditions and in case of Amoeba cyst formation takes place.
(iv) Some species of zooplankton: They undergo diapause.

Question. How does a desert plant adapt to the dry, warmer environmental conditions?
Ans. Adaptations of a desert plant:
(i) Leaf surface has a thick cuticle.
(ii) Stomata are situated in deep pits.
(iii) Stem is flattened and performs photosynthesis.
(iv) Leaves are modified into spines aOs puinn tia. (Any two)

Question. Why do clown fish and sea anemone pair up? What is this relationship called?
Ans. The clown fish gets protection from predators which stay away from stinging tentacles of anemone but anemone does not derive any benefit from the fish. This relationship is called commensalism.

Question. (a) Explain “birth rate” in a population by taking a suitable example.
(b) Write the other two characteristics which only a population shows but an individual
Ans. (a) Birth rate is expressed as the number of births per 1,000 individuals of a population per year.
For example, in a pond there were 200 frogs and 40 more were born in a year. Then, the birth rate of the population will be 40/200 = 0.5 frogs per year.
(b) Sex ratio, age distribution, population density, population growth. (Any two)

Long Answer Questions

Question. (a) List any three parameters used by ecologists under different situations to measure the population size in a habitat.
(b) Mention what do the following stand for in the equation given below:
(i) Nt+1, (ii) B and (iii) E.
Nt+1 = N0 + [(B + I) – (D + E)]
Give an explanation for the above equation.
Ans. Refer to Basic Concepts Point 10.

Question. Differentiate between mutualism, parasitism and commensalism. Provide one example for each of them. 
Ans. Refer to Basic Concepts Point 13 (iii), (iv) & (vi).
Predation
It is an interspecific interaction, where an animal, called predator, kills and consumes the other weaker animal called prey.
Predation is nature’s way of transferring energy to higher trophic levels, e.g., a tiger (predator) eating a deer (prey), a sparrow (predator) eating fruit or seed (prey), etc.
Commensalism
Commensalism is referred to as the interaction between two species where one species is benefited and the other is neither harmed nor benefited.

Mutualism
Mutualism is referred to as the interspecific interaction in which both the interacting species are benefited.
Some examples of mutualism

Question. (a) Why are herbivores considered similar to predators in the ecological context? Explain.
(b) Differentiate between the following interspecific interactions in a population:
(i) Mutualism and Competition (ii) Commensalism and Amensalism 
Ans. (a) Herbivores are animals feeding on plants. Although they are classed differently they are considered predators. Like predators, for transfer of energy across trophic levels, herbivores also do the same. Besides this, they also keep the population of their prey under control. For example, when the prickly pear cactus was introduced in Australia in early 1920s, they spread rapidly, causing havoc. Their population was controlled by introducing cactusfeeding predator (a moth).
(b) (i) Differences between mutualism and competition

S.No.MutualismCompetition
(i)This interaction benefits both the interacting species.In this interaction, both the interacting species suffer negatively.
(ii)The two individuals may be physically or physiologically associated.There is no physical association between the competitors.
(iii)E.g., Lichens represent mutualism between fungus and algae where fungus absorbs nutrition and provides protection, and algae prepares food.E.g., In some American Lakes, visiting flamingoes and resident species compete for their common food.

(ii) Commensalism and ammensalism Refer to Basic concept 1i3v ) (and 13v )

Question. (a) Explain any two defence mechanisms plants have evolved against their predators.
(b) How does predation differ from parasitism?
Ans. (a) Plants have developed the following defence mechanisms:
(i) Thorns as means of defence.
(ii) Plants may produce chemicals such as nicotine, caffeine, quinine, strychnine, opium for defence.
(b) Table 13.8 Differences between predation and parasitism

S.No.PredationParasitism
(i)The predator only feeds on prey.The parasite lives and feeds on the host.
(ii)The predator is not prey specific.The parasite is host specific.
(iii)The predator keeps a check on prey population.The parasite coevolves with the host.

Question. How do organisms like fungi, zooplanktons and bears overcome the temporary short-lived climatic stressful conditions? Explain.
Ans. Fungi form thick-walled spores which help them survive in unfavourable conditions. On availability of suitable environment, these germinate. Zooplanktons in lakes and ponds under unfavourable conditions, enter diapause, a stage of suspended development.
Bears in extreme low temperatures, escape winter time by hibernating.

Question. Highlight the differences and a similarity between the following population interactions: Competition, predation and commensalism.
Ans. Table 13.9 Differences between competition, predation and commensalism

S.No.CompetitionPredationCommensalism
(i)In this type of interaction both the species suffer.In this type of interaction the predator kills and consumes the prey.In this type of interaction one species is benefited and the other is neither harmed nor benefited
(ii)It occurs due to limited resources between closely related species.It is the nature’s way of transferring energy to higher trophic level.It is not particularly for any gain of energy or resources.
(iii)For example, In American lakes visiting flamingos and resident fish.For example, tiger (predator) and deer (prey).For example, sucker fish and shark.

Similarity: All these interactions leads to evolution as the fittest organism survives.

Question. Study the graph given alongside and answer the questions which follow:
(i) The curve ‘b’ is described by the following equation:
dN/dt = rN [K-N/K]

What does ‘K’ stand for in this equation? Mention its significance.
(ii) Which one of the two curves is considered a more realistic
one for most of the animal populations?
(iii) Which curve would depict the population of a species of deer if there are no predators in the habitat? Why is it so?
Ans. (i) ‘K’ stands for carrying capacity. Carrying capacity is defined as the maximum number of individuals of a population that can be sustained by the given habitat/environment.
(ii) Curve b‘’ is more realistic.
(iii) Curve ‘a’. When the predators are absent, the prey population grows exponentially.

Question. Interspecific interactions of two species of any population may be beneficial, detrimental or neutral. Explain each of them with the help of suitable examples.
Ans. Population interactions:

S.No.Species ASpecies BName of interaction
(i)++Mutualism
(ii)Competition
(iii)+Predation
(iv)+Parasitism
(v)+0Commensalism

(i) + = Beneficial; – Detrimental; 0 Neutral. Both species ben, ee.fig.t licihne nsmutualism
(ii) Both species lose in competition, e.g. (detrimental)
(iii) In predation and parasitism the predator and the parasite gets benefit but it is detrimental to the other species (host and prey respectively)
(iv) In commensalism one species is benefitted but the other is neither harmed nor benefitted.

Question. (a) List the different attributes that a population has and not an individual organism.
(b) What is population density? Explain any three different ways the population density can be measured, with the help of an example each.
Ans. (a) Attributes of population Birth rate, death rate, sex ratio, age pyramids/age distribution. (Any two)
(b) Population density: Number of individuals per unit area at a given time/period.
(i) Biomass/%Cover, e.g., Hundred Parthenium plants and 1 huge banayan tree.
(ii) Relative Density, e.g., Number of fish caught per trap from a lake.
(iii) Numbers, e.g., Human population
(iv) Indirect estimation, e.g., without actually counting/seeing them, e.g., tiger census based on pug marks and faecal pellets. (Any three)

Question.

(a) Which of the above represents the increase or decrease of population?
(b) If N is the population density at time t, then what would be its density at time (t+1)? Give the formula.
(c) In a barn there were 30 rats. 5 more rats enter the barn and 6 out of the total rats were eaten by the cats. If 8 rats were born during the time period under consideration and
7 rats left the barn, find out the resultant population at time (t+1).
(d) If a new habitat is just being colonized, out of the four factors affecting the population growth, which factor contributes the most?
Ans. (a) a and d represents increase of population and b and c represent decrease of population.
(b) Nt+1 = Nt + [(B + I) – (D + E)]
(c) Here, Nt = 30; I = 5; E = 7 ; D = 6; B = 8
Putting the value in Nt+1 = Nt + [(B + I) – (D + E)]
Nt+1 = 30 + [(8 + 5) – (6 + 7)]
= 30 + [13 – 13]
= 30 + 0
= 30 rats
(d) Immigration contributes the most.

Question. The following diagrams are the age pyramids of different populations. Comment on the status of these populations.

Ans. Fig. A: It is a ‘pyramid’ shaped age pyramid. In this figure, the base, i.e., pre-reproductive stage is very large as compared with the reproductive and post-reproductive stages of the population.
This type of age structure indicate that the population would increase rapidly.
Fig. B: It is an ‘inverted bell’ shaped pyramid. In this figure, the pre-reproductive and reproductive stages are same. This type of age structure indicates that the population is stable.
Fig. C: It is ‘urn’ shaped pyramid. In this figure, the pre-reproductive and reproductive stages are less than the post-reproductive stage of this population. In this population more older people are present. This type of age structure indicates that the population definitely is declining.

Question. List the various abiotic environmental factors.
Ans. (i) Atmospheric factors: Light, temperature, wind and water.
(ii) Lithosphere: Rock, soil.
(iii) Hydrosphere: Pond, river, lake and ocean.
(iv) Edaphic factors: Soil texture, soil water, soil air, soil micro-organisms, soil pH, minerals.
(v) Topographic factors: Slope, altitude, valley.

Organisms and Populations Exam Questions Class 12 Biology