Important Questions Class 12 Biology Chapter 13

Important Questions Class 12 Biology Chapter 13 

Important Questions for CBSE Class 12 Biology Chapter 13 – Organisms and Populations

The Important Questions Class 12 Biology Chapter 13 Important Questions outline Ecology as a subfield of Biology that focuses on the analysis of interactions between organisms and their surroundings.

In these Class 12 Biology Chapter 13 Important Questions, students will come to learn about a continuous biological system that can adapt and maintain a particular structure and behaviour, referred to as an organism. This encompasses humans, animals, plants, fungi, and bacteria. A population is the group of an organism. A community made up of the population manages the ecosystem. Abiotic and biotic components both contribute to the environment.

Moreover, these Class 12 Biology Chapter 13 Important Questions, will give students a better idea of how questions would be framed in the final examination. Extramarks will provide students with detailed and authentic solutions to important questions according to CBSE past years’ question papers so that students can prepare for their examination according to the CBSE syllabus. 

 Class 12 Biology Chapter 13 Important Questions

Study Class 12 Biology Chapter 13 Important Questions – Organisms and Population:

1. What is the difference between stenohaline and euryhaline organisms? 

Ans. Organisms that are euryhaline can tolerate a variety of salinities. Stenohaline are organisms with a limited tolerance for salinity.

2. List the four features of biological organisation with which ecology works. 

Ans. Biomes, populations, communities, and organisms.

3. What is the difference between ectotherms and endotherms? 

Ans. Ectotherms are creatures whose body temperature fluctuates and matches the environment in which they live, whereas endotherms have generally stable body temperatures due to physiological regulation.

4. Comment on the statement “lichens are considered good examples of obligate mutualisms.” 

Ans. According to lichens, fungi and algae or cyanobacteria have a close mutualistic interaction, in which the fungus aids in nutrient absorption and supplies nutrients to bacteria while the algae or cyanobacteria prepare food.

5. Give examples of defence mechanisms in plants against herbivory. 

  • Plants produce specific morphological defence mechanisms, such as bougainvillea’s thorns and cactus spines.
  • Certain compounds that plants make and store work to either directly kill insects or prevent them from feasting.

6. Define brood parasitism and the type of adaptation that has evolved in this phenomenon. 

Ans. In order to prevent the host bird from recognising the foreign eggs and expelling them from the nest, evolution has occurred in such a way that the parasite bird’s eggs resemble the host bird’s eggs in size, colour, and other characteristics, such as when a cuckoo bird lays eggs in a crow’s nest. It is regarded as a parasitic form of interspecific interaction because of the fact that in this relationship, the parasite, namely the cuckoo bird eggs, rely on the crow’s nest for food and shelter, but the crow gets harmed because there is competition for scarce food and shelter between the crow’s egg and cuckoo’s egg. As a result, in a parasitic interspecific interaction, the parasite benefits when the host is harmed.

7. What is Gauss’s competitive exclusion principle? 

Ans. According to Gauss’s competitive exclusion principle, two closely related species that are vying for the same resources cannot coexist since the competitively weaker one will be wiped out. However, this is only true when resources are scarce and not in other circumstances.

8. Define migration. Why do animals show this phenomenon? 

Ans. Migration is a phenomenon in which organisms temporarily leave stressful environments in favour of friendly habitats, as when birds migrate over great distances in the winter.

9. How do lizards in the desert maintain a constant temperature? 

Ans. Desert lizards can withstand high temperatures by maintaining a somewhat constant body temperature through behavioural mechanisms. When their body temperature is below what is comfortable, they take a sunbath and absorb heat, and when it is higher, they move into the shadows.

10. Describe how the root system, stem, and leaves of xerophytes are specifically adapted.


  • ROOT ADAPTATIONS – Xerophytes have lengthy, well-developed roots that are heavily branched. However, certain succulent perennial xerophytes have deep but shallow root systems. They appear to take in water from dewdrops and tiny raindrops.
  • Woody xerophytes have stems that are relatively stunted, hard, and inflexible. The main stem and branches of an acacia tree may take the form of a thick, fleshy, flattened, and green-modified structure known as a phylloclade.
  • ADAPTATION IN LEAVES – Short leaves reduce the likelihood of overheating when exposed to solar radiation, which in turn slows down the rate of transpiration. The thick, meaty, green, and leathery leaves of xerophytes are noted for their ability to hold water.

11. List and explain the important characteristics of a population.

Ans. These are a population’s four main characteristics:

    • Population Density: Population density is the size of a population relative to a specific unit of space. The upper limit of density is determined by metabolic equilibrium, trophic level nutrition, and energy flow within an ecosystem. The following formula can be used to calculate population density:
    • Birth Rate / Natality – The birth rate, also known as natality, is the number of newborns generated by a natural process in a given amount of time.
    • Death Rate / Mortality – This term refers to the population’s mortality rate. It is expressed as the number of people who pass away in a specific time frame.
    • Carrying Capacity- Depending on the size and productivity of a habitat or ecosystem, a limited number of species can fit in a given area. The term for this is carrying capacity.

12. What unique adaptations do hydrophytes have in terms of their roots, stems, and leaves?


    • ADAPTATIONS IN ROOTS – Some submerged or floating plants lack roots, and root systems are haphazardly formed and unbranched. With the exception of planted floating hydrophytes, there are no root hairs.
    • CHANGES IN STEM- Submerged hydrophytes have stems that are long, slender, and flexible, but free-floating hydrophytes have stems that are thick, stout, and stoloniferous and grow horizontally on the water’s surface.
    • ADAPTATIONS IN LEAVES – Leaves have submerged forms, are long and thin, and are shaped like ribbons. The petioles of leaves of free-floating plants exhibit an endless capacity for expansion.

13. Co-evolution of mutualists is a common aspect of mutualism. Explain this phenomenon, taking the wasp fig as an illustration of an animal-plant connection.

Ans. Animals are required by plants to pollinate their flowers and spread their seeds. It goes without saying that animals should be paid for the assistance they give to plants. “Plant-animal interactions typically entail co-evolution between the mutualists. It simply means, the evolution of the flowers and their pollinators that can be pollinated only by their partner wasp species and no other species exert mutualism,” according to the study. Plants offer rewards or fees in the form of seed dispersers. In addition to using the fruit as a place to lay her eggs, the female wasp also uses a developing seed inside the fruit to feed her larvae.

The wasp pollinates the fig inflorescence while searching for appropriate places to lay eggs. In exchange for pollination, the fig gives the wasp some of its developing seeds to eat as food for the wasp larvae.

14. What is the difference between diapause and hibernation?

Ans. Spending unfavourable climatic circumstances during their development is the phenomenon known as diapauses. Hibernation is the phenomenon whereby cold-blooded creatures spend the winter in slumber or dormancy by hiding in hollow tree trunks, tunnels, caverns, etc., exhibiting minimal physiological activity.

15. Explain how kangaroo rats live in the deserts of North America in the absence of water. 

Ans. The kangaroo rat can meet all of its water needs in the deserts of North America by oxidising fat internally, which produces water as a byproduct. It can also concentrate its pee to a very small volume.

16. Ophrys, an orchid flower, co-evolves so that its petal continues to resemble that of a female bee. Why does it do this and how?

Ans. They make use of “sexual deceit”. Uncanny similarities exist between one petal and the female bee. The male bee is drawn to what it interprets as a female “pseudocopulation”, in which pollen is dusted on the male bee and it is thought to be a body. When the same male bee pseudocopulates with a different bloom, pollen is transferred from one flower to another. Ophrys takes this action to avoid reducing pollination success unless it simultaneously evolves with a female bee.

17.  Explain the exponential growth model with a curve of a diagram. 

Ans. This type of curve is seen when reindeer are underpopulated and growing in an environment free from predators with an abundance of food. As a result of the small population’s initial need for time to transform according to the new environment, the J-shaped curve in this instance prevents population growth. Once embraced, they rapidly grow in number. As long as the food is available, this growth and multiplication will continue. Over time, as the population grows, so does the available food supply. This results in widespread famine increased mortality and the creation of a J-shaped curve. Using the equation, the J-shaped growth form is given.

18. Describe the population’s logistic growth model and provide a suitable curve. Explain the reason why this curve is more realistic. 

Ans. A sigmoid or an S-shaped curve can be seen on the logistic growth curve. There are three stages:

  • Lag-phase: It’s regarded as an early stage with minimal to no growth. Prior to beginning their multiplication, the underpopulation of cells adapts to or stabilises with the growth parameters during the lag phase.
  • Exponential phase or log phase: It is the midway stage of a geometric or fast ascent. When the small population is stable, cells that have already begun to reproduce quickly continue to do so since there is an abundance of food and other necessities for existence.
  • The commencement of the stationary phase, also known as the steady phase, occurs shortly after the amount of food falls in proportion to the number of cells. As a result, there is no particular surge in the number of cells during this phase as the number of newly created cells approaches being equal to the number of cells that die.

19. Mention the various defensive techniques that lessen the effects of predatory behaviour.

Ans. Plant species have developed a variety of defence systems to lessen the effects of predation. Some of them are as follows.

  • Some bug species and frogs have camouflage or cryptic colouration to evade their predators.
  • Some animals, like monarch butterflies, are extremely repulsive to their predators because they build up a particular chemical by consuming noxious weeds while in their caterpillar stage of development.
  • Some preys are poisonous, and as a result, predators avoid them.
  • Plants have developed specific morphological or chemical defensive systems against herbivores, such as the thorns on bougainvillaea.
  • Plants also create several compounds that serve the following purposes:

i. They make animals ill.

ii. They might stop them from eating.

iii. They could hinder digestion.

20. Define altitude sickness and how can one overcome it. 

Ans. Breathing difficulties at high altitudes. Cause: The body does not receive enough oxygen due to low atmospheric pressure at high elevations. Heart palpitations, tiredness, and nausea are the symptoms.

The body adjusts by:

  1. producing more red blood cells.
  2. reducing haemoglobin’s affinity for attaching to haemoglobin.
  3. increasing breathing.

FAQs (Frequently Asked Questions)

1. What are the reasons behind the extinction of species?

  1. Genetic and demographic phenomena
  2. Destroying natural habitats
  3. Spread of invasive species
  4. The environment
  5. Illegal trafficking and hunting

2. Define population variation.

The distribution of data points within a given population can be estimated using population variance.

3. Give an example of an organism that enters ‘diapause’ and why?

In order to avoid unfavourable environmental conditions and to postpone their overall development, many zooplanktons in lakes and ponds go into diapause.

4. Why are there no green plants in the ocean below a certain depth?

Green plants are not found below a certain depth because the habitat lacks light.