Chapter 13: Organisms and Populations Class 12 Biology NCERT Solutions

Understand population ecology, adaptations, and interactions with Chapter 13 NCERT Solutions. Download free PDFs to strengthen your Ecology concepts. Scroll below for detailed solutions.

What You Will Learn in Chapter 13 – Organisms and Populations

This chapter provides insights into the relationships between organisms and their environment, highlighting the dynamic interactions that occur within ecosystems. The chapter explores how populations of species grow, interact with other species, and how environmental factors shape their distribution.

Key Topics Covered:

  1. Organisms and their Environment

    • Definition of environment and types (biotic and abiotic factors).

    • Adaptations of organisms to survive in various environments (e.g., desert, aquatic).

    • Interaction of organisms with environmental factors (light, temperature, water, etc.).

  2. Population

    • Definition of population, its size, density, and distribution.

    • Age structure and sex ratio of populations.

    • Methods of population estimation (mark-recapture method, Quadrat method).

  3. Population Growth

    • Exponential and logistic growth models.

    • Factors affecting population growth (biotic potential, environmental resistance).

    • Carrying capacity of an environment.

    • Density-dependent and density-independent factors.

  4. Population Interactions

    • Intraspecific interactions: Competition, cooperation.

    • Interspecific interactions: Predation, parasitism, mutualism, commensalism.

    • Ecological niche and competitive exclusion principle.

    • Example of predator-prey relationships and symbiotic relationships.

  5. Ecological Adaptations

    • Structural, functional, and behavioral adaptations of organisms.

    • Adaptations in plants and animals to survive extreme conditions (e.g., xerophytes in deserts, aquatic plants in water).

  6. Biotic Interactions

    • The role of organisms in their ecosystems through interactions such as competition, predation, mutualism, and parasitism.

    • Concept of ecological succession (primary and secondary succession).

  7. Population Regulation

    • Factors that regulate population size and stability.

    • Role of biotic and abiotic factors in regulating populations.

    • The concept of homeostasis in population regulation.

Why Use Our NCERT Solutions for Chapter 13?

Our detailed NCERT solutions for Chapter 13: Organisms and Populations help simplify complex ecological concepts such as population growth models, ecological interactions, and adaptations. With clear explanations and diagrams, students can grasp key ideas like population density, growth patterns, and how species interact with their environment.

Highlights of Our Solutions:

  • Clear, concise answers for all NCERT Intext and Exercise questions.

  • Well-labeled diagrams to explain concepts like population growth models, predator-prey interactions, and adaptations.

  • Real-life examples to illustrate complex ecological interactions and adaptations.

  • Definitions of key terms and concepts related to populations, growth patterns, and ecological factors.

  • Ideal for board exam and competitive exam preparation.

NCERT Solutions for Chapter 13 – Organisms and Populations

Intext Questions:

  • Explanation of ecological adaptations and their importance in survival.

  • Diagrams to help visualize ecological interactions (e.g., predator-prey cycles, mutualism).

  • Step-by-step solutions to questions on population estimation and growth patterns.

Exercise Questions (Q.1 to Q.12):

  • Thorough answers to questions on factors affecting population growth, population interactions, and adaptations.

  • Concept-based questions on different types of interactions (e.g., competition, predation, symbiosis).

  • In-depth explanations of logistic and exponential growth models, and the factors influencing them.

Download Chapter 13 Solutions PDF – Organisms and Populations

Access the free, printable PDF containing all solved NCERT questions for offline revision and exam preparation.

What’s Inside the PDF:

  • Well-structured and concise solutions to all questions.

  • Diagrams and flowcharts explaining population growth models, ecological interactions, and adaptations.

  • Key terms and definitions for quick revision.

Recommended Preparation Tips:

  • Understand population dynamics: Focus on the differences between exponential and logistic growth, as well as factors that regulate population size.

  • Revise ecological interactions: Learn the different types of interactions (competition, mutualism, parasitism) and their impact on organisms and populations.

  • Practice population estimation methods: Familiarize yourself with methods like the Quadrat method and mark-recapture method.

  • Learn adaptations: Study examples of adaptations in both plants and animals, especially in extreme environments like deserts and aquatic habitats.

  • Focus on ecological succession: Understand the concept of primary and secondary succession, and how they lead to changes in ecosystems.

Additional Study Resources:

  • Class 12 Biology Notes – Chapter 13

  • NCERT Exemplar Questions with Solutions for additional practice.

  • NEET-targeted MCQs and previous year questions on organisms and populations.

  • Quick revision charts on population growth models and ecological interactions.

  • Flashcards for important ecological terms and examples.

Mastering Organisms and Populations

Chapter 13 of Class 12 Biology connects students with the fascinating world of ecology. It equips them with the knowledge needed to understand how organisms interact with their environment and each other, and how populations evolve and adapt over time. By mastering the concepts in this chapter, students will gain a strong foundation in ecology, essential for understanding more advanced biological studies.

NCERT Solutions for Chapter 13 Organisms and Populations

1. How is diapause different from hibernation?

Ans: Diapause is a period of suspended growth or development occurring in many insects and other invertebrates during which metabolic activities are greatly reduced. On the other hand, hibernation is a sleep-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.

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

Ans: When a marine fish is placed in a freshwater aquarium, the fish will not be able to survive because marine fish are adapted to live in saline seawater. In fresh water, it will not be able to cope with the outside hypotonic environment because of osmoregulation problems. In freshwater, 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 survive and to get rid of the excess salt present in its body.

3. Define phenotypic adaptation. Give one example.

Ans: Phenotypic adaptations are non-genetic changes occurring in living organisms due to various extreme environmental conditions, such as stress, extreme temperature, or change of habitat. These include acclimatization, behavioural changes, etc.

4. Most living organisms cannot survive at temperatures 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 high temperatures due to:

  • (i) Occurrence of branched chain lipids in their cell membranes that reduce the fluidity of cell membranes.
  • (ii) Having a minimum amount of free water in their bodies. Removal of water provides resistance to high temperature.

5. List the attributes that populations but not individuals possess.

Ans: Some significant attributes that populations but not individuals possess are:

  • (i) Natality
  • (ii) Mortality
  • (iii) Growth forms
  • (iv) Population density
  • (v) Population dispersion
  • (vi) Population age distribution
  • (vii) Sex ratio

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

Ans: If the population growing exponentially doubles in size in 3 years, the intrinsic rate of increase of this population will be towards maximum.

7. Name important defense mechanisms in plants against herbivory.

Ans: There are various defense measures for animals against predators. But plants, as they cannot move away, have certain defense mechanisms against herbivory. Their main defenses are chemical toxins, such as strychnine (produced by tropical vine), morphine (produced by opium poppy), nicotine (produced by tobacco plant). Apart from these chemicals, common defense measures include the presence of spines (modified leaves) on the leaves and stems of the plant, modifications of leaves into thorns, and development of sharp, silicated edges in leaves which prevent them from damage caused by herbivores.

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

Ans: An orchid plant growing on the branch of a mango tree is called an epiphyte, i.e., plants growing on other plants or trees. This type of interaction is known as commensalism, where the orchid derives benefit from the interaction, whereas the mango tree is not affected. The orchid growing on the branch of the mango tree gets more light to grow, and also, the mango tree is not harmed in any way. Commensalism can be defined as an interaction between two animal or plant species that habitually live together, where one species benefits from the association while the other is not significantly affected.

9. What is the ecological principle behind the biological control method of managing pest insects?

Ans: The ecological principle behind the biological control method of managing pest insects is the predator-prey relationship. It is based on the ability of the predator to regulate the prey population.

10. Distinguish between the following:

  • (a) Hibernation and Aestivation
  • (b) Ectotherms and Endotherms

11. 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

12. List the various abiotic environmental factors.

Ans: Abiotic factors are non-living factors and conditions of the environment which influence the survival, function, and behavior of organisms. Various abiotic factors include:

  • (i) Temperature
  • (ii) Water
  • (iii) Light
  • (iv) Humidity
  • (v) Precipitation
  • (vi) Soil

13. Give an example for:

  • (a) An endothermic animal
  • (b) An ectothermic animal
  • (c) An organism of the benthic zone

14. 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 community. Community can be defined as a naturally occurring assemblage of species living within a defined area or habitat.

15. Define the following terms and give one example for each:

  • (a) Commensalism
  • (b) Parasitism
  • (c) Camouflage
  • (d) Mutualism
  • (e) Interspecific competition

16. With the help of a suitable diagram, describe the logistic population growth curve.

Ans: The S-shaped growth curve, also called a logistic growth curve, describes a situation in which (in a new environmental condition) the population density of an organism increases slowly, establishes itself, and then increases rapidly, approaching an exponential growth rate. The S-shaped curve is generated when a population approaches the environment’s carrying capacity. Carrying capacity is the maximum number of individuals of a population that can be supported in a given time.

17. Select the statement which explains best parasitism.

  • (a) One organism is benefited.
  • (b) Both organisms are benefited.
  • (c) One organism is benefited, the other is not affected.
  • (d) One organism is benefited, the other is affected.

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

Ans: The three important characteristics of a population are:

  • (a) Density
  • (b) Natality or Birth rate
  • (c) Mortality or Death rate