NCERT Solutions for Class 12 Biology Chapter 11 Organisms and Populations

Organisms and Populations Class 12 NCERT Solutions discusses the various ways different living organisms react to the environment and how the population of organisms changes and develops in a specific span of time. The NCERT Solutions for Class 12 Biology describes important points such as the adaptation of organisms towards temperature, water, and other environmental shifts and how organisms get associated with each other in competition, predation, and other association modes. It also shows important indicators of population such as birth rate, death rate, age distribution, and density of population.

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1. NCERT Solutions for Class 12 Biology Organisms and Populations PDF
2. NCERT Solutions for Class 12 Biology Chapter 11
3. Approach to Solve Questions of Class 12 Chapter 11
4. Important Topics of Organisms and Populations
5. What Extra Should Students Study Beyond the NCERT for NEET?
6. Important Question
7. NCERT Solutions for Class 12 Biology Chapter-wise

The solutions to the chapter are easy, step-by-step solutions to textbook questions, which can make it easy for students to understand complex concepts like ecological adaptations, population growth patterns, and species interactions. The solutions NCERT Solutions make learning easy for the students on ecosystems, biodiversity, and how much of nature needs to be conserved, all in an easy and methodical manner.

NCERT Solutions for Class 12 Biology Organisms and Populations PDF

Students can download the complete questions with detailed answers PDF of this chapter for better learning:

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NCERT Exemplar for Class 12 Biology Chapter 11 Organisms and Populations

NCERT Solutions for Class 12 Biology Chapter 11

The detailed answers to all the questions in this chapter are given below:

Ques:1 List the attributes that populations possess but not individuals.

Ans: Traits that populations have but not individuals:

• Population size, density, birth rate, death rate, and age distribution are traits of a population.
• These traits characterise a group of organisms, not an individual.

Ques:2 If a population growing exponentially double in size in 3 years, what is the intrinsic rate of increase (r) of the population?

Ans: Intrinsic rate of increase (r):

• The formula for exponential growth is $$N_t=N_0\times e^{rt}$$ .

• Given that the population doubles in 3 years, we use $$2N_0=N_0\times e^{3r}$$ .

• Solving for r, we get r ≈ 0.231 per year.

Ques:3 Name important defence mechanisms in plants against herbivory.

Ans: Plant defense mechanisms against herbivory:

• Thorns and spines (e.g., cactus) deter animals from consuming plants.
• Chemical defences such as bitter or toxic chemicals (e.g., alkaloids in tobacco).
• Mimicry and camouflage to evade detection (e.g., passionflower leaves resemble butterfly eggs).

Ques:4 An orchid plant is growing on the branch of the mango tree. How do you describe this interaction between the orchid and the mango tree?

Ans: Interaction between the mango tree and the orchid:

• This is a case of commensalism.
• The orchid gains from receiving support and sunlight, without affecting the mango tree in any way.

Ques:5 What is the ecological principle behind the biological control method of managing with pest insects?

Ans: Ecological principle supporting biological control of pest insects:

• It relies on predation and parasitism.
• Natural predators (e.g., ladybugs consuming aphids) or parasites (e.g., wasps laying eggs on caterpillars) regulate populations of pests using no chemicals.

Ques:6 Define population and community.

Ans:

• Population: A collection of members of the same species inhabiting a particular location (e.g., all the tigers in a forest).
• Community: Various species inhabiting the same location and interacting with each other (e.g., plants, animals, and microbes in a pond).

Ques:7 Define the following terms and give one example for each:

(a) Commensalism

Ans: One species gains, the other is not affected (e.g., barnacles on whales).

(b) Parasitism

Ans: One species gains, the other suffers (e.g., tapeworm in humans).

(c) Camouflage

Ans: An organism matches its environment to hide from predators (e.g., stick insects).

(d) Mutualism

Ans: Both species gain (e.g., bees pollinating flowers).

(e) Interspecific competition

Ans: Two species compete for the same resource (e.g., lions and hyenas competing for food).

Ques:8 With the help of a suitable diagram describe the logistic population growth curve.

Ans: The logistic growth curve shows how a population increases with finite resources.

• Initially, the population increases slowly (lag phase), followed by rapid increase (exponential phase).
• When resources run out, growth slows down to a stable stage (carrying capacity).

The equation of the logistic growth curve is as follows:
dN/dt = rN(K−N/K)
Where N = Population density at time t
R = Intrinsic rate of natural increase
K = Carrying capacity
Since resources for growth for populations are finite and become limiting, the logistic growth model is considered a more realistic one.

Ques:9 Select the statement which explains best parasitism.

(a) One organism is benefited.

(b) Both the organisms are benefited.

(c) One organism is benefited, other is not affected.

(d) One organism is benefited, and another is affected.

Ans: The best explanation of parasitism:

• (d) One organism is benefited, other is affected.

Ques:10 List any three important characteristics of a population and explain.

Ans:

• Population Density: The number of organisms per unit area. Influences resource utilisation and competition.
• Natality (Birth Rate): The number of new organisms added to a population via reproduction. Determines population growth.
• Death Rate (Mortality): The amount of people dying within a period. Affects population decrease.

Approach to Solve Questions of Class 12 Chapter 11

To easily answer Organisms and Populations questions, keep these simple points in mind:

• First Concepts: Read the NCERT chapter slowly to know the concepts like interactions of population, adaptations, and growth models.
• Take Help of NCERT Solutions: Take help from NCERT Solutions for proper concepts of textbook problems.
• Practice Previous Year Questions (PYQs): Practice PYQs to know the type of questions that NEET asks.
• Practice Diagrams and Graphs: Take special care while drawing diagrams like the curve of logistic growth, as they are often asked in the exam.
• Updated Periodically: Update periodic definitions, examples, and concepts of ecology as and when often.
• Highlight Important Lines: Highlight important lines in the NCERT which may come as direct questions in NEET.

NCERT Exemplar Class 12 Solutions

Important Topics of Organisms and Populations

The key topics covered in this chapter are:

Population

• Population refers to a collection of organisms belonging to the same species in a definite area.
• They are affected by the availability of food, climatic conditions, and environmental parameters.
• Population analysis helps in species survival as well as in conservation.

Population Features

• Size: Number of entities present in the population.
• Density: Number of individuals per area unit.
• Birth Rate & Death Rate: No. of births and deaths per population over an interval of time.
• Age Structure: Percentage composition of people in varying age groups.

Population Growth

Populations increase or decrease depending on births, deaths, immigration, and emigration.

Two common types of growth patterns:

• Exponential Growth: Fast population growth without any limiting factors.
• Logistic Growth: Slowing growth due to the limitation of resources.

Variation in Life History

• Organisms possess various survival and reproductive strategies.
• Some species produce a lot of offspring and reproduce rapidly, whereas others produce few offspring but provide care for them.
• Environmental pressures affect life history characteristics such as lifespan and breeding cycles.

Population Interactions

• Competition: Two species competing for the same resources.
• Predation: One animal (predator) preys on and consumes another (prey).
• Mutualism: Both species gain from the association (e.g., flowers and bees).
• Parasitism: One animal (parasite) resides on or within another (host) and harms it.

These are the key topics covered in the organisms and populations NCERT solutions for class 12, giving students a detailed knowledge of health and disease.

Also Check NCERT Books and NCERT Syllabus here:

• NCERT Books Class 12 Biology

• NCERT Syllabus Class 12 Biology

• NCERT Books Class 12

• NCERT Syllabus Class 12

Adaptations of Organisms to Their Environment

Organisms evolve structural, physiological, and behavioural adaptations to thrive in various environments.

Examples:

• Polar bears have thick fur and layers of fat to live in cold climates.
• Desert plants such as cacti have thick cuticles and small leaves to reduce water loss.
• Camouflage helps animals such as chameleons blend into their environment.

NCERT Solutions for Class 12- Subject-wise

What Extra Should Students Study Beyond the NCERT for NEET?

Here is a table for all the important topics from the chapter:

Important Question

Question 1: Which of the following is commensalism in an ecosystem?

A) Cattle egret and grazing cattle

B) Lichen (alga + fungus)

C) Sea anemone and clownfish

D) Cuscuta on a hedge plant

Answer:

Let us consider each of these options:

A) Cattle egret and grazing cattle

This is an example of a commensal relationship.

The cattle trundle through the grass and disturb insects. The cattle egret accompanies them along and eats up the insects flushed out.

The egret profits (gets food), and the cattle are not harmed or profited.

This is commensalism.

B) Lichen (alga + fungus)

This is mutualism.

The alga undergoes photosynthesis and supplies food, and the fungus provides protection and maintains moisture.

Both organisms profit.

C) Sea anemone and clownfish

This is also mutualism, although some texts have it as commensalism.

The clownfish finds refuge from predators when hidden in sea anemone tentacles, and the sea anemone can gain an advantage from food scraps or improved water flow.

Both gain, it's mutualism; only one gains, it's commensalism. But this mutualistic process is more widely accepted.

D) Cuscuta on a hedge plant

This is parasitism.

Cuscuta is a parasitic plant which obtains nutrients from the host plant and damages it.

Hence, the correct answer is option (A), Cattle egret and grazing cattle

NCERT Solutions for Class 12 Biology Chapter-wise

Below given are the solutions: