NCERT Solutions for Class 12 Biology Chapter 11 Organisms and Populations

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Get Class 12 Biology Chapter 11 Organisms and Populations Question Answer (Exercise Questions)

The detailed answers to all the questions in this chapter are given below. Going through the Class 12 Biology Chapter 11 Organisms and Populations question answer, prepared according to the latest NCERT guidelines, helps students understand concepts related to organisms.

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 characterize a group of organisms, not an individual.

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

Ans:

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

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

Dividing both sides by $N_0$:
$2 = e^{3r}$

Taking the natural logarithm on both sides:
$\ln(2) = 3r$

Solving for $r$:
$r = \dfrac{\ln(2)}{3} \approx \dfrac{0.693}{3} \approx 0.231 \text{ per year}$

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

Ans: Plant defense mechanisms against herbivory:

• Thorns and spines (e.g., cactus) deter animals from consuming plants.

• Chemical defenses 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 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 a 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:
$\frac{dN}{dt} = rN \left( \frac{K - N}{K} \right)$

Where:
N = Population density at time t
r = Intrinsic rate of natural increase
K = Carrying capacity of the environment

Since resources for the growth of populations are finite and become limiting, the logistic growth model is considered a more realistic one.

Ques: 9 Select the statement that explains parasitism best.

(a) One organism benefits.

(b) Both organisms benefit.

(c) One organism benefits, and the other is not affected.

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

Ans: The best explanation of parasitism:

• (d) One organism benefits, and the 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 utilization and competition.

• Natality (Birth Rate): The number of new organisms added to a population via reproduction. Determines population growth.

• Death Rate (Mortality): The number of people dying within a period. Affects the population decrease.

NCERT Solutions for Class 12- Subject-wise

• NCERT Solutions for Class 12 Maths

• NCERT Solutions for Class 12 Chemistry

• NCERT Solutions for Class 12 Physics

Approach to Solve Organisms and Populations Class 12 Question Answer

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

• Read the chapter slowly to know the concepts like interactions of population, adaptations, and growth models.

• Take help from the Class 12 Biology Chapter 11 Organisms and Populations question answer to understand the concepts of textbook problems.

• Practice PYQs to know the type of questions that appeared in the boards and the NEET exam.

• Take special care while drawing diagrams like the curve of logistic growth, which are given in the Class 12 Biology Organisms and Populations question answer

• Highlight important diagrams given in the NCERT Solutions for Class 12, which may come as direct questions in NEET.

NCERT Exemplar Class 12 Solutions

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• NCERT Exemplar Class 12 Biology Solutions

• NCERT Exemplar Class 12 Physics Solutions

Important Questions of NCERT Class 12 Biology Chapter 11 Organisms and Populations

Given below are the important questions from this chapter that help students understand the question pattern and its difficulty level. To gain more clarity, students should read the NCERT Solutions for Class 12 Biology Chapter 11 Organisms and Populations thoroughly.

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 move 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.

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 if 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 that obtains nutrients from the host plant and damages it.

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

Question 2: Amensalism is an association between two species where:

A) One species is harmed and the other is benefited.

B) One species is harmed and the other is unaffected.

C) One species is benefited, and the other is unaffected.

D) Both species are harmed.

Answer:

An ecological relationship known as amensalism occurs when one species suffers harm while the other species is unscathed. This interaction can take many different forms, but it is frequently observed when one species physically prevents another from growing or surviving, or when one creature creates a material that is toxic to another.

Hence, the correct answer is option (B), one species is harmed and the other is unaffected.

Question 3: A population has more young individuals compared to older individuals. What would be the status of the population after some years?

A) It will decline

B) It will stabilize

C) It will increase

D) It will first decline and then stabilize

Answer:

A higher percentage of the population among the youth means that more people are born than die in a population, implying an increase in population growth. As more people reach their reproductive age, there will be an increase in births, thereby contributing to the overall growth of the population size. There is, therefore, a positive trend in population growth as the general upsurge in births is expected to lead to further community growth.

Hence, the correct answer is option (C), It will increase

Question 4: A protozoan reproduces by binary fission. What will be the number of protozoans in its population after six generations?

A) 128

B) 24

C) 64

D) 32

Answer:

In binary fission, each organism divides into two daughter cells. Therefore, after six generations, the number of protozoans will be 2⁶ = 64.

Hence, the correct answer is option (C), 64

Question 5: Biosphere is:

A) a component in the ecosystem

B) composed of the plants present in the soil

C) life in outer space

D) composed of all living organisms present on earth, which interact with the physical environment

Answer:

The biosphere is a thin layer of Earth's surface where life exists. It includes the interactions among the hydrosphere (water bodies), atmosphere (air), and lithosphere (land). In this zone, living organisms interact with each other and their environment, allowing life to thrive.

Hence, the correct answer is option (D), composed of all living organisms present on earth, which interact with the physical environment

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

What Students Learn from Organisms and Populations NCERT Solutions

This chapter gives students a clear understanding of how organisms interact with their environment and with each other.

1. Students learn about different population attributes, such as population size, density, age structure, and sex ratio, which help in studying population trends.

2. Using the Organisms and Populations Class 12 question answer, learners understand models of population growth, including exponential and logistic growth.

3. The chapter explains various types of population interactions, such as competition, predation, and mutualism, with real-life examples.

4. Class 12 Biology Organisms and Populations question answer helps students revise concepts like carrying capacity, limiting factors, and population regulation efficiently.

5. Students also explore how ecological principles influence species distribution and community structure.

Why Class 12 Biology Chapter 11 Organisms and Populations NCERT Solutions are Important?

Students will understand how living organisms interact with each other and with their environment with the help of the Organisms and Populations chapter. The solutions make difficult topics easy to understand without any confusion.

• Class 12 Biology Chapter 11 Organisms and Populations NCERT Solutions explain the different levels of organization, such as the organisms, populations, and communities, along with examples.
• Topics such as adaptation, population growth, and interactions are also included in the solutions in an easy-to-understand manner.
• Students will also gain confidence while solving the numerical problems on population density, growth models, and carrying capacity.
• Different environmental factors, such as the biotic and abiotic, are covered in the solutions, which are frequently asked in the NEET and board exams.

What Extra Should Students Study Beyond the NCERT for NEET?

Here is a table for all the important topics from the chapter that students have to study beyond the NCERT for the NEET exam. Along with this, students can practice diagrams, flow charts, etc, given in the NCERT Solutions for Class 12 Biology Chapter 11 Organisms and Populations.

NCERT Solutions for Class 12 Biology Chapter-wise

Below given are the solutions: