Maharashtra Board Class 12 Solutions for Biology Chap Chapter 13 Organisms and Populations

Multiple Choice Questions

1. Which factor of an ecosystem includes plants, animals, and microorganisms?

1. Biotic factor 

2. Abiotic factor

3. Direct factor 

4. Indirect factor

Ans: Correct option: (a) Biotic factor

Explanation: Plants, animals, and microorganisms are part of the biotic factors. Biotic factors also include flora and fauna. These biotic factors affect the lives of other living organisms and the ecosystem.

2. An assemblage of individuals of different species living in the same habitat and having functional interactions is ................

1. Biotic community

2. Ecological niche

3. Population

4. Ecosystem

Ans: Correct option: (a) Biotic community

Explanation: A biotic community is where all living organisms live together in one environment affecting each other's lives. Based on their nutritional practices we divide them into producers, consumers, and decomposers.

3. Association between sea anemone and Hermit crab in gastropod shell is that of ................

1. Mutualism 

2. Commensalism

3. Parasitism 

4. Amensalism

Ans: Correct option: (b) Commensalism

Explanation: Commensalism is a cooperation between two organisms in which one organism has advantages and the other neither advantages nor gets harmed. Association between sea anemone and a hermit crab in gastropod shells is commensalism.

4. Select the statement which explains the best parasitism.

1. One species benefited.

2. Both species benefit.

3. One species is benefited, and another is not affected.

4. One species is benefited, the other is harmed.

Ans: Correct option: d. One species is benefited, other is harmed

Explanation: Parasitism means one species benefits, while the other is harmed. It is a relationship between a parasite and a living organism.

5. Growth of bacteria in a newly inoculated agar plate shows ................

1. Exponential growth

2. Logistic growth

3. Verhulst-Pearl logistic growth

4. Zero growth

Ans: Correct option: a. Exponential growth 

Explanation: Growth of bacteria in a newly inoculated agar plate shows exponential growth. 

Very Short-Answer Questions

1. Define the following terms:

a) Commensalism 

Ans: Commensalism is a cooperation between two organisms in which one organism has advantages and the other neither advantages nor gets harmed. Association between sea anemone and a hermit crab in gastropod shells is commensalism.  Examples: Suckerfish clamps itself beneath the surface of the shark. 

b) Parasitism

Ans: Two organisms of different species, one organism is a parasite which depends on another living organism for livelihood is called parasitism. For example, brood parasitism is when a parasitic bird lays its eggs in another bird's egg nest, where there are eggs of other birds and the mother of these other eggs will grow the parasitic bird's egg-like on its own. 

c) Camouflage

Ans: Plants and animals use this natural phenomenon of harmonising in their surroundings to either pray or hide from predators, which is called camouflage. Example: Tigers, lizards, snakes, etc.

2. Give One Example for Each:

a) Mutualism

Ans: Two organisms of different species who provide each other benefits and depend on each other for livelihood is called mutualism. The symbiotic association of algae and fungi, lichens is an example of mutualism.

b) Interspecific Competition

Ans: It is a competition between different species for the same resources like food, water, light, shelter, etc. In this competition, one species leads to destruction. Example: In the ocean fishes are plentiful where they prey for other species like sharks, dolphins, and birds.

3. Name the Type of Association:

a. Clownfish and Sea Anemone

Ans: There is a symbiotic association between clownfish and sea anemones, and this relationship is called mutualism. 

The clown fish cleans the sea anemones by eating the algae off of the sea anemones' surface and in return, the sea anemone defends the clownfish from its predators.

b. Crow Feeding the Hatchling of Koel

Ans: The type of association between crow and koel is brood parasitism in which koel lays its eggs in a crow's nest.  Brood parasitism is when a parasitic bird lays its eggs in another bird's egg nest, where there are eggs of other birds and the mother of these other eggs will grow the parasitic bird's egg-like its own. 

c. Hummingbirds and Host Flowering Plants

Ans: The hummingbird and host flowering plants have a mutualistic relationship, in which the bird produces nectar to attract bees and birds by which pollen travels from the plants.

4. What is the ecological process behind the biological control method of managing pest insects?

Ans: Predation is the biological control method for managing pest insects. It is a type of interaction between two species, the predator and the prey. In which the predator feeds on the prey they control the population of the prey. 

Short Answer Questions

1. How is the dormancy of seeds different from hibernation in animals?

Ans: Seed dormancy: it prevents the seed from germinating even under suitable environmental conditions, in which it pauses momentarily the growth and development of the seed.

Hibernation: takes place in animals in which they reduce their metabolism by entering the phase of inactivity. 

2. If a marine fish is placed in a freshwater aquarium, will it be able to survive? Give a reason.

Ans: Marine fishes won't be able to survive in a freshwater aquarium as they are adapted to ocean water. Fish' bodies are hypertonic but in aquarium water, it turns hypotonic by which they can't control the metabolic process and they die. 

3. Name important defence mechanisms in plants against herbivores.

Ans: There are two types of mechanisms used by plants against herbivores, morphological and chemical mechanisms. In morphological mechanisms, certain plants develop thorns or spines on leaves margins and sharp edges. Example: Cactus.

In chemical defence mechanisms, certain plants have toxic cardiac glycosides which can be fatal if ingested by herbivores. Example: opium, nicotine, caffeine. 

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: In this interaction, the Orchid plant is an epiphyte (plants that grow on other plants) that grows on the Mango tree but does not depend on it for nutrition. The relationship between the Mango tree and the Orchid plant is commensalism. 

Commensalism is a cooperation between two organisms in which one organism has advantages and the other neither advantages nor gets harmed. 

5. Distinguish between the following:

a. Hibernation and Aestivation

Ans: 

b. Ectotherms and Endotherms

Ans:

c. Parasitism and Mutualism

Ans:

6. Write a short note on

a. Adaptations of Desert Animals

Ans: Desert plants and animals adapt themselves well to cope with desert conditions like water scarcity and intense heat. They develop a vast root system, have thick cuticles and different pathways for synthesis.

b. Adaptations of Plants to Water Scarcity

Ans: Plants adapt to desert conditions by developing the vast root system to tap underground water. 

• They develop thick cuticles to reduce transpiration. 

• They synthesise their food through a special pathway which is the CAM (C4) pathway.

c. Behavioural Adaptations in Animals

Ans: Animals adapt certain behavioural changes like hibernation, aestivation, migration, etc to escape from the environmental stress to suit their natural habitat. These are called behavioural adaptations. Example: Ectotherms. 

7. Define Population and Community.

Ans: Population: is a group of individuals of the same species. It is called population and they live in a certain geographical area.

Example: human population.

• Community: is the group of individuals of different species living within a certain geographical area. They can be similar to each other or not but they do not reproduce with the other community.

Long Answer Questions

1. With the help of suitable diagrams describe the logistic population growth curve.

Ans: A logistic growth curve is a growth model which shows that for each species of the population there are limited resources in a habitat. 

• This limit is known as nature's taming capacity (K) for that particular species and a plot of population density (N) with time (t) results in a sigmoid curve.

Logistic Growth Curve of Population

2. Enlist and explain the important characteristics of a population.

Ans: Population is the group of individuals of the same species. The important characteristics of a population are birth rate or natality, death rate or mortality and age distribution.

• Birth Rate or Natality: is the amount or ratio of live births in a population of an area.

• Death Rate or Mortality: ratio of death in a population of an area.

• Age Distribution: it is a percentage of individuals of different ages in the given population.  

Importance of Maharashtra Board Class 12 biology Chapter 13 Organisms and Populations

This chapter introduces the meaning and definition of ecology, ecosystem, organism, and its population. There are multiple living organisms living in the ecosystem. Even the simplest ecosystems show how organisms live in harmony. This chapter will explain what these terms are and how they are interrelated.

The biological organizations in an ecosystem are determined by the organisms living in it. They form a population of living things that control the ecosystem. In fact, they are a part of the ecological hierarchy and its basic unit is an organism.

An ecosystem defines how an organism has adapted to it. The various abiotic aspects and biotic elements of an ecosystem directly or indirectly influence the evolution and adaptation of an organism.

This chapter will explain how various seasons and topographical features result in the formation of new environments and ecosystems. The ecosystems high on the mountain slopes will differ from that of the plains. In fact, the freshwater biome will differ from that of the oceans.

The biotic components of an ecosystem determine the food chain system too. You will find a remarkable explanation of all these concepts in this chapter. To make it easier, focus on the Organisms and Population Class 12 Solutions prepared by the experts.

Benefits of Maharashtra Board Class 12 Biology Solutions Chapter 13 Organisms and Populations

• These notes have been designed by the experts following the Maharashtra Board Class 12 standards. It means that the students will find it easier to correlate with the syllabus and will be able to comprehend the concepts faster.

• You will also discover an easier explanation of all the concepts, terms, definitions, etc very helpful to complete preparing this chapter.

• Once done, proceed to solve the exercise questions. Find out how the experts have given the Organism and Population Class 12 questions and answers. Learn from the expert methods used to answer them accurately. In this way, you can develop good answering skills and score more in the exams.

• Resolve doubts based on the terms and concepts of this chapter using these solutions. Save your precious time and proceed to prepare this chapter using these solutions.

Download Organism and Population Class 12 Solutions PDF

You can now get the free Organism and Population Class 12 Solutions PDF download. Add them to your study material for this chapter and make your preparation sessions better. Find out how the experts have explained the fundamental principles of an ecosystem, organisms, and their populations in it and develop your concepts.