NIOS Class 12 Environmental Science Chapter 4 Principles of Ecology

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NIOS Class 12 Environmental Science Chapter 4 Principles of Ecology

Also, you can read the NIOS book online in these sections Solutions by Expert Teachers as per National Institute of Open Schooling (NIOS) Book guidelines. These solutions are part of NIOS All Subject Solutions. Here we have given NIOS Class 12 Environmental Science Chapter 4 Principles of Ecology Solutions, NIOS Senior Secondary Course Environmental Science Solutions for All Chapter, You can practice these here.

Principles of Ecology

Chapter: 4

Module 2: Ecological Concepts and Issues

Textual Question Answer

INTEXT QUESTIONS 4.1

1. What does the term ecology mean? 

Ans: Ecology means the scientific study of the relationship of living organisms with each other and with their environment.

2. Define the term niche.

Ans: The term niche means the sum of all activities and relationships a species has while obtaining and using the resources it needs to survive and reproduce.

3. Give one point of difference between habitat and niche.

Ans: Habitat is the physical environment where an organism lives, while the niche is the specific role and activities of an organism in its ecosystem.

INTEXT QUESTIONS 4.2

1. What is meant by the term adaptation? Answer in one sentence.

Ans: The appearance or behaviour or structure or mode of life of an organism that allows it to survive in particular environment.

2. Define: (i) species (ii) variation.

Ans: (i) Species – a group of similar populations of organisms whose members are capable of inter breeding to produce fertile offspring.

(ii) Variation- differences in structure due to differences in gene combinations.

3. Name two sources of variation. 

Ans: (i) Gene combination (ii) Mutation.

4. Name the evolutionary force which brings about greater reproduction of adaptive variation.

Ans: Natural selection.

5. Explain the term (i) speciation and (ii) extinction.

Ans: Speciation is the process by which new species are formed and extinction is dying out of a variety of or a species.

INTEXT QUESTIONS 4.3

1. Define population.

Ans: A group of freely interbreeding individuals of the same species present in a specific area at a given time.

2. Name at least three characteristics of population.

Ans: (i) Density of the population.

(ii) Natality.

(iii) Mortality.

3. What are the factors on which density of a population depends? 

Ans: Mortality, natality, immigration, emigration.

INTEXT QUESTIONS 4.4

1. Explain in brief (one to two sentences) the following ecological terms: 

(i) Succession ________________________.

Ans: Succession is the orderly change of organisms in an environment over time.

(ii) Pioneer species ____________________.

Ans: Pioneer species is the name use for the first time assemblage of plants that inhabit as area undergoing changes during succession. They are the first species in successional process.

(iii) Climax community _______________________.

Ans: Climax community is the final stage of succession. It is a relatively stable, long lasting community.

(iv) Secondary succession ___________________.

Ans: Secondary succession is the term used for the orderly series of changes that begins with the disturbance of an existing community and leads to a climax community.

INTEXT QUESTIONS 4.5

1. Define (a) ecological succession, (b) symbiosis.

Ans: (a) Ecological succession: It is the natural process by which one group of living organisms in an area is gradually replaced by another, leading to a stable community (climax community) over time.

(b) Symbiosis: It is the close relationship between two different species in which at least one benefits. Sometimes both species benefit (e.g., flower and bee).

2. What type of competition exists between members of a deer herd in an area?

Ans: Intraspecific competition.

3. What type of friendship is represented by a garden spider feeding on a grasshopper? 

Ans: Predation as it is preying upon or eating the grasshopper.

4. What type of relationship is represented by a flower being pollinated by a butterfly? 

Ans: Mutualism as both are helped by the relationship.

5. Which term best faith the relationship of a person who has a lice feeding on his scalp? 

Ans: Parasitism (the person is the host, and the lice are the parasites).

6. Which term means two species live together with each providing a benefit to the other through the relationship? 

Ans: Mutualism.

TERMINAL EXERCISE

1. Define the terms : Ecology, niche, species, extinction.

Ans: (i) Ecology: The scientific study of the relationship of living organisms with each other and with their environment.

(ii) Niche: The sum of all activities and relationships a species has while obtaining and using the resources it needs to survive and reproduce.

(iii) Species: A group of similar populations of organisms whose members are capable of interbreeding to produce fertile offspring.

(iv) Extinction: The dying out of a variety or a species.

2. What do you understand by ‘Variation and Natural Selection’? In what way do they interact to cause evolution?

Ans: Variation refers to the differences or distinctiveness among individuals of a species due to differences in their genetic material (DNA). These variations can arise from mutations, genetic recombination, or other genetic processes.

Natural selection is an evolutionary force that acts on these variations. It favors individuals with traits that enhance survival and reproduction in a given environment. Over time, individuals with advantageous traits are more likely to survive, reproduce, and pass on their beneficial genes to the next generation. This leads to the gradual accumulation of adaptive traits within a population.

Darwin described natural selection as a key driver of evolution because it selects for variations that help organisms better adapt to their environment. As a result, these advantageous traits become more common in the population, leading to evolutionary changes over time.

3. What is the role of isolation in the formation of new species and keeping them distinct.

Ans: Isolation plays a crucial role in the formation of new species (speciation) by preventing gene flow between populations. 

There are three main types of isolation:

(i) Behavioral isolation: This occurs when differences in behavior, such as mating rituals or communication, prevent individuals from different populations from mating.

(ii) Temporal isolation: This happens when two populations breed at different times, such as different seasons, days, or times of day, preventing interbreeding.

(iii) Geographical isolation: This is when a physical barrier, such as mountains, rivers, or oceans, separates populations, preventing gene flow between them. It is the most common form of isolation leading to speciation.

In geographical isolation, individuals from the same species are separated by a physical barrier. Over time, genetic differences accumulate due to mutations, natural selection, and genetic drift. These isolated populations may adapt to their local environments, leading to the formation of distinct species.

Reproductive isolation also contributes to speciation by preventing interbreeding between different species or populations, ensuring that the genetic differences remain distinct. As a result, isolated populations evolve separately and may eventually become reproductively incompatible.

Speciation is the process through which new species are formed due to the accumulation of genetic differences and reproductive isolation between populations.

4. In what ways have humans caused the extinction of species?

Ans: Extinction is a natural occurrence, the dying out of a variety of or species. The primary reason for extinction is an environmental change or biological competition. Human activities such as deportation, overexploitation, environmental change are the factors responsible for the extinction. Deforestation for the expansion of industries and human settlements has promoted economic growth, but at the same time, it has resulted in habitat loss for many wild plants and animals. Pollution has also killed many species.

5. What do you understand by

(i) natality.

(ii) speciation.

(iii) mutation.

(iv) extinction.

Ans: (i) Natality: The rate at which new individuals are born and added to the population under certain environment conditions is called natality.

(ii) Speciation: Speciation is the process by which new species are formed.

(iii) Mutation: A change in genetic material that results from an error in the replication of DNA.

(iv) Extinction: Extinction is dying out of a variety of or a species.

6. Explain ‘ecological succession’.

Ans: Ecological Succession is the process of replacing or modifying populations of plant and animal species in an environment over a period of time. This transition affects both biotic (living organisms) and abiotic (non-living) components of the ecosystem. It is driven by both the actions of the species within the community and the physical conditions of the environment. The physical world influences the pace, direction, and limits of the changes during succession. As the process unfolds, both plant and animal populations undergo significant transformations.

There are two main types of ecological succession:

(i) Primary succession: This occurs in barren or unoccupied areas where no previous ecosystem existed, such as on bare rock surfaces, newly formed volcanic islands, lava flows, glacial moraines, or recently formed deltas. Since the area is initially devoid of life, primary succession begins with the colonization of pioneer species that are adapted to harsh conditions.

(ii) Secondary succession: This takes place in areas where an existing ecosystem has been disturbed or damaged, such as after forest fires, floods, or human activities like agriculture. Unlike primary succession, secondary succession occurs in areas that still retain soil and nutrients, and often has a much faster rate of recovery. Secondary succession progresses more rapidly because the soil already contains the necessary nutrients and a large pool of seeds or dormant species.

7. State and explain community characteristics.

Ans: Community or biotic community refers to the populations of different kinds of organisms living together and sharing the same habitat.

Organization:

(i) The roles played by its various populations.

(ii) The ranges of its various populations.

(iii) The type of area that is inhabited by the populations of the community.

(iv) The diversity of species in the community.

(v) Interactions between various populations of communities inhabiting the area.

Stratification of a community refers to the vertical layers of the vegetation. It is a practical strategy to minimize interspecific competition.

Community characteristic:

Species diversity

It is an important attribute; the different kinds of organisms present in a community represents its species diversity. It also influences the stability of the community.

Species variation also impacts the cohesion of the group. A healthy society is one that can revert to its initial state after being disrupted in some way. Communities with a high diversity of species are relatively more stable.

8. What are (i) climax community and (ii) pioneer species?

Ans: Climax Community – The final stage of succession is called a climax community. It is a relatively stable, long-lasting community.

Pioneer Species – The first species that inhabit the area in the successional process are called pioneer species.

9. Write an essay on biotic interaction.

Ans: Biotic interaction refers to the relationships among living organisms in an ecosystem. All plants, animals, and microorganisms interact with one another for food, shelter, reproduction, and survival. These interactions are of two types – positive and negative. Positive interactions include mutualism (both organisms benefit, e.g., bees and flowers), commensalism (one benefits, the other is unaffected, e.g., epiphytes on trees), and protocooperation.

Negative interactions include competition (organisms compete for food or space), predation (one feeds on another, e.g., lion and deer), parasitism (parasites like lice on humans), and amensalism. Such interactions regulate population sizes, maintain ecological balance, and influence biodiversity. Thus, biotic interactions are essential for the stability and proper functioning of ecosystems.

10. Define biotic Interaction. Describe any one type of positive, negative and neutral quotation.

Ans: Biotic interaction is a complex network within the ecosystem of the biological community.

Two basic types of interactions:

Interspecific: The interaction among individuals of different species in a community

Intraspecific: The interaction that occurs among different individuals of the same species.

Type of interaction	1 Result of species 2	Effects of interaction
NEGATIVE INTERACTIONS
Amensalism	0	One species is inhibited while the other species is unaffected.
POSITIVE ASSOCIATIONS
Commensalism	0	One species (the commensal) benefits, while the other species (the host) is neither harmed nor inhibited.
NEUTRAL INTERACTIONS
Neutralism	0                                0	Neither species affects the other.

+ = beneficial; – = harmful, 0 = unaffected or neutral 

Amensalism: This is a negative association between two species in which one species harm or restricts the other species without itself being adversely affected or harmed by the presence of the other species.

Commensalism: In this relationship, one species benefits while the other is neither harmed nor benefited. Some species obtain the benefit of shelter or transport from another species.

Neutralism: Neutralism describes the relationship between two species that do interact but do not affect each other: It is to describe interactions where one species’ fitness has absolutely no effect whatsoever on that of another.