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Karnataka State Syllabus Class 8 Science Important Questions Chapter 2 Our Environment
Question 1.
What is environment?
Answer:
The sum total of all surroundings of a living organism, including natural forces and other living things, which provide conditions for development and growth as well as of danger and damage is known as environment.
Question 2.
Mention the various components of our environment.
Answer:
The components of our environment consist of both biotic and abiotic factors. Plants, animals and microbes together constitute the biotic factors while the non-living components of our environment constitute the abiotic factors.
Question 3.
Why is the earth considered an unique planet?
Answer:
Earth is the only place where life is known to exist. It is the only known place where conditions support life. Hence, earth is considered a unique planet.
Question 4.
List the factors that have made life to exist on earth.
Answer:
Earth is the only planet that supports life. The factors that have made this possible are:
- Earth is the only planet with abundant liquid water. Water has some unique physical and chemical properties which are essential for supporting life.
- The atmosphere surrounding the earth is a mixture of gases, water vapour and fine dust. This is ideally suited for humans and other life forms.
Question 5.
What is hydrosphere?
Answer:
The area on the surface of the earth covered by water is known as hydrosphere. About 71% of the total surface area of the earth constitutes the hydrosphere.
Question 6.
Which is the only planet in the solar system which has large amount of water?
Answer:
Earth is the only planet in the solar system which has large amount of water especially in liquid form.
Question 7.
List some of the unique properties of water which enables it to support life.
Answer:
Water is a unique substance which has physical and chemical properties that support life. Some of these properties are given below:
1. Water requires considerable amount of energy to get heated up and to get converted into gaseous state. On very hot days, water bodies help to reduce atmospheric temperature by absorbing heat from the sun. During night the heat absorbed is returned to the atmosphere. This is crucial for the survival of living organisms.
2. The hydrosphere comprises oceans, rivers, streams, lakes, reservoirs, tanks, ponds, pools and ice caps. A lot of water also exists as water vapour in the atmosphere. It is this which absorbs sun’s heat and regulates atmospheric temperature.
3. Depending on the dissolved salts, water is called salt water or fresh water. The salt water in seas and oceans (marine habitat) provides living space. This is far greater than that provided by fresh water habitat and land. Being heavier than air, water provides buoyancy to aquatic life.
4. Water is the major constituent of protoplasm. As an universal solvent, it allows substances to dissolve in it. It acts as a bridge between the outer environment and body of organism. For example, nutrients enter into the roots of plants in solution. Water has a direct influence on the distribution of plants and animals.
Question 8.
What is atmosphere? State the major constituents of the atmosphere.
Answer:
The envelope of air surrounding the earth is called atmosphere. The atmosphere of the earth consists of 78% nitrogen and 21% oxygen. The other substances present in the atmosphere include carbon dioxide, argon and water vapour.
Question 9.
What is lithosphere? What is it made of?
Answer:
The outer part of the earth consisting of the crust and the upper part of the mantle is called lithosphere. The lithosphere consists of soil, rocks, minerals, hills, mountains, the ocean floor and the plain lands.
Question 10.
What is biosphere? Which are the components of the biosphere?
Answer:
The area of the earth where life exists is called biosphere. The biosphere consists of hydrosphere, lithosphere and atmosphere.
Question 11.
Why is earth considered a dynamic planet?
Answer:
On the earth, life is influenced by its physical environment. At the same time, the various factors in the environment influence the living organisms. This is why the earth is called a dynamic planet.
Question 12.
What is ecology?
Answer:
The branch of Biology that deals with the study of relations of organisms to one another and to their environment is called ecology. Ecology is also called environmental science.
Question 13.
Define the following terms: species, population, biotic community.
Answer:
1. Species:
A group of living organisms consisting of similar individuals capable of exchanging genes or interbreeding is known as species.
2. Population:
All the individuals of a species occupying a particular geographical area at a given time constitute population.
3. Biotic community:
A group of interdependent organisms inhabiting the same geographical region and interacting with each other is called biotic community.
Question 14.
What is meant by an ecosystem? Explain.
Answer:
A network of interactions in nature where there is interaction between living and non-living components in a given area is known as ecosystem.
Question 15.
Give examples for natural ecosystems.
Answer:
Ponds, lakes, grasslands, forests, deserts and sea are some of the examples for natural ecosystems.
Question 16.
How are natural ecosystems broadly classified?
Answer:
Natural ecosystems are broadly classified as Aquatic ecosystems and Terrestrial ecosystems.
Question 17.
What are terrestrial ecosystems? Give two examples.
Answer:
A terrestrial ecosystem is an ecosystem found only on a landform. E.g. Forest ecosystem, Grassland ecosystem.
Question 18.
What are aquatic ecosystems? Give two examples.
Answer:
Ecosystems in a body of water are called aquatic ecosystems. E.g. Pond ecosystem, marine ecosystem.
Question 19.
What are artificial ecosystems? Give an example.
Answer:
Ecosystems created through human efforts and requiring human intervention to sustain are called artificial ecosystems. Such ecosystems do not possess a self-regulating mechanism. Artificial ecosystems are sometimes called man-made ecosystems. E.g. Aquarium.
Question 20.
Give four examples for man-made ecosystems.
Answer:
Aquarium, terrarium, garden, zoo and space stations are some of the examples of man-made (artificial) ecosystems.
Question 21.
What are abiotic components? Give examples.
Answer:
The non-living components of the ecosystem are called abiotic components. They represent the physical and chemical conditions operating in the environment. E.g.: air, light, rainfall, etc.
Question 22.
What are biotic components? Give examples.
Answer:
The living components of the ecosystem are called biotic components. They are represented by plants, animals, bacteria and fungi.
Question 23.
How are organisms classified based on the way they get their food?
Answer:
On the basis of the way they get their food, organisms are broadly classified as autotrophs and heterotrophs.
Question 24.
What are autotrophs? Give two examples.
Answer:
Organisms which prepare their own food and hence do not depend on other organisms for their food are called autotrophs. E.g. Green plants, Algae
Question 25.
Why are algae and green plants called ‘producers’?
Answer:
Food prepared by green plants and algae are consumed by all other organisms either directly, or indirectly. Therefore, green plants in land ecosystems and algae in aquatic ecosystems are termed as producers or autotrophs.
Question 26.
What are heterotrophs? Give four examples for heterotrophs.
Answer:
Organisms which cannot prepare their own food and hence depend on other organisms for their survival are called heterotrophs. E.g. Human beings, elephant,caterpillar,lion, etc. All animals are heterotrophs.
Question 27.
Distinguish between producers and consumers in an ecosystem.
Answer:
Organisms which prepare their own food and hence do not feed on other organisms are called producers. Those organisms which cannot prepare their own food and hence depend on the producers directly or indirectly for their food are called consumers.
Question 28.
How are heterotrophic animals broadly classified? Give an example each.
Answer:
Heterotrophic animals are broadly classified as primary consumers (herbivores), secondary consumers and tertiary consumers.
Question 29.
What are primary consumers? Give two examples.
Answer:
Generally, animals which feed only on plants or plant products are called primary consumers. They are also called herbivores. E.g. Rats, butterfly, rabbits, elephants, etc.
Question 30.
What are secondary consumers? Give two examples.
Answer:
Animals which obtain their food by eating herbivores (plant-eating animals) are called secondary consumers. E.g. Cat, dog, fox, frog, lizard, spider, etc.
Question 31.
What are tertiary consumers? Give two examples.
Answer:
Animals which obtain their food by eating secondary consumers are called tertiary consumers. E.g. Lion, tiger, etc.
Question 32.
What are quaternary consumers? Give two examples.
Answer:
Organisms, usually bigger animals, which derive nutrition by eating tertiary consumers are known as quaternary consumers.
E.g. Hawk, white shark, etc.
Question 33.
What are detrivores? Give two examples.
Answer:
Organisms that eat and digest decaying material present in their environment are called detrivores. E.g. Earthworms, ants, termites, crabs, etc.
Question 34.
What are decomposers? Give two examples.
Answer:
Organisms which break down organic materials such as dead and decaying matter into simpler substances are known as decomposers. E.g. Bacteria, Fungi.
Question 35.
What is the primary energy source for life on earth?
Answer:
The primary energy source for life on earth is the sun. The energy of the sun keeps the planet warm. Sun also provides light energy required for photosynthesis. This energy is converted into organic material by producers (autotrophs). Autotrophs form the food for all other organisms either directly or indirectly.
Question 36.
What is the main means by which autotrophic beings obtain energy?
Answer:
The main means by which autotrophs obtain energy is photosynthesis.
Question 37.
What is food chain?
Answer:
A food chain is the sequence of who eats whom in a biological community (an ecosystem) to obtain nutrition. Thus, a food chain represents a succession of organisms that eat another organism and are, in turn, themselves eaten by other organisms.
Question 38.
Draw a schematic diagram of a simple food chain.
Answer:
Question 39.
Answer:
The trophic level of an organism is the position it occupies in a food chain. The word ‘trophic’ means food or feeding. Each organism in an ecosystem is at a specific feeding stage that represents its trophic level. Food chains start at trophic level 1 with primary producers such as plants, move to herbivores at level 2, predators at level 3 and typically finish with carnivores at level 4. Very rarely a fifth trophic level called quaternary consumer can be recognised.
Question 40.
What is the trophic level of the following organisms: Tiger, Adult frog, Algae, Eagle, Butterfly?
Answer:
- Tiger: Trophic level 4 (Tertiary consumer)
- Adult frog: Trophic level 3 (Secondary consumer)
- Algae: Trophic level 1 (Producer)
- Eagle: Trophic level 4 (Tertiary consumer)
- Butterfly: Trophic level 2 (Primary consumer)
Question 41.
At which trophic level of an ecosystem do you find more organisms?
Answer:
We find more organisms among producers (autotrophs).
Question 42.
At which trophic level do we place foxes?
Answer:
Foxes eat rabbits which are at the 2nd trophic level. Hence, we place foxes at the 3rd trophic level. Thus, foxes are secondary consumers.
Question 43.
Where do you place eagles in the trophic level? Why?
Answer:
Eagles feed on snakes and foxes which are at the 3rd trophic level. Therefore, eagles belong to the 4th trophic level. Thus, eagle is a tertiary consumer.
Question 44.
What is the trophic level of human beings?
Answer:
Human beings derive nutrition by eating both plants and animal products. A vegetarian human being is a primary consumer while a non-vegetarian human being is a tertiary consumer.
Question 45.
In any food chain, trophic level 1 is occupied by green plants. Give reason.
Answer:
Green plants are the producers and hence do not depend on other organisms for their food. In fact, they trap and convert solar energy into chemical energy. Other organisms in a food chain depend on green plants for their food either directly or indirectly. This is why green plants occupy the trophic level 1 in all food chains.
Question 46.
Why are human beings considered double consumers?
Answer:
Human beings feed on both plants and animals. Hence, humans are considered double consumers.
Question 47.
What are parasites? In which group are parasites placed based on their mode of nutrition?
Answer:
An organism that lives on the body or inside the body of another organism (host) and derives nutrition from the host by harming it is called a parasite. Parasites are grouped under special consumers based on their mode of nutrition.
Question 48.
How are the heterotrophic beings divided in the ecological study of food interactions?
Answer:
Heterotrophs are divided into consumers and decomposers.
Question 49.
Which are the three major types of food chains that can be found in a natural ecosystem?
Answer:
Food chains in a natural ecosystem are of three types:
- Grazing type or herbivorous food chain
- Detritivorous food chain
- Parasitic food chain.
Question 50.
What are grazing food chains ? Give an example.
Answer:
The food chains in which the primary consumers are plant-eating animals are called grazing food chains. This type of food chains are also called herbivorous food chains or predatory food chains.
E.g, Grass → Rabbit → Wolf.
In this example, the primary consumer is rabbit. It feeds on plants. Therefore, the food chain is considered a grazing food chain.
Question 51.
What are detritivorous food chains? Give an example.
Answer:
Detritivorous food chains are those in which primary source of energy comes from dead organic matter called ‘detritus’ (fallen leaves, parts of dead trees and similar kinds of organic matter). The primary consumers in such a food chain are the ‘detrivores’ which include bacteria, fungi, ants, termites, earthworms, millipedes, crabs, etc.
E.g. Dead organism → Bacteria → insect larvae → Small fish → Big fish.
Question 52.
Distinguish between grazing food chains and detritivorous food chains.
Answer:
| Grazing food chains | Detritivorous food chains |
| 1. Primary source of energy comes from solar radiation | Primary source of energy comes from dead and decaying organic matter. |
| 2. All herbivores form the first trophic level. | Detrivores which feed on ‘detritus’ form the first trophic level. |
| 3. Food chain is usually lone. | Food chain is usually short. |
Question 53.
What is a parasitic food chain? Explain with an example.
Answer:
Food chains in which the energy is transferred from one trophic level to another through parasitic organisms are called parasitic food chains.
Consider the following food chain:
Tree → fruit-eating birds → lice and bugs → fungi.
In this food chain, birds are parasitic on trees. Lice and bugs are parasitic on birds and fungi are parasitic on I fee and bugs. Such a food chain is an example of a parasitic food chain.
Question 54.
List the characteristics of a food chain.
Answer:
In a food chain:
- There is repeated eating in which each organism eats the smaller one and is in turn eaten by the larger one. Thus, it involves a nutritive interaction between the biotic components of an ecosystem.
- There is unidirectional flow of energy from sun to producers and then to a series of consumers of various types. Thus, a food chain is always straight and proceeds in a progressing straight line.
- Usually almost 90% of energy is lost as heat at each transfer. As we move up the trophic levels, the amount of energy available at each level keeps decreasing.
- Usually there are 4 or 5 trophic levels. Shorter food chains have higher energy transfers and vice versa.
- Omnivores occupy more than one trophic level and, some organisms occupy different trophic positions in different food chains.
Question 55.
What is food web?
Answer:
A network of feeding relationships by which energy and nutrients are passed on from one species of living organisms to another is known as a food web. A food web is a network of several interconnected food chains.
Question 56.
Show by a schematic diagram an example of a food web.
Answer:
Question 57.
Describe briefly the energy flow in an ecosystem.
Answer:
In any ecosystem, the primary source of energy is the sun. Producers (usually green plants) use the solar energy to convert inorganic nutrients derived from the environment to make organic molecules. Thus, energy gets stored in plants. Thus, photo synthesising plants form the first trophic level.
Animals which feed on only producers, called herbivores, form the second trophic level. Here, organisms in the second trophic level derive energy from herbivores. Small predators which eat up the herbivores form the third trophic level. These animals derive energy when they eat up organisms at the second trophic level.
Large predators, if present, form higher trophic levels. Energy flows into the body of these organisms from the animals which they eat. Decomposers, which include bacteria, fungi, moulds, worms, and insects, break ‘ down wastes and dead organisms and return nutrients to the soil.
At each trophic level a large amount of energy is dissipated in the form of heat. Thus, only a small amount of energy gets transferred to higher trophic levels.
Question 58.
What percent of energy gets transferred to the higher trophic level in an ecosystem?
OR
What is 10% law?
Answer:
The energy transfer to each higher trophic level is only about 10%. On an average about 10 percent of net energy production at one trophic level is passed on to the next trophic level. This is known as 10% law.
Question 59.
Why is the energy transfer to higher trophic level as low as 10%?
Answer:
There are several processes that reduce the energy transferred between trophic levels. These processes include respiration, growth and reproduction, defecation, etc. The nutritional quality of material that is consumed also influences how efficiently energy is transferred. During energy transfer from one trophic level to higher trophic level, lot of energy is lost to the environment in the form of heat. This is why the energy transfer between trophic levels is quite low.
Question 60.
A producer has 10000 units of energy. How many units of energy will a primary consumer derive by eating them?
Answer:
The energy transfer from one trophic level to the next higher trophic level is about 10% only. Therefore, a primary consumer will derive only about 1000 units of energy.
Question 61.
In the following food chain, plants provide 2000 J of energy to rats:
Plants → Rats → Snakes → Hawk.
How much energy will be available to hawks from the snakes?
Answer:
Rats get 2000 J of energy, 10% of the 2000 J of energy is transferred to the snakes, which is 200 J. Out of 200 J only 10% is transferred from snakes to hawks. 10% of 200 J is 20 J.
Question 62.
What is an ecological pyramid?
Answer:
A graphical representation in the shape of a pyramid of organisms occupying each trophic level in an ecosystem to show the feeding relationship of groups of organisms, and the flow of energy or biomass through the different trophic levels is called an ecological pyramid.
Question 63.
What are the three main types of trophic pyramids studied in Ecology?
Answer:
The three types of trophic pyramids studied in Ecology are the pyramid of numbers, the pyramid of biomass and the pyramid of energy.
Question 64.
What is ecological pyramid of numbers? Give an example.
Answer:
A graphical representation, in the form of a pyramid, of the number of individuals at each trophic level in a food chain in a given place and time in an ecosystem is called the pyramid of numbers.
Question 65.
What do the pyramid of numbers represent?
Answer:
The pyramid of numbers represent the number of individuals at each trophic level of a food chain.
Question 66.
Explain briefly the pyramid of numbers in an ecosystem.
Answer:
The producers in the ecosystem will form the base of the pyramid. Usually they are largest in number in an ecosystem. The animals at the base of a food chain are relatively abundant while those at the end are relatively few in number, and there is a progressive decrease in between the two extremes.
The pyramid of numbers indicates the numerical relationship between the different trophic levels of the food chain. The pyramid of numbers is usually an upright pyramid since the number of individuals at successive trophic levels keeps on decreasing.
Question 67.
What may happen if all the herbivores are killed in a terrestrial ecosystem?
Answer:
The disappearance of herbivores will result in rapid fall in the number of animals at the higher trophic levels as they run out of food. Eventually the secondary consumers and tertiary consumers will become extinct.
Question 68.
What is biomass?
Answer:
Biomass is the dry weight of all the matter in the organisms.
Question 69.
What is meant by pyramid of biomass? What does it represent?
Answer:
The graphical representation in the form of a pyramid based on the amount of biomass present at each trophic level of a food chain is called pyramid of biomass.
Biomass pyramids show how much biomass (the dry or wet weight of all the matter in the organisms in each trophic level) is present in the organisms at each trophic level.
Question 70.
Explain briefly the pyramid of biomass.
Answer:
Biomass is the total of mass of dry organic matter present in an ecosystem. The pyramid of biomass represents the mass of dry biomass present at each trophic level. In a biomass pyramid, we estimate the entire biomass of all producers in an ecosystem, and this total mass would form the ‘Producer’ level of the pyramid.
The entire mass of all primary consumers in the ecosystem would form the ‘primary consumer’ level of the pyramid, and so on. The pyramid of biomass gives a more accurate assessment of total energy at each trophic level since a pyramid of numbers does not take into account the size of the organisms. Pyramid of biomass is usually an upright pyramid. It may be inverted in some aquatic food chains.
Question 71.
Distinguish between the pyramid of numbers and the pyramid of biomass.
Answer:
Pyramid of numbers shows the population of organisms at each trophic level in a food chain. The pyramid of biomass gives the amount of dry mass of organisms at different trophic levels.
Question 72.
What is pyramid of energy?
Answer:
The graphical representation of the trophic levels on the basis of the amount of energy fixed at each trophic level is known as pyramid of energy. The pyramid of energy in a food chain is always upright.
Question 73.
In a given food chain, at what trophic level do the organisms receive the lowest amount of energy?
Answer:
In any food chain, the organisms at the highest trophic level will receive the lowest amount of energy.
Question 74.
Which laws govern the transfer of energy from one trophic level to another?
Answer:
The transfer of energy from one trophic level to another occurs in accordance with the laws of thermodynamics.
Question 75.
List any two functions of an ecosystem.
Answer:
The basic functions of an ecosystem are as follows:
- It balances the rate of biological energy flow.
- It balances the nutrients cycle.
Question 76.
What is biomagnification? Give an example.
Answer:
The amount of toxic substance such as DDT, mercury, cadmium, etc., that enters a food chain goes on accumulating in increasing amounts at higher trophic levels. This phenomenon is known as biomagnification. The most familiar example of biomagnification is the gradual building up the amount of DDT in higher trophic levels.
Question 77.
Give one effect of biomagnification.
Answer:
Biomagnification disrupts the balance in the food chain.
Question 78.
How does DDT get accumulated at higher trophic levels? Explain.
Answer:
DDT is a non-biodegradable chemical which is widely used as a pesticide. This chemical enters into the plants through the roots. When herbivores eat these plants, the concentration of DDT in the body of herbivores becomes higher. The secondary consumers eat large number of primary consumers. Thus, the concentration of DDT becomes higher in the secondary consumers. This accumulation continues and eventually the amount of DDT at the higher trophic levels would become the highest.
Question 79.
Why is the use of DDT not advised?
Answer:
DDT is a non-biodegradable chemical. Once it enters the food chain, it goes on accumulating at the higher trophic levels. It is detrimental to aquatic organisms, birds and human beings. Further, biomagnification disrupts the balance in food chains. It affects the organisms at higher trophic levels including humans. Therefore, the use of DDT is not advised.
Multiple Choice Questions
Question 1.
Biotic components of an ecosystem include
(a) producers
(b) consumers
(c) decomposers
(d) all of these
Answer:
(d) all of these
Question 2.
Fill in the box with an appropriate organism:
(a) deer
(b) lizard
(c) grasshopper
(d) rat
Answer:
(b) lizard
Question 3.
Which one of the following is a decomposer?
(a) fungi
(b) algae
(c) protozoa
(d) insect
Answer:
(a) fungi
Question 4.
The scientific study of interactions among organisms and between organisms and their environment is
(a) biosphere
(b) ecology
(c) trophic level
(d) community
Answer:
(b) ecology
Question 5.
Organisms are classified into trophic levels on the basis of
(a) where they live
(b) the source of their nutrients
(c) how much they weigh
(d) all the above
Answer:
(b) the source of their nutrients
Question 6.
In a food chain, producers form the
(a) first trophic level
(b) second trophic level
(c) third trophic level
(d) fourth trophic level
Answer:
(a) first trophic level
Question 7.
A network of complex interactions formed by the feeding relationships among the various organisms in an ecosystem is a
(a) food web
(b) trophic level
(c) food chain
(d) community
Answer:
(a) food web
Question 8.
Of the total amount of energy that passes from one trophic level to the next higher trophic level in a food chain, about 10% is
(a) taken by organisms in the lower trophic level
(b) burnt in respiration
(c) used for various life processes
(d) stored in the body tissues
Answer:
(d) stored in the body tissues
Question 9.
Which of the following is the correct sequence in the ecological hierarchy?
(a) species, variety, biosphere, ecosystem, population
(b) population, community, species, biosphere, ecosystem
(c) population, species, community, ecosystem
(d) organism, population, community, ecosystem, biosphere
Answer:
(d) organism, population, community, ecosystem, biosphere
Question 10.
Animals that feed on both plants and animals are called
(a) carnivores
(b) herbivores
(c) omnivores
(d) detritivores
Answer:
(c) omnivores
Question 11.
The nature’s cleaners are
(a) producers
(b) consumers
(c) decomposers and detrivores
(d) omnivores
Answer:
(c) decomposers and detrivores
Question 12.
The total amount of organic material present at various levels of a food chain is represented by the pyramid of
(a) numbers
(b) biomass
(c) energy
(d) both a and c
Answer:
(b) biomass
Question 13.
All individuals of the same species living together in a defined area form
(a) a community.
(b) a genus.
(c) a population.
(d) an ecosystem.
Answer:
(c) a population.
Fill In The Blanks
1. The crust of the earth is called lithosphere
2. Primary consumers are also called herbivores
3. The basic unit of environment study is ecosystem
4. A group of individuals belonging to the same species is called population
5. Different kinds of ecosystems together constitute biosphere
6. In a parasitic food chain, the pyramid of numbers will be inverted
7. Bacteria and fungi are examples for decomposers
8. The non-living components of an ecosystem are known as abiotic components
9. Carnivores that eat herbivores are called secondary consumers
10. The primary source of energy for any grazing ecosystem is sun
Match The Following
Question 1.
| A | B |
| 1. animals that eat only plants | a. detritivores |
| 2. animals that eat other animals | b. omnivores |
| 3. animals that eat only herbivores | c. decomposers |
| 4. animals that eat both plant and animal matter | d. tertiary consumers |
| 5. organisms feeding on decaying organic matter | e. secondary consumers |
| f. primary consumers |
Answer:
1 – f, 2 – d, 3 – e, 4 – b, 5 – a.