SHORT ANSWER QUESTIONS
Q.1. Name two natural ecosystems. [CBSE 2016-17 C]
Ans. Two natural ecosystems are:
(a) Temperate forest
(b) Tropical forest
Q.2. What are decomposers? Write the role of decomposers in the environment. [CBSE 2016-17 C]
Ans. Decomposers are microorganisms that derive their nutrition from dead remains and waste products of organisms.
They play a vital role in our environment by breaking down the complex organic substance into simple inorganic substance which is made available for plants and other organisms. Hence they act as scavengers and not only keep the environment clean but also replenish the minerals.
Q.3. (a) What is an ecosystem? List its two main components.
(b) We do not clean ponds or lakes, but an aquarium needs to be cleaned regularly. Explain. [CBSE 2013,2017]
Ans. (a) A self-sustaining functional unit consisting of living and non-living components is called ecosystem.
Components : Biotic components like plants and animals. Non-biotic components like soil, wind, light etc.
(b) A pond is a complete, natural and self-sustaining ecosystem whereas an aquarium is an artificial and incomplete ecosystem, without decomposers therefore it needs regular cleaning for proper running.
Q.4. You have been selected to talk on “ozone layer and its protection” in the school assembly on ‘Environment Day.’ [Delhi 2017]
(a) Why should ozone layer be protected to save the environment?
(b) List any two ways that you would stress in your talk to bring in awareness amongst your fellow friends that would also help in protection of ozone layer as well as the environment.
Ans. (a) Ozone layer at the higher levels of the atmosphere, acts as a shield to protect earth from the harmful effects of the ultraviolet (UV) radiations; hence, it should be protected.
(b) (i) Urging the people to not to buy aerosol products with CFC that are available in the market.
(ii) Conducting poster making competition or street plays presenting the importance of ozone layer on earth.
Q.5. Your mother always through that fruit juices are very healthy for everyone. One day she read in the newspaper that some brands of fruit juices in the market have been found to contain certain level of pesticides in them. She got worried as pesticides are injurious to our health. (Foreign 2017)
(а) How would you explain to your mother about fruit juices getting contaminated with pesticides?
(b) It is said that when these harmful pesticides enter our body as well as in the bodies of other organisms they get accumulated and beyond a limit cause harm and damage to our organs. Name the phenomenon and write about it.
Ans. (a) • Pesticides are the chemicals used to protect our crops from diseases and pests.
• These chemicals are washed down either into the soil or into water bodies.
• From the soil, they are absorbed by the terrestial plants along with water and minerals.
• From the water bodies, they are absorbed by the aquatic plants.
• When the fruits of these plants are used to prepare fruit juices, they are contaminated with the pesticides.
(b) • The phenomenon is called biomagnification. It is the phenomenon in which certain harmful chemicals enter the food chain and get accumulated and increase in concentration at successive trophic levels.
• It is because they are not degradable.
• The maximum concentration of these chemicals is found in the top level consumers.
Q.6. In the following food chain, 100 J of energy is available to the lion. How much energy was available to the producer? [AI 2017]
Plants → Deer → Lion
Ans. 1,000,000 J of energy was available to the producer.
Q.7. Why should biodegradable and non-biodegradable wastes be discarded in two separate dustbins? [AI 2017(C); Delhi 2013,15]
Ans. The biodegradable and non-biodegradable wastes must be discarded in two different dustbins because biodegradable wastes gets decomposed by the microorganisms whereas non-biodegradable wastes can be recycled and reused.
Q.8. Name any two man-made ecosystems. [Foreign 2017]
Ans. Agricultural/crop fields, aquaria, gardens,
Q.9. We often use the word environment. What does it mean? [Foreign 2016]
Ans. It is the sum total of all external conditions and influences that affect the life and development of an organism, i.e. the environment includes all the physical or abiotic and biological or biotic factors.
Q.10. Why are green plants called producers? [Delhi 2016]
Ans. Green plants can produce their own food by photosynthesis from inorganic compounds and hence are called producers.
Q.11. What is ten per cent law? Explain with an example how energy flows through different trophic levels. [Delhi 2015]
Ans. Energy available at each successive trophic level of food chain is ten per cent of that at the previous level.
This is called ten per cent law. Thus, 90 per cent energy is lost to the surroundings at each trophic level. However, plants absorb only one per cent of radiant energy of the Sun during photosynthesis. This is explained as under :
Q.12. What is ozone? How and where is it formed in the atmosphere? Explain how does it affect ecosystem. [Foreign 2015]
Ans. Ozone is an isotope of oxygen, i.e. it is a molecule formed by 3 atoms of oxygen.
Ozone exists in the ozone layer of stratosphere. At higher level o f atmosphere, O2 molecule breaks down to 2 oxygen atom. The oxygen atom then combines with the oxygen molecule to form ozone.
Ozone layer in the atmosphere prevents UV rays from reaching earth. Exposure to excess UV rays causes skin cancer, cataract and damages eye and immune system. It also decreases crop yield and reduces population of phytoplankton, zooplankton and certain fish larvae which are an important constituent of aquatic food chain. It also disturbs rainfall, causing ecological disturbance and reduces global food production. Thus, it affect the ecosystem.
Q.13. “Energy flow in food chains is always unidirectional.” Justify this statement. Explain how the pesticides enter a food chain and subsequently get into our body. [Foreign 2015]
Ans. The energy flow through different steps in the food chain is unidirectional. The energy captured by autotrophs does not revert back to the solar input and it passes to the herbivores, i.e. it moves progressively through various trophic levels. Thus energy flow from sun through producers to omnivores is in single direction only.
Pesticides are sprayed to kill pests on food plants. The food plants are eaten by herbivores and alongwith the food, pesticides are also eaten by the herbivores. Herbivores are eaten by carnivores and alongwith the herbivore animal, pesticide also enters the body of the carnivore. Man eat both plants and animals and pesticide alongwith food enters the body of human. Concentration of pesticides increases as we move upward in the food chain and the process is called bio-magnification.
Q.14. What is an ecosystem? List its two main components. We do not clean natural ponds or lakes but an aquarium needs to be cleaned regularly. Why is it so? Explain. [AI 2015]
Ans. Ecosystem: It is the structural and functional unit of biosphere, comprising of all the interacting organisms in an area together with the non-living constituents of the environment. Thus, an ecosystem is a self-sustaining system where energy and matter are exchanged between living and non-living components.
Main components of ecosystem:
Biotic Component: It means the living organisms of the environment-plants, animals, human beings and microorganisms like bacteria and fungi, which are distinguished on the basis of their nutritional relationship.
Abiotic Component: It means the non-living part of the environment-air, water, soil and minerals. The climatic or physical factors such as sunlight, temperature, rainfall, humidity, pressure and wind are a part of the abiotic environment.
An aquarium is an artificial and incomplete ecosystem compared to ponds or lakes which are natural, self-sustaining and complete ecosystems where there is a perfect recycling of materials. An aquarium therefore needs regular cleaning.
Q.15. Write the full name of the group of compounds mainly responsible for the depletion of ozone layer. [Foreign 2015]
Ans. CFC → Chloroflurocarbon
Q.16. Which of the following are always at the second trophic level of the food chains?
Carnivores, Autotrophs, Herbivores [AI 2015]
Ans. Herbivores are always at the 2nd trophic level.
Q.17. The following organisms form a food chain. Which of these will have the highest concentration of nonbiodegradable chemicals? Name the phenomenon associated with it.
Insects, Hawk, Grass, Snake, Frog. [Foreign 2015]
Ans. Hawk will have highest concentration of non- biodegradable chemicals. The phenomenon is called biomagnification.
Q.18. The first trophic level in a food chain is always a green plant. Why? [AI 2015]
Ans. Only green plants can make their own food from sunlight. Green plants therefore, always occupy the 1st trophic level in a food chain.
Q.19. What will be the amount of energy available to the organism of the 2nd trophic level of a food chain, if the energy available at the first trophic level is 10,000 joules? [AI 2015]
Ans. 100 Joules of energy will be available to the organism of the 2nd trophic level.
LONG ANSWER TYPE QUESTIONS
Q.1. (a) How can we help in reducing the problem of waste disposal? Suggest any three methods. [Delhi 2019]
(b) Distinguish between biodegradable and nonbiodegradable wastes. [DoE, A1 2011]
Ans. (a) The three methods of waste disposal are:
(i) Recycling: solid, wastes like paper, plastics, metals can be sent to processing factories where they are remoulded or reprocessed to new materials.
(ii) Production of compost: Biodegradable wastes like fruit and vegetable peels, plant products, left over food, grass clippings, human and animal waste can be converted into compost by burying this waste into grund and can be used as manure.
(iii) Incineration: Burning dawn many household waste, chemical waste and biological waste into ash is known as incineration. A large amount of waste can be easily converted into ash which can be disposed off in landfill.
(b) Differences between:
|Biodegradable wastes||Non-biodegradable wastes|
|(i) These wastes can be broken-down into non-poisonous substances in nature by the action of microorganisms.||(i) These wastes cannot be broken-down into non-poisonous substances by microorganisms.|
|(ii) They get recycled thus, do not need any dumping sites.||(ii) They cannot be recycled thus, require dumping sites.|
Q.2. (a) What is biodiversity? What will happen if biodiversity of an area is not preserved? Mention one effect of it. [AI 2015]
(b) With the help of an example explain that a garden is an ecosystem.
(c) Why only 10% energy is transferred to the next trophic level?
Ans. (a) Biodiversity is the existence of a wide variety of species of plants, animals and microorganisms in a natural habitat within a particular environment or existence of genetic variation within a species. Biodiversity of an area is the number of species or range of different life forms found there. Forests are ‘biodiversity hotspots’. Every living being is dependent on another living being. It is a chain. If biodiversity is not maintained, the links of the chain go missing. If one organism goes missing, this will affect all the living beings who are dependent on it.
(b) A garden comprises of different kind of flora and fauna such as grasses, flowering and nonflowering plants, trees, frogs, insects, birds, etc. All these living organisms depend and interact with each other and their growth, reproduction and other vital biological activities depend upon the abiotic component comprising of physical factors like temperature, rainfall, wind, soil and minerals. Therefore, we can say that a garden is an ecosystem.
(c) Only 10% energy is transferred to the next trophic level because other 90 per cent is used for things like respiration, digestion, running away from predators.