CBSE Class 10 Science Our Environment VBQs Set 02

ASSERTION AND REASON QUESTIONS

Question. Assertion: Vegetarian food habit is more beneficial to organisms.
Reason: Only 10% energy is available as food from one trophic level to next.
(a) Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.
(b) The Assertion and the Reason are correct but the Reason is not the correct explanation of the Assertion.
(c) Assertion is true but the Reason is false.
(d) The statement of the Assertion is false but the Reason is true.
Answer: (a) Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.

Question. Assertion: Accumulation of harmful chemicals is maximum in case of organisms at higher trophic level.
Reason: Food chain normally do not go beyond 3 or 4 trophic level.
(a) Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.
(b) The Assertion and the Reason are correct but the Reason is not the correct explanation of the Assertion.
(c) Assertion is true but the Reason is false.
(d) The statement of the Assertion is false but the Reason is true.
Answer: (b) The Assertion and the Reason are correct but the Reason is not the correct explanation of the Assertion.

Question. Assertion: Ozone layer is getting depleted at upper atmosphere which is a cause of concern.
Reason: CFC reacts with ozone and breaks it.
(a) Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.
(b) The Assertion and the Reason are correct but the Reason is not the correct explanation of the Assertion.
(c) Assertion is true but the Reason is false.
(d) The statement of the Assertion is false but the Reason is true.
Answer: (a) Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.

Question. Assertion: Autotrophs can produce food on its own.
Reason: Green plants can absorb 1% energy of sunlight that fall on the leaves.
(a) Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.
(b) The Assertion and the Reason are correct but the Reason is not the correct explanation of the Assertion.
(c) Assertion is true but the Reason is false.
(d) The statement of the Assertion is false but the Reason is true.
Answer: (b) The Assertion and the Reason are correct but the Reason is not the correct explanation of the Assertion.

Question. Assertion: Biodegradable waste and non-biodegradable waste should be discarded separately.
Reason: Biodegradable waste are not harmful.
(a) Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.
(b) The Assertion and the Reason are correct but the Reason is not the correct explanation of the Assertion.
(c) Assertion is true but the Reason is false.
(d) The statement of the Assertion is false but the Reason is true.
Answer: (c) Assertion is true but the Reason is false.

Question. Assertion: Decomposers act as cleaning agents of environment.
Reason: The decomposers recycle waste material in hydrosphere. 
(a) Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.
(b) The Assertion and the Reason are correct but the Reason is not the correct explanation of the Assertion.
(c) Assertion is true but the Reason is false.
(d) The statement of the Assertion is false but the Reason is true.
Answer: (c) Assertion is true but the Reason is false.

Question. Assertion: Garden is an artificial ecosystem.
Reason: Biotic and abiotic components are manipulated by humans. 
(a) Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.
(b) The Assertion and the Reason are correct but the Reason is not the correct explanation of the Assertion.
(c) Assertion is true but the Reason is false.
(d) The statement of the Assertion is false but the Reason is true.
Answer: (a) Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.

CASE-BASED QUESTIONS

Every living thing plays a role in the food chain and Earth’s ecosystems, and the extinction of certain species, whether predators or prey, can leave behind significant impacts. Since the origin of life on Earth, it’s fair to say that more species have gone extinct than are currently alive now. Extinction itself is part of the normal course of evolution. The effect of a species would have if it were to fade from existence depends largely on its role in the ecosystem. Predators, for example, are often the first to be threatened by hunting or competition with people and resources. When a predator goes extinct, all of its prey are released from that predation pressure, and they may have big impacts on ecosystems. The loss of a predator can result in what is called a trophic cascade, which is an ecological phenomenon triggered by a predator’s extinction that can also impact populations of prey, which can cause dramatic ecosystem and food web changes. If there are too many deer, for example, they can really change the ecosystem because they can destroy forests, and they also carry disease.

Question. What is an ecosystem?
Answer: An ecosystem is a structural and functional unit of the biosphere consisting of a community of living organisms interacting with their physical environment (abiotic components) and with each other, such that energy and materials are exchanged.

Question. List two man-made ecosystems.
Answer: Two man-made ecosystems are: (i) Crop fields and (ii) Aquarium.

Question. What will be the impact if all the organisms of one trophic level die? Give any one effect.
Answer: If all organisms of one trophic level die, it will cause an ecological imbalance. For example, if all herbivores die, the producers will grow unchecked while the carnivores will die due to starvation.

Question. Justify the statement; ‘All the flesh of a carnivore is grass’.
Answer: This statement means that carnivores ultimately depend on grass for their food. Carnivores eat herbivores, and herbivores eat grass. Therefore, the energy and nutrients stored in the flesh of a carnivore were originally derived from grass through the food chain.

There are more than 1000 pesticides used around the world to ensure food is not damaged or destroyed by pests. Each pesticide has different properties and toxicological effects. Many of the older, cheaper pesticides can remain for years in soil and water. These chemicals have been banned by countries who signed the 2001 Stockholm Convention – an international treaty that aims to eliminate or restrict the production and use of persistent organic pollutants. The toxicity of a pesticide depends on its function and other factors. None of the pesticides that are authorized for use on food in international trade today are genotoxic. Adverse effects from these pesticides occur only above a certain safe level of exposure. When people come into contact with large quantities of pesticide, this may cause acute poisoning or long-term health effects, including cancer and adverse effects on reproduction.

Question. Name the pesticides banned by Stockholm Convention.
Answer: Pesticides like DDT, Endrin, and Heptachlor are some of the persistent organic pollutants (POPs) targeted or banned by the Stockholm Convention.

Question. What is biological magnification?
Answer: Biological magnification is the process by which non-biodegradable chemicals, like pesticides, accumulate and increase in concentration at each successive trophic level in a food chain.

Question. Why is DDT is termed as a non-biodegradable substance?
Answer: DDT is termed non-biodegradable because it cannot be broken down into simpler, harmless substances by the action of microorganisms in nature and persists in the environment for a long time.

Question. Which level of food chain will have the maximum biological magnification? Will the levels of this magnification be different at different levels of the ecosystem?
Answer: The highest trophic level (the final consumer) will have the maximum biological magnification. Yes, the levels will be different; the concentration of the chemical increases as we move from lower trophic levels to higher trophic levels.

Human body is made up of five important components of which water is the main component. Food as well as potable water are essential for every human being. The food is obtained from plants through agriculture. Pesticides are being used extensively for a high yield in the fields. These pesticides are absorbed by the plants from the soil along with water and minerals and from the water bodies, these pesticides are taken up by the aquatic animals and plants. As these chemicals are not biodegradable, they get accumulated progressively at each trophic level. The maximum concentration of these chemicals gets accumulated in our bodies and greatly affects the health of our mind and body.

Question. Why is the maximum concentration of pesticides found in human beings?
Answer: Maximum concentration is found in human beings because they occupy the top position in many food chains, and according to the phenomenon of biological magnification, non-biodegradable chemicals accumulate in the highest concentrations at the top trophic level.

Question. Give one method which could be applied to reduce our intake of pesticides through food to some extent.
Answer: Thoroughly washing fruits and vegetables before consumption can help remove surface residues of pesticides.

Question. Write an aquatic food chain with 4 trophic levels.
Answer: Phytoplankton \( \rightarrow \) Zooplankton \( \rightarrow \) Small Fish \( \rightarrow \) Large Fish (or Bird like Crane).

Question. Give two examples to illustrate that indiscriminate use of pesticides may result in the degradation of the environment.
Answer: (i) Pesticides can leach into groundwater, making it unfit for drinking. (ii) Pesticides can harm non-target beneficial organisms like bees and butterflies, disrupting pollination.

The stratosphere is very dry and rarely allows clouds to form. In the extreme cold of the polar winter, however, stratospheric clouds of different types may form. These clouds are called Polar Stratospheric Clouds (PSCs). Scientists recently discovered that polar stratospheric clouds, long known to play an important role in Antarctic ozone destruction, are occurring with increasing frequency in the Arctic. These high-altitude clouds form only at very low temperatures help destroy ozone in two ways: (1) They provide a surface which converts benign forms of chlorine into reactive, ozone-destroying forms, and (2) they remove nitrogen compounds that moderate the destructive impact of chlorine. In recent years, the atmosphere above the Arctic has been colder than usual, and polar stratospheric clouds have lasted into the spring. As a result, ozone levels have been decreasing. (Information credit: NASA) 

Question. How is ozone formed in the outer atmosphere?
Answer: Ozone is formed when high-energy UV radiation splits oxygen molecules \( (O_2) \) into free oxygen atoms (O). These free atoms then combine with molecular oxygen to form ozone \( (O_3) \).
\( O_2 \xrightarrow{UV} O + O \)

\( \implies \) \( O + O_2 \rightarrow O_3 \)

Question. Ozone is being continuously destroyed due to extreme low temperatures. However, ozone formation is also a continuous process. Why is there a depletion in the ozone layer still?
Answer: Depletion occurs because human-made chemicals like CFCs release chlorine and bromine atoms into the stratosphere. These atoms act as catalysts, breaking down ozone into oxygen at a rate much faster than natural ozone formation can replace it.

Question. What can be a positive effect of global warming on the depletion of the ozone layer?
Answer: While global warming heats the lower atmosphere (troposphere), it can lead to a cooling of the stratosphere. This cooling might theoretically impact the frequency of Polar Stratospheric Clouds, though the net effects are complex and generally harmful.

Question. How does ozone layer depletion impact human health?
Answer: Depletion allows more harmful UV radiation to reach Earth, causing increased cases of skin cancer, cataracts, and weakening of the human immune system.

Question. What is the role of decomposers in the ecosystem?
Answer: Decomposers decompose dead remains of plants and animals. By doing so, they serve two purposes. Firstly, they reduce the burden on the environment by clearing dead remains. Secondly, they channelize the raw materials back to the environment.

Question. Why are some substances biodegradable and some non-biodegradable?
Answer: Those substances which are of organic origin are biodegradable, while those of inorganic origin are non-biodegradable. Decomposers such as bacteria and saprophytes breakdown natural substances using enzymes, but they lack specific enzymes to break down synthetic substances like plastic. Examples: Biodegradable: Agricultural waste and cloth. Non-Biodegradable: DDT and polythene bags.

Question. Give any two ways in which biodegradable substances would affect the environment.
Answer: (a) Biodegradable substances on decomposing provides a breeding ground for flies, cockroaches and other insects, spreading diseases like cholera. (b) During decomposition, foul smell and some harmful gases are released which cause discomfort to nearby living people.

Question. Give any two ways in which non-biodegradable substances would affect the environment. 
Answer: (a) Chemicals like BHC and DDT are carcinogenic and induce tumors through biological magnification. (b) Non-biodegradable substances do not decompose easily, leading to soil and water pollution.

Question. What is ozone and how does it affect any ecosystem?
Answer: Ozone \( (O_3) \) is a form of oxygen. It is a triatomic molecule that forms the ozone layer in the stratosphere. It plays an important role by absorbing harmful ultraviolet radiations from the sun, protecting living beings from skin cancer and DNA damage.

Question. How can you help in reducing the problem of waste disposal? Give any two methods.
Answer: (a) By using more biodegradable substances and reducing the use of non-biodegradable substances (e.g., using cloth bags instead of plastic). (b) By proper segregation of waste into biodegradable and non-biodegradable categories before disposal.

EXERCISES

Question. Which of the following groups contain only biodegradable items?
(a) Grass, flowers and leather
(b) Grass, wood and plastic
(c) Fruit-peels, cake and lime-juice
(d) Cake, wood and grass
Answer: (a), (c) and (d) groups contain only biodegradable items.

Question. Which of the following constitute a food-chain?
(a) Grass, wheat and mango
(b) Grass, goat and human
(c) Goat, cow and elephant
(d) Grass, fish and goat
Answer: (b) Grass → Goat → Human, constitutes a food chain.

Question. Which of the following are environment-friendly practices?
(a) Carrying cloth-bags to put purchases in while shopping.
(b) Switching off unnecessary lights and fans.
(c) Walking to school instead of getting your mother to drop you on her scooter.
(d) All of the options.
Answer: (d) All of the options.

Question. What will happen if we kill all the organisms in one trophic level?
Answer: (i) The population of organisms in the previous trophic level will increase exponentially. (ii) Organisms in the next trophic level will die of starvation or migrate. (iii) It will cause a total ecological imbalance.

Question. Will the impact of removing all the organisms in a trophic level be different for different trophic levels? Can the organisms of any trophic level be removed without causing any damage to the ecosystem?
Answer: Yes, the impact is different. Removing producers collapses the entire chain immediately. Removing top predators causes an overpopulation of prey. No, organisms of any level cannot be removed without causing damage.

Question. What is biological magnification? Will the levels of this magnification be different at different levels of the ecosystem?
Answer: It is the process where harmful chemicals accumulate progressively at each trophic level. Yes, the concentration is highest at the top level and lowest at the producer level.

Question. What are the problems caused by the non-biodegradable wastes that we generate?
Answer: (i) Water pollution. (ii) Soil fertility loss. (iii) Clogging of drains. (iv) Air pollution when burnt.

Question. If all the waste we generate is biodegradable, will this have no impact on the environment?
Answer: It will still have an impact: (a) Accumulation can cause burden and foul smell. (b) It can produce greenhouse gases during decomposition. (c) Overloading water bodies can cause oxygen deficiency.

Question. Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this damage?
Answer: Concern is due to harmful UV rays causing skin cancer and DNA mutations. Steps: (i) Reducing CFC use in aerosols. (ii) Banning large-scale nuclear explosions. (iii) International agreements like the UNEP Montreal Protocol to freeze CFC production.