CBSE Class 10 Science HOTs Our Environment Set 05

Question. Write one negative effect on the environment, of affluent lifestyle of few persons of a society.
Answer: An affluent lifestyle often leads to excessive consumption and high waste generation (especially non-biodegradable waste like electronics and luxury packaging), which depletes natural resources and increases environmental pollution.

Question. Why should biodegradable and non-biodegradable wastes be discarded in two separate dustbins?
Answer: Separating them allows for proper disposal: biodegradable waste can be composted to produce manure, while non-biodegradable waste can be sorted for recycling or safe industrial disposal, preventing landfill overflow and environmental toxicity.

Question. “Although gardens are created by man but they are considered to be an ecosystem.” Justify this statement.
Answer: A garden is considered an ecosystem because it consists of biotic components (plants, insects, birds, soil microbes) interacting with abiotic components (soil, water, sunlight). Even though it is man-made, the biological processes of production, consumption, and decomposition still occur within it.

Question. What is the difference between biodegradable and non-biodegradable substances? List two methods of safe disposal of biodegradable domestic waste.
Answer: Biodegradable substances are broken down by biological processes (microbes), whereas non-biodegradable substances cannot be broken down by microbes and persist in the environment. Methods for safe disposal of biodegradable waste include:
1. Composting: Converting waste into nutrient-rich manure.
2. Biogas production: Using organic waste to produce fuel gas.

Question. Kulhads (disposable cups made of clay) and disposable paper cups both are used as an alternative for disposable plastic cups. Which one of these two can be considered as a better alternative to plastic cups and why ?
Answer: Paper cups are considered a better alternative. While kulhads are biodegradable, making them on a large scale involves using topsoil (the most fertile layer of soil), which can lead to soil erosion and loss of fertility. Paper cups are biodegradable and can be made from recycled paper without depleting fertile soil.

Question. (a) What is meant by garbage? List two classes into which garbage is classified.
(b) What do we actually mean when we say that “enzymes are specific in their action”?
Answer: (a) Garbage refers to the household waste or refuse generated daily. It is classified into biodegradable and non-biodegradable waste.
(b) It means that a particular enzyme can only catalyze a specific chemical reaction or act on a specific substrate. For example, enzymes that break down food cannot break down plastic because their structure does not "fit" the plastic molecules.

Question. “Industrialisation has adversely deteriorated the environment.” Give four reasons in support of this statement.
Answer: 1. Large-scale deforestation for setting up factories.
2. Release of harmful gases causing air pollution and global warming.
3. Discharge of industrial effluents into water bodies polluting them.
4. Generation of huge amounts of hazardous non-biodegradable chemical waste.

Question. Why is Government of India imposing a ban on the use of polythene bags? Suggest two alternatives to these bags and explain how this ban is likely to improve the environment.
Answer: The ban is due to polythene being non-biodegradable, causing soil pollution, choking drains, and harming stray animals. Alternatives: Jute bags and Cloth bags. The ban reduces non-biodegradable waste accumulation and prevents the clogging of urban sewage systems.

Question. In some states of our country there is a ban on the use of polythene bags for shopping. Why? List three advantages of using jute or cloth bags over polythene bags.
Answer: The ban exists because polythene causes environmental pollution. Advantages of jute/cloth bags:
1. They are biodegradable.
2. They are reusable and more durable.
3. They are made from natural renewable resources.

Question. “Affluent lifestyle has a negative effect on the environment.” Justify this statement with the help of an example.
Answer: Affluent lifestyles involve high consumption. Example: Extensive use of air conditioners and refrigerators releases CFCs, which deplete the ozone layer. Also, high consumption of packaged goods leads to massive plastic waste generation.

Question. Give one example each from your daily life where the domestic waste can be effectively reused and recycled.
Answer: Reuse: Using old plastic jam or pickle jars to store pulses or spices in the kitchen. Recycle: Selling old newspapers, cardboard boxes, and glass bottles to the junk dealer (kabadiwala) so they can be processed into new paper or glass products.

Question. “To discard the household waste we should have two separate dust-bins, one for the biodegradable waste and the other for the non-biodegradable waste.” Justify this statement suggesting the proper way of disposal of these wastes.
Answer: Separation is necessary because the two types of waste require different treatments. Biodegradable waste should be put in a pit for composting to make manure. Non-biodegradable waste (plastics, metals) should be sent to recycling units or disposed of in designated landfills to prevent them from entering the natural food chain or polluting soil/water.

Question. We often observe domestic waste decomposing in the bylanes of residential colonies. Suggest ways to make the residents realise that the improper disposal of their waste is harmful to the environment.
Answer: 1. Organizing community meetings or street plays to demonstrate how rotting waste attracts pests and spreads diseases like cholera or malaria.
2. Installing posters showing the long-term impact of non-biodegradable waste on soil health and local groundwater contamination.

Question. Write one difference between biodegradable and non-biodegradable wastes. List two impacts of each type of the accumulated waste on environment if not disposed off properly.
Answer: Difference: Biodegradable waste can be broken down by microbes, whereas non-biodegradable waste cannot.
Impact of Biodegradable waste: 1. Foul smell from decomposition. 2. Breeding ground for disease-carrying flies.
Impact of Non-biodegradable waste: 1. Clogging of sewage drains. 2. Soil pollution and potential poisoning of animals that ingest it.

Question. (a) Write two harmful effects of using plastic bags on the environment. Suggest alternatives to the usage of plastic bags.
(b) List any two practices that can be followed to dispose off the waste produced in our homes.
Answer: (a) Harmful effects: They block drainage systems and cause soil pollution as they take hundreds of years to decompose. Alternatives: Cloth, jute, or paper bags.
(b) 1. Segregation of waste into dry and wet bins. 2. Composting of kitchen vegetable peels and leftover food in a backyard pit.

Question. After the examinations, Rakesh with his friends went on a picnic to a nearby park. All friends carried cooked food packed in plastic bags or plastic cans. After eating the food some friends collected the leftover food and plastic bags etc., and planned to dispose them off by burning. Rakesh immediately checked them and suggested to segregate the leftover food and peels of fruits from the plastic materials and respectively dispose them off separately in the green and red dustbins placed in the corner of the park.
(a) In your opinion, is burning plastic an eco-friendly method of waste disposal? Why? State the advantage of method suggested by Rakesh.
(b) How can we contribute in maintaining the parks and roads neat and clean?
Answer: (a) No, burning plastic is not eco-friendly because it releases highly toxic gases like dioxins and furans into the air, causing air pollution and health issues. Rakesh’s method allows for the biodegradable waste to decompose naturally (compost) and the plastic to be sent for recycling.
(b) By not littering, using public dustbins for disposal, and educating others about the importance of waste segregation.

Question. Differentiate between biodegradable and non-biodegradable substances with the help of one example each. List two changes in habit that people must adopt to dispose non-biodegradable waste, for saving the environment.
Answer: Biodegradable substances are those that can be broken down into simple harmless substances by microorganisms (e.g., fruit peels). Non-biodegradable substances are those that cannot be broken down by biological processes (e.g., plastic bottles).
Habit changes:
1. Stop using single-use plastic items and switch to reusable alternatives.
2. Always segregate non-biodegradable waste (like glass, metal, plastic) so it can be sent to recycling centers instead of general landfills.

Ecosystem-What are its Components?

Question. Assertion (A) : Food chain is responsible for the entry of harmful chemicals in our bodies.
Reason (R) : The length and complexity of food chains vary greatly.
(a) Both (A) and (R) are true and (R) is the correct explanation of (A).
(b) Both (A) and (R) are true and (R) is not the correct explanation of (A).
(c) (A) is true but (R) is false.
(d) (A) is false but (R) is true.
Answer: (b) Both (A) and (R) are true and (R) is not the correct explanation of (A).

Question. Assertion (A) : Greater number of individuals are present in lower trophic levels.
Reason (R) : The flow of energy is unidirectional.
(a) Both (A) and (R) are true and (R) is the correct explanation of (A).
(b) Both (A) and (R) are true and (R) is not the correct explanation of (A).
(c) (A) is true but (R) is false.
(d) (A) is false but (R) is true.
Answer: (b) Both (A) and (R) are true and (R) is not the correct explanation of (A).

Question. Give reason why a food chain cannot have more than four trophic levels.
Answer: According to the 10% law of energy transfer, only 10% of the energy available at one trophic level is transferred to the next higher level. The amount of energy goes on decreasing at each successive trophic level. After four trophic levels, the amount of energy remaining is so small that it is insufficient to support the metabolic needs of another level of organisms.

Question. DDT was sprayed in a lake to regulate breeding of mosquitoes. How would it affect the trophic levels in the following food chain associated with a lake? Justify your answer.
HAWK
LARGE FISH
SMALL FISH
PLANKTON
AQUATIC ENVIRONMENT
Answer: DDT is a non-biodegradable chemical. When sprayed in the lake, it enters the food chain through planktons. Since it cannot be metabolized or excreted, its concentration increases at each successive trophic level through a process called biological magnification. Consequently, the hawk, being at the highest trophic level, will have the highest concentration of DDT in its body, leading to harmful physiological effects.

How do Our Activities Affect the Environment?

Question. Explain how ozone being a deadly poison can still perform an essential function for our environment.
Answer: Although ozone (\( O_3 \)) is a deadly poison at ground level, in the upper atmosphere (stratosphere), it forms a protective layer. Its essential function is to shield the Earth's surface by absorbing the majority of the harmful ultraviolet (UV) radiation from the sun, which can cause skin cancer, cataracts, and immune system damage in humans and harm other life forms.

Question. A lot of waste is generated in neighborhood. However, almost all of it is biodegradable. What impact will it have on the environment or human health?
Answer: If biodegradable waste is disposed of properly (e.g., through composting), it has a positive impact by recycling nutrients back into the soil. However, if it is allowed to accumulate in large quantities in the open, it can lead to foul smells and become a breeding ground for flies and mosquitoes, which can spread diseases like cholera, typhoid, and malaria, thus negatively affecting human health and the local environment.

Question. Plastic cups were used to serve tea in trains in early days- these could be returned to the vendors, cleaned and reused. Later, Kulhads were used instead of plastic cups. Now, paper cups are used for serving tea. What are the reasons for the shift from plastic to Kulhads and then finally to paper cups?
Answer: 1. Shift from Plastic to Kulhads: Plastic cups were non-biodegradable and posed a major environmental disposal problem. Kulhads (clay cups) were introduced as a biodegradable alternative.
2. Shift from Kulhads to Paper Cups: Making kulhads on a large scale resulted in the loss of fertile topsoil, which is a valuable resource. Paper cups were eventually adopted because they are biodegradable, light-weight, hygienic, and can be manufactured without depleting fertile soil.

Question. Why is damage to the ozone layer a cause for concern? What are its causes and what steps are being taken to limit this damage?
Answer: Damage to the ozone layer is a concern because it allows harmful UV radiation to reach the Earth, leading to health hazards like skin cancer and environmental damage. The primary cause is the release of synthetic chemicals like chlorofluorocarbons (CFCs) used in refrigeration and fire extinguishers. To limit this damage, international agreements like the UNEP (United Nations Environment Programme) were formed to freeze CFC production at 1986 levels, and countries are now shifting to CFC-free alternatives.

Question. Gas A, found in the upper layers of the atmosphere, is a deadly poison but is essential for all living beings. The amount of this gas started declining sharply in the 1980s.
(a) Identify gas A. How is it formed at higher levels of the atmosphere?
(b) Why is it essential for all living beings? State the cause for the depletion of this gas.
Answer: (a) Gas A is Ozone (\( O_3 \)). It is formed at higher levels of the atmosphere by the action of high-energy UV radiation on oxygen (\( O_2 \)) molecules. The UV radiation splits molecular oxygen into free oxygen atoms (\( O \)), which then react with existing \( O_2 \) molecules to form ozone:
\( O_2 \xrightarrow{UV} O + O \)
\( O + O_2 \rightarrow O_3 \)
(b) It is essential because it absorbs harmful UV radiation from the sun, protecting life on Earth from its damaging effects. The main cause for its depletion is the release of Chlorofluorocarbons (CFCs).

A & R Questions

In the following questions a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following.
(a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
(b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
(c) Assertion is correct statement but reason is wrong statement.
(d) Assertion is wrong statement but reason is correct statement.

Question. Assertion : Autotrophs are also called transducers.
Reason : Autotrophs change one form of energy into another.

Answer: (a) Assertion and reason both are correct statements and reason is correct explanation for assertion.

Question. Assertion : Ozone is present in the layer of earth’s atmosphere.
Reason : Ozone is a gas released by burning fuels.

Answer: (c) Assertion is correct statement but reason is wrong statement.

Multiple Choice Questions

Question. Which of the following pyramids is always upright?
(a) Pyramid of energy
(b) Pyramid of biomas
(c) Pyramid of numbers
(d) None of the options

Answer: (a) Pyramid of energy

Question. Detritus food chain begins with
(a) protozoan
(b) algae
(c) virus
(d) bacteria.

Answer: (d) bacteria.

Question. Which of the following is biodegradable?
(a) Cow dung
(b) Plastic wastes
(c) DDT
(d) Heavy metals

Answer: (a) Cow dung

Question. Select the incorrect statement.
(a) Food we eat is digested by various enzymes in our body.
(b) Non-biodegradable substances are not broken down by biological processes.
(c) All enzymes have same action on each substance.
(d) Plastics cannot be broken down by the action of bacteria and other saprophytes.

Answer: (c) All enzymes have same action on each substance.

Question. Shorter food chains provide
(a) more energy
(b) less energy
(c) same energy
(d) any of the options.

Answer: (a) more energy

Question. Identify the correct food chain.
(a) Grass \( \rightarrow \) Frog \( \rightarrow \) Insect \( \rightarrow \) Snake
(b) Grass \( \rightarrow \) Insect \( \rightarrow \) Frog \( \rightarrow \) Snake
(c) Insect \( \rightarrow \) Frog \( \rightarrow \) Grass \( \rightarrow \) Snake
(d) Grass \( \rightarrow \) Frog \( \rightarrow \) Snake \( \rightarrow \) Insect

Answer: (b) Grass \( \rightarrow \) Insect \( \rightarrow \) Frog \( \rightarrow \) Snake

VSA Type Questions

Question. Name two natural and artificial ecosystem.

Answer: Natural ecosystems: Forest, Pond. Artificial ecosystems: Crop field, Aquarium.

Question. Autotrophs are called ‘producers’. Give reason.

Answer: Autotrophs are those organisms which are able to synthesise organic food from inorganic raw materials with the help of solar radiations. They produce the food for all other organisms in the ecosystem.

Question. Why are plastics called non-biodegradable substances?

Answer: Plastics are called non-biodegradable because they cannot be broken down or decomposed into simpler substances by the action of biological processes or microorganisms like bacteria.

SA I Type Questions

Question. Explain briefly about CFCs. Name two gases which have replaced CFCs.

Answer: CFCs stands for Chlorofluorocarbons. These are synthetic chemicals used in refrigeration and fire extinguishers which cause depletion of the ozone layer. They have been replaced by hydrofluorocarbons (HFCs) and hydrocarbons in many applications.

Question. Grass \( \rightarrow \) Grasshopper \( \rightarrow \) frog \( \rightarrow \) snake \( \rightarrow \) Eagle. In the above food chain, which of the organism will have (i) maximum available energy? (ii) minimum available energy?

Answer: (i) Grass will have the maximum available energy as it is the producer at the first trophic level. (ii) Eagle will have the minimum available energy as it is at the highest trophic level.

Question. Write two causes of depletion of ozone layer.

Answer: 1. Excessive use of chlorofluorocarbons (CFCs) in refrigerators, air conditioners and fire extinguishers. 2. Release of nitrogen oxides from the exhaust systems of supersonic aircrafts.

Question. Differentiate between biodegradable and non biodegradable substances.

Answer: Biodegradable substances are those that can be broken down into simpler, harmless substances by the action of microorganisms (like bacteria) over time. Example: vegetable peels, paper. Non-biodegradable substances are those that cannot be broken down by biological processes and persist in the environment for a long time. Example: plastics, DDT.

Question. (a) In an ecosystem, insects feed on plant matter. Name the trophic level to which the insects belong.
(b) Give examples of autotrophs in a garden ecosystem.

Answer: (a) Insects belong to the second trophic level (primary consumers). (b) Examples of autotrophs in a garden are grass, rose plants, sunflower plants, and trees.

Question. Differentiate between natural and artificial ecosystems.

Answer: Natural ecosystems are those which occur naturally in the environment without human intervention, such as forests, ponds, and oceans. Artificial ecosystems are man-made and maintained by human beings, such as crop fields, gardens, and aquariums.

SA II Type Questions

Question. Why are only four or five trophic levels present in each food chain?

Answer: Only about 10% of the energy is available at each trophic level to be passed on to the next higher trophic level. As the energy flow progresses, the amount of available energy decreases significantly. After four or five trophic levels, the amount of energy remaining is very small and insufficient to support the metabolic needs of another trophic level.

Question. Differentiate between autotrophs, heterotrophs and decomposers by giving one example of each.

Answer:
1. Autotrophs: Organisms that can synthesize their own food using inorganic raw materials and solar energy. Example: Green plants.
2. Heterotrophs: Organisms that cannot produce their own food and depend on producers or other organisms for nutrition. Example: Animals like humans, deer.
3. Decomposers: Microorganisms that break down dead organic matter into simpler inorganic substances. Example: Fungi, Bacteria.

Question. Mention the advantages of paper bags over plastic bags.

Answer: Paper bags are biodegradable, meaning they decompose naturally and do not pollute the environment. They can be easily recycled and are made from renewable resources like wood pulp. Unlike plastic, they do not release toxic chemicals into the soil or water.

Question. Give three differences between food chain and food web.

Answer:
1. A food chain is a single, straight linear sequence of organisms, whereas a food web consists of many interconnected food chains.
2. In a food chain, one organism occupies a specific trophic level, while in a food web, an organism can occupy more than one trophic level simultaneously.
3. A food web is more stable and complex than a food chain, as it provides alternative food sources for organisms.

Question. Write three characteristics features of energy transfer in an ecosystem.

Answer:
1. The flow of energy is unidirectional, i.e., it flows from producers to consumers and cannot go back.
2. At each trophic level, a large portion of energy is lost as heat to the environment.
3. Only about 10% of the energy available at one trophic level is transferred to the next higher trophic level (10% law).

LA Type Questions

Question. What practices we can follow to change our lifestyles so that less waste is generated?

Answer:
1. Use the 3Rs: Reduce the use of non-biodegradable items, Reuse things like containers, and Recycle waste like paper and metal.
2. Switch to biodegradable products like jute or cloth bags instead of plastic bags.
3. Practice composting of kitchen and garden organic waste to make manure.
4. Avoid using single-use plastics like straws and disposable plates.
5. Carry your own water bottles and tiffins to avoid buying packaged items.

Question. Explain the phenomenon of ozone depletion. What are the factors responsible for it? What are its consequences?

Answer: Ozone depletion refers to the thinning of the ozone layer in the stratosphere. Factors responsible include the release of synthetic chemicals like chlorofluorocarbons (CFCs), which release chlorine atoms that break down ozone (\( O_3 \)) into oxygen (\( O_2 \)). Consequences include:
1. Increased UV radiation reaching Earth, causing skin cancer and cataracts in humans.
2. Damage to the immune system.
3. Disruption of aquatic food chains by harming phytoplankton.
4. Reduced crop yields and damage to terrestrial plants.

Question. Describe the different components of a pond ecosystem.

Answer:
1. Abiotic components: Water, dissolved oxygen, minerals, sunlight, and temperature.
2. Biotic components:
- Producers: Phytoplankton (algae), floating or submerged aquatic plants.
- Consumers: Zooplankton, insects, small fish, large fish, frogs, and birds.
- Decomposers: Bacteria and fungi found at the bottom of the pond that break down dead organic matter.

Question. (a) List the fundamental steps in the operation of an ecosystem.
(b) Draw a diagrammatic representation of trophic levels in an ecosystem.

Answer: (a) The fundamental steps are: 1. Energy flow (unidirectional). 2. Nutrient cycling. 3. Productivity (production of organic matter). 4. Decomposition. (b) [A pyramid diagram showing: Top Carnivores at the apex, followed by Carnivores, Herbivores, and Producers at the broad base].

Question. Explain some harmful effects of agricultural practices on the environment.

Answer:
1. Biomagnification: Excessive use of pesticides like DDT leads to their accumulation in the food chain, reaching toxic levels in top consumers.
2. Eutrophication: Run-off of fertilizers into water bodies promotes excessive algae growth, depleting oxygen and killing aquatic life.
3. Soil degradation: Continuous use of chemical fertilizers reduces soil fertility and changes soil pH.
4. Groundwater depletion: Over-extraction of groundwater for irrigation leads to a falling water table.