CBSE Class 10 Science Our Environment Important Questions Set 02

Answer: (d) Decrease in energy at higher trophic levels. Only about 10% of energy passes to the next level, so little energy remains after a few steps.

Teacher's Note:
1. The loss of energy at every step is the cause.
2. It is not due to a shortage of water or air.

Answer: (a) The population of tiger decreases and the population of grass increases. Without deer the tiger loses its food and declines, while the grass is no longer eaten and increases.

Teacher's Note:
1. Tigers are carnivores and cannot live on grass.
2. The food chain is disturbed at both ends.

Answer: (a) 1%. Only about 1% of the sunlight falling on terrestrial plants is converted into food.

Teacher's Note:
1. The rest is reflected or used as heat.
2. This 1% supports almost all life.

Answer: (a) unidirectional. Energy moves from the sun to producers and then to consumers and cannot be passed back.

Teacher's Note:
1. It is lost as heat at every step.
2. Nutrients, unlike energy, are recycled.

Answer: (a) only bacteria and fungi. Decomposers are the bacteria and fungi that break down dead remains.

Teacher's Note:
1. Herbivores and carnivores are consumers.
2. Decomposers release nutrients back to the soil.

Answer: (a). Both statements are true and the breakdown of dead matter is the reason they are called cleaners. So R explains A.

Teacher's Note:
1. Without decomposers dead matter would pile up.
2. Their enzymes act on organic waste.

Answer: (a). Both are true and the human control over what is grown and how is what makes the garden artificial. So R explains A.

Teacher's Note:
1. Natural ecosystems such as forests are self-sustaining.
2. Aquariums and crop fields are also artificial.

Answer: An ecosystem is a system formed by interactions among the living organisms of an area and the non-living components of that area.

Teacher's Note:
1. Examples are a pond, a forest and a garden.
2. It has biotic and abiotic components.

Answer: Each step of a food chain at which food energy is transferred is a trophic level. The first level is made of producers, i.e. green plants, blue-green algae and phytoplankton.

Teacher's Note:
1. Herbivores occupy the second trophic level.
2. Carnivores occupy the third and higher levels.

Answer: Making kulhads on a large scale needs a huge amount of clay, and removing it leads to the loss of fertile top soil. Hence it was given up in favour of other options.

Teacher's Note:
1. Top soil takes thousands of years to form.
2. Clay cups are biodegradable but the damage is done at the time of making them.

Answer: Bacteria and other decomposers do not have the enzymes needed to break down the chemical bonds in plastic. So plastic remains in the environment for hundreds of years.

Teacher's Note:
1. Biodegradable materials are broken down by enzymes.
2. Plastic waste harms soil, drains and animals.

Answer: The vegetarian habit is safer. Because of biomagnification, DDT concentration is higher at higher trophic levels, and a vegetarian eats at a level close to the producers.

Teacher's Note:
1. DDT is non-biodegradable and accumulates in body fat.
2. Non-vegetarian food from higher levels carries more DDT.

Answer: A lake has many kinds of organisms and many food chains, so wastes are recycled naturally and the ecosystem is stable. An aquarium has very few organisms and food chains, so it cannot clean itself.

Teacher's Note:
1. Decomposers in a lake break down wastes.
2. Excess growth of algae can still make a lake need cleaning.

Answer: 1. Nutrients are locked up in the waste and do not return to the soil.
2. The waste becomes a breeding site for pests and spreads disease.

Teacher's Note:
1. The waste should be composted instead.
2. Composting turns it into useful manure.

Answer: The producers (grass) are the most numerous at the base, and the top carnivores are the fewest at the top. Only about 10% of the energy passes to each next level, so the energy available falls steeply and can support fewer organisms.

Teacher's Note:
1. The pyramid is therefore broad at the base and narrow at the apex.
2. This is the reason a pyramid of energy is always upright.

Answer: I do not agree, because individuals also share the responsibility. We can (i) cut down waste generation by reusing and refusing single-use plastic, and (ii) segregate waste, compost kitchen waste and give non-biodegradable waste for recycling.

Teacher's Note:
1. Small actions by many people make a large difference.
2. Segregation at home makes recycling easier.

Answer: A food chain is a single straight sequence of organisms in which each eats the one before it, e.g. grass, deer, lion. A food web is a network of many interconnected food chains in an ecosystem. A food web gives organisms alternative food sources and so keeps the ecosystem more stable.

Teacher's Note:
1. Most animals eat more than one kind of food.
2. So real ecosystems have webs rather than isolated chains.

Answer: Biodegradable substances can be broken down by bacteria and fungi, e.g. vegetable waste and paper. Non-biodegradable substances cannot be broken down by these decomposers, e.g. plastic and DDT. The second type persists and accumulates in the environment.

Teacher's Note:
1. Biodegradable waste can be turned into compost.
2. Non-biodegradable waste should be reduced, reused or recycled.

Answer: With no lions to control them, the deer population would increase greatly. The deer would overgraze and finish off the plants, and finally they too would starve. The balance of the ecosystem would be disturbed.

Teacher's Note:
1. Each trophic level controls the population of the one below it.
2. Predators are therefore important for ecological balance.

Answer: UV radiation splits some oxygen molecules (O₂) into atoms, and each atom combines with an O₂ molecule to form ozone (O₃). The ozone layer absorbs harmful UV rays from the sun, so its depletion would expose living beings to skin cancer, cataract and damage to crops.

Teacher's Note:
1. The main cause of depletion is CFCs.
2. Countries agreed to control CFC production in 1987.

Answer: Only about 10% of the energy of one trophic level is passed to the next, and the rest is used in life processes or lost as heat. If a producer level has 10,000 J, the primary consumer gets 1,000 J, the secondary consumer 100 J and the tertiary consumer 10 J. As very little energy is left by the fourth or fifth step, longer chains cannot be supported. The flow of energy is also one-way, which is why it must be supplied continuously by the sun.

Teacher's Note:
1. Energy decreases at every trophic level.
2. This is why a top carnivore needs a large area to survive.

Answer: Biomagnification is the increase in the concentration of non-biodegradable harmful chemicals at each higher trophic level. Pesticides sprayed on crops are washed into soil and water, absorbed by plants and then passed on to the herbivores that eat them. As these chemicals are neither broken down nor excreted, each consumer collects the amount present in all the organisms it eats. Hence the top carnivores, including humans, have the highest concentration.

Teacher's Note:
1. Use of fewer pesticides and organic farming can reduce the problem.
2. The effect was first noticed in birds of prey.