CBSE Class 10 Biology Our Environment MCQs Set 25

Answer: (c) Phytoplankton to zooplankton to fishes

Explanation:
1. Phytoplankton are producers and are eaten by zooplankton.
2. Zooplankton are eaten by fishes.

Teacher's Note:
1. A food chain begins with a producer.
2. Arrows show the direction of food and energy.

Answer: (d) Producers, herbivores, carnivores, decomposers

Explanation:
1. Energy enters through producers, passes to herbivores and then to carnivores.
2. Decomposers act on dead remains at every level.

Teacher's Note:
1. Energy flow is one-way.
2. The sun is the source of energy.

Answer: (a) Biomagnification

Explanation:
1. Non-biodegradable chemicals like DDT build up in the bodies of organisms and become more concentrated at each higher level.
2. This is biomagnification.

Teacher's Note:
1. Top carnivores have the highest concentration.
2. The chemicals are not broken down or excreted.

Answer: (b) Natural

Explanation:
1. A natural pond is a self-sustaining aquatic ecosystem formed without human help.
2. An aquarium would be artificial.

Teacher's Note:
1. Natural ecosystems include forests, ponds and oceans.
2. Crop fields are artificial.

Answer: (d) Plankton

Explanation:
1. Plankton are tiny organisms that float in water.
2. Phytoplankton are plant-like and zooplankton are animal-like.

Teacher's Note:
1. Plankton are the base of aquatic food chains.
2. They drift with water currents.

Answer: (a) Phytoplankton

Explanation:
1. The vast oceans are full of phytoplankton.
2. They carry out the largest share of the world's photosynthesis.

Teacher's Note:
1. Zooplankton are consumers and do not photosynthesise.
2. Phytoplankton also supply much of the oxygen.

Answer: (d) Tansley

Explanation:
1. A. G. Tansley coined the term ecosystem in 1935.
2. Odum is called the father of modern ecology.

Teacher's Note:
1. An ecosystem includes the living and non-living parts.
2. Haeckel coined the term ecology.

Answer: (a) a and c

Explanation:
1. Fertiliser run-off caused excess algae growth (algal bloom).
2. When the algae died and rotted, oxygen was used up, making the water green and stinky and killing the fish.

Teacher's Note:
1. This is eutrophication.
2. DDT would have acted more slowly.

Answer: (d) Destruction of natural habitats

Explanation:
1. Habitat loss through deforestation and urbanisation is the biggest threat to biodiversity.
2. Species cannot survive when their homes are destroyed.

Teacher's Note:
1. Hunting and pollution add to the problem.
2. Protected areas help in conservation.

Answer: (d) A bioindicator for air pollution

Explanation:
1. Lichens are very sensitive to sulphur dioxide in the air.
2. They disappear in polluted areas, so they indicate air pollution.

Teacher's Note:
1. Lichens are a partnership of an alga and a fungus.
2. They grow on tree bark and rocks.

Answer: (c) Oxygen and oxygen

Explanation:
1. UV radiation splits O₂ molecules into atoms which join with other O₂ to form O₃.
2. So ozone forms from oxygen alone.

Teacher's Note:
1. Ozone absorbs harmful UV rays.
2. CFCs destroy it.

Answer: (c) (i) and (iii)

Explanation:
1. UV radiation can weaken the immune system and cause skin cancer.
2. It does not directly damage the lungs or cause ulcers.

Teacher's Note:
1. It also causes cataract and sunburn.
2. The ozone layer shields us from UV.

Answer: (a) Methyl isocyanate

Explanation:
1. Methyl isocyanate (MIC) leaked from a pesticide plant in Bhopal.
2. It killed thousands of people.

Teacher's Note:
1. It is one of the worst industrial accidents.
2. The date was the night of 2-3 December.

Answer: (d) Both municipal sewage and industrial discharge

Explanation:
1. Untreated sewage and industrial effluents are the largest sources of water pollution in India.
2. So both are correct.

Teacher's Note:
1. Treatment plants are needed before discharge.
2. Pollution lowers dissolved oxygen.

Answer: (d) Both green manure and biofertilisers

Explanation:
1. Green manure and biofertilisers are natural materials that enrich the soil.
2. Bio-insecticides control pests.

Teacher's Note:
1. Biofertilisers include Rhizobium and blue-green algae.
2. They do not pollute the soil.

Answer: (b) Evaporation, condensation and precipitation

Explanation:
1. Water evaporates, condenses into clouds and falls as precipitation.
2. This is the water cycle.

Teacher's Note:
1. Transpiration also adds water vapour.
2. Water returns to the sea through rivers.

Answer: (b) Few organisms can directly use atmospheric nitrogen gas

Explanation:
1. Nitrogen gas is very unreactive.
2. Only some bacteria, like Rhizobium and Azotobacter, can fix it.

Teacher's Note:
1. Nitrogen makes up about 78% of the air.
2. Lightning can also fix some.

Answer: (b) Photosynthesis

Explanation:
1. In photosynthesis, plants convert CO₂ into glucose using sunlight.
2. This is how carbon enters living things.

Teacher's Note:
1. Respiration returns CO₂ to the air.
2. Plants are the producers of food.

Answer: (a) Carbon

Explanation:
1. Photosynthesis takes in CO₂ and respiration gives it out.
2. This is the carbon cycle.

Teacher's Note:
1. Carbon moves between air, plants and animals.
2. Decay also releases it.

Answer: (a) Burning fossil fuels

Explanation:
1. Burning coal, oil and gas releases large amounts of CO₂.
2. This is the main cause of global warming.

Teacher's Note:
1. Deforestation also adds CO₂.
2. Mining does not itself release much carbon.

Answer: (b) Surface and sub-surface run-off

Explanation:
1. Rain water carries minerals away by run-off over and under the ground.
2. This is how they spread to rivers and seas.

Teacher's Note:
1. Plants take minerals up rather than disperse them.
2. Evaporation moves only water.

Answer: (b) 3-6

Explanation:
1. Acid rain has a pH lower than normal rain (about 5.6), usually 3 to 6.
2. It is caused by oxides of sulphur and nitrogen.

Teacher's Note:
1. Acids have a pH below 7.
2. It damages buildings like the Taj Mahal.

Answer: (d) All of the above

Explanation:
1. Climate change affects food production, ecosystems, water, air, oceans, energy and health.
2. So all the areas are affected.

Teacher's Note:
1. Rising sea level is one effect.
2. Global warming is caused by greenhouse gases.

Answer: (d) An algal bloom

Explanation:
1. Excess nutrients cause rapid growth of algae, called an algal bloom.
2. It reduces oxygen when the algae die.

Teacher's Note:
1. The process is eutrophication.
2. Fish die due to lack of oxygen.

Answer: (b) Natural gas processing

Explanation:
1. Processing natural gas and burning fuels with sulphur release sulphur dioxide.
2. Hydro-electric plants do not burn fuel.

Teacher's Note:
1. SO₂ causes acid rain.
2. Thermal power plants are also a major source.

Answer: (b) Sulphur and nitrogen oxides

Explanation:
1. Oxides of sulphur and nitrogen dissolve in rain water to form sulphuric and nitric acids.
2. These cause acid rain.

Teacher's Note:
1. Vehicles and industries release them.
2. CO₂ only makes rain slightly acidic.

Answer: (d) The carbon cycle

Explanation:
1. The carbon cycle describes the movement of carbon among air, living things, water and soil.
2. It is a biogeochemical cycle.

Teacher's Note:
1. Energy flows in one direction, but matter like carbon is cycled.
2. CO₂ is the main form in the air.