Our Environment - MCQ Test (22-11-2017) - Class 10 MCQ

A volcanic eruption is both an international pollutant source and an international hazard. Active volcanoes can contribute to air pollution through the release of toxic gases.

The driving force of an ecosystem is solar energy. A food chain in an ecosystem always starts with photosynthesis. The autotrophs or the producers are at the first trophic level. They fix up the solar energy and make it available for heterotrophs or the consumers.

The autotrophs capture the energy present in sunlight and convert it into chemical energy. Therefore, the energy available for transfer from one trophic level to the next trophic level in an ecosystem is in the form of chemical energy. When one form of energy is changed to another, some energy is lost.

Excessive exposure of humans to UV (ultraviolet) rays results in damage to the immune system. Exposure to UV radiation is also a risk factor for most skin cancers.

Nitrous oxide occurs in small amounts in the atmosphere, but has been found to be a major scavenger of stratospheric ozone, with an impact comparable to that of the CFCs.  According to an estimation, 30% of the N₂O in the atmosphere is the result of human activity, chiefly agriculture. It also has a significant global warming potential as a greenhouse gas

A food chain in an ecosystem always starts with photosynthesis. The autotrophs or the producers are at the first trophic level. They fix up the solar energy and make it available for heterotrophs or the consumers.

Disposable plastic plates should not be used because they are made of non-biodegradable material. Non-biodegradable substances may be inert, are not broken down and persist in the environment for a long time. They may thus cause harm to the various members of the ecosystem.

Organisms in groups B and C do not make up a food chain. A food chain is a series of organisms in order of who eats whom. In B, grasshopper is out of place. In D, nobody out of wolf, snake or tiger eats grass.

Soil is an abiotic (non-living) component of an ecosystem. It provides the substratum for plant growth as also water, nutrients and minerals. Soil contains a number of micro-organisms and it cannot provide a disease-resistant environment for plants.

According to 10% law, the energy available to each successive trophic level is 10% of the previous trophic level. An average of 10% of the food eaten by a consumer is turned into its own body and made available for the next level of consumers. 10% can be taken as the average value for the amount of organic matter that is present at each step and reaches the next level of consumers.

If deer is missing from the given food chain, the population of tiger will decrease and the growth of grass will increase. A missing link in a food chain will create an imbalance in the ecosystem.

A habitat is an ecological or environmental area that is inhabited by a particular species of organism. The term refers to the special environment in which an organism lives and breeds and where it can find food, shelter, and protection.

An aquarium is not a terrestrial ecosystem. Forest, desert and grassland are terrestrial ecosystems. An ecosystem may be a terrestrial ecosystem or an aquatic ecosystem.

An ecosystem consists of biotic components comprising living organisms and abiotic components comprising physical factors like temperature, rainfall, wind, soil and minerals.

The ecosystem of the earth is known as biosphere. The term "biosphere" was coined by geologist Eduard Suess in 1875, which he defined as the place on Earth's surface where life dwells.

The second trophic level is of the primary consumers (herbivores). Small fish and grasshopper belong to this level. A snake is not a primary consumer. Free-living protozoa occupy a range of trophic levels.

The following chain constitutes a food chain (organisms in order of who eats whom):-

Grass →Goat →Human

The decomposers in an ecosystem are microorganisms, comprising bacteria and fungi. They break down the complex organic substances (dead remains and waste products of organisms) into simple inorganic substances, which go into the soil and are used up once more by the plants.

Secondary treatment in sewage treatment plant involves biological treatment (use of microorganisms)

All given ecosystems are terrestrial ecosystems. Forest, grassland and desert are natural ecosystems. An aquarium is an example of a human-made (artificial) ecosystem.

Plants are producers. The herbivores or the primary consumers come at the second trophic level. Small carnivores or the secondary consumers come at the third trophic level. Larger carnivores or the tertiary consumers form the fourth trophic level.

According to 10% law, the energy available to each successive trophic level is 10% of the previous trophic level. 
Given, energy available at the third trophic level = 50 KJ
Energy available at second trophic level = 50 KJ x 10 = 500 KJ
Therefore, energy available at the producer level (first trophic level) = 500 KJ x 10 = 5000 KJ

Exposure to ultraviolet (UV) radiation can cause eye diseases like the cataract. A cataract is a clouding of the lens in the eye which leads to a decrease in vision. 

Different essential nutrients like nitrogen, carbon, oxygen and water are cycled and changed from one form to another in separate biogeochemical cycles in an ecosystem. The producers convert the solar energy received from the Sun into chemical energy and also fix up the nutrients from the soil, and make them available to the higher trophic levels in the ecosystem.

The flow of energy in an ecosystem is always unidirectional. It means that as the energy moves progressively through the various trophic levels, it is no longer available to the previous level. The energy that is captured by the autotrophs (producers) does not revert back to the solar input. The energy which passes to the herbivores (primary consumers) does not come back to the autotrophs (producers).

Substances that are not broken down into simpler substances by biological processes are said to be non-biodegradable. Polythene, detergents and PVC (Polyvinylchloride) are non-biodegradable substances. Substances that can be broken down by biological processes are said to be biodegradable. Paper, wood, grass, leather and cloth are biodegradable.

Pesticides and other chemicals that are used to protect our crops from diseases and pests, do not get degraded, enter the food chain, and get accumulated in human bodies. The human beings occupy the top level in any food chain. Therefore, the maximum concentration of the chemicals is in the human body. This phenomenon is known as biological magnification.

An ecosystem may be classified as a natural ecosystem or a man-made ecosystem. A garden is an example of a man-made ecosystem. Deserts, rivers and grasslands are examples of natural ecosystems.

Frog and snake - both secondary consumers - belong to the same trophic level. Plant is a producer and belongs to the first trophic level. Deer is a herbivore (a primary consumer) and belongs to the second trophic level, Hawk belongs to the last trophic level.

DDT is dichloro diphenyl trichloroethane. It is used as a pesticide.