Class 7 General Science NCERT Based - 4 - Free MCQ Practice Test with solutions,

2. Tiny droplets of water on the surface of a glass containing ice are formed due to condensation. Air contains water vapour, and when air comes in contact with a cold surface, the water vapour cools down and condenses to form droplets of water.

3. Evaporation and transpiration, both change water from liquid to vapour.

2. In the atmosphere, water remains in the form of clouds. This water reaches the earth’s surface in the form of rain, snow and hail.

3. In the last step, water reaches the oceans through the rivers and streams. This is how the water cycle is completed. It is responsible for maintaining a fixed volume of water on earth.

Explanation:

• Snow is not a liquid form of water, it is a solid form of water.


• Lake water and river water are both liquid forms of water.


• Water vapour is a gaseous form of water, not a liquid form.


• Ice is a solid form of water, not a liquid form.

Therefore, the correct options are A: 1, 4 and 5 only.

• All animals, whether herbivores or carnivores, depend ultimately on plants for food. Organisms which feed on plants often get eaten by other organisms, and so on.

• For example, grass is eaten by insects, which in turn, is taken by the frog. The frog is consumed by snakes.

• This is said to form a food chain: Grass → insects → frog → snake → eagle. Many food chains can be found in the forest. All food chains are linked. If any one food chain is disturbed, it affects other food chains too.

• The micro-organisms which convert the dead plants and animals to humus are known as decomposers.

• These microorganisms play an important role in the forest. The presence of humus ensures that the nutrients of the dead plants and animals are released into the soil.

• From there, these nutrients are again absorbed by the roots of the living plants and the dead animals become food for vultures, crows, jackals and insects.” In this way, the nutrients are cycled. So, nothing goes waste in a forest.

• A primary consumer is an organism that feeds on primary producers. Organisms of this type make up the second trophic level and are consumed or predated by secondary consumers, tertiary consumers or apex predators.

• Primary consumers are usually herbivores that feed on autotrophic plants, which produce their own food through photosynthesis.

• Adaptation does not occur over a short period of time. It is related to the plants and animals adapting themselves to the changes having occurred over millions of years.

• If we live in the plains and suddenly go to high mountain regions, we may experience difficulty in breathing and doing physical exercise for some days. We need to breathe faster when we are on high mountains.

• After some days, our body adjusts to the changed conditions on the high mountain. Such small changes that take place in the body of a single organism over short periods, to overcome small problems due to changes in the surroundings, are called acclimatisation.

• Cactus is a desert plant. Desert plants lose very little water through transpiration. The leaves in desert plants are either absent, very small, or they are present in the shape of spines.

• This helps in reducing loss of water from the leaves through transpiration.The leaf-like structure you see in a cactus is, in fact, photosynthesis in these plants is usually carried out by the stems. The stem is also covered with a thick waxy layer, which helps to retain water.Most desert plants have roots that go very deep into the soil for absorbing water.

• Changes occuring in the environment are called stimuli, like pricking of a thorn, bright light, etc. All the living things show response towards stimulus. Leaves of touch me not (Mimosa) plants fold/shrink when touched.

• This is an example of response to stimulus. Reproduction occurs in both plants and animals, but the methods are different.

• While respiration, the exchange of gases in plants occurs through the leaves. Plants take in the air through the stomata and utilise the oxygen.

• They release carbon dioxide into the atmosphere. During photosynthesis, plants use carbon dioxide in the presence of sunlight to make their own food and release oxygen. Plants make their food only during the day; while they respire during the day and night both.

• Oxygen released during photosynthesis is much more than that used during respiration.

• Municipal Solid Waste, also called garbage or trash, is nonhazardous disposable materials generated by households, institutions, industries, agriculture, and sewage.

• It is made up of waste, organics, and recyclable materials, with the municipality overseeing its disposal. Typically, municipal solid waste is collected, separate and sent to either a landfill or municipal recycling center for processing.

• An aerobic organism or aerobe is an organism that can survive and grow in an oxygenated environment. In contrast, an anaerobic organism (anaerobe) is any organism that does not require oxygen for growth. Some anaerobes react negatively or even die if oxygen is present.

Arsenic ; Fluoride ; Uranium can be found as pollutants in the drinking water in some parts of India.

• Pollution of water bodies by mercury causes Minamata disease in humans and Dropsy in fishes. Lead causes dysplasia, cadmium poisoning causes Itai – Itai disease.

• Accumulation of arsenic in the body parts like blood, nails and hairs causing skin lesions, rough skin, dry and thickening of skin and ultimately skin cancer.

• Discharge of domestic waste, agricultural surface runoff, land drainage and industrial effluents in a water body leads to rapid nutrients enrichment in a water body.

• The excessive nutrient enrichment in a water body encourages the growth of algae, water hyacinth, Phytoplankton and other aquatic plants.

• The biological demand for oxygen (BOD) increases with the increase in aquatic organisms.

• Eutrophication occurs when fresh water is artificially supplemented with nutrients, which causes an abnormal plant growth. The output of waste into the water bodies from industries, agriculture, and urban communities generally exceeds the biological capacities of aquatic systems.

• Runoff of chemical fertilizers from fields is a major cause. When organic matter exceeds the capacity of those microorganisms in water that break it down and recycle it, it encourages rapid growth, or blooms of algae.

• When they die, remains of the dead algae add further to the organic wastes already in water; eventually, water becomes deficient in oxygen.

• Realizing the magnitude of the problem with regard to the pollution of the river Ganga, the Government of India launched the Ganga Action Plan in 1985 to clean this holy river.

• This was the first time that the problem of water pollution was being tackled at a national level with interest being shown by all.

• It effectively functions in three states - Uttar Pradesh, Bengal, and Bihar - the three states through which it flows.

• Though there has been some change in the water quality of the river since this programme began, the improvement is very marginal and is far below the expected rate. Work on this project is still underway and it is yet to be seen whether they will be able to achieve their target.

• Wetlands are areas lying along the banks of rivers and lakes, and coastal regions. They are life-supporting systems providing fish, forest products, water, flood control, erosion buffering, a plant gene pool, wildlife, recreation, and tourism areas.

• Though they are endowed with a rich biodiversity yet of late, they are being greatly exploited.

• A number of factors have been responsible for the depletion of wetland areas mainly the mangrove forests, along the coasts of India. Intensive aquaculture development, deforestation, pollution from tankers, domestic waste, agricultural runoff, and industrial effluents are some of the factors.

• In 1981, Chilika Lake, India's largest brackish water lagoon, was the first site to be designated a Ramsar Wetland of International Importance.

• In a country like India where more than 50% of the population is rural-based, agriculture is one of the most important professions.

• The fields have to be regularly watered and there are large networks of irrigation systems all over the country. This sector is therefore the largest consumer of water in the country.

• In the past few years, various methods have been introduced to decrease the wastage of water in this sector. One of the methods that is becoming popular is that of drip irrigation.