Question

Answer the following questions.

(a) Name the constituents of air and give their proportion in air.

(b) Of what use is carbon dioxide to plants?

(c) What is meant by nitrogen fixation? How does it happen?

(d) Which measures are necessary for arresting pollution?

(e) What ill-effects of pollution are being seen?

(f) What function does an observatory perform?

Answer 1

(a) The composition of air is 78% nitrogen, 21% oxygen, and 1% various other gases, dust particles and pollen grains. The other gases usually found in air are xenon, carbon dioxide, hydrogen, argon, neon, helium, krypton, water vapours etc. The composition of air varies with the altitude. The higher we go, the concentrations of water vapours, dust particles and pollen grains get lowered.

(b) Plants use carbon dioxide gas to make their own food with the help of water and this process is known as photosynthesis.

6CO₂ + 12H₂O → C₆H₁₂O₆ + 6H₂O + 6O₂

In this process, carbon dioxide gets reduced into carbohydrates.

(c) Nitrogen is essential for plants. The concentration of nitrogen in the atmosphere is about 78%. Nitrogen forms a structural component of many important molecules such as DNA, RNA, and other vitamins. Plants cannot absorb nitrogen directly from the atmosphere. The process in which the atmospheric nitrogen is converted into usable forms is known as nitrogen fixation. Two such methods are given below:

(i) During lightning and thunder, the high temperature and pressure in the air convert atmospheric nitrogen into oxides of nitrogen that dissolve in water to produce nitric and nitrous acids. These acids fall along with the rain.

(ii) Certain forms of bacteria are able to convert atmospheric nitrogen into usable forms such as nitrates and nitrites. Such nitrogen−fixing bacteria are commonly found in the roots of legumes (plants of pulses) inside special structures called root nodules.

These usable forms of nitrogen are absorbed by plants to produce many compounds such as amino acids that in turn form proteins. When an animal feeds on plants, nitrogen enters its body.

(d) Pollution - Pollution is the introduction of substances that can pose threat to the environment.

Measures to prevent pollution:

(i) To prevent water pollution - It is necessary to keep the sources of water clean and uncontaminated. Following are some more ways to prevent water pollution:

• Avoid using pesticides and fertilizers as these off into water bodies during rains

• Do not throw waste materials or other chemicals into sewers.

• Do not wash paint brushes in the sink.

(ii) To prevent air pollution - To prevent air pollution, the first thing we can do is walk more and drive less. This can prevent fossil fuels from polluting the air. Following are some other ways to prevent air pollution:

• Get your vehicles pollution checked

• Avoid purchasing products that come in aerosol spray cans.

(iii) To prevent land pollution - The best way to prevent land pollution is to recycle. Following are some ways to reduce land pollution:

• Store chemicals and waste in spill−proof containers.

• Reuse and recycle the waste material.

• Use biodegradable products.

• Do not use pesticides

(e) Effects of pollution: Pollution causes harmful effects on living as well as non−living organisms. Some of the harmful effects are as follows:

(i) Water pollution contaminates the sources of water such as rivers, lakes and oceans.

(ii) When water gets polluted, it adversely affects the aquatic life and disturbs the ecological balance.

(iii) Many harmful gases are released in the air due to air pollution.

(iv) Acid rain is also one of the consequences of air pollution.

(v) Land pollution affects the fertility of soil.

(vi) The grasses that are grown upon polluted soil become poisonous for the grazing animals.

(vii) Pesticides that are applied to the crops may contaminate the grains that are consumed by the animals. These pesticides indirectly cause harm to the animals.

(viii) The washed away pesticides also contaminate the water sources that are used by the animals for drinking purpose.

Consequently, the water, air and land pollution adversely affect the human health and natural environment.

(f) An observatory records the observations of atmospheric factors such as temperature, pressure, velocity of winds and humidity. It keeps a record of the changes occurring in them and forecasts the weather based on the changes observed. Observations of weather are recorded every hour with the help of machines. For example, scientists of the Indian Meteorological Department at Pune have developed a system that accurately predicts the arrival of south−west monsoons.