question_answer

Explain the main effects of water pollution.

OR

Give an account of energy flow in an ecosystem.

 

Answer:

Pollutants causing physical and chemical changes in water. Their main effects are outlined below.

1. Pollutants make water unfit for domestic and industrial use. This occurs in many ways:

(a) Addition of very fine, solid suspended particles or colloidal substances makes water turbid.

(b) Addition of dyes and compounds of chromium and iron changes colour of water.

(c) Addition of iron, free chlorine, phenol, manganese, oils, detergents and hydrocarbons changes taste of water, a

(d) Addition of free chlorine, phenol, hydrogen sulphide and ammonia gives unpleasant odour to water. Growth of algae and microorganisms also imparts unpleasant odour to water.

2. Pollutants also make water harmful to living organisms. This occurs by

(a) Addition of very fine, solid suspended particles or colloidal substances makes water turbid.

(b) Addition of plant nutrients such as nitrates and phosphates. This occurs by addition of plant nutrients such as nitrates and phosphates. This promotes the growth of oxygen consuming algae, which deoxygenate water, killing fish and other animals.

(c) Addition of poisonous chemicals broad spectrum pesticides such as mercury, arsenic and lead. This kills aquatic animals. Mercury is changed by bacteria to methyl mercury, which undergoes biomagnification. Taking animals poisoned with methyl mercury causes deformity called minamata disease. It is characterized by diarrhoea, hemolysis, impairment of senses, meningitis and death.

OR

Each organism needs energy for carrying on vital activities and for building up and repairing the body tissues. The ultimate source of entire energy used by living things is sunlight. Solar energy received by an ecosystem depends on the latitude, slope, cloud cover, air pollutants, etc. Only about 1% of the light energy striking the green parts of the plants is changed by photosynthesis into the potential energy of the organic substances, the rest dissipates as heat. The loss of energy is not due to the inefficiency of the photosynthetic mechanism of the plants but to the operation of the second law of thermodynamics. This law states that "whenever energy is transformed from one form into another, there is a decrease in the amount of useful energy some energy is degraded into heat and dissipated."

When a second animal eats the first, a further loss of energy as heat occurs as the second animal oxidizes the organic substances of the first to release energy for synthesizing its own cellular constituents. Decomposition of dead animals also releases chemical energy. Eventually, whole of the energy originally entrapped in plants by photosynthesis is converted into heat and lost, and all the carbon of the organic substances ends up as carbon dioxide.