Greenhouse Effect, Ozone Depletion & Deforestation

1 Mark Questions

1. Why is Gambusia introduced into drains and ponds? [All India 2014]

Ans. Gambusia is introduced into drains and ponds to control breeding and propagation of mosquitoes as they feed on mosquito larva. Thus, controls mosquito population.

2.Name the greenhouse gases that contribute to global warming. [Delhi 2014]

Ans. The greenhouse gases that contribute to global warming are <math>C0_2</math>, <math>CH_4</math>, <math>N_20</math> and CFCs.

1. State the purpose of signing the Montreal Protocol. [Foreign 2014]

Ans. The purpose of signing the Montreal Protocol is to control the emission of ozone depleting substances.

1. Where is good ozone present? Why is it called SO? [All India 2014C]

Ans. Good ozone is present in stratosphere, the upper part of atmosphere.

It is called 'good ozone' because it acts as a shield absorbing ultraviolet radiations from sun.

1. Name the two gases contributing maximum to the greenhouse effect. [Delhi 2014C]

Ans. The two gases contributing maximum to greenhouse effect are CO₂ and CH₄.

1. Write the unit used for measuring ozone thickness. [Delhi 2011]

Ans. Dobson Unit (DU) is used for measuring ozone thickness.

1. How does jhum cultivation promotes deforestation? [All India 2011c]

Ans. In jhum cultivation, the farmers cut down the trees of forest and burn the plant remains. The ash is used as fertiliser and land is used for farming. After cultivation the area is left free for several years for recovery. The recovery phase is often ignored leading to deforestation.

1. How is snow blindness caused in humans? [All India 2010]

Ans. Snow blindness is caused by absorption of UV-B radiation.

1. Name two greenhouse gases produced by anaerobic microbes. [Foreign 2010]

Ans. Carbon dioxide and methane are the green house gases produced by anaerobic microbes.

1. Mention the causes of thinning of ozone layer. [Delhi 2010c]

Ans. CFCs release chlorine atoms, when UV-rays act on them. Chlorine degrades the ozone into molecular oxygen. Thus, causing thinning of ozone layer.

2 Marks Questions

1. Write, what was the percentage of forest cover of India at the beginning and at the end of

twentieth century? How different is it from the one recommended by National Forest Policy? [Foreign 2014]

Ans. In the beginning of the twentieth century, the forest cover was about 30% while towards its end is reduced to only 19.4%. The National Forest Policy of India recommends approximately 60% forest cover for hilly regions including Himalayas, while 33% for plains. However, the situation is contrastingly different as the production of forests in India is very slow.

1. (i) State the cause of depletion of ozone layer.
2. Specify any two ill effects that it can cause in the human body. [Foreign 2014]

Ans. (i) The main cause of depletion of ozone layer is due to imbalance between production and degradation of ozone in the stratosphere. This balance is disrupted mainly due to increase in ozone degradation by GFCs.

1. The two ill-effects that ozone depletion can cause in human body are:

• Allows UV-B radiation to enter atmosphere that increases mutation and damages DNA.
• Causes ageing of skin and damage to skin cells and cancer.
• Inflammation of cornea (snow blindness), cataract, etc.

1. Refrigerants are considered to be a necessity in modem living, but are said to be

responsible for ozone holes detected in Antarctica. Justify. [Foreign 2012]