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Our Environment - 13.213.2 13.213.2 HOW DO OUR ACTIVITIES AFFECT THEHOW DO OUR ACTIVITIES AFFECT THEHOW DO OUR ACTIVITIES AFFECT THEHOW DO OUR ACTIVITIES AFFECT THEHOW DO OUR ACTIVITIES AFFECT THE

Grade 10CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Ozone (O3O_3) is a molecule formed by three atoms of oxygen. While oxygen (O2O_2) is essential for all aerobic forms of life, ozone is a deadly poison at the ground level.

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The ozone layer shields the surface of the earth from ultraviolet (UVUV) radiation from the Sun. This radiation is highly damaging to organisms, for example, it is known to cause skin cancer in human beings.

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Ozone at the higher levels of the atmosphere is a product of UVUV radiation acting on oxygen (O2O_2) molecules. The higher energy UVUV radiations split apart some molecular oxygen into free oxygen (OO) atoms, which then combine with molecular oxygen to form ozone.

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The decline of the ozone layer in the 1980s is linked to synthetic chemicals like chlorofluorocarbons (CFCsCFCs), which are used as refrigerants and in fire extinguishers. In 1987, the United Nations Environment Programme (UNEPUNEP) forged an agreement to freeze CFCCFC production at 1986 levels.

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Substances that are broken down by biological processes (by action of bacteria or other saprophytes) are called biodegradable. Examples include kitchen waste, paper, and sewage.

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Substances that are not broken down by biological processes are called non-biodegradable. These substances may be inert and simply persist in the environment for a long time or may harm the various members of the eco-system. Examples include plastics, glass, and DDTDDT.

📐Formulae

O2→UVO+OO_{2} \xrightarrow{UV} O + O

O+O2→O3O + O_{2} \rightarrow O_{3}

Ozone Depletion Rate∝Concentration of CFCs\text{Ozone Depletion Rate} \propto \text{Concentration of } CFCs

💡Examples

Problem 1:

Why are some substances biodegradable and some non-biodegradable?

Solution:

Substances are classified based on the ability of enzymes to break them down. Enzymes are specific in their action; they can break down natural products like cellulose but cannot break down man-made materials like plastics.

Explanation:

Biodegradable substances like paper can be decomposed by the action of microorganisms because the enzymes they secrete can catalyze the breakdown. Non-biodegradable substances like C2H4C_{2}H_{4} (polyethylene) have chemical bonds that these biological enzymes cannot recognize or break.

Problem 2:

What are the consequences of the ozone layer depletion?

Solution:

  1. Increased risk of skin cancer and cataracts in humans. 2. Damage to the immune system. 3. Reduction in phytoplankton population, affecting the marine food chain.

Explanation:

The ozone layer absorbs the majority of the Sun's harmful UVUV radiation. Without it, these high-energy rays reach the Earth's surface and damage DNADNA and proteins in living cells.