CBSE Questions for Class 10 Biology Our Environment Quiz 2 - MCQExams.com

• The presence of the layer of ozone (trioxygen) prevents the UV rays from reaching the surface of the earth.
• The reactions that occurs to form ozone from oxygen are shown below:

• An ozone hole is a depletion of the ozone layer which is present in the stratosphere region around 26-30kms above the Earth's surface. 
• It is caused by chlorofluorocarbons (CFCs) found in air-conditioners, aerosol spray cans, refrigerants, etc. 
• CFCs can not be removed in the troposphere and moves in the stratosphere layer where it reacts with ozone, thereby releasing free chlorine atoms and causes the ozone layer to deplete. 

• A food chain is defined as a linear network of links in a food web starting from producer organisms and ending at an apex predator species, or decomposer species. 
• Green plants are known as producers as they trap energy from the sun and then pass it to all the consumers occupying successive trophic levels.

• An ecosystem is a segment of the biosphere consisting of a community of living beings and the abiotic or physical environment interacting and exchanging materials between them. 
• A community is a group of potentially interacting species living in the same region.
  

A)  Correct Option – C
B)  Explanation for correct option -

The two forms of oxygen found in the atmosphere are a diatomic molecular form that has a chemical formula as O22 or oxygen, the life-giving gas that we breathe in to survive. 
Another is a triatomic molecular form that has a chemical formula O33 called ozone gas, which protects us from harmful UV rays.

• Biomagnification refers to an increase in the concentration of toxic chemicals at successive trophic levels. 
• This happens because a toxic substance accumulated by an organism cannot be metabolized or excreted, and it is passed on to the next higher trophic level. 
• In an aquatic ecosystem, birds are at the highest trophic level. 
• Thus, the correct answer is option B.

• Biodegradable items are those, which can be degraded by biological agencies like detrivores. 
• These organisms feed on the dead and decaying matter and convert them into minerals and return those minerals back to the environment, thus completing the cycle of nutrients. 
• Non-biodegradable items are those which cannot be acted upon by detrivores. Thus, such items cannot be degraded or decomposed. In a way, they are a permanent addition to the environment and cannot be done away with. 
• For example, polythene, thermosetting plastics like bakelite, insecticides like DDT, detergent, PVC, etc. These items cannot be degraded biologically.
• Thus the correct answer is option D. 

• The sun is considered the primary energy source since it is the source of nearly all the earth’s energy.
• Plants produce food using sunlight, and the food we get from plants and animals also has its primary sunlight source.
• The fossil fuels we use in our everyday lives come from dead plants and animals that have their origins as solar energy again.
• Hence, the correct answer is option D. 

• Rat is a herbivore animal, who used to eat plant products (primary consumer).
• The potato plant is a producer that traps solar energy and produces food (carbohydrates), which are stored in potato tubers. 
• The rat cannot produce their own food by the use of solar energy and hence, feeds on potato tuber for his life processes.

$$\textbf{Correct option: }$$ B

$$\textbf{ Solution: }$$

$$\textbf{ Option (A): }$$

$$\bullet$$The increase in the natural resource is not the consequences occurring due to the over exploitation of natural resources by man. 

$$\bullet$$Natural resources are the resources available in the environment and are useful for the survival of the living organism on earth. 

$$\bullet$$Overexploitation of natural resources leads to ecological balance. 

$$\bullet$$Human activities like deforestation are a major threat which causes global warming. 

$$\textbf{ Option (B): }$$

$$\bullet$$Ecological imbalance bought in by human activities in the environment is the major consequences of the  over exploitation of natural resources by man. 

$$\textbf{ Option (C): }$$

$$\bullet$$Ozone layer is responsible for protecting the earth's atmosphere from the harmful ultraviolet rays received from the sunlight.

$$\bullet$$The thinning of the ozone layer is known as the ozone layer depletion that can result in the increase of the UV radiation reaching the earth's atmosphere.

$$\textbf{ Option (D): }$$

$$\bullet$$Reappearance of some extinct species is not possible in the environment. 

$$\bullet$$The extinction of the animal results in the extinction of genes as well as its alleles from the gene pool. 

Hence, the correct answer is option (B)