CBSE Questions for Class 7 Biology Forests Our Lifeline Quiz 3 - MCQExams.com

• Sheesham produces rosewood, while bamboo produces wood. These are used for construction purpose.
• Wheat is consumed as food and not used for construction.

• Teak, bamboo and Sheesham are used to obtain different types of wood. they are commonly used in the furniture industry for making tables, chairs, beds etc. 
• Neem is a medicinal plant, which is used as a herb most of the time.

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

$$\textbf{Solution:}$$

$$\textbf{Explanation for correct statements:}$$

Statement (ii):

$$\bullet$$ Carnivores are placed at third trophic level (T3) in a food chain and they feed on herbivores like deer (present at T2).

$$\bullet$$ If carnivores are removed from an ecosystem, then the population of deers will increase as the population of their predators decrease.

Statement (iii):

$$\bullet$$ The length of a food chain is generally limited to 3-4 trophic levels due to energy loss.

$$\bullet$$ As producers are present at T1 and synthesize most of the energy, this energy will pass to the herbivores (T2), then to carnivores (T3) and finally to the top-carnivores (T4).

$$\bullet$$ During this energy transfer from one trophic level to the next, there is a loss of $$10\%$$ energy. If the number of trophic level increases more than 3 or 4, then there will be no energy left for the organism present at 5th trophic level.

$$\textbf{Explanation for incorrect statements:}$$

Statement (i):

$$\bullet$$ Tigers are the carnivores which are placed at third trophic level of a food chain.

$$\bullet$$ They feed on herbivores like deer (present at T2) which feed on vegetation (T1) of an ecosystem like plants herbs, etc 

$$\bullet$$ If the population of tigers is decreased, then the population of herbivores will be increased due to less number in their predators which is tiger.

$$\bullet$$ Because the herbivore population is increased, the vegetation will be decreased because herbivores feed on plants.

$$\bullet$$ So, removal of $$80\%$$ tigers from an area will not result in greatly increased growth of vegetation.

Statement (iv):

$$\bullet$$ The length of food chain is 3 - 4 trophic levels and it cannot be 2 to 8 due to energy loss at each trophic level.

Hence the correct option is option B.

• Plants provide shelter for animals and they make oxygen for the animals to live. When animals die they decompose and become natural fertilizer plants. Plants depend on animals for nutrients, pollination and seed dispersal. 
• Hence Plants and animals in the forest are dependent on one another.
• Hence the given statement Plants and animals in the forest are not dependent on one another is a wrong statement.
• So, the correct answer is 'Option D'.

• If forest disappears or deforestation continues to exist then the amount of carbon dioxide in the atmosphere will increase. 
• This is because the green plants capable of fixing atmospheric carbon dioxide into organic material such as glucose by the action of photosynthesis are no longer available. 
• Thus, increasing the carbon dioxide level in the air. 

• Cutting down trees reverses the effects of carbon sequestration and releases greenhouse gases (including carbon dioxide) into the atmosphere.
• Deforestation changes the landscape and reflectivity of earth's surface, i.e. decreasing albedo.
• So, the correct answer is option A.

• Semal, sal, khair, neem, and palash are examples of trees. 
• Hornbill, chinkara, and blue bull are animals.