NCERT Class VII: Science-Exercise Solutions
01-Nutrition in Plants
02-Nutrition in Animals
03-Fibre to Fabric
05-Acids Bases and Salts
06-Physical and Chemical Changes
07-Weather Climate and Adaptations of Animals to Climate
08-Winds Storms and Cyclones
10-Respiration in Organisms
11-Transportation in Animals and Plants
12-Reproduction in Plants
13-Motion and Time
14-Electric Current and its Effects
16-Water A Precious Resource
17-Forests Our Lifeline
Chapter 17-Forests: Our Lifeline-Exercise Solutions
NCERT Book Page Number-217
Q.1. Explain how animals dwelling in the forest help it grow and regenerate.
Answer: Various types of animals (herbivores, carnivores, omnivores) live in forests and contribute to food chain.
Interconnection of food chain will form food web. Following activities show how animals help forests grow and regenerate.
• Animals help in dispersal of seeds from one part of the forest to other part.
• Animal’s excreta and their dead bodies when decomposed into soil act as manure for the plants.
• Microorganisms convert dead plants and leaves into humus which is rich in nutrients. Humus in soil provides necessary minerals for plant growth.
Q.2. Explain how forests prevent floods.
Answer: Forest acts as a natural absorber of rainwater and allows it to seep because of roots of trees.
When rainwater falls on leaves of trees and plants, it does not fall directly on the ground. It drips slowly on the forest ground (does not stagnate) and hence prevent floods.
Q.3. What are decomposers? Name any two of them. What do they do in the forest?
Answer: The micro-organisms which convert the dead plants and animals to humus are known as decomposers.
Examples: Fungi and Bacteria.
Decomposers recycle and convert the dead matter into humus which mixes with forest soil and provide necessary nutrients to plants.
Thus decomposers help in maintaining the necessary nutrient balance in the soil.
Q.4. Explain the role of forest in maintaining the balance between oxygen and carbon dioxide in the atmosphere.
Answer: Forests play an important role in maintaining the balance between oxygen and carbon dioxide in the atmosphere.
Forest works like a self-sustaining system. Whatever is produced in the forest is utilized by different components of the forest.
Animals during respiration take in oxygen and release carbon dioxide. Plants take in carbon dioxide and release oxygen through the process of photosynthesis.
Q.5. Explain why there is no waste in a forest.
Answer: Forests are excellent, perfect and natural recycling factories. All animals, whether herbivores or carnivores, depend ultimately on plants for their food.
Herbivores eat plants and their products. Carnivores eat herbivores.
Dead remains of animals and plants are decomposed by micro-organisms into humus.
Whatever is produced in the forest is ultimately utilized by different components of the forest.
There is a food chain in every ecosystem. Forests maintain a network of food chains called food web and hence nothing goes waste in a forest.
Q.6. List five products we get from forests?
(i) Fruits and Vegetables
(ii) Timber and wood
(iii) Turpentine, latex (rubber raw product)
(iv) Spices, resin, gum
(v) Medicines and herbs
NCERT Book Page Number-218
Q.7. Fill in the blank:
(a) The insects, butterflies, honeybees and birds help flowering plants in _____________.
(b) A forest is a purifier of _____________ and _____________.
(c) Herbs form the _____________ layer in the forest.
(d) The decaying leaves and animal droppings in a forest enrich the _____________.
(a) The insects, butterflies, honeybees and birds help flowering plants in pollination.
(b) A forest is a purifier of air and water.
(c) Herbs form the lowest layer in the forest.
(d) The decaying leaves and animal droppings in a forest enrich the soil.
Q.8. Why should we worry about the conditions and issues related to forests far from us?
Answer: Forests are very important resources. We should be careful and concerned about the issues related to forest due to following reasons:
(i) If there are no forests, there would be more floods and more soil erosion.
(ii) Forests affect the global environment in a great way. For example; reduced forest cover in a particular area leads to global warming which affects the whole earth.
(iii) Forests act as habitat for many animals. Deforestation will endanger our life and environment.
(iv) In absence of trees and plants, animals will not get food and shelter.
(v) Forests provide us large number of useful products including wood, fruits and medicines. These products would not be available in the absence of trees and plants.
Q.9. Explain why there is a need of variety of animals and plants in a forest.
Answer: Variety of animals and plants living in forests build a rich biodiversity.
Different animals and plants play different role in the system of a forest. For example; herbivores are needed to eat green plants and to provide food for the carnivores.
Similarly, carnivores are needed to eat the herbivores and check their population. This biodiversity make forests more productive, stable and resilient. If there is no grass, all herbivores would die. If there are no carnivores,
all herbivores would eat up all the plants and there is shortage of food.
If there are no decomposers, the dead remains of plants and animals would pollute the environment. Due to such biodiversity a balance in nature is maintained.
Q.10. In Fig. 17.15, the artist has forgotten to put the labels and directions on the arrows. Mark the directions on the arrows and label the diagram using the following labels: clouds, rain, atmosphere, carbon dioxide, oxygen, plants, animals, soil, roots, water table.
Q.11. Which of the following is not a forest product?
(iii) Sealing wax
Answer: (iv) Kerosene (as it is the fossil fuel found beneath the sea due to dead sea plants and animals’ decay thousand years back).
Q.12. Which of the following statements is not correct?
(i) Forests protect the soil from erosion.
(ii) Plants and animals in a forest are not dependent on one another.
(iii) Forests influence the climate and water cycle.
(iv) Soil helps forests to grow and regenerate.
Answer: (ii) Plants and animals in a forest are not dependent on one another.
Q.13. Micro-organisms act upon the dead plants to produce
Answer: (iii) humus( Humus is produced by dead and decay of plants and animals by the action of photosynthesis).