NCERT Exemplar Problems
Short Answer Questions
Question 25: Prepare a list of five items that you use daily in the school. Identify from the list such items that can be recycled.
Answer: Five items being used daily in school: Paper, pencil, bag (cotton or nylon), water bottle (plastic or metal), and lunch box (plastic or metal).
Items that can be recycled: Paper, cotton, metal and wood (from pencil).
Question 26: List two advantages associated with water harvesting at the community level.
Answer: Two advantages of water harvesting at community level are as follows:
- This ensures availability of water throughout the year.
- Each person in the community gets access to water for various purposes.
Question 27: In a village in Karnataka, people started cultivating crops all around a lake which was always filled with water. They added fertilisers to their field in order to enhance the yield. Soon they discovered that the water body was completely covered with green floating plants and fishes started dying in large numbers. Analyse the situation and give reasons for excessive growth of plants and death of fish in the lake.
Answer: The situation is highly alarming because growth of green floating plants creates deficiency of oxygen for aquatic animals. Most of the oxygen is utilized by the floating plants. Algae and hyacinth are the plants which grow in a water body because of availability of nitrates in water. This happens because of addition of nitrates which come from fertilizers. Excess growth of green floating plants in a water body is called eutrophication.
Question 28: What measures would you take to conserve electricity in your house?
Answer: I will take following measures to conserve electricity in my house:
- I will ensure that fan and light are switched off if nobody is in the room.
- I will keep the windows open during the day so that natural light comes in the room. This will help in minimizing the use of electricity.
- I will switch on the airconditioner or air cooler only when absolutely necessary.
- I will ensure that all the bulbs are replaced with LED lights.
Question 29: Although coal and petroleum are produced by degradatioin of bio- mass, yet we need to conserve them. Why?
Answer: Coal and petroleum are non-renewable resources because they cannot be renewed in the foreseeable future. Formation of coal and petroleum takes millions of years. We are using coal and petroleum at a faster rate. Hence, they are going to be exhausted in the near future. So, we need to conserve coal and petroleum.
Question 30: Suggest a few measures for controlling carbon dioxide levels in the atmosphere.
Answer: Following steps can be taken to control carbon dioxide levels in the atmosphere:
- Government should ensure availability of LPG in all villages. This will help in reducing the use of firewood and cow dung cakes. This will reduce the emission of carbon dioxide.
- Dry leaves should not be burnt. Instead, they should be used for making manure.
- Use of CNG and PNG should be encouraged in automobiles and factories. This will reduce dependency on coal, diesel and petrol.
- People should be encouraged to use public transport. This will help in reducing the number of private vehicles on road.
Question 31: What are the advantages of groundwater over water in rivers and ponds?
Answer: Groundwater has advantage over water in rivers and ponds. Unlike the water in rivers and ponds, groundwater is covered. Thus, groundwater is less prone to getting contaminated. Moreover, there is no risk of loss due to evaporation in case of groundwater. Groundwater at most of the places is suitable for drinking without any treatment of water.