7 NCERT SCIENCE SUBJECTIVE QUESCTION

Q1. What is sludge? Solution Solid faecal matter which is generated after the water treatment plant is known as sludge. Q2. Why it is that cooking oil and fats should not be thrown down the drain? Where should they be thrown? Solution Cooking oil and fats should not be thrown down the drain as it can harden and block the pipes. In an open drain, the fats clog the soil pores reducing its effectiveness in filtering water. We should throw cooking oil and fats in the dustbin. Q3. Which trees should we plant near sewage ponds? Why? Solution We should plant eucalyptus trees all along sewage ponds. These trees absorb all surplus wastewater rapidly and release pure water vapour into the atmosphere. Q4. In waste water treatment plant, discuss the first step of treatment? Solution In the first step, wastewater is passed through bar screens. Large objects like rags, sticks, cans, plastic packets, napkins are removed. Q5. During waste water treatment,(a) H...

Q1. Write three damages caused by heavy rains, if the trees are absent. Solution (i) If trees are not present, rain hits the ground directly and may flood the area around it. (ii) Heavy rain may also damages the soil. (iii) Roots of trees normally bind the soil together, but in their absence the soil is washed away or eroded. Q2. How do trees play an important role in regulating the climate? Solution Forests have a key role in regulating the climate, because trees by their photosynthesis absorb carbon dioxide from the atmosphere and store carbon as wood and organic matter in the soil. Q3. Write any three problems encountered if forests disappear. Solution (i) If forests disappear, the amount of carbon dioxide in air will increase, resulting in the increase of earth's average temperature. (ii) In the absence of trees and plants, the animals will not get food, protection and shelter. (iii) In the absence of trees, the soil will not hold water, which will cau...

Q1. Discuss how increasing population causes depletion of water table? Solution Increasing population creates demand for construction of houses, shops, offices, roads and pavements. This decreases the open areas like parks, and playgrounds which affects the seepage of rainwater into the ground. Also, increasing population consumes more water for all their activities. So, the increasing population ends up consuming more groundwater as well as allowing lesser water to seep into the ground. This results in depletion of water table. Q2. What is drip irrigation? Why is this technique advantageous in regions of water scarcity? Solution Drip irrigation is a technique of watering plants by making use of narrow tubings which deliver water directly at the base of the plant. Water falls drop by drop just at the position of the roots. Hence water is not wasted at all. Thus, it proves advantageous in regions of water scarcity. Q3. Name any six factors causing depletion of water...

Q1. How does light enable us to see an object? Solution An object reflects light falling on it. The reflected light, when received by our eyes enables us to see that object. Q2. What is the difference between a concave and convex lens? Solution A convex lens is thicker at the centre but thinner at the edges whereas a concave lens is thinner in the middle but thicker at the edges. Q3. Which mirrors are used as side mirrors in scooters? Give reason. Solution Convex mirrors are used as side mirrors in scooters because convex mirrors can form images of objects spread over a large area. This helps the drivers to see traffic behind them. Q4. (a) Why concave mirrors are used as reflectors? (b) Which color light bends the most and which the least while passing through a prism? Solution (a) The concave mirrors are used as reflectors because when lighted bulb is placed at the focus of concave reflector it produces powerful beam of light rays which helps us...

Q1. What are the causes of short circuiting and overloading? Solution The short circuiting may occur due to the touching of live wire and neutral wire directly. Overloading may be due to the flow of excessive current when many devices are connected to a single socket. Q2. Who first noticed the deflection of compass needle due to current carrying wire? Solution The scientist named 'Hans Christan Oersted' noticed the deflection of compass needle when the current passed through the wire. Q3. How a fuse wire prevents damages to electrical circuits and possible fires? Solution There is a maximum limit for the current to flow through the circuit. If accidentally, the current exceeds the safe limit, the wire may become overheated and may cause fire. In this case, the fuse wire blows off and breaks the circuit thus prevents the damages to electrical circuit. Q4. What is a circuit diagram? What is its use? Solution A diagram which tells us how the var...

Q1. Two boys ran in a race of 10 km. First boy ran with a constant speed 2 km/h for the whole race, while the second boy ran at 1 km/h for half of the race and at 5 km/h for the other half. Who won the race? Solution Total time taken by first boy = 10/2 = 5 h. Total time taken by second boy = (5/1) + (5/5) = 5 + 1 = 6 h. Thus first boy won the race. Q2. Represent the following motion by a graph Velocity m s -1 40 30 20 10 Time second 1 2 3 4 Find the acceleration from the graph and Find the time taken to travel a distance of 35 m from the graph. Solution 1. Acceleration is the slope of v-t graph. 2. t = 1.5 sec for travelling a distance of 35 m. Q3. What is the definition of time? What is its necessity? Solution Time is a moment or duration in which things occur. The knowledge of time is essential for carrying on our daily life activities. For example, our school starts at a particular 'time'. We use our wrist watch t...

Q1. What happens when the male and female gamete are fused together? What does it develop into? Solution A zygote is formed by the fusion of male and female gamete. It develops into an embryo. Q2. From which part of flower do the below parts develop:(a) Fruit(b) Seeds Solution (a) Fruit develops from ovary(b) Seeds develop from ovules Q3. Name two plants which can be propagated through:(i) stem cutting(ii) Roots Solution (i) Rose and Champa(ii) Sweet potato and Dahlia. Q4. What do you understand by:(a) unisexual flowers(b) bisexual flowers Solution (a) The flowers which contain either only the pistil or only the stamens are called unisexual flowers.(b) The flowers which contain both stamens and pistil are called bisexual flowers Q5. Name the following: (i) Parts of a stamen. (ii) The process in which the pollen of a flower lands on the stigma of a another plant (of the same kind) situated far away. (iii) The process of fusion of male and female ...

Q1. Which important function is carried out by the human heart? Solution The heart beats continuously to act as a pump for the transport of blood throughout the body. Q2. List the factors which affect transpiration. Solution Factors affecting transpiration are Sunlight: During the day, the rate of transpiration is faster because stomata remain open which allows the inward diffusion of carbon dioxide for photosynthesis. Temperature: Transpiration is faster in summer as compared to winter. Wind: Transpiration is more when wind blows faster because water vapour is removed more quickly from the leaves. Humidity: Transpiration is reduced if the air is humid. Q3. How the deoxygenated blood is reoxygenated? Solution The deoxygenated blood from different parts of the body enters the right auricle and is sent to the right ventricle. From here, the blood is pumped through the pulmonary artery to the lungs for reoxygen...