CBSE Class 7

NCERT Solutions for Class 7 Science Chapter 17 Forests: Our Lifeline are part of NCERT Solutions for Class 7 Science. Here we have given NCERT Solutions for Class 7 Science Chapter 17 Forests: Our Lifeline.

NCERT Solutions for Class 7 Science Chapter 17 Forests: Our Lifeline

Question 1.
Explain how animals dwelling in the forest help it grow and regenerate.
Answer:
Animals help in dispersing seeds of certain plants. The decaying animal dung also provides nutrients to the seedling to grow. This is how animals help the forest to grow and regenerate.

Question 2.
Explain how forests prevent floods.
Answer:
Raindrops in a forest do not hit the ground directly. The uppermost layer of the forest canopy intercepts the raindrops, and most of the water comes down up to soil through the branches and the stems of the trees. From the leaves, it drops slowly over the branches of the shrubs and herbs. Thus forests act as a natural absorber of rainwater and allow it to seep and therefore help in controlling floods.

Question 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. Bacteria, mushrooms, etc. are decomposers. They decompose dead organisms and provide nutrients to trees.

Question 4.
Explain the role of forests in maintaining the balance between oxygen and carbon dioxide in the atmosphere.
Answer:
Plants release oxygen as a byproduct during the process of photosynthesis. This oxygen is inhaled by animals for respiration. This respiration process releases carbon dioxide which is used again by plants during photosynthesis. In this way, use and consumption of oxygen and carbon dioxide go on. Thus, they maintain the balance of oxygen and carbon dioxide in the atmosphere.

Question 5.
Explain why there is no waste in a forest.
Answer:
The decomposers decompose the dead organisms. The decomposed matter is absorbed by plants as nutrients. So, there is no waste in a forest.

Question 6.
List five products we get from forests.
Answer:

• Honey
• Wax
• Gum
• Herbs
• Wood.

Question 7.
Fill in the blanks:

1. The insects, butterflies, honeybees, and birds help flowering plants in ……..
2. A forest is a purifier of …….. and ………
3. Herbs form the ………. layer in the forest.
4. The decaying leaves and animal droppings in a forest enrich the ………..

Answer:

1. pollination
2. air, water
3. lowest
4. soil

Question 8.
Why should we worry about the conditions and issues related to forests far from us?
Answer:
Forests are very helpful for us. They clean air, play a vital role in the water cycle, provide various items, and so on. So, we should worry about the conditions and issues related to forests far from us.

Question 9.
Explain why there is a need for a variety of animals and plants in a forest.
Answer:
A variety of animals and plants are necessary for their survival and maintenance of the food chain. For example, the grass is eaten by insects, which in turn, are eaten by the frog. The frog is consumed by a snake which is eaten by an eagle. Thus it forms a food chain.
Grass ➜ insects ➜ frog ➜ snake ➜ eagle.
Many food chains can be found in the forest. All food chains are linked together. If anyone’s food chain is disturbed, it affects other food chains. Every part of the forest is dependent on the other parts. If we remove one component, say trees, all other commonest would be affected.

Question 10.
In Fig., 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.
Answer:

Question 11.
Which of the following is not a forest product?
(i) Gum
(ii) Plywood
(iii) Sealing wax
(iv) Kerosene
Answer:
(iv) Kerosene.

Question 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.

Question 13.
Microorganisms act upon the dead plants to produce
(i) sand
(ii) mushrooms
(iii) humus
(iv) wood
Answer:
(iii) Humus.

We hope the NCERT Solutions for Class 7 Science Chapter 17 Forests: Our Lifeline help you. If you have any query regarding NCERT Solutions for Class 7 Science Chapter 17 Forests: Our Lifeline, drop a comment below and we will get back to you at the earliest.

NCERT Solutions for Class 7 Science Chapter 16 Water: A Precious Resource are part of NCERT Solutions for Class 7 Science. Here we have given NCERT Solutions for Class 7 Science Chapter 15 Light.

NCERT Solutions for Class 7 Science Chapter 16 Water: A Precious Resource

Question 1.
Mark ‘T if the statement is true and F’ if it is false:
(а) The freshwater stored in the ground is much more than that present in the rivers and lakes of the world. (T/F)
(b) Water shortage is a problem faced only by people living in rural areas. (T/F)
(c) Water from rivers is the only source for irrigation in the fields. (T/F)
(d) Rain is the ultimate source of water. (T/F)
Answer:
(a) T
(b) F
(c) F
(d) T

Question 2.
Explain how groundwater is recharged?
Answer:
The rainwater and water from other sources such as rivers and ponds seeps through the soil and fills the empty spaces and cracks deep below the ground. The process of seeping water into the ground is called infiltration. The groundwater thus gets recharged by this process.

Question 3.
There are ten tube wells in a lane of fifty houses. What could be the long-term impact on the water table?
Answer:
A huge amount of water will be pumped out from these ten tube wells and it will result in the depletion of the groundwater. Consequently, the water table will go deeper and deeper with time and in the longer-term, it will affect the availability of water in that area.

Question 4.
You have been asked to maintain a garden. How will you minimize the use of water?
Answer:
The use of water can be minimized by:

• using drip irrigation.
• preventing the leakage in the drains in the delivery pipes.
• filling the burrows of snakes and rats.
• protecting the boundaries of the field from breakage.

Question 5.
Explain the factors responsible for the depletion of the water table.
Answer:
There are three main causes of depletion of the water table.
(i) Increasing population:
The increasing population creates demand for the construction of houses, shops, offices, roads, and pavements. This decreases the open areas like parks and playgrounds. This, in turn, decreases the seepage of rainwater into the ground. Moreover, a huge amount of water is required for construction work. Often groundwater is used for this purpose. So, on the one hand, we are consuming more groundwater whereas, on the other hand, we are allowing lesser water to seep into the ground. This results in depletion of the water table.

(ii) Increasing industries:
Water is used by all industries. Almost everything that we use needs water somewhere in its production process. The number of industries is increasing continuously. Water used by most industries is drawn from the ground.

(iii) Agricultural activities:
A majority of farmers in India depend upon rains for irrigating their crops. Irrigation systems jUcîi Cl’îs equals are there only in a few places. Even these systems may suffer from a lack of water due to erratic rainfall. Therefore, farmers have to use groundwater for irrigation. The increased use of groundwater day by day results in depletion of the water table.

Question 6.
Fill in the blanks with the appropriate answers:

1. People obtain groundwater through ……. and ……….
2. Three forms of water are …….,……. and ……….
3. The water-bearing layer of the earth is ………..
4. The process of water seepage into the ground is called ………..

Answer:

1. tubewells, hand pumps
2. solid, liquid, gas
3. aquifer
4. infiltration

Question 7.
Which one of the following is not responsible for water shortage?
(i) Rapid growth of industries
(ii) Increasing population
(iii) Heavy rainfall
(iv) Mismanagement of water resources
Answer:
(iii) Heavy rainfall.

Question 8.
Choose the correct option.
The total water
(i) in the lakes and rivers of the world remains constant
(ii) under the ground remains constant
(iii) in the seas and the oceans of the world remains constant
(iv) of the world remains constant.
Answer:
(iv) of the world remains constant.

Question 9.
Make a sketch showing the groundwater and water table. Label it.
Answer:

We hope the NCERT Solutions for Class 7 Science Chapter 16 Water: A Precious Resource help you. If you have any query regarding NCERT Solutions for Class 7 Science Chapter 16 Water: A Precious Resource, drop a comment below and we will get back to you at the earliest.

NCERT Solutions for Class 7 Science Chapter 15 Light are part of NCERT Solutions for Class 7 Science. Here we have given NCERT Solutions for Class 7 Science Chapter 15 Light.

NCERT Solutions for Class 7 Science Chapter 15 Light

Question 1.
Fill in the blanks:

1. An image that cannot be obtained on a screen is called ………
2. The image formed by a convex ……… is always virtual and smaller in size.
3. An image formed by a ………. mirror is always of the same size as that of the object.
4. An image which can be obtained on a screen is called a ………. image.
5. An image formed by a concave ………. cannot be obtained on a screen.

Answer:

1. virtual image
2. mirror
3. plane
4. real
5. lens

Question 2.
Mark “T” if the statement is true and ‘F’ if it is false:

1. We can obtain an enlarged and erect image by a convex mirror. (T/F)
2. A concave lens always forms a virtual image. (T/F)
3. We can obtain a real, enlarged, and inverted image by a concave mirror. (T/F)
4. A real image cannot be obtained on a screen. (T/F)
5. A concave mirror always forms a real image. (T/F)

Answer:

1. F
2. T
3. T
4. F
5. F

Question 3.
Match the items given in Column I with one or more items of Column II.

Answer:

Question 4.
State the characteristics of the image formed by a plane mirror.
Answer:
Image formation by a plane mirror. We are able to see images using a mirror. An image formed by a mirror (flat) has the following features:

In a plane mirror, the image is formed behind the mirror. It is erect, of the same size, and is at the same distance from the mirror as the object is in front of it.

Question 5.
Find out the letters of the English alphabet or any other language known to you in which the image formed in a plane mirror appears exactly like the letter itself. Discuss your findings.
Answer:
A, H, I, M, 0, T, U, V, W, X, Y.

Question 6.
What is a virtual image? Give one situation where a virtual image is formed.
Answer:
The image that cannot be formed on a screen is called a virtual image. The image formed by a plane mirror is virtual because the image cannot be obtained on a screen when placed either in front of the mirror or behind it.

Question 7.
State two differences between a convex and a concave lens.
Answer:

Question 8.
Give one use each of a concave and a convex mirror.
Answer:

1. Concave mirror: Used by dentists to see teeth.
2. Convex mirror: Used in vehicles as a rearview mirror.

Question 9.
Which type of mirror can form a real image?
Answer:
A concave mirror can form a real image.

Fig. Convex mirror as a side-view mirror

Question 10.
Which type of lens forms always a virtual image?
Answer:
A concave lens.

Choose the correct option in questions 11-13:

Question 11.
A virtual image larger than the object can be produced by a
(i) concave lens
(ii) concave mirror
(iii) convex mirror
(iv) plane mirror
Answer:
(ii) Concave mirror

Question 12.
David is observing his image in a plane mirror. The distance between the mirror and his image is 4 m. If he moves 1 m towards the mirror, then the distance between David and his image will be:
(i) 3 m
(ii) 5 m
(iii) 6 m
(iv) 8 m
Answer:
(iii) 6 m

Question 13.
The rearview mirror of a car is a plane mirror. A driver is reversing his car at a speed of 2 m/s. The driver sees in his rearview mirror the image of a truck parked behind his car. The speed at which the image of the truck appears to approach the driver will be:
(i) 1 m/s
(ii) 2 m/s
(iii) 4 m/s
(iv) 8 m/s
Answer:
(iii) 4 m/s

We hope the NCERT Solutions for Class 7 Science Chapter 15 Light helps you. If you have any query regarding NCERT Solutions for Class 7 Science Chapter 15 Light, drop a comment below and we will get back to you at the earliest.

NCERT Solutions for Class 7 Science Chapter 14 Electric Current and its Effects are part of NCERT Solutions for Class 7 Science. Here we have given NCERT Solutions for Class 7 Science Chapter 14 Electric Current and its Effects.

NCERT Solutions for Class 7 Science Chapter 14 Electric Current and its Effects

Question 1.
Draw in your notebook the symbols to represent the following components of electrical circuits: connecting wires, switch in the ‘OFF’ position, bulb, cell, switch in the ‘ON’ position and battery.
Answer:

Question 2.
Draw the circuit diagram to represent the circuit shown in Fig.

Answer:

Question 3.
Figure shows four cells fixed on a board. Draw lines to indicate how you will connect their terminals with wires to make a battery of four cells.

Answer:

Question 4.
The bulb in the circuit shown in Fig. does not glow. Can you identify the problem? Make necessary changes in the circuit to make the bulb glow.

Answer:
The problem in this circuit is the connection of two cells. Here both the positive terminals of the cells are connected to each other. This must be reversed for anyone cell to make the bulb glow i.e., the positive terminal of one cell should be connected with the negative terminal of the other.

Question 5.
Name any two effects of electric current.
Answer:

• Heating effect.
• Magnetic effect.

Question 6.
When the current is switched on through a wire, a compass needle kept nearby gets deflected from its north-south position. Explain.
Answer:
When an electric current passes through a wire, it behaves like a magnet. This is the magnetic effect of the electric current due to the attraction of the wire. So, the compass needle which is a magnet gets deflected.

Question 7.
Will the compass needle show deflection when the switch in the circuit shown by Fig. is closed?

Answer:
No. Since, there is no cell so, no current will flow.

Question 8.
Fill in the blanks:

1. A longer line in the symbol for a cell represents its ………… terminal.
2. The combination of two or more cells is called a …………..
3. When current is switched ‘on’ in a room heater, it ………….
4. The safety device based on the heating effect of electric current is called a ……….

Answer:

1. positive battery
2. battery
3. becomes red hot
4. fuse

Question 9.
Mark ‘T’ if the statement is true and ‘F’ if it is false:

1. To make a battery of two cells, the negative terminal of one cell is connected to the negative terminal of the other cell. (T/F)
2. When the electric current, through the fuse exceeds a certain limit, the fuse wire melts and breaks. (T/F)
3. An electromagnet does not attract a piece of iron. (T/F)
4. An electric bell has an electromagnet. (T/F)

Answer:

1. False
2. True
3. False
4. True

Question 10.
Do you think an electromagnet can be used for separating plastic bags from a garbage heap? Explain.
Answer:
No. This is because electromagnets can only attract magnetic materials. The plastic bag is a non-magnetic material and will not be attracted by an electromagnet.

Question 11.
An electrician is carrying out some repairs in your house. He wants to replace a fuse with a piece of wire. Would you agree? Give reasons for your response.
Answer:
No, we would not agree to replace the fuse with a wire. The electric wire will not melt even if a high current flows through it. So, it will not prevent the damage done by high current.

Question 12.
Zubeda made an electric circuit using a cell holder shown in the following Fig., a switch, and a bulb. When she put the switch in the ‘ON’ position, the bulb did not glow. Help Zubeda in identifying the possible defects in the circuit.

Answer:
One of the reasons may be that the rubber band used in the cell holder may not be tight enough to keep the two cells in contact with each other. If the cells are not in proper contact with each other, then the circuit will not be complete, and the current will not flow through the circuit. Hence, the bulb will not glow. The other reason may be that the two cells are not connected properly. The negative terminal of one cell must be connected to the positive terminal of the other cell.

Question 13.
In the circuit shown in the following Fig.:

1. Would any of the bulbs glow when the switch is in the ‘OFF’ position?
2. What will be the order in which the bulbs A, B, and C will glow when the switch is moved to the ‘ON’ position?

Answer:

1. No bulb will glow
2. All bulbs will glow at a time.

We hope the NCERT Solutions for Class 7 Science Chapter 14 Electric Current and its Effects help you. If you have any query regarding NCERT Solutions for Class 7 Science Chapter 14 Electric Current and its Effects, drop a comment below and we will get back to you at the earliest.