Write a note on how forests influence the quality of our air, soil and water resources.
Forests influence the quality of our air, soil, and water resources in various ways.
Some of them are:
(i) Adds nutrients to the soil due to the lot of vegetation present in the forest getting decomposed . Water : Forest helps in bringing rain and increasing the level of water in the underground and water bodies.
(ii) Forests prevent soil erosion. Roots of plants bind the soil tightly in a way that the surface of the soil cannot be eroded away by wind, water, etc.
(iii) Forests maintain the oxygen level in the atmosphere and also reduce the carbon dioxide level. Forests maintain the temperature of the environment.
List any three human activities that you think would lead to air pollution.
What causes winds?
Why is the atmosphere essential for life?
Why do organisms need water?
Why is water essential for life?
We know that many human activities lead to increasing levels of pollution of the air, water-bodies and soil. Do you think that isolating these activities to specific and limited areas would help in reducing pollution?
List any three human activities which would lead to an increase in the carbon dioxide content of air.
How does the atmosphere act as a blanket?
How is our atmosphere different from the atmospheres on Venus and Mars?
You have seen weather reports on television and in newspapers. How do you think we are able to predict the weather?
Which of the following has more inertia: (a) a rubber ball and a stone of the same size? (b) a bicycle and a train? (c) a five-rupees coin and a one-rupee coin?
State the universal law of gravitation.
Which of the following are matter?
Chair, air, love, smell, hate, almonds, thought, cold, cold-drink, smell of perfume.
A force of 7 N acts on an object. The displacement is, say 8 m, in the direction of the force (Fig. 11.3). Let us take it that the force acts on the object through the displacement. What is the work done in this case?
What is meant by a pure substance?
How does the sound produced by a vibrating object in a medium reach your ear?
In a reaction, 5.3 g of sodium carbonate reacted with 6 g of ethanoic acid. The products were 2.2 g of carbon dioxide, 0.9 g water and 8.2 g of sodium observations are in agreement with the law of conservation of mass.
sodium carbonate + ethanoic acid → sodium ethanoate + carbon dioxide + water
What are canal rays?
State any two conditions essential for good health.
Who discovered cells, and how?
Name the regions in which parenchyma tissue is present.
You find your mass to be 42 kg on a weighing machine. Is your mass more or less than 42 kg?
Explain how animals in Vertebrata are classified into further subgroups.
The speed-time graph for a car is shown is Fig. 8.12.
Fig. 8.12
(a) Find how far does the car travel in the first 4 seconds. Shade the area on the graph that represents the distance travelled by the car during the period.
(b) Which part of the graph represents uniform motion of the car?
What is reverberation? How can it be reduced?
What is the work done by the force of gravity on a satellite moving round the earth? Justify your answer.
Which of the following is true for displacement?
(a) It cannot be zero.
(b) Its magnitude is greater than the distance travelled by the object.
Why does an object float or sink when placed on the surface of water?
What is the utility of tissues in multi-cellular organisms?
How many types of elements together make up the xylem tissue? Name them.