1
Nitrogen in air is about —
💡 Hint:
Oxygen is 21.
Explanation:
About 78 percent.
Class 9 · Science · Chapter 14 · बिहार बोर्ड (BSEB)CBSE · NCERT 2026-27
Natural Resources
Natural Resources
How to use this page:
1. Read — 14.1 temperature · 14.2 smoke · 14.3 bottle · 14.4 rain gauge · 14.5 monsoon · 14.6 lichen · 14.7 harvest · 14.8 water life · 14.9 dry land · 14.10 soil · 14.11 erosion · 14.12 greenhouse · 14.13 ozone, diagram, worked example, board tip
2. Check — each lesson has its own questions; the number follows the lesson
3. Mastery ★ — all of that lesson correct. Redo the wrong ones
4. The picture to remember is the nitrogen cycle, with four arrows labelled fixation, uptake, food and return.
In the Bihar book this is chapter 14, while chapter 13 of the separate Exploration book is Earth as a System. Progress stays in this browser.
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- 1 Air and wind — Activities 14.1, 14.2
- 2 Rain and air pollution — Activities 14.3 to 14.6
- 3 Water — Activities 14.7, 14.8, 14.9
- 4 Soil — Activities 14.10, 14.11
- 5 The nitrogen and carbon cycles
- 6 The greenhouse and ozone — Activities 14.12, 14.13
- Chapter winner — every lesson at mastery ★
🎬 Shorts
This chapter has no Short on the channel yet, so ten empty cards are not shown. The notes, diagrams and checks are complete.
📄 PDF download — notes + answer key
Air and wind — Activities 14.1, 14.2
वायु और हवा — क्रियाकलाप 14.1, 14.2 · Section 14.1 · Activities 14.1, 14.2
Two main gasesNotes
Our air is about 78 percent nitrogen and about 21 percent oxygen. There is also a little carbon dioxide, water vapour and dust. On Venus and Mars carbon dioxide is 95 to 97 percent.
With oxygen many cells break glucose for energy and release carbon dioxide. Burning a fuel does the same. Air does not let the temperature jump suddenly, so it is also a blanket for life.
Activities 14.1 and 14.2Activity
In 14.1 keep three vessels in sunlight for three hours: a beaker of water, a beaker of soil or sand, and a closed bottle with a thermometer. Also take the temperature in the shade. Soil heats faster than water, so land heats faster than the sea. Measure the air temperature in the shade, or the sun itself heats the thermometer. Closed glass can stay warmer than the open air.
In 14.2 light a candle in a beaker and bring incense smoke near the mouth. The direction of the smoke differs at the edge, above the flame and in other places. Warm air rises and cool air fills its place. This uneven heating makes the wind.
Worked exampleExample
Question: The beaker of sand heated faster than the beaker of water. What follows for the sea and the land?
Answer: By day the land heats faster than the sea. Air over the land becomes lighter and rises, and cooler air from the sea takes its place. At night the order of cooling can reverse.
10-second revision
- 78 percent nitrogen, 21 percent oxygen
- Land heats faster than water
- Uneven heating makes the wind
Board tip · BSEBBoard tip
Write why the temperature is taken in the shade: sunlight heats the thermometer directly.
Board tip · CBSEBoard tip
Keep the figures 78 and 21 together in an air answer.
Check your understandingall correct = mastery ★
2
In sunlight soil can heat faster than water.
Explanation:
True — Activity 14.1. For the same reason land heats faster than the sea.
3
Air temperature should be measured in the ______, not by leaving the thermometer in direct sun.
💡 Hint:
Activity 14.1.
Explanation:
In the shade.
4
Incense smoke rises above the candle because —
💡 Hint:
Activity 14.2.
Explanation:
Warm air becomes lighter and rises.
5
Why can a breeze blow from the sea toward the land by day?
Model answer (board format)
The land heats faster. The air above it rises and cooler air from the sea comes to fill the place.
Check your answer:
Rain and air pollution — Activities 14.3 to 14.6
वर्षा और वायु प्रदूषण — क्रियाकलाप 14.3 से 14.6 · Sections 14.1.3–14.1.4 · Activities 14.3–14.6
Activities 14.3, 14.4 and 14.5Activity
In 14.3 put 5 to 10 mL of water in a bottle, close it and fill the air with vapour by sun or shaking. Let in a little incense smoke and tighten the cap. Press the bottle and release it. Fog appears at low pressure, when the air expands and cools. Pressing raises the pressure and the fog clears. Smoke particles become centres for drops.
In 14.4 follow rainfall reports and make a rain gauge. Write the month of the most rain. Not every rain comes with thunder. In 14.5 read about the monsoon and cyclones in the library. The monsoon is not the cause of every rain in the world.
Pollutants and lichenNotes
Coal and petrol contain a little nitrogen and sulphur. On burning, their oxides form. These dissolve in rain and give acid rain. Unburnt carbon particles and hydrocarbons make a haze called smog. Such air can increase allergy, cancer and heart disease.
In Activity 14.6 look for lichen. They are very sensitive to pollutants such as sulphur dioxide and form a green-white crust on bark. Compare lichen near a busy road and farther away, and on the side facing the road and the side away from it. Fewer lichens can mean more pollution.
Worked exampleExample
Question: Fog appeared when the bottle was released and cleared when it was pressed. What is the link with pressure?
Answer: On release the pressure inside is low and the air cools, so vapour gathers into drops. On pressing the pressure is higher and the fog clears. Without smoke particles the drops do not gather easily.
10-second revision
- Fog forms at low pressure
- Oxides of nitrogen and sulphur make acid rain
- Lichens decrease with sulphur dioxide
Board tip · BSEBBoard tip
Write the fog answer with the pressure. Smoke alone is not enough.
Board tip · CBSEBoard tip
Lichen is a living measure of pollution, not a food crop.
Check your understandingall correct = mastery ★
1
In the bottle experiment fog appears when —
💡 Hint:
On release.
Explanation:
At low pressure the air expands, cools and fog forms.
2
Thunder and lightning are compulsory with every rain.
Explanation:
False — Activity 14.4 asks you to check this.
3
Smoke particles become ______ for drops in the fog.
💡 Hint:
Try the experiment without smoke too.
Explanation:
Centres.
4
One cause of acid rain is —
💡 Hint:
Coal and petrol.
Explanation:
These oxides dissolve in rain and make acids.
5
How would you check pollution near a road with lichen?
Model answer (board format)
Compare lichen on trees by a busy road and farther away. Also compare the side facing the road and the side away from it. Fewer lichens can signal more sulphur dioxide.
Check your answer:
6
The monsoon is the only cause of rain in every country of the world.
Explanation:
False — Activity 14.5 asks you to check this.
Water — Activities 14.7, 14.8, 14.9
जल — क्रियाकलाप 14.7, 14.8, 14.9 · Section 14.2 · the water cycle
The medium of the cellNotes
The processes of a cell happen in water. Substances travel from place to place in dissolved form. So organisms keep a level of water in the body. Land organisms need fresh water for this work.
In the water cycle vapour forms, cools into cloud, and falls as rain, snow or hail. Flowing water carries dissolved minerals from rock. The path of the wind decides where the rain will fall.
Activities 14.7, 14.8 and 14.9Activity
In 14.7 ask about the water-harvesting methods of the municipal corporation. How do they increase the water that can be used. In 14.8 count the kinds and the numbers in 1 square metre near water. Compare with a dry rocky area of the same size. Diversity is greater near water.
In 14.9 choose 1 square metre of unused land near the school and count kinds and numbers there too. Comparing the three places shows that water is tied to a dense presence of life.
Worked exampleExample
Question: Why can the number of kinds differ near a pond and on dry rock?
Answer: Near a pond water is available for cells and plants, so more kinds persist. On dry rock water is scarce, so diversity falls. That is the comparison of Activity 14.8.
10-second revision
- Cell processes happen in water
- Water cycle: vapour, cloud, rain
- Diversity of life is greater near water
Board tip · BSEBBoard tip
1 m² is in both activities. Do not write a square kilometre.
Board tip · CBSEBoard tip
Water harvesting increases usable water. Only the name rain is not enough.
Check your understandingall correct = mastery ★
1
Land organisms need water because —
💡 Hint:
Dissolved substances.
Explanation:
Processes and transport happen in water.
2
The diversity of life near water and on dry rock is always the same.
Explanation:
False — in Activity 14.8 diversity is greater near water.
3
Water-harvesting methods increase the usable ______.
💡 Hint:
Activity 14.7.
Explanation:
Water.
4
In the water cycle clouds form when —
💡 Hint:
Before rain.
Explanation:
Clouds form by condensation of vapour.
5
Write three steps of the water cycle.
Model answer (board format)
Water becoming vapour, cooling into cloud, and falling as rain or snow.
Check your answer:
Soil — Activities 14.10, 14.11
मिट्टी — क्रियाकलाप 14.10, 14.11 · Section 14.3 · Activities 14.10, 14.11
Soil is a mixtureNotes
Soil contains rock particles, humus from decayed organisms, and microscopic life. The average size of the particles decides the type of soil. Humus and the microscopic life decide the quality. Humus makes the soil porous, so water and air enter.
The topsoil is the most fertile layer. Fast water carries it away. Plant roots bind the soil and reduce this erosion.
Activities 14.10 and 14.11Activity
In 14.10 stir soil in at least five times as much water and let it settle. Layers form. Something may float on top. Some substances may also dissolve. Dissolving can be checked by filtering or by drying the water.
In 14.11 take two identical trays. Grow mustard, green gram or paddy in one. Tilt both at the same angle and pour equal water gently. Then pour more water from a height. Less soil leaves the tray with plants. More and faster water carries more soil from both trays.
Worked exampleExample
Question: Why does more soil wash out of the empty tray?
Answer: Plant roots bind the particles. The empty tray has no such binding, so the same water carries more soil. Water poured from a height causes still more erosion.
10-second revision
- Humus makes soil porous
- Water at least five times the soil
- Plants reduce erosion
Board tip · BSEBBoard tip
Five times the water belongs to 14.10. In 14.11 the angle of the two trays stays the same.
Board tip · CBSEBoard tip
In an erosion answer write both the roots and the speed of the water.
Check your understandingall correct = mastery ★
1
Humus adds to soil —
💡 Hint:
Decayed organisms.
Explanation:
Humus makes the soil porous.
2
More soil washes from the tray with plants than from the empty tray.
Explanation:
False — roots bind the soil, so less washes away.
3
When soil is stirred, the water should be at least ______ times the soil.
💡 Hint:
Activity 14.10.
Explanation:
Five times.
4
Write one way to save the top layer of soil.
Model answer (board format)
Grow plants. Roots bind the particles and the erosion by fast water decreases.
Check your answer:
The nitrogen and carbon cycles
नाइट्रोजन और कार्बन के चक्र · Sections 14.4.2–14.4.3 · four arrows
From the air into life, then backNotes
Nitrogen is in proteins, DNA, RNA and some vitamins. Most organisms cannot take the nitrogen of the air directly. Nitrogen-fixing bacteria, often in the root nodules of pulses, turn it into nitrates and nitrites. Lightning also makes oxides in the air, which fall on land as acids with the rain.
Plants take nitrates and make amino acids and proteins. Animals eat these proteins. After death, bacteria turn the compounds into nitrates again. Other bacteria turn nitrates back into elemental nitrogen.
Carbon is elemental in diamond and graphite, is carbon dioxide in the air, and is bound in the molecules of living things. Photosynthesis makes it into glucose. Respiration and the burning of fuel return carbon dioxide.
Worked exampleExample
Question: What do the nodules of pulses and lightning do in the nitrogen cycle?
Answer: Both change the nitrogen of the air into a form living things can take. Bacteria in the nodules make nitrates. Lightning makes oxides, which become acids in water and fall on the land. Without this step proteins are not made.
10-second revision
- Fixation: bacteria and lightning
- Plants make proteins from nitrates
- Carbon dioxide returns by respiration and burning
Board tip · BSEBBoard tip
Write the four arrow names in order: fixation, uptake, food, return.
Board tip · CBSEBoard tip
Diamond is an elemental form of carbon. Do not write it as a greenhouse gas.
Check your understandingall correct = mastery ★
1
The root nodules of pulses contain —
💡 Hint:
They make nitrates.
Explanation:
These bacteria turn the nitrogen of the air into nitrates.
2
Most organisms make proteins directly from the nitrogen of the air.
Explanation:
False — nitrates or nitrites are needed first.
3
Lightning turns the nitrogen of the air into ______.
💡 Hint:
Then acids and rain.
Explanation:
Oxides.
4
Carbon enters living things mainly by —
💡 Hint:
Glucose.
Explanation:
Photosynthesis turns carbon dioxide into glucose.
5
Write the four arrows of the nitrogen cycle in your own words.
Model answer (board format)
Fixation makes nitrates from the air. Plants take the nitrates. Animals eat the plants. Bacteria return nitrogen to the air.
Check your answer:
6
Burning fuel can increase carbon dioxide in the air.
Explanation:
True — burning returns carbon dioxide in the cycle.
The greenhouse and ozone — Activities 14.12, 14.13
ग्रीनहाउस और ओज़ोन — क्रियाकलाप 14.12, 14.13 · Sections 14.4.3–14.5 · Activities 14.12, 14.13
Holding heat and blocking radiationNotes
The closed bottle of Activity 14.1 stayed warmer than the outside, because glass holds heat. Such enclosures were called greenhouses. Some gases of the air also stop the heat of the Earth from leaving. Carbon dioxide is one such gas. If the amount rises, the average temperature rises. This is called the greenhouse effect.
Oxygen is about 21 percent of the air and is also in the crust as oxides and carbonates. Some organisms draw energy without oxygen. High in the atmosphere there is a molecule of three atoms, O3. That is ozone. Near the ground it is poisonous. Up above it absorbs harmful radiation from the Sun.
Activities 14.12 and 14.13Activity
In 14.12 find the consequences of global warming and the names of other greenhouse gases. Carbon dioxide is not the only such gas.
In 14.13 ask which other molecules thin the ozone layer. CFCs are carbon compounds that contain both fluorine and chlorine. Biological processes do not break them. On reaching the height they react with ozone. Newspapers discuss a hole over Antarctica. Also find whether the size of the hole is changing and what effect that can have on life.
Ozone is not a gas to breatheCaution
The layer above protects. Ozone near the nose is a poison. Saving the layer does not mean ozone at the ground is good.
Worked exampleExample
Question: How is carbon dioxide both a gas of the cycle and a greenhouse gas?
Answer: In the cycle it moves among photosynthesis, respiration and burning. In the greenhouse effect the same molecule holds heat near the Earth. The jobs are two and the molecule is one. A rise in the amount can raise the average temperature.
10-second revision
- Glass and CO2 hold heat
- Ozone is O3 and absorbs radiation above
- CFCs thin the layer
Board tip · BSEBBoard tip
Do not join the greenhouse effect and the ozone hole in one sentence. One is heat, the other is radiation.
Board tip · CBSEBoard tip
21 percent is oxygen. 78 is nitrogen. Do not swap the figures.
Check your understandingall correct = mastery ★
1
One gas that holds heat in the greenhouse effect is —
💡 Hint:
There are other gases too.
Explanation:
Carbon dioxide is a greenhouse gas.
2
Ozone near the ground is safe oxygen for breathing.
Explanation:
False — ozone is poisonous. The protection is the layer above.
3
The formula of ozone is ______.
💡 Hint:
Three oxygen atoms.
Explanation:
O3.
4
CFCs harm the ozone layer because —
💡 Hint:
Fluorine and chlorine.
Explanation:
CFCs are not broken by biological processes and they reduce ozone above.
5
In the oxygen cycle, how does oxygen return to the air and how is it used?
Model answer (board format)
Photosynthesis releases oxygen into the air. Respiration and burning use it. In the air it is about 21 percent.
Check your answer:
❓ Full question bank — with answers and explanations — 66 questions
Pick a type. The 31 lesson checks are separate — each lesson has as many as its topic needs. All correct earns mastery ★.
BSEB modelpractice · not annual60 tried · 0 correctMultiple choiceMCQ130 tried · 0 correctTrue / falseTrue / false80 tried · 0 correctFill in the blanksFill80 tried · 0 correctMatchMatch20 tried · 0 correctAssertion–reasonAssertion–reason50 tried · 0 correctBalancingBalancing40 tried · 0 correctIdentifyIdentify20 tried · 0 correctShort and longVSA, SA, LA120 tried · 0 correctCBSE-stylenot a PYQ60 tried · 0 correct
No question is marked as a verified past paper. The BSEB set is a model for practice. CBSE items are CBSE-style, not a copy of any year’s paper.
Multiple choice
0/13Pick one option.
1
Oxygen in air is about —
💡 Hint:
Nitrogen is 78.
Explanation:
21 percent.
2
The air of Venus and Mars is mainly —
💡 Hint:
95 to 97 percent.
Explanation:
Carbon dioxide.
3
By day land heats faster than the sea. Evidence is —
💡 Hint:
Activity 14.1.
Explanation:
Soil or sand heats faster than water.
4
Fog forms in the bottle —
💡 Hint:
On release.
Explanation:
At low pressure.
5
Lichens are sensitive to —
💡 Hint:
Activity 14.6.
Explanation:
Sulphur dioxide.
6
Smog is —
💡 Hint:
Water can also condense in the cold.
Explanation:
A visible haze of pollution.
7
The aim of water harvesting is —
💡 Hint:
Activity 14.7.
Explanation:
To increase usable water.
8
Humus comes from —
💡 Hint:
Pores.
Explanation:
Decayed organisms.
9
Erosion is less when —
💡 Hint:
Activity 14.11.
Explanation:
Roots bind the particles.
10
Nitrogen is fixed by —
💡 Hint:
Nodules.
Explanation:
Bacteria and lightning.
11
Photosynthesis makes —
💡 Hint:
From carbon dioxide.
Explanation:
Glucose.
12
High in the atmosphere the job of ozone is —
💡 Hint:
A poison near the ground.
Explanation:
To absorb harmful radiation.
13
CFCs contain —
💡 Hint:
Stable compounds.
Explanation:
Fluorine and chlorine.
True or false
0/81
Air temperature should be measured only with a thermometer left in direct sun.
Explanation:
False — measure in the shade.
2
Warm air rises.
Explanation:
True — Activity 14.2.
3
Acid rain is linked to oxides of nitrogen and sulphur.
Explanation:
True.
4
Diversity of life near water is always less than on dry rock.
Explanation:
False — it is greater near water.
5
Humus makes soil porous.
Explanation:
True.
6
Most organisms use the N2 of the air directly.
Explanation:
False — fixation is needed.
7
Carbon dioxide is a greenhouse gas.
Explanation:
True.
8
Ozone near the ground is a useful breath.
Explanation:
False — it is poisonous.
Fill in the blanks
0/81
Nitrogen is about ______ percent of the air.
💡 Hint:
78.
Explanation:
Oxygen is 21.
2
Oxygen is about ______ percent of the air.
💡 Hint:
21.
Explanation:
Nitrogen is 78.
3
Fog appears in the bottle at ______ pressure.
💡 Hint:
Low pressure.
Explanation:
On release.
4
Lichens are sensitive to ______ dioxide.
💡 Hint:
Sulphur.
Explanation:
The road.
5
The part of decayed organisms in soil is called ______.
💡 Hint:
Humus.
Explanation:
Pores.
6
Nitrogen bacteria in the roots of pulses live in ______.
💡 Hint:
Nodules.
Explanation:
Fixation.
7
The formula of ozone is ______.
💡 Hint:
O3.
Explanation:
Three atoms.
8
One example of a greenhouse gas is ______.
💡 Hint:
Carbon dioxide.
Explanation:
It holds heat.
Match
0/21
Match the step with the cycle.
Column B: A. Turning carbon into glucose · B. Decayed part of soil · C. Turning nitrogen into nitrate · D. Oxides dissolving in rain
1. Fixation
2. Photosynthesis
3. Acid rain
4. Humus
Explanation:
Fixation makes nitrate, photosynthesis makes glucose, acid rain is dissolved oxides, humus is the decayed part.
2
Match the activity with its job.
Column B: A. Lichen · B. Soil layers · C. The ozone hole · D. Temperature in sunlight
1. 14.1
2. 14.6
3. 14.10
4. 14.13
Explanation:
14.1 temperature, 14.6 lichen, 14.10 layers, 14.13 ozone.
Assertion–reason
0/51
Assertion (A): By day a sea breeze can blow toward the land.
Reason (R): Land heats faster than water.
Explanation:
Both are true and R is the reason.
2
Assertion (A): Lichens are sensitive to pollution.
Reason (R): The formula of ozone is O3.
Explanation:
Both are true, but R does not explain the lichens.
3
Assertion (A): Plants reduce soil erosion.
Reason (R): Roots loosen the soil and wash it away.
Explanation:
A is true. R is false — roots bind the soil.
4
Assertion (A): Ozone near the ground is good to breathe.
Reason (R): Ozone above absorbs harmful radiation.
Explanation:
A is false. R is true.
5
Assertion (A): A rise in carbon dioxide can raise the average temperature.
Reason (R): It is a greenhouse gas and holds heat.
Explanation:
Both are true and R explains A.
Coefficient practice
0/4These equations are not results of this chapter. They are only coefficient practice on H2 + O2 → H2O.
1
This is coefficient practice. This equation is not a result of this chapter. Balance it by filling coefficients (blank = 1).
H2 + O2 → H2O
Explanation: 2H2 + O2 → 2H2O
2
This is coefficient practice. This equation is not a result of this chapter. Balance it by filling coefficients (blank = 1).
H2 + O2 → H2O
Explanation: 2H2 + O2 → 2H2O
3
This is coefficient practice. This equation is not a result of this chapter. Balance it by filling coefficients (blank = 1).
H2 + O2 → H2O
Explanation: 2H2 + O2 → 2H2O
4
This is coefficient practice. This equation is not a result of this chapter. Balance it by filling coefficients (blank = 1).
H2 + O2 → H2O
Explanation: 2H2 + O2 → 2H2O
Classify
0/21
Place each fact with the right resource.
78 percent
Humus
Damage by CFCs
21 percent oxygen
Explanation:
78 and 21 belong to air. Humus belongs to soil. CFCs thin the ozone layer.
2
Place each step on an arrow of the nitrogen cycle.
Oxides from lightning
An animal taking protein
Bacteria making elemental nitrogen
Bacteria of a nodule
Explanation:
Lightning and nodules are fixation. The animal is the food arrow. Elemental nitrogen is the return.
Very short answer
0/51
Write the approximate percentages of nitrogen and oxygen in air.
Model answer (board format)
Nitrogen about 78 percent and oxygen about 21 percent.
Check your answer:
2
Explain acid rain in one line.
Model answer (board format)
Oxides of nitrogen and sulphur from fuel dissolve in rain and make acids.
Check your answer:
3
What is humus?
Model answer (board format)
The part of decayed organisms in soil, which makes it porous.
Check your answer:
4
Write the formula of ozone.
Model answer (board format)
O3.
Check your answer:
5
What is the greenhouse effect?
Model answer (board format)
Some gases holding the heat of the Earth, so the average temperature can rise.
Check your answer:
Short answer
0/41
In Activity 14.3, when does fog form and why is smoke needed?
Model answer (board format)
When the bottle is released the pressure is low and fog forms. Smoke particles become centres for the drops.
Check your answer:
2
Write two ways of nitrogen fixation.
Model answer (board format)
Bacteria in the nodules of pulses make nitrates. Lightning makes oxides that fall on the land with rain.
Check your answer:
3
How do plants reduce soil erosion? Use Activity 14.11.
Model answer (board format)
Roots bind the particles. Less soil washes from the tilted tray with plants than from the empty tray.
Check your answer:
4
Write one cause of damage to the ozone layer and one possible harm.
Model answer (board format)
CFCs react with ozone and thin the layer. More harmful radiation can damage living things.
Check your answer:
Long answer
0/31
Write the composition of air, the cause of wind, and one experiment about rain.
Model answer (board format)
Air is about 78 percent nitrogen and 21 percent oxygen. Uneven heating makes warm air rise and the wind blow. In a bottle fog forms at low pressure, and smoke particles are centres for drops.
Check your answer:
2
Write the four arrows of the nitrogen cycle and two paths by which carbon returns.
Model answer (board format)
Fixation, uptake by plants, food of animals, and the return of N2 by bacteria. Carbon returns as carbon dioxide by respiration and by the burning of fuel.
Check your answer:
3
Compare the greenhouse effect and the ozone layer. Keep CFCs and carbon dioxide apart.
Model answer (board format)
The greenhouse effect holds heat. Carbon dioxide is such a gas. Ozone above absorbs harmful radiation and is a poison near the ground. CFCs reduce ozone. The two problems are different.
Check your answer:
BSEB model paper · practice
0/6This model set is for practice. It is not a question from any year’s annual examination.
1
In Activity 14.10, water should be at least how many times the soil?
💡 Hint:
Stir and settle.
Explanation:
Five times.
2
The discussion over Antarctica is about —
💡 Hint:
Activity 14.13.
Explanation:
The ozone hole.
3
Closed glass holds heat. This recall comes from the bottle of Activity ______.
💡 Hint:
14.1.
Explanation:
The greenhouse paragraph.
4
Why is water necessary for organisms?
Model answer (board format)
Cell processes happen in water and substances move in dissolved form.
Check your answer:
5
This is coefficient practice. This equation is not a result of this chapter. Balance H2 + O2 with H2O. A blank means 1.
H2 + O2 → H2O
Explanation: 2H2 + O2 → 2H2O
6
Explain the nitrogen-cycle figure with four arrows. How is carbon dioxide different in the greenhouse effect?
Model answer (board format)
The arrows are fixation, uptake by plants, food of animals and the return. Carbon dioxide both moves in the cycle and holds heat as a greenhouse effect.
Check your answer:
CBSE-style questions
0/6These are competency-based practice questions. They are not copies of a CBSE paper.
1
One of two trays has plants. With the same water the empty tray loses more soil. The conclusion is —
💡 Hint:
Activity 14.11.
Explanation:
Roots bind the particles.
2
Lichen is scarce on the road side of a tree and greater on the far side. A fair reading is —
💡 Hint:
Activity 14.6.
Explanation:
Fewer lichens can signal more pollutant.
3
Assertion (A): The temperature of a closed bottle can be higher than the open shade.
Reason (R): Glass holds heat.
Explanation:
Both are true and R is the reason.
4
Assertion (A): The nodules of pulses are linked to nitrogen fixation.
Reason (R): These nodules make CFCs and open the ozone hole.
Explanation:
A is true. R is false — bacteria in the nodules make nitrates.
5
In a town coal is burnt, lichens are decreasing and life is richer near a pond. Join the three in separate sentences.
Model answer (board format)
Oxides of nitrogen and sulphur from coal can increase acid rain and smog. A fall in lichen can signal sulphur dioxide. Diversity is greater near the pond because water is there.
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6
A student treats the greenhouse effect and the ozone hole as one problem. How would you separate them?
Model answer (board format)
The greenhouse effect is gases such as carbon dioxide holding heat. The ozone hole is a fall in O3 above, and one cause is CFCs. Ozone near the ground is a poison.
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🏛️ Board exam corner — Bihar Board (BSEB)— CBSE
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🧠 What you learned + equation sheet
What you learned
- Air is about 78 percent nitrogen and 21 percent oxygen.
- Uneven heating moves the air, and condensation of water vapour brings rain.
- Water is the medium of every cell process. Soil contains humus and minerals.
- Nitrogen cycles from the air to nitrates, then into living things, and back to the air.
- Carbon enters living things by photosynthesis and returns by respiration and burning.
- Ozone blocks harmful radiation. CFCs thin the layer. CO2 is a greenhouse gas.
| What | Keep this |
|---|---|
| Nitrogen | about 78 percent |
| Oxygen | about 21 percent |
| Fog in the bottle | at low pressure |
| Lichen | sensitive to sulphur dioxide |
| Ozone | O3, absorbs harmful radiation |
| Greenhouse | CO2 holds heat |
The notes are original writing. The textbook was used only for activity order and numbers. “Verified” will be used only on a question that has a source page.