Chapter 10: Life Processes in plants Class 8th Science (Curiosity) NCERT Solution

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We know that animals eat food to grow, but what about plants? Have you ever seen plants eating food like animals do? What changes do you notice in plants when they grow?

✔ Answer

No — plants are never seen “eating” food the way animals do. Plants have no mouth and no digestive system. Instead, plants prepare (synthesise) their own food inside their green leaves using carbon dioxide, water, sunlight and chlorophyll. This is why they are called autotrophs (self-feeders), while animals are heterotrophs.

Changes we notice in a plant as it grows:

Height increases — the stem becomes taller.
New leaves and new branches emerge from buds.
Stem becomes thicker and stronger (girth increases).
Roots spread deeper and wider in the soil.
Total weight (biomass) increases.
Later, flowers, fruits and seeds appear.

All this new material (leaves, wood, fruit) is built from the food the plant makes itself + water and minerals absorbed from the soil.

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Activity 10.1

Three pots A, B and C are kept under different conditions for two weeks. Record your observations in Table 10.1. What differences did you observe between the plants in the three pots? Which pot has the plant with the maximum growth? Which pot has the plant with the least growth?

✔ Answer

Fig 10.1 Experimental set-up with pots A, B and C — Fig. 10.1: Experimental set-up to understand the role of sunlight and water in plant growth

Step 1 — Understand the design Only one factor is changed at a time. Pot A has both sunlight and water (this is the control). Pot B has sunlight but no water. Pot C has water but no sunlight. So any difference in growth must be due to the missing factor.

Step 2 — Table 10.1 (Typical observations)

Pots kept under different conditions	Availability of		Height of plant (cm)		Number of leaves		Colour of leaves (Green / Yellow)
Pots kept under different conditions	Sunlight	Water	Day 1	After 2 weeks	Day 1	After 2 weeks	Colour of leaves (Green / Yellow)
Pot A: In direct sunlight, with water	Yes	Yes	10	16	6	12	Green (healthy, fresh)
Pot B: In direct sunlight, without water	Yes	No	10	10 (no increase)	6	1–2 (leaves dried & fell)	Yellow / brown, dried — plant wilts and may die
Pot C: In the dark, with water	No	Yes	10	13 (thin, weak, leggy)	6	7 (small, drooping)	Pale yellow (loses green colour)

(Heights and leaf numbers are sample values — your own readings may differ, but the pattern will be the same.)

Step 3 — Differences observed

Pot A: Grows well — taller, more leaves, dark green and healthy.
Pot B: Soil dries up, leaves wilt, turn yellow-brown and fall; growth stops and the plant dies, even though it got plenty of sunlight.
Pot C: Stem grows thin, weak and pale; leaves turn pale yellow because chlorophyll is not formed in the dark; very little healthy growth.

Maximum growth → Pot A (it gets both sunlight and water).

Least growth → Pot B (no water at all, so the plant dries up and dies).

Inference: Plants require both sunlight and water for their growth.

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Activity 10.2 • Dive Deeper

Did you wonder why we decolourise the leaf in the beginning of this activity? Also — how is the starch test performed and what result shows the presence of starch?

✔ Answer

Fig 10.2 Starch test in a leaf — Fig. 10.2: Starch test in a leaf — (a) Boiling set-up (b) Iodine test

Step 1 — Soften the leafKeep the leaf in boiling water for about 5 minutes. This kills the leaf cells and makes the leaf soft, so that alcohol and iodine can enter easily.

Step 2 — Remove the green colourDip the leaf in a test tube containing alcohol, and place the test tube in a beaker of boiling water. Chlorophyll dissolves in the hot alcohol and the leaf becomes colourless (white).

Step 3 — Iodine testPut the decolourised leaf on a plate and add a few drops of dilute iodine solution with a dropper. Wait a few minutes.

Step 4 — Read the resultIf the leaf turns blue-black → starch is present. If there is no colour change → starch is absent.

Why do we decolourise the leaf? The leaf is green because of chlorophyll. The green colour would hide/mask the blue-black colour formed by iodine and starch. Once the chlorophyll is removed, the leaf is almost white, so the blue-black colour is clearly and easily visible — making the presence of starch easy to detect.

⚠️ Caution: Alcohol is highly inflammable. Never heat it directly on a flame — always heat it indirectly by placing the test tube of alcohol inside a beaker of boiling water.

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Activity 10.3

How does sunlight contribute in the production of starch in plants? Analyse Bhaskar’s observations in Table 10.2. Also — the non-green patches of the leaf kept in sunlight did not turn blue-black. Does it indicate that there is no chlorophyll present in those patches?

✔ Answer

Table 10.2 Presence of starch in green and non-green parts of leaves — Table 10.2: Presence of starch in green and non-green parts of the leaves of plants

Step 1 — What Bhaskar didHe took a variegated leaf (having green + non-green patches) from two identical plants — one kept in sunlight, the other kept in the dark for 36 hours — traced the patches on tracing paper, and performed the iodine test on both leaves.

Step 2 — Observations

Leaf from plant kept in	Green patches after iodine	Non-green patches after iodine	Conclusion
Sunlight	Turned blue-black ✔ (starch present)	No change ✘ (no starch)	Starch is made only where chlorophyll + sunlight are both present
Dark (36 hours)	No change ✘	No change ✘	Without sunlight, no starch is made at all — even in green patches

Step 3 — Reasoning Compare the two green patches. Both have chlorophyll; the only difference is sunlight. The one in sunlight made starch, the one in the dark did not. ⇒ Sunlight is essential for the production of starch.
Now compare the green and non-green patches of the same sunlit leaf. Both got the same sunlight, water and air; the only difference is chlorophyll. Only the green part made starch. ⇒ Chlorophyll is essential for the production of starch.

Sunlight provides the energy, and chlorophyll is the green pigment that captures that energy and uses it to convert carbon dioxide and water into glucose, which is then stored as starch.

Does the non-green patch mean there is NO chlorophyll there? Not necessarily. As the textbook explains, the non-green patches may not have sufficient chlorophyll to prepare enough starch to be detected by the iodine test. A very small amount of chlorophyll (or none at all) may be present — the iodine test only tells us that a detectable amount of starch was not made there.

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Activity 10.4

Which gas from the air is essential in the process of food preparation in plants? Record your observations in Table 10.3. What does this experiment show? Based on Activities 10.3 and 10.4, what do you conclude? Which part of the plant is involved in the synthesis of starch?

✔ Answer

Fig 10.3 Testing the role of chlorophyll and air — Fig. 10.3: Testing the role of chlorophyll and air — (a) The set-up (b) Iodine test on the leaf

Step 1 — Destarch the plantKeep the potted plant in the dark for 2–3 days. All stored starch is used up, so any starch found later must be newly made during the experiment.

Step 2 — Remove CO₂ from one halfCaustic soda (sodium hydroxide) is put in a wide-mouthed bottle. It absorbs carbon dioxide from the air inside the bottle. Half the leaf is inserted into the bottle through a split cork; the other half stays outside in normal air.

Step 3 — Expose & testKeep the set-up in sunlight for a few hours, then remove the leaf and do the iodine test (as in Activity 10.2).

Step 4 — Table 10.3 (Observations)

Part of the leaf	Availability of				Starch present (Yes / No)
Part of the leaf	Water	Sunlight	Chlorophyll	Carbon dioxide	Starch present (Yes / No)
Part of the leaf inside the bottle	Yes	Yes	Yes	No (absorbed by caustic soda)	No — did not turn blue-black
Part of the leaf outside the bottle	Yes	Yes	Yes	Yes	Yes — turned blue-black

Step 5 — ReasoningBoth halves belong to the same leaf, so both had water, sunlight and chlorophyll. The only difference is carbon dioxide. Starch was formed only in the half that had CO₂.

Answer: Carbon dioxide is the gas from the air that is essential for the preparation of food (starch) in plants.

Conclusion from Activities 10.3 + 10.4: Four things are essential for making food in plants — sunlight, water, chlorophyll and carbon dioxide. The process by which plants prepare food in the presence of sunlight and chlorophyll is called photosynthesis.

Which part of the plant synthesises starch? The leaf — it is the primary site of photosynthesis and is therefore called the “food factory” of the plant. Any other green part of the plant that contains chlorophyll (green stems, green sepals, etc.) can also carry out photosynthesis.

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Activity 10.5

Compare set-ups A and B in Fig. 10.4. What difference do you observe in the two set-ups? Do you observe air bubbles emerging in the inverted test tube in set-up A? Which gas is this?

✔ Answer

Fig 10.4 Activity showing release of oxygen during photosynthesis — Fig. 10.4: Activity showing the release of oxygen during photosynthesis (A — in sunlight, B — in the dark)

Step 1 — The difference between A and B Set-up A (kept in sunlight): Air bubbles are seen rising from the water plant. They collect at the top of the inverted test tube and gradually push the water down.
Set-up B (kept in the dark): No bubbles are formed and no gas collects in the test tube.

Step 2 — Identify the gas When enough gas was collected, Barkha didi closed the mouth of the test tube with her thumb, lifted it out, and quickly inserted a lit matchstick into it. The matchstick burned with an intense (bright) flame.

Step 3 — Reasoning A gas that makes a flame burn more brightly is a gas that supports burning. Therefore the collected gas is rich in oxygen.

The gas is OXYGEN. Oxygen is released during photosynthesis, and it is produced only in the presence of sunlight (which is why set-up B, kept in the dark, gave no bubbles).

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Section 10.2.3

Photosynthesis in a nutshell — write the word equation of photosynthesis. What food is actually produced, and do other green parts of the plant also perform photosynthesis?

✔ Answer

Fig 10.5 A diagram showing photosynthesis — Fig. 10.5: A diagram showing photosynthesis

Word equation of photosynthesis:

$$\text{Carbon dioxide} + \text{Water} \;\xrightarrow[\;\text{Chlorophyll}\;]{\;\text{Sunlight}\;}\; \text{Glucose} + \text{Oxygen}$$

In symbols (for your understanding — not required in Grade 7):

$$6\,\mathrm{CO_2} + 6\,\mathrm{H_2O} \;\xrightarrow[\;\text{Chlorophyll}\;]{\;\text{Sunlight}\;}\; \mathrm{C_6H_{12}O_6} + 6\,\mathrm{O_2}$$

What food is actually made? Food is first produced in the form of glucose, a simple carbohydrate.
Glucose serves as an instant source of energy, and the extra glucose is later converted into starch for storage.
Raw materials: carbon dioxide (from air) + water (from soil). Conditions: sunlight + chlorophyll. Products: glucose + oxygen.
Do other green parts photosynthesise? Yes. The leaf is the primary site, but any part of the plant containing chlorophyll (e.g., green stems of cactus, green sepals) also performs photosynthesis.

🧑‍🔬 Know a Scientist: In India, Rustom Hormusji Dastur (1896–1961) studied photosynthesis. He headed the Botany Department at the Royal Institute of Science, Bombay (1921–1935), and examined the importance of water, temperature and the colour of light in photosynthesis.

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Activity 10.6

Which part of the plant helps in the exchange of carbon dioxide and oxygen? On observing the leaf peel under the microscope — what do you observe? Do you notice tiny pores on the peel?

✔ Answer

Fig 10.6 Stomata on the lower surface of a rhoeo leaf — Fig. 10.6: Stomata on the lower surface of a rhoeo leaf

Method (in brief)Peel a thin layer from the lower surface of a leaf (rhoeo, money plant, hibiscus, coleus, grass…), float it in water in a watch glass, transfer it with forceps onto a slide with a drop of water, add a drop of ink, cover with a coverslip and observe under a microscope.

Observation: Yes — many tiny pores are seen scattered on the peel. Each pore is surrounded by two bean-shaped guard cells. (The ink does not enter the pores, which makes them stand out clearly.)

These tiny pores are called STOMATA (singular: stoma). Stomata are present mainly on the surface (usually the lower surface) of leaves and they help in the exchange of gases — carbon dioxide enters and oxygen goes out during photosynthesis (and the reverse during respiration). Water vapour also escapes through them.

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Activity 10.7

How did different parts of the plant acquire the red colour? How does the red ink move upwards? How do water and minerals taken up by the roots move to all parts of the plant? And how does food get transported to other parts of a plant?

✔ Answer

Fig 10.7 Experiment to check for water transportation in plants — Fig. 10.7: Experiment to check for water transportation in plants — (a),(b) on Day 1; (c),(d) after one day; (e) enlarged view of the cut end of the twig

Step 1 — ObservationThe twig placed in plain water (Tumbler A) shows no change. The twig placed in red-inked water (Tumbler B) shows a red colour in the stem, in the veins of the leaves and in the white flowers after one day.

Step 2 — Cut and examineOn cutting the stem above the water level and viewing it with a magnifying glass, red-coloured dots/lines are seen inside the stem (Fig. 10.7e). This shows the ink travelled inside the stem through definite narrow channels — not over its surface.

Step 3 — ExplanationThese narrow, continuous, tube-like channels are called XYLEM. Xylem is present in the roots, stem, branches and leaves and forms a continuous pipeline from root to leaf.

Fig 10.8 Transport of water and minerals in a plant — Fig. 10.8: Transport of water and minerals in a plant (xylem carries water upward; phloem carries food)

Tissue	What it transports	Direction
Xylem	Water + dissolved minerals absorbed by roots	Roots → stem → leaves and all other parts (upward)
Phloem	Food (glucose/sugar) prepared in the leaves	Leaves → all parts of the plant, including stem, roots, seeds, fruits (both up and down)

Just like the red ink, minerals dissolved in water move up the stem through the xylem. The food made in the leaves is carried to every part of the plant through the phloem, and may be stored in parts such as seeds and roots.

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Activity 10.8

Do plants also respire like we do? Compare both the test tubes for any change in colour. Does the lime water turn milky in both the test tubes? Why does the lime water turn milky in the test tube connected to the flask? Where does this carbon dioxide come from?

✔ Answer

Fig 10.9 Set-up to test respiration in plants — Fig. 10.9: Set-up to test respiration in plants (germinating moong seeds on wet cotton, connected to lime water)

Step 1 — ObservationNo, the lime water does not turn milky in both test tubes. It turns milky only in the test tube connected to the flask containing the germinating seeds. The other test tube (not connected) stays clear — it acts as the control.

Step 2 — Why does lime water turn milky?Lime water turns milky in the presence of carbon dioxide. This is the standard test for CO₂.

Step 3 — Where does the CO₂ come from?Carbon dioxide is present in normal air only in a very small quantity — not enough to turn lime water milky quickly. The extra (additional) carbon dioxide in the flask is produced by the germinating moong seeds while they respire. The flask was kept in the dark for 24 hours so that photosynthesis could not happen and the CO₂ produced was not used up.

Word equation of respiration:

$$\text{Glucose} + \text{Oxygen} \;\longrightarrow\; \text{Carbon dioxide} + \text{Water} + \text{Energy}$$

Yes — plants do respire. During respiration, glucose is broken down in the presence of oxygen, releasing carbon dioxide, water and energy. This energy is used by the plant for its growth and development. All parts of a plant — green or non-green (roots, stem, leaves, flowers) — carry out respiration, day and night.

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Complete the following table.

✔ Answer

S.No.	Feature	Photosynthesis	Respiration
1.	Raw materials	Carbon dioxide and water (sunlight and chlorophyll are essential conditions)	Glucose and oxygen
2.	Products	Glucose (food) and oxygen (extra glucose is stored as starch)	Carbon dioxide, water and energy
3.	Word equation	$$\text{CO}_2 + \text{Water} \xrightarrow[\text{Chlorophyll}]{\text{Sunlight}} \text{Glucose} + \text{Oxygen}$$	$$\text{Glucose} + \text{Oxygen} \longrightarrow \text{CO}_2 + \text{Water} + \text{Energy}$$
4.	Importance	• It is the only way plants synthesise food, on which all living beings ultimately depend. • Stores energy of sunlight in the form of food. • Releases oxygen into the atmosphere and uses up carbon dioxide.	• Releases energy stored in food. • This energy is used for growth, development and all other life processes. • Takes place in all parts of the plant, all the time (day and night).

Notice that photosynthesis and respiration are opposite (complementary) processes — the products of one are the raw materials of the other.

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Imagine a situation where all the organisms that carry out photosynthesis on the earth have disappeared. What would be the impact of this on living organisms?

✔ Answer

If every photosynthesising organism (green plants, algae, phytoplankton) vanished, life on the Earth would collapse. The effects, in order:

No food would be produced. Green plants are the producers — the very first link of every food chain. Without them, no new food would enter the living world.
Herbivores would starve and die (cows, deer, grasshoppers…), and then carnivores would starve because their prey is gone. All food chains and food webs would break down.
Oxygen would be used up. Oxygen in the air is replenished by photosynthesis. Since all organisms keep respiring (and fuels keep burning), the oxygen in the atmosphere would slowly get exhausted and organisms would suffocate.
Carbon dioxide would keep increasing, because nothing would remove it from the air. This would make the Earth much hotter (a runaway greenhouse effect).
Other losses: no fruits, grains, vegetables, wood, fibres or medicines; soil would erode; the water cycle and carbon–oxygen cycles would be disturbed.

Ultimately, almost all life on the Earth would come to an end. This shows how completely every living being depends on photosynthesis.

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A potato slice shows the presence of starch with iodine solution. Where does the starch in potatoes come from? Where is the food synthesised in the plant, and how does it reach the potato?

✔ Answer

Step 1 — Where does the starch come from? The starch in a potato is not made in the potato. It comes from the glucose produced during photosynthesis in the green leaves of the potato plant. Extra glucose is converted into starch, which is an insoluble storage form of carbohydrate.

Step 2 — Where is the food synthesised? In the leaves — the “food factories” of the plant — using carbon dioxide + water in the presence of sunlight and chlorophyll. $$\text{Carbon dioxide} + \text{Water} \xrightarrow[\text{Chlorophyll}]{\text{Sunlight}} \text{Glucose} + \text{Oxygen}$$

Step 3 — How does it reach the potato? The food (glucose) made in the leaves is transported through the phloem — the tube-like tissue that carries food from the leaves to all parts of the plant. It travels down the stem and reaches the underground stem (tuber), which is the potato.

Step 4 — Storage In the potato, the glucose is converted back into starch and stored. That is why a potato slice turns blue-black with iodine solution.

Transport of food through phloem and water through xylem — Fig. 10.8: Food made in the leaves travels through the **phloem** to storage organs such as the potato

Leaves (photosynthesis → glucose) ⟶ phloem ⟶ potato (stored as starch).

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Does the broad and flat structure of leaves make plants more efficient for photosynthesis? Justify your answer.

✔ Answer

Yes — the broad, flat shape of a leaf makes it far more efficient at photosynthesis. Justification:

Large surface area for sunlight: A broad, flat blade catches the maximum amount of sunlight. More light energy captured ⇒ more food made.
More chlorophyll exposed: A large flat surface spreads out a huge number of chlorophyll-containing cells so that most of them receive light directly.
More stomata: A big surface can hold a very large number of stomata, allowing plenty of carbon dioxide to diffuse in and oxygen to diffuse out.
Leaves are thin: Because the leaf is thin, the gases (CO₂ and O₂) and the sunlight have to travel only a very short distance to reach the inner cells. Diffusion becomes quick and easy.
Well-spread veins: The flat blade allows a network of veins (xylem and phloem) to reach every part of the leaf, so water is supplied everywhere and food is carried away efficiently.

Broad + flat + thin = maximum sunlight + maximum CO₂ + fast diffusion ⇒ maximum photosynthesis. That is why the leaf is called the “food factory” of the plant.

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X is broken down using Y to release carbon dioxide, Z, and energy.
$$X + Y \longrightarrow \text{Carbon dioxide} + Z + \text{Energy}$$ X, Y, and Z are three different components of the process. What do X, Y, and Z stand for?

✔ Answer

Step 1 — Identify the process Something is broken down and energy is released, giving carbon dioxide as one product. This is the word equation of RESPIRATION.

Step 2 — Recall the standard equation $$\text{Glucose} + \text{Oxygen} \longrightarrow \text{Carbon dioxide} + \text{Water} + \text{Energy}$$

Step 3 — Match term by term Compare $X + Y \rightarrow \text{CO}_2 + Z + \text{Energy}$ with the equation above.

Symbol	Stands for	Role in the process
X	Glucose (food)	The substance that is broken down (the fuel)
Y	Oxygen	The gas used to break down the glucose
Z	Water	Product formed along with carbon dioxide and energy

$$\underbrace{\text{Glucose}}_{X} + \underbrace{\text{Oxygen}}_{Y} \longrightarrow \text{Carbon dioxide} + \underbrace{\text{Water}}_{Z} + \text{Energy}$$

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Krishna set up an experiment with two potted plants of the same size and placed one of them in sunlight and the other in a dark room, as shown in Fig. 10.10. Answer the following — (i) What idea might she be testing through this experiment? (ii) What are the visible differences in plants in both the conditions? (iii) According to you, leaves of which plants confirm the iodine test for the presence of starch?

✔ Answer

Fig 10.10 Experimental pots — one in sunlight and one in complete dark — Fig. 10.10: Experimental pots — (a) Sunlight (b) Complete dark

(i) The idea being tested

Everything else (same size of plant, same pot, same soil, same water) is kept the same; only the light is different. So Krishna is testing the idea/hypothesis that:

“Sunlight is essential for the growth of plants and for the preparation of their food (starch) by photosynthesis.”

(ii) Visible differences in the two plants

Feature	Plant kept in sunlight (a)	Plant kept in complete dark (b)
Colour of leaves	Healthy dark green	Pale yellow / whitish (chlorophyll not formed)
Leaves	Broad, firm, erect, more in number	Small, thin, drooping, wilted; some fall off
Stem	Sturdy and strong	Thin, weak, elongated and leggy (bends easily)
Overall health	Fresh and growing well	Weak, unhealthy; will eventually die

(iii) Which plant’s leaves confirm the iodine test?

The leaves of the plant kept in sunlight (a) will confirm the iodine test — they will turn blue-black, showing that starch is present.

The leaves of the plant kept in the dark (b) will show no colour change, because without sunlight photosynthesis cannot take place, so no starch is made (and whatever starch was stored earlier gets used up).

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Vani believes that ‘carbon dioxide is essential for photosynthesis’. She puts an experimental set-up, as shown in Fig. 10.11, to collect evidence to support or reject her idea. Answer — (i) In which plant(s) will starch be formed? (ii) In which plant(s) will starch not be formed? (iii) In which plant(s) will oxygen be generated? (iv) In which plant(s) will oxygen not be generated?

✔ Answer

Fig 10.11 Four set-ups a, b, c, d with and without sunlight and carbon dioxide — Fig. 10.11: A potted plant with sufficient water is placed under the prescribed conditions — (a) Sunlight with CO₂ (b) Sunlight without CO₂ (c) Dark with CO₂ (d) Dark without CO₂

Step 1 — Recall the rule Photosynthesis needs ALL FOUR together: sunlight + chlorophyll + water + carbon dioxide. If even one is missing, photosynthesis stops — so neither starch nor oxygen is produced. (Water and chlorophyll are available in all four set-ups.)

Step 2 — Check each set-up

Set-up	Sunlight	Carbon dioxide	Photosynthesis?	Starch formed?	Oxygen generated?
(a) Sunlight with CO₂	Yes	Yes	Yes ✔	YES	YES
(b) Sunlight without CO₂	Yes	No	No ✘ (CO₂ missing)	NO	NO
(c) Dark with CO₂	No	Yes	No ✘ (sunlight missing)	NO	NO
(d) Dark without CO₂	No	No	No ✘ (both missing)	NO	NO

(i) Starch will be formed only in plant (a).
(ii) Starch will not be formed in plants (b), (c) and (d).
(iii) Oxygen will be generated only in plant (a).
(iv) Oxygen will not be generated in plants (b), (c) and (d).

Vani’s conclusion: Comparing (a) and (b) — both had sunlight, water and chlorophyll; only CO₂ differed, and only (a) made starch. This supports her idea that carbon dioxide is essential for photosynthesis.

8

Ananya took four test tubes filled three-fourth with water, labelled A, B, C and D (Fig. 10.12). A — a snail; B — a water plant; C — both a snail and a plant; D — only water. She added a carbon dioxide indicator to all test tubes and observed colour changes after 2–3 hours. What do you think she wants to find out? How will she know if she is correct?

✔ Answer

Fig 10.12 Experimental set-up with four test tubes A, B, C and D — Fig. 10.12: Experimental set-up — A (snail), B (water plant), C (snail + plant), D (only water)

What does she want to find out?

Ananya wants to find out how animals and plants affect the amount of carbon dioxide in water — that is:

that the snail (an animal) respires and releases carbon dioxide;
that the water plant uses up carbon dioxide for photosynthesis (in light);
and that when both are kept together, the CO₂ released by the animal is used up by the plant and the O₂ released by the plant is used by the animal — showing the interdependence of plants and animals and the balance of gases in nature.

Role of test tube D: It has only water — no living organism. It is the control, and shows what happens when no plant/animal is present (no change). All other tubes are compared with it.

How will she know if she is correct? — Expected results (assuming the set-ups are kept in light):

Test tube	Contains	What happens	CO₂ indicator shows
A	Snail + water	Snail respires → CO₂ is added to the water	CO₂ increases → indicator changes colour
B	Water plant + water	Plant photosynthesises → CO₂ is used up (more than it respires)	CO₂ decreases → indicator changes in the opposite direction
C	Snail + plant + water	CO₂ given out by the snail is used by the plant; O₂ given out by the plant is used by the snail — the two balance each other	Little or no change in CO₂ level
D	Only water (control)	No living organism, so nothing uses or produces CO₂	No change — colour stays the same

She will know she is correct by comparing the colour of the indicator in A, B and C with the control D. If A shows more CO₂, B shows less CO₂, and C shows almost no change, her idea is confirmed: animals release CO₂, plants consume CO₂, and together they keep the gases balanced.

9

Design an experiment to observe if water transportation in plants is quicker in warm or cold conditions.

✔ Answer

Aim: To find out whether water is transported faster in a plant in warm conditions or in cold conditions.

Materials required: Two identical glass tumblers, water, red ink (or eosin), two similar tender twigs of the same plant with white flowers (e.g., white sadabahar or balsam), a scale/ruler, a clock, a warm place (or a beaker of warm water ~40 °C) and a cold place (a refrigerator, or a beaker of ice-cold water ~10 °C), and labels.

Step 1 — Prepare identical set-ups Fill both tumblers with the same amount of water and add the same number of drops of red ink to each. Label them P (warm) and Q (cold).

Step 2 — Prepare the twigs Take two twigs of the same plant, same length and same thickness, with the same number of leaves and white flowers. Cut the base of each twig obliquely, while keeping it under water (so no air enters the xylem), and place one twig in each tumbler.

Step 3 — Create the two conditions Keep tumbler P in a warm place (e.g., a sunny window, or stand it in warm water at about 35–40 °C). Keep tumbler Q in a cold place (e.g., in a refrigerator, or stand it in a bowl of ice-cold water at about 10 °C). Everything else must be identical — same light, same twigs, same ink concentration.

Step 4 — Observe and measure After a fixed time (say every 30 minutes, for 2–4 hours), note for each twig:

How high the red colour has risen in the stem (measure in cm with a ruler).
Whether the veins of the leaves and the white flowers have turned red, and how deeply.

Step 5 — Record in a table

Set-up	Condition	Height risen after 1 h (cm)	Height risen after 2 h (cm)	Colour in flowers/leaves
P	Warm (~40 °C)	… (larger)	… (larger)	Red colour appears earlier & deeper
Q	Cold (~10 °C)	… (smaller)	… (smaller)	Red colour appears later & fainter

Step 6 — Expected result & reasoning The red colour rises higher and faster in the warm set-up (P). In warm conditions, water evaporates from the leaves (transpiration) more quickly. This creates a stronger “pull”, so water is drawn up the xylem faster. In cold conditions, transpiration is slow, so water moves up slowly.

Conclusion: Water transportation in plants is quicker in warm conditions than in cold conditions.

🔬 Fair test tips: Change only one factor (temperature). Keep the twigs, ink, water level, container and light identical, and take readings at exactly the same times.

10

Photosynthesis and respiration are essential to maintain balance in nature. Discuss.

✔ Answer

Photosynthesis and respiration are opposite but complementary processes. What one takes in, the other gives out — and this is exactly what keeps nature in balance.

$$\text{Carbon dioxide} + \text{Water} \xrightarrow[\text{Chlorophyll}]{\text{Sunlight}} \text{Glucose} + \text{Oxygen} \qquad \text{(Photosynthesis)}$$ $$\text{Glucose} + \text{Oxygen} \longrightarrow \text{Carbon dioxide} + \text{Water} + \text{Energy} \qquad \text{(Respiration)}$$

	Photosynthesis	Respiration
Takes in	Carbon dioxide + water	Oxygen + glucose
Gives out	Glucose + oxygen	Carbon dioxide + water + energy
Energy	Stores sunlight energy in food	Releases the energy stored in food
Where	Only in green parts, only in light	In all parts, all the time

How they maintain balance in nature:

Balance of oxygen and carbon dioxide: All living things (and burning fuels) use up oxygen and add carbon dioxide to the air. Photosynthesis does the reverse — it uses up CO₂ and releases O₂. Because of this, the percentage of oxygen (~21%) and carbon dioxide (~0.04%) in the atmosphere stays almost constant.
Balance of food and energy: Photosynthesis makes and stores the food (chemical energy); respiration breaks it down and releases that energy for life processes. Energy therefore keeps flowing continuously through all food chains.
Carbon cycle: Carbon keeps moving from the air → plants (as food) → animals → back to the air (as CO₂ through respiration and decay). Photosynthesis and respiration are the two “pumps” that drive this cycle.
Check on global warming: By removing CO₂ from the air, photosynthesis helps prevent excessive build-up of this greenhouse gas.

Because the products of one process are the raw materials of the other, photosynthesis and respiration together keep the gases, food and energy of the Earth in balance. If either stopped, life on the Earth could not continue. (This is exactly what is demonstrated by a sealed bottle garden.)

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Exploratory Projects — (a) Develop a bottle garden. (b) How are plant processes like photosynthesis, respiration, and water and food transportation crucial for crop production? (c) Visit a greenhouse and find out how light, water and carbon dioxide are regulated.

✔ Answer / Guidance

Fig 10.13 Bottle garden — Fig. 10.13: Bottle garden

(a) Bottle garden

Plant a growing plant such as a spider plant or jade plant in a large transparent bottle with moist soil. Let it grow well, then seal the mouth of the bottle.
Observe the plant over the next few weeks. If it keeps growing well, it means the plant is maintaining the exchange of gases on its own:
The carbon dioxide produced during respiration is used up for photosynthesis, and the oxygen produced during photosynthesis is used up for respiration. Water also keeps recycling inside (it evaporates and condenses on the glass).
This is a beautiful mini-model of how photosynthesis and respiration balance each other in nature.

(b) Why these processes matter for crop production

Photosynthesis makes the food; the grain, fruit or tuber we harvest is basically stored photosynthetic food. More photosynthesis (good sunlight, healthy green leaves, enough CO₂) ⇒ higher yield.
Respiration supplies the energy the crop needs to grow, absorb minerals and develop seeds. This is also why waterlogged soil harms crops — the roots cannot get oxygen to respire.
Water transport (xylem) carries water and minerals from the soil to the leaves — needed for photosynthesis and for keeping the plant firm. Hence irrigation and fertilisers/manure directly affect yield.
Food transport (phloem) carries the food from the leaves into the grains, fruits, roots and tubers — this is what actually fills up the crop we eat.

(c) In a greenhouse

Light: transparent roofs/walls let sunlight in; shade nets, curtains or artificial grow-lights are used to increase or reduce light as needed.
Water: supplied through drip irrigation or sprinklers; humidity is controlled by foggers and ventilation.
Carbon dioxide: its level may be enriched (CO₂ enrichment) to speed up photosynthesis and increase yield.
Temperature: kept within an ideal range using heaters, fans and vents — so plants grow even out of season and are protected from pests, cold and heavy rain.

Chapter 10: Life Processes in plants Class 8th Science (Curiosity) NCERT Solution

Chapter 10 — Life Processes in Plants

In-Text Questions & Activity Solutions

Exercise — “Let Us Enhance Our Learning”

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