Chapter 10 – Life Processes in Plants

1 · When you look at plants, what changes do you notice as they grow?

A growing plant makes new leaves and branches, becomes taller, and its stem gradually becomes thicker and stronger.

2 · What do you infer from Activity 10.1?

The plant that got both sunlight and water grew best.
A plant given sunlight but no water wilted or died, and a plant given water but no sunlight grew poorly, became pale, or stopped growing.
Conclusion: Plants must have both sunlight and water to grow well.

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10.2 How Do Plants Get Food?

3 · How did the iodine test (Activity 10.2) help us?

After boiling a leaf in alcohol to remove its green colour, adding iodine turned the leaf blue-black, showing starch is stored in leaves; therefore leaves are the place where food is made and kept.

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ACTIVITY 10.3 (Green vs. non-green patches)

4 · What do the results of Bhaskar’s test tell us?
Only the green parts of a leaf placed in sunlight turn blue-black with iodine, so chlorophyll is essential for making starch.
A green leaf kept in the dark shows almost no blue-black colour, proving sunlight is also essential.
Non-green patches usually remain light because little or no chlorophyll is there.

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ACTIVITY 10.4 (Leaf half inside a bottle without CO₂)

5 · What does this experiment show?
The half-leaf that had no access to carbon dioxide (inside the flask with caustic soda) produced no starch.
The half-leaf exposed to ordinary air did make starch.
Therefore, carbon dioxide from air is required for photosynthesis.

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ACTIVITY 10.5 (Barkha didi’s inverted test tube)

6 · Which gas filled the inverted test tube and how do we know?
Oxygen. When a glowing splint was inserted into the collected gas it flared up brightly—a classic test for oxygen.
Hence oxygen is released in photosynthesis when a plant is kept in sunlight.

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10.2.3 Photosynthesis in a Nutshell

7 · Do other green parts of the plant, besides leaves, photosynthesise?

Yes. Any part of the plant that contains chlorophyll—such as young green stems or green fruit skins—can photosynthesise.

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10.3 Transport in Plants

8 · In Activity 10.7, why did the plant placed in coloured water become red inside its stem, leaves, and flowers?

Because water (along with dissolved red ink) moved upward through xylem vessels, proving that xylem carries water and minerals from roots to aerial parts.

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10.4 Do Plants Respire?

9 · What did Activity 10.8 with germinating seeds prove?

Lime-water in the test tube turned milky because germinating seeds released carbon dioxide. Thus seeds (and plants generally) respire, using oxygen to break down food and releasing carbon dioxide and energy.

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“LET US ENHANCE OUR LEARNING” QUESTIONS

Below, each numbered item is copied exactly and answered in full.

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1. Complete the following table.

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2. 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?

• No new oxygen would be released, so atmospheric oxygen would slowly decline and aerobic organisms (including humans) would suffocate.

• No fresh food (glucose) would be produced; herbivores would starve, followed by carnivores and omnivores, collapsing all food chains.

• Carbon dioxide would continually rise because respiration, decay, and combustion would keep adding it, causing extreme climate change.
  Therefore, life as we know it would cease.

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3. 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?

Leaves make glucose by photosynthesis. That glucose travels through phloem to the underground stem (potato tuber) where it is converted to and stored as starch.

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

Yes. A broad, flat leaf has a large surface area to capture more sunlight and to expose more stomata for carbon-dioxide intake, both of which speed up photosynthesis.

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**5. X is broken down using Y to release carbon dioxide, Z, and energy.

  X + Y → Carbon dioxide + Z + Energy
  What do X, Y, and Z stand for?**
X = Glucose (food)
Y = Oxygen
Z = Water

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**6. Krishna set-up an experiment with two potted plants—one in sunlight, one in complete dark.

  (i) What idea might she be testing?**
She is testing whether sunlight is necessary for photosynthesis and starch formation in leaves.

  (ii) What visible differences in plants will appear?
Plant in sunlight will stay green, grow, and remain healthy; plant kept in dark will turn pale/yellow, show little growth or begin to wilt.

  (iii) According to you, leaves of which plant will confirm the iodine test for the presence of starch?
Leaves from the sunlit plant will turn blue-black with iodine (starch present); leaves from the dark-kept plant will not (little or no starch).

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**7. Vani believes that “carbon dioxide is essential for photosynthesis.” Four set-ups are shown.

  (a) Sunlight + CO₂ (b) Sunlight – CO₂ (c) Dark + CO₂ (d) Dark – CO₂**

Thus Vani’s idea is supported.

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8. Ananya’s four test tubes (A water + snail, B water + plant, C water + snail + plant, D only water) with a CO₂ indicator: What is she trying to find out and how will she know?

She wants to see which combinations add or remove carbon dioxide:

• Tube A (snail only): indicator turns more acidic/changes colour → CO₂ produced by animal respiration.

• Tube B (plant only) under light: CO₂ level drops (indicator shows less CO₂) because plant photosynthesises and uses CO₂.

• Tube C (both): In light, plant may use CO₂ from snail so indicator change is small; in dark, both respire so CO₂ rises.
  She judges by colour change of the indicator: more CO₂ = colour for acidity; less CO₂ = indicator stays original or turns basic.

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

Take two equal twigs of the same plant (white-flowered if possible). Cut stems under water.

1. Place twig 1 in a beaker of water with red food dye and keep it in a warm place (≈30 °C).

2. Place twig 2 in identical dyed water but keep it in a cold place (e.g., near ice packs or in a refrigerator at 10 °C).

3. After exactly one hour, cut the stems cross-wise and measure how far the red colour has risen in centimetres.

4. Compare distances; the twig showing a greater height indicates faster water movement at that temperature.

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

• Photosynthesis removes CO₂ from the air and adds O₂; respiration does the reverse, keeping both gases in balance.

• Photosynthesis stores solar energy as chemical food; respiration releases that energy for living processes, completing the energy cycle.

• Together they drive the food chain: plants make food; animals (and plants at night) respire, using it.
  Without either step, life and atmospheric balance would collapse.

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Exploratory Project Questions

These are open projects rather than single-sentence questions, so concise guidance is provided:

1. Bottle garden project: Demonstrates a closed cycle where the plant’s photosynthesis supplies O₂ for its own respiration and vice-versa.

2. How plant processes affect crop production: Adequate photosynthesis, respiration, and transport ensure better yield; lack of any limits growth.

3. Greenhouse visit: Observe control of light, water, CO₂ enrichment to boost photosynthesis.

4. Box-breathing technique: Slow deep breathing calms the nervous system, increases lung efficiency.

5. Bird respiration at high altitude: Birds have air-sacs and one-way airflow through lungs, extracting more O₂ in thin air.