Science 3 Marks Question

Ananya wants to find out how plants and animals affect the amount of carbon dioxide in water. She is testing the role of respiration and photosynthesis. The carbon dioxide indicator changes colour depending on how much carbon dioxide is present in the water. Ananya will know she is correct by observing the colour changes in the carbon dioxide indicator in each test tube :
1. Test Tube A (Snail only): The indicator will turn yellow/orange, showing increased carbon dioxide due to the snail’s respiration.
2. Test Tube B (Plant only): The indicator will turn blue/purple, showing decreased carbon dioxide because the plant uses it during photosynthesis.
3. Test Tube C (Snail + Plant): The colour may stay neutral or slightly blue, showing a balance as the snail gives out carbon dioxide and the plant uses it.
4. Test Tube D (Only water): No colour change, as there is no living organism to add or remove carbon dioxide.

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1. (a) Oxygen
2. Chlorophyll
3. The presence of reserve food material (i.e. starch) in the leaves of plant indicates the occurrence of photosynthesis.

(i) A schematic diagram showing photosynthesis is as following:

(ii) The products of photosynthesis are glucose and oxygen.
(iii) The oxygen is liberated, and carbon dioxide is utilised in photosynthesis.
(iv) All plants cannot do photosynthesis, only green plants, which contain chlorophyll pigment, can do photosynthesis.

To test the presence of starch in leaves, following steps is followed:
1. Keep the leaf in boiling water for 5 minutes to soften it.
2. Dip this leaf in a test tube containing alcohol to remove the chlorophyll,
3.Place the test tube in a beaker with boiling water.
4. Wait for the leaf to become colourless,
5. Take out the leaf and place it on a plate,
6. Finally, add a few drops of iodine solution to the leaf. Wait for few minutes and observe.
7. If the leaf turns blue-black, it indicates the presence of starch.

(i)The plants in the three pots showed noticeable differences after two weeks.
Pot A, which received both sunlight and water, grew the tallest, had the most leaves, and stayed green, showing healthy development.
Pot B, with sunlight but no water, showed very little growth, fewer leaves, and yellowing due to dehydration.
Pot C, kept in the dark but watered, exhibited limited growth, with slightly pale yellow leaves and fewer new leaves, indicating that light is essential for healthy, green plants.
(ii) Pot A
(iii) Pot C

(i) In set-up A (kept in sunlight), we observe bubbles on the inverted test tube. While in set¬up B (kept in the dark), no bubbles are seen.
(ii) Yes, air bubbles are seen rising and collecting in the inverted test tube in set-up A.
(iii) The gas produced is oxygen, which is released during photosynthesis.
Observation and Conclusion :
When a test tube is taken off the set-up and a lit matchstick is inserted into the tube, it produces an intense flame, which confirms that oxygen gas is released during the process of photosynthesis.

To test whether water transportation in plants is quicker in warm or cold conditions, take two identical potted plants. Place one plant in a warm location (near a heater or sunny spot) and the other plant in a cool place (like in the shade). Add a few drops of food colouring to the water and water both plants. After a few hours, observe the movement of the coloured water up the stem and into the leaves. The plant in the warm conditions will show faster movement of the coloured water, as higher temperatures increase the rate of evaporation and water transportation.

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(b) Iodine test
(c) They had chlorophyll
(b) Starch is formed in green areas with chlorophyll