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Science · 2024 · 5 marks
CBSE 2024 · Region 5 · Set 2 · Q36
(a) Design an experiment to demonstrate that carbon dioxide is essential for photosynthesis. Write the observation and conclusion of the experiment.
(a)
Design an experiment to demonstrate that carbon dioxide is essential for photosynthesis. Write the observation and conclusion of the experiment.
(II)
(I)
In the experimental set-up shown above in diagram (I) atmospheric air is being passed into lime water with a syringe while in diagram (II) air is being exhaled into lime water. The time taken for the lime water to turn milky in both the test tubes is different. Give reason.
(ii)
Draw the diagram of an open stomatal pore and label
(I)
Guard cells, and (II) Chloroplast on it. Mention two functions performed by stomata.
Marking-scheme solution
Take two healthy potted plants, A and B of nearly the same size.
Keep them in darkness for three days. (Destarch the plant)
Place a watch glass containing potassium hydroxide by the side of potted plant A but not in potted plant B.
Cover both the plants with separate bell jars and seal the bottom of the jars with Vaseline.
Keep both the plants in sunlight for two hours.
Pluck one leaf each from both the plants and test for the presence of starch with iodine solution.
Observation: The leaf of the potted plant A with KOH did not turn blue - black. The leaf of the potted plant B turns blue.
Conclusion: KOH absorbs \(\displaystyle \mathrm{CO}_{2}\) so photosynthesis did not occur in potted plant A.
OR (b) (i) In set up (I) lime water turns milky in more time as compared to set up (II) because the air we exhaled contains high percentage of \(\displaystyle \mathrm{CO}_{2}\) as compared to atmospheric air.
(ii)
Open Stomatal Pore
Two labellings: (I) Guard Cells
(II)
Chloroplast
Two functions performed by stomata :
Gaseous exchange
Transpiration
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CBSE Class 10 Science past-paper question from the 2024 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.