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Write in sequence the steps… (Class 10 Science 2023, Q29b)

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ScienceCBSE Class 10 · Board exam 2023, set 31/2/1 · 3 marks · Short answer

CBSE Class 10 Science 2023: question 29(b)

Set in the CBSE Class 10 board exam of 2023, paper 31/2/1, section C, question 29(b), for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q29(b) · 3 marks · Short answerLife Processes

Write in sequence the steps for experimental verification of the fact that "sunlight is essential for photosynthesis".

Source: official question paper from cbse.gov.in (PDF). See it in the full 2023 board paper, set 31/2/1.

Hints

Open one hint at a time and try again before the next.

Hint 1

First make sure the leaf has no starch already present.

Hint 2

Block light from only part of a leaf so you have a comparison.

Hint 3

Which reagent turns starch blue-black, and why must chlorophyll be removed first?

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

  1. 1. Keep a healthy potted plant in the dark for about 24 hours so that its leaves are destarched.

    ½ mark

  2. 2. Cover part of one leaf on both sides with a strip of black paper, so that this part gets no sunlight.

    ½ mark

  3. 3. Place the plant in bright sunlight for several hours (about a day).

    ½ mark

  4. 4. Pluck the leaf and remove the black paper. Boil the leaf in water and then in alcohol over a water bath to remove chlorophyll. Wash it and dip it in dilute iodine solution.

    ½ mark

  5. 5. Observation: the covered part does not turn blue-black, showing that no starch was formed there in the absence of sunlight.

    ½ mark

  6. 6. The uncovered part turns blue-black, showing that starch was made there. Conclusion: sunlight is essential for photosynthesis.

    ½ mark

Answer: Destarch the plant → cover part of a leaf with black paper → keep in sunlight → boil leaf in alcohol and test with iodine → covered part shows no starch, uncovered part turns blue-black; so sunlight is essential.

Where the marks are

  • Destarching the plant in the dark (½ mark)
  • Covering part of the leaf with black paper (½ mark)
  • Exposing the plant to sunlight (½ mark)
  • Removing chlorophyll with alcohol and testing with iodine (½ mark)
  • Covered part shows no blue-black colour (½ mark)
  • Uncovered part turns blue-black, so sunlight is essential (½ mark)

Revise the chapter

  • Chapter: Life Processes (notes, formulas, where marks are lost and every past question)
Practise this chapterBoard-style questions from Life Processes, one at a time, marked against the answer key and marking points.Back to the full paper2023 board paper, set 31/2/1: every question, by section.

The question is transcribed from the official paper; figures are described in words. The solution, hints and chapter tag are ours. Spotted an error? Write tosupport@questionbuddy.in.