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Answer the following. (Class 10 Science 2023, Q29)

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ScienceCBSE Class 10 · Board exam 2023, set 31/5/1 · 3 marks · Short answer

CBSE Class 10 Science 2023: question 29

Set in the CBSE Class 10 board exam of 2023, paper 31/5/1, section C, question 29, for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q29 · 3 marks · Short answerLife Processes

Answer the following.

  1. (a)

    With the help of an activity, explain the action of saliva on the food we eat.

    0 marks
  2. (b)

    Why is bile juice important in the process of digestion ?

    0 marks

Source: official question paper from cbse.gov.in (PDF). See it in the full 2023 board paper, set 31/5/1.

Hints

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

Hint 1

Which reagent tests for starch, and what colour does it give?

Hint 2

Set up two tubes so that only one of them gets saliva.

Hint 3

For bile, think about the pH of food leaving the stomach, and about fat droplets.

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. (a) Activity: take 1 mL of 1% starch solution in each of two test tubes, A and B.

    ½ mark

  2. Add 1 mL of saliva to test tube A only. Leave both tubes undisturbed for 20–30 minutes, then add a few drops of dilute iodine solution to each.

    ½ mark

  3. Observation in A: the colour of iodine does not change (no blue-black). The salivary amylase in saliva has broken the starch down into sugar.

    ½ mark

  4. Observation in B: the solution turns blue-black because the starch is still present. Conclusion: saliva digests starch into sugar.

    ½ mark

  5. (b) Bile is important because it makes the acidic food coming from the stomach alkaline, so that pancreatic enzymes can act on it. It also emulsifies fats, breaking large fat globules into smaller ones (either point).

    1 mark

Answer: (a) Starch + saliva gives no blue-black colour with iodine (starch converted to sugar by salivary amylase), starch alone gives blue-black; (b) bile makes the medium alkaline for pancreatic enzymes and emulsifies fats

Where the marks are

  • Takes starch solution in two test tubes (½ mark)
  • Adds saliva to one, waits, then adds iodine to both (½ mark)
  • Tube with saliva: no blue-black colour, starch converted to sugar (½ mark)
  • Control tube turns blue-black (½ mark)
  • Role of bile: alkaline medium or emulsification of fats (1 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 31/5/1: 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.