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(i) What is the first step… (Class 10 Science 2023, Q29a)

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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(a)

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

Q29(a) · 3 marks · Short answerLife Processes

(i) What is the first step in the breakdown of glucose during aerobic and anaerobic respiration ? Where does it take place ?
(ii) ATP is called the energy currency of the cell. Why ?
(iii) What is meant by "residual volume of air" in a breathing cycle ?

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

Glucose has 6 carbon atoms. What 3-carbon molecule is formed first?

Hint 2

Is this step inside the mitochondria or outside them?

Hint 3

Do the lungs ever become completely empty of air?

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. (i) The first step in both kinds of respiration is the breakdown of glucose, a six-carbon molecule, into pyruvate, a three-carbon molecule:

    ½ mark

  2. (i) This step takes place in the cytoplasm of the cell.

    ½ mark

  3. (ii) The energy released during respiration is stored in ATP. When ATP is broken down to ADP, a fixed amount of energy is released. This energy drives the energy-requiring (endothermic) reactions and all other activities of the cell. Because ATP is used like money for energy everywhere in the cell, it is called the energy currency.

    1 mark

  4. (iii) Residual volume is the volume of air that always stays in the lungs even after forceful exhalation. Because of it, there is enough time for oxygen to be absorbed into the blood and carbon dioxide to be released.

    1 mark

Answer: (i) Glucose → pyruvate, in the cytoplasm; (ii) ATP releases a fixed amount of energy that drives all cell activities; (iii) air left in the lungs after exhalation, allowing continuous gas exchange

Where the marks are

  • Glucose broken into pyruvate (½ mark)
  • Takes place in the cytoplasm (½ mark)
  • ATP acts as fuel for all cell activities, releasing a fixed amount of energy on breakdown (1 mark)
  • Residual volume is the air remaining in the lungs after exhalation, allowing time for gas exchange (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 31/2/1: 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.