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With the help of a schematic… (Class 10 Science 2023, Q23b)

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ScienceCBSE Class 10 · Board exam 2023, set 31/1/1 · 2 marks · Very short answer

CBSE Class 10 Science 2023: question 23(b)

Set in the CBSE Class 10 board exam of 2023, paper 31/1/1, section B, question 23(b), for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q23(b) · 2 marks · Very short answerLife Processes

With the help of a schematic flow chart, show the breakdown of glucose in a cell to provide energy –

  1. (i)

    in the presence of oxygen

    0 marks
  2. (ii)

    in lack of oxygen

    0 marks

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

Hints

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

Hint 1

Both pathways begin the same way. What does glucose first break into, and where does this happen?

Hint 2

After pyruvate forms, the presence or absence of oxygen decides what comes next. Which organelle is used when oxygen is available?

Hint 3

With oxygen the end products are CO₂ and water. Think about what accumulates in your leg muscles after hard exercise.

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. In both cases the first step is the same. In the cytoplasm, glucose (a 6-carbon molecule) breaks down into pyruvate (a 3-carbon molecule) and releases a small amount of energy. This step is called glycolysis.

  2. (i) In the presence of oxygen (aerobic respiration):

    Glucose Pyruvate + Energy Carbon dioxide + Water + Energy

    The breakdown is complete, so a large amount of energy is released.

    1 mark

  3. (ii) In lack of oxygen (in human muscle cells):

    Glucose Pyruvate + Energy Lactic acid + Energy

    Lactic acid builds up in the muscles and causes cramps. Yeast, under anaerobic conditions, gives ethanol + + energy instead.

    1 mark

Answer: (i) Glucose → (cytoplasm) Pyruvate → (oxygen, mitochondria) CO₂ + H₂O + energy; (ii) Glucose → (cytoplasm) Pyruvate → (lack of oxygen, muscle cells) Lactic acid + energy

Where the marks are

  • Correct flow chart for aerobic breakdown: glucose → pyruvate in cytoplasm → CO₂ + water + energy in mitochondria (1 mark)
  • Correct flow chart for breakdown in lack of oxygen: glucose → pyruvate → lactic acid + energy in muscle cells (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 31/1/1: 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.