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(i) What is regeneration?… (Class 10 Science 2025, Q35A)

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ScienceCBSE Class 10 · Board exam 2025, set 31/4/1 · 5 marks · Long answer

CBSE Class 10 Science 2025: question 35(A)

Set in the CBSE Class 10 board exam of 2025, paper 31/4/1, section D, question 35(A), for 5 marks. Try it first; the hints and our step-by-step solution are below.

Q35(A) · 5 marks · Long answerHow do Organisms Reproduce?

(i) What is regeneration? Give one example of an organism that shows this process and one organism that does not. Why does regeneration not occur in the latter?

(ii) Water in a pond appears dark green and contains filamentous structures. Name these structures and the method by which they reproduce. Explain the process.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 31/4/1.

Hints

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

Hint 1

Think of the flatworm that can be cut into pieces and still survive.

Hint 2

Regeneration needs cells that can turn into many cell types. Does a simple alga filament have them?

Hint 3

Green, thread-like algae in ponds simply break apart to multiply.

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) Regeneration is the ability of a fully differentiated organism to give rise to new individuals from its body parts. If the organism is cut into pieces, each piece grows into a complete organism.

    1 mark

  2. (i) An organism that shows regeneration: Planaria (or Hydra).

    ½ mark

  3. (i) An organism that does not show regeneration: Spirogyra.

    ½ mark

  4. (i) Reason: regeneration needs specialised cells that can proliferate and form different cell types and tissues. Spirogyra is a simple filament without such specialised cells, so it cannot regenerate.

    1 mark

  5. (ii) The filamentous structures are Spirogyra (a green alga).

    ½ mark

  6. (ii) They reproduce by fragmentation.

    ½ mark

  7. (ii) Process: on maturing, the Spirogyra filament simply breaks up into smaller pieces (fragments). Each fragment grows into a new individual filament.

    1 mark

Answer: (i) Regeneration means forming new organisms from body parts; Planaria regenerates, Spirogyra does not because it lacks specialised cells. (ii) Spirogyra reproduces by fragmentation: the mature filament breaks into pieces that each grow into a new individual.

Where the marks are

  • Correct definition of regeneration (1 mark)
  • Example of an organism that regenerates, e.g. Planaria or Hydra (½ mark)
  • Example of an organism that does not, e.g. Spirogyra (½ mark)
  • Reason: lack of specialised cells for regeneration (1 mark)
  • Names Spirogyra (½ mark)
  • Names fragmentation (½ mark)
  • Explains the process of fragmentation (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from How do Organisms Reproduce?, one at a time, marked against the answer key and marking points.Back to the full paper2025 board paper, set 31/4/1: 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.