Skip to content

Answer the following. (Class 10 Science 2023, Q35b)

questionbuddy.in/q/cbse-10-science-2023-31-5-1-q35b

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

CBSE Class 10 Science 2023: question 35(b)

Set in the CBSE Class 10 board exam of 2023, paper 31/5/1, section D, question 35(b), for 5 marks. Try it first; the hints and our step-by-step solution are below.

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

Answer the following.

  1. (i)

    What happens when : (1) Leaves of Bryophyllum fall on the soil ? (2) Planaria is cut into many pieces ? (3) Sporangia of Rhizopus on maturation liberate spores ? Mention the modes of reproduction in each of the above three cases.

    0 marks
  2. (ii)

    Write the changes that occur in a flower once the fertilisation has taken place.

    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

For each case, think about which part of the parent gives rise to the new organism.

Hint 2

Bryophyllum uses a body part (the leaf), Planaria uses cut pieces, and Rhizopus uses tiny reproductive units held in sporangia.

Hint 3

For (ii), follow what each part becomes after fertilisation: zygote, ovule, ovary and the remaining floral parts.

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)(1) When a Bryophyllum leaf falls on moist soil, the buds in the notches along its margin sprout and grow into new plantlets. Mode: vegetative propagation (by leaves).

    1 mark

  2. (i)(2) When Planaria is cut into many pieces, each piece grows into a complete new organism. Mode: regeneration.

    1 mark

  3. (i)(3) When the sporangia of Rhizopus burst, the spores are released. On reaching a moist, suitable surface, each spore germinates into a new Rhizopus plant. Mode: spore formation.

    1 mark

  4. (ii) The zygote divides many times and forms an embryo inside the ovule.

    ½ mark

  5. The ovule develops a tough coat and becomes the seed.

    ½ mark

  6. The ovary grows rapidly and ripens into the fruit.

    ½ mark

  7. The petals, sepals, stamens, style and stigma usually shrivel and fall off.

    ½ mark

Answer: (i) (1) Buds on the leaf margin grow into new plants (vegetative propagation); (2) each piece grows into a complete Planaria (regeneration); (3) the released spores germinate into new Rhizopus plants (spore formation). (ii) Zygote → embryo; ovule → seed; ovary → fruit; other floral parts shrivel and fall off.

Where the marks are

  • Bryophyllum: buds in the leaf notches grow into new plants, and names vegetative propagation (½ + ½ mark)
  • Planaria: each piece grows into a complete organism, and names regeneration (½ + ½ mark)
  • Rhizopus: spores germinate on a moist surface, and names spore formation (½ + ½ mark)
  • Zygote divides to form the embryo within the ovule (½ mark)
  • Ovule becomes the seed (½ mark)
  • Ovary ripens into the fruit (½ mark)
  • Petals, sepals, stamens, style and stigma shrivel and fall off (½ 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 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.