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(a) From which end of the… (Class 12 Biology 2023, Q18)

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BiologyCBSE Class 12 · Board exam 2023, set 57/1/1 · 2 marks · Very short answer

CBSE Class 12 Biology 2023: question 18

Set in the CBSE Class 12 board exam of 2023, paper 57/1/1, section B, question 18, for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q18 · 2 marks · Very short answerSexual Reproduction in Flowering Plants

(a) From which end of the ovule, and how does the pollen tube gain its entry into the embryo sac of a Hibiscus flower ?
(b) State the fate of the male nuclei present in the pollen tube.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2023 board paper, set 57/1/1.

Hints

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

Hint 1

Recall the opening at the tip of the ovule nearest the egg apparatus.

Hint 2

Which special cellular thickening in the synergids guides the tube?

Hint 3

There are two male gametes and two separate fusion events, which together make double fertilisation.

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) The pollen tube enters the ovule through the micropylar end (micropyle).

    ½ mark

  2. It then enters one of the synergids. The filiform apparatus at the micropylar tip of the synergids guides the pollen tube into the embryo sac.

    ½ mark

  3. (b) One male nucleus fuses with the egg nucleus to form the diploid zygote. This is syngamy.

    ½ mark

  4. The other male nucleus fuses with the two polar nuclei to form the triploid primary endosperm nucleus (PEN). This is triple fusion.

    ½ mark

Answer: (a) Through the micropyle, entering a synergid guided by the filiform apparatus; (b) one male nucleus + egg → zygote (syngamy), the other + two polar nuclei → PEN (triple fusion)

Where the marks are

  • Micropylar end (½ mark)
  • Entry via synergid guided by filiform apparatus (½ mark)
  • Syngamy: male nucleus + egg → zygote (½ mark)
  • Triple fusion: male nucleus + two polar nuclei → PEN (½ mark)

Revise the chapter

Practise this chapterBoard-style questions from Sexual Reproduction in Flowering Plants, one at a time, marked against the answer key and marking points.Back to the full paper2023 board paper, set 57/1/1: 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.