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(i) With the help of… (Class 12 Biology 2024, Q32b)

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BiologyCBSE Class 12 · Board exam 2024, set 57/5/1 · 5 marks · Long answer

CBSE Class 12 Biology 2024: question 32(b)

Set in the CBSE Class 12 board exam of 2024, paper 57/5/1, section E, question 32(b), for 5 marks. Try it first; the hints and our step-by-step solution are below.

Q32(b) · 5 marks · Long answerSexual Reproduction in Flowering Plants

(i) With the help of labelled diagram only, show the different stages of embryo development in a dicot plant. (4)
(ii) Endosperm development precedes embryo development. Justify. (1)

Source: official question paper from cbse.gov.in (PDF). See it in the full 2024 board paper, set 57/5/1.

Hints

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

Hint 1

Recall the NCERT figure of Capsella: how many named stages lie between the zygote and the mature embryo?

Hint 2

Name the stages in order by their shape (round, then two-lobed), and decide which embryo parts to label in the last figure.

Hint 3

For (ii), ask what the endosperm stores and who uses it.

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) Diagram: stages of embryo development in a dicot (e.g. Capsella). Draw five figures in sequence, left to right, joined by arrows, with a heading for each stage (½ mark per correct label, 8 labels):
    1. Zygote: a single cell at the micropylar end of the embryo sac, surrounded by endosperm nuclei.
    2. Proembryo (2-celled and 4-celled): the zygote divides into a terminal (apical) cell and a basal cell. The basal cell forms a row of cells, the suspensor.
    3. Globular embryo: a spherical mass of cells borne at the tip of the suspensor.
    4. Heart-shaped embryo: two lobes, the developing cotyledons, appear on the suspensor.
    5. Mature embryo: shows two cotyledons, the plumule (stem tip) between them, the embryonal axis with hypocotyl below the cotyledons, the radicle (root tip) at the lower end, and the remains of the suspensor.

    4 marks

  2. (ii) The primary endosperm nucleus divides before the zygote does, so endosperm forms first. Endosperm is a nutritive tissue that stores food. The developing embryo absorbs this food as it grows, so the embryo can develop only after the endosperm is ready.

    1 mark

Answer: (i) Labelled diagrams: zygote → proembryo (suspensor) → globular → heart-shaped → mature embryo (plumule, cotyledons, hypocotyl, radicle). (ii) Endosperm forms first because it provides nutrition to the developing embryo.

Where the marks are

  • Any eight correct labels on the diagrams of embryo stages, such as zygote, proembryo, suspensor, globular embryo, heart-shaped embryo, cotyledons, plumule, hypocotyl, radicle, mature embryo (½ × 8 = 4 marks)
  • States that endosperm develops first to supply nutrition to the developing embryo (1 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 paper2024 board paper, set 57/5/1: 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.