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Answer the following. (Class 12 Biology 2023, Q31b)

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BiologyCBSE Class 12 · Board exam 2023, set 57/5/1 · 5 marks · Long answer

CBSE Class 12 Biology 2023: question 31(b)

Set in the CBSE Class 12 board exam of 2023, paper 57/5/1, section E, question 31(b), for 5 marks. Try it first; the hints and our step-by-step solution are below.

Q31(b) · 5 marks · Long answerHuman Reproduction

Answer the following.

  1. (i)

    Explain the formation of placenta after the implantation in a human female.

    3 marks
  2. (ii)

    Draw a diagram showing human foetus within the uterus and label any four parts in it.

    2 marks

Source: official question paper from cbse.gov.in (PDF). See it in the full 2023 board paper, set 57/5/1.

Hints

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

Hint 1

Start from the outer layer of the blastocyst that attaches to the endometrium.

Hint 2

Name the finger-like projections and say what they become interlocked with.

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) After implantation, finger-like projections called chorionic villi appear on the trophoblast.

    1 mark

  2. These villi are surrounded by uterine tissue and maternal blood. The chorionic villi and the uterine tissue become interdigitated with each other.

    1 mark

  3. Together they form the placenta, a structural and functional unit between the developing embryo (foetus) and the maternal body. It is connected to the embryo by the umbilical cord and supplies oxygen and nutrients, removes CO₂ and wastes, and secretes hormones such as hCG, hPL and progesterone.

    1 mark

  4. (ii) Diagram (described): a section of the uterus with the foetus lying in the amniotic cavity, which is filled with amniotic fluid. The umbilical cord joins the foetus to the placenta on the uterine wall. A yolk sac and the plug of mucus in the cervix may also be shown, with the endometrium and myometrium of the uterine wall.

    2 marks

Answer: Chorionic villi form on the trophoblast and interdigitate with the uterine tissue and maternal blood, forming the placenta, the structural and functional link between embryo and mother. Diagram labels: placenta, umbilical cord, amniotic cavity, uterine wall, plug of mucus in cervix, yolk sac.

Where the marks are

  • Chorionic villi appear on the trophoblast (1 mark)
  • Villi surrounded by uterine tissue and maternal blood and interdigitated with it (1 mark)
  • Together form the placenta, the structural and functional unit between embryo and mother (1 mark)
  • Diagram with any four correct labels (½ × 4 = 2 marks)

Revise the chapter

  • Chapter: Human Reproduction (notes, formulas, where marks are lost and every past question)
Practise this chapterBoard-style questions from Human Reproduction, one at a time, marked against the answer key and marking points.Back to the full paper2023 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.