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Explain the phases in… (Class 12 Biology SQP 2023-24, Q23)

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BiologyCBSE Class 12 · Sample paper, session 2023-24 · 3 marks · Short answer

CBSE Class 12 Biology sample paper 2023-24: question 23

From the official CBSE sample question paper for 2023-24, section C, question 23, for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q23 · 3 marks · Short answerHuman Reproduction

Explain the phases in embryonic development from the morula stage till the establishment of pregnancy in a human female.

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2023-24.

Hints

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

Hint 1

List the stages in order after the morula.

Hint 2

Name the two cell groups in the blastocyst and say what each does.

Hint 3

What is the embedding of the blastocyst in the uterine wall called?

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. The zygote divides by cleavage, and the embryo with 8–16 blastomeres is called a morula.

    ½ mark

  2. The morula keeps dividing and becomes a blastocyst as it moves further towards the uterus.

    ½ mark

  3. The blastomeres of the blastocyst form an outer layer called the trophoblast.

    ½ mark

  4. An inner group of cells attached to the trophoblast forms the inner cell mass, which differentiates into the embryo.

    ½ mark

  5. The trophoblast attaches to the endometrium. The uterine cells then divide rapidly and cover the blastocyst.

    ½ mark

  6. The blastocyst becomes embedded in the endometrium. This is called implantation, and it leads to pregnancy.

    ½ mark

Answer: Morula (8–16 cells) → blastocyst (trophoblast + inner cell mass) → trophoblast attaches to endometrium → uterine cells cover it → implantation → pregnancy.

Where the marks are

  • Morula defined (0.5 mark)
  • Morula becomes blastocyst while moving to uterus (0.5 mark)
  • Outer trophoblast layer (0.5 mark)
  • Inner cell mass, which forms the embryo (0.5 mark)
  • Trophoblast attaches to endometrium; uterine cells cover blastocyst (0.5 mark)
  • Embedding = implantation, leading to pregnancy (0.5 mark)

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 paperSample paper 2023-24: 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.