Match List I with List II related to embryonic development at various months of pregnancy:

List-I	List-II
(A) The foetus movement starts and hair appears on the head	(I) 24 weeks of pregnancy
(B) The foetus develops limbs and digits	(II) 20 weeks of pregnancy
(C) The foetus develops external genital organs	(III) 8 weeks of pregnancy
(D) The foetus body is covered with fine hair; eyelids separate and eyelashes are formed	(IV) 12 weeks of pregnancy

Choose the correct answer from the options given below:

Related Formula

aligned Spermatogonia (2n) & Mitosis Primary Spermatocyte (2n) & Meiosis I Secondary Spermatocyte (n) & Meiosis II Spermatid (n) & Spermiogenesis Spermatozoa (n) aligned$\begin{aligned} \text{Spermatogonia (2n)} &\xrightarrow{\text{Mitosis}} \text{Primary Spermatocyte (2n)}\\ &\xrightarrow{\text{Meiosis I}} \text{Secondary Spermatocyte (n)}\\ &\xrightarrow{\text{Meiosis II}} \text{Spermatid (n)}\\ &\xrightarrow{\text{Spermiogenesis}} \text{Spermatozoa (n)} \end{aligned}$

Core Logic

Analysis of each statement:

• A (Incorrect): Spermatogonia multiply by mitotic division.
• B (Incorrect): Primary spermatocytes undergo 1st meiotic division (not mitosis) to form secondary spermatocytes.
• C (Correct): Secondary spermatocytes undergo 2nd meiotic division to produce 4 equal haploid spermatids.
• D (Incorrect): Spermatids do not undergo mitosis; they differentiate into spermatozoa.
• E (Correct): Spermatids transform into functional spermatozoa via the process of spermiogenesis.

Step 1: Conclusion

Only statements C and E are correct.

Pattern Recognition

Sees: "Secondary spermatocytes 2nd meiotic division" and "spermatids transform spermiogenesis". Shortcut: Spermatogonia arrow$\rightarrow$ Mitosis; Primary arrow$\rightarrow$ Meiosis I; Secondary arrow$\rightarrow$ Meiosis II; Spermatid arrow$\rightarrow$ Spermiogenesis.

Chapter Mix

Class 12 Biology: Human Reproduction

Related Formula

Core Logic

The structural arrangement around the human ovum from the outermost layer to the innermost side is:

• Corona radiata (outer follicle cell layer) (C)
• Zona pellucida (non-cellular acellular glycoprotein layer) (A)
• Perivitelline space (space between zona pellucida and plasma membrane) (B)
• Plasma membrane of ovum (D)

Step 1: Diagrammatic Representation

The correct sequence is C arrow$\rightarrow$ A arrow$\rightarrow$ B arrow$\rightarrow$ D.

Pattern Recognition

Sees: "ovum layers outer to inner". Shortcut: Corona radiata arrow$\rightarrow$ Zona pellucida arrow$\rightarrow$ Perivitelline space arrow$\rightarrow$ Plasma membrane.

Chapter Mix

Class 12 Biology: Human Reproduction