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Biology · 2025 · 5 marks
CBSE 2025 · Region 7 · Set 2 · Q33
(a) Study the given diagram showing the sectional view of a seminiferous tubule. Answer the following questions: (i) Label A, B, C and D in the…
Study the given diagram showing the sectional view of a seminiferous tubule.
Answer the following questions :
(i)
Label A, B, C and D in the figure.
(ii)
What will be the number of chromosomes in secondary spermatocyte and spermatid respectively ?
(iii)
Explain the terms - Spermiogenesis and Spermiation.
Study the figures given below showing initial stages in the formation of female gametophyte and answer the questions that follow.
(i)
Identify (P) and (Q).
(ii)
I. What kind of division does cell (P) undergo to form (Q) ? II. How many (Q) cells form the embryo sac ? What is the name given to such kind of development ? III. How many free nuclear mitotic divisions will the functional megaspore undergo to form the embryo sac ? IV. Describe the structure of a mature female gametophyte.
Marking-scheme solution
(i)
A – Spermatozoa
B – Spermatid /Spermatozoa
C – Sertoli cells
D – Spermatogonium
(ii)
Secondary spermatocyte – $\displaystyle 23$ chromosomes
Spermatid – $\displaystyle 23$ chromosomes
(iii)
Spermiogenesis – Process by which spermatids are transformed into spermatozoa.
Spermiation – Process by which sperm had their head embedded in Sertoli cells are released from seminiferous tubules.
(i)
P-Megaspore mother cell
Q-Megaspores (four megaspores)
(ii)
(I)
Meiosis.
(II)
• Only one cell
• Monosporic development
(III)
Three free nuclear division
(IV)
The mature female gametophyte has $\displaystyle 3$ cells at micropylar end – Egg apparatus (two synergids and one egg cell) with thickenings called filiform apparatus in synergids, three cells at chalazal end – Antipodals, large central cell with two polar nuclei, so it is $\displaystyle 8$-nucleated and $\displaystyle 7$-celled. /
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CBSE Class 12 Biology past-paper question from the 2025 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.