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Biology · 2026 · 5 marks
CBSE 2026 · Region 3 · Set 1 · Q33
(a) Oogenesis is a discontinuous process that begins before birth and is completed after puberty. (i) Trace the development of a gamete mother cell…
Oogenesis is a discontinuous process that begins before birth and is completed after puberty.
(i)
Trace the development of a gamete mother cell till its release from the ovary during ovulation.
(ii)
Name the two pituitary hormones that play an important role in the process.
(i)
Draw a labelled two-celled structure of male gametophyte of an angiosperm.
(ii)
Name the three layers that surround the cytoplasm of a male gametophyte starting from innermost to outermost layer.
(iii)
Which organic material makes the outermost layer ? Mention its advantage.
(iv)
Why is the outermost layer of male gametophyte not continuous?
Marking-scheme solution
(i)
• Oogonia (gamete mother cells) 2n multiply by mitosis during foetal
ovary and differentiate into primary oocytes, each primary oocyte gets surrounded by follicle cells to form a primary follicle.
• The primary oocyte remains arrested in prophase-I till puberty, after
puberty oocyte inside the tertiary follicle completes meiosis-I to form a haploid secondary oocyte and a first polar body.
• Tertiary follicle changes into Graafian follicle.
• The secondary oocyte starts meiosis-II and then stops, Graafian follicle
ruptures to release secondary oocyte (ovum) from the ovary
(ovulation).
(ii)
Luteinizing hormone (LH) and Follicle stimulating hormone (FSH)
(i)
(ii)
Three layers
• Plasma membrane
• Intine
• Exine
(iii)
• Sporopollenin.
• It is very resistant/ cannot be degraded by enzymes/ acids/ alkali/
temperature.
(iv)
Outermost layer is disrupted at some places to form the germ pores through which pollen germinates to form pollen tube.
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CBSE Class 12 Biology past-paper question from the 2026 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.