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Biology · 2024 · 5 marks
CBSE 2024 · Region 4 · Set 1 · Q31
(a) The given diagram shows the sectional view of a seminiferous tubule of Human testis: (i) Name and describe the process depicted in the diagram…
The given diagram shows the sectional view of a seminiferous tubule of Human testis:
(i)
Name and describe the process depicted in the diagram which results in the development of spermatozoa.
(ii)
Identify the cell where you are seeing a cluster of spermatozoa attached in the diagram. Write the function of the cell.
Observe the picture of Commelina plant bearing two types of flowers given above.
(i)
Identify the two types of flowers labelled 'A' and 'B' in the picture.
(ii)
Compare the two types of flowers with reference to :
(1)
Characteristic feature
(2)
modes of pollination
(iii)
List any two 'out breeding devices' in flowering plants. Explain why do plants develop such devices.
Marking-scheme solution
(a)
(i)
Spermatogenesis
Spermatogonia → Mitosis / differentiation → Primary spermatocytes → 1st meiotic division → Secondary spermatocytes → 2nd meiotic division → Spermatids → Differentiation / spermiogenesis → Spermatozoa
(ii)
Sertoli cells, provides nourishment to the developing sperm.
(i)
A- chasmogamous flower
B- cleistogamous flower
(ii)
‘A’
‘B’
(1) open flower / blossom
closed flower/ Do not
blossom
(2)
Autogamy as well as
geitonogamy and
xenogamy/cross
pollination
only autogamy/self-
pollination
(iii)
•
In some species, pollen release and stigma receptivity are not
synchronized. Either the pollen is released before the stigma becomes
receptive or stigma becomes receptive much before the release of pollen.
The anther and stigma are placed at different positions so that the pollen
cannot come in contact with the stigma of the same flower.
Self-incompatibility. This is a genetic mechanism and prevents self-
pollen from fertilizing the ovules.
Production of unisexual flowers.
•
To prevent inbreeding depression/ to discourage self-pollination and to encourage cross pollination/ to develop genetic variation
All Human Reproduction questions2024 question paperNCERT solutions: Human ReproductionPractice Human Reproduction →
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CBSE Class 12 Biology past-paper question from the 2024 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.