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Biology · 2024 · 5 marks
Sexual Reproduction in Flowering PlantsPre-fertilisation: Structures and Events5 marksApplylong answer
CBSE 2024 · Region 5 · Set 1 · Q32
(a) (i) Draw a diagram of a human sperm. Label any four parts and write their functions. (ii) In a human female, probability of an ovum to get…
(a)(i)
Draw a diagram of a human sperm. Label any four parts and write their functions.
(ii)
In a human female, probability of an ovum to get fertilized by more than one sperm is impossible. Give reason.
OR
(b)(i)
With the help of labelled diagram only, show the different stages of embryo development in a dicot plant.
(ii)
Endosperm development precedes embryo development. Justify.
Marking-scheme solution
(i)
Head: Contains chromosomal / genetic / nuclear material
Acrosome: Filled with enzymes that helps in fertilisation of the ovum / its secretion help the sperm enter into the cytoplasm of the ovum
Middle piece: Possess mitochondria (which produce energy)
Mitochondria: Produce energy (for the movement of the tail / for swimming)
Tail: Provide motility / helps in swimming
Plasma membrane: Envelop of the sperm / protection (while passing through acidic medium of reproductive tract)
Nucleus: Contains genetic / chromosomal material / DNA
(ii)
When a sperm comes in contact with Zona Pellucida (layer of the ovum), it
induces changes in the membrane which blocks the entry of any additional sperm.
(i)
(ii)
Providing nutrition to the developing embryo
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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.