Class 12th Biology 2014 Set3 Delhi Board Paper Solution
(a) Draw a labelled diagrammatic view of human male reproductive system.
(b) Differentiate between :
(i) Vas deferens and vasa efferentia
(ii) Spermatogenesis and spermiogenesis
OR
(a) Explain the phenomenon of double fertilisation. (b) Draw a labelled diagram of a typical anatropous ovule.
(a) Diagrammatic view of a human male reproductive system
The male Reproductive System
(b) (i)
| Vas deferens | Vasa efferentia |
| It is a tube-like structure which conducts the spermatozoa from the epididymis to the penis. | It connects the rete testis to the epididymis. |
(ii)
| Spermatogenesis | Spermiogenesis |
| It is the process of production of sperms from immature germ cells in males. | It is the process of transformation of a circular spermatid to a motile spermatozoa. |
| Number of cells are increased as each spermatogonium produces four spermatids. | There are no changes in the number of cells as only one spermatid develops into a spermatozoa. |
| This makes a diploid cell, haploid. | No effects on the genetic material of the germ cells. |
OR
(a) Phenomenon of double fertilisation
When the pollen grains gets transferred from the anther to the stigma, the pollen tube enters one of the synergids and releases two male gametes. One of them moves towards the egg cell and fuses with it to complete the syngamy to form the zygote.
The other fuses with the two polar nuclei and forms triploid primary endosperm nucleus (PEN). This fusion of one male gamete with two polar nuclei is termed as triple fusion.
Since, two kinds of fusion—syngamy and triple fusion—take place during fertilisation in a flower, the process is known as double fertilisation. It is a characteristic of flowering plants.
After triple fusion, the central cell becomes the primary endosperm cell (PEC). The primary endosperm nucleus gives rise to the endosperm, while the zygote develops into the embryo.
(b) Labelled diagram of a typical anatropous ovule
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