Q.1. Explain the process of gametogenesis in animals with suitable examples.
Answer- The biological process for the formation of gametes, i.e., the production of sperms and oocytes is known as gametogenesis. The process for the formation of sperms is known as spermatogenesis and that for oocytes is known as oogenesis.
Spermatogenesis
- Testosterone and Follicle Stimulating Hormones are involved in the process.
- Mitosis and meiosis take place in the seminiferous tubules of the testis which helps in the formation of spermatozoa.
- Spermatogonia undergo mitosis and produces diploid primary spermatocytes.
- The primary spermatocytes divide into two secondary spermatocytes during the first mitosis.
- The secondary spermatocytes further divide by meiosis and form four spermatids.
- Spermatids differentiate into functional sperms by a process called the spermiogenesis.
Oogenesis
- Estrogen, follicle-stimulating hormone, luteinizing hormone and progesterone are involved in the process.
- Primordial follicles of ovaries transform into oogonia and produce diploid primary oocytes.
- Primary oocytes undergo meiosis to form ootids. These get arrested at prophase I
- On reaching puberty, the primary oocytes undergo meiosis and form haploid secondary oocytes and a polar body which disintegrates later.
- The secondary oocytes get arrested at metaphase II.
- If the egg gets fertilized the meiosis gets completed forming a polar body and an ootid.
- The ovum matures and the polar bodies disintegrate.
Q.2. Rose plants have large flowers but rarely do they produce fruits. On the contrary, the tomato plant produces fruit but has very small flowers. Comment with suitable reasons.
Answer- Rose plants do not produce fruits due to the following reasons:
- No fertilization takes place in a rose flower due to the absence of viable pollen.
- The eggs produced are non-functional.
- They are self-incompatible.
- The ovule is defective and non-functional.
- Since rose plants reproduce vegetatively, they might be sterile.
Q.3. List the important differences between zoospore and zygote.
Answer- Following are the important differences between zoospore and zygote:
| Zoospore | Zygote |
| This structure is associated with asexual reproduction. | This structure is associated with sexual reproduction. |
| It is thin-walled. | It is thick-walled and helps to resist any damage and desiccation. |
| It has flagella for locomotion. | It is non-motile |
| It is formed during favourable conditions and germinates immediately. | It undergoes a period of dormancy in algae and fungi. |
Q.4. What are the post-fertilization changes that occur in plants?
Answer- The post-fertilization changes that occur in plants include:
1. Development of Endosperm: The endosperm cell divides to form a triploid endosperm tissue. The cells have reserve food material that provides nutrition to the developing embryo.
2. Embryo Development: The zygote divides only after a certain amount of endosperm is formed. The endosperm provides nutrition for development.
3. Development of Seed: The ovule gets transformed into a seed after double fertilization.
4. Fruit Formation: Fruits are formed by cell division and differentiation in the ovary. The wall of the ovary develops into the wall of the fruit.
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