Plus Two Botany Class Notes First Bell 2.0

CHAPTER 1 Part-02


Textual Exercise Answers  Part -02 

9. Higher organisms have resorted to sexual reproduction in spite of its complexity. Why?

Sexual reproduction involves formation of the male and female gametes, either by the same individual or by different individuals of the oppositesex. These gametes fuse to form the zygote  which develops to form the new organism. It is an elaborate, complex and slow process. Offspring have better chances of survival and helps in evolution. 

10. Explain why meiosis and gametogenesis are always interlinked?

Parent body of sexually reproducing organisms are diploid (2n) . Fusion of male gametes and female gametes they should be haploid (n). Through meiosis diploid is converted into haploid cell.

11. Identify each part in a flowering plant and write whether it is haploid

(n) or diploid (2n).

(a)Ovary ———————————

(b)Anther ———————————

(c)Egg ———————————

(d)Pollen ———————————

(e)Male gamete ———————————

(f)Zygote ———————————









Male gamete




12.Define external fertilisation. Mention its disadvantages.

syngamy occurs in the external medium (water), i.e., outside the body of the organism. This type of gametic fusion is called external fertilisation. A major disadvantage is that the offspring are extremely vulnerable to predators threatening their survival up to adulthood.

13. Differentiate between a zoospore and a zygote

Zygote - Formation of the diploid zygote is universal in all sexually reproducing organisms. In organisms with external fertilisation, zygote is formed in the external medium (usually water), whereas in those exhibiting internal fertilisation, zygote is formed inside the body of the organism. Its non motile structure 

Zoospore - The  most common of these structures are  zoospores that usually are microscopic  motile structures.

         Zoospores                                                      zygote

14. Differentiate between gametogenesis from embryogenesis

Gametogenesis - gametogenesis refers to the process of formation of the two types of gametes – male and female. Gametes are haploid cells. There are two types of gametogenesis there are oogenesis and spermatogenesis.  It result in fertilization 

Embryogenesis - Embryogenesis refers to the process of development of embryo from the Zygote. It involves fertilization,  cleavage , gastrulation and organogenesis as a result give into birth.

15. . Describe the post-fertilisation changes in a flower

In flowering plants, the zygote is formed inside the ovule. After fertilisation the sepals, petals and stamens of the flower wither and falloff.  The pistil however, remains attached to the plant. The zygote develops into the embryo and the ovules develop into the seed. The ovary develops into the fruit which develops a thick wall called pericarp that is protective in function. After dispersal, seeds germinate under favourable conditions to produce new plants.

16. What is a bisexual flower? 

Collect five bisexual flowers from your neighbourhood and with the help of your teacher find out their common and scientific names

Bisexual flower – flower those contain stamen and pistil. Ex – sunflower. ( for collecting bisexual flower consult your teacher)

17. Examine a few flowers of any cucurbit plant and try to identify the stamina and pistillate flowers. Do you know any other plant that bears unisexual flowers?

(Consult your teacher)

18. Why are offspring of oviparous animals at a greater risk as compared to offspring of viviparous animals?

In oviparous animals like reptiles and birds, the fertilised eggs covered by hard calcareous shell are laid in a safe place in the environment; after a period of incubation young ones hatch out. On the other hand, in viviparous animals (majority of mammals including human beings), the zygote develops into a young one inside the body of the female organism. After attaining a certain stage of growth, the young ones are delivered out of the body of the female organism. Because of proper embryonic care and protection, the chances of survival of young ones is greater in viviparous organisms.

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