1. Why is reproduction essential for organisms?

Answer: Reproduction is the biological process through which an organism gives rise to its offspring. In the absence of reproduction there would be drastic decline in the population of the organism and it will eventually extinct due to mortality. Therefore, to ensure the continuity of the species the process of reproduction is considered essential for organisms.

2. Which is a better mode of reproduction sexual or asexual? Why?

Answer: Sexual mode of reproduction is considered a better mode of reproduction as compared to asexual mode. Sexual mode of reproduction involves the formation of diploid male and female gametes by meiosis(usually), which later on fuses to form zygote. Unlike asexual reproduction, in the case of sexual reproduction the offspring isn’t completely identical to the parent, they contain a combination of two different sets of DNAs. This facilitates the process of evolution as new variants are produced.

3. Why is the offspring formed by asexual reproduction referred to as clone?

Answer: Offspring formed by asexual reproduction are morphologically and genetically identical to the parent organism that’s why they’re termed as clones.

4. Offspring formed due to sexual reproduction have better chances of survival. Why? Is this statement always true?

Answer: Offspring formed due to sexual reproduction have better chances of survival. Sexual reproduction introduces genetic variation in the offspring which helps to adjust according to environmental changes.

This statement cannot be validated always as in some cases the offspring might be genetically inferior to the parents.

5. How does the progeny formed from asexual reproduction differ from those formed by sexual reproduction?

Answer: In asexual reproduction there’s no fusion of gametes and the offspring are produced by a single parent so they’re morphologically and genetically identical to the parent.

In the case of sexual reproduction there’s fusion of male and female gamete resulting in genetic variation in the offspring.

6. Distinguish between asexual and sexual reproduction. Why is vegetative reproduction also considered as a type of asexual reproduction?

Answer:

ASEXUAL REPRODUCTIONSEXUAL REPRODUCTION
New individuals are formed from a single parent.Commonly two parents are involved in the formation of new individuals through sexual reproduction.
Asexual reproduction does not involve gametogenesis or syngamy.In sexual reproduction male and female gametes fuse together to give rise to zygote.
Offspring are morphologically and genetically similar to the parent.Offspring show genetic variation from the parent.
No evolutionary importance.Genetic variations introduce evolution.
Quick method of multiplication.Slow and complex process.

Vegetative reproduction is also considered as a type of asexual reproduction as in this method new plants or individuals are produced from vegetative parts of plants or without the fusion of gametes.

7. What is vegetative propagation? Give two suitable examples.

Answer: Vegetative propagation is a type of asexual reproduction seen in higher plants, in which new plants are formed from the vegetative parts of plants like stem, root, or bulbil without the fusion of gametes.
Examples: vegetative propagation of sweet potato by roots,

          Vegetative propagation of potato by underground stem(tuber)

8. Define

(a) Juvenile phase

Answer: Juvenile phase is defined as the growth period between the birth and before attaining reproductive maturity. The duration varies from organism to organism depending on their life span and environmental condition.

(b) Reproductive phase

Answer: The time period when an organism reaches the reproductive maturity and start reproducing sexually, is termed as reproductive phase. This period is characterised by maturity of reproductive organs in animals and the flowering in plants.

(c) Senescent phase

Answer: The phase of life starting with the loss of reproductive abilities characterised by slowing of metabolism and growing old is called as senescent phase. This phase ends with the death of the organism.

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

Answer: Despite of its complexity sexual reproduction leads to genetic variation due to fusion of gametes from two different individuals. This has an important role in the course of evolution as it helps the offspring to adapt to different environmental factors and increases the chance of survival. Due to the above-mentioned reasons the higher organisms have resorted to sexual reproduction.

10. Explain why meiosis and gametogenesis are always interlinked?

Answer: Meiosis is a process of reductional division in which the amount of genetic material is reduced i.e., a diploid cell gives rise to 4 haploid cells. It involves two successive nuclear and cell divisions with a single cycle of DNA replication.

Gametogenesis is the process of the formation of gametes. Gametes produced by organisms are haploids (containing only one set of chromosomes), while the body of an organism is diploid.

Therefore, for producing haploid gametes (gametogenesis), the meiocyte undergo meiosis to form the haploid gametes.

Thus, meiosis and gametogenesis are always interlinked.

11.Identify each part in a flowering plant and write whether it is haploid (n) or diploid (2n).

(a) Ovary                  Diploid (2n)

(b) Anther                 Diploid (2n)

(c) Egg                       Haploid (n)

(d) Pollen                  Haploid (n)

(e) Male gamete       Haploid (n)-

(f) Zygote                  Diploid (2n)

12. Define external fertilisation. Mention its disadvantages.

Answer: External Fertilisation is the process in which syngamy occurs outside the parent body in external medium.

As the zygote is formed outside the body there’s very less chance of survival of the offspring.

13. Differentiate between a zoospore and a zygote.

Answer:

ZOOSPORE ZYGOTE
A zoospore is a motile asexual spore that utilizes the flagella for movement. A zygote is a non-motile diploid cell formed as a result of fertilisation.
It is an asexual reproductive structure. It is formed as a result of sexual reproduction.

14. Differentiate between gametogenesis from embryogenesis.

Answer: Gametogenesis is the process of formation of haploid male or female gametes from diploid meiocytes through the process of meiosis whereas embryogenesis is the process of the development of the embryo from the repeated mitotic divisions of the diploid zygote.

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

Answer: The post-fertilization changes exhibited by a flower are:

  1. The sepals, petals and stamens fall off
  2. The pistil remains attached to the flower
  3. The zygote develops into an embryo
  4. The ovule develops into the seed
  5. The ovary develops into fruit.

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.

Answer: Flowers that contain both female and male reproductive structures are considered a bisexual flower. The male reproductive structure is called androecium while the female reproductive structure is gynoecium.

Examples:
i. Brassica (Mustard)

ii. Tulipa (Tulip)

iii. Solanum lycopersicum (Tomato)

iv. Nymphaea odorata (Water lily)

v.  Rosa multiflora (Rose) 

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

Answer: Separate male and female flowers can be seen in the cucurbit plants i.e., unisexual condition. The male flowers (staminate) bear bright yellow petals and stamens, the male reproductive structure. The female flowers (pistillate) bear only pistil, the female reproductive structure.

Plants that bear unisexual flowers are: corn, papaya, cucumber etc.

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

Answer: In the case of oviparous animals the eggs are laid outside the body in the external medium and then after a fixed time period it hatches the young ones. This makes the offspring prone to predators reducing their chances of survival.

While in viviparous organisms the fully differentiated young ones are born increasing the chances of their survival.



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