Reproduction in Organisms - Exercises

Question 1: Why is reproduction essential for organisms?

Ans: It is a biological process through which living organisms produce offspring of their own kind.

Reproduction ensures the continuance of various species generation after generation.

Absence of reproduction leading to extinction of species.

 

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

Ans: Sexual reproduction is a better mode of reproduction. It is done by the formation and fusion of gametes. It involves the fusion of the male and the female gamete to produce variants, which are not identical to their parents and to themselves. It allows the formation of new variants by the combination of the DNA from two different individuals, typically one of each sex. This variation allows the individual to adapt to constantly changing and challenging environments. Also, it leads to the evolution of better suited organisms which ensures greater survival of a species. On the contrary, asexual reproduction allows very little or no variation at all. As a result, the individuals produced are exact copies of their parents and themselves.

 

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

Ans: A clone is a group of individuals which are morphologically and genetically identical. In the process of asexual reproduction, only one parent is involved and there is no fusion of the male and the female gamete. As a result, the progenies are morphologically and genetically similar to their parents and are thus, called clones.

 

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

Ans: Sexual reproduction involves the fusion of the male and the female gamete. This fusion allows the formation of new variants by the combination of the DNA from two (usually) different members of the species. The variations allow the individuals to adapt under varied environmental conditions for better chances of survival. However, it is not always necessary that the offspring produced due to sexual reproduction has better chances of survival. Under some circumstances, asexual reproduction is more advantageous for certain organisms.

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

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

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

Ans: Vegetative propagation is a mode of asexual reproduction in which new plants are obtained from the vegetative parts (Propagules) of plants. It does not involve the production of seeds or spores for the propagation of new plants. Vegetative parts of plants such as runners, rhizomes, suckers, tubers, etc. can be used as propagules for raising new plants.

Examples of vegetative reproduction are:

Bulbil – Bulbil

Bulbs – Onion, Garlic

Eyes – Potato

Leaf buds – Bryophyllum

Offset – Hyacinth and

Rhizome – Ginger

Runner – Oxalis

Sucker – Mint

Question 8: Define

(a) Juvenile phase,

(b) Reproductive phase,

(c) Senescent phase.

Ans:

(a) Juvenile phase: It is the period of growth in an individual organism after its birth and before it reaches reproductive maturity.

(b) Reproductive phase: It is the period where an organism possesses all the capacity and potential to reproduce sexually.

(c) Senescent phase: It is the period when an organism slowly loses the rate of metabolism and reproductive potential.

 

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

Ans: Higher organisms have resorted to sexual reproduction to get over the unfavourable condition

Introduce variation to enable better adaptive capacity and biological tolerance.

Restore high gene pool in a population.

Restore vigour and vitality of the race.

Get proper parental care during vulnerable condition.

 

Question 10: Explain why meiosis and gametogenesis are always interlinked?

Ans: Meiosis is a process of reductional division in which the amount of genetic material is reduced. 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 germ cells of an organism undergo meiosis. During the process, the meiocytes of an organism undergo two successive nuclear and cell divisions with a single cycle of DNA replication to form the haploid gametes.

 

Question 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 ——————————

 

Ans:

(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)

 

Question 12: Define external fertilization. Mention its disadvantages.

Ans: External fertilization is the process in which the fusion of the male and the female gamete takes place outside the female body in an external medium, generally water. Fish, frog, starfish are some organisms that exhibit external fertilization.

 

Disadvantages of external fertilization:

In external fertilization, Chances of fertilization is very less i.e., it’s a chance matter

The offspring are extremely vulnerable to predators.

 

Question 13: Differentiate between a zoospore and a zygote.

Question 14: Differentiate between gametogenesis from embryogenesis.

Question 15: Describe the post-fertilization changes in a flower.

Ans: The formation of zygote which letter developed into an embryo and primary endosperm cell which develops into endosperm

Sepals, petals and stamens are shed, the pistil remains intact.

The fertilised ovule develops into seeds.

The ovary matures into a fruit, that later developes a thick protective wall called pericarp.

Seeds after dispersal germinate under favourable conditions into a new plant.

 

Question 16: What is a bisexual flower? Collect five bisexual flowers from your neighborhood and with the help of your teacher find out their common and scientific names.

Ans: A flower that contains both the male and female reproductive structure (stamen and pistil) is called a bisexual flower. Examples of plants bearing bisexual flowers are:

(1) Water lily ( Nymphaea odorata)

(2) Rose (Rosa multiflora )

(3) Hibiscus (Hibiscus Rosa-sinensis )

(4) Mustard ( Brassica nigra)

(5) Petunia (Petunia hybrida)

 

Question 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?

Ans: A staminate or male flower has only stamens and no carpel. A pistillate flower has only carpel and no stamens.

Plants that bear unisexual flowers are papaya, coconut, corn and date palm.

Question 18: Why are offspring of oviparous animals at a greater risk as compared to offspring of

viviparous animals?

Ans: In viviparous animals, the young one develops inside the female body. As a result of this the young one gets better protection and nourishment for proper development.

In the case of oviparous animals, they lay eggs and young ones develop outside the body and inside the calcareous shell. So, young ones are not effectively protected by their parents.

 

Important Questions from the Chapter

  1. What are homogametes and heterogametes? (2-marks)

  2. Mention the vegetative propagules of the following plants: a. Water hyacinth b. agave c. Banana (3-marks)

  3. Name the asexual reproductive structure of Chlamydomonas. (1-mark)

  4. Distinguish between homothallic and heterothallic plants. (2-marks)

  5. What is parthenogenesis? Name any two organisms exhibiting parthenogenesis. (2-marks)

  6. What are meiocytes? (1-mark)

  7. How does the progeny formed from asexual reproduction differ from those formed by sexual preproduction? (2-marks)

  8. Mention the asexual reproductive structure of penicillium. (1-mark)

  9. Define reproduction. Mention its significance. (2-marks)

  10. Differentiate between menstrual cycle and oestrus cycle. (3-marks)

  11. Explain the phases of life span in organisms. (3-marks)

  12. What is asexual reproduction? mention any two types. (3-marks)

  13. What is life span? (1-mark)

  14. Write short notes on fertlilization. (3-marks)

  15. Differentiate asexual reproduction from sexual reproduction. (3-marks)