NCERT Class 12 Biology: Chapter –1 Reproduction in Organisms Part 6

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Question 11:

Justify the statement ‘Vegetative reproduction is also a type of asexual reproduction’.

Answer:

Asexual reproduction is the kind of reproduction in which only one parent is involved, which reproduces asexually to produce similar young ones. Vegetative reproduction is also a type of asexual reproduction because of the following reasons.

1. It involves only one parent.

2. Clone formation takes place that is the young one is exact copy of the parent.

3. No gamete formation takes place.

4. The off spring has the same genetic composition as the parent.

5. Only mitotic division takes place.

These evidences prove that vegetative reproduction is a type of asexual reproduction.

Long Answer Type Questions

Question 1:

Enumerate the differences between asexual and sexual reproduction. Describe the types of asexual reproduction exhibited by unicellular organisms.

Answer:

Differences between Asexual and Sexual Reproduction
Differences between asexual and sexual reproduction

Asexual Reproduction

Sexual Reproduction

1. Only one parent is involved in the reproduction.

1. Both male and female parents are involved

2. No gamete formation takes place

2. Male and female gamete formation takes place

3. Fusion of male gamete does not take place.

3. Fusion of male and female gametes takes place.

4. Off-springs are like the parent.

4. Off springs are physically and genetically varied than the parent.

5. This type of reproduction is

5. This kind of reproduction is very useful in the evolution of species.

6. Genetic variation does not take place

6. Genetic variation takes place because of the recombination of both male and female gametes.

7. Only mitotic division takes place in this type of reproduction.

7. Only meiotic division takes place

8. It is a fast process.

8. It is a slow and elaborate process

Asexual reproduction is the type of reproduction in which there is only one parent is involved and no fusion of gametes take place. The various kinds of asexual reproduction are as follows:

1. Binary Fission: In this type of asexual reproduction, the parent cell divides its DNA into two, these DNA than incorporates into two identical daughter cells produced from the parent body, example: Amoeba

2. Budding: A small nod or growth on the surface of the parent body derives nutrition from the parent, then detaches and grow into another being. Example: Hydra, Yeast.

3. Fragmentation: In this, the parent body divides into many fragments and every fragment develops into off springs. Example: starfish, sponges etc.

4. Parthenogenesis: The unfertilized eggs develop into an embryo to form an invertebrate like fish, frog and other reptiles.

Question 2:

Do all the gametes formed from a parent organism have the same genetic composition (identical DNA copies of the parental genome)? Analyse the situation with the background of gametogenesis and provide or give suitable explanation.

Answer:

The gametes formed from a parent organism do not have the same genetic composition (identical DNA copies of the parental genome) because in sexual reproduction the fusion of male and female gamete takes place. The male gamete has different genetic makeup and female gamete has different genetic makeup their recombination leads to the formation of a gamete that has different DNA composition.

Question 3:

Although sexual reproduction is a long drawn, energy-intensive complex form of reproduction, many groups of organisms in Kingdom Animalia and Plantae prefer this mode of reproduction. Give atleast three reasons for this.

Answer:

Sexual reproduction is the fusion of male and female gametes to produce genetically variant offspring. The sexual reproduction leads to:

1. Genetically varied offspring due to the recombination of the qualitatively different male and female DNA.

2. Due to recombination of DNA genetical variations are seen in the off springs.

3. This type of reproduction is useful as due to genetical variation the adaptation and survival compatibility increases.

Question 4:

Differentiate between (a) oestrus and menstrual cycles; (b) ovipary and vivipary. Cite an example for each type.

Answer:

Oestrus Cycle and Menstrual Cycle
Oestrus Cycle and Menstrual Cycle

Oestrus Cycle

Menstrual Cycle

(i) Female is sexually active only during the ovulation phase.

(i) Ovulation has no correlation with sexual activity of the female.

(ii) Endometrium is absorbed in case conception does not take place.

(ii) Endometrium is shed in fragments if conception does not take place

(iii) Is marked by visible signs on female genitalia.

(iii) Is marked by discharge of blood and tissue fragments from female genitalia

(iv) Examples: cat, dog, horse, 1sec.

(iv) Examples: humans, chimpanzee, monkey

Ovipary and Vivipary
Ovipary and Vivipary

Ovipary

Vivipary

(i) Animal lays eggs

(i) Animal gives birth to young ones.

(ii) Less demand of resources from the female’s body.

(ii) Greater demand of resources from the female’s body.

(iii) Chances of survival of progeny is low.

(iii) Chances of survival or progeny is high.

(iv) Examples: reptiles and aves.

(iv) Examples: most of the mammals, shark, dolphin

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