NCERT Class 12 Biology: Chapter –1 Reproduction in Organisms Part 4

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Question 12:

Why do gametes produced in large numbers in organisms exhibit external fertilisation?

Answer:

Gametes produced in large numbers in organisms exhibit external fertilisation because gametes are released in open environment. Due to which they are constantly exposed to factors like predators, desiccation etc. This leads to reduced number of gametes.

2. Increased number of gametes increases the chances of syngamy. Which is the fusion of the male and female gametes. Increased number of gametes increases the probability of Syngamy.

Question 13:

Which of the followings are monoecious and dioecious organisms.

a. Earthworm ______________

b. Chara ______________

c. Marchantia ______________

d. Cockroach ______________

Answer:

(a) Dioecious

(b) Monoecious

(c) Dioecious

(d) Monoecious

Question 14:

Match the organisms given in Column-’A’ with the vegetative propagules given in column ‘B’.

Table of Match the Column a and B
Table of Match the Column A and B

Column A

Column B

i.

Bryophyllum

a)

Offset

ii.

Agave

b)

Eyes

iii.

Potato

c)

Leaf buds

iv.

Water hyacinth

d)

Bulbils

Answer:

(i) (c)

(ii) (d)

(iii) (b)

(iv) (a)

Question 15:

What do the following parts of a flower develop into after fertilisation?

a. Ovary ______________

b. Ovules ______________

Answer:

(a) Fruits

(b) Seeds

Short Answer Type Questions

Question 1:

In haploid organisms that undergo sexual reproduction, name the stage in the life cycle when meiosis occurs. Give reasons for your answer.

Answer:

Haploid organisms are those which have half the number of chromosomes than their parents. These organisms do not undergo meiosis, as only diploid cells undergo meiosis. These haploid cells only show meiotic division when the formation of zygote takes place as the zygote is the only diploid cell in their life cycle.

Question 2:

The number of taxa exhibiting asexual reproduction is drastically reduced in higher plants (angiosperms) and higher animals (vertebrates) as compared with lower groups of plants and animals. Analyse the possible reasons for this situation.

Answer:

The higher plants that are the angiosperms, and the higher animals that are the vertebrates have complex structural organisation, this allows them to use sexual mode of reproduction. It allows them to have:

1. Genetically variable offspring are produced.

2. They have more superior survival and adaptation capability than those which are produced asexually.

Lower plants and animals do not have these variations as they produce by asexual reproduction.

Question 3:

Honeybees produce their young ones only by sexual reproduction. Inspite of this, in a colony of bees we find both haploid and diploid individuals. Name the haploid and diploid individuals in the colony and analyse the reasons behind their formation.

Answer:

A honeybee hive has three kinds of members which are

1. Diploid Queen which are fertile females.

2. Worker bees which are sterile females.

3. Drones which are haploid males.

4. When the male and female gametes combine to produce off springs they could either produce diploid female or haploid males.

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