NCERT Class 12 Biology: Chapter –1 Reproduction in Organisms Part 5

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Question 4:

With which type of reproduction do we associate the reduction division? Analyse the reasons for it.

Answer:

1. Meiosis is known as reduction division because, Meiosis occurs in sexual reproduction, as it is involved in the production of gametes. The gametes are haploid by nature which means that the gametes have half the number of chromosomes than the parents. Hence, the name reduction division.

Question 5:

Is it possible to consider vegetative propagation observed in certain plants like Bryophyllum, water hyacinth, ginger etc., as a type of asexual reproduction? Give two/three reasons.

Answer:

Vegetative reproduction is a type of asexual reproduction because:

1. It involves only one parent.

2. No gamete formation takes place.

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

4. Only mitotic division takes place in this reproduction.

5. Clone formation takes place.

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

Question 6:

‘Fertilisation is not an obligatory event for fruit production in certains plants’. Explain the statement.

Answer:

‘Fertilisation is not an obligatory event for fruit production in certain plants’ because in some plants unfertilized egg grows into an embryo, this process is known as parthenogenesis. In some fruits chemical fertilisers are also given to enhance the growth.

Question 7:

In a developing embryo, analyse the consequences if cell divisions are not followed by cell differentiation.

Answer:

If in a developing embryo, cell divisions are not followed by cell differentiation the embryo would not grow into an organism as the cells would not differentiate to forms tissues and then organs and would remain as a mass.

Question 8:

List the changes observed in an angiosperm flower subsequent to pollination and fertilisation.

Answer:

Following changes take place in an angiosperm flower after pollination and fertilization

(a) Sepals, petals and stamens wither and fall off

(b) Zygote develops into the embryo and ovule develops into the seed

(c) Ovary develops into fruit

(d) Fruit develops a thick outer covering called pericarp

Question 9:

Suggest a possible explanation why the seeds in a pea pod are arranged in a row, whereas those in tomato are scattered in the juicy pulp.

Answer:

This is due to the different types of placentation shown by the pea and the tomato plants. Placentation is the term used to describe the type of arrangement of ovules inside the ovary. The pea plant shows Marginal Placentation which means that the ovules are arranged into two rows along the rigid ventricular suture, whereas the tomato plant shows Axileplacentation, that means the ovules are arranged along the central axis of the ovary. Hence, the arrangement.

Question 10:

Draw the sketches of a zoospore and a conidium. Mention two dissimilarities between them and atleast one feature common to both structures.

Answer:

Zoospores and Conidium
Zoospores and Conidium

Zoospores

Conidium

(i) They are motile

(i) They are non-motile.

(ii) Flagella is present

(ii) Flagella is absent

(i) Both are involved in asexual reproduction

(ii) Both help the organism to tide over the bad phase.

Zoospore and Conidium

Zoospore and Conidium

Zoospore and Conidium

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