Biology Class 11 NCERT Solutions: Chapter 2 Biological Classification Part 3

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Q: 12. Organise a discussion in your class on the topic- Are viruses living or non-living?

Answer:

Viruses are microscopic organisms that have characteristics of both living and non- living. A virus consists of a strand of DNA or RNA covered by a protein coat. This presence of nucleic acid (DNA or RNA) suggests that viruses are alive. In addition, they can also respond to their environment (inside the host cell) in a limited manner. However, some other characters, such as their inability to reproduce without using the host cell machinery and their acellular nature, indicate that viruses are non-living. Therefore, classifying viruses has remained a mystery for modern systematics.

Exercise -2

Q: 1. Name the parts of an angiosperm flower in which development of male and female gametophyte take place.

Q 1 Image of Angiosperm

Q 1 Image of Angiosperm

Q 1 Image of Angiosperm

Answer:

The male gametophyte or the pollen grain develops inside the pollen chamber of the anther, whereas the female gametophyte (also known as the embryo sac) develops inside the nucellus of the ovule from the functional megaspore.

Q: 2. Differentiate between microsporogenesis and megasporogenesis. Which type of cell division occurs during these events? Name the structures formed at the end of these two events.

Answer:

(A)

Q_2_A_Table of Microsporogenesis Megasporogenesis
Q_2_A_Table of Microsporogenesis Megasporogenesis

Microsporogenesis

Megasporogenesis

1.

It is the process of the formation of microspore tetrads from a microspore mother cell through meiosis.

It is the process of the formation of the four megaspores from a megaspore mother cell in the region of the nucellus

through meiosis

2.

It occurs inside the pollen sac of the anther.

It occurs inside the ovule.

Differentiate between microsporogenesis and megasporogenesis

Differentiate Between Microsporogenesis and Megasporogenesis

Differentiate between microsporogenesis and megasporogenesis

(B) Both events (microsporogenesis and megasporogenesis) involve the process of meiosis or reduction division, which results in the formation of haploid gametes from the microspore and megaspore mother cells.

(C) Microsporogenesis results in the formation of haploid microspores from a diploid microspore mother cell. On the other hand, megasporogenesis results in the formation of haploid megaspores from a diploid megaspore mother cell.

Q: 3. Arrange the following terms in the correct developmental sequence:

Pollen grain, sporogenous tissue, microspore tetrad, pollen mother cell, male gametes

Answer:

The correct development sequence is as follows:

Image of the correct development sequence

Image of the Correct Development Sequence

Image of the correct development sequence

Sporogenous tissue − Pollen mother cell − Microspore tetrad − Pollen grain – Male gamete

During the development of microsporangium, each cell of the sporogenous tissue acts as a pollen mother cell and gives rise to a microspore tetrad, containing four haploid microspores by the process of meiosis (microsporogenesis). As the anther matures, these microspores dissociate and develop into pollen grains. The pollen grains mature and give rise to male gametes.

Q: 4. With a neat, labelled diagram, describe the parts of a typical angiosperm ovule.

Answer:

An ovule is a female megasporangium where the formation of megaspores takes place.

Q 4 Image of Parts of Ovule

Q 4 Image of Parts of Ovule

Q 4 Image of Parts of Ovule

The various parts of an ovule are −

(1) Funiculus − It is a stalk-like structure which represents the point of attachment of the ovule to the placenta of the ovary.

(2) Hilum − It is the point where the body of the ovule is attached to the Funiculus.

(3) Integuments −They are the outer layers surrounding the ovule that provide protection to the developing embryo.

(4) Micropyle − It is a narrow pore formed by the projection of integuments. It marks the point where the pollen tube enters the ovule at the time of fertilization.

(5) Nucellus − It is a mass of the parenchymatous tissue surrounded by the integuments from the outside. The nucellus provides nutrition to the developing embryo. The embryo sac is located inside the nucellus.

(6) Chalazal − It is the based swollen part of the nucellus from where the integuments originate.

Q: 5. What is meant by monosporic development of female gametophyte?

Answer:

The female gametophyte or the embryo sac develops from a single functional megaspore. This is known as monosporic development of the female gametophyte. In most flowering plants, a single megaspore mother cell present at the Micropyle pole of the nucellus region of the ovule undergoes meiosis to produce four haploid megaspores. Later, out of these four megaspores, only one functional megaspore develops into the female gametophyte, while the remaining three degenerate.