Sunday, January 3, 2021

Sexual Reproduction in Flowering Plants | Class 12 Botany| Previous Years Questions and Answers (2018 to 2020)

2. SEXUAL REPRODUCTION IN FLOWERING PLANTS


2020 SAY

1.   Observe the relationship between the first two terms and fill in the blank: (1)

Endothecium: Protection;             

Tapetum: ......................

ü Answer:

Nutrition

2.   Flowers are classified into Chasmogamous and Cleistogamous flowers. (2)

(a)    Cleistogamous flowers are autogamous. Justify.

(b)   Define autogamy.

ü Answer:

(a) Anthers and stigma lie close to each other. They are not exposed.

(b) It is the transfer of pollen grains from the anther to the stigma of the same flower.

3.   Observe the figure given below: (2)


(a)    Identify the parts a, b, c.

(b)   Write the functions of c.

ü Answer:

(a) a. Funicle, b. Micropyle, c. Integuments.

(b) Protective covering of ovule.

4.   A typical angiosperm embryo sac is 8-nucleate and 7-celled. (3)

(a)    Name the cells that constitute egg apparatus.

(b)   Explain monosporic type of embryo sac development.

ü Answer:

(a) Synergids and egg.

(b) In this, one of the megaspores is functional while other three are degenerate.

2020 MARCH

1.   How can you differentiate true fruits from false fruits? (2)

ü Answer:

True fruit is developed from ovary.

False fruit is developed from any parts other than ovary (e.g. from thalamus).

2.   Define the following terms: (3)

a.      Autogamy

b.     Geitonogamy

c.      Xenogamy

ü Answer:

(a) Autogamy: Transfer of pollen grains from the anther to the stigma of the same flower.

(b) Geitonogamy: Transfer of pollen grains from the anther to the stigma of another flower of the same plant.

(c) Xenogamy: Transfer of pollen grains from the anther to the stigma of a different plant.

2019 SAY June

1.   Observe the relationship between the first two terms and fill in the blank. (1)

Funicle: Stalk of the ovule.

...................: Protective envelopes of the ovule. 

ü Answer:

Integuments. 

2.   Wind pollination is common in grasses. Write any three floral features in grasses that help in wind pollination. (3)

ü Answer:

Pollen grains are light and non-sticky.

Well exposed stamens.

Large and feathery stigma.

3.   Write any three parts of a monocot embryo and write one peculiarity of each of these three parts. (3)

ü Answer:

Scutellum: Single cotyledon.

Radicle: Lower end of the embryonal axis.

Coleorhiza: Sheath that encloses radicle.

2019 MARCH


1.   The early stages of embryo development are similar in both dicots and monocots. However, mature embryos have differences. Write two major differences between dicot embryo and monocot embryo. (2)

ü Answer:

Differences between dicot embryo and monocot embryo:


Dicot embryo

Monocot embryo

Two cotyledons

One cotyledon

Coleoptile absent

Coleoptile present

Coleorhiza absent

Coleorhiza present


2.   Double fertilization is a characteristic feature of angiosperms. (2)

a.      Which are the events in double fertilization?

b.     Name the triploid nucleus formed as a result of double fertilization.


ü Answer:

(a) Syngamy and Triple fusion.

(b) Primary Endosperm Nucleus (PEN).


3.   Observe the diagram of young anther given below. (3)



a.      Identify the parts labelled as A, B, C and D.

b.     Which layer nourishes the developing pollen grains?

ü Answer:

(a) A= Epidermis, B= Endothecium, C= Middle layers, D= Tapetum.

(b) Tapetum.


2018 SAY June


1.   Pollination by water is seen in Zostera and Vallisnaria. Enumerate its adaptations. (2)

ü Answer:

In Vallisneria, the female flower reaches the surface of water by the long stalk and the male flowers or pollen grains are released on to the surface of water.

In Zostera, female flowers remain submerged in water. Pollen grains are long and ribbon like. They are carried inside the water and reach the stigma.


2.   Depending on the source of pollen, pollination can be divided into three types. What are they? Explain each. (3)


ü Answer:

(a) Autogamy (self-pollination): It is the transfer of pollen grains from the anther to stigma of the same flower.

(b) Geitonogamy: It is the transfer of pollen grains from the anther to the stigma of another flower of the same plant.

(c) Xenogamy: It is the transfer of pollen grains from anther to the stigma of a different plant.


2018 MARCH


1.   Synergids have a special cellular thickening at micropylar tip. Write the name of name and function of the structure. (2)

ü Answer:

Filiform apparatus. It guides pollen tube into the synergids.

2.   In angiosperms, female gametophyte is known as embryo sac. Explain its development. (3)

ü Answer:

The functional megaspore develops into the female gametophyte.

Nucleus of the functional megaspore divides mitotically to form two nuclei. They move to the opposite poles, forming 2-nucleate embryo sac.

The nuclei again divide two times forming 4-nucleate and 8-nucleate stages of the embryo sac.

These divisions are free nuclear.

After the 8-nucleate stage, cell walls are laid down leading to the organization of the typical female gametophyte.


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