Sexual Reproduction in Flowering Plants 1

Question 1

what are the features of sexual reproduction

Answer 1

• 2 parents are involved
• gametogenesis( meiosis occurs which leads to variation).
• fertilisation

The defining feature of sexual reproduction is fertilisation. not gametogenesis.

Question 2

Types of flowers based on presence of reproductive whorls

Answer 2

i) Unisexual - well differentiated male and female organisms are present

a) Staminate - flower has only androecium and is dioecious (datepalm, papaya, coconut)

b) pistillate- flower has only gynoecium and is dioecious (datepalm, papaya, coconut)

ii) Bisexual - both androecium and gynoecium are present on the same flower and the plant is monoecious.eg china rose

Question 3

types of flower base don reprodutive phase and lifespan

Answer 3

i) Monocarpic- flowering and fruiting takes place only once in a lifetime
a) Annual plant- lifespan 1 year, 6 months vegetative growth and 6 months sexual growth

b) Biennial plant- lifepsan 2 years, 1 year veg. growth and 1 year sex. growth

ii) Polycarpic plants- flowering and fruiting takes place multiple times in a lifetime

Perennial plants- live for many years and hence polycarpic

Question 4

what are some plants which are perennial but monocarpic

Answer 4

Bamboo and Strobilanthus kunthiana

Question 5

general features of anther exception

Answer 5

Family Malvaceae( china rose family) have anther which is monothecous and bisporangiate.

Question 6

describe epidermis ( layer of microsporangium)

Answer 6

epidermis is outermost protective covering, it consits of parenchymatous cells that are arranged in a single cell thick layer.

Question 7

describe endothecium ( layer of microsporangium)

Answer 7

The endothecial cells help in dehiscence of anther.

Endothecial cells develop a fibrous thickening of α-cellulose fibres prior to dehiscence.

These develop on the inner side of the cell ( towards microsporangium), and are hygroscopic. They absorb water and hence remain in contact with the epidermal cells.

When these cells lose water, they lose contact with the epidermis and hence the epidermis ruptures leading to dehiscence

Callose bands are also present in the radial walls of endothecial cells.

In certain areas, the endothecial cells do not have fibrous thickenings or callose bands. These regions are called stomium or line of dehiscence

Question 8

what is the other name of line of dehiscence

Answer 8

Stomium

Question 9

describe middle layers ( layer of microsporangium)

Answer 9

1-3 cell thick layers of parenchymatous cells.

Perform function fo storage of food for nutrition of pollen grains.

It is ephemeral ( short lived) in nature and absent in mature anther.

Question 10

describe tapetum ( layer of microsporangium)

Answer 10

it is the innermost layer and acts as nutritive tissue

cells of tapetum have dense cytoplasm and more than 1 nuclei( it is polyploid and multinucleate)

absent in mature anther

Question 11

functions of tapetum

Answer 11

• provides nutrition to sporogenous tissue/ microspore mother cell/ pollen mother cells.
• form ubisch bodies ( which help to form exine of pollen grain, however these vesicular bodies are present in the tapetal cells).
• secrete sporopollenin ( whcih is present in ubisch bodies), which is used for formation of exine of pollen grain.
• secrete enzymes and hormones( callase enzyme)

-secrete pollen kitt substances

Question 12

what is pollen kitt substance

Answer 12

In plants which are pollinated via insects, the pollen grains have an oily outer layer called as pollen kitt. it is composed of lipids and carotenoids.

functions:
- oily outer covering to protect it from uv radiation
-yellow colour to attract insects
- sticky surface to attach to insects body.

Question 13

explain how anthers are developed from primary meristematic tissue

Answer 13

one part of the tissue is converted into the epidermis, and the rest of it remains as homogenous tissue within the epidermis.

from this homogenous tissue, any 4 singular cells ( one from each corner) differentiate into archesporial cells.

Archesporial cells undergo periclinal division( divison parallel to the longitudinal axis)

The daughter cell present outward forms the primary parietal cells which further mature into endothecium , middle layers and tapetum

The daughter cell present inwards forms the primary sporogenous tissue. On repeated mitosis it forms sporogenous tissue which forms microspore mother cells.

Question 14

explain microsporogenesis

Answer 14

out of Sporogenous tissue differentiates into a microspore mother cell.

The microspore mother cell develops a layer of callose around it which acts as the chekpoint for differentiation of mother cell.

the PMC/MMC undergoes meiosis to form microspore tetrad.

Callase enzyme, synthesized by tapetum. is used to break down the callose layer, hence the microspores seperate.

Question 15

describe the arrangement of microspore tetrad

Answer 15

The microspore tetrad has different arrangements ind ifferent species of plants.

In dicots, its tetrahedral

and monocots, its isobilateral

Question 16

explain formation of polllen

Answer 16

one microspore undergoes vacuolarisation- enlargement of cell due to the enlargement of vacuole.

Then the cell undergoes asymmetrical/unequal mitosis. The spindle fibres formed are of unequal length hence the chromosomes lie closer to one spindle pole. The division occurs unequally forming a larger and a smaller cell.

Question 17

what is the tube cell and generative cell

Answer 17

The tube cell is the bigger cell and it forms the pollen tube and provides noursihment to the generative cell

the generative cell is smaller and forms 2 male gametes by mitosis. 2 male gametes are non motile

When just tube cell and generative cell are present it is 2 cell stage

when tube cell and 2 male gametes are present it is the 3 cell stage.

Question 18

in which cell stage does fertilisation occurs? 2 cell or 3 cell?

Answer 18

in 60% of angiosperms, fertilisation occurs in 2 cell stage
in remaining plants at 2 cell stage.

This is because, energy si required to undergo mitosis to form 2 male gametes. In order to conserve energy, the mitosis does not take place until, the plant is assured that it has landed on a suitable stigma and is ready to germinate.

Question 19

describe exine

Answer 19

It is outermost, protective layer.

It is made of sporopollenin, the most resistant organic material/ It ismade of oxidative polymers of carotenoids.

it is resistant to
-phy- temp, humidity
-chem- acids, alkali
-bio-enzyme

Question 20

what are germpores

Answer 20

Germpores are regions where exine is absent. This regions give rise to the pollen tube.

monocolpate- 1 germpore- monocots and primitive dicots -
tricolpate- 3 germ pores - higher dicots

Question 21

describe intine

Answer 21

It is inner wall and continuous
It is made of cellulose and pectin

together, intine and exine are called SPORODERM or pollen wall

Question 22

what is palynology

Answer 22

study of pollen grains is called palynology

pollen grains are airborne allergens hence are called aeroallergens

Fever caused due to pollen grains is called hay fever.

Question 23

I) male gametophyte
ii) microsporophyll

Answer 23

I) pollen grains
II) Anther