Sexual Reproduction in Flowering Plants 1 Flashcards
what are the features of sexual reproduction
- 2 parents are involved
- gametogenesis( meiosis occurs which leads to variation).
- fertilisation
The defining feature of sexual reproduction is fertilisation. not gametogenesis.
Types of flowers based on presence of reproductive whorls
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
types of flower base don reprodutive phase and lifespan
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
what are some plants which are perennial but monocarpic
Bamboo and Strobilanthus kunthiana
general features of anther exception
Family Malvaceae( china rose family) have anther which is monothecous and bisporangiate.
describe epidermis ( layer of microsporangium)
epidermis is outermost protective covering, it consits of parenchymatous cells that are arranged in a single cell thick layer.
describe endothecium ( layer of microsporangium)
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
what is the other name of line of dehiscence
Stomium
describe middle layers ( layer of microsporangium)
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.
describe tapetum ( layer of microsporangium)
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
functions of tapetum
- 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
what is pollen kitt substance
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.
explain how anthers are developed from primary meristematic tissue
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.
explain microsporogenesis
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.
describe the arrangement of microspore tetrad
The microspore tetrad has different arrangements ind ifferent species of plants.
In dicots, its tetrahedral
and monocots, its isobilateral
explain formation of polllen
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.
what is the tube cell and generative cell
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.
in which cell stage does fertilisation occurs? 2 cell or 3 cell?
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.
describe exine
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
what are germpores
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
describe intine
It is inner wall and continuous
It is made of cellulose and pectin
together, intine and exine are called SPORODERM or pollen wall
what is palynology
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.
I) male gametophyte
ii) microsporophyll
I) pollen grains
II) Anther
