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Angiosperms :smiley: (features (flowers, ovules ad seeds enclosed (ovary…
Angiosperms :smiley:
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life cycle
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OVULE(S) in OVARY
:check: young (immature) ovule= megasporangium surrounded by integuments
:fountain_pen: mega sporagium contains nucellus(nutritive) + megasporocyte (2n)->meiosis->megaspore(n) (one functional)
:fountain_pen: megaspore-> mitosis -> megagametophyte(8 nucli)= 'embryo sac'(n)
:check: so older(mature) ovule= megagametphyte(embryo sac) surrounded by nucleus and integuments
DEVELOPMENT OF MEGAGAMETOPHYTE (FEMALE)
:large_blue_circle:Diploid megaspore mother cell divides meiotically to yield four megaspores,three are degenerate
:large_blue_circle:nucleus of remaining mwgaspore divides 3 times by mitosis to produce 8-celled female gametophyte(embryo sac)
:large_blue_circle: Two of these nuclei migrate toward centre of embryo sacs to form the polar nuclei. These may fuse into a diploid nucleus
:large_blue_circle: Three nuclei are found at the inner end + antipodial cells and three at mycropylar end = two synergids and the female gamete, egg
POLLEN,male
:check: pollen sac is microsporangium in Anther (normally 4 per anther)
:fountain_pen: microsporangium contains tapetum layer(nutritive)+ many microsporocytes (2n)--> meiosis-->microspores(n)=young pollen(pollen grains;all functional)
:fountain_pen:microspore--> mitosis--. young microgametophyte(2nuclei= mature pollen
:fountain_pen:germinating pollen tube(3 nuclei)= mature microgametophyte
pollen (10 to 25 um diam) has the following features:
:wavy_dash: thick outer weall of pllen grain called exine- the exine of sporopollenin,composite of substances (similiar to cutin and suberin),one of the most durable natural substances and enable pollen to remain unchanged for thousand of years.
:wavy_dash:Intine- inner wall,thin,made of celluose and pectin; may protude throough holes in exine(pollen tubes protrudes through such a hole)
DEVELOPMENT OF MICROGAMETOPHYTE(male)
:black_circle: each microspore nucleus in pollen grain undergoes mitosis once to form two celled strcture
:black_circle: The microgametophyte is just three nuclei within the pollen/pollen tube(polle tube normally forms by 2nd division)
:black_circle: one sperm will fertilize the egg while the other will fuse with the polar nuclei to form the tripliod endosperrm cell: DOUBLE FERTILIZATION
pollination
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Types of Pollination
:green_cross:self-Pollination
withi same flower or btwen flowers on the same plant
:green_cross:Cross'Pollination
between anther of one plant and stigma of another plant of same species (if different = hybrids)
n.b elaborate systems evolved with animal-pollinator in many angiosperm species
Pollination systems
:check: A flower is usually adapted for its pollinator
:check: Floral morphology is directly related to pollinator type
:check:The specialized adaptations of the flower fr a pollinator type are collectely know as pollination Syndromes or systems
:check:Plants differ in degree of their specialization for a particular pollinator (specialist or generalist)
Pollinators
1.Abiotic agents
:green_cross: Anemophily: Pollination by wind
:green_cross: Hydrophily:
Pollination by water
- Biotic agents :animals
:green_cross: Zoophily: pollination by animals such as birds,bats,insects,e.g
Entomophilly:insect pollination
