plant reproduction Flashcards
parts of a flower
petal, sepal, stamen (anther, filament), carpel (stigma, style, ovary)
function of petal
- brightly coloured to attract insects
- provide a platform for insects to land
- have nectar guides that guide insects to nectaries for nectar
function of sepals
enclose and protect flower bud
function of stamen
anther: produces pollen grains that are released when the anther matures
filament: holds the anther in a suitable position to disperse pollen
function of carpel
stigma: receives pollen grains, releases a sugary fluid that stimulates pollen grains to germinate
style: connects stigma to ovary
ovary: contains 1 or more ovules which are the site of fertilisation
what is pollination
the transfer of pollen grains from the anther to the stigma
what is self-pollination
the transfer of pollen grains from the anther to the stigma of the same flower or different flower on the same plant
factors favouring self pollination
- flowers are bisexual with anthers and stigmas maturing at the same time
- stigma situated directly below anthers
- (some bisexual flowers never open)
advantages of self pollination
- only 1 parent needed
- may inherit beneficial qualities from parent
- higher chance of pollination
- less pollen and energy wasted
disadvantages of self-pollination
- less genetic variation in offspring to be well adapted to environmental change
- weaker offspring, less resistant to diseases
what is cross pollination
- transfer of pollen grains from 1 plant to the stigma of a flower on a different plant of the same species
features favouring cross-pollination
- flowers are either male or female
- anthers and stigma of flower mature at different times
- stigmas are situated far from anthers
advantages of cross pollination
- may inherit beneficial qualities from both parents
- greater genetic variation among offspring
- more viable seeds produced
disadvantages of cross pollination
- 2 plants required
- depends on external factors for pollination → lower probability of pollination
- more energy and pollen required
insect vs wind pollinated flowers in terms of petals
petals are large and brightly coloured vs petals are small and dull
insect vs wind pollinated flowers in terms of nectar and scent
nectar present and fragrant + sweet smelling vs nectar absent + odourless
insect vs wind pollinated flowers in terms of stigmas
small, compact, do not protrude out of flower vs large, feathery, protrude out of flower
insect vs wind pollinated flowers in terms of stamens
not pendulous, do not protrude out flower vs large, pendulous, protrude out flower
insect vs wind pollinated flowers in terms of pollen
fairly abundant, larger with rough surfaces to cling onto pollinators vs more abundant, smooth surfaces, tiny and light
insect vs wind pollinated flowers in terms of nectar guide
may be present to guide pollinators toward nectar vs absent
how does a pollen grain reach the ovary from the stigma?
- pollen grain germinates after coming into contact with the stigma, in response to the sugary fluid secreted by the stigma
- a pollen tube grows out from the pollen grain, and the male gamete enters the pollen tube
- as the pollen tube grows, it secretes enzymes to digest the surrounding tissue of the stigma and style. the pollen tube grows down the style into the ovary
- pollen tube enters the ovule through the micropyle, an opening in the ovule
how does plant fertilisation occur
- in the ovule, the tip of the pollen tube absorbs sap and bursts, releasing the male gamete
- the nuclei of the male gamete and ovum fuse to form a zygote
