4.2 Plant reproduction Flashcards
what is an angiosperm
plants that produce flowers
what is the reproductive organ of an angiosperm
flower
label an angiosperm
what is the stamen
male reproductive organs
what does the stamen contain
anther and filament
what is the carpel
female reproductive organ
what does the carpel consist of
stigma
style
ovary
function of sepal
protects the flower when in bud
function of receptacle
the thickened part of the cell, from which the flower grows
function of corolla
a ring of colourful petals inside the sepal
function of the nectary
found at the base of the flower, releases scented nectar to attract pollinators such as insects
function of petals
in insect pollinated plants they are colourful and have scent to attract insects
function of stamen
male parts
made of an anther and attached to a long filament
function of anther
pollen grains are produced inside 4 pollen sacs by meiosis
function of the filament
contains vascular tissue, which transports mineral ions and water to the developing pollen grains
function of the carpel
female parts
made of the stigma, style and ovary
function of ovules
made inside the ovary
contain an egg cell formed by meiosis
what is a calyx
a collection of sepals
are most adult flowers haploid or diploid
diploid
where does meiosis occur
within their reproductive tissues to make haploid spores
what are male spores also known as
pollen grains
what happens to pollen grains during pollination
each pollen grain produces 2 male gametes
what are female spores called
ovules
what do the ovule contain
the female gamete called the egg cell nucleus
definition:
pollination
the transfer of pollen grains from anther to the stigma of plant of the same species
insect pollinated vs wind pollinated
(6 comparisons)
- colourful petals, sometimes nectar guides vs usually no petals or small green and inconspicuous
- scent and nectar vs no scent or nectar
- anthers within the flowers vs anthers hanging outside flower
- stigma within the flower vs large, feathery stigmas hanging outside of flower
- small quantities of sticky, sculptured pollen produced vs large quantities of pollen produced
- produces larger pollen grains vs produces smaller pollen grains
what is the benefit of plants having anthers that hang outside the flower
pollen is caught easier
benefit of sticky sculptures pollen for pollination
pollen will stick to insects
DEFINITION
self-pollination
pollen is transferred from the anthers of one flower to the stigmas of the same flower/another flower of the same plant
DEFINITION
cross-pollination
pollen transferred from the anthers of one flower to the stigmas of a different flower of the same species
consequences of self-pollination
-results in inbreeding
- reduces genetic variation in the population
-increases chances of infavourable double recessive alleles
-depends upon random assortment of chromosomes and crossing over during meiosis and mutations to bring about variations
advantages of self-pollination
preserves good genomes which are suited for a stable environment
advantages of cross-pollination
- greater variation
-reduces the chance of producing harmful allele combinations
-greater evolutionary significance
what does having greater evolutionary significance mean
more different combinations of alleles means some members of a population are more likely to survive if the environment changes (natural selection)
3 ways plants reduce self-pollination
-stamen and stigma ripen at different times of the year
- the anthers are below the stigmas so the pollen cannot fall onto it
-separate male and female flowers on the same plant
what is protandry
where the stamens ripen first
what is protogyny
stigma ripens first
label cross section of male gamete (anther)
what is the tapetum
layer of cells surrounding the pollen sacs
function of tapetum
provides nutrients to the developing pollen grains
protects the pollen grains from chemicals, UV light and drying out
what does an anther contain
4 pollen sacs (in pairs) which is where the pollen grains develop
what are found in the pollen grains
male gametes
what do pollen sacs contain
diploid pollen mother cells
what are large number of pollen mother cells produced by
mitosis
what happens to each pollen mother cell
meiosis to form 4 pollen grains
what happens to young pollen grains
exit in groups callled tetrads
explain the formation of pollen
pollen mother cell (d) is developed by mitosis, undergo meiosis to produce a tetrads of four haploid cells. the tetrads undergo. tetrad will undergo mitosis and a pollen grain with 2 haploid nucleus will be formed. the cell wall of the pollen grain thickens and a mature pollen grain is formed
label a mature pollen grain
what happens to the nucleus of a mature pollen grain
divides by mitosis to form 2 nuclei and a tube nucleus
explain dehiscence
when pollen is mature, anthers outer layers dry out, this causes tension in lateral grooves and dehiscence occurs
pollen sacs burst exposing the pollen grains into the air
what happens in each ovule
(female gamete)
a megaspore mother cell, surrounded by cells of the nucleus undergo meiosis making 4 haploid cells. three disintegrate and the remaining undergo three rounds of mitosis producing 8 haploid nuclei . one is the female gamete. 2 of the haploid nuclei fuse to make a diploid nucleus called the polar nuclei
where is the polar nuclei found
embryo sac
briefly explain pollen grain maturation
pollen cell mother (2n)
(MEIOSIS)
4 immature pollen grains in tetrad (n)
each nucleus—-mitosis
-generative nucleus. —–tube nucleus
gn undergo mitosis to form 2 male nuclei
briefly explain embryo sac maturation
megaspore mother cell
(meiosis)
4 megaspore
3 disintegrate/2 undergo 3 rounds of mitosis
3 antipodals
2 synergies
1 oosphere
1 polar nucleus
why is double fertilisation double
- one forms a zygote
-one to form the endosperm
role of synergids
play a role in pollen tube guidance during fertilisation
ovule development
role of antipodal cells
-antipodal cells are thought to play a role in embryo nutrition as seeds germinate into seedlings
what does double fertilisation invovle
2 male gametes in 2 separate fertilisation events
what are the 2 fertilisation events
fertilisation of female gamete to form a diploid zygote and fertilisation of the polar nuclei to form a triploid endosperm nucelus
explain the first step of double fertilisation
- pollen grain lands on stigma and absorbs water. if pollen grain and stigma are compatible, the pollen grain will germinate
what will the stigma contain
- a sticky sugary solution, allows pollen grain to adhere and provides nutrition
double fertilisation
what happens after the pollen grain germinates
pollen tube will be produced, at the tip of this is a male tube nucleus and behind it is the generative nucleus
double fertilisation
role of the tube nucleus
controls the growth of the pollen tube
double fertilisation
what is found behind the tube nucleus
generative nucleus
double fertilisation
what happens as the the pollen tube grows and during germination
the generative nucleus undergoes mitosis to form 2 nuclei (male gametes)
double fertilisation
what does the pollen tube nucleus code for
the synthesis of hydrolase enzymes (cellulase and protease)
double fertilisation
describe the growth of pollen tube
grows out of the pollen grain through a gap in the cell wall called the pit. it grows against a gradient of chemo attractants (e.g GABA) from the ovules
double fertilisation
what type of response is the growth of the pollen tube
positive chemotrophic response, the pollen tube grows towards chemicals secreted by the embryo sac
double fertilisation
what does the pollen tube do after growing against the gradients
digests its way down the style,
pollen tube continues to grow through the micropyle and into the embryo sac
double fertilisation
what are the products of digestion used for
used by the growing pollen tubes
double fertilisation
after the pollen tube grows through the micropyle and into the embryo sac, what happens to the tube nucleus
it disintegrates as it is no longer needed
double fertilisation
what happens to the tip of the pollen tube after the tube nucleus disintegrates
the tip of the pollen tube opens to release the two male gametes ( generative nuclei) into the embryo sac
double fertilisation
what happens after the 2 male gametes are released
one of the male gametes fuse with the female gamete (oosphere) to form a diploid zygote (2n)
the other male gamete fuses with the diploid polar nuclei to form a triploid endosperm nucleus (3n)
double fertilisation
what happens to synergids and antipodal cells
they play no further role
summary of double fertilisation
- generative nucleus (n) + polar nucleus (2n) = endosperm nucleus (3n)
- generative nucleus (n) + egg cell nucleus (n) = zygote (2n)
seed and fruit development
what does the fertilised ovule develop into
a seed
what happens within a seed
the diploid zygote divides by mitosis to become the embryo
what does the embryon consist of
the plumule
the radicle
one/two cotyledons
what is the plumule
radicle
cotyledon
developing shoot
developing root
seed leaves
what is the testa
the outer coat, the integument hardens
monocot vs dicot
dicotyledon has 2 seed leaves (cotyledon) e.g broad bean. they are endospermic
monocotyledon has 1 cotyledon e.g. maize
explain cereal grains
are a monocot
remain as food store because they’re endospermic. remain small as seeds become dormant when active growth is suspended. germination will only happen when specific conditions are met
what would happen if seeds fell close to parent plant
- parent plant would be more successful at obtaining water and minerals from soil.
- parent plant would be taller and cast shade on seedling (lack of photosynthesis)
- seedling would be out-competed
explain how seeds have developed for dispersal of seeds
seeds have evolved as a survival strategy for a terrestrial mode of life
plants have developed different mechanisms to enable the dispersal of seeds which reduces competition following germination and increases the chances of growth into mature plants, also allows the colonisation of new habitats
different methods of seed dispersal
rolling
wind
transport
carrying
bursting
seeds and survival
seeds can remain dormant for very long times, dormant seeds have very low metabolic rates. the testa is chemically resistant (to allow seeds to survive adverse chemical conditions)
dormant seeds have a water content below 10%
the cotyledons of the endosperm provide nutrients to the seed until germination when the seedling photosynthesise
definition
germination
is the biochemical and physiological process through which a seed becomes a photosynthesising plant
what is needed for germination
suitable temp- enzymes to work best (synoptic)
water- mobilise enzymes (synoptic)
oxygen- aerobic respiration (links)
light/dark- some species germinate in the light, some in the dark
germination in a non-endospermic seed
(broad bean/ dicotyledon)
- cotyledons have absorbed the food reserves, the seed imbibes water through the micropyle
what is imbibing
means to absorbs water through ultramicroscopic
germination in a non-endospermic seed
(broad bean/ dicotyledon)
what happens after the seed imbibes water
the cotyledons swell, the testa splits to allow entry of more oxygen for hydrolysis.
food reserves from the cotyledons, starch and proteins are mobilised through hydrolysis into soluble products
what happens to these soluble products after they are hydrolysed
transported to the embryo and carried in the phloem to the apical (lots of mitosis) meristem of the plumule and radicle
germination in a non-endospermic seed
(broad bean/ dicotyledon)
what happens in the plumule and radicle
rapid cell division, some sugars are converted to cellulose for cell walls, aerobic respiration releases energy from sugars and amino acids to synthesise new proteins (CO2 produced)
germination in endospermic seed (e,g, maize)
following imbibition of wate, giberellin is released by the embryo
what is maize
a monocotyledon, its food reserves are stored within the endosperm
what is giberellin
is a plant growth regulator
germination in endospermic seed (e,g, maize)
what does gibberellin do
diffused to the aleurone layer which contains proteins. it switches on genes in the aleurone layer to synthesis amylase and protease
germination in endospermic seed (e,g, maize)
what do the amino acids produces in the aleurone layer used for
used to synthesise amylase. amylase diffuses from the aleurone layer into the endosperm to hydrolyse starch.
germination in endospermic seed (e,g, maize)
what is the job of the maltose and glucose that are produced
they diffuse into the radicle and plumule of the embryo. in the emrbyo they are used in aerobic respiration and growth i.e. brings the seed out of dormancy
explain the growth of the radicle and plumule in a DICOT
radicle is positive geotrophic and negative phototrophic = grow downwards
plumule is positively phototrophic and negatively geotrophic =grows upwards
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