Unit 4.2 - Sexual reproduction in plants (physicsandmathstutorflashcards)
what is a dicotyledon
a plant that produces seeds containing 2 cotyledons
2 primary leaves
what is an insect-pollinated flower
a type of flower that relies on insects to transfer pollen grains between flowers
what is the calyx
-first part of a flower which is formed
-consists of leafy structures that protect the flower during development
what is the corolla
all of the petals of a flower
what is the carpel
the female part of the plant
what does the carpel consist of
- stigma
- style
- ovary
what is the stamen
the male part of the plant involved in the production of male gametes
what form do male gametes take
pollen grains
what are the parts of the stamen
- anther
- filament
what are the 5 adaptations of insect-pollinated plants
- internal anthers + small stigma (directly touch insects)
- large, bright petals and nectar from glands (attract insects)
- produce chemicals (to mimic scent of female insects)
- grow individually
- large pollen grains with projections (attach to insect)
what is a wind-pollinated plant
a type of flower that relies on wind to transfer pollen grains between flowers
describe the 6 adaptations of wind-pollinated plants
- external anthers (optimise pollen dispersal)
- excess pollen (compensates for wind wastage)
- feathery stigma (catches pollen from air)
- small dull petals
- grow densely
- light pollen grains
how does a pollen grain form in the anther
- large number of pollen (2n) mother cells produced by mitosis
- meiosis of mother cells in anther = four (1n) haploid microspores
- (1n) microspores mature into pollen grains via mitosis
describe the role of the tapetum in pollen grain development
- specialised layers of cells in the anther
- provides nutrients to developing pollen grains
describe the structure of mature pollen grains
- generative cell (haploid nucleus) produces two male gametes via mitosis
- pollen tube cell (has own nucleus) elongates to penetrate ovule
- outer protective coating
define dehiscence
splitting of the anther resulting in the release of pollen grains.
how does the ovule form in the ovary
- meiosis of megaspore cell = four (1n) megaspores
- growth + development (3 mitotic divisions of a megaspore)
- embryo sac forms (contains eight 1n nuclei)
Describe the structure of the embryo sac
- 2 polar nuclei (form endosperm)
- ovum (forms zygote)
- two synergids (help generative nucleus of pollen grain to reach ovum)
- three antipodal cells
- outer protective coating
define pollination
the deposition of pollen into a stigma from an anther
what are the 2 types of pollination
- cross pollination
- self pollination
what is cross pollination
when pollen is transferred from an anther of one plant to a stigma of a DIFFERENT plant
what is self-pollination
when pollen is transferred from an anther of one plant to a stigma of the SAME plant
where does double fertilisation occur
embryo sac of ovule
how do the male nuclei reach the embryo sac
- pollen grain from one plant lands on the stigma of another
- mitosis of pollen grain to form a pollen tube nucleus and two male gametes
- pollen tube grows from the grain down to the ovule via the digestion of the style
- pollen tube delivers two male gametes
how does the pollen tube enter into the embryo sac
via the micropyle
what is the micropyle
- pore in the ovule where the pollen tube enters the embryo sac
- remains as a pore in the testa (seed coat)
what happens during double fertilisation
in the embryo sac of ovule:
- 1st male gamete fuses with female gamete = (2n) zygote
- 2nd male gamete fuses with 2 polar nuclei = (3n) primary endosperm
what happens to the ovule during double fertilisation
develops into the seed
how is the (2n) embryo formed following double fertilization
diploid zygote undergoes mitosis = 2n embryo
how is endosperm formed
nucleus of triploid endosperm divides by mitosis = endosperm
what is the function of the endosperm
acts as a nutrient source for the embryo
what structure forms the testa
integuments develop into the testa
what happens to the ovary following double fertilization
it develops into a fruit wall surrounding the seed
what is the plumule
the part of a plant embryo that develops into the primary shoot
what is the radicle
the part of a plant embryo that develps into the root
what is the hilum
a scar on the testa as a result of separation from its funicle
define germination
the process by which a plant grows from a seed
give an example of a non-endospermic seed
broad bean
describe the stages of germination in a non-endospermic seed
- seed absorbs water (through micropyle) causing cotyledon swelling = enzyme activation + rupture of seed coat
- food reserves from cotyledon are hydrolysed
- provides energy for growth of plumule+radicle (and respiration)
describe the stages of germination in an endospermic seed
- seed absorbs water (activating embryo to secrete gibberellin)
- gibberellins induce the synthesis of amylase
- amylase diffuses to the endosperm layer and causes the hydrolysis of starch into glucose
state the factors affecting seed germination
- water availability
- temperature
- availability of O₂ (for respiration)
- use of fertilisers provide extra nutrients for growth
