2.4 - sexual reproduction in plants Flashcards
what’s a dicotyledon
plant that produces seeds that contain 2 cotyledons; they have 2 primary leaves
what’s an insect pollinated flower
type of flower that relies on insects to transfer pollen grains between flowers
what’s the calyx
- first part of flower formed
- consists of leafy structures that protect flower during development
what’s the corolla
all the petals of a flower
what’s the carpel
female part of plant consisting of stigma, style, + ovary
what’s the stamen
male part of plant consisting of anther + filament that’s involved in production of male gametes in form of pollen grains
describe the adaptations of insect pollinated plants
- internal anthers + small stigma directly touch insects
- large, bright petals + nectar from glands attract insects
- may produce chemicals to mimic sent of female insects or to intoxicate insects
- grow individually
- large pollen grains, sometimes w/ projections that attach to insect
what’s a wind pollinated plant
type of flower relying on wind to transfer pollen grains between flowers
describe the 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 (no need to attract insects)
- grow densely over large area
- light pollen grains
how does pollen grain form in anther
- large numbers of pollen mother cells produced by mitosis
- meiosis of diploid mother cells in anther forms 4 haploid microspores
- haploid microspores mature into pollen grains via mitosis
describe role of tapetum in pollen grain development
- specialised layer of cells in anther
- provides nutrients to developing pollen grains
describe the structure of mature pollen grains
generative cell (haploid nucleus) - produces 2 male gametes via mitosis
pollen tube cell (has own nucleus) - elongates to penetrate ovule
outer protective coating
define dehiscence
splitting of anther resulting in release of pollen grains
how does ovule form in ovary
- meiosis of megaspore cell produces 4 haploid megaspores
- growth + development (involving 3 meiotic divisions) of one of the megaspores
- embryo sac forms containing 8 haploid nuceli
describe the structure of the embryo sac
- 2 polar nuclei form endosperm
- ovum forms zygote
- 2 synergids help generative nucleus of pollen grain to reach ovum
- 3 antipodal cells
- outer protective coating
define pollination
deposition of pollen onto stigma from anther
name the 2 types of pollination
- cross pollination
- self pollination
what’s cross pollination
type of pollination in which pollen is transferred from anther of one plant to stigma of different plant
what’s self pollination
type of pollination in which pollen is transferred from anther of plant to stigma of same plant
compare genetic diversity produced by cross + self pollination
cross pollination results in plants w/ greater genetic diversity
self pollination produces plants w/ less diversity
compare genetic diversity produced by cross + self pollination
cross pollination results in plants w/ greater genetic diversity
self pollination produces plants w/ less diversity
outline the adaptations of flowers that promote cross pollination
- maturation of pollen + ovary at different times
- physical features prevent self pollination, e.g: heterostyly, male + female flowers on different parts of the plant
where does double fertilisation occur
embryo sac of ovule
how do male nuclei reach embryo sac
- pollen grain from one plant lands of stigma of another
- mitosis of pollen grain to form a pollen tube nucleus + 2 male gametes
- pollen tube grows from grain down to ovule via digestion of style
- pollen tube delivers 2 male gametes
how does pollen tube enter into embryo sac
via micropyle
define micropyle
- pore in integument of ovule through which pollen tube enters embryo sac
- remains as pore in testa (seed coat)
what happens in double fertilisation
in embryo sac of ovule:
- one sperm fertilises ovum to form diploid zygote
- one sperm cell fuses w/ 2 polar nuclei to form triploid primary endosperm
what happens to ovule following double fertilisation
develops into seed
how is diploid embryo formed following double fertilisation
diploid zygote undergoes mitosis to form diploid embryo
how is endosperm formed
nucleus of triploid endosperm divides by mitosis to form endosperm
what’s the function of the endosperm
acts as nutrient source for embryo
what structure forms the testa
integuments develop into testa
what happens to ovary following double fertilisation
develops into fruit wall surrounding seed
what’s the plumule
part of plant embryo that develops into primary shoot
what’s the radicle
part of plant embryo that develops into root
what’s the hilum
scar of testa as result of separation from its funicle
define germination
process by which plant grows from seed
give an example of non-endospermic seed
broad bean (Vicia faba)
describe the stages of germination in a non-endospermic seed
- seed absorbs water through micropyle causing swelling of cotyledon, enzyme activation + rupture of seed coat
- food reserves from cotyledons are hydrolysed
- provides energy for growth of plumule + radicle, as well as respiration
describe the stages of germination in an endospermic seed
- seed absorbs water, activating embryo to secrete cell-signalling plant growth factor, gibberellin
- gibberellins induce synthesis of amylase
- amylase diffuses to endosperm layer + causes hydrolysis of starch to glucose
state the factors affecting seed germination
- water availability (trigger secretions of gibberellin)
- temperature
- availability of O2 for respiration
- use of fertiliser provides extra nutrients for growth
