Sexual Reproduction In Flowering Plants Flashcards
asexual reproduction
a type of reproduction where there is no fusion of gametes as only one parent is involved, and offspring produced are identical to the parent
sexual reproduction
a type of reproduction which gives rise to variation as it involves the fusion of male and female gametes, one from each parent
pollination
transfer of pollen from the anther to the stigma of a flower of the same species
self-pollination
transfer of pollen from the anther to the stigma of a flower on the same plant
cross-pollination
transfer of pollen from the anther to the stigma of a flower on a different plant of the same species
fertilisation
the fusion of the male (n) and female (n) gametes to produce a zygote (2n)
radicle
grows into the root
plumule
grows into the shoot
cotyledon
embryonic seed leaf
monocotyledon
contains one embryonic seed leaf
dicotyledon
contains two embryonic seed leaves
fruit
a developed seed leaf
dispersal
transfer (spreading out) of seeds away from parent plant
dormancy
a resting period when seeds undergo no growth and have reduced cell activity or metabolism
germination
the re-growth of the embryo after a period of dormancy, if the environmental conditions are suitable
location of male gamete formation
pollen grain
pollen grain development (Male)
microspore mother cell (2n) divides by meiosis in the pollen sac in the anther
tetrad of pollen is produced
pollen grains separate and the nucleus in each divides by mitosis
generative nucleus and tube nucleus formed, both haploid
tube nucleus
forms pollen tube
generative nucleus
divides by mitosis to produce two male gametes
location of female gamete formation
embryo sac
embryo sac formation (female)
megaspore mother cell (2n) divides by meiosis in the ovule
four haploid cells produced
three die off and one becomes the embryo sac
embryo sac divides by mitosis 3 times to produce eight haploid nuclei: two are polar nuclei one is egg cell
pollination methods
wind or animals/insects
wind pollination
eg sycamore tree, oak tree adaptations: no nector stigmas large, feathery anthers large, outside petal
animal/insect pollination
eg bees, dandelions, buttercups adaptations: petals brightly coloured, scented with nectaries small amounts of sticky pollen pollen larger
events leading to fertilisation
chemotropism; release of chemicals from the ovary which stimulates the pollen tube to develop from the tube nucleus in the pollen grain
pollen tube develops down the style to the ovule through the micropyle
generative nucleus moves down the pollen tube behind the tube nucleus
generative nucleus divides by mitosis twice; forms the male gametes
two male gametes enter the embryo sac through the micropyle
location of fertilisation
embryo sac
Double fertilisation
one male gamete fuses with the two polar nuclei to form the triploid endosperm nucleus
one male gamete fuses with the egg nucleus to form the diploid zygote
seed formation
integuments(ovule walls) - seed coat (testa)
ovule- seed
ovary-fruit
zygote 2n- embryo 2n (after dividing by mitosis) containing plumule, radicle, cotyledon
Endosperm nucleus 3n- endosperm( food store;fats,oils proteins)
cotyledon absorbs endosperm
classification of seeds
non endospermic (monocot) endospermic (dicot)
non endospermic seed
all of endosperm is absorbed
cotyledon is food store
eg peanut, broad bean
endospermic seed
retains some endosperm
endosperm is food store
eg maize,corn
walls of fruit
pericarp
seedless fruit
egg hasnt been fertilised
fruit formation
stimulated by auxins produced by the seeds
- Genetically - either naturally or by special breeding porgrammes eg bananas, pineapples
- Growth regulators- eg gibberllins produce seedless grapes
commercial regulator
ethene (inhibitor) breaks down chlorophyll
advantages of seed and fruit dispersal
minimises competition
avoids overcrowding
increases chance of survival
methods of fruit and seed dispersal
animal, wind, water, self
animal dispersal
hooked, sticky (to attach to coat), juicy, tasty (to allow digestion)
eg raspberries, stick-weed
water
air spaces, light, buoyant
eg coconut
wind
light, winged
eg sycamore
self
in a pod that bursts to release seeds
eg peas
advantages of dormancy
plant avoids harsh winter conditions
gives the embryo time to develop
provides time for dispersal
how dormancy is brought about
growth inhibitors on outer part of seed
testa is impermeable to oxygen,water
testa is too tough for embryo to emerge
application of dormancy in agriculture
optimum storage conditions can be provided, allows maximum growth
grower can choose when to sow seeds
artificial/commercial procedures used to break dormancy
physical damage - slightly damaging seed coat with a knife (scarifying)
pre-chilling- storing seeds in cold temp
light availability- exposing seeds to light/dark
factors necessary for germination
water- medium for metabolic reactions eg digestion, transport
oxygen- aerobic respiration
warmth- allows maximum enzyme activity, optimum for metabolic reactions
main events in germination
digestion of stored food in endosperm/cotyledon to provide soluble nutrients
respiration to produce ATP to carry out cell division
germination of a typical seed eg broad bean
water absorbed through micropyle - activates enzymes
food store broken down- brought to growing embryo
respiration occurs in embryo- ATP produced
radicle bursts and grows downward, plumule later develops in shoot above ground and photosynthesis in leaves begins
cotyledons below ground, remain as food store
cotyledons above ground
sunflower
cotyledons below ground`
broad bean
changes in dry mass in seeds during germination
endosperm or cotyledon mass decreases as embryo uses glucose stored here for respiration
embryo mass increases as glucose produced in photosynthesis
dry mass of total seed decreases due to respiration; loss of carbon dioxide causes loss in mass
dry mass
the mass of a tissue with its water content removed
why is dry mass recorded
water content varies from seed to seed
