Sexual reproduction of plants

Gametes

haploid cells capable of fusion (into zygote)

stamen

male parts of flower - anther + filament

Gametes

haploid cells capable of fusion (into zygote)

stamen

male parts of flower - anther + filament

anther

produces pollen grains by meiosis

filament

contains vascular bundle to bring food and water to anther

receptacle

part from which flowering parts arise, supports plant

sepal

• leaf-like

• green, turns brown

• protects flower when it is a bud

carpel

female parts of flower - style, ovary, stigma

style

pollen tube goes through

stigma

where pollen lands

after fertilisation the ovule becomes

and ovary becomes

seed

fruit

cells lining inside of the anther are

diploid

tapetum role

feed pollen sac

pollen grain formation

1. pollen mother cells divide by x

2. forming x

3. breaks apart into pollen grains / x

4. divide by x to form male gamete nuclei

meiosis

tetrad

microspores

mitosis

male gamete nuclei

generative nucleus, tube nucleus

pollen grain makes

2 male haploid gametes

when pollen grains mature walls of anther x

causes anther to x

dry and shrivel

split (dehiscing), burst and expose the pollen grains

female gamete formation 1

diploid embryo sac mothercell (megaspore mothercell) in ovule divides by meiosis to form 4 haploid cells (3 degenerate nuclei + embryo sac)

female gamete formation 2

embryo sac (megaspore) undergoes mitosis a further 3 times forming 8 haploid nuclei

female gamete formation 3

5 haploid nuclei die, 2 form polar nuclei and 1 forms egg

fertilisation definition

the fusion of a male gamete with a female gamete to form a diploid zygote

fertilisation process

1. Pollen grain lands on stigma

2. tube nucleus forms from pollen tube - connects to micropyle in integuments

3. generative nucleus divides by mitosis in pollen tube to form 2 sperm nuclei

4. double fertilisation occurs

double fertilisation

sperm nucleus + egg cell → zygote

sperm nucleus + 2 polar nuclei → endosperm (3n)

endosperm

• acts as food store

• lipids and starch

• dicots will absorb it to produce leaves

cotyledon

embryonic seed leaf

endospermic seed

contains some endosperm when fully formed

pollination

transfer of pollen from an anther to a stigma of a flower from the same species

self pollination

same plant

advantage: guarantees reproduction if pollenating agent is not there

cross pollination

different plant same species

advantage: increases genetic variation, improves survival chances

wind pollination adaptions

• long stamens outside the flower

• large quantities of very light pollen

• long feathery stigmas

animal pollination flower adaptions

• brightly coloured petals

• sticky stigma

seed formation

• ovule develops into seed

• growth regulators or selective propagation for seedless fruit

testa

protects embryo

plumule

develops into shoot

radicle

develops into roots

embryo

develops into new plant

monocots vs dicots seed

monocots don’t store food in cotyledon, embryo absorbs endosperm

dicots store food in cotyledon, embryo absorbs food from endosperm and cotyledon

germination

the regrowth of the embryo after a period of dormancy if environmental conditions suitable

germination conditions

• water (solvent)

• suitable temperature - optimum enzyme activity

• oxygen - aerobic respiration (energy)

fruit develops from

ovary

dispersal of seeds important for

increased survival rates and to prevent competition

Dormancy

The resting period when seeds undergo no growth and have reduced metabolism

Causes of dormancy

• Growth inhibitors present in testa

• testa may be impermeable to water and oxygen

• testa too hard for embryo to emerge

advantages of dormancy

• survival, germination when conditions suitable

• greater time for embryo development

• reduced competition

dormancy in horticulture

• maximise growing season

• optimum storage and sowing conditions

Seedling growth 1 : absorbs water

• enters through micropyle through testa

• allows enzymes to activate → digestion

seedling growth 2 : digestion

oils by lipase to fatty acids and glycerol

starch to glucose by amylase

protein to amino acids by proteases

seedling growth 3 (uses of digestion products)

• glucose and amino acids used to make cell walls + enzymes

• fat + some glucose used for some energy in respiration

seedling growth 4 : products

• the products of digestion are moved to the growing embryo

• it absorbs them

seedling growth 5 : weight

• dry weight of seed falls as food stores used up in respiration

• as weight of food stores fall, weight of embryo increases

seedling growth : bursting

• radicle bursts through testa and the plumule is now above ground with leaves

• once leaves photosynthesise, dry weight of seedling increases again

formation of fruit

• from ovary under influence of growth regulators (auxins produced by seeds)

• wall of ovary becomes wall of fruit - pericarp

parthenocarpy

seedless fruit production

commercial plant growth regulator (ripen fruit)

ethene

ethene production inhibitor (storage in winter)

Carbon dioxide

why dry weight (weight excluding water)?

different amount of water in different seeds would affect the readings

changes in dry mass of seeds during germination

• mass drops - respiration of stored food

• mass increases again - photosynthesis

changes in dry mass of seeds during germination DICOTS

• endosperm mass decreases as used up by embryo

• embryo mass increases due to food from endosperm