angiosperms and reproduction
DESCRIPTION
For part of topic 9.3 in the IB curriculumTRANSCRIPT
REPRODUCTION IN
ANGIOSPERMSTopic 9.3•Flower structure•Pollination•Fertilization•Germination
Flower structure• Flowers are reproductive structures• They have evolved to send and receive pollen
from one flower to another• This is the process of pollination• Flowers are developed from a series of modified
leaves• These leaves are arranged in a rings (whorls)
Types of pollination• Wind• Animal• Water
Bumble bee Bombus hortorum on red clover Trifolium pratense
Yorkshire fog grass Holcus lanatus
Animal pollination• Usually insects• Also other flying
animals • e.g. hummingbirds or
fruit bats
Cerambycid beetle pollinating bramble Rubus fruticosus
Flower structureStigma
Style
OvaryPetal
Sepal
Filament
Anther
Pollination• Pollen grains contain the
male gametes of the plant• They are picked up by a
pollinator and transferred to another flower
• Plants tend to specialise in pollinators
• This ensures the pollen is delivered to same species of plant
Yellow archangel Lamiastrum galobdolon being pollinated by a bumble bee Bombus hortorum
Pollination
• Most species of flowering plants are hermaphroditic• Pollen from a flower could land on the stigma of the
same flower or another flower on the same plant = self-pollination• Less genetic variation in species
• Pollen transferred from the anther on one flower to the stigma of another flower on a different plant = cross-pollination
The honey bee Apis melifera on marsh thistle Cirsium palustris
Fertilization• Pollination ≠ Fertilization• The male gamete (the male nucleus) has to get
to the egg cell• The egg cell lies in an ovule in an ovary at the
centre of the plant• The pollen grain germinates on the stigma• It grows a pollen tube down the style• It male nuclei travel down the pollen tube to the
ovule
Fertilization
Style
StigmaPollen grain
Ovule
Embryo sac
Pollen tubeOvary
Fertilization
Egg cell
Polar nuclei
Embryo sac
Micropyle
Fertilization
Pollen grains of the daisy Bellis perennis
Fruits and seed dispersal
Animal dispersal Strawberry Fragaria vesca
Wind dispersal Ragwort Senecio
Explosive dispersal Bird’s foot trefoil Lotus corniculatus
Animal dispersalWood avens Geum urbanum
Conditions for seed germination
Other seeds require more specific conditions:• Fire • Freezing • Passing through digestive system of a seed
dispersing animal • Washing to remove inhibitors (beans) • Erosion of the seed coat (Poppy)
Seeds require a combination of certain conditions to germinate: • Oxygen for aerobic respiration• Water to metabolically activate the cells• Temperature for optimal function of enzymes• Each seed has its own particular combination of the above three
factors
• Water is absorbed (imbibition)• Giberillin (plant growth hormone) is
made• Giberillin causes enzymes to be made
(amylase)• Starch is hydrolysed to maltose which
can then be absorbed by the young plant• Maltose can be further hydrolysed to
glucose for cellular respiration or polymerised to form cellulose for the cell walls.