Transcript Flower Structure

ANGIOSPERMS
The flowering
plants
© 2008 Paul Billiet ODWS
Spring crocus Crocus vernus
Flower structure
Flowers are reproductive structures
 The have evolved to send and receive
pollen from one flower to another
 This is process of pollination
 Flowers are developed from a series of
modified leaves
 These leaves are arranged in a rings
(whorls)
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© 2008 Paul Billiet ODWS
Types of pollination
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Wind
Animal
Water
Bumble bee Bombus hortorum on red clover Trifolium pratense
Yorkshire fog grass Holcus lanatus
© 2008 Paul Billiet ODWS
Animal pollination
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Usually insects
Also other flying
animals
e.g. hummingbirds or
fruit bats
Cerambycid beetle
pollinating bramble
Rubus fruticosus
© 2008 Paul Billiet ODWS
Flower structure
Dog rose Rosa canina
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Flower structure
Stigma
Style
Ovary
Petal
Anther
Sepal
Filament
© 2008 Paul Billiet ODWS
Pollination
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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
© 2008 Paul Billiet ODWS
Pollination
Small skipper Thymelicus flavus on marsh thistle Cirsium palustris
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Pollination
The honey bee Apis melifera on marsh thistle Cirsium palustris
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Pollination
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Some flowers are
highly specialised to
encourage only one
type of insect
Fox glove flowers
Digitalis purpurea
© 2008 Paul Billiet ODWS
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
 Pollen transferred from the anther on one
flower to the stigma of another flower on
a different plant = cross pollination
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© 2008 Paul Billiet ODWS
Fertilisation
Pollination ≠ Fertilisation
 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
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© 2008 Paul Billiet ODWS
Fertilisation
Pollen grain
Stigma
Style
Ovule
Embryo sac
Ovary
© 2008 Paul Billiet ODWS
Pollen tube
Fertilisation
Embryo sac
Polar nuclei
Egg cell
Micropyle
© 2008 Paul Billiet ODWS
Fertilisation
Pollen grains of the daisy
Bellis perennis
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Fertilisation
Germinating pollen grains of blue
bell, Hyacinthoides non-scripta
© 2008 Paul Billiet ODWS
The double fertilisation
Ovule
Nucellus
Pollen
tube
Male nucleus
+ 2 polar
nuclei =
endosperm
nucleus (3n)
Male nucleus
+ egg cell
= zygote (2n)
© 2008 Paul Billiet ODWS
Pollen tube
entering
micropyle
From flower to fruit
Marsh marigold Caltha palustris
© 2008 Paul Billiet ODWS
Fruits and seed dispersal
Animal dispersal Strawberry Fragaria vesca
Explosive dispersal
Bird’s foot trefoil
Lotus corniculatus
Animal dispersal
Wood avens
Geum urbanum
Wind dispersal
Ragwort Senecio
© 2008 Paul Billiet ODWS