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Sexual reproduction in plants
Structure
Receptacle
Calyx
Sepal
Corolla
Petal
Stamen
Filament
Anther
Carpel
Ovary
Ovule
Style
Stigma

Function
Swollen, hollow base of carpel
...

The outer whorl of sepals around the flower
...

The inner whorl or collection of petals
Brightly coloured whorl or leaf like structures
A male reproductive organ of a flower, made of the filament and the anther
Elongated structure to carry food and water to the anther
The site of pollen production in the flower through meiosis, which is then
stored in pollen sacs
...

The female reproductive organ of a flower, made of the stigma, style and ovary
The fertile part of the carpel, containing ovules then developing into fruit
...

The female gamete which produces an egg after fertilisation
...
It is digested through by the pollen
tube nucleus during fertilisation
...


Wind vs insect pollinated flowers
Wind pollinated e
...
Rye grass
Flowers occur in groups (inflorescenes) on the
plant e
...
Graminae
Plants often occur in dense groups covering
large areas
Stigmas protrude outside the flower on long
styles
Anthers dangle outside the flower on long
filaments so the pollen is easily released into
the air
Petals are dull and much reduced in size
Flowers are often unisexual with excess of
male flowers
Stigmas are often feathery, giving them a large
surface area to filter pollen from the air
Pollen is smooth, light and small
...

Pollen isn’t compatible with other species; the
chromosome number may not match
...
g
...
g
...
g
...
The nucleus is surrounded by two
protective integuments except for a narrow channel at the tip- micropyle
...
This divides by meiosis
forming four haploid megaspore cells
...
This divides by mitosis and resultant nuclei migrate to
opposite poles
...
One nucleus from each polar group moves to the centre of the sac- the polar
nuclei
...
The three cells at the opposite end to the
micropyle are antipodal cells and play no further role
...

Development of pollen
The anthers comprise pollen sacs, usually four, which contain a mass of diploid pollen mother
cells
...
The cells
round off- microspores
...
The wall thickens forming an inner layer, the intine and often highly
sculptured outer layer- exine
...
The tube nucleus moves down the tube first followed by the generative
nucleus which divides mitotically giving two male nuclei
...
e
...

Pollination
Self-pollination- transfer of pollen to stigma on the same or different flower on the same plant
Cross pollination- transfer of pollen to the stigma of another plant of the same species
Pollination is essential to bring the two male gametes in the pollen grain to the female gamete
...

Insect pollination e
...
white dead nettle
Pollinated by long tongued insects e
...
bumble bees, which can reach nectaries from the landing
platform
...
They may also collect
pollen for food
...
Its back may have pollen from another deadnettle flower
...
The anthers
touch the bee’s back shedding pollen onto it
...
The inflorescence (cluster of flowers) is conspicuous to attract bees
...

Wind pollen e
...
meadow fescue
Flowers are small and inconspicuous as they don’t need to attract insects
...
There are no petals, nectaries or
scent
...
Stamens hang outside when
ripe and swing in the air
...
Flowers are on tall, loose, nodding inflorescences
...

Self vs cross pollination
Self-pollination is more reliable especially if species members are widely scattered
...
Genetic uniformity could be
an advantage if well adapted to a constant environment
...
Cross pollination:




X
X
X
X
X
X

Allows diversity in species enabling greater adaptability to environmental changes
Spreads good genes through a plant population so plants increasing survival change
Promotes evolution
Creates genetic variation
Relies on pollinators travelling from plant to plant
Expends energy on attracting pollinators
Greater wastage of pollen
May introduce some undesirable characteristics
Pollination may fail due to distance barrier as another plant is needed
Fewer offspring may be produced

Self-pollination is very common and can occur in more than half of plant species
...
A simple self-pollination mechanism is for anthers
and stigmas to occur at the same time and pollen is shed directly onto the stigma
...
Self-pollination could produce some variety
...
There are two types; pin-eyed
and thrum eyed primrose, these flowers are produced on separate plants
...
Inside the tube are anthers and the style and stigma
...
In thrum-eyed flowers the style reaches half way up the
tube so the stigma is halfway up the inside tube
...

Insects visit the flower for nectar which is at the bottom of the tube
...
An insect e
...
Brimstone butterfly, gets pollen
stuck to the middle of its proboscis from the anthers half way down the tube
...
The
reverse is also true
...
This is ideally placed to be transferred to the stigma of the
next pin-eyed flower it visits
...


Fertilisation
Germination of the pollen grain occurs it if lands on a compatible species
...
This grows down the style towards the ovarychemotropism (pollen tube responded to chemicals secreted by the ovary)
...

During the growth of the pollen tube, the haploid generative nucleus divides by mitosis to two
haploid nuclei- male gametes
...
One fuses with
the ovum forming the diploid zygote
...
This is double fertilisation
...
The nuclei
become separated by thin cell walls
...
In non-endospermous seeds (broad beans, shepherd’s purse)
cotyledons grow at the endosperm’s expense which may then disappear
...
In some seed e
...
peas or beans, the cotyledons
become swollen with nutrients
...

 The most common food stored in seeds is carbohydrates
...
g
...
Many young seeds store
sugar but this changes to starch as they mature
...
E
...
60% in walnuts and coconuts
...

 As the seed matures, water content drops from 90% to 10-15% by mass, to prepare for
dormancy
 The remaining flower parts (petals, sepals, stamen) wither, die and are shed
...
The ovule
becomes the seed, the ovary becomes the fruit
...
The fruit wall is the
pericarp
...

Before fertilisation
Ovary and contents
Ovary wall
Ovule
Integuments

After fertilisation
Fruit
Pericarp (fruit wall)
Seed
Testa (seed coat)

Comparing the maize fruit (endospermic) and broad bean seed (non-endospermic)
Endosperms are monocotyledons e
...
sweetcorn veins on leaves in straight lines
...
The testa and endosperms are the two covering
layers of the embryo e
...
maize and grasses
...
Non- endospermic seeds- cotyledons are the food storage
organs
...
The endosperm is mostly degraded so the embryo is enclosed by the testa alone
...

Numerous maize fruits develop on one cob
A large proportion of the seed is endosperm which
is fused to the single cotyledon
...

The plumule is surrounded by a protective sheath
The radical is enclosed in a hollow tube
Features
Outer covering
Number of cotyledons
Endosperm
Location of embryo
Food stores

Broad bean seed
Non-endospermic- food for the embryo
supplied by 2 large cotyledons (which
have absorbed the endosperm)
...


Maize fruit
Pericarp
1
Present
Attached to the cotyledon
Endosperm

Broad bean seed
Testa as the seed coat
2
Absent
Between the 2 cotyledons
Cotyledon

Germination of broad bean seed
Germination follows a period of dormancy to ensure conditions for growth are right
...
Some seeds also require light e
...
lettuce, but not in
most as germination occurs underground
...
This causes the seed contents to swell
and ruptures the testa (seed coat)
...
g
...

Proteins are hydrolysed to amino acids, carbohydrates to glucose, and fats to fatty acids and
glycerol
...
The glucose, fatty acids,
and glycerol provide respiratory substrates which energy is released from for growth
...
Amino acids form new enzymes and structural proteins
within new cells
...


Oxygen is needed for respiration for energy as ATP for growth and metabolism
...


Death of plant
Yield being harvested
Seeds being dispersed
Dry mass
Photosynthesis- glucose/
starch is being synthesised
...

A loss in mass in caused by loss
of carbon as CO2 in respiration

Time

If carrying out an experiment with seeds; clean them and place them in the oven for 12 hours
below 100C to evaporate water but not kill the seeds
...
Use a minimum of 10 seeds per day,
or interval

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