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Biology Topic 3 - Reproduction in flowering plants (Structure &…
Biology Topic 3 - Reproduction in flowering plants
Differences between Asexual and Sexual
Asexual
1 parent needed
No Gametes (sex cells) produced
Mitosis is the only cell division involved
No mate needed to be found
No fertilisation occurs
No variation in offspring
Usually many number of offspring
Sexual
Gametes (sex cells) are produced
Meiosis and mitosis are involved
A mate is needed to be found
Fertilisation does occur
2 parents needed
There is a variation in off spring
Usually few number of offspring
Fertilisation
Male gamete (haploid) + female gamete (haploid) = zygote (diploid)
Fertilisation occurs when the nucleus from the pollen grain fuses with the nucleus in the ova to form zygote. The zygote develops into a plant embryo.
The outer layer of the ovule becomes the seed coat (to protect the embryo).
The ovary becomes the fruit.
Seeds can either be dispersed from the parent plant in fruits (For animals to eat and egest the seeds elsewhere) or dispersed in the wind. Both methods ensure the offspring are not competing with the parent and each other for space,food,light etc.
Structure & Function of a Generalised flower
Anther
Produces pollen grains by meiosis.
Filament
supports anther
Petal
Attracts insects
Stigma
receives pollen grain
Structure
Function
Stamen
male parts
Ovules
produce ova (egg cells) by meiosis
Style
supports stigma
Carpel
female parts
Ovary
contains ovules
Nectary
produces nectar
Sepal
Protect flower when in bud
Wind pollinated flower and Insect pollinated flower
Wind pollinated flower
Petals: Petals are small and inconspicuous
Scent: None
Nectaries: Absent
Anthers: There are many large anthers which hang outside flower to disperse pollen in the wind.
Stigmas: There are large, feathery stigmas that hang outside the flower to collect pollen from the wind.
Pollen Grains: Pollen grains are large, light and smooth to float in the wind; relatively many pollen grains are produced.
Insect pollinated flower
Nectaries: Nectaries produce sugary liquid to attract insects.
Anthers: There are few small anthers held inside flower to stick pollen onto insects.
Scent: Flowers are often scented to attract insects.
Stigmas: There are small, sticky stigmas held inside the flower to collect pollen from insects.
Petals: Petals are large and brightly coloured to attract insects.
Pollen Grains: Pollen grains are small,heavy and have sticky or spiky surfaces to stick to insects; relatively few pollen grains are produced.
Definitions
Pollination: Transfer of pollen grains form a stamen to a stigma.
Cross-pollination: Transfer of pollen grains from a stamen on one plant to a stigma on a
different
plant.
Self-pollination: Transfer of pollen grains from a stamen of one plant to a stigma on the
same
plant (this reduces variation in offspring but does not eliminate it)
Fertilisation Process
The
pollen grain
sticks on the sticky
stigma
.
The pollen grain grows a
pollen tube
down the style of the carpel.
The pollen tube grows down into the ovary and into an
ovule
.
The
haploid nucleus
from the pollen grain fuses with
haploid nucleus
from the ova - this is called
fertilisation.
PRACTICAL: Investigate the conditions needed for seed germination
The seed absorbs lots of water by osmosis.
The water allows enzymes to work.
Enzymes break down the insoluble starch store to soluble sugars.
The soluble simple sugars reduce the water potential of the seed so more water enters by osmosis.
The simple sugars are respired to release energy for growth (some energy is released as heat).
The plumule (embryo shoot) and radical (embryo root) grow out of the seed. Leaves are grow which can carry out photosynthesis.
Reproduction methods
Runners (e.g. strawberry plants
A natural method of asexual reproduction.
A runner grows off from the base of a parent plant along the ground until it reaches a suitable area.
It develops roots and when the root system is functional the stem connecting the new plant to the parent withers.
Cuttings (e.g. common box)
An artificial method of asexual reproduction.
A side shoot is cut off of a parent plant and planted in soil.
Rooting powder is added so the shoot develops roots.
