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Plant Reproduction
Lifecycle of a flowering plant
Two main stages to the lifecycle
– Sporophyte
• Diploid stage
– The plant produces a flower with both male and female parts. The
majority of a plants life is spent as the sporophyte
– Gametophyte
• Haploid stage
– Gametes (egg and male gametes). The plant only spends a brief
amount of time in the gametophyte stage.
The Flower
The Reproductive Organs
– Stamen:
• The male part and is made up of the anther and the
filament. The anther produces pollen which contains the
male gamete
– Carpel:
• The female part and is made up of the stigma, style and
ovary. The ovary produces the egg cells.
Wind and Insect Pollinated Flowers
Pollination
Pollination is the transfer of pollen from one flower
to the stigma of another flower of the same species
There are two types of pollination
– Wind (Grasses and cereals)
– Insect (Dandelions, daisies etc.)
Both wind and insect pollinated flowers have many
adaptations for pollination.
Adaptations of wind pollinated and
insect pollinated flowers
Fertilisation
 The pollen lands on the stigma,
the tube nucleus in the pollen
grain forms a pollen tube down
to the ovary
 The male gametes travel down
to the ovary
 One nucleus will fuse with the
egg to form the plant embryo.
 The other nucleus will fuse with
two other egg nuclei to form the
endosperm which will be used
as a food source for the embryo
Seed Formation
 In monocots, the
endosperm usually
remains
(Maize seed)
 In dicots, the cotyledons
usually absorb the
endosperm.
Seed formation
The embryo consists of:
– Radicle: future root
– Plumule: future shoot
– Cotyledons: seed leaves
A seed coat (testa) develops around the embryo
In many cases, the ovary develops into a fruit.
Seed Structure
 The outside of the seed is called the testa.
 The embryo of a seed develops into a seedling and also
provides a supply of food.
 The embryo contains a radicle which forms a root and a
plumule which forms a shoot.
 The seed leaves are called cotyledons.
 Seeds with one cotyledon are called monocotyledons
and seeds with two cotyledons are called dicotyledons.
Seed dispersal
 Seed dispersal avoids competition
between the new plant and the parent
plant.
 Seeds can be dispersed by
–
–
–
–
Wind
Animals
Self
Water
Germination
Moisture, temperature and oxygen are needed
for germination.
Two types:
– Epigeal – cotyledons emerge above ground.
– Hypogeal – cotyledons do not emerge above ground.
Epigeal vs. Hypogeal
Hypogeal Germination
Epigeal Germination
Modified Organs and Vegetative Reproduction
Many plants have modified organs for food storage,
while others use their modifications for asexual
reproduction.
– Strawberries reproduce asexually by producing
horizontal stems known as runners (stolons) above the
ground
– Scutch grass reproduces asexually by producing
underground stems known as rhizome.
Modified organs
The majority of modifications for food storage in
plants are associated with the plants lifespan
– Annuals: complete their lifecycle in one year
– Biennials: complete their lifecycle in two years
– Perennials: is a plant that lives for more than two years
• Perennials flower and produce seeds many times during the
course of their life time.
Modified roots
Modified roots:
– Tap root is modified to store food
• Examples include carrots and sugar beet
– If lateral roots are modified for food storage then it
is called a tuberous root
• For example, dahlias.
Modified stems
The potato plant produces tubers which are
modified underground stems for the storage of
food.
Modified stems
 Rhizomes are modified
stems.
– If these stems are broken
into pieces, each piece can
produce a new plant
 Corms are modified
stems
– The crocus is an example.
Modified Leaves
 A bulb is an example of
modified leaves used for
food storage.
– An onion is a bulb
Plant Tropisms
A tropism is a plant’s growth response to an
external stimulus
– Phototropism is a plant’s growth response to light
– Geotropism is a plant’s growth response to gravity
Growth responses to stimuli in plants are under
the control of plant hormones.
Phototropism