Fertilisation & Germination

1. Fertilisation in
Plants
Concluding Plant Reproduction

2. Plant fertilisation
When pollen sticks
to the stigma it
absorbs water and
starts to germinate
A pollen tube will
grow out of the
grain and through
the style towards
the ovary

3. Plant fertilisation
The pollen tube
nucleus remains close
to the tip of the tube.
Digestive enzymes are
secreted from the tube.
The tube is attracted by
chemicals given out by
the ovary.

4. Plant fertilisation
As the tube grows
the generative
nucleus divides by
mitosis to form two
haploid male
gametes.

5. Plant fertilisation
The pollen tube enters
the ovule through the
micropyle.
Once inside the ovule
the tube nucleus
degenerates and the
male gametes enter
the embryo sac

6. Plant fertilisation
One of the male gametes fuses with
the female gamete forming a diploid
zygote.
In plants a double fertilisation takes
place as the other male gamete fuses
with the diploid nucleus in the centre
of the embryo sac forming a triploid
nucleus – called the endosperm
nucleus.

7. Outbreeding
mechanisms
How plants prevent self-fertilisation

8. Protandry
Most flowers use
this mechanisms,
e.g. rose-bay
willowherb
The stamens ripen
before the stigma is
receptive to pollen.
So pollen is gone
by the time stigma
is ready.

9. Protogyny
More unusual than
protandry e.g. the
bluebell
The stigma ripens
before the anthers.
By the time the
anthers shed their
pollen the stigma is
no longer receptive
to it.

11. Dioecious Plants
With dioecious
plants each
individual plant
bears either male or
female flowers, but
never both.

12. Dioecious Plants
Paw-paw and holly
are examples of
dioecious plants.
Clearly self-
pollination is
impossible!