Upload
scuffruff
View
2.807
Download
1
Embed Size (px)
DESCRIPTION
Citation preview
Fertilisation in Plants
Concluding Plant Reproduction
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
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.
Plant fertilisation As the tube grows
the generative nucleus divides by mitosis to form two haploid male gametes.
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
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.
Outbreeding mechanisms
How plants prevent self-fertilisation
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.
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.
Dioecious Plants With dioecious
plants each individual plant bears either male or female flowers, but never both.
Dioecious Plants Paw-paw and holly
are examples of dioecious plants.
Clearly self-pollination is impossible!