Video Transcript
What structure within a flower is
usually sticky to catch grains of pollen?
A flower is a structure that
contains the reproductive organs of certain plants, called flowering plants. This diagram is of a bisexual
flower, which contains both male and female reproductive organs. The male organ of a flower is
called the stamen. Each stamen consists of a
stalk-like filament that supports bulbs called anthers, which produce pollen
grains. The female organ is called the
carpel or pistil. It contains a stigma, a style, and
an ovary. Inside the ovary are structures
called ovules.
The diagram here shows four stamens
and eight ovules. But the number of both of these
structures varies between plant species. An extreme case of this is found in
the giant saguaro cactus, whose flowers can have over 3,000 stamens. For flowering plants to produce
seeds, they must undergo sexual reproduction. You may remember that sexual
reproduction requires the fusion of male and female gametes. In the case of flowering plants,
the male gametes, or sperm, are contained in pollen grains. The female gametes, called ova, or
ovum in the singular, are found in the ovules. So, how does a plant sperm actually
reach an ovum?
Well, this occurs through the
process of pollination. During pollination, nectar-feeding
animals, such as the bee drawn here, pick up pollen grains from the anthers. This is represented by the small
red dots on the bee’s legs and abdomen. Wind can also move pollen. If the animals brush against the
stigma or the wind blows pollen in the right direction, the pollen will be deposited
on the stigma. The sperm within the pollen grains
can then travel down to an ovule to fuse with the ovum.
You might be wondering why the
pollen doesn’t just blow off the stigma the same way it can blow off of an
anther. Well, the cells of the stigma often
secrete a special sticky substance, which ensures that any pollen grains that land
on the stigma will stay put, allowing pollination to occur.
Now we have the information we need
to answer our question. The structure within a flower that
is usually sticky to catch grains of pollen is the stigma.
