Video Transcript
Cross-pollination is generally more
advantageous for a population of plants than self-pollination, as cross-pollination
introduces more genetic variation. Which of the following is a
strategy used by plants to prevent self-pollination? (A) The stamens and the carpels
being positioned close together and at the same height in the flower. (B) The development of multiple
carpels but only one stamen. (C) The development and maturation
of stamens and carpels happening at different times. Or (D) the plants relying on wind
pollination rather than insect pollination.
Genetic variation is beneficial
because it makes a species more resilient to diseases and more adaptable to
environmental changes. Cross-pollination is a method of
pollination used by some flowering plants, which are also known as angiosperms, that
introduces comparatively more genetic variation than self-pollination.
This question is asking us to
identify which of the options is describing a strategy that can be used by
angiosperms to prevent self-pollination. So, to figure this out, let’s
remove the answer options for now so we have some more space to work with.
The male gametes, or sex cells, of
a flower are found within pollen grains that are produced in the flower’s
anthers. Each anther that produces these
male gametes is supported by a filament. And together each anther and
filament make up a single stamen, several of which can usually be found in each
flower. Many flowering plants are
hermaphroditic, meaning they contain both female and male reproductive organs on the
same plant, and can therefore produce both male and female gametes. The female reproductive organ is
called the carpel. And it consists of a stigma that
receives the pollen grains connected by a style to an ovary that often contains
several ovules within which the female gametes can be found.
When pollen grains land on the
stigma in pollination, the male gametes travel down the style and into the ovary,
where they can potentially fertilize the female gamete. If this pollen is produced by the
anthers of the same flower or a different flower on the same plant, this process is
called self-pollination. If the pollen is produced by the
anthers of a flower on a different plant, the process is called
cross-pollination.
A strategy used by some plants to
reduce the chances of self-pollination is called dichogamy and involves the
development and maturation of stamens and carpels at different times. For example, the stamens of a
single flower may mature earlier than the carpel. So the pollen that is produced by
the anther of the stamen is unable to fertilize the same flower’s female gametes, as
it simply cannot reach them until the carpel is fully mature. By the time the carpel has matured,
the anthers of that particular plant will no longer be producing pollen. So the stigma will only receive
male gametes from a different plant, thereby reducing the risk of
self-pollination.
Let’s bring back our answer choices
to figure out which one is describing the correct strategy that plants can use to
prevent self-pollination. The strategy of dichogamy, which is
used by plants to prevent self-pollination, is described in answer choice (C), the
development and maturation of stamens and carpels happening at different times.
