In the momentous move from water
, plants have had
to overcome several barriers in order to survive
. They’ve had to change
in three major categories: reproductive strategies
, physical structure
and combat dehydration
Evolved reproductive Strategies:
Because the sperm
can no longer freely float through
, plants have had to adapt other methods for fertilization
s attract insect
s with promises of nectar
the insects then cross-fertilize
the plants. The sperm’s convalescence
is another adaptation that makes the sperm stick better to
the insects or float through the wind, increasing the chances of fertilization.
The evolution of the seed
—keeping a greater supply of food while protecting
newly wedded sperm and egg—is another sexual advancement for plants that
helped them deal with a non-aqueous environment. Seed dispersal, such as
with dandelions where the seeds are transported by the wind, or with burr
where the seeds are transported by animals, is another evolved trait. It is important to note that not all land plants use seeds or pollen to propogate themselves: ferns send out runners
that fertilize underground while other plants spawn off asexually when a piece of the root breaks off or simply grows in another direction, much like worm
s, in the popular conception, create two worms when cut in half (false, but a useful analogy).
Evolved Physical Structure:
Plants have developed several structures to help support them
on land that they didn’t need, as much anyways, in water
. Stems are
one... while before plants could float in water, stems allow land-bound plants
to support themselves and reach for more light
. And since they are no longer
free-floating, plants have developed several diverse types of root systems
to anchor them, support them by propping them up, and, of course, absorbing
water. A firmer cell wall
has also developed to keep what water they do
have inside them, where as before this wasn’t an issue since they were in
an aqueous environment (Note: it actually was still an issue in keeping
the inside/outside environments pH balanced, ion gradient, etc. But it
wasn't as difficult as in a dry environment.)
. Plants have also evolved
to take advantage of Turgor pressure
, where osmosis
swells the cell and
reinforces it. This allows the plant to remain upright.
Plants also must now face dehydration on land. Plants
have developed waxy cuticles
, so that water is kept inside the leaves.
Similarly, seeds are coated to protect against dehydration. Seeds also remain
dormant until wet conditions are present, increasing the chance of survival.
s also developed to absorb water—they twist around and have a high
surface-area: volume ratio
. They also have tiny hairs that aid in absorbing
have developed to control water movement in and out of the
Cam and c4 plants have modified stomata to deal
with their unique environments. Plants also lose leaves during cold
weather so as not to waste, and lose, precious water resources.
Thanks to m_turner for some help on reproduction... err, the plant reproduction information.