Plant Structure and Adaptations
By Micah Moen
Captioning is on. Click CC button at bottom right to turn off. Follow us on Twitter (@amoebasisters) and Facebook! Plants might not seem all that exciting and
you might wonder, ”Why must I learn about plants?” But plants are so important for
life—they are producers which means that they are the main support for food webs. Many
medications that we have today are derived from plants. They produce oxygen for us to
breathe by the photosynthesis that they do. Not to say that everything that does photosynthesis
is necessarily a plant, but plants play a major role in oxygen production. You know how there are many different types
of animals—-well there are many different types of plants as well. To get to plant structure,
we need to outline two major plant categories. Vascular and nonvascular. Recall that in the
human body, your vascular system includes arteries and veins. Well plants don’t have
arteries or blood… for that matter. When we’re talking about a vascular system
in plants, we’re talking about two major types of tubes—or vessels— called the
xylem and phloem. The xylem carries water. Xylem is found throughout a vascular plant—water
is absorbed from the roots of vascular plants and carried upwards. Roots are specially designed
to help anchor plants and also to absorb the water found in the soil that they are in.
The phloem carries sugars—which are typically produced in the leaves of the plants during
photosynthesis. This sugar is their food source that plants make In photosynthesis. It needs
to be carried throughout the plant. The phloem might start with a p but it does have the
same “f” sound that food has so it helps me remember that it carries the plant’s
food. If a plant is nonvascular, it does not have vessels like the xylem and phloem. However,
it still needs water and it still produces sugar. It can’t carry water upwards in the
xylem because it doesn’t have one. That means, nonvascular plants typically are limited
in size. A giant tree needs a xylem for water transport; the water is being carried against
gravity. Nonvascular plants instead get their water by osmosis. Kind of like soaking up
water like a sponge. A great example of a nonvascular plant is moss. Much of a plant’s structure is actually
designed to facilitate photosynthesis. Photosynthesis is the ability to make sugar—the plant’s
own food source—from sunlight. We can’t do this. Yeah, you might go in the kitchen
to make a sandwich but you are just preparing your food. Wouldn’t it be amazing if you
could go out in your backyard and sunbathe and conjure up a sandwich in your stomach?
Our little analogy isn’t perfect but you get what a big deal photosynthesis is. If
you understand the importance of this function for plants, you can really understand many
structure adaptations that plants have. Photosynthesis needs three reactants to work: water, light,
and carbon dioxide. Water— we mentioned already how a plant can obtain it in different
ways depending on whether they’re vascular or nonvascular. So what about the sunlight—-how
does plant structure deal with that? Well plant cells have organelles called chloroplasts.
These amazing organelles are not found in animal cells. They are the site of photosynthesis
so they help capture light energy for the process of photosynthesis. This is a complicated
process that is made up of a light dependent reaction and a light independent reaction
(also called the calvin cycle). It’s a big enough process that we’ll have to have another
video clip for that. Leaf structure is designed to capture this light energy with their chloroplasts.
Last thing on our photosynthesis checklist after the water and the light is carbon dioxide.
So how does the structure of plants help them obtain carbon dioxide? First of all, please
realize that plants do something in addition to photosynthesis called cellular respiration—just
like you—-and they do need the gas oxygen. Sometimes students get confused and think
that plants “breathe” carbon dioxide. This is not true. Plants also need oxygen—but
they typically produce more oxygen than they use which makes them so helpful as oxygen
producers. For photosynthesis, plants need the gas CO2. Conveniently, this is the gas
that we exhale (which means, we breathe out). Many plants have these fascinating little
openings—pores really—called “stomata.” Stomata is the plural and stoma is the singular.
Stomata are typically found on the bottom of leaves, in some species, they are on the
top. Stomata have a major role in gas exchange. Gases can flow in through these openings,
and the CO2 that enters is really needed for photosynthesis. There is only one little problem.
The plant can’t keep those stomata open all the time. If so, water can escape. And
remember, plants need water too for photosynthesis. So the plant has to determine whether to open
or close its stomata, and it does this with the help of guard cells. If guard cells have
the stomata open, it gets the gases it needs but it can lose water. If guard cells have
the stomata closed, it gets to save its water but then it can’t get any gases. At night,
most plants (few exceptions which we’ll talk about toward the end of our clip) close
their stomata so that they can conserve their water. Why? Well at night, they can’t do
much photosynthesis because there’s not much sunlight…so what’s the point in keeping
them open? During sunny days, most plants tend to open their stomata to get the gases
they need to do photosynthesis. But if the day gets way too hot and the plant is low
on water, it may close its stomata. Different plant species have all kinds of adaptations
in their structure to help them survive. Because if one thing is true about plants—they are
survivors. Here’s some great examples of plant structure adaptations that help them
with various functions. Plants that have to conserve water tend to have very thin leaves
so that they don’t have much surface area to lose water. Think about pine trees with
their skinny pine needle leaves…or think about the plants that live in the desert.
Remember how we said most plants close their stomata at night? Well some desert plants
have adapted by opening stomata at night—-when it’s not ridiculously hot—and they have
a specialized way to store the gases they need for the daytime. This allows them to
close their stomata during the day to prevent water loss under that hot desert sun. Plants
that have lots of access to water—but maybe are shaded by a lot of taller plants in a
jungle—might have really broad, wide leaves so that they can soak up as much sun as possible.
It’s hard to live in someone else’s shadow. Since there is plenty of water, these big
leaved plants don’t have to worry about all that surface area losing water as there’s
plenty of water to go around. Or have you heard about carnivorous plants? Like the venus
fly trap or the pitcher plant? These plants still do photosynthesis to make their sugar.
But carnivorous plants also have the ability to digest insects typically by using special
enzymes in a juice they secrete. These plants tend to live in areas where the soil is low
in nitrogen. Plants, and other organisms, use nitrogen in the building of proteins.
Insects are a great way to supplement this nitrogen need. If you ever look at the ingredients
in plant fertilizer, you will find many fertilizers are high in nitrogen. And you know when people
hang up mistletoe? So sweet, right, you’re supposed to get a kiss under it? Is it terribly
ironic that you are hanging out a potentially parasitic plant that uses its roots to steal
nutrients and water from its host plant? Hmm. Probably the most fascinating parts of plant
structure and function have to do with plant reproduction. But that’s a whole other subject—and
we have another clip for that. That’s it for the amoeba sisters and we remind you to
stay curious. Follow us on Twitter (@amoebasisters) and Facebook!