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!