BIO 106 Photosynthesis Pre lab lecture

- [Professor] Hi everyone,
it's your friendly neighborhood Biology professor
with a little introduction to photosynthesis.
We'll cover photosynthesis in more detail in chapter seven,
but for now we need to have a little introduction
to allow you to enjoy your lab this week.
The word photosynthesis gives you a key
to what's going on in the process.
Photo is light and synthesis is to make.
So, we are using light to make something.
Organisms such as plants and some
algae are photosynthetic.
They use the energy in sunlight, or solar energy,
to convert carbon dioxide and water into sugars.
In the process, they also release oxygen.
Directly or indirectly, these organisms
pretty much feed the entire world.
But remember, they're making these foods,
these sugars, for themselves.
We just happen to benefit
from that by eating them.
Here are some examples of
photosynthetic organisms.
Some of them are probably very familiar.
Now we see a forest floor up at the top.
Plants are usually the first thing that comes
to mind when we think about photosynthesis.
Unicellular protists like the one shown here.
Also, multicellular protists which are algae,
shown on the left bottom.
Some bacteria are also photosynthetic.
Clearly they don't have chloroplasts
because they don't have membrane-bound
organelles, but they do have
the machinery to do photosynthesis.
And, also, some bacteria called purple
sulfur bacteria are photosynthetic.
The process of photosynthesis is
very similar in all of these organisms.
Some of the differences are going to be
where things happen since anything
eukaryotic does have a chloroplast
and anything prokaryotic does not,
but the processes themselves
are very very similar.
Here's a picture of a chloroplast
that we are exploring in chapter four.
The part that we're really gonna be thinking
about with photosynthesis is on the inside.
These are called the thylakoids.
They're almost like tiny little
flattened pancakes of membrane
with a space in the middle, and they're
all interconnected.
A lot of what happens in photosynthesis
happens here on the inside of the chloroplasts,
in these thylakoids.
Just as an interesting note, photosynthetic
bacteria or prokaryotes that are
photosynthetic have infolded regions
in their plasma membrane so they can
sort of duplicate this folded membraneous
structures with their plasma membranes.
And it's in those infolded regions that you have
the pigment and the enzymes for photosynthesis.
So remember we're here in the chloroplast.
Photosynthesis takes place in the green organs
of our plant, usually, or green protist.
So when we think about green organs
in the plant we usually think leaves.
Sometimes we're in the stem as well.
So we're looking at the leaves of this plant.
Carbon dioxide needs to come into
the cells of the plant in order
to be used for photosynthesis.
So that carbon dioxide comes in in pores called
stomata on mostly the undersurface of the leaf.
In these pores, when they're open,
carbon dioxide goes in, and in the process
of photosynthesis oxygen is released.
The oxygen is then either used by the organism
or, if there's an excess, the oxygen
is released through these stomata pores.
So here's where we're having our gas exchange.
The carbon dioxide goes in and is
among these cells inside the leaf.
The oxygen, once produced by these cells,
if it's in excess, comes out.
Chloroplasts are mostly found in special
cells called mesophyll cells, and that's these
cute little spongy cells within the leaf
that you can see in this picture.
It's not in the epidermal cells,
or the skin cells, of the leaf.
And often when we draw our cells,
we tend to put a chloroplast or maybe a couple
of chloroplasts, but, in reality, there are
lots and lots of chloroplasts in some cells.
There tend to be 30 to 40 of them,
so if you look at the picture here,
all those little green balls are chloroplasts.
If we look at the chloroplasts themselves,
the green pigment is called chlorophyll.
So chlorophyll is the molecule that's
very very important to photosynthesis.
It's also what makes plants green,
or some algae green.
That chlorophyll would be imbedded
in the thylakoid membrane.
So if you look at these little thylakoid disks,
we'd see chlorophyll in the membrane
of those disks, also shown in the
microscope picture of the chloroplast.
As I mentioned, chlorophyll gives
plants their green color,
the green pigment in the chloroplasts.
Chlorophyll is what absorbs the light energy
and then directs that light energy
to synthesize organic molecules,
in this case sugars in the chloroplast.
So I have a picture of a leaf, nice green leaf.
If we look inside the leaf,
we would see chloroplasts.
There's one chloroplast here,
and there's one chloroplast here.
These are chloroplasts that haven't
been doing a lot of photosynthesis.
Let's turn the light on 24 hours a day,
and here's the chloroplast.
This whole big thing that comes out of there
is a big chloroplast, and this big thing
is, something that we talked about very very
briefly in chapter three, is a starch grain.
So as the plant makes lots of sugars through
photosynthesis, if it can't use them all,
it stores them as these
big grains of starch in the chloroplasts.
This is a representation
of a wavelength of light.
You can sort of think of it like
a jump rope being pushed up and down.
That light is actually a form of energy,
and that's important to understand
in what's going on with photosynthesis.
It's solar energy; it's light energy.
It's also called electromagnetic energy
or electromagnetic radiation.
Light behaves as little packets
of energy called photons, and you'll
hear physicists are about this.
Is light a particle?
Is light a wave?
For us, we kind of don't care.
It's both.
It's a particle that has a wave-like function.
So you can think of light
as having these wavelengths,
and these wavelengths represent energy.
So light, like other electromagnetic energy,
travels in rhythmic waves.
And how big the waves are, which
means how close from peak to peak,
is characteristic of each wavelength of light.
So a wavelength is from one crest,
or one peak, to the next.
And we want to relate that to energy.
How much energy is present in that light?
So if we look at it, we have a short wavelength
of light and we have longer wavelengths of light.
And the shorter wavelengths of light
have higher energy, and that makes sense.
Think about holding a jump rope between
you and a friend, in order to make those
short wavelengths, you have to move your hand
up and down much faster than long
languid movements which make longer wavelengths.
This is kind of what light looks like.
We have all of the electromagnetic spectrum here.
Everything from gamma rays, x-rays, UV.
Visible light is what we're
gonna be talking about.
And then infrared, microwaves, and radio waves.
So I want you to focus in on the visible light
because that's what we're going to be
exploring with photosynthesis.
Our shorter wavelengths are over on the left
in our purples, and our longer wavelengths
are over on the right in our reds.
What that tells us is our purples are higher
energy because they have shorter wavelengths,
and our reds are lower energy
because they have longer wavelengths.
Now it may make sense to us to think about
well, of course the plants only use the higher
energy wavelength, but not necessarily.
Ya know, think about some
experiences you may have.
Sometimes the higher energy isn't
the best way to get things done.
Sometimes when we're cooking, if you
start off at a very high energy,
you end up with not a very good schematic.
Think about cooking a big piece of meat.
You might cook the outside if you heat it
at a very high temperature, but if you have
a very high temperature, you'll burn the outside
before you get the inside cooked.
So higher energy isn't necessarily better,
and lower energy isn't necessarily worse.
What we want to determine is which one
do plants use, or do photosynthetic
organisms use, in photosynthesis.
One of the ways that we think about this is:
what's absorbing the light energy?
What's absorbing the light
energy are the pigments.
So pigments in general are molecules
that absorb energy, the light energy,
and they're specific to what wavelength
they use or absorb in the process.
Specifically, in photosynthesis,
we're thinking about chlorophyll.
What wavelength of light
does chlorophyll absorb?
And absorbing it means it must use it.
Wavelengths that aren't absorbed are reflected
or passed through the pigment.
So, in reality, if you think about chlorophyll
making plants green, but really
what it's doing is chlorophyll is
reflecting the green light back.
It's not absorbing it.
Any light that's absorbed by the pigment,
you're not going to see that color.
So the color that you see as green
because the pigment reflects it
or transmits it through.
So leaves are green because they
reflect green light.
So we need to figure out, well,
they reflect green so we know green
is not the wavelength that's used by plants
for photosynthesis, what wavelengths are used?

BIO 106 Photosynthesis Pre lab lecture

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