Bio 20 Lesson 1: Parts of the Chloroplast, Pigments & the Light Spectrum

Hey bio20s, welcome to my video series

where I'll be going over the main topics

um in the course. Today we're going to

be discussing photosynthetic pigments,

chloroplast and the light spectrum.

So when you look at a plant, so a plant

appears green to us because of a very

special pigment called chlorophyll. Now,

chlorophyll is the pigment that resides

within the chloroplast. And you might

remember learning about this in previous

science courses, remembering that

chlorophyll inside of a chloroplast.

Chloroplast being the part of a plant

cell where photosynthesis occurs. Now,

not only do the chloroplast give the

plant their green color, they also allow

it to perform the process of

photosynthesis. So, let's take a look at

a chloroplast. So this is what a

chloroplast will look like. And you can

see here, this is what one would look

like under a microscope. In this diagram

here, there's two main areas that I want

to highlight. So there's two main areas

I want to highlight. And this will be

more important as we talk about this in

our next couple of videos. The first one

I want to highlight is the philyloid. So

the thyloid are these little green discs

here. They kind of look like little

pancakes stacked on top of one another.

This is where one part of photosynthesis

takes care. This this is where the light

dependent reaction occurs. And when we

look at a stack of philyloids, we call

that stack of philyloids a granom. So a

granom would be a stack of philyloids.

Then we see these little kind of bridges

connecting the philyloids. We refer to

these as the lamela. The other thing I

want to highlight, the other really

really important part I want to

highlight is this which is called the

stroma. This is kind of the area the

fluid fil area surrounding the

philyloids and this is where the second

half of photosynthesis takes place which

is called the light independent

reaction. Other than that though the

photo the chloroplast has a outer

membrane. It has a inner membrane. So

two membranes. And then the space

between the membranes is called, you

guessed it, the intermembrane space. Now

if we look even closer inside of a

philyloid, so once again, this is where

the light dependent reaction takes

place. We're going to see those pigments

we just talked about, the chlorophyll.

The chlorophyll are actually embedded in

the membrane of the thyloid itself. and

the chlorophyll it's going to play a

major major role in the light dependent

reaction. So this is what the philyloid

membrane would look like. So this is the

outside of a philyloid. This is the

inside of a philyloid. And then embedded

in that membrane would be those

chlorophyll pigments.

Now when we talk about chlorophyll,

chlorophyll the main job of chlorophyll

and other photo photosynthetic pigments

the main job is to capture light energy.

Photons they are small bundles of light

that the chlorophyll are going to

capture and then use that light to

almost power the process of

photosynthesis.

When we think of light energy, it can

come in two different wavelengths. a

shorter wavelength or a lower

wavelength. And this will determine how

much energy it has. Higher energy will

have a shorter wavelength. Lower

wavelengths will have a lower or sorry

longer wavelengths will have a lower

energy. So if you think of all the

different energy that we have, gamma

rays, x-rays, UV, infrared, microwaves,

radio waves, all this different energy,

this little sliver here what we can

actually see. This is our very very tiny

visible light spectrum that our eyes can

actually process. So we can see light on

the lower end here like your purple,

blue, green in the middle all the way to

the higher end being your

yellow, orange and red. So these would

be the colors that we can see. Then at

your lower energy frequency, right at

your lower energy frequency, you have

your radio waves, microwaves, and then

your infrared waves. Radio waves,

microwaves, they're lower energy,

they're lower frequency, they have a

longer wavelength in general. They're

they're not as dangerous for us, right?

Um, so for example, like right now as

you're watching this video, I'm sure

some radio waves are passing through you

right now. Not to be concerned, but it

it it wouldn't really cause anything bad

to happen. Then we move forward with the

visible light. Once again, this is the

light we can see. And then there's UV.

So UV, this would be the radiation

coming from the sun. um little bit

higher frequency, not too too dangerous,

but once again, if we're not wearing

sunscreen, if we're not protecting

ourselves, can cause issues, can cause

ourselves to mutate, become cancerous.

We go further to X-rays and gamma rays.

If we're being exposed, hopefully no

one's exposed to gamma rays, but if

you're exposed to things like X-rays,

you probably want to take the necessary

safety precautions because it is on the

higher energy side of the spectrum. And

you'll notice here that the wavelengths

do get shorter as we go more to this

side of the light spectrum. Now, light

from the sun is a mixture of things,

right? There's some visible light so we

can see it. There's some UV light.

There's a whole bunch of there's a

little bit infrared. There's a lot of

mixes in there. Now, the visible light

is captured by the photosynthetic

organism like your plants, your algae,

etc. And then it is transformed into

chemical energy. that is stored for

later. Now, you might remember this from

previous science classes, but we know

that energy cannot be created or

destroyed. It can only be transformed

from one form to another. So, what the

plant is going to try and do is going to

try and take that solar energy and

transform it into chemical energy. So,

in this case, glucose.

Okay. Now, chlorophyll, it comes in

different versions. The main type of

chlorophyll that all photosynthetic

plants will have is called chlorophyll

A. Now chlorophyll A, all photosynthetic

plants have this. This is like your main

pigment. This is the one doing the heavy

lifting. It will be the primary pigment

that will capture light. Then we have

what are called accessory pigments.

These are pigments that help the

chlorophyll A. So we have something like

chlorophyll B. It doesn't absorb as well

as chlorophyll A, but it maybe picks up

some pieces that the chlorophyll A

misses. And then we have something like,

and there's other pigments out there.

These are just a few examples. Uh,

corotenoids I want to bring up because

they're interesting. We actually have a

ton of them in things like carrots. Uh,

they're an accessory pigment and they

only pick up like one part of the light

spectrum. So when we look at different

pigments and what they do, basically

what happens is they will absorb the

light and the light that they don't

absorb will be reflected. Well, guess

what? The color that they don't absorb

is the color green. And that's why

plants appear green to us because they

absorb the reds, the blues, the yellows,

and then something like grass,

chlorophyll a full of chlorophyll a

can't actually absorb the green light.

So the green light will then be

reflected back at us which our eyes will

process as green. Now in some cases

right we look at okay we got our

chlorophyll A we got our chlorophyll B

they're working together to almost like

fill in the gaps that they have. So

chlorophyll A pretty good at reds

oranges not so good at yellow but that's

okay. Chlorophyll B can pick up and get

some yellow. both very good at blue,

purple, violet. Neither of them very

good at green, though. So, because of