the

The Chloroplast

hi it's mr. Andersen and in this video

I'm going to talk about the chloroplast

that's the organelle found in plants

where photosynthesis takes place a great

place to find them would be in the leaf

of a tree so if we look at that in

cross-section we're going to have a

number of cells and these are going to

be the organelles found within that cell

if you've got a structure that we'll

talk about in just a second but it's

important to understand that they're not

fixed within the cell they can move

around and so if we apply a little bit

of light to a cell all of the

chloroplasts will line up so that you

can get the maximum amount of light if

we apply too much light to that cell

they'll hide on the sides of the cell

they're doing that to protect themselves

from damage but they're not alone if we

look at a chloroplast it's going to be

surrounded by a set of mitochondria that

will follow it throughout the cell and

the reason they're following it is they

need the energy they need the energy

that was once in the Sun and is now in

molecules like glucose the structure of

a mitochondria is pretty simple they've

got two membranes around the outside and

then they're filled with stroma it's

going to be this liquid on the inside

inside that liquid we've got ribosomes

they've got their own genome so they

have their own DNA but most of the

action is going to take place along the

thylakoid membrane we have a series of

these membranes and when they're stacked

up it makes a structure inside called

the grana if we look specifically at one

Granum that's where everything is taking

place we have both the light reaction

and the calvin cycle I won't go into the

specifics of photosynthesis but if we

think about the Calvin cycle what's the

function of that well the plant is

taking in carbon dioxide and we want to

add energy to that molecule we're making

something like glucose when I say adding

energy to it what do I mean we're adding

high-energy electrons and so there are

bonds between the carbon and the

hydrogen and glucose and so we have to

add energy to those electrons where is

that energy coming from originally it's

coming from the Sun where is this all

take place it takes place along the

thylakoid membrane so we're going to

zoom in to this rectangle right here and

what we'll find is there's a membrane

but there's also a series of proteins

that's going to be everything in purple

one of the most famous ones is ATP

synthase but we also have these giant

Tanna complexes those are going to be

proteins that are filled with pigments

one of the most famous ones obviously is

chlorophyll and so as we let Sun hit

that membrane what's going on well the

energy of those photons is used to get

the chlorophyll excited and it's passing

its electrons down an electron transport

chain now there's a few other things in

play we've got a series of protons

protons are going to be atoms of

hydrogen that are missing their

electrons and we also have water so

water that's taken in in photosynthesis

and so as these electrons get excited

they move down an electron transport

chain and we really have a hole right

here so we have to get more electrons to

fill that hole and that comes from the

water so watch carefully what happens

right here is that we break that water

apart we're making oxygen that's the

oxygen that a plant gives off we're also

donating these electrons and we're

making some more of these protons if we

watch specifically what happens to one

of those electrons that went really fast

let's go back and look at that again if

we watch that electron what it's doing

is as it moves through this electron

transport chain is it's using its energy

because it's gained energy right here to

pump a proton from the outside to the

inside of the thylakoid membrane now we

have a bunch of positive charges on the

inside they would like to leave and the

only way to leave is to go through ATP

synthase as you do that you generate ATP

let's watch another electron go through

so we see that same thing occur but

where did the electron go well we give

it even more energy after it goes

through this electronic transport chain

and then that electron eventually goes

to a carrier molecule you can see that

everything is positioned perfectly it's

outside the thylakoid membrane in the

stroma and so that energy that was in

the photons has now been converted to

energy in this carrier molecule and in

the ATP where is it going it's going to

the Calvin cycle in the Calvin cycle

we're taking that energy and adding it

to carbon dioxide we're also adding

hydrogen and we're making high-energy

molecules like glucose now where did the

chloroplasts come from if we look at the

chloroplast it's found in all plants

it's very similar to a type of

cyanobacteria the algae that's pictured

right here and if we put those next

each other there are going to be a lot

of structures that are the same between

the two so they're going to have a

double membrane their own genome they're

going to have their own thylakoid

membrane it's almost as if we took a

cyanobacteria and got rid of all its

defenses on the outside and that's how

we think chloroplasts came to be we

think at one time endosymbiosis occurred

we have these cyanobacteria or ancestors

of cyanobacteria that were taken into a

cell now already inside there we had a

mitochondria and previous to that the

mitochondria had been taken into the

cell as well but as we engulf it instead

of breaking down the cyanobacteria the

cell got rid of those phagocytes around

the outside of it and it became the

chloroplast that we have today so what

does a chloroplast do it takes energy

from the Sun to make high-energy

molecules that can be utilized to grow

the plant or to generate ATP inside

mitochondria and I hope that was helpful