- [Voiceover] Structure and function of cells.
This chapter.
The concept of cell doctrine.
Now this is an idea that holds true
for all the cells you'll ever see.
First off, every living thing, plant, animal, you name it,
every living thing is composed of cells.
Each and every single cell
can be an individual, small unit of life.
So if you try to look at what the smallest unit of life is,
according to these characteristics of life,
what life really is,
a cell is the only structure that's the same size,
so talking microscopic,
the only structure that small
that exhibits all the characteristics of life.
And what's kind of unique and interesting at the same time
is every single cell comes from a preexisting cell.
Cells do not miraculously appear.
They have to come from someplace.
So in the case of a cell,
it's coming from a preexisting one that was already there,
whether it's one cell that divides and makes two,
whether it's two cells coming together to make one,
but every cell comes from these preexisting cells.
All these cells are categorized and classified
into two main categories.
The first category to look at is the prokaryotic cell.
These prokaryotic cells are the more simplistic
of the two categories.
They contain a plasma membrane, that's a lipid membrane
that goes around the outside of the cell.
Helps contain things, keep them inside.
Prokaryotic cells do not have a nucleus.
The nucleus is what stores,
now what was that again?
That material?
Let's see if you can remember back to the chemistry eval.
Ah yes.
The nucleus stores DNA.
DNA, or deoxyribonucleic acid.
So if you didn't remember that part,
you might want to go back and refresh back in chapter two
the chemistry stuff.
Cytoplasm.
A liquid, a fluid.
This fluid is found filling the inside of the cell
and there's basically no true organelles.
So you have the plasma membrane
filled with cytoplasm,
and really no set organelles in there instead.
The second category, the eukaryotic cells.
You have a plasma membrane,
same lipid membrane around the outside.
There is a nucleus, which means it contains what again?
Yeah, it contains DNA, deoxyribonucleic acid.
So that's where all the information is found
within the eukaryotic cell.
You still have the cytoplasm,
so it's a fluid within a membrane,
but now you do have organelles.
The organelles are structures found within the cell.
These are very tiny, microscopic structures.
But each one of them has a particular function.
You get to go this way.
Your body, the skin, is the outside layer.
It contains everything inside.
All the stuff inside are organs.
Each organ has a specific function.
Heart pumps blood, lungs exchange gasses.
Well, the organelle is the same idea.
Plasma membrane surrounds.
Organelles inside.
And each organelle has a very specialized function.
So every cell that you see in your body,
all the human cells, are all eukaryotic.
That means every cell in our body,
we're looking at the plasma membrane.
We have organelles, we have cytoplasm.
We have all these basic features in every cell of our body.
This is showing a comparison
between the eukaryotic and the prokaryotic cell.
On the left, under A,
that more roundish cell is a eukaryotic animal cell.
What you notice is, you can see the red inside.
Those are organelles.
The blue with the yellow, that's the nucleus.
But if you compare that to the prokaryotic cell on the right
it's a little more oval shaped.
You do not see a nucleus, you do not see organelles.
So even though they're both cells, they're both alive,
they both contain genetic material,
they have very distinct functions.
Well cell structures can change quite a bit.
You think of what your muscles versus your bones
versus your blood cells versus your skin all look like.
They're all different.
They all have different structures.
Their cells all have different structures.
So it's important to note that your cell structure
reflects the function of that cell.
So a lot of eukaryotic cells are pretty similar
but there are structural differences.
For example, your muscle cell.
You have muscle cells found in your skeletal muscles.
Things like bitza brachii, tricep brachii, pectoralis major.
Well, those muscle cells are just a little bit different
than muscle cells found in your heart, cardiac muscle.
But all these muscle cells can contract.
They can physically move something.
Well, look at nerve cells.
The last time I checked a nerve was not lifting anything up.
Nerve cells instead, or neurons,
travel over longer distances.
They carry an impulse or a signal.
So you might carry a signal from your brain
down a nerve to the muscle.
The muscle then can create the movement.
Over here in portion A you're seeing muscles of the heart.
Those are cardiac muscles.
Compare that to the middle one, B.
That's going to be a neuron,
part of your central nervous system.
And C on the right,
those almost square-shaped cells in pink.
They're forming a tubule, or basically a tube,
within the kidney.
All have drastically different shapes
but all have the same basic idea.
Cell membrane, nucleus, organelles, cytoplasm.
It's all there.
Majority of cells you can't see.
They're microscopic.
So most of these cells, even if you look at your hand,
can you see a cell?
No.
The reason it keeps smaller
is it helps them to stay efficient.
It helps with their volume,
or the amount of stuff inside, to surface area ratio.
If cells got too big they wouldn't be as efficient.
But even though these cells need to remain small,
some cells are larger.
So any guesses or thoughts
on a large cell that we see without magnification?
You can simply look at it and say, "Hey, there is a cell."
Any thoughts?
I want to bet you've seen this numerous times in your life,
if not on at least a weekly basis, if not daily even.
Well, have you ever seen an egg?
That's it.
An egg is actually a single cell.
The reason it's so large
is that egg not only must contain the material
to form a new organism, new genetic material,
but it must also contain enough nutrients
for the developing embryo to survive before it hatches.
So an egg, one single cell, we can see with our own eyes.
Here we have three different types of microscopes.
On the left you can see a cell light microscope.
The light microscope is the simplest,
probably most basic of all of these.
All you need is a light source,
something to hold the specimen, that has a slide,
and then you need to have your lenses above it
to magnify your field of vision.
These are great to a point
but they can only magnify so much.
To have a larger or higher magnification,
you can move into the middle one, an electron microscope.
Now again, you can see the electron microscope
is the same basic idea.
There is a specimen in there.
You have different lenses
and that's to make the images larger.
The difference is
you can have much higher magnification rates.
But from that electron microscope, if you look at the cell,
that cell is only seen in two dimensions.
Move over to the right-hand side
under the scanning electron microscope.
Now we can see it, again very highly magnified,
but in three dimensions.
We're not looking at one particular plane.
We're able to look above, below, and around
the entire field of view.
So light microscope is the most common.
Electron microscope and scanning electron
are very useful to see even small.
To continue on with the idea of cells stays small
to stay efficient.
The reason they must stay small
is to keep a high surface-to-volume ratio,
which means that there's a lot more surface area,
or space on the outside,
than there is volume or liquid particles on the inside.
This is necessary because it helps promote efficiency,
helps things occur easier,
as far as acquisition of nutrients and disposal of waste.
By having a large surface area to small volume,
that means you have plenty of locations
all around the entire cell surface.
Well all of that gives you plenty of space
to bring in or acquire nutrients.
So it's really easy to get nutrients
to almost any spot inside the cell.
Disposal of waste?
Well, that means pretty much you have a cell plasma membrane
around the outside of the cell
in close proximity to any particle inside
that needs to be disposed of.
So it's easy to get rid of waste, easy to pick up nutrients.
So what ends up happening is
when you look at one large cell, or eight small cells,
if you're looking at the eight small cells,
each side, all of the six sides of the cell,
can take in nutrients, can release waste.
So if you look at that one large cell now,
that surface area of a large cell is the equivalent
of a top, bottom, left, right, front, and back
of the entire cube of eight cells.
What you've gained advantage to
is now you have that split in the middle
that'll increase surface area.
More surface area, more nutrients absorbed,
more waste removed.
But that's not the only way to increase surface area.
You could have special cell adaptions.
In letter C to the right,
you notice that we have microvilli.
Those are those tiny little finger-like projections.
The main purpose of microvilli is to increase surface area.
All those tiny up and down columns
will increase the amount of surface area
making absorption of nutrients more efficient
and removal of waste more efficient.