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- [Voiceover] Structure
and function of cells.

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This chapter.

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The concept of cell doctrine.

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Now this is an idea that holds true

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for all the cells you'll ever see.

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First off, every living thing,
plant, animal, you name it,

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every living thing is composed of cells.

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Each and every single cell

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can be an individual, small unit of life.

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So if you try to look at what
the smallest unit of life is,

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according to these
characteristics of life,

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what life really is,

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a cell is the only structure
that's the same size,

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so talking microscopic,

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the only structure that small

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that exhibits all the
characteristics of life.

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And what's kind of unique and
interesting at the same time

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is every single cell comes
from a preexisting cell.

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Cells do not miraculously appear.

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They have to come from someplace.

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So in the case of a cell,

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it's coming from a preexisting
one that was already there,

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whether it's one cell that
divides and makes two,

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whether it's two cells
coming together to make one,

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but every cell comes from
these preexisting cells.

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All these cells are
categorized and classified

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into two main categories.

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The first category to look
at is the prokaryotic cell.

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These prokaryotic cells
are the more simplistic

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of the two categories.

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They contain a plasma membrane,
that's a lipid membrane

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that goes around the outside of the cell.

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Helps contain things, keep them inside.

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Prokaryotic cells do not have a nucleus.

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The nucleus is what stores,

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now what was that again?

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That material?

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Let's see if you can remember
back to the chemistry eval.

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Ah yes.

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The nucleus stores DNA.

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DNA, or deoxyribonucleic acid.

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So if you didn't remember that part,

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you might want to go back and
refresh back in chapter two

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the chemistry stuff.

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Cytoplasm.

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A liquid, a fluid.

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This fluid is found filling
the inside of the cell

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and there's basically no true organelles.

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So you have the plasma membrane

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filled with cytoplasm,

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and really no set
organelles in there instead.

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The second category, the eukaryotic cells.

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You have a plasma membrane,

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same lipid membrane around the outside.

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There is a nucleus, which
means it contains what again?

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Yeah, it contains DNA,
deoxyribonucleic acid.

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So that's where all the
information is found

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within the eukaryotic cell.

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You still have the cytoplasm,

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so it's a fluid within a membrane,

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but now you do have organelles.

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The organelles are structures
found within the cell.

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These are very tiny,
microscopic structures.

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But each one of them has
a particular function.

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You get to go this way.

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Your body, the skin, is the outside layer.

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It contains everything inside.

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All the stuff inside are organs.

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Each organ has a specific function.

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Heart pumps blood, lungs exchange gasses.

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Well, the organelle is the same idea.

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Plasma membrane surrounds.

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Organelles inside.

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And each organelle has a
very specialized function.

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So every cell that you see in your body,

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all the human cells, are all eukaryotic.

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That means every cell in our body,

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we're looking at the plasma membrane.

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We have organelles, we have cytoplasm.

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We have all these basic features
in every cell of our body.

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This is showing a comparison

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between the eukaryotic
and the prokaryotic cell.

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On the left, under A,

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that more roundish cell is
a eukaryotic animal cell.

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What you notice is, you
can see the red inside.

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Those are organelles.

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The blue with the yellow,
that's the nucleus.

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But if you compare that to the
prokaryotic cell on the right

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it's a little more oval shaped.

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You do not see a nucleus,
you do not see organelles.

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So even though they're both
cells, they're both alive,

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they both contain genetic material,

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they have very distinct functions.

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Well cell structures
can change quite a bit.

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You think of what your
muscles versus your bones

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versus your blood cells versus
your skin all look like.

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They're all different.

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They all have different structures.

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Their cells all have different structures.

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So it's important to note
that your cell structure

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reflects the function of that cell.

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So a lot of eukaryotic
cells are pretty similar

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but there are structural differences.

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For example, your muscle cell.

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You have muscle cells found
in your skeletal muscles.

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Things like bitza brachii,
tricep brachii, pectoralis major.

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Well, those muscle cells are
just a little bit different

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than muscle cells found in
your heart, cardiac muscle.

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But all these muscle cells can contract.

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They can physically move something.

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Well, look at nerve cells.

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The last time I checked a nerve
was not lifting anything up.

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Nerve cells instead, or neurons,

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travel over longer distances.

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They carry an impulse or a signal.

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So you might carry a
signal from your brain

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down a nerve to the muscle.

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The muscle then can create the movement.

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Over here in portion A you're
seeing muscles of the heart.

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Those are cardiac muscles.

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Compare that to the middle one, B.

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That's going to be a neuron,

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part of your central nervous system.

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And C on the right,

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those almost square-shaped cells in pink.

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They're forming a tubule,
or basically a tube,

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within the kidney.

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All have drastically different shapes

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but all have the same basic idea.

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Cell membrane, nucleus,
organelles, cytoplasm.

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It's all there.

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Majority of cells you can't see.

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They're microscopic.

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So most of these cells, even
if you look at your hand,

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can you see a cell?

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No.

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The reason it keeps smaller

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is it helps them to stay efficient.

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It helps with their volume,

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or the amount of stuff
inside, to surface area ratio.

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If cells got too big they
wouldn't be as efficient.

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But even though these
cells need to remain small,

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some cells are larger.

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So any guesses or thoughts

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on a large cell that we
see without magnification?

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You can simply look at it and
say, "Hey, there is a cell."

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Any thoughts?

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I want to bet you've seen this
numerous times in your life,

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if not on at least a weekly
basis, if not daily even.

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Well, have you ever seen an egg?

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That's it.

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An egg is actually a single cell.

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The reason it's so large

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is that egg not only
must contain the material

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to form a new organism,
new genetic material,

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but it must also contain enough nutrients

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for the developing embryo to
survive before it hatches.

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So an egg, one single cell,
we can see with our own eyes.

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Here we have three different
types of microscopes.

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On the left you can see
a cell light microscope.

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The light microscope is the simplest,

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probably most basic of all of these.

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All you need is a light source,

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something to hold the
specimen, that has a slide,

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and then you need to
have your lenses above it

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to magnify your field of vision.

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These are great to a point

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but they can only magnify so much.

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To have a larger or higher magnification,

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you can move into the middle
one, an electron microscope.

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Now again, you can see
the electron microscope

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is the same basic idea.

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There is a specimen in there.

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You have different lenses

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and that's to make the images larger.

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The difference is

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you can have much higher
magnification rates.

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But from that electron microscope,
if you look at the cell,

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that cell is only seen in two dimensions.

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Move over to the right-hand side

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under the scanning electron microscope.

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Now we can see it, again
very highly magnified,

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but in three dimensions.

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We're not looking at one particular plane.

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We're able to look
above, below, and around

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the entire field of view.

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So light microscope is the most common.

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Electron microscope and scanning electron

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are very useful to see even small.

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To continue on with the
idea of cells stays small

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to stay efficient.

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The reason they must stay small

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is to keep a high surface-to-volume ratio,

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which means that there's
a lot more surface area,

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or space on the outside,

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than there is volume or liquid
particles on the inside.

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This is necessary because
it helps promote efficiency,

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helps things occur easier,

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as far as acquisition of
nutrients and disposal of waste.

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By having a large surface
area to small volume,

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that means you have plenty of locations

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all around the entire cell surface.

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Well all of that gives you plenty of space

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to bring in or acquire nutrients.

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So it's really easy to get nutrients

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to almost any spot inside the cell.

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Disposal of waste?

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Well, that means pretty much
you have a cell plasma membrane

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around the outside of the cell

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in close proximity to any particle inside

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that needs to be disposed of.

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So it's easy to get rid of
waste, easy to pick up nutrients.

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So what ends up happening is

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when you look at one large
cell, or eight small cells,

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if you're looking at
the eight small cells,

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each side, all of the
six sides of the cell,

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can take in nutrients, can release waste.

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So if you look at that one large cell now,

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that surface area of a
large cell is the equivalent

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of a top, bottom, left,
right, front, and back

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of the entire cube of eight cells.

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What you've gained advantage to

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is now you have that split in the middle

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that'll increase surface area.

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More surface area, more
nutrients absorbed,

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more waste removed.

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But that's not the only way
to increase surface area.

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You could have special cell adaptions.

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In letter C to the right,

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you notice that we have microvilli.

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Those are those tiny little
finger-like projections.

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The main purpose of microvilli
is to increase surface area.

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All those tiny up and down columns

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will increase the amount of surface area

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making absorption of
nutrients more efficient

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and removal of waste more efficient.