Download © Weston, 2010

© Weston, 2010
Cells, the units of LIFE!
Back in 3rd grade, Joe got separated from his class on the field trip to the local prison…
Cells, the units of LIFE!
It was life or death for Joe (at least in his imagination). Leaving a trail of yellow liquid,
Joe made his way past all the prison cells back to his class!
Cells, the units of LIFE!
blah blah Joe blah blah blah can’t
believe that you would blah blah blah
and I’ve been worried blah blah blah
blah learn some responsibility blah
blah
And since that fateful
field trip, Joe has never
forgotten what “cells”
were like…individual
spaces, separated from
others, where interesting
things go on.
Cells, the units of LIFE!
In every middle school and high school test…
…Joe made great grades, always
remembering how cells have similar
structures, but often unique
differences.
Let’s learn more.
#1 What are cells?
You probably remember from the last powerpoint that one of the 5 characteristics of
living things is that they are made of at least one cell. Many critters are made of just
one cell all by itself, but you’re far more complex—you are made of trillions of cells that
all have specific functions.
Cells are the basic unit of life, containing organelles—structures with specific functions.
Celery cells
Blood cells
Cell diagram
#2 Cells have structures (which
have functions)
That last diagram… is QUITE
complicated.
There are dozens of structures
that make up the cell or are found
inside of them. Where do we start?
First, it’s important to realize that
cells come in two varieties, depending
on how “complex” they are.
The cells in your body are complex. Bacteria??? Not so much.
#3 Prokaryotic Cells
Pro-kayr-ee-ott-ik
Prokaryotic cells are simply constructed and are found in the simplest living things—
bacteria.
What makes these so simple? A prokaryotic cell is a cell with no membrane-bound
structures (simple bacteria).
This means that all of its important structures inside
aren’t wrapped up inside of a membrane. If the whole
cell was a swimming pool, you’d see structures like
blocks and noodles and hot dogs floating around in it.
You could “feed” the cell by just pouring coke into the
water and watch the brown liquid spread through the
whole cell.
Everything mixes and just moves around in the cell.
#4 Eukaryotic Cells
Yoo-kayr-ee-ott-ik.
Eukaryotic cells are more complex and developed. The cells in plants and animals are
eukaryotic. The biggest difference between these and prokaryotic cells is that a
eukaryotic cell is a cell with membrane-bound structures (complex, human).
If a swimming pool was a eukaryotic cell,
you’d find everything in the water wrapped in
a ziploc bag or foil. The blocks and noodles
and food (like hot dogs and coke liquid)
would all be inside a baggie as they float
around in the pool. This keeps all the items
separate and controls how quickly food (the
hot dogs and coke) gets used.
The structures in a eukaryotic cell are
membrane-bound.
#5 All those Organelles
“Organelle” just means “little organ.” Your heart is an organ (structure) with a specific
function. So is your stomach, brain, and kidney.
Organelles are just structures that are so small they’re found inside of cells.
On your paper, you’ll fill in the name of the cell part or organelle, it’s function, and then
make a brief sketch of what it looks like. Your sketches won’t be perfect, but that’s ok.
#6 The Skin of a cell—cell
membrane
The cell membrane is like a backpack. All of the important stuff is found inside the
backpack, but if the backpack wasn’t there…the stuff inside would scatter and fall apart.
Without a cell membrane, the cell would die as its parts would squish away, like poking
a hole in a water balloon.
The cell membrane surrounds the cell like foil—controls what comes in and what
leaves.
In your sketch box, draw a blob-like shape and point to its outline.
#7 The gunk inside—cytoplasm
Cytoplasm is the gel-like substance that fills the cell. Cytoplasm is like the water inside
a water balloon or the chocolate milk inside a paper carton.
Cytoplasm is mostly water, but contains dissolved chemicals and other materials the
cell wants or needs to get rid of. You’re made of cells, which means you’re made of
cytoplasm. It’s because cytoplasm is so watery that it’s said “your body is mostly
water” even though you feel pretty solid. That’s because a solid cell membrane
surrounds the watery cytoplasm.
In your sketch box, sketch a cell again, but this time draw an arrow to the interior of the
cell.
#8 The big boss—the nucleus
Each of your cells is a living unit. But to live, the cell has to carry out certain processes.
It has to digest this, remove that, move this from here to there…so on and so on.
The nucleus is the control center of the cell. Contains DNA which commands the cell
to do its function. Your DNA commands the cell of what kinds of functions it needs to
perform. Muscle cells need to do this. Bone cells need to do something else. Liver
cells need to do other things. It’s all found in the commands of your DNA.
In your sketch box, draw a cell with a membrane-bound nucleus in the middle. Inside
the nucleus should be DNA. You can either draw squiggles or write “DNA.”
DNA
#9 The cell’s battery – mitochondria
For a cell to do all of the things it needs to do to stay alive, it needs energy.
It gets its energy from the food you eat after it is digested and broken down into tiny
sugar molecules. The sugar flows through your blood and each of your body’s cells
absorbs some.
At this point, the mitochondria inside each cell start to work. These look like jelly beans
with folded membranes inside them. They take sugar and convert it into usable forms
of energy for the other structures within this cell. For this reason, mitochondria are
often called the powerhouse of the cell—release energy from food.
#10 Construction Workers –
ribosomes
Ribosomes look like tiny spheres within the cell. They receive commands from the
DNA in the nucleus to construct new solid structures—proteins—that are used both
in and outside the cell. Pretty cool.
Ribosomes are spheres that construct solid structures in the cell.
#11 The cell’s highways –
endoplasmic reticulum
Endoplasmic reticulum look like a towel you’ve folded several times. “ER” are folded
membranes in the cell that helps move materials around. Ribosomes are sometimes
found attached to the E.R., which makes them look bumpy. We call this “rough ER.”
ER without ribosomes is referred to as “smooth ER.”
Endoplasmic reticulum help materials move around within the cell, acting like roads or
hallways.
#12 The cell’s post office – Golgi
bodies
Moving substances around inside the cell often requires putting those materials inside
of little bubbles. Think of the bubbles as envelopes or packages. It is the job of the
Golgi bodies inside cells to do this function.
Golgi bodies are layered structures that package & move items around the cell.
#13 The garage of the cell –
vacuole
The people on your street use garages for all sorts of reasons—a place to put their
cars, a place to put trash, a place to put random stuff, or as a place to even live in.
Vacuoles are similar. They are all-purpose storage areas for a cell.
A vacuole is a storage container for water, wastes, food, etc.
H2O
food
#14 The trash man – lysosome
The structures inside a cell often break down or wear out and need replacing. It’s the
job of the lysosome to digest these worn out parts, destroying them. Digestive
chemicals are stored inside the lysosome’s membrane, which keeps it from digesting
the entire cell, killing it.
A lysosome recycles cell parts using digestive chemicals.
Lysosomes are cool. It’s lysosomes that allow white blood cells to digest and eat
bacteria, keeping you from getting sick.
trash
#15 Organelles associated with
PLANT cells.
Plant cells have a couple structures that aren’t found in animals.
Write in the structure box:
Cell Wall
*PLANTS ONLY*
Like a brick wall or metal box around each cell, plants surround their cells by a thick
wall of fiber. The cell wall provides tough, rigid support around the cell. This is why
wood is so strong. Without cell walls, trees would fall right over as they would be
squishy and soft like an octopus.
#16 It ain’t easy being green. Or is
it?
Plant cells, and little organisms like euglena, contain another organelle called a
chloroplast. In your structure box, write:
Chloroplast
*PLANTS ONLY*
Chloroplasts are green. They’re green because they contain a special chemical called
chlorophyll. This allows these cells to perform photosynthesis—making sugar directly
from sunlight. If only OUR cells had chloroplasts.
In summary, a chloroplast is a green organelle that performs photosynthesis.
photosynthesis
#17 Plant cells vs. Animal cells.
So, plant cells have a thick cell wall surrounding the cell membrane. Animal cells don’t
(which allows them to take on new shapes—useful in some situations).
Plant cells have chloroplasts to perform photosynthesis. Animal cells don’t (and aren’t
green colored because of it).
There’s one more distinction I’d like you to know about…
Remind us what a vacuole is or does…
Excellent.
Plant cells usually have a humongous water-filled
vacuole, called a central vacuole, that pushes out
on the cell membrane to keep the cell rigid and
tough. If the vacuole loses too much water, it will
cause the cell to become limp. If too many cells
suffer this fate, the entire plant will “wilt” and its
leaves will lose their shape and strength and
droop.
#18 Just like a lot of units…
…this one is going to have a LOT of vocabulary—most of it will be new to you.
Keep this notes sheet and use it to study and help you with other assignments. You’ll
need it!
And That’s…