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From the smallest bacteria to the largest mammal (the blue whale), all living things are
composed of cells.
Simple organisms, like bacteria are made of just one cell (unicellular).
Complex organisms, like humans and blue whales are made of many cells (multicellular). If
you were to count all of the cells in you, you would be counting for quite awhile – over 300
trillion (300,000,000,000,000).
Regardless of what cell you pick to look at, you will find that each cell is filled with special
tiny structures that give the cell (and you) life. These tiny structures in cells are called
organelles, and if they ever quit working correctly the cell will die.
The Organelles
Cell Membrane – This thin layer of lipid (fat) molecules surrounds the outside of EVERY cell. This
membrane is SEMI-PERMEABLE and works like a gate letting only certain molecules to pass in
and out of the cell.
Cytoplasm – This thick, clear liquid fills up every cell like water in a water balloon. Dissolved in
this liquid are molecules the cell needs to survive.
Nucleus – A large sphere-like mass usually found in the center of the cell. The nucleus holds all the
cell’s genetic information (DNA).
Nuclear Membrane – This thin layer of lipid (fat) molecules surrounds the entire nucleus and helps
protect the genetic information.
DNA/Chromosomes – These long, thin, string-like molecules are your genetic information and are
in the nucleus. DNA molecules are like a set of encyclopedias that contain all the
information/instructions that makes you YOU!! Why didn’t you develop into an octopus??
Because you were given a set of DNA encyclopedias to produce a human – however – you don’t
look exactly like the human sitting beside you because some of the “pages” in your DNA
encyclopedia are not exactly like your neighbor’s (Unless you are both identical twins!!). Every
human cell has 46 DNA molecules in its nucleus. (Every dog cell has 78 DNA molecules in its
nucleus, each housefly has 12 DNA in each nucleus.)
Ribosomes – These organelles look like little black dots all over the cell’s cytoplasm. Ribosomes
are important because they make proteins for the cell. (When you eat a meal, your stomach
secretes enzymes to digest the food – these digestive enzymes are only one kind of protein
molecules made by ribosomes in your cells.)
Endoplasmic Reticulum – (Just say ER for short!). These organelles are made of thin membranes
folded back and forth all throughout the cytoplasm of the cell.They actually form a bunch of
interlocking tunnels that help move molecules around in the cell. There are two kinds of ER
found in cells:
Rough ER – This ER is covered with ribosomes and looks bumpy.
Smooth ER – This ER does not have ribosomes and is as smooth as a baby’s bottom.
Golgi Body – This organelle is made of thin membranes and looks kind of like several bowls sitting
one inside another, inside of another, etc. You know you are close to a Golgi Body when you see
a bunch of clear, round, bubbly-looking things in the cytoplasm. The Golgi Body packages up
molecules that the cell has made.
Vesicles – These are the clear, round, bubbly-looking things around the Golgi Body. They are the
packages that the Golgi Body makes. Inside a vesicle package are molecules that the cell has
made. The vesicle can store chemicals for the cell until they are needed.
Lysosome – These are special vesicles that contain strong digestive enzymes. When one of your
white blood cells swallows a bacteria that is trying to infect you, the lysosomes in the white
blood cell break open and digest the swallowed bacteria. In cell drawings, lysosomes are usually
made another color, or it is shaded in to make them look different from regular vesicles.
Mitochondria – This important organelle looks like a little hot-dog. If you cut open a mitochondria
you’ll find that the inside is filled with a folded membrane. Mitochondria produce all the energy
for your cells. Need to scratch your nose?? The mitochondria in your muscle cells supplies the
energy your muscle cells need to contract. To produce energy, the inner folded membranes of the
mitochondria complete a reaction called RESPIRATION where food that you eat is converted
into the energy every cell needs. Here is the Respiration reaction that occurs in the
mitrochondria. Learn it!!
You eat
You breathe in
You breathe out
You breathe out
GLUCOSE + OXYGEN  CARBON DIOXIDE + WATER +
C6H12O6
+
O2

CO2
+
H2O
Your cell gets
ENERGY
+
ENERGY(ATP)
Cell Wall – This structure is found in plant cells only. It is a rigid wall made of cellulose that
surrounds each plant cell.
Chloroplasts – These organelles are found in plant cells only. They are the green spheres that you
can find in the cytoplasm of most plant cells. Plants use their chloroplasts to turn the sun’s
energy into glucose – a food for the plant cell and the source of glucose (food) for every animal
cell on earth!! The reaction that occurs in the chloroplast is called PHOTOSYNTHESIS and it
looks like this:
ENERGY + CARBON DIOXIDE
(sunlight)
(from the air)
Sunlight Energy +
CO2
+ WATER  GLUCOSE + OXYGEN
(from the ground)
(food) (waste gas released to air)
+ H2O

C6H12O6
+
O2
Animal cells never have chloroplasts. That’s why animals always have to eat something (like a
salad or a juicy steak) to get their food.