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Cells
Unit Notes
We knew nothing about cells until the invention of the microscope by Robert Hook in the 1600s.
 The Cell Theory:
1. All living things are made up of cells.
2. The cell is the basic unit of structure and function in all living things.
structure: what something is made of or looks like
function: what something does (its job)
3. All cells come from other cells.
Levels of Organization in Living Things:
A group of similar cells working together make a tissue (ex/ muscle cells working together make muscle
tissue); a bunch of tissues working together make an organ (ex/ blood and muscle tissue and nerve tissue
and fat tissue make a heart); a bunch of organs working together make an organ system (ex/the stomach,
the intestines, the liver, and the esophagus make the digestive system); a bunch of organ systems working
together make an organism (ex/ a person!)
cells

tissues

organs

organ systems

organism
 Types of Cells
There are two basic kinds of cells: prokaryotic and eukaryotic
A prokaryotic cell is a simple cell without a nucleus. Bacteria are prokaryotic organisms (prokaryotes).
A eukaryotic cell is a complex cell with a nucleus and other membrane-bound structures. All other
organisms besides bacteria are eukaryotes.
ANIMAL CELL
Animal Cell Structures (called organelles) and Functions
Nucleus: directs all cell activities, contains the cell’s genetic/hereditary material (DNA in chromosomes)
Nuclear envelope/membrane: determines what goes in and out of nucleus
Nucleolus: inside the nucleus, it makes ribosomes
Cytoplasm: gel-like substance that holds organelles
Cell membrane: determines what goes into and out of cell, provides shape and support
Endoplasmic reticulum: passageways that transport materials (mostly proteins) throughout cell
Ribosomes: make proteins
Mitochondria: “power-house of the cell” where respiration occurs to give the cell energy
Golgi Bodies/Complex: packages and transports materials for the cell
Vacuoles: store food, water, and waste for the cell
Lysosomes: break down dead cell parts
PLANT CELL
Additional structures found in plant cells and their functions:
Cell wall: nonliving material (made of cellulose) that supports and protects the cell
Chloroplasts: contain the green pigment chlorophyll, where photosynthesis takes place
(Plant cells also tend to have one large vacuole for storing water, instead the many smaller vacuoles that
an animal cell has.)
Prokaryotic (Bacteria) cell:
 Cell Processes
Reproduction
Body cells reproduce by the process of cell division. If a cell were to just divide, however, each new
“daughter” cell would have only half the number of chromosomes, therefore only half the directions for
survival and wouldn’t live. So before cell division, the cell must undergo mitosis, which is the duplication of
the chromosomes. Because only one parent is involved (no sperm or egg), this is a type of asexual
reproduction.
Mitosis
Sex cells (eggs and sperm) reproduce slightly differently. If they just did mitosis and cell division, then
every sperm and egg would have the full count of chromosomes (in humans, that’s 23 pairs or a total of
46). Then, if a sperm and egg meet, the resulting fertilized egg would have double the number of
necessary chromosomes (92) with too many directions for survival and would die. Therefore, sperm and
egg cells, unlike every other type of cell in the body, should only have half the number of chromosomes
(23). The process where sex cells duplicate their chromosomes, then split in half, then split in half again,
is called meiosis. The result is four “daughter” cells. [Organisms that reproduce using sperm and eggs
perform sexual reproduction.]
Transport
Most materials move into and out of the cell through the cell membrane simply because of a difference in
concentration of substances. For instance, if there is more oxygen (O 2) outside of the cell in the
bloodstream than there is inside the cell, those O2 molecules will try to balance themselves out by moving
into the cell. If there is more carbon dioxide (CO2) inside the cell, those CO2 molecules will try to balance
themselves out and leave the cell to go into the blood. This simple movement of molecules from an area of
high concentration to an area of low concentration is called diffusion. If the substance moving across a
cell membrane is water (H20), it’s a special kind of diffusion called osmosis.
Energy
Cells get energy to live through the process of cellular respiration. Although the chemical formula for
this process can seem scary at first, it really makes a lot of sense if you think about it. You eat food so
you’ll have energy. You already know that you breathe in oxygen and breathe out carbon dioxide, and you
already know that you sweat and urinate water out of your body. The chemical formula for this process
just looks at this in a little more detail. For instance, most of the food you eat gets broken down by your
digestive system into a simple sugar called glucose (C6H12O6). The glucose goes into all of your body cells,
along with oxygen, and then into the mitochondria where they are broken down into individual carbon,
hydrogen, and oxygen atoms. Then, these atoms rearrange themselves into new substances (water and
carbon dioxide), giving off a whole bunch of energy in the process which the cell uses to live. The water
and carbon dioxide leave the cells, go through the body, and are excreted by you.
Chemical reaction for respiration:
C6H12O6
+
glucose
O2
H2O
oxygen
water
+
CO2
+
energy
carbon dioxide
Respiration is done by all plant and animal cells to get energy to survive. Since plants don’t ingest food,
they need to make their own in a process called photosynthesis., which is essentially the opposite of
respiration. Think about it: you know plants take in water and breathe in your carbon dioxide, and you
know they give off our oxygen and they make their own food (glucose)vwith sunlight (energy).
Chemical reaction for photosynthesis:
H 2O
water
+
CO2
carbon dioxide
(sunlight)
C6H12O6
glucose
+
O2
oxygen