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The
Cell
Theory
1. How are cells like bricks in
a wall?
Cells are the individual units
used to build living things just
like bricks are the individual
units used to build the wall.
2. How are cells different
from bricks in a wall?
“Cells are alive. Bricks are
not alive.”
3. Draw pictures of the
following cells to illustrate
different cell shapes:
Red Blood Cell
Skin cell
Bone cells
Nerve Cell
SPERM
Why do these cells have such
different shapes?
“The different shapes helps
the cell do its job more
efficiently.”
How do these cells get such
different shapes?
“The cell is following a
genetic design to construct the
plasma membrane a certain
way.”
4. Robert Hooke:
Year of his cellular
discovery:
1665
What was he observing?
A THIN slice of cork from
under the bark of a tree.
What was he observing with?
A very weak, homemade
microscope
What did he discover?
He was the first to observe
cells. He was actually looking
at the cell walls.
Why did he name his
discovery : “CELLS”?
The cell looked like the tiny
rooms that the priest slept in at
the monastery…which were
called cells.
5.How long did it take the Cell
theory to be developed?
200 years
Was it the result of just one
scientist work?
NO
6. Matthias Schleiden:
Who was he?
A German Botanist.
What year did he make his
cellular discovery:
1838
Schleiden
Discovered that
ALL parts of the
Plant were made
Of cells..Not just
Cork!
7. THEODOR SCHWANN
Who was he?
A German Zoologist
Year of his discovery?
1839
Schwann
German zoologist
Discovered that
All parts of an
Animal were
made up of cells.
8. Rudolf Virchow:
Who was he?
A Russian Biologist
What did he discover?
VIRCHOW
Russian scientist
that first
observed mitosis.
Learned that cells
come from other
cells.
9. State the three points of the
cell theory:
All living things are made of cells.
The cell is the basic unit of life!
Cells come from other cells!
10. Why is the Cell theory
considered to be the
Cornerstone of Biology?
“The cell theory applies to
ALL LIVING THINGS!”
11. What type of environment
are cells found in?
“All cells are surrounded by a
nutrient rich fluid.”
Fluid environment
12. Why are human cells
surrounded by blood and
tissue fluids?
Cells must obtain materials
from the fluid environment
and release waste materials
back into the fluid
environment.
What is the name of this fluid
that surrounds the cells?
“Interstitial fluid”
13. What keeps the cytoplasm
from mixing with the
interstitial fluids?
“A semi-permeable plasma
membrane called the CELL
MEMBRANE.”
14. Why is the plasma
membrane (cell membrane)
considered the cell “gate
keeper”?
The job of the cell membrane is
to control what enters and
leaves the cell.
15. What is Homeostasis?
A healthy balance of nutrients
entering and waste leaving a
cell.
16. How does the plasma
membrane function in
maintaining homeostasis?
It maintains homeostasis by
only allowing those things to
pass into the cell that the cell
needs.
If there is no need, the cell
membrane will not allow it to
pass into the cell.
17. Why is the cell membrane
called a “selectively
permeable membrane”?
“It only allows certain
molecules to pass through or
permeate the membrane”
18. Are all cell permeable to
the same molecules?
No!
Different cells have different
jobs..Thus different nutrient
requirements.
19. Why would a particular cell
be permeable to a specific
molecule yesterday, but
impermeable today?
Yesterday it needed that
molecule. Today it doesn’t need
it.
20.Why do you suppose some
molecules will move freely
across the membrane while
others require active
transport?
Tiny molecules like oxygen and
carbon dioxide gas can move
freely.
Fat soluable molecules can
move freely.
Big molecules like sugar require
active transport.
21. How long have scientist
been working on a model of the
plasma membrane?
50 years
22. Why is it necessary to keep
adjusting the model?
As technology improves, such
as the invention of the electron
microscope, we keep learning
new things.
23. Describe the lipid bilayer:
The plasma membrane is
composed of TWO LAYERS
of molecules called
phospholipids.
24. What is the difference
between the structure of a lipid
and a phospholipid?
A lipid is composed of two
strands of fatty acids.
The phospholipid has a
phosphate head attached to the
lipid.
26. Describe a phopholipid:
The phosphate
head is Polar! It is
hydrophilic – It
draws water to it.
The fatty acid
tails are nonpolar. They are
hydrophobic!
They push water
away.
27. Draw a picture of the
plasma membrane showing
the arrangement of the
phospholipids in the lipid
bilayer:
28. Explain the properties that
make the cell membrane act
like a very fine film of oil:
Within each layer, the fatty
acid tails can wag back and
forth, and entire
phospholipids can glide
sideways through their
layers.
29. Explain the job of the
cholesterol molecules found in
the plasma membrane:
JOB #1
The cholesterol molecules
bind the two layers of the
lipid bilayer together.
JOB #2
It makes the lipid bilayer
strong, yet flexible.
30. Describe the two ways
proteins are found in the
plasma membrane:
Some proteins are embedded in
the bilayer providing
passageways through the cell
membrane.
Others lie on top and act as
recognition markers
31. Why is the model of the
plasma membrane called the
Fluid Mosaic Model?
It is called the fluid mosaic
model because the
phospholipids and plasma
proteins are constantly
moving like a fluid, and the
membrane has a pattern of
proteins embedded in it.
32. What is the job of the
phospholipid bilayer?
“To provide structure,
determine shape, and forms
most of the cell’s outer
boundary.”
33. List the four functional
roles of the plasma proteins:
Role #1:
.Control which particles can
cross the membrane.
Role #1:
.Serve as enzymes and take
part in chemical reactions.
Role #1:
.Act as recognition markers
Role #1:
.Help fight disease by sending a
chemical message to the next
cell, warning it of viruses in the
area. Causes the neighboring
cells to secrete INTERFERON
to block the virus from
attacking it.
34. Could different cells in
your body perform different
functions if their membranes
were all permeable to exactly
the same materials? Explain.
No.
Some cells, like bone, need
calcium.
Nerve cells need copper.
Different cells have different
needs.