Name ______________________
Date ________________ Period__________
Biology
Study Guide
Chapter 3 Part 2:
Cell Membrane, Osmosis/Diffusion and Active Transport
1. Describe what it means to have a cell membrane that is semi- permeable.
The membrane allows some or certain molecules to pass through as long as they are small
enough to fit through the cellular pores.
2. Draw, label, and describe the cell membrane.
3. Describe and label a phospholipid.
4. Explain why the cell membrane is described as being a fluid mosaic model.
It describes the arrangement of molecules that make up a cell membrane. It is a flexible
membrane that moves from side to side like a fluid. It also has a variety of molecules in it
like a mosaic (different textures/patterns).
5. Fill in the chart below:
Function
Why/when
does it take
place?
Diffusion
Osmosis
Movement of substances from an area Diffusion of water across a
where there are more to where there membrane from an area where there
is less.
is more water to an area where
there is less water in order to reach
equilibrium.
This occurs until there is a balance of
substances called
equilibrium.
The moving substance has to be
smaller than the cellular pore.
This occurs when a solute or
substance is too large to pass
through the cell membrane.
Water moves to dilute the substance
that is too large!
Draw a
picture
6. Using the table tell the difference between each of the following types of solutions.
Sketch what an animal cell would look like in each.
Term
Hypertonic
Definition
The solution outside
the cell is greater than
inside the cell.
There is more water
inside the cell.
Outcome
Water will
leave; causing
the cell to
shrink.
Sketch
Hypotonic
Isotonic
The solution outside
the cell is less than
inside the cell.
There is more water
outside of the cell.
Water will
enter;
causing the
cell to swell.
The solution outside
the cell is equal or the
same as inside the cell.
Water will
continue to
move back
and forth at
an equal rate.
7. What does equilibrium mean?
Both sides of the membrane are at equilibrium. The molecules do not stop moving once
equilibrium is reached. They continue to move back and forth but at an equal and constant
rate.
8. Distinguish between diffusion and facilitated diffusion.
Diffusion is the movement of substances that are small enough to pass through the cellular
pores from an area where there are more to where there is less in order to reach
equilibrium.
Facilitated diffusion is the movement of substances that are too big to cross the
membrane so they use a protein channel “like a bridge” to get across the membrane. They
still move from an area where there are more to where there is less in order to reach
equilibrium.
9. On the T table below contrast both cell transports.
Passive
Active
Requires no energy from the cell.
Requires energy from the cell
Examples include diffusion, osmosis
and facilitated diffusion.
Examples include pumps, endocytosis and
exocytosis.
*** They both have in common the fact that they both transport material across a cell
membrane.
10. In the osmosis and diffusion lab, was the glucose able to move through the tube?
Explain your answer.
Yes. We know this because when we tested the solution outside the tube with the glucose
testing strip, the glucose testing strip changed color and indicated the presence of sugar.
11. In the osmosis and diffusion lab, was the iodine able to move through the tube?
Explain your answer.
Yes. We know this because the inside of the tube changed from a white color to a
purple/blue/black color because the iodine moved inside. Starch was inside the tube.
When iodine comes in contact with starch it will change from a yellow color into a
purple/blue/black color.
12. In the osmosis and diffusion lab, was the starch able to move through the tube?
Explain your answer.
No. We know this because if the starch moved out of the tube, then the solution outside
the tube would have changed from yellow to a purple/blue/black color. When iodine comes
in contact with starch it will change from a yellow color into a purple/blue/black color.
13. Suppose you have a container divided by a membrane that is permeable to water but
not to sugar. Side A has a 10% sugar solution. Side B has a 40% sugar solution. Both start
out at 10 cm in height. Over time, the height of one side drops to 7 cm, and the height of
the other side increases to 13 cm. Which side of the container is now at 7cm? Explain
your answer. If you need to, draw a picture to help.
Side A because the sugar cannot cross the membrane, it is too big, but water can cross.
The water has a greater concentration on side A and a lower concentration on side B so the
water moves from side A to side B to dilute the sugar.
Refer to reinforcement 3.4 worksheet.
14. If you are lost at sea, why do you not want to drink the water in the ocean?
Surrounding your cells with salt will make the water inside your cells come out to dilute the
salt. This will cause your cells to shrink and become dehydrated at a very quick rate,
causing you to become dehydrated very quickly.
15. Why are vegetables on display misted at the supermarket?
So that the water can move inside the cells of the vegetables, keeping them fresh and
plump. The vegetables will dry out easily when sitting in the open air and exposed to light,
so they are misted with water to keep them hydrated.
16. In the osmosis-egg lab, identify when the egg was in hypertonic solution and what
happened to the egg in that solution?
The egg was placed in a hypertonic solution when the egg was sitting in the corn syrup. The
egg shrunk or got smaller because water left the egg to dilute or dissolve the corn syrup
outside. Corn syrup was too big to cross the membrane so water had to dilute it.
17. In the osmosis egg lab, identify when the egg was in a hypotonic solution and what
happened to the egg in that solution?
The egg was placed in a hypotonic solution when the egg was sitting in pure water. The egg
expanded or got larger because water moved into the egg to dilute or dissolve the yolk.
The yolk was too big to cross the membrane so water had to dilute it.
18. Contrast the difference between Endocytosis and Exocytosis.
 Endocytosis – process of taking molecules into a cell by engulfing them in a
membrane
 Exocytosis – process of releasing a substance out a cell by the fusion of a vesicle
with the cell membrane.