Welcome to Biology Regents Review… Session 9
Today’s date: ________________
Topics: Diffusion, active transport, osmosis, Diffusion through a Membrane state lab
Diffusion:
 Molecules tend to move from __________ concentration to __________ concentration.
 __________ is reached when the molecules are equally distributed.
 A __________ membrane will only allow molecules of a certain size to pass through it.
 The cell membrane will allow certain substances to __________ and __________ the cell.
 Substances will diffuse into a cell if the concentration of that substance is higher __________ the cell than
__________ the cell.
 Substances will diffuse out of the cell if the concentration of that substance is higher __________ the cell than
__________ the cell.
Refer to the diagram to the right to answer the following
questions:
A. If the concentration of oxygen is greater outside the cell
than inside the cell, in which direction will
oxygen diffuse?
B. What is the name of the outer layer of a cell that
controls what goes in and out of the cell?
C. CO2 is diffusing out of the cell into the capillary. nearby.
Does that mean the concentration of CO2 is less
inside the cell or inside the capillary?
D. If the concentration of water inside the cell is 97% and it is removed
from the organism and placed in a beaker filled with a 10% salt
solution will that cause the cell to remain the same size, expand, or
decrease in
size? Why?
E. In which direction do molecules diffuse?
Draw the before and after pictures of a cell placed
in distilled water then in a solution consisting of 80%
water.
Active transport:
“The ________ of substances from ________ to ________ concentration with an
________ input.”
Label:
Before / After
Transport channel
Lipid bilayer
Cell membrane
Cytoplasm
Low concentration
High concentration
Direction of movement
Energy input
Receptor protein
Osmosis:
“The ________ of water – ONLY.”
Did water flow in or out of
the cell?
Was the concentration of
water greater inside or
outside of the cell?
Was the concentration of
solute greater inside or
outside of the cell?
Diffusion through a Membrane state lab:
1. Define the following terms:
Semipermeable membrane:
Passive transport:
2. Suppose that you have a diffusion/osmosis apparatus similar to the one
that you used in the lab. In one side of the apparatus, there are 100 mL of
solution composed of distilled water and iodine. In the other side, there is
a 10% starch solution. The liquid levels in both sides are initially the same. Answer the following questions:
A. What will happen to the level of the water and iodine solution (Side A)?
B. Explain why this will occur.
C. What will happen to the color of the water and iodine solution? Why?
D. What will happen to the color of the starch solution? Why?
3. Often when a person is ill they must be given fluids intravenously (by injection directly into the blood vessel). Why
must the person never be given pure water intravenously? Be sure to explain your answer using the concepts of diffusion
and osmosis.
4. Describe the process by which the red onion pictured in the diagram to the left can be made to appear like
the diagram at the right using a substance you will identify, a piece of paper towel, and an eyedropper. You are not
allowed to raise the cover slip on the slide.
5. What process is responsible for the changes observed above?
6. Describe a technique that could make this process go in reverse.
7. Based on the state lab we completed…
A. List the two substances that diffused through the membrane.
B. Which substance did not diffuse through the membrane?
C. State the major factor that appears to determine whether or not substances pass through our membranes.
8. The arrows in the diagram represent the direction of movement of a certain type of molecule through the cell
membrane of two different cells. The dots represent the relative concentrations of this molecule. Which processes are
illustrated in the diagram?
A. phagocytosis and diffusion
B. active transport and diffusion
C. pinocytosis and osmosis
D. dehydration synthesis and circulation
9. The process of osmosis would explain the net movement of water into a cell if the percentage of
A. water was 90% inside the cell and 95% outside the cell
B. water was 95% inside the cell and 90% outside the cell
C. protein was 30% inside the cell and 35% outside the cell
D. water and protein was equal inside and outside the cell