Membrane Transport Animations
Name:
Key
Using the following website to fill out and answer the questions on this worksheet.
http://www.northland.cc.mn.us/biology/Biology1111/animations/transport1.html
The animation viewer is small so you may want to zoom in on the animation to better see what is going
on. Pay attention. The “back” button can only be used at the end of the animation segment. You may
need to watch each segment more than one time to answer the questions.
From the Main Menu, Click on Passive Transport.
Passive Transport
1. Passive transport is the movement of molecules across the cell that does not require an
expenditure of energy______. (What does expenditure mean?)
2. What are the three types of passive transport?
a. Simple diffusion________________________________________
b. Facilitated diffusion________________________________________
c. osmosis________________________________________
Click “Next”
Cell Membrane
3. Fill in the blanks of the following two diagrams. (Integral proteins and lipid bilayer)
In
____________________
____________
__
____________
__________
Watch the rest of the animation, follow along carefully. If you read this, draw an arrow by your name.
4. Why is the cell membrane described as a lipid bilayer?
It is made of lipid molecules arranged in two layers.
5. Why is it important to note that the lipid bilayer is fluid?
This fluidity provides for permeability.
6. Label the diagram to the right:
a. Which part of the lipid bilayer is polar (hydrophilic — water liking)?
b. Which is non-polar (hydrophobic — water non-liking)?
7. Which type of molecules have difficulty passing through the membrane?
Why do you think so? Polar molecules have difficulty passing
through. Probably because the non-polar middle of the membrane repels them.
8. Which type of molecules pass easily through the membrane? Why do you think so?
Non-polar molecules pass through easily, because the non-polar middle doesn’t repel them.
Click Next or Click on “Simple”
Simple Diffusion
9. Diffusion is the movement of molecules from an area of _high concentration__ to an area of _low
concentration_.
10. The term _Concentration gradient___refers to the relative density of one chemical substance versus
another.
Click Next
11. The rate of diffusion is dependent on these four things:
a. Steepness of the concentration gradient
b. Temperature (the warmer it is, the faster the rate of molecular movement)
c. Charge (electrical charge of the molecule)
d. Diameter of the diffusing molecule (the smaller the molecule, the faster the rate.)
12. Simple Diffusion ends when equilibrium is met.
a. What is meant by “equilibrium”? The concentration of molecules is the same all over/ on both
sides of a membrane.
b. Since we are talking about living things, what is better / more accurate word choice to describe this
condition in living cells _Dynamic equilibrium________________. (Check the Intro to Chapter 7.)
Click Next or Click on Facilitated
Facilitated Diffusion
13. Facilitated diffusion is the _passive transport _______ of molecules down a concentration gradient
with the aid of _special(ized) transport proteins_______________________.
14. Does facilitated diffusion require the use of energy (ATP)? NO (What is ATP?)
15. List the characteristics of some molecules that make them need help getting across the cell membrane?
They may be too big, have too much of an electrical charge, or be in scarce supply.
16. How does a protein “facilitate” the diffusion of the molecule?
Facilitate means make it easier, and the protein changes shape so the molecule can pass through the
membrane.
17. Sketch two protein channels in a membrane (before and after) showing facilitated diffusion.
[answer]
Click Next or Click on Osmosis
Osmosis
18. Define the term Osmosis. Osmosis is the passage / movement of water molecules across a membrane from
(an area of) high concentration to a (an area of) low concentration.
19. Compare and contrast Simple Diffusion and Osmosis. What is similar? What is different?
Use a Venn Diagram or T-chart for this please.
Simple diffusion: Any molecules, moving through any liquid or gas,
Osmosis: water molecules only,
moving through a membrane,
down a concentration gradient
down a concentration gradient.
20. Compare a hypertonic solution to a hypotonic solution. Draw a picture or two showing what is going on.
[hyper = more solute (dots) in external environment]
[hypo = less solute in external environment]
21. Water travels across a cell membrane… (Circle one)
a. from a hypotonic environment to a hypertonic environment 
b. from a hypertonic environment to a hypotonic environment.
or
22. Explain why water molecules move across a cell membrane. The water molecules move across the cell
membrane because they are more concentrated than the cytoplasm if they are in a hypotonic solution
and less concentrated than they are in the cytoplasm in a hypertonic solution
Click Next
Active Transport
22. _Active transport_______________________ is the pumping of molecules _against____their
___concentration gradient_________________________ with the expenditure of energy (ATP).
23. Why is active transport necessary?
Because some molecules needed by the cell cannot be supplied by simple or facilitated diffusion.
24. Explain the difference between Passive and Active Transport.
Passive transport requires no energy from the cell because molecules are moving down the
concentration gradient.
Active transport requires an input of energy to move molecules against their concentration gradient.
25. Why do cells need to move molecules against the concentration gradient into the cells or out of the cells?
Living cells often require molecules in large supply that are naturally scarce in their environment.
26. Describe the three different types of Active Transport used by cells to get molecules inside.
1. Ion pumps
2. Co-transport
3. Endocytosis
27. What are the three different kinds of Endocytosis? Use the back of this page for more space & drawings.
a. Phagocytosis
b. Pinocytosis
c. Receptor-mediated endocytosis