Pre-AP Cell Membrane Study Guide - KEY
1. Why were phospholipids so critical in the formation of the first cells?
Cell membranes are made of phospholipids. They are what allow the inside of the cell to
remain separate from the outside environment.
2. What does the “fluid mosaic model” explain?
Fluid – cell membranes actually move because of the unsaturated fatty acid tails
Mosaic – cell membranes are made of many different parts (phospholipids, proteins,
cholesterol)
3. List 4 functions of proteins found in the cell membrane.
Enzymes – speed up reactions
Glycoproteins – I.D. badges
Receptor proteins – receive signals from outside the cell
Transport proteins – move larger or polar solutes into and out of the cell
4. List the 3 types of transport proteins and describe them.
Channel – move polar/ionic molecules down their concentration gradient
Pump – move polar/ionic molecules against their concentration gradient
Carrier – bind to one (or a few) specific molecules and move then individually across the
membrane; much slower than channel protein
5. Why are glycoproteins important to the immune system?
Let your body tell the difference in your cells and bacteria/viruses
6. What does selective permeability mean?
Some things are allowed in/out of the cell but not everything
7. Explain how the fact that transport proteins have a shape that fits a specific solute aids
the cell in being selectively permeable.
Only certain solutes can come through transport proteins. Not everything outside the cell can
come in.
8. Why do receptor proteins have a shape that fits a specific messenger?
Each receptor protein will only receive 1 kind of messenger. This allows the body to know
that when it releases a message that it will only be picked up by the cells that need it.
9. How does a glucose molecule cross the cell membrane? How about ions?
Through transport proteins (both are large and have charges)
10. What is a “concentration gradient” and what is going “down or with” it and going
“against it”?
Difference in concentration across a cell membrane.
Going down the concentration gradient = going from high to low
Going against concentration gradient= going from low to high
11. What does tonicity refer to?
The ability of a solution to make a cell gain/lose water
12. Explain the movement of water if a cell were placed in a…
Hypertonic – Water leaves the cell (cell shrivels up like a skinny hyper kid)
Hypotonic – Water enters the cell (cell swells up like a fat hippo)
Isotonic – Water enters and leaves at the same rate
13. What type of solutions do plant & animal cells prefer?
plants = hypotonic (so they can gain water and be turgid – they have central vacuoles to store
water)
animals = isotonic
14. If an animal cell is placed in a hypotonic solution for too long, what will happen to it?
What prevents a plant cell from doing this?
Animal cell would lyse (burst). Plant cell has a cell wall that resists pressure (and a central
vacuole to store water)
15. When a plant cell is in a hypotonic solution, it is not flaccid, but ___turgid__________.
16. If solution A has a higher concentration of solute than solution B, what will move (solute
or water) and which direction if diffusion is occurring?
From A to B (it will go down it’s concentration gradient – more solute in A than B
17. If solution A has a higher concentration of solute than solution B, what will move (solute
or water) and which direction if osmosis is occurring?
From B to A (water will go down its own concentration gradient – there is more water in B
than in A)
18. List 2 differences between active & passive transport.
Passive = no energy (ATP) and down the concentration gradient
Active = energy (ATP) and up the concentration gradient
19. List and define the 3 examples of passive transport.
Diffusion – movement of small, nonpolar molecules directly across the phospholipid bilayer
going down their concentration gradient
Facilitated Diffusion – movement of larger or polar molecules across transport proteins going
down their concentration gradient
Osmosis – movement of water through aquaporins (transport proteins for water) going down
its own concentration gradient (will be the opposite direction of diffusion)******
20. Give 2 similarities and 1 different between diffusion and facilitated diffusion.
Both require no energy because they are going down their concentration gradient
Diffusion occurs directly across the phospholipid bilayer where facilitated diffusion occurs
through transport proteins
21. Give 1 similarity and 2 differences between facilitated diffusion and active transport.
Both use transport proteins
Differences = facilitated diffusion requires no energy and goes down its concentration
gradient while active transport requires energy and goes against the concentration gradient
22. Why do some molecules have to use vesicular transport to enter or leave the cell?
The molecule is too big to fit through a transport protein (For example, if a protein is coming
into or out of the cell then it would be too big to fit through another protein)
23. Endocytosis is a type of vesicular transport. Give three examples of endocytosis, and
explain each.
Phagocytosis – “cellular eating” A cell engulfs a particle by wrapping extensions called
pseudopodia around it and packaging it within a vacuole.
Pinocytosis – “cellular drinking” A cell gulps droplets of fluid into tiny vesicles.
Receptor – mediated endocytosis –
Receptor proteins for specific molecules are embedded in cell membrane.
These receptors have picked up particular molecules.
Then the cell membrane pinches off to form vesicle containing receptors and their
attached molecules
24. What is signal transduction?
After a receptor protein receives a signal, signal transduction pathway occurs which is a series
of steps to turn on a process inside the cell.
25. Be sure to be able to identify and explain the functions of all of the components of the
cell membrane. Use diagram to the right.