Download KEY Unit 3 Plasma Membrane and Cellular Transport

KEY
Unit 2 Content
1. Describe the function of the following organelles

Vesicles- Used to transport cellular products throughout the cell.

Ribosomes- Produces proteins (including enzymes) by following coded instructions that come
from the nucleus of the cell.

Lysosomes- Spherical structures that digest and recycle the cells used components by

breaking down proteins, nucleic acids, lipids and carbohydrates
Endoplasmic reticulum- ‘Rough Draft’ of a protein is transported from one part of a cell to another
via the ER. Part of the ER also synthesizes proteins are breaks down toxins.

Golgi apparatus- Organelle which modifies cell products, packages them for distribution, and
sends them off in a vesicle.
2. What happens to the amount of ATP generated by your muscle cells as you go through a period
of intense training for an upcoming marathon? Why?
It increases. As the energy demands of the cell increase, more mitochondria are needed to meet
that demand (remember, they are self replicating). Cell Respiration rate increases as the energy
demands of the cell increase. More mitochondria &/or energy demands = more cell respiration =
more ATP generated.
3. What happens to the amount of ATP generated by your muscle cells as you go through a period
of recovery after hurting yourself in a sports injury? Why?
It decreases. As the energy demands of the cell decrease, the rate of cell reparation in our
mitochondria also decreases. Less cell respiration = less ATP generated.
4. What happens to the rate of photosynthesis if the amount of water decreases?
It decreases. It is one of the ‘inputs’ for photosynthesis. If you have less of it, the rate will
decrease.
5. If there was a drought next summer, what would happen to the amount of oxygen that plants
produce?
It would decrease. A drought means less water. Less water means a lower rate of
photosynthesis. A lower rate of photosynthesis means less oxygen (product of the reaction)
produced.
What would happen to the amount of glucose that plants produce? It would also decrease, for
the same reason, as glucose is also a product of the reaction.
Unit 3 Content
Plasma Membrane Dynamics
1. What is the function of the cell (plasma) membrane?
It regulates what materials enter and leave the cell.
2. Explain how the cell membrane helps our cells maintain homeostasis.
Substances move across the membrane (either through the lipid bilayer or via proteins) based on
their concentrations. This helps our cells maintain homeostasis.
3. What is the name of the molecules that make up the foundation of the lipid bilayer?
Phospholipids
4. What are the parts of a phospholipid? Include their polarity in your answer.
A phosphate group (the ‘head’) which is POLAR & two fatty acids (the ‘tails’) which are
NONPOLAR.
5. The plasma membrane is selectively permeable. What does that mean?
A selectively permeable membrane allows some substances to cross more easily than others,
and blocks other substances from crossing into the cell.
6. What part of the plasma membrane blocks many large/ polar molecules from entering the cell?
The interior portion (the ‘tails’)
7. What are some of the ‘jobs’ done by the proteins that are embedded in the lipid bilayer?
They bring in polar/ ionic substances to the interior of the cell. This is how glucose is brought into
our cells for example. (through protein channels)
Some act as receptors; Some act as chemically identify the cell to other cells
8. How do membrane proteins stay in place within the plasma membrane?
They have two polar ends that are attracted to water and a nonpolar middle section.
* Note: Although proteins are held in place by this dual attraction, some are free to float within the cell
membrane.
Membrane Transport
9. What is a concentration gradient?
Difference in concentration across a space.
10. What does it mean if a cell in solution is said to be in ‘equilibrium’?
The concentration of a substance is balanced on both sides of a membrane.
When this happens, there is still movement across the membrane, but it happens in both
directions as there is no net change in concentration on either side.
11. What is passive transport? (use the word concentration gradient in your answer)
Movement of a substance DOWN its concentration gradient. (‘Down’ its gradient means from a region of
HIGH concentration to a region of LOW concentration).
12. List and describe several examples of passive transport as discussed in class.
** All types of passive transport involve movement of a substance from a region of HIGH concentration to
a region of LOW concentration.
Simple Diffusion- Movement of a substance down its concentration gradient, directly through the
phospholipids.
Example- the dispersal of ink in a beaker of water.
Osmosis- The diffusion of water across a semi-permeable membrane. The concentration of solute on
either side of the membrane is what determines which direction water will flow.
Ion Channels- Membrane proteins that allow ions passage into or out of the cell DOWN their
concentration gradient.
Facilitated Diffusion- Movement of a substance down its concentration gradient with the help of a carrier
protein. Ex. This is how glucose enters our cells.
13. Give an example of a substance that can diffuse across the plasma membrane with no protein
assistance.
Only small and nonpolar substances (sometimes small and polar too) can do this. Substances like O 2,
CO2 and water.
14. How is simple diffusion different than facilitated diffusion?
Both involve substances that follow their concentration gradient; however the substance goes
through a protein channel or carrier protein in facilitated diffusion.
15. Use the u-tube below to answer the question below it.
A
B
The black dots represent a solute that is dissolved in water. Which direction will the water move?
A B or B A. Explain your answer.
Toward side A. There is a greater solute concentration, and less free water on side A. Water moves from
where it is abundant to where it is rare (high to low).
16. Indicate whether a cell would shrink, swell, or remain the same size when placed in the following
solutions. Circle the answer that you think is correct.
Hypotonic solution

The cell would…….
shrink
swell
remain the same size
shrink
swell
remain the same size
shrink
swell
remain the same size
Hypertonic solution

The cell would…….
Isotonic solution

The cell would…….
17. A cell has a 5 % solute concentration and is placed in a solution that has a 10% solute
concentration. Draw a picture to depict this scenario. Include arrows to show where
movement of water molecules.
5% Solute
10% Solute
Hypertonic Solution
18. A cell that has a 10% solute concentration is placed in a solution that also has a 10% solute
concentration. Draw a picture to depict this scenario. Include arrows to show where
movement of water molecules.
10% Solute
10% Solute
Isotonic Solution
19. A cell has a 10% solute concentration and is placed in a solution that has an 8% solute
concentration. Draw a picture to depict this scenario. Include arrows to show where
movement of water molecules.
10% Solute
8% Solute
Hypotonic Solution
20. What would happen to a saltwater aquarium fish that was mistakenly placed in a freshwater tank
at Petco? Explain.
It will die. Since the fish was placed into a hypotonic solution, water will move into the cells of the
fish, causing them to burst.
21. How do large polar molecules enter our cells?
Membrane Proteins
22. What is active transport? (use the word concentration gradient in your answer)
Transport of materials into a cell against a concentration gradient (from LOW to HIGH).
23. How is passive transport different than active transport?
Active transport requires the use of energy, whereas passive transport does not.
24. Identify & describe the 2 types of active transport that were discussed in class. Provide an
example for each type as well.
1)
Molecular Pumps- Carrier proteins are used to move a substance into or out of a cell against
its concentration gradient. Example- Sodium-Potassium pump pumps Na+ ions OUT of our
cells and K- ions INTO our cells against their gradients.
2) Vesicle Mediated Transport (bulk transport)- The cell membrane forms a vesicle, which
moves the substance either in or out of the cell. This method is used to move large amounts
of substances in or out. Examples- Endocytosis and Exocytosis.
25. When would a cell use exocytosis or endocytosis?
When a cell needs to remove (exocytosis) or bring in (endocytosis) large amounts of
material. This is how single celled organisms like amoeba’s ‘eat’ and ‘expel waste’.