5.E: Structure and Function of Plasma Membranes (Exercises)
5.1: Components and Structure
Multiple Choice
Which plasma membrane component can be either found on its surface or embedded in the membrane structure?
A. protein
B. cholesterol
C. carbohydrate
D. phospholipid
- Answer
-
A
The tails of the phospholipids of the plasma membrane are composed of _____ and are _______?
A. phosphate groups; hydrophobic
B. fatty acid groups; hydrophilic
C. phosphate groups; hydrophilic
D. fatty acid groups; hydrophobic
- Answer
-
D
What is the primary function of carbohydrates attached to the exterior of cell membranes?
A. identification of the cell
B. flexibility of the membrane
C. strengthening the membrane
D. channels through membrane
- Answer
-
A
Free Response
Why is it advantageous for the cell membrane to be fluid in nature?
- Answer
-
The fluidity of the cell membrane is necessary for the operation of some enzymes and transport mechanisms within the membrane.
Why do phospholipids tend to spontaneously orient themselves into something resembling a membrane?
- Answer
-
Phospholipids spontaneously orient themselves into structures resembling membranes due to their structure. They have both hydrophobic and hydrophilic regions and the orientation into a bilayer allows the hydrophilic heads to interact with water on the interior and exterior of the bilayer while the hydrophobic tails avoid water and cluster together on the interior. This orientation is the most energetically favorable and creates a stable structure suited for biological membranes
5.2: Passive Transport
Multiple Choice
Water moves via osmosis _________.
A. throughout the cytoplasm
B. from an area with a high concentration of other solutes to a lower one
C. from an area with a low concentration of solutes to an area with a higher one
D. from an area with a low concentration of water to one of higher concentration
- Answer
-
C
The principal force driving movement in diffusion is __________.
A. temperature
B. particle size
C. concentration gradient
D. membrane surface area
- Answer
-
C
In which situation would passive transport not use a transport protein for entry into a cell?
A. water flowing into a hypertonic environment
B. glucose being absorbed from the blood
C. an ion flowing into a nerve cell to create an electrical potential
D. oxygen moving into a cell after oxygen deprivation
- Answer
-
D
Free Response
Why does osmosis occur?
- Answer
-
Water moves through a semipermeable membrane in osmosis because there is a concentration gradient across the membrane of solute and solvent. The solute cannot effectively move to balance the concentration on both sides of the membrane, so water moves to achieve this balance.
A cell develops a mutation in its potassium channels that prevents the ions from leaving the cell. If the cell’s aquaporins are still active, what will happen to the cell? Be sure to describe the tonicity and osmolarity of the cell.
- Answer
-
In the scenario described, the inactivation of the potassium channel would result in an accumulation of potassium ions in the interior of the cell, resulting in an overall increase in concentration of this dissolved solute making the cell cytoplasm hypertonic to the extracellular environment. If the aquaporin proteins are still active and osmosis still occurring the new imbalance of solute concentrations would lead to the movement of water into the cell. Water would be moving from the hypotonic extracellular space, where solute concentration is low and water concentration is high, to the intracellular space, where solute concentration is high and water concentration is low. Overtime osmosis into the cell could result in a burst membrane.
5.3: Active Transport
Multiple Choice
Active transport must function continuously because __________.
A. plasma membranes wear out
B. cells must be in constant motion
C. facilitated transport opposes active transport
D. diffusion is constantly moving the solutes in the other direction
- Answer
-
D
What happens to the membrane of a vesicle after exocytosis?
A. It leaves the cell.
B. It is disassembled by the cell.
C. It fuses with and becomes part of the plasma membrane.
D. It is used again in another exocytosis event.
- Answer
-
C
Which transport mechanism can bring whole cells into a cell?
A. pinocytosis
B. phagocytosis
C. endocytosis
D. facilitated-transport
- Answer
-
B
Free Response
Where does the cell get energy for active transport processes?
- Answer
-
The cell harvests energy from ATP produced by its own metabolism to power active transport processes, such as pumps.
Contributors and Attributions
Remixed and/or curated from the following works:
Fowler, S., Roush, R., & Wise, J. (2013). 3.E Cell Structure and Function (Exercises) . In Concepts of Biology . OpenStax (CC BY 4.0; Access for free at https://openstax.org/books/concepts-biology/pages/1-introduction ).
Clark, M. A., Douglas, M., & Choi, J. (2018). 2.2.9 Review Questions and 2.2.10 Critical Thinking Questions . In Biology 2e . OpenStax (CC BY 4.0; Access for free at https://openstax.org/books/biology-2e/pages/1-introduction ).