Topic 2.1: Structure and Function of the Cell Membrane

Question 1

Define Plasma Membrane

Answer 1

Membrane surrounding the cytoplasm that consists of a phospholipid bilayer with embedded proteins; functions to regulate the entrance and exit of molecules to and from the cell.

Question 2

Define fluid-mosaic model

Answer 2

Model for the plasma membrane based on the changing location and pattern of protein molecules in a fluid phospholipid bilayer.

Question 3

Define glycolipid

Answer 3

Lipid in plasma membranes that contains an attached carbohydrate chain; assembled in the Golgi apparatus.

Question 4

Define glycoprotein

Answer 4

Protein in plasma membranes that has an attached carbohydrate chain; assembled in the Golgi apparatus.

Question 5

Define channel proteins

Answer 5

Protein that forms a channel to allow a particular molecule or ion to cross the plasma membrane.

Question 6

Define carrier protein

Answer 6

Protein in the plasma membrane that combines with and transports a molecule or ion across the plasma membrane.

Question 7

Define cell recognition protein

Answer 7

Glycoproteins in the plasma membrane that identify self and help the body defend itself against pathogens.

Question 8

Define receptor protein

Answer 8

Protein located in the plasma membrane or within the cell; binds to a substance that alters some metabolic aspect of the cell.

Question 9

Define enzymatic protein

Answer 9

Protein that catalyzes a specific reaction; may be found in the plasma membrane or the cytoplasm of the cell.

Question 10

Describe the roll of proteins, steroids, and phospholipids in the fluid-mosaic model.

Answer 10

*Phospholipids compose a bilayer that separates the inside from the outside of the cell.
*Steroids in the bilayer regulate the fluidity of the membrane
*Proteins present in the membrane contribute to its structure, the package of molecules across the membrane, signal pathways, cell recognition and enzyme functions.

Question 11

What is the function of Carbohydrate chains in the plasma membrane?

Answer 11

These are long chains of sugar molecules that are attached to the outside of the plasma membrane. They serve as identification tags, helping cells to recognize each other and interact with one another.

Question 12

What is the function of Phospholipid bilayer in the plasma membrane?

Answer 12

This is the main structural component of the plasma membrane. It is made up of two layers of phospholipids, which are molecules with a hydrophilic (water-loving) head and a hydrophobic (water-fearing) tail. The phospholipid bilayer forms a barrier that allows only certain molecules to pass through the membrane.

Question 13

What is the function of Filaments of cytoskeleton in the plasma membrane?

Answer 13

Filaments of cytoskeleton: The cytoskeleton is a network of protein filaments that provides support and shape to the cell. The filaments of the cytoskeleton are also involved in the movement of the cell, including the movement of organelles within the cell and the movement of the cell itself.

Question 14

What is the function of cholesterol in a plasma membrane?

Answer 14

Cholesterol is a type of lipid (fat) molecule that is found in the plasma membrane. It helps to maintain the fluidity of the membrane, allowing it to remain flexible and responsive to changes in the cell’s environment.

Question 15

Define selectively permeable

Answer 15

Property of the plasma membrane that allows some substances to pass, but prohibits the movement of others.

Question 16

Define diffusion

Answer 16

Movement of molecules or ions from a region of higher to lower concentration; it requires no energy and tends to lead to an equal distribution (equilibrium).

Question 17

Define solute and solvent

Answer 17

A solute is a substance that is dissolved in a solvent, forming a solution. (salt)

A solvent is a liquid portion of a solution that serves to dissolve a solute. (water)

Question 18

Define osmosis

Answer 18

Diffusion of water through a selectively permeable membrane.

Question 19

Define osmotic pressure

Answer 19

Measure of the tendency of water to move across a selectively permeable membrane; visible as an increase in liquid on the side of the membrane with higher solute concentration.

Question 20

Define isotonic solution

Answer 20

Solution that is equal in solute concentration to that of the cytoplasm of a cell; causes cell to neither lose nor gain water by osmosis.

Question 21

Define hypotonic solution

Answer 21

Solution that contains a lower solute (more water) concentration than the cytoplasm of a cell; causes cell to gain water by osmosis.

Question 22

Define hypertonic solution

Answer 22

Higher solute concentration (less water) than the cytoplasm of a cell; causes cell to lose water by osmosis.

Question 23

Define facilitated transport

Answer 23

Passive transfer of a substance into or out of a cell along a concentration gradient by a process that requires a protein carrier.

Question 24

Define active transport

Answer 24

Use of a plasma membrane carrier protein to move a molecule or ion from a region of lower concentration to one of higher concentration; it opposes equilibrium and requires energy.

Question 25

Define sodium transfer pump

Answer 25

Carrier protein in the plasma membrane that moves sodium ions out of, and potassium ions into, cells; important in the function of nerve and muscle cells in animals.

Question 26

Define exocytosis

Answer 26

Process in which an intracellular vesicle fuses with the plasma membrane so that the vesicle’s contents are released outside the cell.

Question 27

Define endocytosis

Answer 27

Process by which substances are moved into the cell from the environment; includes phagocytosis, pinocytosis, and receptor-mediated endocytosis.

Question 28

Define phagocytosis

Answer 28

Process by which cells engulf large substances, forming an intracellular vacuole.

Question 29

Define pinocytosis

Answer 29

Process by which vesicle formation brings macromolecules into the cell.

Question 30

Define receptor-mediated endocytosis

Answer 30

Selective uptake of molecules into a cell by vacuole formation after they bind to specific receptor proteins in the plasma membrane.

Question 31

Contrast diffusion with facilitated transport

Answer 31

During diffusion, molecules move from an area of high concentration to an area of low concentration. Facilitate transport promotes the movement of these molecules down a concentration gradient across a plasma membrane. Carrier proteins reversibly bind to the molecule and speed up their passage.

Question 32

Explain the movement of water between hypertonic and hypotonic environments

Answer 32

A hypertonic environment has a lower concentration of water and a higher concentration of solutes than a hypotonic environment. Water will move from the hypotonic environment where it is present at a higher concentration, to the hypertonic environment across a semipermeable membrane by osmosis.

Question 33

Describe the differences between facilitated and active transport.

Answer 33

Both move molecules across the plasma membrane and require a carrier molecule. Facilitated transport does not require energy, but active transport does. Facilitated transport moves moves items down their concentration gradient, while active transport moves against it.

Question 34

Discuss the potential benefit of receptor-mediated endocytosis.

Answer 34

Allows the cell to target specific molecules to be brought in by endocytosis, thus increasing efficiency.

Question 35

What factors influence the rate of diffusion?

Answer 35

Temperature, pressure, electrical currents, and molecular size.

Question 36

Define tonicity

Answer 36

Tonicity is a measure of the effective osmotic pressure gradient; the water potential of two solutions separated by a partially-permeable cell membrane.

Question 37

Define extracellular matric (ECM)

Answer 37

Nonliving substance secreted by some animal cells; is composed of protein and polysaccharides.

Question 38

Define adhesion junction

Answer 38

Junction between cells in which the adjacent plasma membranes do not touch but are held together by intercellular filaments attached to buttonlike thickenings.

Question 39

Define tight junction

Answer 39

Junction between cells when adjacent plasma membrane proteins join to form an impermeable barrier.

Question 40

Define gap junction

Answer 40

Junction between cells formed by the joining of two adjacent plasma membranes; it lends strength and allows ions, sugars, and small molecules to pass between cells.

Question 41

Define plasmodesmata

Answer 41

In plants, cytoplasmic connections in the cell wall that connect two adjacent cells.

Question 42

Describe the molecule complex of an extracellular matrix of an animal cell

Answer 42

*Collagen and elastin fibers provide structure to the ECM
*Fibronectin binds to the integrin in the membrane and can signal the cells cytoskeleton
*Proteoglycans, shaped as bottle brushes, assist in cell signaling by regulating the passage of molecules through the ECM

Question 43

Explain the differences among the adhesion, tight, and gap junction.

Answer 43

Adhesion junction: mechanically attaches adjacent cells
Tight junction: Connects plasma membranes, creating a tight barrier
Gap junction: allows cells to communicate through channels

Question 44

Contrast the extracellular matrix with the cell wall of an animal cell with the cell wall of a plant cell

Answer 44

The ECM of an animal cell is a meshwork of proteins and polysaccharides that can vary in amount and flexibility depending on the cell type. The plant cell wall, external to the plasma membrane, is composed of cellulose fibrils and pectin that allows flexibility during growth and eventually hardens into a rigid structure.

Question 45

Eukaryotic cells contain
a) a nucleus
b) DNA
c) a plasma membrane
d) mitochondria
e) all of the above

Answer 45

E) All of the above

Question 46

The combination of DNA and protein in the nucleus of a eukaryotic cell is called
a) nucleoplasm
b) plasmids
c) nucleoids
d) chromatin

Answer 46

D) Chromatin

Question 47

This organelle act as a processing center for vesicles leaving the endoplasmic reticulum
a) perxisome
b) ribosome
c) Golgi apparatus
d) nucleolus

Answer 47

C) Golgi apparatus

Question 48

This organelle acts as a digestive organelle and may also be used to recycle the internal components of a cell
a) ribosome
b) lysosome
c) peroxisome
d) Golgi apparatus

Answer 48

B) lysosome

Question 49

The mitochondria of a eukaryotic cell is the site of
a) photosynthesis
b) fatty acid metabolism
c) cellular respiration
d) protein synthesis

Answer 49

c) cellular respiration

Question 50

In the fluid-mosaic model, the fluid properties are associated with the nature of the _______, and the mosaic pattern is established by the ______.
a) nucleic acids; phospholipids
b) phospholipids; embedded proteins
c) embedded proteins; cholesterol
d) phospholipids; nucleic acid

Answer 50

b) phospholipids; embedded proteins

Question 51

Which of the following is not a function of proteins present in the plasma membrane?
a) proteins assist the passage of materials into the cell
b) proteins interact with and recognize other cells
c) proteins bind with specific hormones
d) proteins carry out specific metabolic reactions
e) proteins produce lipid molecules

Answer 51

e) proteins produce lipid molecules

Question 52

The carbohydrate chains projecting from the plasma membrane are involved in
a) adhesion between cells
b) reception of molecules
c) cell-to-cell recognition
d) all of the above

Answer 52

d) all of the above

Question 53

When a cell is placed in a hypotonic solution,
a) solute exits the cell to equalize the concentration on both sides of the membrane
b) water exits the cell toward the area of lower solute concentration
c) water enters the cell toward the area of higher solute concentration
d) there is no net movement of water or solute

Answer 53

c) water enters the cell toward the area of higher solute concentration

Question 54

When a cell is placed in a hypertonic solution,
a) solute exits the cell to equalize the concentration on both sides of the membrane
b) water exits the cell toward the area of lower solute concentration
c) water enters the cell toward the area of higher solute concentration
d) there is no net movement of water or solute

Answer 54

c) water enters the cell toward the area of higher solute concentration

Question 55

Which of the following is incorrect regarding facilitated diffusion?
a) it is a passive process
b) it allows the movement of molecules from areas of low concentration to areas of high concentration
c) it may use either channel or carrier proteins
d) it allows the rapid transport of glucose across the membrane

Answer 55

b) it allows the movement of molecules from areas of low concentration to areas of high concentration

Question 56

The sodium-potassium pump
a) helps establish an electrochemical gradient across the membrane
b) concentrates sodium on the outside of the membrane
c) uses a carrier protein and chemical energy
d) is present in the plasma membrane
e) all of the above

Answer 56

e) all of the above

Question 57

Which of the following processes is involved in the bulk transport of molecules out of the cell?
a) phagocytosis
b) pinocytosis
c) receptor-mediated endocytosis
d) exocytosis
e) none of the above

Answer 57

d) exocytosis

Question 58

Which process uses special proteins on the surface of the membrane to identify specific molecules for transport into the cell
a) phagocytosis
b) pinocytosis
c) receptor-mediated endocytosis

d) exocytosis

Answer 58

c) receptor mediated

Question 59

The extracellular matrix
a) assists in the movement of substances across the plasma membrane
b) prevents the loss of water when cells are placed in a hypertonic solution
c) has numerous functions that affect the shape and activities of the cell that produced it

d) contains the junctions that sometimes occur between cells
e) all of the above

Answer 59

c) has numerous functions that affect the shape and activities of the cell that produced it

Question 60

Which of the following junctions allows for cytoplasm- to cytoplasm communication between cells?
a) adhesion junctions
b) tight junctions
c) gap junctions
d) none of the above

Answer 60

c) gap junctions

Question 61

When a signal molecule such as a growth hormone bincds to a receptor protein in the plasma membrane, it stays on the outside of the cell. How might the inside of the cell know that the signal has bound?