3.3 The Cellular Level Of Organization: Transport Across The Plasma Membrane

Front 1

What are the two transport processes?

Back 1

1. Passive Transport

2. Active Transport

Front 2

What are the types of passive transport?

Back 2

Diffusion and osmosis

Front 3

What is diffusion?

Back 3

A passive process in which there is a net or greater movement of molecules or ions from a region of high concentration to a region of low concentration until equilibrium is reached.

Front 4

What is a solute? What is a solvent?

Which undergoes diffusion?

Back 4

Solute: the dissolved substance

Solvent: the liquid that does the dissolving

Both undergo diffusion.

Front 5

How would having a fever affect body processes that involve diffusion?

Back 5

Because fever involves an increase in body temperature, the rates of all diffusion processes would increase.

Front 6

Five factors that influence the diffusion rate of substances across plasma membranes:

Back 6

1. Steepness of the concentration gradient

2. Temperature

3. Mass of the diffusing substance

4. Surface area

5. Diffusion distance

Front 7

How does rate of diffusion change with steepness of the concentration gradient?

Back 7

The greater the difference in concentration between the two sides of the membrane, the higher is the rate of diffusion.

Front 8

How does rate of diffusion change with temperature?

Back 8

The higher the temperature, the faster the rate of diffusion.

Front 9

How does rate of diffusion change with the mass of the diffusing particle?

Back 9

The larger the mass of the diffusing particle, the slower its diffusion rate.

Front 10

How does rate of diffusion change with the surface area?

Back 10

The larger the membrane surface area available for diffusion, the faster is the diffusion rate.

Front 11

How does rate of diffusion change with the diffusion distance?

Back 11

The greater the distance over which diffusion must occur, the longer it takes.

Front 12

What is simple diffusion?

Back 12

A passive process in which substances move freely through the lipid bilayer of the plasma membranes of cells without the help of membrane transport proteins.

Front 13

Which substances move across the lipid bilayer through simple diffusion?

Back 13

Nonpolar, hydrophobic molecules and small, uncharged polar molecules.

Front 14

What type of non polar, hydrophobic molecules move through simple diffusion?

Back 14

Oxygen, carbon dioxide, and nitrogen gases; fatty acids; steroids; and fat-soluble vitamins (A, D, E, and K).

Front 15

What type of small, uncharged polar molecules move through simple diffusion?

Back 15

Water, urea, and small alcohols.

Front 16

What happens in facilitated diffusion?

Back 16

An integral membrane protein assists a specific substance across the membrane. The integral membrane protein can be either a membrane channel or a carrier.

Front 17

What kind of solutes move through the lipid bilayer by facilitated diffusion?

Back 17

Solutes that are too polar or highly charged.

Front 18

What are the different types of facilitated diffusion?

Back 18

Channel-mediated facilitated diffusion and carrier-mediated facilitated diffusion.

Front 19

What happens in channel-mediated facilitated diffusion?

Back 19

A solute moves down its concentration gradient across the lipid bilayer through a membrane channel.

Front 20

In typical plasma membranes, ion channels are for what ions?

Back 20

The most numerous ion channels are selective for K+ or Cl− ; fewer channels are available for Na+ or Ca2+.

Front 21

What is a gated channel?

Back 21

Happens when part of the channel protein acts as a “plug” or “gate,” changing shape in one way to open the pore and in another way to close it.

Front 22

Is the concentration of K+ in body cells higher in the cytosol or in the extracellular fluid?

Back 22

The concentration of K+ is higher in the cytosol of body cells than in extracellular fluids.

Front 23

What happens in carrier-mediated facilitated diffusion?

Back 23

A carrier (also called a transporter) moves a solute down its concentration gradient across the plasma membrane.

Front 24

The solute binds more often to the carrier on the side of the membrane with a _________ concentration of solute.

Back 24

The solute binds more often to the carrier on the side of the membrane with a higher concentration of solute.

Front 25

What substances move across the plasma membrane by carrier-mediated facilitated diffusion?

Back 25

Glucose, fructose, galactose, and some vitamins.

Front 26

How does glucose enter body cells by carrier-mediated facilitated diffusion? (3 steps).

Back 26

1. Glucose binds to a specific type of carrier protein called the glucose transporter (GluT) on the outside surface of the membrane.

2. As the transporter undergoes a change in shape, glucose passes through the membrane.

3. The transporter releases glucose on the other side of the membrane.

Front 27

Does insulin alter glucose transport by facilitated diffusion?

Back 27

Yes. Insulin promotes insertion of glucose transporter (GluT) in the plasma membrane, which increases cellular glucose uptake by carrier-mediated facilitated diffusion.

Front 28

What is diabetes mellitus?

Back 28

An inability to produce or utilize insulin.

Front 29

What is osmosis?

Back 29

The net movement of water molecules through a selectively permeable membrane from an area of higher water concentration to an area of lower water concentration until equilibrium is reached.

Front 30

Water molecules pass through a plasma membrane in which two ways?

Back 30

(1) by moving between neighboring phospholipid molecules in the lipid bilayer via simple diffusion

(2) by moving through aquaporins, integral membrane proteins that function as water channels

Front 31

In osmosis, the solvent (water) moves from an area of _______ water concentration to an area of _______ water concentration.

Back 31

In osmosis, the solvent (water) moves from an area of higher water concentration to an area of lower water concentration.

Front 32

Osmosis only occurs when:

Back 32

A membrane is permeable to water but is not permeable to certain solutes.

Front 33

What is hydrostatic pressure?

Back 33

Pressure exerted by a liquid.

Front 34

What is osmotic pressure?

Back 34

Force exerted by the solution with the impermeable solute.

Front 35

The ______ the solute concentration, the ______ the solution's osmotic pressure.

Back 35

The higher the solute concentration, the higher the solution's osmotic pressure.

Front 36

What is a solution's tonicity?

Back 36

A measure of the solution's ability to change the volume of cells by altering their water content.

Front 37

What is an isotonic solution?

Back 37

A solution having the same concentration of impermeable solutes as cytosol. Maintains its normal shape and volume.

Front 38

What is a hypotonic solution?

Back 38

Solution that causes cells to swell and perhaps rupture due to gain of water by osmosis.

Front 39

What is a hypertonic solution?

Back 39

Solution that causes cells to shrink due to loss of water by osmosis.

Front 40

What is active transport?

Back 40

The movement of substances across cell membranes against a concentration gradient, requiring the expenditure of cellular energy (ATP).

Front 41

What kind of substances are transported by active transport?

Back 41

Polar or charged solutes.

Front 42

What are the two types of active transport?

Back 42

Primary active transport

Secondary active transport

Front 43

What is primary active transport?

Back 43

Active process in which a substance moves across the membrane against its concentration gradient by pumps (carriers) that use energy supplied by hydrolysis of ATP.

Front 44

What substances are transported by primary active transport?

Back 44

Na+, K+, Ca2+, H+, I−, Cl−, and other ions.

Front 45

What is secondary active transport?

Back 45

Coupled active transport of two substances across the membrane using energy supplied by a Na+ or H+ concentration gradient maintained by primary active transport pumps.

Front 46

What are symporters and antiporters (in secondary active transport)?

Back 46

Symporters: Transporters that move two substances in the same direction.

Antiporters: Transporters that move two substances in opposite directions across the membrane.

Front 47

What substances are transported by secondary active transport?

Back 47

Antiport: Ca2+, H+ out of cells.

Symport: glucose, amino acids into cells.

Front 48

What is the main difference between primary and secondary active transport mechanisms?

Back 48

In secondary active transport, hydrolysis of ATP is used indirectly to drive the activity of symporter or antiporter proteins; this reaction directly powers the pump protein in primary active transport.

Front 49

What are the three types of transport in vesicles?

Back 49

Endocytosis, Exocytosis, Transcytosis

Front 50

What is endocytosis?

Back 50

Movement of substances into a cell in vesicles.

Front 51

What are the three types of endocytosis?

Back 51

Receptor-mediated endocytosis

Phagocytosis

Bulk-phase endocytosis

Front 52

What is receptor-mediated endocytosis?

Back 52

Ligand-receptor complexes trigger infolding of a clathrin-coated pit that forms a vesicle containing ligands.

Front 53

How does receptor-mediated endocytosis of LDLs (and other ligands) occur?

Back 53

1. Binds to receptor

2. Vesicle formation

3. Vesicle loses cathrin coat and becomes uncoated

4. Fusion with endosome

5. Recycling of receptors to plasma membrane

6. Degradation in lysosomes

Front 54

What substances are transported by receptor-mediated endocytosis?

Back 54

Ligands: transferrin, low-density lipoproteins (LDLs), some vitamins, certain hormones, and antibodies.

Front 55

What is phagocytosis?

Back 55

“Cell eating”; movement of a solid particle into a cell after pseudopods engulf it to form a phagosome.

Front 56

What substances are transported by phagocytosis?

Back 56

Bacteria, viruses, and aged or dead cells.

Front 57

What are phagocytes?

Back 57

Body cells that engulf large solid particles.

Front 58

What are the two main types of phagocytes?

Back 58

Two main types of phagocytes are macrophages, located in many body tissues, and neutrophils, a type of white blood cell.

Front 59

What are pseudopods?

Back 59

Temporary protrusions of the leading edge of a migrating cell; cellular projections that surround a particle undergoing phagocytosis.

Front 60

What triggers pseudopod formation?

Back 60

The binding of particles to a plasma membrane receptor triggers pseudopod formation.

Front 61

What is bulk-phase endocytosis?

Back 61

“Cell drinking” movement of extracellular fluid into a cell by infolding of plasma membrane to form a vesicle.

Front 62

What substances are transported by bulk-phase endocytosis?

Back 62

Solutes in extracellular fluid.

Front 63

What is exocytosis?

Back 63

Movement of substances out of a cell in secretory vesicles that fuse with the plasma membrane and release their contents into the extracellular fluid.

Front 64

What substances are transported by exocytosis?

Back 64

Neurotransmitters, hormones, and digestive enzymes.

Front 65

What is transcytosis?

Back 65

Movement of a substance through a cell as a result of endocytosis on one side and exocytosis on the opposite side.

Front 66

What substances are transported by transcytosis?

Back 66

Substances, such as antibodies, across endothelial cells. This is a common route for substances to pass between blood plasma and interstitial fluid.

Front 67

How do receptor-mediated endocytosis and phagocytosis differ from bulk-phase endocytosis?

Back 67

Receptor-mediated endocytosis and phagocytosis involve receptor proteins; bulk-phase endocytosis does not.