Membrane Transport

Question 1

What is simple diffusion?

Answer 1

Passive movement of molecules from a region of its high concentration to a region of its low concentration

Question 2

Why does simple diffusion occur?

Answer 2

Occurs because more particles move from the region of higher concentration to the region of lower concentration than vice versa

Question 3

What is an example of simple diffusion within the cell?

Answer 3

Small and non-polar molecules will be able to freely diffuse across cell membranes (O2)

Question 4

What is facilitated diffusion?

Answer 4

Passive movement of molecules across the cell membrane via the aid of a channel protein or a carrier protein

Question 5

What is an example of facilitated diffusion within the cell?

Answer 5

Sodium and potassium channel proteins in the membranes of neurons that open and close depending on the voltage across the membrane

Question 6

What is the function of potassium channels during an action potential?

Answer 6

1. During depolarization, sodium channel is opened while potassium channel remains closed, resulting in a net increase of positive charge within the membrane
2. Following the influx of sodium, potassium channels open and results in the eflux of potassium

Question 7

What is osmosis?

Answer 7

Passive net movement of water molecules from a region of lower solute concentration to a region of higher solute concentration, across a partially permeable membrane

Question 8

Why does osmosis occur?

Answer 8

Water molecules move in and out through the membrane, but more move in than out (if solute is higher inside) as there is more attraction of water by the solutes

Question 9

What is osmolarity?

Answer 9

The concentration of solutes in a solution expressed as the total number of solute particles per litre

Question 10

What is the relation between osmosis and osmolarity?

Answer 10

If two solutions are separated by a partially permeable membrane, water will move by osmosis from the solution with the lower osmolarity to the solution with the higher osmolarity

Question 11

What is a hypertonic solution?

Answer 11

Type of solution that has a greater concentration of solutes on the outside of a cell when compared with the inside of a cell

Question 12

What happens if a cell is placed into a hypertonic solution?

Answer 12

Water will leave the cell causing its cytoplasm to shrink in volume

Question 13

What is a hypotonic solution?

Answer 13

Type of solution that has a lower concentration of solutes on the outside of a cell when compared with the inside of a cell

Question 14

What happens if a cell is placed into a hypotonic solution?

Answer 14

Water moves into the cell, causing lysis

Question 15

What is an isotonic solution?

Answer 15

Isotonic solutions contain equal concentrations of impermeable solutes on either side of the membrane and so the cell neither swells nor shrinks.

Question 16

How can osmolarity of a tissue be measured?

Answer 16

Tissue can be placed in a range of solute concentrations (0, 0.1, 0.2 moles/liter) and determine the weight loss or gain.

• If weight is loss, osmolarity of the tissue is lower than that of the solution
• If weight is gained, osmolarity of the tissue is higher than that of the solution
• True osmolarity is at the concentration at which there is no weight change

Question 17

How to prevent osmosis in donor organs?

Answer 17

1. A solution of salts called isotonic saline is used for some procedures
2. Donor organs are surrounded by isotonic slush when they are being transported

Question 18

What is active transport?

Answer 18

Movement of substances against a concentration gradient, using energy from ATP

Question 19

What is the general process of active transport through the help of carrier proteins?

Answer 19

1. A specific solute will bind to the protein pump
2. The hydrolysis of ATP causes a conformation change in the pump protein
3. Solute molecule is consequently translated across the membrane and released

Question 20

What is the process of active transport of sodium and potassium in axons?

Answer 20

1. Three sodium ions bind to intracellular sites on the sodium-potassium pump
2. A phosphate group is transferred to the pump via the hydrolysis of ATP
3. The pump undergoes a conformational change, translocating sodium across the membrane
4. The conformational change exposes two potassium binding sites on the extracellular surface of the pump
5. The phosphate group is released which causes the pump to return to its original conformation
6. This translocates the potassium across the membrane, completing the ion exchange

Question 21

What is endocytosis?

Answer 21

Process by which substances enter the cell without crossing the membrane

Question 22

What is an example of endocytosis?

Answer 22

Proteins from mother are absorbed into the fetus by endocytosis

Question 23

How do vesicles move materials within the cell?

Answer 23

1. Proteins are synthesized by ribosomes in the rER
2. Membrane bulges and buds to create vesicles
3. Vesicles carry these proteins to Golgi Apparatus, where they are processed
4. Proteins are processed, and then vesicles bud off Golgi Apparatus
5. The vesicles fuse with plasma membrane and protein is secreted

Question 24

What is exocytosis?

Answer 24

Process by which substances exit cell without crossing membrane