Membrane Transport

Question 1

Define Diffusion

Answer 1

Diffusion — passive movement of particles from a region of higher concentration to a region of lower concentration

Question 2

Differentiate between Simple diffusion and Facilitated diffusion

Answer 2

Simple Diffusion – is the movement of small molecules from a region of higher concentration to a region of lower concentration

(e.g 02, CO2, Glycerol)

Facilitated Diffusion — is the movement of large molecules via membrane proteins (channel proteins or in some cases carrier protein) from a region of higher concentration to a region of lower concentration

(e. g Chloride channels — only allow chloride ions to pass through)
(e. g Potassium channels — allow passage of potassium ions but restrict the passage of alternative ions)

(Simple Diffusion — small molecules)
(Facilitated — big molecules, thus, necessitates protein channels)

Question 3

State the 2 key features of cellular membranes in the movement of particles in and out of a cell

Answer 3

Cellular Membranes are:

1. Semi Permeable — allow only certain materials to freely diffusion in and out (large molecules are usually blocked)
2. Selective — membrane proteins often strictly regulate the passage of material in and out of a cell

Question 4

What is Passive transport?

Answer 4

involves the movement of material along a concentration gradient (high concentration ⇒ low concentration)

Question 5

Why does Passive Transport not require energy?

Answer 5

(Because materials are moving down a concentration gradient, it does not require the expenditure (use) of energy

Question 6

State the 3 types of Passive Transport

Answer 6

1. Simple Diffusion
2. Facilitated Diffusion
3. Osmosis

Question 7

What is Active Transport?

Answer 7

Involves the movement of materials against a concentration gradient (low concentration ⇒ high concentration)

— still requires a protein channels and carrier proteins (called as protein pumps) but what distinguishes it is that ATP is used

Question 8

Why does Active Transport require energy?

Answer 8

Because materials are moving against the gradient, it requires the expenditure (use) of energy

Question 9

State the 2 types of active Transport

Answer 9

1. Primary (direct) active Transport

2. Secondary (Indirect) active Transport

Question 10

Differentiate between Direct and Indirect Active Transport

Answer 10

Primary (direct) active transport —- Involves the direct use of metabolic energy to mediate transport

Secondary (indirect) active transport — Involves coupling the molecule with another moving along an electrochemical gradient

Question 11

Have does Voltage affect Channel proteins

Answer 11

Opening and closing of channel protein usually depends on the voltage across the membrane

Question 12

Case study of Facilitated diffusion: Describe how Potassium channels function in axons

Answer 12

a nerve impulse is transmitted along the axon of a nerve cell by a momentary reversal in electrical potential difference (voltage) in the axon membrane, brought about by rapid movements of sodium and potassium ions. These ions pass by facilitated diffusion via pores in the membrane called ion channels. One type of channel (Potassium channel) is exclusively permeable to potassium ions. Potassium channels open or close depending on a
certain threshold membrane potential being reached. They are closed when the axon is polarized but open in response to depolarization of the axon membrane, allowing K+ ions to exit by facilitated diffusion, which repolarizes the axon. Potassium channels only remain open for a very short time before a globular sub-unit blocks the pore. The channel then returns to its original closed conformation.

Question 13

Define Bulk Transport

Answer 13

Transport of large molecules via vesicles across the membrane by
processes known generally as cytosis (e.g Endocytosis & Exocytosis)

Question 14

State 3 differences between active transport & passive transport

Answer 14

1. Active transport requires energy (ATP)
   
   • • Passive transport doesn’t require energy
2. Active transport requires a membrane
   
   • – Passive transport doesn’t require a membrane
3. In Active transport, particles move against the concentration gradient (from a low concentration to a high concentration)

In passive transport, particles move down the concentration gradient (from a high concentration to a low concentration)

Question 15

Define Osmosis

Answer 15

is the passive movement of water molecules from
a region of lower solute concentration to a region ofƒ higher solute concentration, across a partially permeable membrane
– no energy is used

Question 16

Define a solvent and a solute

Answer 16

A solvent is a liquid in which particles dissolve

Dissolved particles are called solutes

Question 17

Define Osmolarity

Answer 17

The osmolarity of a solution is the number of moles of solute particles per unit volume of solution. Pure water has an
osmolarity of zero. The greater the concentration of solutes, the higher the osmolarity.

Question 18

Differentiate between Hypotonic, Hypertonic and Isotonic

Answer 18

1. Hypotonic Solution (loses water) — low solute concentration outside the cell with high solute concentration inside the cell
   - - has relative low osmolarity
2. Hypertonic Solution (gains water) — high solute concentration outside the cell with low solute concentration inside the cell
   - -has relative high osmolarity
3. Isotonic — solute concentration outside the cell is equal to solute concentration inside the cell (net movement of water is zero)

Question 19

Explain the meaning of the Suffix “Lysis”

Answer 19

Lysis means bursting or shrinking

Question 20

Differentiate between Plasmolysis & Cytolysis

Answer 20

Plasmolysis – cell shrinking due to decrease in turgur pressure

Cytolysis – the burst of a cell due to the increase in turgur pressure

Question 21

Describe how Osmolarity relates to plant cells

Answer 21

If two solutions at equal pressure but with diferent osmolarity 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. Plant cells absorb
water from a surrounding solution if their osmolarity is higher than that of the surrounding solution (hypotonic) or lose water if their osmolarity is lower than that of the surrounding solution (hypertonic). This principle can be used to estimate
the osmolarity of a type of plant tissue, such as potato through identifying the concentration of solution at which there is no weight change (isotonic)

Question 22

Why do Medical specialists avoid Osmosis in Donor organs

Answer 22

Osmosis can cause cells in human tissues or organs to swell up and burst, or to shrink due to gain or loss of water by
osmosis. To prevent this, tissues or organs used in medical procedures such as kidney transplants must be bathed in a
solution with the same osmolarity as human cytoplasm.

Question 23

How do Medical Specialists avoid Omosis in Donor Organs

Answer 23

A solution of salts called isotonic saline is used for some procedures to surround donor organs when they are being transported, with the low temperatures helping to keep them in a healthy state.

Question 24

How is ATP used in active transport?

Answer 24

1. Particle enters the protein pump from
   the side with a lower concentration
2. Particle binds to a specific site.
3. Energy from ATP is used to change
   the shape of the pump
4. Particle is released on the side with a
   higher concentration and the pump then
   returns to its original shape

5) the cycle is now repeated again

Question 25

State 2 difference between Carrier Proteins and Channel Proteins

Answer 25

1) Carrier proteins have a much slower rate of transport than channel proteins
Channel proteins have a much faster rate of transport than carrier proteins

2) Channel proteins only move molecules along a concentration gradient (i.e. are not used in active transport)
Carrier proteins move molecules against concentration gradients in the presence of ATP (i.e. are used in active transport) but some carrier proteins (which are involved in facilitated diffusion) can also move molecules along a concentration gradient

Question 26

Case study of Active transport: Describe how Sodium Potassium pumps function in axons (State the 6 steps)

Answer 26

The process of ion exchange against the gradient is energy-dependent and involves a number of key steps:

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

Keynote: 3 sodium ions (moves out of cell) with two potassium ions (moves into cell

Question 27

Define Endocytosis & Exocytosis

Answer 27

Endocytosis — The process by which large substances (or bulk amounts of smaller substances) enter the cell without crossing the membrane

Exocytosis — The process by which large substances (or bulk amounts of small substances) exit the cell without crossing the membrane

Question 28

State the function of Vesicles

Answer 28

1) Vesicles help move materials, such as proteins and other molecules, from one part of a cell to another (e.g transport proteins created by ribosomes to the Golgi apparatus, from Golgi to the plasma membrane for exocytosis or to other compartments (e.g to lysosome))

Question 29

Explain the processes of Endocytosis & Exocytosis

Answer 29

Endocytosis
Small pieces of the membrane are pinched off the plasma
membrane, creating a vesicle containing some material from outside
the cell. This enables materials from outside the cell to permeate through and enter the cell.

Exocytosis
Vesicles can also move to the plasma membrane and fuse with it, releasing the contents of the vesicle outside the cell in the process

Question 30

State the 2 types of Endocytosis

Answer 30

1) Phagocytosis – The process by which solid substances are ingested (usually to be transported to the lysosome)
2) Pinocytosis – The process by which liquids / dissolved substances are ingested (allows faster entry than via protein channels)