1.4 Membrane transport

Question 1

Types of transport

Answer 1

passive transport

active transport

Question 2

Passive transport

Answer 2

involves the movement of material along a concentration gradient (high to low concentration) thus do not require energy

Question 3

Main types of passive transport

Answer 3

simple diffusion
osmosis
facilitated diffusion

Question 4

Diffusion

Answer 4

the net movement of molecules from a region of high concentration to a region of low concentration

Question 5

What factors affect the rate of diffusion + how?

Answer 5

temperature - affects kinetic energy of particles in solution
molecular size - larger particles are subjected to greater resistance within a fluid medium
steepness of gradient - rate of diffusion will be greater with a higher concentration gradient

Question 6

Osmosis

Answer 6

the net movement of water molecules across a semi-permeable membrane from a region of low solute concentration to a region of high solute concentration (until equilibrium is reached)

Question 7

Osmolarity

Answer 7

a measure of solute concentration, as defined by the number of osmoles of a solute per litre of solution (osmol/L)

Question 8

Hypertonic

Answer 8

solutions with a relatively higher osmolarity (high solute concentration ⇒ gains water)

Question 9

Hypotonic

Answer 9

solutions with a relatively lower osmolarity (low solute concentration ⇒ loses water)

Question 10

Isotonic

Answer 10

solutions that have the same osmolarity (same solute concentration ⇒ no net water flow)

Question 11

How do we estimate osmolarity?

Answer 11

The osmolarity of a tissue may be interpolated by bathing the sample in solutions with known osmolarities

The tissue will lose water when placed in hypertonic solutions and gain water when placed in hypotonic solutions
Water loss or gain may be determined by weighing the sample before and after bathing in solution
Tissue osmolarity may be inferred by identifying the concentration of solution at which there is no weight change (i.e. isotonic)

Question 12

What are the effects of uncontrolled osmosis?

Answer 12

In hypertonic solutions, water will leave the cell causing it to shrivel (crenation)
In hypotonic solutions, water will enter the cell causing it to swell and potentially burst (lysis)

Question 13

How are the effects of uncontrolled osmosis present in plant tissues?

Answer 13

In hypertonic solutions, the cytoplasm will shrink (plasmolysis) but the cell wall will maintain a structured shape
In hypotonic solutions, the cytoplasm will expand but be unable to rupture within the constraints of the cell wall (turgor)

Question 14

Facilitated diffusion

Answer 14

the passive movement of molecules across the cell membrane via the aid of a membrane protein

Question 15

What are the two types of transport proteins?

Answer 15

channel proteins

carrier proteins

Question 16

Carrier proteins

Answer 16

carrier proteins will bind to a specific molecule that needs to be transported, similar to an enzyme-substrate interaction

Question 17

Channel proteins

Answer 17

channel proteins contain a pore in which ions may cross from one side of the membrane to another

Question 18

Active transport

Answer 18

uses energy to move molecules against a concentration gradient

Question 19

How does active transport work?

Answer 19

involves the use of carrier proteins (protein pumps)

1. a specific solute will bind to the protein pump on one side of the membrane
2. hydrolysis of ATP causes a conformational change in the protein pump
3. the solute molecule is translocated across the membrane and released

Question 20

Vesicular transport

Answer 20

the movement of particles or fluid droplets through the plasma membrane by the process of endocytosis or exocytosis

Question 21

Endoplasmic reticulum

Answer 21

Rough ER is embedded with ribosomes and synthesises proteins destined for extracellular use
Smooth ER is involved in lipid synthesis and also plays a role in carbohydrate metabolism

Question 22

Golgi apparatus

Answer 22

Materials move via vesicles from the internal cis face of the Golgi to the externally oriented trans face
While within the Golgi apparatus, materials may be structurally modified (e.g. truncated, glycosylated, etc.)

Question 23

Plasma membrane

Answer 23

Released immediately into the extracellular fluid (constitutive secretion)
Stored within an intracellular vesicle for a delayed release in response to a cellular signal (regulatory secretion)

Question 24

Endocytosis

Answer 24

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

Question 25

What are the two main types of endocytosis?

Answer 25

Phagocytosis

Pinocytosis

Question 26

Phagocytosis

Answer 26

The process by which solid substances are ingested

Question 27

Pinocytosis

Answer 27

The process by which liquids / dissolved substances are ingested

Question 28

Exocytosis

Answer 28

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