Transport Across Membranes

Question 1

What forms the basis of a cell membrane?

Answer 1

Phospholipid bilayer

Question 2

What is the fluid mosaic model?

Answer 2

The phospholipids are constantly moving relative to each other (fluid structure)
Proteins are distributed along the membrane giving it selective permeability (mosaic)

Question 3

What can pass through the bilayer?

Answer 3

Small non-polar molecules like O2, large polar molecules need proteins to pass through
Lipid soluble molecules can pass through by simple diffusion

Question 4

What does cholesterol do to the structure and function of the membrane?

Answer 4

Strength and stability which prevents leakage and prevents lateral movement

Question 5

Facilitates diffusion along the membrane

Answer 5

Channel protein

Question 6

Facilitates diffusion and actively transports ions

Answer 6

Carrier protein

Question 7

Bind to hormones and allow a cell to respond. Only certain cells have certain receptors

Answer 7

Specific receptors (protein molecule)

Question 8

Enzyme-substrate complexes are formed on the membrane by…

Answer 8

Enzymes

Question 9

Present on the outer surface of the membrane and are important in cell recognition, sometimes acting as antigens detecting foreign invaders

Answer 9

Glycoproteins

Question 10

Allows water to pass through the membrane by osmosis

Answer 10

Aquaporin

Question 11

It is a passive process that measures the net movement of molecules from a higher concentration to a lower concentration across a partially permeable membrane

Answer 11

Diffusion

Question 12

Four factors that effect the rate of diffusion:

Answer 12

. Temperature - Increasing the kinetic energy increases the movement of molecules
. SA - More “space” so molecules to pass through so faster
. Concentration gradient - Concentration difference increases the rate of diffusion
. Diffusion difference - Thinner surface means the molecules will pass through faster

Question 13

Proteins help molecules pass through the bilayer

Answer 13

Facilitated diffusion

Question 14

What happens if the temperature is increased too much?

Answer 14

Proteins in the membrane could denature making the membrane ‘leaky’

Question 15

Fick’s law

Answer 15

Rate of diffusion is proportional to:

(surface area x concentration gradient)/Diffusion distance

Question 16

Net movement of water molecules from a higher water potential to a lower water potential through a partially permeable membrane

Answer 16

Osmosis

Question 17

Water molecules collide with the membrane which exerts a pressure measured in kPa

Answer 17

Water potential

Question 18

What is the highest water potential?

Answer 18

0kPa - pure water, adding a solute make the solution negative

Question 19

Why does adding a solute make the solution have a negative water potential

Answer 19

Water is a di-pole and is attracted to the charges on the ions, therefore the number of free moving molecules decreases

Question 20

Hypotonic -

Answer 20

Water moves in which results in swelling & lysis in animal cells and turgor of plant cells

Question 21

Hypertonic -

Answer 21

Water moves out which results in shrivelling in animal cells and plant cell membrane pulling away from the cell wall/plasmolysed in plant cells

Question 22

Isotonic -

Answer 22

No net movement

Question 23

Transporting molecules against their concentration gradient using carrier proteins specific with a complimentary binding site and uses ATP

Answer 23

Active transport

Question 24

Transport using vesicles from inside the cell to outside. Also used to move enzymes and glycoproteins from the golgi to the cell surface membrane (REQUIRES ATP)

Answer 24

Exocytosis

Question 25

Transport using vesicles from outside the cell to inside. The cell surface membrane is “pulled” inwards to form a vesicle and any material next to it are enclosed (REQUIRES ATP)

Answer 25

Endocytosis