1: Active Transport

Question 1

Define ‘active transport’.

Answer 1

the movement of substances across membranes using energy from ATP

Question 2

What can active transport do that diffusion cannot?

Answer 2

move substances against the concentration gradient - from a region of lower concentration to a region of higher concentration

Question 3

What are protein pumps in the membrane used for?

Answer 3

active transport

Question 4

How many different substances can a protein pump transport? How, then, do cells control what is absorbed and what is expelled?

Answer 4

• one substance only

- by changing the type of protein pump

Question 5

How many different directions do protein pumps work? What does this mean for the substance?

Answer 5

• one specific direction

- substance can only enter the pump on one side and only exit on the other side

Question 6

Draw and label a diagram of a protein pump transporting a particle. (p12)

Answer 6

1. particle enters the pump from the side with a lower concentration
2. particle binds to a specific site. Other types of particle cannot bind.
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.

Question 7

Where can sodium-potassium pumps be found? What do they do?

Answer 7

• found in the axons of neurons

- moves sodium ions and potassium ions across the membrane

Question 8

In a sodium-potassium pump: which direction are sodium and potassium ions pumped (relative to each other)? What, therefore, is the technical term for this sort of pump?

Answer 8

• opposite directions

- an antiporter

Question 9

How is the energy required for pumping sodium and potassium ions in a sodium-potassium pump obtained? What therefore is this type of reaction called?

Answer 9

• by converting ATP –> ADP and phosphate

- an ATPase (or Na+/K+ -ATPase)

Question 10

In a sodium-potassium pump, how much energy does one ATP provide?

Answer 10

• enough energy to pump two potassium ions in and three sodium ions out of the cell

Question 11

What does the pumping of potassium ions and sodium ions in a sodium-potassium pump achieve? Why is this necessary?

Answer 11

• a concentration gradient between the inside and outside of the neuron
• needed for the transmission of nerve impulses in axons

Question 12

What is situated in the centre of a sodium-potassium pump?

Answer 12

5 binding sites:

• 2 binding sites for K+ ions
• 3 binding sites for Na+ ions

Question 13

How many states does a sodium-potassium pump have? How does the sodium-potassium pump change states?

Answer 13

• two alternate states

- using energy from ATP

Question 14

Describe the two alternate states in a sodium-potassium pump.

Answer 14

in one:

• access to binding sites from outer side of membrane
• stronger attraction to K+ ions, so Na+ ions are discharged from the cell an K+ ions bind.

in the other:

• access to binding sites from the inside of membrane
• stronger attraction to Na+ ions, K+ ions discharged

Question 15

What does fluidity of membranes allow them to do?

Answer 15

move and change shape

Question 16

Outline endocytosis?

Answer 16

small piece of the plasma membrane can be pinched off to create a vesicle containing some material from outside the cell

Question 17

What is the opposite of endocytosis? Outline the opposite of endocytosis.

Answer 17

• exocytosis

- vesicles move to the plasma membrane and fuse with it, releasing the contents of the vesicle outside the cell

Question 18

What are vesicles in a cell used for? Give an example.

Answer 18

• used to move materials from one part of the cell to another
• vesicles move proteins from the RER to the Golgi apparatus

Question 19

Draw a diagram showing the process of endocytosis. (p12)

Answer 19

-

Question 20

Draw a diagram showing the process of exocytosis. (p12)

Answer 20

-

Question 21

Draw a diagram showing the process of vesicles transporting proteins in a cell. (p12)

Answer 21

-