Active transport

Question 1

What is active transport?

Answer 1

• transport of a molecule that requires energy because it moves a solute against its concentration gradient (up)

Question 2

What are four examples of active transport?

Answer 2

• pumps
• cotransport
• exocytosis
• endocytosis

Question 3

Active transport requires energy in the form of ATP. What is ATP (2)

Answer 3

• adenosine triphosphate is an energy source used by cells

- it is a modified RNA nucleotide

Question 4

What does ATP do? (2)

Answer 4

• it can transfer the terminal phosphate group to the transport protein which changes the shape of the transport proteins to better move a substance
• also known as conformational change

Question 5

What do pumps (such as sodium-potassium pumps in neurons) do?

Answer 5

Maintain membrane potential

Question 6

What is membrane potential?

Answer 6

Unequal concentration of ions across the membrane that result in an electrical charge (electrochemical gradient)

Question 7

What are 3 examples of pumps?

Answer 7

Electrogenic, sodium potassium, proton pump

Question 8

What is an electrogenic pump?

Answer 8

• proteins that generate voltages across membranes, which can be used later as an energy source for cellular processes

Question 9

Why is the sodium potassium pump important, and what happens?

Answer 9

• animal cells will regulate their relative concentrations of Na+ and K+
• 3 Na+ pumped out of cell, 2 k+ into cell
• results in a +1 net charge to the extracellular fluid (outside the neuron)

Question 10

What is a proton pump? (3)

Answer 10

• integral membrane proteins that builds up a proton gradient (hydrogen ions) across the membrane
• used by plants, fungi, and bacteria
• pumps H+ out of cell

Question 11

What is cotransport and who benefits from it? (2)

Answer 11

• The coupling of a favourable movement of one substance with an unfavourable movement of another substance
• plants use it for sugars and amino acids

Question 12

What does cotransport use in order to do what it has to do?

Answer 12

• uses the energy stored in electrochemical gradients (generated by pumps) to move substances against their concentration gradient

Question 13

What is favourable movement, and what is unfavourable movement?

Answer 13

• favourable movement is downhill diffusion from high to low

- unfavourable movement is uphill transport from low to high

Question 14

An example of cotransport in plants is the sucrose-H + cotransporter. What happens here?

Answer 14

• sucrose can travel into a plant cell against its concentration gradient only if it is COUPLED with H+ that is diffusing down it’s electrochemical gradient

Question 15

The transport of large molecules is done through what two types of active transport specifically?

Answer 15

Exocytosis and endocytosis

Question 16

What is exocytosis?

Answer 16

The secretion of molecules via vesicles that fuse to the plasma membrane

Question 17

How can vesicles fuse to the plasma membrane in exocytosis? (3)

Answer 17

• vesicles can fuse to the membrane by forming a bilayer
• once fused, the contents of the vesicle are released to the extracellular fluid
• an example would be nerve cells releasing neurotransmitters during an action potential

Question 18

What is endocytosis?

Answer 18

• The uptake of molecules from vesicles fused from the plasma membrane (opposite of exocytosis)

Question 19

Three examples of endocytosis?

Answer 19

Phagocytosis, pinocytosis, receptor-mediated endocytosis

Question 20

What is phagocytosis?

Answer 20

When a cell engulfs particles to be later digested by lysosomes

Question 21

How does phagocytosis work? (3)

Answer 21

• cell surrounds particle with pseudopodia (meaning false foot)
• packages particles into a food vacuole
• food vacuole fuses with a lysosome to be digested

Question 22

What is pinocytosis?

Answer 22

Nonspecific uptake of extracellular fluid containing dissolved molecules

Question 23

What happens in pinocytosis?

Answer 23

• The cell takes in dissolved molecules in a protein coated vesicle

Question 24

In pinocytosis, cells essentially take in vesicles coated in proteins. Why?

Answer 24

The protein coating helps to mediate the transport of molecules

Question 25

What is receptor mediated endocytosis?

Answer 25

• specific uptake of molecules via the solute binding to receptor proteins on the plasma membrane

Question 26

Why is receptor mediated endocytosis important?

Answer 26

• it allows the cell to take up large quantities of a specific substance

Question 27

What happens in receptor mediated endocytosis?

Answer 27

• when the solute binds to the receptors, they cluster in a coated vesicle to be taken into the cell