3.2.2 Transport Across Cell Membranes

Question 1

Water is dipolar. What do we mean by dipolar?

Answer 1

One end of the molecule has a slight positive charge, the other end is slightly negative

Question 2

Why is water important for living things?

Answer 2

It is used in metabolism (condensation/ hydrolysis), it is a solvent for many substances, water potential has to be at the right level so cells don’t shrivel or burst due to osmosis

Question 3

Answer 3

Question 4

How does ATP release energy to a cell?

Answer 4

ATP undergoes hydrolysis to form ADP + Pi, releasing energy.

Question 5

Answer 5

Question 6

Which part of a phospholipid is hydrophobic?

Answer 6

Tail

Question 7

What is the role of cholesterol in the plasma membrane?

Answer 7

add strength, reduce lateral movement, stop leakage

Question 8

Describe the importance of a partially permeable membrane.

Answer 8

The membrane will only allow certain molecules through- regulates movements of solutes

Question 9

What does the fluid mosaic model describe?

Answer 9

The phospholipid bilayer is interspersed with proteins (like tiles in a mosaic), & constantly move (fluid)

Question 10

Answer 10

Question 11

The centre of the bilayer is hydrophobic. So which type of molecules can diffuse through.

Answer 11

Small & non-polar. (Water also does! As it’s so small).

Question 12

How would chloride (Cl-) ions move across the membrane?

Answer 12

Across a channel protein

Question 13

What is a glycoprotein?

Answer 13

Proteins with a carbohydrate attached- usually protrude from the membrane.

Question 14

Answer 14

Question 15

Would you expect a red blood cell, or an epithelial cell of the small intestine, to contain more cholesterol in the plasma membrane?

Answer 15

Red blood cell- unsupported & free-floating cell, so needs to maintain own shape.

Question 16

If high temperatures are applied to the Plasma membrane, what happens?

Answer 16

Channel/carrier proteins denature, so membrane becomes more permeable (it can’t control what is going in/out)

Question 17

What is diffusion?

Answer 17

The net movement of molecules from an area of high concentration to an area of low concentration (DOWN the conc. gradient)

Question 18

Is diffusion a passive or active process?

Answer 18

Passive-no energy is needed.

Question 19

Give an example of a molecule which can use simple diffusion to pass through the membrane.

Answer 19

Small, non-polar e.g. oxygen, carbon dioxide

Question 20

Describe the role of a carrier protein.

Answer 20

Use to move large molecules across the membrane- when ion/molecule attaches to protein, it changes shape & releases molecules on other side of membrane.

Question 21

What is facilitated diffusion?

Answer 21

Movement of particles from a high to low concentration, down the conc. gradient, using a membrane protein.

Question 22

Which types of molecules would be transported using facilitated diffusion across the membrane?

Answer 22

Large, polar, water-soluble (e.g. glucose, amino acids)

Question 23

Describe the role of a channel protein.

Answer 23

Acts as a pore in the membrane to allow larger/polar molecules to diffuse across.

Question 24

Answer 24

Question 25

A graph showing the uptake of glucose by GLUT1 carrier proteins, shows that the rate increases as the number of glucose molecules increases. However the graph plateaus, why?

Answer 25

The system reaches equilibrium- there are only so many carrier proteins- if most of these are in use, then the rate of glucose uptake would slow.

Question 26

How can the gradient of a straight line or tangent by calculated?

Answer 26

Change in y / change in x

Question 27

Is facilitated diffusion a passive or active process?

Answer 27

Passive-no energy is needed.

Question 28

What is osmosis?

Answer 28

The net movement of water molecules through a partially permeable membrane, from an area of high water potential (less negative) to an area of lower water potential (more negative).

Question 29

What is the water potential of pure water?

Answer 29

Water potential ψ = 0

Question 30

Answer 30

Question 31

Answer 31

Question 32

If more of a solute (e.g. salt) is added to a beaker of water, what would happen to the water potential of the solution?

Answer 32

More solute = less water molecules, so LOWER water potential (more negative)

Question 33

Answer 33

Question 34

Describe how you would use a calibration curve to identify the water potential of a sample.

Answer 34

Identify the point at which the curve meets the x axis (where % change in mass is 0). Find the concentration at this point & look up water potential.

Question 35

Pieces of potato with a ψ of -350 kPa are placed into a solution with a ψ of -275 kPa. Explain what will happen to the potato.

Answer 35

Potato gains mass (has a lower ψ than the solution OR MORE negative ψ) so water moves from solution into the potato.

Question 36

what words describe what happens to red blood cells if placed in solutions of high, the same, and low water potential?

Answer 36

Question 37

what words describe what happens to plant cells if placed in solutions of high, the same, and low water potential?

Answer 37

Question 38

What is active transport?

Answer 38

The movement of particles from an area of lower concentration to higher concentration, requiring energy. (AGAINST a conc. gradient)

Question 39

Will the rate of active transport increase or decrease if the number of carrier proteins in the membrane is increased?

Answer 39

Increase

Question 40

Describe the importance of sodium ions in the transport of glucose from the ileum into the blood.

Answer 40

Na + ions diffuse through a carrier protein down their conc. gradient, carrying glucose in simultaneously, which is moving AGAINST it’s gradient. Glucose can then diffuse into the blood & be transported around the body.

Question 41

Describe the importance of the villi in the small intestine.

Answer 41

Villi- increase surface area of ileum, so more products of digestion can be absorbed.

Question 42

Define facilitated diffusion

Answer 42

Larger molecules and charged particles cannot diffuse through the phospholipid bilayer as they are insoluble. They diffuse through carrier or channel proteins in the cell membrane instead. Passive process

Question 43

What are carrier proteins?

Answer 43

Move large molecules into or out of the cell down their concentration gradient. Different carrier proteins facilitate the diffusion of different molecules

Question 44

How do carrier proteins work?

Answer 44

A large molecule binds to a specific site in the carrier protein. The protein changes shape and releases the molecule on the opposite side of the membrane

Question 45

What is a channel protein?

Answer 45

Channel proteins - Form pores in the membrane for charged particles to diffuse through. Different channel proteins facilitate the diffusion of different charged particles. All have a specific shape and can be opened or closed

Question 46

Define active transport

Answer 46

Active transport - Uses energy to move molecules and ions across the plasma membranes against a concentration gradient. Use carrier proteins

Question 47

Explain how active transport works

Answer 47

A molecule attaches to the carrier protein. ATP is hydrolysed in the cell to release energy. This energy is used to make the carrier protein change shape. This moves the molecule across the membrane, releasing it on the other side.