Cell Membranes

Question 1

What are the components of a cell surface membrane? Clue= there are 4

Answer 1

Phospholipid bilayer, proteins, carbohydrates, cholesterol

Question 2

What is a cell surface membrane?

Answer 2

The barrier between a cell and its environment. It controls the entry and exit of substances and is partially permeable meaning it only lets some molecules through.

Question 3

Why is the arrangement of molecules described as the fluid mosaic model?

Answer 3

The phospholipids in the membrane are in constant motion (fluid) and there is a mosaic pattern of proteins throughout the membrane.

Question 4

What do receptor proteins do?

Answer 4

Detective chemicals released from other cells.

Question 5

Describe the phospholipid bilayer

Answer 5

Hydrophilic head - attracts water (faces out towards water on either side of membrane)
Hydrophobic tail - repels water (centre of membrane to stop water-soluble substances through it
Acts as a barrier

Question 6

What does cholesterol do in a cell membrane?

Answer 6

Attached to tails between phospholipids causing them to pack closer together which restricts moment making less fluid and more rigid. Helps to maintain shape of animal cells where there is no cell wall.

Question 7

What is diffusion?

Answer 7

Net movement of particles from an area of high to low concentration. It is passive so no energy is required.

Question 8

What is simple diffusion?

Answer 8

When small and non polar particles diffuse directly through a membrane, down a concentration gradient.

Question 9

What is facilitated diffusion?

Answer 9

Uses carrier or channel proteins in the membrane to speed up larger and charged particles.
Moves particles down a conc gradient, high to low.
Passive - doesn’t require energy

Question 10

What kind of molecules do carrier proteins transport? Give an example too.

Answer 10

Large molecules e.g glucose and amino acids

Question 11

What kind of molecules do channel proteins transport?

Answer 11

Charged particles e.g ions.

Question 12

What are the factors affecting simple diffusion?

Answer 12

• The concentration gradient - higher = faster. During diffusion the difference in concentration between the two sides decreases into it reaches equilibrium.
• thickness of the exchange surface. Thinner = faster rate.
• surface area = larger = faster rate of diffusion.

Question 13

Give an example of how an increase in surface area results in faster diffusion rate

Answer 13

Microvilli in epithelial cells in this small intestine. Microvilli are projections formed by the cell surface membrane folding up. It gives the cell a larger surface area and so more particles can be exchanged in the same amount of time increasing the rate of diffusion.

Question 14

What are the factors affecting facilitated diffusion? (2)

Answer 14

• the concentration gradient. Higher concentration gradient result in a faster rate of diffusion.
• the number of channel or carrier proteins. The greater number of proteins result in a faster rate. Once all are in use it can’t happen any faster.

Question 15

What is osmosis?

Answer 15

The diffusion of water molecules across a partially permeable membrane from an area of high water potential to an area of low water potential

Question 16

What is water potential?

Answer 16

The likelihood of water molecules to diffuse out of or into a solution. Higher water potential means a higher concentration of water molecules.

Question 17

What is an isotonic solution?

Answer 17

A solution with the same water potential

Question 18

Why does pure water have the highest water potential?

Answer 18

There are no solids to restrict movement. Solutes lower the kinetic energy and therefore water potential.

Question 19

What is a hypotonic solution? What direction is the net movement?

Answer 19

Solution has a higher water potential compared to the inside of the cell. Net movement is into the cell.

Question 20

What is a hypertonic solution? What direction is the net movement?

Answer 20

Solution has lower water potential and ban the cell so net movement is out of the cell.

Question 21

Factors affecting osmosis (3)

Answer 21

• water potential gradient. The higher the water potential gradient; the faster the rate.
• thickness of the exchange surface. Thinner = faster rate.
• surface area of the exchange surface. Larger = faster

Question 22

How is active transport different to facilitated diffusion?

Answer 22

A.T moves solutes from a low to high concentration, F.D moves from high to low.
A.T requires energy, unlike f.d

Question 23

Which molecule provides the energy for active transport?

Answer 23

ATP

Question 24

Describe the process by which energy is released by the cell for active transport

Answer 24

Energy is released by the hydro lists of ATP into ADP and Pi

Question 25

Describe how carrier proteins actively transport substances across the cell membrane

Answer 25

A molecule attaches to the carrier protein, the protein changes shape and this moves the molecule across the membrane, releasing it on the other side.

Question 26

What are co-transporters?

Answer 26

A type of carrier protein that bind two molecules at a time. The conc gradient of one is used to move the other molecule against its own concentration gradient. Using a carrier protien

Question 27

Factors affecting rate of active transport

Answer 27

•speed of individual carrier proteins. •number of carrier proteins present. •the rate of respiration in the cell and availability of ATP. If respiration is inhibited, a.t can’t take place.

Question 28

How is glucose absorbed?

Answer 28

By co-transport into the bloodstream in the small intestine in the ileum (final part of the small intestine)

Question 29

What transporter proteins are in an epithelial cell?

Answer 29

Sodium-glucose co-transporter protein Sodium - potassium pump Protein channel

Question 30

What does the protein channel in the epithelial cell do?

Answer 30

Glucose diffuses through into the blood out of the cell, down its conc gradient by facilitated diffusion

Question 31

What does the sodium glucose do transporter protein do?

Answer 31

Carries glucose into the cell with sodium. Sodium gets actively transported OUT of the cell into the lumen of ileum but diffuses into the cell.

Question 32

Explain the effect of a higher percentage of cholesterol would have on a fluid mosaic model

Answer 32

It would make the phospholipid by layer less able to move so less fluid and more rigid

Question 33

Explain two ways the cell surface membranes of the epithelial cells in the mammalian ileum might be adapted to their function.

Answer 33

• villi - for larger surface area to maximise rate of absorption • higher proportion of carrier and channel proteins to carry nutrients by facilitated diffusion or active transport.

Question 34

How does temperature (0-45 degrees) affect membrane permeability?

Answer 34

From 0-45 degrees C, the phospholipids can move and aren’t packed as tightly together. the membrane is partially permeable. As temperature increases, the phospholipids move more because they have more energy. This increases the permeability of the membrane.

Question 35

How does temperature above 45°C affect membrane permeability?

Answer 35

The phospholipid bilayer starts to break down and the membrane becomes more permeable. Channel proteins and carrier proteins deformed so they can’t control into leaves the cell – this increases the permeability of the membrane

Question 36

How does active transport happen across a cell membrane?

Answer 36

Using a carrier protein and ATP against a concentration gradient.

Question 37

What is the water potential and unit of pure water?

Answer 37

0 KiloPascals