2B - Cell Membranes

Question 1

What is a cell surface membrane

Answer 1

A partial permeable barrier between the cell(or organelle) and its environment, controlling the substances which enter and leave it.

Question 2

How do molecules move across a membrane

Answer 2

• Diffusion
• Osmosis
• Active Transport
• Facilitated diffusion

Question 3

Another name for a cell surface membrane

Answer 3

Plasma membrane

Question 4

What is a cell membrane composed of

Answer 4

Lipids
Proteins
Carbohydrates

Question 5

What is the fluid mosaic model

Answer 5

Phospholipid molecules form a continuous bilayer(Double layer) which is ‘fluid’ as they are constantly moving. Proteins, such a carrier and channel proteins, are scattered across the layer like a mosaic. Receptor cells on the membrane allow the cell to detect chemicals from other cells.

Question 6

What is a protein with a carbohydrate attached called?

Answer 6

Glycoprotein

Question 7

What is a lipid with a carbohydrate attached called?

Answer 7

Glycolipid

Question 8

Describe the arrangement of phospholipid molecules in the plasma membrane.

Answer 8

The molecules are arranged in a bilayer with the hydrophilic heads facing away from the centre and towards the water in the cells and outside of the cells.
The hydrophobic tails point towards the centre of the bilayer as they are repelled by the water molecules on each side.

Question 9

What substances cant diffuse through the bilayer?

Answer 9

Water soluble substances such as ions and polar molecules as the centre is hydrophobic.

Question 10

What is the role of cholesterol in the plasma membrane?

Answer 10

Gives the membrane stability by binding to the hydrophobic tails of the phospholipids and causing them to pack closer. This restricts their movement and so makes the layer less fluid and so helps to maintain the shape of the cell membrane.

Question 11

The effect of temperatures below 0 on plasma membranes.

Answer 11

Phospholipids don’t have much energy and so cant move very much. They are packed close together making a rigid membrane. Channel and carrier proteins denature, increasing permeability.
Ice crystals form and puncture the membrane which makes it highly permeable once thawed.

Question 12

The effect of temperatures between 0 and 45 on plasma membranes.

Answer 12

Phospholipids are fluid and can move more as the temperature increases

Question 13

The effect of temperatures above 45 on plasma membranes.

Answer 13

Bilayer starts to melt
Water inside the cell expands which puts pressure on the membrane
Channel and carrier proteins denature
All of which increase permeability.

Question 14

Diffusion is…

Answer 14

the net movement of molecules from an area of high concentration to an area of lower concentration.

Question 15

If diffusion is said to be passive what does this mean?

Answer 15

It requires no energy

Question 16

Factors affecting the rate of diffusion.

Answer 16

Concentration gradient - larger will increase the rate
Length of diffusion pathway - thinner surfaces increase the rate
Surface area - increasing S.A will increase diffusion

Question 17

What is facilitated diffusion

Answer 17

When large or polar molecules that cant diffuse through the bilayer are moved across a membrane by carrier or channel proteins.

Question 18

Describe the action of a carrier protein.

Answer 18

Large molecule attaches to a carrier protein
Carrier protein changes shape
Releases molecule on the other side of the membrane.

Question 19

Describe the action of a channel protein.

Answer 19

The form pores in the membrane which allows charged molecules to diffuse through.

Question 20

Which proteins moves laree molecules

Answer 20

Carrier protein - channel proteins move charged particles

Question 21

Factors that affect facilitated diffusion

Answer 21

Concentration gradient - Higher increases the rate

Number of channel/carrier proteins - more increase diffusion

Question 22

What is osmosis?

Answer 22

The diffusion of water across a partially permeable membrane from an area of higher water potential to an area of lower water potential.

Question 23

What is water potential?

Answer 23

The likelihood of water molecules diffusing out of or into a solution.

Question 24

What is the water potential of pure water?

Answer 24

0

Question 25

What does adding solute do to the water potential.

Answer 25

Lowers it and makes t more negative.

Question 26

If two solutions have the same water potential they are…

Answer 26

Isotonic

Question 27

Solutions with a higher water potential than inside the cell are called….

Answer 27

Hypotonic

Question 28

Solutions with a lower water potential than inside the cell are called….

Answer 28

Hypertonic

Question 29

In a hypertonic solution the net movement of water is…

Answer 29

Out of the cell

Question 30

In a hypotonic solution the net movement of water is…

Answer 30

Into the cell

Question 31

The factors affecting osmosis

Answer 31

The same as those for diffusion.

Question 32

What is active transport

Answer 32

Using energy to move molecules against a concentration gradient.

Question 33

Active transport by carrier proteins.

Answer 33

Molecule attaches to protein
Protein changes shape
Molecule released on the other side.
This is the same process as facilitated diffusion apart from ATP is used to move the molecule against the concentration gradient

Question 34

Active transport with Co-transporters

Answer 34

Same process as carrier proteins apart from two molecules bind to the same protein and the concentration gradient of one is used to move the other against its own.

Question 35

How is glucose absorbed from the ileum?

Answer 35

1) Sodium ions are actively transported out of epithelial cells and into the blood by a potassium sodium pump, creating a concentration gradient.
2) Sodium ions diffuse from the ileum and into the epithelial cells, via sodium glucose co-transporters. The co-transporters also carry glucose into the cell which increases the concentration of glucose in the epithelial cells.
3) Glucose diffuses out of the cell an into the blood down its concentration gradient through a protein channel by facilitated diffusion.

Question 36

Factors affecting the rate of active transport.

Answer 36

Speed of individual carrier proteins - faster proteins increase the rate of diffusion
Number of carrier proteins - more proteins increases the rate of diffusion
Rate of respiration in the cell and the availability of ATP