Transport Across Membranes

Question 1

What is a cell-surface membrane?

Answer 1

They surround cells and regulates the movement of substances into and out of the cell. They also contain receptors, which can act as antigens or respond to chemicals like hormones

Question 2

What does partially permeable mean?

Answer 2

They let some molecule through but other cannot get through. This can depend on the molecules size, charge, lipid solubility etc…

Question 3

Why is the structure of a cell-surface membrane described as ‘Fluid-Mosaic’?

Answer 3

The phospholipid molecules cause the membrane fluidity as it constantly moving. The mosaic part refers to the large proteins and lipids which are scattered in the bilateral like tiles in a mosaic. These proteins and lipids include: transport proteins, glycoproteins, glycolipids and cholesterol.

Question 4

Name the molecules that make up the cell surface membrane.

Answer 4

Phospholipids, cholesterol, glycolipids, glycoproteins, channel proteins and proteins carriers, co-transporters.

Question 5

What part of the phospholipid is hydrophilic?

Answer 5

Phosphate Head.

Question 6

What part of the phospholipid is the fatty acids?

Answer 6

The hydrophobic tails.

Question 7

What does a phospholipid bilayer mean?

Answer 7

Continuous phospholipid double layer with the phosphate heads facing out and the fatty acid tails facing inward.

Question 8

Why can’t water soluble substances (ions) diffuse osmotically through the phospholipid bilayer?

Answer 8

The centre hydrophobic tails prevents water-soluble substances through, acting as a barrier.

Question 9

What’s the function of cholesterol?

Answer 9

Type of lipid which fit between phospholipids and bind to the hydrophobic tails, causing them to pack more closely together. This increases the membrane rigidity. They maintain the Membranes shape in animal cells.

Question 10

What is an extrinsic proteins?

Answer 10

A membrane protein that partially span the membrane and is attached to either the outer or inner phospholipid layer. Glycolipids and glycoproteins are two examples.

Question 11

What is the function of glycoproteins and glycolipids?

Answer 11

Both act as cell surface receptors for specific chemicals and they act as recognition sites. Glycolipids also help maintain membrane stability and glycoproteins allow cells to recognise one another.

Question 12

What effect does temperature have on membrane permeability?

Answer 12

Increasing the temperature, increases the membrane permeability.

Question 13

What’s the affect of temperatures below 0 degrees on membrane permeability.

Answer 13

Phospholipids don’t have much energy, so can’t move very much. Rigid. Transport deform, allowing more molecules to come through.

Question 14

Above what temperature does the bilayer start to melt and so becomes permeable?

Answer 14

Above about 45 degrees Celsius.

Question 15

Define diffusion.

Answer 15

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

Question 16

Is diffusion passive or active?

Answer 16

Passive - No energy required.

Question 17

What does a concentration gradient mean?

Answer 17

Path from high concentration to low concentration.

Question 18

Name two molecules that can pass through the phospholipid bilayer freely by simple diffusion.

Answer 18

Oxygen and carbon dioxide.

Question 19

Can a small, non-polar and lipid soluble molecule get through the phospholipid bilayer?

Answer 19

Yes.

Question 20

What is simple diffusion?

Answer 20

Molecules move directly through the phospholipid bilayer.

Question 21

Name the two transport proteins that facilitated diffusion happens through.

Answer 21

Protein channel and carrier proteins.

Question 22

Why are Channel and carrier proteins needed?

Answer 22

To carry large, polar molecules across the membrane.

Question 23

How does a carrier protein transport molecules?

Answer 23

A molecule attaches to carrier protein in membrane. Protein changes shape and releases its content on the opposite end of the membrane.

Question 24

What are Channel proteins?

Answer 24

Pores in the membrane for charged particles to diffuse through. Different proteins cater for different molecules (specific).

Question 25

What are the three factors that increase simple diffusion?

Answer 25

Steep concentration gradient, thin exchange surface and large surface area.

Question 26

Name a structure that increases surface area of a cell surface membrane.

Answer 26

Microvilli

Question 27

Name the two factors that would increase the rate of facilitated diffusion.

Answer 27

Steep concentration gradient and high numbers of transport proteins.

Question 28

What is the name of the Channel proteins which allow the diffusion of water?

Answer 28

Aquaporins.

Question 29

Define Osmosis.

Answer 29

The net movement of water molecules from an area of high water potential to an area of lower water potential through partially permeable membrane.

Question 30

What does water potential mean?

Answer 30

The potential of water molecules to diffuse out of or into a solution. Pure water has the highest water potential.

Question 31

What does isotonic mean?

Answer 31

If two solutions have the same water potential.

Question 32

Name the three factors that affect the rate of osmosis.

Answer 32

Water potential gradient, thickness of the exchange surface and the surface area.

Question 33

Define active transport.

Answer 33

Active transport is the movement of molecules through a cell surface membrane from an area of low concentration to an area of higher concentration using ATP and carrier proteins.