Chapter 5

Question 1

Where are membranes found?

Answer 1

Surrounding the outside of a cell
Found inside a cell surrounding an organelle

Question 2

What are the 4 main roles of a membrane?

Answer 2

Compartmentalisation- separating out areas for specific conditions

Site of chemical reactions- holds proteins involved in certain reactions

Cell signalling- membranes contain receptors that can lead to a response

Barrier- partially permeable membranes- controls what goes in/out

Question 3

Why is it called fluid in the mosaic model?

Answer 3

This is because the phospholipids are free to move within the layer relative to each other.

Question 4

Why is is called mosaic in the fluid mosaic model?

Answer 4

The proteins randomly embedded in the bilayer are different sizes and shapes.

Question 5

What are intrinsic proteins?

Answer 5

Transmembrane proteins that are embedded through both layers of the membrane.
Held in place due to the interaction between R groups and the hydrophobic core of the membrane.

Role- transport across the membrane.

Question 6

What are channel proteins?

Answer 6

Hydrpphillic channel
Passive movement of polar molecules and ions
Down concentration gradient

Question 7

What are carrier proteins?

Answer 7

Passive transport
Active transport
Into cell
Shape of protein changes

Question 8

What are glycoproteins?

Answer 8

Embedded in the cell-surface membrane
Has a carbohydrate attached
Role- cell adhesion
Role- receptors for hormones
Role-cell signalling
Role-act as antigens for cell recognition
Role- attach to water molecules

Question 9

What are glycolipids?

Answer 9

Lipids with attached carbohydrate chain.

Role- Cell marker recognised by the immune system as self or no self.

Question 10

What are extrinsic proteins?

Answer 10

Only present one side of the membrane
Loosely attached so can easily be displaced from the membrane
Hydrophilic R groups which interact with polar heads of phospholipids/intrinsic proteins

Question 11

What is cholesterol?

Answer 11

A lipid with a hydrophilic head and a hydrophobic end.

Role: it binds to phospholipids phosphate heads, increasing the packing of the membrane, reducing the fluidity of membrane. Regulates the fluidity/stability of membranes.

How it stays in place?
Hydrophobic end interacting with tails.
Hydrophilic end interacting with the heads.
Pulling them together

Question 12

How does temperature affect membrane structure?

Answer 12

Increased kinetic energy will lead to the breaking of weak intermolecular forces between fatty acids tails. This will lead to an increase in the permeability.

The increased kinetic energy will also denature channel and carrier proteins and this will affect the permeability.

Question 13

How does solvent affect membrane structure?

Answer 13

It can enter the phospholipid blister and disrupt the interactions between fatty acid tails.

This will increase the permeability and fluidity and will break the membrane.

Question 14

Why is diffusion?

Answer 14

It is the passive net movement of particles down the concentration gradient, until equilibrium is reached.

Question 15

Can diffusion occur across a membrane?

Answer 15

Diffusion can occur without a membrane.

Particles can diffuse through a membrane without assistance if they are non-polar.

Polar particles need a protein channel to move through a membrane.

Question 16

What is facilitated diffusion?

Answer 16

Diffusion across a protein channel on a plasma membrane.

Question 17

What are the factors that affect the rate of diffusion?

Answer 17

Temperature- increase the KE

Concentration difference- Steeper difference between two concentrations.

Surface area to volume ratio- increases diffusion

Thickness of membrane- thinner the membrane , shorter diffusion distance.

Question 18

What do carrier proteins do?

Answer 18

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

1) First, a large molecule attaches to a carrier protein in the membrane.

2) Then, the protein changes shape.

3) This releases the molecule on the opposite side of the membrane.

Question 19

What do channel proteins do?

Answer 19

It forms pores in the membrane for charged particles to diffuse through. Different channel proteins facilitate the diffusion of different charged particles.

Question 20

What is active transport?

Answer 20

The movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher. This requires energy and carrier proteins.

Question 21

Factors affecting active transport

Answer 21

Carrier proteins are needed for active transport.

No matter how high the concentration of particles the rate of movement is limited by the number of carrier proteins.

Carrier proteins availability is a limiting factor.

Question 22

What is the process of active transport?

Answer 22

1) Molecules or ions bind to the channel of the carrier protein.

2) ATP binds to the inside of the carrier protein and is hydrolysed.

3) The phosphate molecule is left and the carrier protein changes shape. Molecules or ions are released.

4) Phosphate molecules is released and recombines with ADP to make ATP.

5) Carrier protein returns to shape

Question 23

Examples of active transport

Answer 23

Sodium potassium pump to transport nervous impulses.

Minerals moving into the root hair cell.

Hydrogen ions out of companion cells.

Question 24

What is bulk transport?

Answer 24

Form of active transport that moves large molecules and whole cells.

Question 25

What is exocytosis?

Answer 25

The bulk transport of materials out of a cell.

Question 26

What is endocytosis ?

Answer 26

The bulk transport of materials into a cell.

Question 27

What is endocytosis?

Answer 27

Some molecules are way too large to be taken into a cell by carrier proteins.

Membrane folds in and engulfs with itself and pinches off.
Formation of vesicles, it’s completely surrounded by membrane
Uptake of solid and liquid.

Question 28

What is exocytosis?

Answer 28

Some substances produced by the cell need to be released from the cell- done by exocytosis.

Vesicles containing these substances pinch off the from the sacs of the Golgi apparatus and move towards the plasma membrane .

Vesicles fuse with the plasma membrane and release their contents outside the cell.

Some substances aren’t released outside the cell- instead they are inserted straight into plasma membrane .

Uses ATP as energy source.

Question 29

What is osmosis?

Answer 29

Diffusion/net movement of water
Down the water potential gradient
Through a partially permeable membrane

Question 30

What is water potential?

Answer 30

The pressure exerted by water onto membranes
Measured in kPa
Lower the water potential the more concentrated the solution

Question 31

What is hydrostatic pressure?

Answer 31

The pressure exerted by water in an enclosed space.

Question 32

What is cytolysis?

Answer 32

Too much hydrostatic pressure on a cell surface membrane will cause it to burst.

Question 33

What is shrivel/ crenation?

Answer 33

Too little hydrostatic pressure will cause it to shrivel.

Question 34

Why won’t cytolosis happen in plant cells?

Answer 34

Have a cellulose cell wall

Question 35

What will happen to plant cell if hydrostatic pressure is too low?

Answer 35

Contraction of the protoplast of a plant cell as a result of loss water from the cell

Question 36

What is protoplast?

Answer 36

The living part of the cell excluding the cell wall.

Question 37

What is a serial dilution?

Answer 37

It is a succession of step dilutions, each with the same dilution factor, where diluted material of previous step is used to make th subsequent dilution.