Chapter 5

Question 1

What is the role of membranes ?

Answer 1

Membranes are partially permeable barriers between the cell and its environment, between organelles and the cytoplasm and within organelles.
Membranes are sites of chemical reactions
Membranes are sited of cell communication

Question 2

What is the fluid mosaic model?

Answer 2

The fluid mosaic model is the model of the structure of a cell membrane in which phospholipids within the phospholipid bilayer are free to move and proteins of various shapes and sizes are embedded in various positions

Question 3

The structure and function of the phospholipid bi layer

Answer 3

The phospholipid bilayer is made of fluid phospholipids with hydrophilic heads and hydrophobic tails and it allows some substances to diffuse through while stopping others like water soluble substances which cannot pass through the hydrophobic core .

Question 4

Function of channel proteins

Answer 4

channel proteins provide a hydrophilic channel allowing the movement of polar molecules and ions

Question 5

Function of cholesterol in the plasma membrane

Answer 5

Adds stability by binding to the hydrophobic tails packing them more closely together

Question 6

Function of glycoproteins in the plasma membrane

Answer 6

Glycoproteins are intrinsic proteins attached to a carbohydrate chain that play a role in cell adhesion and cell signalling

Question 7

Function of glycolipids in the membrane

Answer 7

Glycolipids are a lipid with an attached carbohydrate chain which act as antigens so the immune system can recognise cells as ‘self’

Question 8

What are membrane bound receptors?

Answer 8

Membrane bound receptors are proteins which act as receptors that have specific shapes and respond to a particular message molecule

Question 9

How does low temperature affect membrane structure and permeability?

Answer 9

Temperatures below 0 degrees hugely increase permeability because the phospholipids have little energy so the membrane is ridged and channel and carrier proteins deform and ice crystals pierce the membrane

Question 10

How does average temperatures affect membrane permeability and structure ?

Answer 10

Temperatures between 0-45 degrees make the membrane partially permeable, the permeability will increase as temperature rises as phospholipids have more energy so move about more increasing fluidity but overall fairly low

Question 11

How does high temperatures affect membrane permeability and structure ?

Answer 11

At high temperatures of 45 degrees or higher the phospholipids melt and proteins deform so permeability is incredibly high

Question 12

How do organic solvents affect membrane permeability and structure ?

Answer 12

Organic solvents such as ethanol disrupt membranes making them more permeable

Question 13

How can we investigate membrane permeability?

Answer 13

1) cut 5 equal pieces of beetroot and wash and dry to remove pigment
2) out then in test tubes with 5cm3 of water and place each one in a different temperature water bath (or place each one in a different concentration or different solvent)
3) after a set time remove the beetroot and use a colorimeter to measure the absorbance the higher absorbance the higher permeability

Question 14

Diffusion

Answer 14

The net movement of particles from an area of high concentration to an area of lower concentration down a concentration gradient

Question 15

What molecules diffuse through the membrane ?

Answer 15

Small non polar molecules can diffuse through spaces between phospholipids

Question 16

What does passive means?

Answer 16

Passive means no energy is needed

Question 17

What factors effect diffusion?

Answer 17

Concentration gradient, thickness of exchange surface, SA and temperature affects diffusion

Question 18

How can we measure the effect of factors on diffusion ?

Answer 18

1) make up agar jelly and cut cubes of equal size
2) put each in a boiling tube of HCL and either
- heat to different temperatures
- use different concentrations of HCL
- cut cubes to different sizes and calculate the SA:V
3) then time how long each cube takes to go colourless to find diffusion rate

Question 19

What is facilitated diffusion?

Answer 19

Facillitated diffusion is diffusion if larger molecules, ions and polar molecules across a membrane either through channel proteins or carrier protein which change shape when the molecule bonds and realise it at the other side

Also passive

Question 20

What is active transport?

Answer 20

Active transport is the movement of particles across the membrane against a concentration gradient using energy

Question 21

What happens during active transport?

Answer 21

1) Molecule binds to receptors on the carrier protein
2) Inside the ATP binds and is hydrolysed into ADP and phosphate. The binding of the phosphate causes the protein to change shape
3) The ion is released inside the cell and ADP and phosphate recombine to make ATP making the protein its original shape

Question 22

What is endocytosis?

Answer 22

Endocytosis is the bulk transport of materials into a cell via invagination of the cell-surface membrane forming a vesicle using ATP

Question 23

What is exocytosis

Answer 23

Exocytosis is the bulk transport of material out of cells the vesicle fuses with the cell surface and its content is released using ATP

Question 24

What is osmosis?

Answer 24

Osmosis is the diffusion of water molecules across a partially permeable membrane down the water potential gradient

Question 25

What is the effect of a plant/animal cell being put in a hypotonic solution?

Answer 25

The net movement of water molecules will be into the cell the plant cell will become Turgid and the animal cell will burst

Question 26

What is the effect of putting a plant/animal cell in an isotonic solution?

Answer 26

There is no net movement of particles so both cells stay the same

Question 27

what Is the effect of putting a plant/animal cell in a hypertonic solution?

Answer 27

The net movement of water molecules will be out of the cell so a plant cell will become flaccid and the contents will put away with it which is called plasmolysis and an animal cell will shrink

Question 28

How can we find the concentration inside a potato cell?

Answer 28

1) Cut equal pieces of potato
2) Measure the starting mass of each
3) put it in a different concentration of sucrose solution only for a set time
4) Reweigh and calculate the percentage change in mass
5) Plot and where the line meets the axes is the concentration inside the cell