Cell membranes

Question 1

Facilitated diffusion

Answer 1

Channel/carrier proteins
Large/polar molecules
Complementary to substrate
Net movement of particles down a concentration gradient
Passive process
Aquaporins are protein channels that allow water to pass through the membrane

Question 2

The cell membrane

Answer 2

Selectively permeable

Question 3

Role of cholesterol

Answer 3

A lipid found within the bilayer
Not found in bacterial cell membranes
Make the membrane more rigid
Maintains shape

Question 4

What affects the permeability of cell membranes

Answer 4

pH affects structure of enzymes and proteins
Buffer solutions can be used to control pH
Solvent concentration
The phospholipid bilayer is more permeable in acidic conditions
High temperatures increase permeability

Question 5

Investigating cell membrane permeability

Answer 5

Beetroot often used because of coloured pigment
Use cork borer to collect samples of uniform diameter
Rinse in cold water to remove excess pigment that may have been released from broken cell membranes
Prepare dilution series of ethanol and distilled water
Place in test tubes for 10 minutes
Remove discs
Calibrate colourimeter using a cuvette of distilled water
Measure the absorbance of each solution
Plot a graph of concentration and absorbance

Question 6

What is diffusion

Answer 6

The net movement of particles from an area of high to low concentration
It’s passive

Question 7

What is a carrier protein

Answer 7

When a substance binds to a carrier protein it changes shape allowing the molecule to pass through

Question 8

Factors affecting diffusion

Answer 8

The concentration gradient - the bigger the concentration gradient the fast the rate of diffusion
Higher temperature results in higher rate
The larger the surface area of the membrane the faster the diffusion rate
The thicker the exchange surface the slower the rate
The number of channel or carrier proteins

Question 9

What is osmosis

Answer 9

The diffusion of water across a partially permeable membrane from a high (dilute) to low (concentrated) water potential
A partially permeable membrane allows water to pass through but not substances dissolved in water
The lower the water potential gradient the slower the rate of osmosis

Question 10

What is active transport

Answer 10

Requires energy (ATP)
Movement of ions and molecules against a concentration gradient
Uses carrier proteins
Affected by surface area and number of carrier proteins

Question 11

What is co-transport

Answer 11

Glucose and amino acids into the epithelial cells in the ileum
Sodium binds to sodium-glucose co transporter proteins allowing glucose and amino acids to be actively transported