DNA and cells - CELL MEMBRANE/MOVEMENT ACROSS

Question 1

Why is the cell membrane called the fluid mosaic model?

Answer 1

• It has different components that make up the model
• It is fluid because it can partly move

Question 2

List the features of the fluid mosaic model

Answer 2

• Phospholipids
• Channel proteins
• Carrier proteins
• Aquaporins
• Glycoproteins
• Glycolipids
• Cholesterol

Question 3

Give the definition of diffusion

Answer 3

The net movement of particles from areas of high to areas of low concentration across a partially permeable membrane, down the concentration gradient.

Question 4

What factors affect rate of diffusion?

Answer 4

• Concentration
• Temperature
• Surface area: volume ratio
• Diffusion distance
• Concentration gradient

Question 5

What is simple diffusion and where does it occur?

Answer 5

• The movement of substances across the membrane
• Occurs all over the plasma membrane

Question 6

What is facilitated diffusion and where does it occur?

Answer 6

• The movement of charged, large and polar molecules
• Via intrinsic proteins

Question 7

Give the definition of active transport

Answer 7

The net movement of particles from an area of low to high concentration, against the concentration gradient across a partially permeable membrane, using ATP

Question 8

How does active transport occur?

Answer 8

• Molecule binds to the carrier protein on its receptor sites
• ATP is hydrolysed to form ADP + Pi. The phosphate binds to the transport molecule causing the transport protein to change shape
• The change in shape moves the molecule across the cell membrane
• Phosphate removes binding and carrier protein returns to normal shape

Question 9

What is exocytosis?

Answer 9

Molecules leaving the cell as vesicles fuse with plasma membrane using ATP

Question 10

What is endocytosis?

Answer 10

Molecules entering the cell using ATP

Question 11

What is co-transport?

Answer 11

The coupled transport of one molecule down its concentration gradient with another against its concentration gradient (same direction or one each way)

Question 12

How are sodium and glucose co-transported together?

Answer 12

• Electrochemical gradient created by actively transporting Na ion down its concentration gradient is a source of energy.
• This energy can be used to transport other molecules (glucose) against its concentration gradient at the same time

Question 13

Contrast the processes of facilitated diffusion and active transport PPQ (3 marks)

Answer 13

• Facilitated diffusion is passive, active transport requires ATP
• Facilitated diffusion uses both transport proteins
• Active transport only uses carrier proteins
• Facilitated diffusion is down the conc. gradient/Active transport is against conc. gradient