Topic 2 - Biological membranes

Question 1

What is the role of cell membranes in cells

Answer 1

Cell membranes act as barriers and can control what passes into and out of cells and organelles

Question 2

What is the cell membrane composed of (5 marks)

Answer 2

​The cell membrane is composed of phospholipids, proteins, glycoproteins, glycolipids and cholesterol.

Question 3

What is the role of glycolipids and glycoproteins in the cell membrane

Answer 3

Glycolipids and glycoproteins allow cell adherence, stability and act as recognition sites

Question 4

what is the role of cholesterol in the cell membrane

Answer 4

Cholesterol has a hydrophilic end and a hydrophobic end & regulates membrane fluidity by intercalating between the phospholipids.

Question 5

What happens to the phospholipid bilayer in high temperatures

Answer 5

At high temperatures the phospholipid bilayer increases its fluidity and permeability, increasing the risk of the proteins becoming denatured.

Question 6

What happens to the phospholipid bilayer at low temperatures

Answer 6

At low temperatures, the phospholipids are compressed, making the membrane stiff

Question 7

What effect do organic solvents have on the phospholipid bilayer / cell membrane

Answer 7

Organic solvents disrupt the bilayer and dissolve the membrane

Question 8

What is passive transport

Answer 8

Passive transport involves exchange of substances without requiring metabolic energy from the cell

Question 9

What is diffusion

Answer 9

Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration (down their concentration gradient).

Question 10

What is facilitated diffusion

Answer 10

Facilitated diffusion is the net movement of particles down their concentration gradient across a partially permeable cell membrane via carrier or channel proteins.

Question 11

What is water potential

Answer 11

Water potential is a measure of the tendency of water molecules to move from one area to another area and describes the pressure created by these water molecules; the more dilute a solution, the higher (less negative) the water potential (Ѱ).

Question 12

What is osmosis

Answer 12

Osmosis is the net movement of water from an area of higher water potential to an area of lower water potential across a partially permeable membrane.

Question 13

How can the rate of diffusion be increased (4 marks)

Answer 13

• increasing the number of channel and carrier proteins
• increasing the surface area of the cell membrane
• reducing the diffusion distance
• creating a steeper concentration gradient

Question 14

What is active transport

Answer 14

Active transport is the movement of particles from an area of low concentration to an area of high concentration (against their concentration gradient) across a cell membrane, using ATP and carrier proteins.​

Question 15

What does bulk transport do

Answer 15

Bulk transport transports large substances across the cell membrane

Question 16

What is endocytosis

Answer 16

Endocytosis is the bulk transport of large molecules into a cell. The membrane invaginates and encloses the material being taken up into a vesicle, which pinches off.

Question 17

What is exocytosis

Answer 17

Exocytosis is the bulk transport of large molecules out of a cell. A vesicle fuses with the cell membrane, releasing its material