Cell Membrane

Question 1

What is the phospholipid bilayer made up off?

Answer 1

Phospholipids that have hydrophilic heads and hydrophobic tails, cholesterol, protein channels and glycoproteins. (Refer to fluid mosaic model)

Question 2

Describe diffusion across a membrane

Answer 2

Diffusion if a process of passive transport (no energy) where molecules are moved along a concentration gradient from a region of higher concentration to a lower concentration across a semipermeable membrane.

Question 3

Describe osmosis

Answer 3

Osmosis is a form of passive transport where water molecules move across a semipermeable membrane from a region of lower solution concentration to a higher solute concentration (hypotonic to hypertonic environment).

Question 4

Describe cytosis and the two types of it

Answer 4

Cytosis is a form of active transport where the cell uses energy to engulf the molecules forming vesicles. It can be endocytosis or exocytosis. Endocytosis- bringing molecules in that are usually large and polar. Exocytosis- moving molecules out.

Question 5

Describe facilitated diffusion

Answer 5

Moves molecules from a high concentration to a low concentration and uses membrane proteins.

Question 6

describe phagocytosis

Answer 6

A form of endocytosis in which the cell uses it’s plasma membrane to engulf the molecules to bring them into the cell.

Question 7

Explain how concentration, physical and chemical factors of molecules affect their movement across the membrane.

Answer 7

Molecules will move from areas of higher concentration to areas of lower concentration.
The size of the molecule affect whether or not it can pass through the membrane.
Polar molecules will need to travel through carrier proteins to enter the cell whereas non-polar molecules if small enough can travel through the phospholipid bilayer.

Question 8

Explain how the size of a cell is limited by the surface area to volume ratio and the rate of diffusion

Answer 8

Smaller cells have maximised efficiency in exchanging matter within their environment as they have a more proportionate surface area for the exchanges than a larger cell would. In a larger cell the surface area to volume ratio would be smaller decreasing the needed efficiency for exchanges.