Transport Across Cell Membrane

Question 1

Why is the phospholipid bilayer described as the ‘fluid mosaic’ model?

Answer 1

Fluid – because the phospholipids are constantly moving. Makes the membrane flexible.

Mosaic – because the proteins that are embedded in the bilayer vary in shape, size and pattern.

Question 2

What is a glycoprotein?

Answer 2

A protein with a carbohydrate attached.

Question 3

State the definition of diffusion. Is it an active or passive process?

Answer 3

The net/passive movement of particles from an area of higher concentration to an area of lower concentration. It’s a passive process.

Question 4

Define active transport.

Answer 4

The movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher concentration using ATP and carrier proteins.

Question 5

Describe how co-transport is used to transport substances across a cell-membrane.

Answer 5

· Sodium ions are actively transported out of the ileum epithelial cells into the blood

· By the sodium-potassium pump

· This creates a concentration gradient of sodium ions between the lumen of the ileum and the interior of the epithelial cells.

· Sodium ions diffuse down this concentration gradient into the epithelial cells

· Via sodium-glucose co-transporter proteins.

· The co-transporter proteins transport glucose into the cells along with the sodium ions.