Cell Transport Mechanisms

Question 1

What is the function of cell-surface membranes

Answer 1

The control what exits and enters the cell, the are semi permeable and have specific structures to enable the movement of substances

Question 2

Why is it described as the fluid mosaic model?

Answer 2

•The membranes consist of proteins, glycoproteins, phospholipids and carbohydrates.
•The phospholipid molecules form a double layer (bilayer) is constantly moving around forming a fluid structure.
•The proteins are unevenly distributed throughout the membrane forming a mosaic.
•The structure is based upon experimental evidence so is classed as a model

Question 3

What is an intrinsic protein

Answer 3

A protein that is embedded completely through the bilayer

Question 4

What is an extrinsic protein

Answer 4

A protein that is loosely bound on the outside of the lipid bilayer

Question 5

Phospholipids

Answer 5

The hydrophobic tails are attracted towards each other and the hydrophilic heads are orientated either inwards toward the cytoplasm or outwards towards the watery cellular fluid. This forms a phospholipid bilayer

Question 6

What do phospholipid bilayer a allow to pass and not pass

Answer 6

They allow lipid soluble (non polar) molecules to pass through by simple diffusion and prevent the passage of small, polar molecules (like ions)

Question 7

Cholesterol

Answer 7

Decreases the permeability and increases the stability (more rigid) of cell membrane. The more cholesterol the less fluidity of the cell membrane.

Question 8

Channel proteins

Answer 8

Are like pores within the membrane and only allow specific charged ions or small molecules to pass across the membrane by facilitated diffusion. They are intrinsic. They also have specific tertiary structures and only transport molecules with complementary shapes

Question 9

Carrier proteins

Answer 9

Aid the transport of polar molecules and large molecules by facilitated diffusion and active transport

Question 10

Diffusion

Answer 10

Net movement of molecules form an area of higher concentration to an area of lower concentration across a partially permeable membrane

Question 11

What type of process is diffusion

Answer 11

Diffusion is a passive process as it doesn’t require ATP. Diffusion will stop when the molecules have reached equilibrium. Only occurs with non polar, lipid soluble, small molecules such as O2, CO2 and oestrogen