54 WJEC Biology AS Level - Marianne Izen - 2nd Edition (1.3 Cell Membranes And Transport)

Question 1

What is the model of cell membranes called?

Answer 1

The fluid-mosaic model of cell membranes

Question 2

What is the cell membrane made up of?

Answer 2

The cell membrane is made up almost entirely of proteins and phospholipids.

Question 3

What forms the basis of membrane structure?

Answer 3

Phospholipids are important components of cell-surface membranes and form the basis of membrane structure.

Question 4

How are phospholipids arranged in the cell membrane?

Answer 4

Phospholipids can form bilayers, with one sheet of phospholipid molecules opposite another.

Question 5

How is the hydrophilic heads of the inner layer of phospholipids arranged in the cell membrane?

Answer 5

The inner layer of phospholipids has its hydrophilic heads pointing in, towards the cell, and interacts with the water in the cytoplasm.

Question 6

How is the hydrophilic heads of the outer layer of phospholipids arranged in the cell membrane?

Answer 6

The outer layer of phospholipids has its hydrophilic heads pointing outwards, interacting with the water surrounding the cell.

Question 7

How is the hydrophilic tails of the phospholipid layers arranged in the cell membrane?

Answer 7

The hydrophobic tails of the two phospholipid layers point towards each other, to the centre of the membrane.

Question 8

What molecules does the phospholipid component of the cell membrane allow to pass through?

Answer 8

The phospholipid component of a membrane allows lipid-soluble molecules across, but not water-soluble molecules.

Question 9

What is the location of proteins in the cell membrane?

Answer 9

Proteins are scattered throughout the phospholipid bilayer of the membrane.

Question 10

How many ways can proteins be embedded in the cell membrane?

Answer 10

There are two ways in which they are embedded.

Question 11

What are the types of proteins embedded in the cell membrane?

Answer 11

1. Extrinsic proteins
2. Intrinsic proteins

Question 12

Where are extrinsic proteins found in the cell membrane?

Answer 12

Extrinsic proteins are on either surface of the bilayer.

Question 13

What are the functions of extrinsic proteins?

Answer 13

They provide structural support.
They form recognition sites, by identifying cells
They form receptor sites for hormone attachment.

Question 14

Where are intrinsic proteins found in the cell membrane?

Answer 14

Intrinsic proteins extend across both layers of the phospholipid bilayer.

Question 15

What are the functions of intrinsic proteins?

Answer 15

They include transport proteins.
These transport proteins use active or passive transport to move molecules and ions across the cell membrane.

Question 16

What is the fluid-mosaic model?

Answer 16

The way in which the phospholipids and proteins are arranged in the membrane is called the fluid-mosaic model.

Question 17

Who proposed the fluid-mosaic mode?

Answer 17

It was proposed by Singer and Nicolson in 1972.

Question 18

What are the two parts of a phospholipid molecule?

Answer 18

1. Phosphate head
2. Fatty acid end made up of two fatty acid tails

Question 19

Tell me about the phosphate head of a phospholipid molecule.

Answer 19

The phosphate head of a phospholipid molecule is polar (hydrophilic).

It interacts with other polar molecules, such as water.

Question 20

Tell me about the fatty acid end of a phospholipid molecule.

Answer 20

The fatty acid end of a phospholipid comprises two fatty acid tails.

It is non-polar (hydrophobic).

It does not interact with water.

Question 21

What are biological membranes made up of?

Answer 21

Biological membranes are phospholipid bilayers which contain protein molecules.

Question 22

Do all biological membranes have the same properties? Why?

Answer 22

No.

Different fatty acids and proteins give the membranes different properties.

Question 23

Fluid-mosaic model (Key-Term)

Answer 23

Model of the structure of biological membranes, in which proteins are studded through a phospholipid bilayer, as in a mosaic.

The movement of molecules within a layer of the bilayer is its fluidity.

Question 24

Can protein hormones enter the cell? Why

Answer 24

No.

Protein hormones, such as insulin and adrenalin, are insoluble in lipids.

Hence they cannot diffuse through the phospholipid membrane into the cell.

Question 25

How do protein hormones influence cell behaviour?

Answer 25

They bond to extrinsic protein receptor molecules, which influences the behaviour of cells.

Question 26

What does this picture show?
Label its parts?

Answer 26

3D arrangement of molecules in a biological membrane