Unit 4 - Cell membranes and transport

Question 1

Active transport

Answer 1

The active movement of substances from a low concentration to a higher concentration (up their concentration gradient) with the use of energy in the form of ATP.

Question 2

Antigen

Answer 2

Marker molecule on the cell surface membrane (usually a protein or glycoprotein) that can be detected by antibodies and triggers an immune response.

Question 3

Carrier protein

Answer 3

Protein involved in active transport that uses energy in the form of ATP to change conformation.

Question 4

Cell signalling

Answer 4

Cells release chemicals which bind to complementary receptors on their target and trigger specific responses.

Question 5

Cell surface receptor

Answer 5

A component on the cell membrane which binds to extracellular signals.

Question 6

Channel proteins

Answer 6

Transmembrane proteins for transporting large or charged substances. Some are involved in facilitated diffusion and do not use ATP; others are involved in active transport and do require energy in the form of ATP.

Question 7

Cholesterol

Answer 7

A steroid hormone which adds stability to the lipid bilayer.

Question 8

Diffusion

Answer 8

The passive spreading out of substances from a high concentration to a lower concentration (down their concentration gradient) without the use of energy.

Question 9

Endocytosis

Answer 9

A method of bulk transport into a cell which relies on invagination of the cell membrane and requires energy in the form of ATP.

Question 10

Exocytosis

Answer 10

A method of bulk transport out of a cell which occurs when vesicles fuse with the cell membrane and release their contents. It requires energy in the form of ATP.

Question 11

Facilitated diffusion

Answer 11

The passive movement of substances from a high concentration to a lower concentration (down their concentration gradient) through transport proteins without the use of energy.

Question 12

Fluid mosaic model

Answer 12

A model that describes membrane structure as a sea of mobile phospholipids studded with various proteins.

Question 13

Glycolipid

Answer 13

A lipid which is bound to a monosaccharide.

Question 14

Glycoprotein

Answer 14

A protein which is bound to a carbohydrate chain.

Question 15

Ligand

Answer 15

An ion or molecule that transmits signals within or between cells. It has a role in cellular signalling and recognition.

Question 16

Osmosis

Answer 16

The passive diffusion of water molecules from a region of high water potential to a region of lower water potential (down a water potential gradient) through a selectively permeable membrane without the use of energy.

Question 17

Passive transport

Answer 17

The movement of substances without the use of energy.

Question 18

Phospholipid

Answer 18

The type of lipid which forms the cell surface membrane bilayer. It is formed by the condensation of one molecule of glycerol, two molecules of fatty acid and a phosphate group. The two fatty acid chains are the non-polar hydrophobic tails whilst the phosphate group is the polar hydrophilic head.

Question 19

Phospholipid bilayer

Answer 19

A polar membrane made of two layers of phospholipid molecules. It is a selectively permeable barrier to the passage of ions and molecules into and out of cells.

Question 20

Surface area to volume ratio

Answer 20

The volume of an object compared with the amount of area where it contacts its environment. Calculated by dividing the surface area of an object by its volume.

Question 21

Visking tubing

Answer 21

A semipermeable material which can be used to model the cell surface membrane.

Question 22

Water potential

Answer 22

A measure of the tendency of water molecules to move from one area to another measured in kilopascals (kPa) and given the symbol.