Biological Membranes

Question 1

What is active transport

Answer 1

Transport of molecules or ions against a concentration gradient. Requires additional energy, usually in the form of ATP.

Question 2

What is allostery

Answer 2

Where binding of a molecule at one site triggers a change in shape of the protein

Question 3

What’s cholesterol

Answer 3

Steroid that inserts between the fatty acid tails of the phospholipids and regulates the fluidity of a membrane

Question 4

What does crenated mean

Answer 4

When an animal cell is placed in a solution of low water potential, water leaves the cell by osmosis down the water potential gradient, causing the cell to shrivel up.

Question 5

What is Cytolysis

Answer 5

When an animal cell is placed in a solution with a high water potential (e.g. pure water), water enters the cell by osmosis down the water potential gradient, rupturing its cell surface membrane. (Termed haemolysis in red blood cells)

Question 6

What’s endocytosis

Answer 6

The inward transport of large quantities of molecules through the cell surface membrane. This requires an input of energy in the form of ATP

Question 7

What’s exocytosis

Answer 7

The outward transport of large quantities of molecules through the cell surface membrane. This requires an input of energy in the form of ATP

Question 8

What’s facilitated diffusion

Answer 8

Transport of molecules or ions across a membrane down a concentration gradient that require a transport protein (channel or carrier) to cross the membrane

Question 9

What is meant by the term flaccid

Answer 9

Plant cell in an isotonic solution that has lost its turgidity or a plant tissue in which the plant cells are plasmolysed

Question 10

What’s the fluid mosaic model

Answer 10

Current model for the structure of membranes

Question 11

What are hormones

Answer 11

Chemicals released by endocrine glands which acts as chemical signalling molecules

Question 12

What does hydrophilic mean

Answer 12

A molecule able to associate with water as it possesses a charge which interacts with the dipoles on water molecules

Question 13

What does hydrophobic mean

Answer 13

A molecule not able to associate with water as it is uncharged. It repels water

Question 14

What is incipient plasmolysis

Answer 14

The point at which water leaving a plant cell by osmosis shrinks the protoplast so much that it no longer exerts any pressure on the cell wall.

Question 15

What’s osmosis

Answer 15

A specialised form of diffusion where water molecules move from an area of higher water potential to one of lower water potential - down the water potential gradient - through a partially permeable membrane

Question 16

What is meant by partially permeable

Answer 16

Able to let some molecules or ions pass through and not others

Question 17

What is phagocytosis

Answer 17

‘Cell-eating’. Uptake of large quantities of sold materials by endocytosis.

Question 18

What’s a phospholipid

Answer 18

Specialised lipid molecule containing a phosphate group, two fatty acids and glycerol. Forms a bilayer that is the structural basis of membranes.

Question 19

What’s pinocytosis

Answer 19

‘Cell-drinking’. Uptake of large quantities of solutes in solution by endocytosis

Question 20

What’s plasmolysis

Answer 20

When a pant cell is placed in a solution of low water potential, water leaves the cell by osmosis, causing the protoplast to shrink, pulling the plasma membrane away from the cell wall.

Question 21

What’s a protoplast

Answer 21

Cell contents inside plasma membrane

Question 22

What’s meant by selectively permeable

Answer 22

Presence of transport proteins determines which molecules can be transported across

Question 23

What’s a tonoplast

Answer 23

The membrane surrounding the vacuole in a plant cell.

Question 24

What’s meant by turgid

Answer 24

When a plant cell is placed in a solution of low water potential, water enters by osmosis and the protoplast pushes against the cell wall.

Question 25

What is water potential

Answer 25

Measure of the tendency of water molecules to move from one region to another. Affected by solute concentration and any external applied pressure.
Always a negative value measured in kilopascals (kPa) and given the symbol
Ч.