Cell Membranes and Transport

Question 1

What is meant by the term ‘fluid mosaic model’?

Answer 1

fluid describes the movement of phospholipids and proteins by diffusion in the bilayer, mosaic refers to the appearance of scattered proteins

Question 2

What is the structure of a membrane?

Answer 2

a phospholipid bilayer consisting of hydrophobic tails facing towards each other, hydrophilic heads facing outwards, cholesterol molecules, proteins

Question 3

What is a phospholipid?

Answer 3

a molecule consisting of two hydrophobic fatty acid tails and a hydrophilic phosphate head

Question 4

What is cholesterol?

Answer 4

a molecule made of a hydrophobic and hydrophilic region

Question 5

What are membrane proteins?

Answer 5

intrinsic or extrinsic proteins in the membrane, intrinsic found on the inside, outside, or whole membrane (transmembrane)

Question 6

What are glycoproteins?

Answer 6

carbohydrate chains attached to membrane proteins, the chains form a glycocalyx and project into the watery fluid outside the membrane, forming hydrogen bonds

Question 7

What are channel proteins?

Answer 7

a gated, water filled pore that forms a hydrophilic channel for ions to pass through

Question 8

What are carrier proteins?

Answer 8

can flip between two shapes, opening at different sides of a membrane

Question 9

What are cell surface receptors?

Answer 9

glycoproteins/lipids which bind to substances at cell surface, three types are signalling receptors, endocytosis receptors, cell adhesion receptors

Question 10

What are cell surface antigens?

Answer 10

glycoproteins/lipids acting as markers, allowing cell-to-cell recognition

Question 11

What is cell signalling?

Answer 11

the process of sending a message from one place to another over a signalling pathway

Question 12

What are the different cell signalling pathways?

Answer 12

• hydrophobic signalling molecule diffuses directly across membrane and binds to intracellular receptor somewhere else in the cell
• signalling cascade
• open ion channel
• act as membrane bound enzyme
• cell-cell contact

Question 13

What is diffusion?

Answer 13

process of substances moving across membrane down a gradient from a place of high to low concentration

Question 14

What is active transport?

Answer 14

molecules use ATP to move across membrane against concentration gradient through carrier proteins

Question 15

What is osmosis?

Answer 15

diffusion of water across a membrane from a dilute to concentrated solution

Question 16

What is endocytosis?

Answer 16

the engulfing of material into cell by pino/phagocytosis, making phagocytic vacuoles

Question 17

What is exocytosis?

Answer 17

secretion of material out of cell by vesicles

Question 18

What is the surface area: volume ratio?

Answer 18

the larger the cell, the smaller its surface are in relation to its volume

Question 19

What is water potential?

Answer 19

the tendency of water to move out of a solution, from a solution of high water potential to low

Question 20

What is solute potential?

Answer 20

the extent to which solute molecules decrease the water potential of a solution

Question 21

What is pressure potential?

Answer 21

the contribution of pressure on the water potential of a solution

Question 22

What happens to animal cells when they are placed in a solution of lower water potential?

Answer 22

cells shrink

Question 23

What happens to plant cells when they are placed in a solution of higher water potential?

Answer 23

cell becomes turgid as cell wall regulates pressure

Question 24

What is the signalling cascade?

Answer 24

polar signalling molecule binds to specific receptor, signal transduction, G protein, many second messengers (amplification), enzymes activated, final enzyme produced

Question 25

What factors affect rate of diffusion?

Answer 25

steepness of gradient, temperature, surface area, nature of ions or molecules

Question 26

How do water molecules move across the phospholipid bilayer?

Answer 26

by diffusing directly across the membrane due to their small size

Question 27

What is facilitated diffusion?

Answer 27

the diffusion of ions and polar molecules across the cell membrane by carrier or channel proteins

Question 28

What happens to plant cells when they are placed in a solution of lower water potential?

Answer 28

plasmolysis

Question 29

What happens to animal cells when they are placed in a solution of higher water potential?

Answer 29

cells burst