transport across a cell membrane 3.2.3 (module 2)

Question 1

what is the fluid mosaic model?

Answer 1

• the membrane is fluid because the phospholipid heads which move around their layer
• the membrane is mosaic because there are proteins embedded in the membrane

Question 2

why is the fluid mosaic model useful?

Answer 2

• provide an attachment site for metabolic enzymes like ATP synthase
• allow electrical impulse to travel along them

Question 3

describe the structure of phospholipid bilayer

Answer 3

• heads are hydrophilic so face outside of membrane
• tails are hydrophobic fatty acid chains so face centre of membrane

Question 4

what can move pass through the phospholipid bilayer?

Answer 4

• lipid soluble molecules can pass through phospholipid part
• small non polar molecules can enter and leave
• prevents water soluble and charged ions to enter and leave

Question 5

what proteins are embedded into the cell membrane and what do they do?

Answer 5

• channel protein (allow transport of charged molecules)
• carrier proteins (allow facilitated diffusion and active transport)
• aquaporins (special channel protein for diffusion of water)

Question 6

what is the purpose of cholesterol?

Answer 6

• found in all cells besides bacterial cells
• help maintain stability and rigidity of membrane
• because it fits between phospholipids and binds to hydrophobic tail

Question 7

what is the structure and purpose of glycolipids?

Answer 7

• made up of carbohydrates chain binded with a phospholipid
• acts as a cell surface receptor (cell signalling and cell to cell recognition to form tissues)

Question 8

what is the structure and purpose of glycoproteins?

Answer 8

• made up of carbohydrate chain binded with extrinsic protein
• acts as a cell surface receptor (cell signalling and cell to cell recognition to form tissues)

Question 9

what is simple diffusion?

Answer 9

the passive movement of small non polar and lipid soluble molecules from an area of high concentration to an area of low concentration (O2 CO2 etc)

Question 10

what factors effect the rate of diffusion?

Answer 10

• temperature: an increase of temperature increase KE so higher rate of diffusion
• concentration gradient: greater difference faster rate
• thickness of exchange surface
• surface area: larger area for diffusion so quicker rate

Question 11

what is osmosis?

Answer 11

the diffusion of water from a high water potential to a low water potential from a partially permeable membrane

Question 12

what affects water potential?

Answer 12

• more solute added means a lower water potential
• standard water potential is 25 C and 100Kpa

Question 13

what is facilitated diffusion?

Answer 13

the passive movement of large lipid insoluble, water soluble and charged ions down the concentration gradient with the help of carrier/channel proteins

Question 14

how does a carrier protein work?

Answer 14

• molecules attach to a carrier protein
• protein changes shape so it fits around molecule
• molecule is then passively transported down the concentration gradient to other side of protein and released

Question 15

how does a channel protein work?

Answer 15

• channel with water filled pores so allows water soluble ions and molecules to be transported
• some are gated so can open/close
• transport molecules down concentration gradient passively

Question 16

what is active transport?

Answer 16

movement of molecules across a membrane against the concentration gradient with the use of ATP and a carrier protein