3.2.3 Cell Membranes

Question 1

Structure of cell membrane

Answer 1

Fluid mosaic model

• phospholipid bilayer
• proteins (channel, carrier,receptor)
• glycoproteins
• glycolipids
• cholesterol

Question 2

Characteristic of cell membrane

Answer 2

partially permeable

Question 3

function on cell membrane

Answer 3

allows selected molecules in and out

Question 4

Role of phospholipid bilayer

Answer 4

• hydrophobic tail and hydrophilic head
• head out (attract to H2O in cytoplasm/surrounding) , tail in (repel)
• centre is hydrophobic, doesn’t allow water soluble sunstances in (e.g. ions)

Question 5

role of cholesterol

Answer 5

• controlling membrane fluidity
• regulating cell temperature
• maintain shape of animal cells

Question 6

diffusions rate of small,non polar molecules (O2, CO2)

Answer 6

rapid

Question 7

diffusion rate of small, polar molecules (water, urea)

Answer 7

steady

Question 8

function of channel protein

Answer 8

water filled tubes allow water soluble ions to diffuse across the membrane (facilitated diffusion)

Question 9

function of carrier protein

Answer 9

binds to ions or molecules which then changes shape to allow the molecules to move across membrane (active transport & facilitated diffusion)

Question 10

glycoprotein function

Answer 10

• recognition sites
• binding cells together
• cell signalling

Question 11

glycolipid function

Answer 11

• cell signalling

- cell recognition

Question 12

receptor proteins

Answer 12

on cell surface membrane which allow cell to detect chemicals released from other cells

Question 13

how does temperature affect permeability

Answer 13

affects how much the phospholipids in the bilayer can move

Question 14

temps below 0

Answer 14

• v little energy
• phospholipids barely move, tightly packed together
• channel proteins & carrier proteins denature (increase permeability)
• ice crystals form & pierce membrane (highly permeable)

Question 15

temps between 0 & 45

Answer 15

• phospholipids can move a little - not tightly packed as more kinetic energy
• membrane is partially permeable

Question 16

temps above 45

Answer 16

• bilayer begins to melt (more permeable)
• water inside cell expands putting pressure on membrane
• channel proteins & carrier proteins denature (cannot control what enters/leaves cell) so membrane more permeable

Question 17

simple diffusion

Answer 17

The movement of particles (molecules or ions) from a region of high concentration to a region of low concentration

Question 18

facilitated diffusion

Answer 18

involves presence of protein carrier molecules to allow passive movement of substances (large, polar, charged molecules) across a plasma membrane

Question 19

factors that affect rate of diffusion

Answer 19

• concentration gradient
• thickness of exchange surface
• surface area of exchange surfaces

Question 20

factors affecting facilitated diffusion

Answer 20

• concentration gradient

- number of channel/carrier proteins

Question 21

osmosis

Answer 21

Movement of water from an area of high water potential to an area of low water potential

Question 22

isotonic

Answer 22

a solution which has the same water potential as the cell within it

Question 23

hypotonic

Answer 23

solutions with a higher water potential than the cell, cell swells

Question 24

hypertonic

Answer 24

solutions with lower water potential than cell, cell shrinks

Question 25

factors affecting osmosis

Answer 25

• water potential gradient
• thickness of exchange surface
• surface area of exchange surface

Question 26

active transport

Answer 26

movement of a substance from low concentration to a region where it is in a high concentration. Requires energy (ATP)

Question 27

process of active transport

Answer 27

1) molecule/ion binds to receptor site of carrier protein in plasma membrane
2) ATP binds to the protein on the other side, causing it to split by by hydrolysis into ADP and Pi, releasing energy
3) protein changes shape and opens on the opposite side of the membrane
4) the molecule/ion is released on the other side of the membrane
5) ATP is reformed and protein reverts to its normal shape

Question 28

factors affecting rate of active transport

Answer 28

• speed of individual carrier proteins
• number of carrier proteins
• rate of respiration/availability of ATP

Question 29

co-transport of glucose in the ileum

Answer 29

• sodium ions actively transported out of epithelial cells into ileum
• higher concentration of sodium in the ileum
• sodium diffuses back into epithelial cell through sodium-glucose co transporter, so the sodium also moves glucose into the epithelial cell
• a high concentration of glucose inside the epithelial cell so diffuses into blood by facilitated diffusion

Question 30

why co-transport works

Answer 30

the concentration gradient of one of the molecules is used to move the other molecule against its own concentration gradient

Question 31

Types of bulk transport

Answer 31

Endocytosis and exocytosis

Question 32

Endocytosis

Answer 32

moving into a cell
(pinocytosis-liquids)
(phagocytosis- solids)

Question 33

Exocytosis

Answer 33

moving out of cell
( secretion-useful)
(excretion- useless)