1. Cell membrane structure

Question 1

purpose of cell membranes

Answer 1

barrier between cell and its environment
control which substances enter and leave
partially permeable - let some things in not others (applies to entire cell membrane and organelle membranes)

Question 2

fluid mosaic model

Answer 2

phospholipid molecules constantly moving ‘fluid’

proteins scattered through bilayer ‘mosaic’

Question 3

what is present in the cell surface membrane

Answer 3

phospholipid bilayer 
cholesterol (lipid)
proteins (channel, carrier, receptor)
glycoproteins (protein with sugar attached)
glycolipids (lipids with sugar attached

Question 4

purpose of phospholipid bilayer

Answer 4

barrier to dissolved substances

Question 5

structure of phospholipid bilayer

Answer 5

hydrophilic head (attracts water)
hydrophobic tail (repels water)
molecules arrange themselves into a bilayer (heads face out towards water either side of membrane)

Question 6

centre of phospholipid bilayer is

Answer 6

hydrophobic (tails)

doesn’t allow water soluble substances through it (barrier)

Question 7

how does cholesterol help maintain the shape of animal cells

Answer 7

bind to hydrophobic tails of phospholipids = pack more closely together = restricts movement making membrane less fluid and more rigid

Question 8

what is permeability of cell membrane affected by

Answer 8

temperature

solvent concentrations

Question 9

how to investigate how temperature affects beetroot permeability

Answer 9

1. scalpel equal sized pieced of beetroot
2. rinse
3. add pieces to different testube’s (5cm3 of water)
4. water bath at different temp for same time
5. remove beetroot
6. use colorimetre to measure how much light absorbed
7. higher absorbance = more pigment = higher permeability.

Question 10

temperature affect on phospholipids

below 0C

Answer 10

packed closely together, rigid.
channel proteins and carrier proteins deform = permeability increased.
ice crystals pierce membrane = highly permeable

Question 11

temp affect on phospholipids

0-45C

Answer 11

phospholipids move, less tightly packed = partically permeable.
temp increase = move more (more energy) = increased permeability

Question 12

temp affect on phospholipids

above 40C

Answer 12

phospholipid melts (breaks down)
= more permeable
water inside cell expands = channel and carrier proteins deform
can’t control what enters/leaves

Question 13

fluid =

Answer 13

cell can change shape/stretch without bursting