Cell Membranes

Question 1

cell membrane

Answer 1

controls what goes in and out of the cell

Question 2

phospholipid

Answer 2

phosphate head- negatively charged, polar, hydrophilic
glycerol molecule
2 fatty acid chains - no charge, non polar, hydrophobic

Question 3

phospholipid bilayer

Answer 3

arranged with hydrophilic head on the outside and hydrophobic tails on the inside

Question 4

water

Answer 4

polar molecule
partially positive- hydrogen
partially negative- oxygen

Question 5

polar molecules

Answer 5

polar (charged) molecules like PL are attracted to water
they are soluble in water as they form h bonds with water
hydrophobic group together in water as they are non polar

Question 6

non polar

Answer 6

hydrophobic - not charged
are not soluble in water because they are not attracted to water molecules + clump together
are soluble in non polar liquid eg oil will mix with more oil

Question 7

PL bilayer functions

Answer 7

allows lipid soluble (non polar) molecules in and out of the cell
prevents water soluble (polar) molecules in and out of cell
makes membrane flexible

Question 8

proteins

Answer 8

interspersed throughout membrane
span the membrane from one side to the other- transmembrane
on the inside (intrinsic) or the outside (extrinsic)

Question 9

transmembrane protein

Answer 9

facilitated diffusion uses carrier and channel proteins
protein channels- have a hole/ channel all the way through to allow polar molecules (water soluble)

carrier proteins- span membrane and help transport ions or larger substances eg glucose + amino acids by changing shape

Question 10

carrier proteins

Answer 10

some are involved in diffusion and do not require ATP to change shape

some are involved in active transport and require ATP to move molecules against conc gradient from low to high

Question 11

glycoproteins and glycolipids

Answer 11

proteins/ lipids with branches of sugars attached
carbohydrate (sugar) portion extends to the outside of the cell

both- act as recognition sites
help cells attach/adhere together to form tissue
GP- acts as receptors to receive chemicals eg NT and hormones

Question 12

cholesterol

Answer 12

found within PLB of eukaryotic cells, in cell surface membrane
provides stability to cell membrane as it prevents too much lateral movement of other molecules in membrane

Question 13

permeability of PL

Answer 13

only small non polar molecules can diffuse through easily
they are soluble in non polar fatty acid tails

charged ions and polar molecules do not diffuse through easily as they are not soluble in fatty acid tails
polar molecules are only soluble in polar substances eg water
-transported using protein channels and carrier molecules

Question 14

fluid mosaic model

Answer 14

fluid- individual phospholipid molecules can move so it is flexible
mosaic- proteins and phospholipids interspersed in the membrane vary in shape and size

Question 15

active transport

Answer 15

requires ATP from aerobic respiration- mitochondria
uses carrier proteins- molecule attaches, protein changes shape, moves molecule across membrane and releases it on other side

Question 16

co transport

Answer 16

type of carrier protein that bind two molecules at a time and the conc gradient of one molecule is used to move the other molecule against its conc gradient
eg in ileum cell

Question 17

water potential

Answer 17

more water= higher wp
pure water = high wp of 0
more solute= more negative wp
water moves down wp gradient by osmosis

Question 18

hypertonic

Answer 18

solution has high conc of solute and less water
lower wp
cells in hypertonic solution lose water and become plasmolyse

Question 19

hypotonic

Answer 19

solution has low conc of solute and more water
high wp
cells in hypotonic solution gain water and become turgid

Question 20

isotonic

Answer 20

solution same concentration of solute as that in a cell

Question 21

plant cells

Answer 21

lose water = flaccid
lose water and cell membrane pulls away from cell wall= plasmolyse
gain water = turgid

Question 22

animal cells

Answer 22

gain too much water + burst= lyse (swell)

lose too much water= shrink

Question 23

water movement

Answer 23

water cannot usually move through membrane as it is a dipole and is polar
can sometimes slip through small gaps
aquaporins- channel proteins for water

Question 24

root cells

Answer 24

adapted for absorption of water and mineral ions
specialised shape that increases surface area so rate of water uptake by osmosis is greater
thin walls so shorter diffusion pathway
permenent vacuole containing cell sap which ensures high wp gradient is maintained

Question 25

epithelial cells

Answer 25

microvilli- (folded sections of membrane) to increase surface area so rate of diffusion is greater
have lots of mitochondria to provide ATP for active transport of substances

Question 26

cell membranes adapted for rapid uptake

Answer 26

membrane folded increases surface area for faster diffusion
large number of protein channels/carriers for facilitated diffusion
large number of carrier proteins for active transport
large number of carrier/channel proteins for active transport