transport across cell membranes

Question 1

The structure of the cell membrane

Answer 1

bilayer of phospholipids with a phosphate head pointing out where there is water
and tails that face inwards, away from anything polar

Question 2

the functions of the phospholipid bilayer

Answer 2

1) act as a barrier form internal contents of cell + external environment / organelle from cytoplasm

2) separates parts of the organelle

3) location of chemical reactions

4) cell signalling

Question 3

what type of molecules cannot enter the membrane freely - why

Answer 3

cell surface has a hydrophobic centre that prevents hydrophilic molecules from entering

water is exception because it is small, enters through very slow rate

Question 4

what types of molecules does the cell surface contain

Answer 4

• proteins
• cholesterol - increasing strength of cell by rigidity,
  restricts movement of phospholipid tails so controls fluidity in hot + cold temps
  reduces movement of water soluble chemicals leaving the cell surface

Question 5

why is it called the fluid mosaic model

Answer 5

fluid - phospholipids move like a fluid - they are flexible

mosaic - includes proteins of different shapes, sizes scattered over the membrane like tiles

Question 6

what are intrinsic proteins + examples

Answer 6

proteins fully embedded in bilayer of phospholipid - helping with transport

carrier proteins - change shape in order to transfer molecules

protein channel - act as walls and inside they are hydrophilic

Question 7

what are extrinsic proteins

Answer 7

protein that span on only one phospholipid layer - structural role / enzyme/ receptor

Question 8

cholesterol and the phospholipid bilayer

Answer 8

• cholesterol - increasing strength of cell by rigidity,
  restricts movement of phospholipid tails so controls fluidity in hot + cold temps
  reduces movement of water soluble chemicals leaving the cell surface

Question 9

glycolipids and the phospholipid bilayer

Answer 9

carbohydrate + covalent bond + lipid

extends from the phospholipid bilayer into the water environment, where it acts as a RECEPTOR

• maintains stability
• helps cells to attach to one anther

Question 10

glycoproteins + the phospholipid bilayer

Answer 10

attached to extrinsic proteins

• receptor
• allows cells to attach together
• present as antigens

Question 11

process of diffusion

Answer 11

1) we have a concentration gradient
2) movement happens across concentration gradient
3) continues until equilibrium is reached

Question 12

definition of diffusion

Answer 12

net movement of particles from a region of high concentration to low concentration gradient

Question 13

factors affecting diffusion

Answer 13

1) concentration (greater concentration = grater ROD
2) particle charge / size (charged ions do not enter + smaller molecules enter easily
3) temperature (movement is from kinetic energy, mammals have constant body temp
4) surface area (greater surface area = more area for site of diffusion
5) distance (thin membranes) more energy to move
6 the Prescence of channel/ carrier proteins

Question 14

why do we need facilitated diffusion

Answer 14

for particles that are too big or polar that are repelled by the hydrophobic tails

so those particles can get in WITHOUT INTERACTING WITH THE HYDRTOPHOBIC CENTRE

Question 15

what type of proteins are involved in facilitated diffusion

Answer 15

intrinsic proteins

Question 16

the role of carrier proteins in facilitated diffusion

Answer 16

carrier proteins have a binding site for specific chemicals.
when chemical binds, the tertiary structure changes (change carrier chemical across membrane)

Question 17

the role of protein channels in facilitated diffusion

Answer 17

this acts as a barrier between the hydrophobic tails
they have hydrophilic central pore, lined with hydrophilic amino acids

Question 18

the process of active transport

Answer 18

move chemicals from one side against concentration gradient (requires metabolic energy - ATP)

1) molecule attaches to receptor site of carrier protein (LOW concentration side)

2) ATP binds to carrier proteins

3) ATP undergoes hydrolysis to become ADP and pi. phosphate attaches to carrier protein causes shape change - transports the molecule needed

4) phosphate leaves causing it to change shape to normal
ADP + pi will react again to make ATP

Question 19

why is there many mitochondria in cells of active transport

Answer 19

mitochondria need to be able to form ATP which is needed in active transport because its active, so energy is quickly transported

Question 20

carrier proteins - being unique

Answer 20

they have a unique active site for each chemical. so its only able to transport one type of molecule at a time

Question 21

why do we need cotransport in the ileum

Answer 21

diffusion relies on a steep concentration gradient in order for particles to travel

after digestion, glucose is high but then decreases, not all molecules can be transported so we need cotransport

Question 22

glucose in ileum to bloodstream

Answer 22

glucose ————> lumen of ileum

                  -----------> epithelial cell
                   
                 -------------> bloodstream

Question 23

co - transport

Answer 23

after digestion there’s high concentration of glucose, diffusion is rapid

gradually glucose is carried away concentration reaches equilibrium

there is a sodium potassium pump that remove sodium actively and create low concentration of sodium within epithelium

in lumen, there is a high concentration of sodium. Sodium is transported down concentration gradient by sodium glucose cotransporter that brings glucoses along with it. glucose transported AGAINST gradient
energy comes indirectly from concentration gradient of sodium

Question 24

mitochondria in epithelial cells

Answer 24

many mitochondria for ATP synthesis for sodium potassium pump which is active transport

Question 25

how is there a steep concentration gradient between bloodstream and epithelial cell

Answer 25

blood stream rapidly takes glucose away, creates a steep concentration gradient for more glucose

Question 26

how are epithelial cells adapted well for co transport of glucose

Answer 26

cell lining of epithelial cell is covered in microvilli
increases surface area for more carrier / channel proteins available to carry ions

Question 27

osmosis definition

Answer 27

the movement of water from a region of high water potential to a low water potential through a partially permeable membrane

Question 28

hydrostatic pressure

Answer 28

the pressure resulting from an increase in water molecules from osmosis
pressure is exerted on cell wall / membrane

Question 29

haemolysis due to

Answer 29

bursting of a red blood cell due to weak membrane

Question 30

the result of a plant cell in a higher water potential

Answer 30

cell vacuole has many solutes dissolved in it, so water comes in through partially permeable cell wall
h2o enters, - hydrostatic pressure created. protoplast pushes out on cell wall
cellulose strong to withstand hydrostatic pressure

firm = turgor pressure

prevents wilting, plant is upright