Biological membranes

Question 1

Describe the role of cell membranes within cells(5)

Answer 1

1. compartmentalises organelles e.g vesicles,lysososmes
2. isolates content of organelles e.g lysosomes contain hydrolytic enzymes,would be dangerous if they were released when they’re not needed as cell will be broken down.
3. Site of attachment of enzymes,ribosomes & other molecules
4. Provide selective permeability. Phospholipid bilayer only let in large,polar,charged molecules and channel and carrier protein are specific to certain molecules ∴ controlling what enters + leaves.
5. Creates conc. gradients + specific environments e.g membrane maintains acidic environment inside lysosomes.

Question 2

Outline the role of membrane bound receptors

Answer 2

• Have a role in cell signalling/communication
• Glycoproteins or glycolipids
• Hormones can bind to receptors which triggers a cascade of reactions in cell
• Drugs- bind to receptors and either TRIGGER a response in cell or BLOCK receptor-prevent it from working.

Question 3

Outline the role of cell membranes as barriers

Answer 3

cell membranes only let certain substances in and unwanted substances out.It is able to do this due to it’s selective permeability. Selectively permeable due to Phospholipid bilayer + carrier & channel proteins

Question 4

Describe how channel + carrier proteins work (draw out) and how they make cell membrane selectively permeable

Answer 4

Channel : check google images

form aqueous channels/pores across cell membranes for specific small ions and polar molecules.

Carrier:

• Large molecules binds to carrier protein
• carrier protein changes shape
• molecules released on the other side.

Question 5

Describe the role of cell membranes as sites of cell communication+signalling

Answer 5

involved with releases signal molecules by exocytosis as well as receiving these signal molecules by receptors on cell membrane.

cell membranes have glycoproteins/lipids which act as receptors with specific complementary shapes.

Only a messenger molecule with complementary shapes can bind to.

Attachment of signal molecules triggers a change in cell.

Question 6

List components of cell surface membranes.

Answer 6

P phospholipds
E xtrinsic protein
G lycoprotein
 I ntrinsic protein
G lycolipids
C holestrol
C arrier protein
C hannel proteins

Question 7

Roles of components of fluid mosaic model

Answer 7

Phospholipids
forms a barrier because phospholipid head hydrophilic and tails are hydrophobic. Ions + Polar molecules can’t come through(water soluble).Allows fat-soluble substances e.g vitamins.

Cholesterol
Gives membrane stability.Fit between phospholipids and binds to tails making them fit closely together and rigid

Proteins
controls what enters/leaves channel + carrier proteins.Acts as receptors, cell signalling.

Glycolipids/proteins
Stabilises membrane by forming HB bonds with surrounding water molecules

Question 8

Describe role of cell membranes as sites of chemical reactions

Answer 8

Proteins in membranes forming organelles, or present within organelles have to be in particular positions for chemical reactions to take place.

Question 9

State factors affecting membrane permeability

Draw graph for each factor

Answer 9

• solvents
• Temp

cgp pg.127

Question 10

Explain how Temp affect permeability

Answer 10

Above 45C- membrane breaks down,becomes permeable.h2o inside cell expands,puttibg pressure on membrane.Channel + carrier proteins denature cant control what enters and leaves cell

0-45C- phospholipids can move around and aren’t packed tightly.Membrane partially permeable.↑ temp,↑ phospholipid movement-↑ permeability

0C- phospholipid little kinetic energy,packed closely,rigid.Channel+ carrier protein denature,increasing permeability .Ice crystals form piercing membrane,when thawed even higher permeability

Question 11

Explain how solvents affect permeability

Answer 11

Some solvents e.g ethanol increases permeability

Organic solvents will dissolve membrane

Question 12

Write a method to investigate the effects of temp on beetroot membrane permeability.

Answer 12

1. use scalpel to cut 5 equal-sized pieces of beetroot on a cutting board.Rinse/wipe each piece to remove any pigment released when cutting.
2. put 5 pieces into 5 different test tubes, each containing 5cm3 of h2o.Use pipette/measuring cylinder to measure h2o.
3. Put each test tube into a h2o bath with diff. temps for the same amount of time.
4. After the water bath remove the beetroot,water changes from colourless to pink.
5. colorimetry.Turn it on and stabilise for 5mins . Put filter on blue.
6. Put cuvette containing distilled water into colorimeter and calibrate to 0.
7. Use a pipette to transfer solutions in each test tube into diff. cuvettes.Put cuvette in colorimeter one by one and record absorption
8. Analyse results.The higher the absorbance the more pigment released ∴ the higher the permeability

Question 13

Identify the control,independant,dependant variables

Answer 13

control:

• size of beetroot pieces
• beetroot the cube pieces are coming from
• volume of water
• time beetroot stayed in waterbaths
• colorimeter used.

Independant:
Temp

Dependant:
Concentration of pigment released

Question 14

How can experiment be changed to see effects of organic solvents on membrane permeability

Answer 14

Same procedure but instead of putting beetroot pieces into water, you will have to put to create a serial dilution of ethanol(organic solvent) using water

Question 15

State the appropriate units for temp,vol,conc,absorbance

Answer 15

temp: C degrees

vol : cm3/dm3

conc: moldm-3 / gdm-3
absorbance: Au

Question 16

State limitations of procedure and ways to improve these limitations

Answer 16

Difficulty maintaining temp,so SET WATERBATHS FOR HIGHER TEMPS

difficulty in getting accurate beetroot pieces so USE A SCALPEL AND RULER TO CUT EACH PIECE,THEN USE THE ONES WITH MOST SIMILAR SIZES

Question 17

Describe how experiment could be made more reliable and accurate

Answer 17

reliable

• use more samples of beetroot
• maintain temp thermostatically(controlled water baths)

Accurate:

-use more intermediate temps within existing range

Question 18

Define diffusion

Answer 18

net movement from an area of high concentrate to an area of low concentration down a concentration gradient

Question 19

Define facilitated diffusion and why does it take place

Answer 19

: net movement of particles from an area of high concentration to an area of low concentration down a concentration gradient across a partially permeable membrane via carrier/channel proteins

∵ phospholipid bilayer prevents polar, charged,large molecules from diffusing easily,so diffusion is made easier by carrier + channel proteins

Question 20

state factors affecting diffusion

Answer 20

large S.A
conc. gradient
thickness of exchange surface
temp.

Question 21

Explain how these factors affect diffusion

Answer 21

the greater the S.A,the higher the number of particles that can diffuse across the cell membrane in a given amount of time

the steeper the conc. gradient the faster the rate of diffusion

the shorter the distance the faster the rate of diffusion

Higher temp- particles have more kinetic energy and so they move more and collide at a faster rate ∴ faster rate of diffusion

low temp- particles will have less kinetic energy and so they move and collide at slower rate ∴ slow rate of diffusion

Question 22

Write a method to investigate factors affecting diffusion rates on model cells

Answer 22

1. make up agar jelly with phenolphthalein and dilute NaOH.This will make the jelly pink
2. Preparr 5 test tubes containing HCl in increasing concs.
3. Using scalpel, cut out 5 equal-sized cubes from agar jelly.
4. Put one of the cubes into the 1st test tube and use a stopwatch to time how long it takes for cube to turn colourless.
5. do the same for rest test tubes of HCl us9ng new cube each time

Question 23

How can experiment be changed to measure affect of temp + S.A on diffusion

Answer 23

1. Prepare agar jelly same way
2. cut into diff. sized cubes and work out S.A: Vol
3. Time how long it takes for cues to get colourless when placed in same conc. of HCl.
4. Prepare agar jelly same way
5. prepare test tubes of same conc. of HCl and put boiling tubes in water baths of diff. temps
6. When HCl in each tube reaches desired temp. place cubes in.
7. Time how long it takes for cues to get colourless

Question 24

Define osmosis

Answer 24

Diffusion of water molecules across a partially permeable membrane from an area of high water potential to an area of low water potential

Question 25

Define water potential

Answer 25

the likelihood of water molecules to diffuse into or out of a solution

the more negative a water potential the stringer the conc of solutes are in the solution

Question 26

Outline what is meant by isotonic,hypertonic, hypotonic and

Answer 26

Isotonic-There’s an equal water potential in either side of cell membrane.

hypertonic- solutions outside with a lower water potential than inside cell.

hypotonic- solutions with a higher water potential compared with inside the cell

Question 27

Describe how animal and plant cells behave in each type of solution

Answer 27

isotonic:
animal + plant -stays the same

Hypertonic:
animal-will shrink loses function
plant- FLACCID .cytoplasm and plasma membrane pull away from cell wall=plasmolysis

Hypotonic:
animal:cell will get swollen and eventually burst= cytolysis
plant-becomes TURGID

Question 28

Explain the effect of o concentrated solution on water potential

Answer 28

water potential decreases as there will be more solute molecules which the water molecules will interact with , so fewer h2o molecules inside the cell.

Question 29

Write a method to investigate the effects of water potential on plant cells

Answer 29

1. prepare sucrose solutions with conc:0.0M,0.2M,0.4M,0.6M,0.8M,1.0M
2. Use cork borer to cut potatoes into identical sized cylinders,about 1cm in diameter.Divide the cylinders into groups of 3 and measure the mass of each group using a mass balance.
3. Place 1 group into each of your sucrose solutions and leave the cylinders in the solutions for at least 20 minutes.
4. Remove the cylinder and pat them try dry gently with paper towel.Weigh each group again and record your results.
5. Calculate the % change in mass for each group.