Biological Membranes

Question 1

All cells have ___ on its cell membrane

Answer 1

Antigens

Question 2

What do antigens do?

Answer 2

1. Used for cell recognition
2. Allows cell signalling/communication

Question 3

Functions of organelles membranes

Answer 3

1.Keeps enzymes together/ in one place so reactions happen efficiently.
2. Controls what enters and exits the organelles.

Question 4

What do membranes within organelles do?

Answer 4

1.increase surface area for reactions to take place.
2. It acts as barriers within organelles as diff reactions happen in different parts (cristae- mitochondria) (thylakoid membrane in chloroplasts)

Question 5

Structure of a phospholipid

Answer 5

A phosphate group, glycerol and 2 fatty acid chains.

Question 6

The structure of the phospholipid bilayer is described by the ____

Answer 6

Fluid mosaic model.
-phospholipids and small proteins move around
-proteins arranged randomly in a mosaic pattern

Question 7

What are protein channels?

Answer 7

-They help in facilitated diffusion/osmosis
-they allows ions through. Eg:- Na+, K+, Cl-
-some are pumps associated with ATP+ ATPase
-they pump ions against a concentration gradient via active transport

Question 8

What’s the glycocalyx

Answer 8

1. It has glycoprotein: proteins+carbs
2. It has glycolipids: lipids+ carbs
   Uses:
   -Antigens/ cell recognition
   -can act as receptors, cell signalling
   -help stabilise the membrane as they form h-bonds with H2O.
   -help cells adhere to other cells

Question 9

Osmosis

Answer 9

Movement of water from a high water potential to low water potential; down a water potential gradient through a semi-permeable membrane

Question 10

What are carrier/ transport proteins

Answer 10

1. Larger/ polar molecule use them.
2. Some are co-transport proteins as they allow 2 substances to pass through at once.
3. Can allow active transport
4. When correct substances bind to carrier proteins it causes a change in tertiary structure = allows substances through

Question 11

How does cholesterol stabilize the phospholipid bilayer

Answer 11

-Phospholipids have low kinetic energy so they move around less.
-increases the packing of the membrane
-pushes the phospholipids apart and INCREASES THE FLUIDITY of the membrane

Question 12

Cholesterol at warmer temps

Answer 12

-Phospholipids have move KE and move around more and are further apart
-this could make the bilayer likely to fall apart
-cholesterol pushes the phospholipids together and decreases the fluidity of the membrane

Question 13

Factors that affect the permeability of a membrane

Answer 13

-temperature, ethanol, pH, no of protein channels, carrier proteins, cholesterol, no of saturated/ unsaturated fatty acid tails in Phospholipids

Question 14

Membrane permeability PAG steps

Answer 14

1. 6 test tubes with 10 ml water in each
2. Label each tube with temp increase
3. Take beet cylinders and rinse + pat dry in a water bath. Put one in each tube and incubate at required temp for 15 mins
4. swirl each one, remove beetroot with foreceps and throw away.
5. Pour into a cuvette and measure absorbance.
6. Record results in a table and plot a graph.

Question 15

How to use scale factors:
You have been give a 20M sucrose soln, and told to make up 10cm³ of an 8M sucrose soln

Answer 15

1. Work out the scale factor:- 20m/8m = 2.5
2. Work out vol needed from the original soln:- 10cm³/2.5 = 4cm³
3. Take this volume (4 cm³) and fill up to the needed volume with water (4cm³ sucrose +6cm³ water) to form 10cm³ of 8 M sucrose soln.

Question 16

3 ways of making serial dilutions

Answer 16

1. To take 20cm³ of solution (e.g0.8M) and add 20cm³ of H2O to form (0.4M)
2. to carry out serial dilutions via factor of 10
3. Using scale factors

Question 17

Results of potatoes being soaked in different sucrose solutions.

Answer 17

1. Hypotonic soln (0-0.1M) : water enters the potato mass increases
2. isotonic soln (0.2M) : mass stays the same
   3 hypertonic soln (0.8- 1M) : mass decreases as water exits the cell.

Question 18

Simple diffusion

Answer 18

-passive (no ATP needed)
-small, non polar molecules can easily pass through (CO2, O2, fat soluble vitamins and steroid hormones)

Question 19

Facilitated diffusion

Answer 19

-it is passive
-high to low conc gradient
-includes large polar molecules (ions use protein channels) (glucose and amino acids use transport proteins)
-sometimes 2 substances/molecules/ions move through the membrane together (via co-transport proteins)

Question 20

Define Active transport

Answer 20

-the substance moves against the conc gradient
-Uses energy (ATP)
-the protein channels will be associated with ATP-ase and have a binding site for ATP)

Question 21

What is Osmosis

Answer 21

Movement of water from high water potential to low water potential across a semi-permeable membrane.

Question 22

What increases the rate of osmosis?

Answer 22

Aquaporins

Question 23

___ are most vulnerable to damage via osmosis

Answer 23

RBC’s or erythrocytes

Question 24

If plant cells gain water they are _____

If animal cells gain water they are ______

Answer 24

1. Turgid
2. Cytolysed

Question 25

If plant cells lose too much water they are ______
If animal cells lose too much H2O they’re_____

Answer 25

Plasmolysed/flaccid

Question 26

When is Endocytosis/exocytosis used?

Answer 26

-when substrate is too big to pass through protein channels or carrier proteins
-it is active, microtubules and filaments need to contract to “move” the membrane

Question 27

Endocytosis

Answer 27

Used to bring pathogens or large proteins into a cell

Question 28

Exocytosis

Answer 28

Used to secrete/excrete large proteins or hormones