Topic 2B- Cell Membranes + RP3, RP4 Flashcards
Including RP4, RP3
1
Q
What surrounds cells?
A
A cell-surface membrane
2
Q
What is a cell-surface membrane?
A
A barrier between the cell and its environment, controlling which substances enter and leave the cell.
3
Q
What does partially permeable mean?
A
They let some molecules through but not others
4
Q
How can substances move across the cell-surface membrane?
A
Diffusion
Osmosis
Active transport
5
Q
In what type of cell can the organelles also be surrounded by a membrane?
A
Eukaryotic
6
Q
What is the fluid mosaic model?
A
A description of the arrangement of molecules in the membrane.
7
Q
Describe the phospholipids arrangement in a plasma membrane
A
- Bilayer
- Hydrophobic tails to inside
- Hydrophilic heads to outside
8
Q
Why is the phospholipid bilayer described as fluid?
A
Because the phospholipids are constantly moving
9
Q
What type of biological molecule is cholesterol?
A
Lipid
10
Q
What is cholesterol’s function?
A
It gives the membrane stability
11
Q
What type of membrane is cholesterol not present in?
A
Bacterial cell membranes
12
Q
Where are cholesterol molecules found in cell membranes?
A
Between phospholipids
13
Q
Describe how cholesterol gives cell membranes stability
A
- Cholesterol molecules bind to hydrophobic tails of phospholipids = causes them to pack more closely together
- Restricts movement of phospholipids
- Makes membrane less fluid and more rigid
14
Q
What is the role of cholesterol in cell membranes?
A
- helps maintain the shape of animal cells
- controls fluidity of the membrane
15
Q
How are proteins arranged in the bilayer?
A
They are scattered across it like a mosaic
16
Q
How do proteins move in the bilayer?
A
Some are able to move sideways, while others are fixed in position
17
Q
What is a glycoprotein?
A
A protein with a carbohydrate (polysaccharide chain) attached
18
Q
What is a glycolipid?
A
A lipid with a polysaccharide chain attached
19
Q
What do channel proteins and carrier proteins allow?
A
Allow large molecules and ions to pass through membrane
20
Q
What do receptor proteins on the cell-surface membrane do?
A
Detect chemicals released from other cells
(chemicals signal to cell to respond in some way)
21
Q
Name 3 functions of phospholipids in plasma membranes
A
- Allow lipid-soluble substances to enter & leave the cell
- Prevent water-soluble substances entering and leaving the cell
- Makes membrane flexible
22
Q
Describe how the plasma membrane acts as a barrier to water-soluble substances
A
Centre of bilayer is hydrophobic ∴ membrane doesn’t allow water-soluble substances (like ions) through it
23
Q
What are intrinsic proteins?
A
Proteins that span entire bilayer from one side to the other
24
Q
What are extrinsic proteins?
A
Proteins are partly embedded in bilayer (occur either on surface of it)
25
What is Beetroot RP 4 investigating?
The permeability of cell membrane
26
RP4- State 2 factors that affect the permeability of cell membranes
Temperature
Concentration of solvents (ethanol)
27
RP4- How is beetroot used to measure the permeability of cell membranes?
The higher the permeability, the more red pigment that leaks out into the surrounding solution within a given time. A colorimeter can be used to determine the absorbance, hence concentration of pigment.
28
RP4- Outline the procedure to investigate the effect of temperature on permeability of cell membrane
1. Cut beetroot into 6 identical cubes with a scalpel
2. Place each cube in a different test tube with equal volumes of distilled water
3. Place each test tube into water baths ranging from 30-80°C. Leave for 20 minutes
4. Filter each solution out into a cuvette and measure the absorbance using a colorimeter
29
RP4- What are the safety hazards involved in testing the effect of ethanol concentration on membrane permeability?
Ethanol is an irritant, and is flammable, keep away from flames and wear eye protection
Keep sharp scalpel away from fingers
Handle hot liquid with care
30
RP4- What is the effect of temperature on membrane permeability?
Increasing temperature, increases membrane permeability
31
RP4- What is the effect of ethanol concentration on membrane permeability?
Increasing concentration, increases permeability
32
Define diffusion
The net movement of molecules or ions from an area of high concentration to an area of low concentration.
33
Is diffusion active or passive?
Passive
34
Give two examples of molecules which can use simple diffusion to pass through the membrane
Oxygen
Carbon Dioxide
35
What is simple diffusion?
When molecules diffuse directly through a cell membrane
36
Name the proteins used in facilitated diffusion
Carrier
Channel
37
Is facilitated diffusion an active or passive process?
passive
38
What type of molecule do carrier proteins transport?
Large molecules
39
Describe how a carrier protein facilitates diffusion
1. Firstly, a large molecule attaches to a carrier protein in the molecule
2. Then, the protein changes shape
3. This releases the molecule on the opposite side of the membrane
40
What do channel proteins facilitate the diffusion of?
Charged particles
(remember: the ‘ch’ sound)
41
How do channel proteins work?
They form pores in the membrane for charged particles to diffuse through (down their concentration gradient)
42
Name and explain three things that affect the rate of simple diffusion
1. The concentration gradient: the higher it is the faster the rate of diffusion.
2. The thickness of the exchange surface: the thinner the surface, the faster the rate
3. The surface area: the larger the surface area, the faster the rate. e.g. microvilli can increase the rate of diffusion
43
Name and explain two things that effect the rate of facilitated diffusion
1. The concentration gradient: the higher it is, the faster the rate of diffusion
2. The number of channel or carrier proteins: once all the proteins are in use, facilitated diffusion can’t happen any faster, even if you increase the concentration gradient
44
Define Osmosis
Osmosis is the diffusion of water molecules across a partially permeable membrane, from an area of high concentration to an area of low concentration
45
What is water potential?
The potential of water molecules to diffuse in or out of a solution
46
What type of water has the highest water potential?
Pure water
47
What does isotonic mean?
Two solutions have the same water potential
48
Name and explain 3 things that affect the rate of osmosis
1. The water potential gradient: the higher this is, the faster the rate
2. The thickness of the exchange surface: the thinner the surface, the faster the rate of osmosis
3. The surface area of the exchange surface: the larger the surface area, the faster the rate of osmosis
49
RP3- What is the purpose of calibration curves?
They are used to determine the concentration of an unknown sample by comparing it to a set of standard values with known concentrations
50
RP3- How is a calibration curve used to find the concentration of plant tissue?
Plot a calibration curve of percentage change in mass against concentration. Find the x- intercept where the plant tissue is isotonic to the sucrose solution
51
RP3- What occurs when plant tissue is placed in a hypotonic solution?
Water moves into the plant tissue by osmosis, plant tissue increases in mass
52
RP3- What occurs when plant tissue is places in a hypertonic solution?
Water moves out of the plant tissue by osmosis, plant tissue decreases in mass
53
RP3- Why are the potato discs left in solution for 20 minutes?
To allow time for osmosis until the plant tissue reaches equilibrium with its surrounding solution
54
RP3- What is water potential determined by?
- The concentration of solutes
The higher the solute concentration then the lower the water potential
55
RP3- Outline the procedure of investigating osmosis using potato tissue
1. Make a simple dilution of 1M sucrose to produce 5 concentrations. Add 5cm^3 to 5 different test tubes.
2. Cut a potato into equal sized chips and weigh
3. Place a chip in each test tube and leave for 20 minutes
4. Take out, dab the excess water and weigh them again
5. Calculate the percentage change in mass
56
RP3- Why is the percentage change used rather than the actual change in mass?
Potato chips may not all have the same starting mass
Percentage change allows comparison
57
RP3- What is indicated by the x-intercept of the calibration curve?
The concentration that is isotonic to the solution tested
58
RP3- Explain the change in mass of the potato chips
The potato chips with concentration lower than the sucrose solution (higher water potential) lose mass as there is a net movement of water out of the cells.
The potato chips with concentration higher than the sucrose solution (lower water potential) gain mass as there is a net movement of water into the cells.
59
RP3- Why are the potato chips dabbed dry after removing from the sucrose solution?
To remove any excess water clinging to its surface
60
RP3- What are the controlled variables of this practical?
1. Volume of sucrose solution
2. Size of potato chips
3. Length of time left in solution
4. Dabbing each one with paper towel
61
Define active transport
The movement of particles against the concentration gradient, using energy (ATP)
62
What process produces ATP?
respiration
63
What are co-transporters?
A type of carrier protein
64
What type of movement are co-transporters involved in?
Active transport
65
How do co-transporters work?
1) they bind two molecules at a time
2) the concentration gradient of one of the molecules is used to move the other molecule against its own concentration gradient
66
State and explain two factors affecting the rate of active transport
1. The speed of individual carrier proteins- the faster they work, the faster the rate of active transport
2. The number of carrier proteins present- the more proteins there are, the faster the rate of active transport
3. The rate of respiration in the cell and the availability of ATP. If respiration is inhibited, active transport can't take place
67
Where is glucose absorbed in the body?
Ileum epithelium
68
What ions are involved in the co-transport in the ileum?
sodium
potassium
69
What cells line the small intestine?
epithelial cell
70
What substance is absorbed in the ileum?
glucose
71
What is the name of the pump?
sodium-potassium pump
72
Why does glucose have to be co-transported in the ileum?
because the concentration of glucose is too low for glucose to diffuse out into the blood
73
Explain how co-transport is involved in the absorption of glucose/amino acids in the small intestine
1. Sodium ions actively transported out of epithelial cells and into bloodstream
2. Sodium ion concentration lower in epithelial cells than lumen of ileum.
3. Transport of glucose/ amino acids from lumen to epithelial cells is 'coupled' to facilitated diffusion of Na+ down electrochemical gradient
73
What ion does glucose enter the ileum epithelium with?
sodium
