1
Q
Which of the following are not surrounded by a membrane?
-Mitochondria
-Nucleus
-Chloroplast
-Ribosomes
A
Ribosomes
2
Q
Cell membranes only allow some molecules to pass into and out of the cell because they are partially ___.
A
Permeable
3
Q
The model used to describe the structure of the cell-surface membrane is known as the ___.
A
Fluid-mosaic model
4
Q
Why are cell membranes described as being ‘fluid’?
A
Phospholipid molecules are constantly moving
5
Q
Name 5 components of a cell-surface membrane
A
-Phospholipids
-Cholesterol
-Proteins
-Glycoproteins
-Glycolipids
6
Q
Each phospholipid is made up of a hydro___ head and a hydro____ tail.
A
Hydrophilic head
Hydrophobic tail
7
Q
True or False?
A phospholipid bilayer allows water-soluble substances to pass through.
A
False.
Phospholipid bilayers allow lipid-soluble substances through, not water-soluble substances.
8
Q
What is the role of cholesterol in the cell-surface membrane?
A
-Provide stability - restrict lateral movement
-Reduce fluidity at high temp
- Prevent water and ion leakage
9
Q
Which type of cell-surface protein can transport large molecules and ions across the membrane?
A
Intrinsic proteins
10
Q
Proteins that are only present on one side of the phospholipid bilayer are known as ____ proteins.
A
Extrinsic
11
Q
Glycoproteins consist of proteins attached to _______?
A
Carbohydrates
12
Q
Give 3 cell processes involving glycoproteins or glycolipids.
A
-Cell adhesion
-Cell recognition
-Cell signalling
13
Q
What is the definition of diffusion?
A
The net movement of particles, from an area of higher concentration to an area of lower concentration.
14
Q
Is diffusion an active or passive process?
A
Passive
It doesn’t require an energy from the cell
15
Q
Name 2 types of diffusion.
A
-Simple diffusion
-Facilitated diffusion
16
Q
What is simple diffusion in the context of membranes?
A
Simple diffusion is the process in which molecules diffuse directly across membranes
17
Q
Explain why oxygen can enter cells via simple diffusion
A
-Small
-Non-polar
18
Q
Explain why carrier and channel proteins are described as being specific
A
Only allow specific molecules to pass through them
as they have specific tertiary structures with binding sites
19
Q
Explain how some large molecules can enter cells via facilitated diffusion
A
-Attach to carrier proteins, which causes them to change shape
-Carrier proteins release the molecules on the opposite side of the membrane
20
Q
Explain how ions enter cells via facilitated diffusion
A
Ions pass through channel proteins in the cell membrane
21
Q
Name 5 factors that affect the rate of diffusion across a membrane
A
- Temperature
- Concentration gradient
- Thickness of membrane
- Surface area
- Number of carrier/channel proteins
22
Q
Why does a higher temperature increase the rate of diffusion?
A
-More kinetic energy
-Particles move around more quickly
-Diffuse more quickly
23
Q
How does the number of carrier proteins affect the rate of facilitated diffusion?
A
More carrier proteins, faster rate
24
Q
Why does a thin membrane increase the rate of diffusion?
A
Particles do not have to travel as far, so they diffuse faster
25
What is the definition of water potential?
Water potential is a measure of the pressure exerted by water molecules on the membrane or container surround a solution
26
What is the water potential of pure water?
0 kPa
27
How does adding a solute to water affect the water potential?
Adding a solute to water lowers the water potential,
making it more negative
28
What is osmosis?
Osmosis is the movement of water molecules
from a higher water potential to a lower water potential
through a partially permeable membrane
29
What happens to animal cells in hypertonic solutions?
-A hypertonic solution has a lower water potential than the animal cells
-water molecules move out of the cell
-causing the cell to shrink
30
What happens to animal cells in hypotonic solutions?
-A hypotonic solution has a higher water potential than the animal cells
-water molecules move into the cell
-causing cell to swell and burst
31
What happens to animal cells in isotonic solutions?
-An isotonic solution has the same water potential as the animal cells
-no net movement of water
-cell stays the same size
32
What happens to plant cells in hypertonic solutions?
-A hypertonic solution has a lower water potential than the plant cells
-water molecules move out of the cell
-cell shrinks and becomes plasmolysed
33
What happens to plant cells in hypotonic solutions?
-A hypotonic solution has a higher water potential than the plant cell
-water molecules move into the cell
-cell swells and becomes turgid
34
What are 4 factors affecting the rate of osmosis?
1. Temperature
2. Water potential gradient
3. Thickness of membrane
4. Surface area
35
Is osmosis an active or passive process?
Passive
It doesn’t require any energy from the cell
36
When animal cells are placed in pure water they burst, whereas plant cells become turgid.
Why is this?
Plant cells have a strong cell wall made of cellulose which prevents them from bursting
37
If you add sugars and salts to a beaker of water, what will happen to the water potential?
The water potential will decrease
38
What is the definition of active transport?
-movement of molecules across a membrane
-from a region of lower concentration to a region of higher concentration
-requires energy (in form of ATP) from respiration
- and carrier proteins
39
What do we mean by against the concentration gradient?
Substances are moving from an area of lower concentration to an area of higher concentration
40
Is active transport an active or passive process?
Active
It requires energy
41
What type of protein is used in active transport?
Carrier proteins
42
Carrier proteins that bind to two molecules at once are known as ____.
co-transporters
43
What is the primary function of co-transport of glucose in the ileum?
To absorb glucose from the lumen into the bloodstream
44
Which protein uses active transport in the co-transport of glucose?
Sodium-potassium pump
45
Which 2 proteins use facilitated diffusion in the co-transport of glucose?
1. Glucose protein channels
2. Sodium-glucose co-transporter proteins
46
What happens to the concentration of glucose in the lumen during co-transport in the ileum?
It decreases
47
What is the role of ATP in the co-transport of glucose in the ileum?
It is used to maintain the concentration gradient of sodium ions between the lumen and the epithelial cells of the ileum
48
What happens to glucose after it is transported into the epithelial cells in the ileum?
It diffuses from the epithelial cells into the bloodstream
49
Why is ATP used in active transport?
directly move molecules by co-transport
50
In which of the following states can molecules diffuse?
-liquid
-gas
-solid
Liquid and Gas
51
The process in which molecules diffuse directly across cell membranes is known as _____ diffusion.
Simple diffusion
52
Name 2 examples of molecules that cross cell membranes via simple diffusion.
Any small, non-polar molecules
- Oxygen
- Carbon dioxide
- Water
53
How do large, polar molecules cross cell membranes?
Facilitated diffusion
54
Facilitated diffusion involves carrier and channel _____.
Proteins
55
During facilitated diffusion, which component of the cell membrane do large molecules bind to?
Carrier proteins
56
Will a larger surface area increase of decrease the rate of diffusion?
Increase
57
Which type of molecule do channel proteins transport?
Ions
58
What are channel proteins?
tubes filled with water that allow water-soluble ions through
59
Why does a higher temperature increase the rate of diffusion?
-particles have more kinetic energy
-move around faster
-can diffuse more quickly
60
What do carrier proteins do?
bind to ions/molecules
then change shape to move these molecules across the membrane
61
Explain how molecules enter cells via active transport
-the molecule and ATP bind to the carrier protein
-ATP is hydrolysed to ADP and phosphate which causes the carrier protein to change shape
-this releases the molecule on the opposite side of the membrane
-the phosphate is released from the carrier protein causing it to return to its original shape
- phosphate recombines with ADP to form ATP during respiration
62
Name 4 factors that affect the rate of active transport
1. Temperature
2. Thickness of membrane
3. Number of carrier proteins
4. Rate of respiration
63
Explain how the number of carrier proteins affects the rate of active transport
The more carrier proteins,the faster the rate of active transport
64
What is a cell-surface membrane and what does it do?
-A membrane surrounding cells
-acts as a barrier between the cell and its environment
-to control which substances enter and leave the cell
65
What does it mean when a membrane is partially permeable?
The membrane lets some molecules through
66
What is the name of the 1972 model used to describe the cell membrane structure?
Fluid-mosaic model
67
Why are cell membranes described as being fluid-mosaic?
Fluid: phospholipid molecules are constantly moving
Mosaic: proteins of different shapes and sizes embedded in the phospholipid bilayer
68
How does cholesterol play a role in preventing water loss?
it is very hydrophobic
69
Why do phospholipids form a bilayer in aqueous environments?
Hydrophilic heads face outwards, towards the water
Hydrophobic heads face inwards, away from the water
70
Can most water-soluble substances pass through the phospholipid bilayer? Why?
No
The core of the bilayer is hydrophobic
71
Which substances can pass through the phospholipid bilayer? Why?
-small
-non-polar (lipid soluble)
72
How does cholesterol provide stability in the membrane?
pulls together tails of fatty acids, limiting their movement
73
Describe the roles of channel and carrier proteins in the cell-surface membrane
Transport large molecules and ions across the membrane
74
What are glycoproteins?
Intrinsic proteins attached to carbohydrates
75
What are glycolipids?
Lipids covalently bonded to carbohydrates
76
The water potential of pure water is _ kPa
0 kPa
77
Will increasing the concentration of solute increase or decrease the water potential of the solution?
Decrease
78
True or false?
Osmosis is a special form of diffusion
True
79
Osmosis is the movement of which molecules?
Water
80
Osmosis is the movement if water from an area of ____ water potential to an area of ____ water potential, across a _______ - permeable membrane.
Higher
Lower
Partially
81
What happens to an animal cell in a hypertonic solution?
It shrinks
82
A solution that has the same water potential as cells is known as an ______ solution
Isotonic
83
What happens to a plant cell in a hypotonic solution?
It swells and becomes turgid
84
Which cell component prevents a plant fell from bursting in a hypotonic solution?
Cell wall
85
Temperature, water potential gradient, thickness of membrane and surface area are all factors that affect the rate of _______.
Osmosis
86
Will a thicker membrane increase or decrease the rate of osmosis?
Decrease
Particles have to travel further
Diffuse more quickly
87
Active transport is the movement of molecules across a membrane, from a region of _______ concentration to a region of _______ concentration. This requires ______ from respiration.
Lower
Higher
energy
88
In active transport, which way do molecules move on a concentration gradient?
Up
89
Active transport involves ____ proteins
carrier
90
What are the 3 functions of phospholipids in the membrane?
- allow lipid-solubl substances to enter and leave the cell
- prevent water-soluble substances entering and leaving the cell
- make the membrane flexible and self-sealing
91
Why do phospholipids align as a bilayer?
hydrophilic heads are attracted to water
hydrophobic tails are repelled by water
92
What are the 5 functions of proteins in the membrane?
- provide structural support
- act as a channel transporting water-soluble substances that cross the membrane
- allow active transport across the membrane through carrier proteins
- for cell-surface receptors for identifying cells/ for hormones
- help cells adhere together
93
What are the 5 functions of membranes within cells?
- control entry and exit of materials
- separate organellesfrom cytoplasm so specific metabolic reactions can take place within them
- provide an internal transport systm
- isolate enzymes that might damage cells
- provide surfaces for reactions to occur
94
Which substances can't pass through phospholipid bilayer?
- large
- water-soluble
- polar
95
Define solute
any substance that is dissolved in a solvent
96
Define solution
a solute and solvent together
97
What happens to pure water when a solute is added to it?
its water potential lowers
= solutions have negative water potential
98
What is one way to find the water potential of cells/tissues?
places them in a series of solutions of different water potentials
99
What is the term for when water potentials on either side of the plasma membrane are equal?
dynamic equilibrium
=no net movement of water
100
What is the water potential of pure water?
0
101
What happens when the water potential of external solution is higher compared to animal cell solution?
- water enters cell
- cell swells and bursts
102
What happens when the water potential of external solution is lower compared to animal cell solution?
- water leaves cell
- cell shrinks
103
What happens when the water potential of external solution is equal to animal cell solution?
- no net movement of water
- no change in cell state
104
What happens when the water potential of external solution is higher compared to plant cell solution?
- water enters cell
- cell protoplast swells and becomes turgid
105
What happens when the water potential of external solution is lower compared to plant cell solution?
- water leaves cell
- cell protoplast shrinks and becomes plasmolysed
106
What happens when the water potential of external solution is equal to plant cell solution?
- no net movement of water
- incipient plasmolysis of cell
107
How does active transport differ from passive forms of transport (4)?
- ATP needed
- against conc gradient
- carrier proteins needed
- selective process
108
What aree microvilli and how are they helpful?
projection on lining of ileum
provide more surface area
for insertion of carrier proteins
109
How is the concentration gradient between the blood and the ileum maintained?
- glucose continuously absorbed into ileum = higher conc
- blood constantly circulating, glucose absorbed into it is constantly removed by cells during respiration
110
Describe the process of co-transport
1. sodium ions are actively transported out of epithelial by sodium-potassium pump into blood
2. this maintains higher conc of sodium ions in lumen than epithelial cells
3. sodium ions diffuse into epithelial cells down con gradient through a co-transport protein carried along with glucose/amino acid into cell
4. glucose/amino acids pass into blood plasma by facilitated diffusion by carrier protein
111
Sodium ions move ------ their conc gradient, whereas glucosee molecules move ------- their con gradient
sodium = down conc grad
glucose/amino acids = against conc grad
112
Suggest 2 properties that a drug should possess if it is to enter a cell rapidly
lipid-soluble
small
no electrical charge
113
Contrast facilitated diffusion and diffusion
facilitated only occurs at channels on the membrane where there are special protein carrier molecules
114
List 2 changes to the structure of cell-surface membranes that would increase the rate at which glucose in transported into a cell
- increase surface area - microvilli
- more proteins across phospholipid bilayer
115
Explain why an animal cell placed in pure water bursts while a plant cell placed in pure water does not
- both cells have a lower water potential than pure water = water enters by osmosis
- animal cell is surrounded by thin membrane so swells and bursts
- plant cell supported by rigid cellulose cell wall
- as plant cell is turgid, water cannot enter = prevents swelling
116
State one similarity and one difference between active transport and facilitated diffusion
SIMILARITY
- both use carrier proteins in the plasma membrane
DIFFERENCE
- active transport requires energy/ occurs against conc grad
117
Explain why reabsoption of glucose is more efficient by active transport rather than diffusion
diffusion can only reabsorb about 50%
active transport can absorb all the glucose
118
BIO
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