1
Q
Q: What is the function of the nucleus?
A
A: Contains DNA and controls the cell’s activities.
2
Q
Q: What is the function of the mitochondrion?
A
A: Site of aerobic respiration and ATP production.
3
Q
Q: What is the function of the rough endoplasmic reticulum?
A
A: Synthesises and transports proteins.
4
Q
Q: What is the function of the smooth endoplasmic reticulum?
A
A: Synthesises and processes lipids.
5
Q
Q: What is the function of the Golgi apparatus?
A
A: Modifies, sorts, and packages proteins and lipids.
6
Q
Q: What is the function of lysosomes?
A
A: Contains digestive enzymes to break down waste.
7
Q
Q: What is the function of ribosomes?
A
A: Site of protein synthesis.
8
Q
Q: What is the function of the cell surface membrane?
A
A: Regulates movement of substances into and out of the cell.
9
Q
Q: What is the function of the cell wall in plants?
A
A: Provides structural support and prevents osmotic lysis.
10
Q
Q: What is the function of the vacuole?
A
A: Maintains cell pressure and stores ions and molecules.
11
Q
Q: What is the function of the chloroplast?
A
A: Site of photosynthesis.
12
Q
Q: What are prokaryotic cells?
A
A: Cells without a nucleus or membrane-bound organelles.
13
Q
Q: What is the role of plasmids in prokaryotic cells?
A
A: Carry genes that may benefit survival, such as antibiotic resistance.
14
Q
Q: What is the structure of a virus?
A
A: Contains genetic material (DNA or RNA), a protein coat (capsid), and attachment proteins.
15
Q
Q: How do viruses replicate?
A
A: Attach to host cell, inject genetic material, and hijack host cell machinery.
16
Q
Q: What is the difference between magnification and resolution?
A
A: Magnification is how much bigger an image is, resolution is the clarity or detail.
17
Q
Q: What is the formula for magnification?
A
A: Image size / Actual size.
18
Q
Q: What is the purpose of cell fractionation?
A
A: To isolate different organelles.
19
Q
Q: What are the three steps of cell fractionation?
A
A: Homogenisation, filtration, ultracentrifugation.
20
Q
Q: What is the order of organelle separation in ultracentrifugation?
A
A: Nucleus → mitochondria → lysosomes → ER → ribosomes.
21
Q
Q: What is the difference between light and electron microscopes?
A
A: Electron microscopes have higher resolution and magnification.
22
Q
Q: What are the two types of electron microscopes?
A
A: Transmission (TEM) and Scanning (SEM).
23
Q
Q: What is the function of the plasma membrane?
A
A: Controls substance movement; site of cell signalling.
24
Q
Q: What are the main components of a plasma membrane?
A
A: Phospholipids, proteins, cholesterol, glycoproteins, glycolipids.
25
Q: What is the fluid mosaic model?
A: Describes membrane as a flexible layer with proteins scattered throughout.
26
Q: What factors affect membrane permeability?
A: Temperature, solvent concentration, pH.
27
Q: What is simple diffusion?
A: Passive movement of molecules from high to low concentration.
28
Q: What is facilitated diffusion?
A: Passive movement via channel or carrier proteins.
29
Q: What is osmosis?
A: Movement of water across a semi-permeable membrane from high to low water potential.
30
Q: What is active transport?
A: Movement of substances against the concentration gradient using ATP.
31
Q: What is co-transport?
A: When one substance helps move another across the membrane.
32
Q: How is glucose absorbed in the ileum?
A: Sodium-glucose co-transport via active transport.
33
Q: What is an antigen?
A: A molecule on the surface of a cell that triggers an immune response.
34
Q: What is phagocytosis?
A: Ingestion of pathogens by phagocytes.
35
Q: What is the role of T cells?
A: Recognise antigens and activate other immune cells.
36
Q: What is the role of B cells?
A: Produce antibodies specific to an antigen.
37
Q: What is the difference between the primary and secondary immune response?
A: Secondary is faster and stronger due to memory cells.
38
Q: What are monoclonal antibodies?
A: Identical antibodies produced from a single B cell clone.
39
Q: What are monoclonal antibodies used for?
A: Cancer treatment, pregnancy testing, targeted drug delivery.
40
Q: What is a vaccine?
A: Contains antigens that stimulate the production of memory cells.
41
Q: What is herd immunity?
A: When enough of a population is immune, reducing disease spread.
42
Q: What is the difference between active and passive immunity?
A: Active involves memory cells; passive is temporary with no memory cells.
43
Q: Why is antigenic variation a problem for immunity?
A: It allows pathogens to evade the immune system and vaccines.
44
Q: How does HIV infect the body?
A: Attaches to T helper cells and uses them to replicate.
45
Q: Why do antibiotics not work against viruses?
A: Viruses replicate inside host cells and lack metabolic pathways targeted by antibiotics.
46
why might a babies whose mother is HIV positive, test positive for it too, without having HIV? (2)
- child receives antibodies from mother
- so solution will test positive (before 18 months)
47
suggest two purposes of the control well in ELISA tests? (2)
- shows that only the enzyme is causing the colour change
- shows that all unbound antibody is washed away
48
suggest the purpose of a control well in ELISA test (2)
- compare to to show that only enzyme brings about colour change
- compare to show that all unbound antibodies have been washed away
49
explain why in mitosis practical, the first 5mm from onion root tip is used?
where mitosis occurs (most)
50
explain why in mitosis practical, press down on coverslip firmly?
to produce single layer of cells, so that light can pass through the specimen
51
explain why in mitosis practical, acid is added to the root?
to break down links between cells/ cell walls
52
in mitosis practical, why do use a stain?
to stain chromosomes, to make them visible
53
when counting the cells to calculate mitotic index, what should you do to ensure your count is accurate? (2)
- examine larger number of fields of view/ many cells
- to ensure representative sample
54
what is meant by processed results? (1)
calculations made (from raw data)
55
What are the distinguishing features of eukaryotic cells? (2)
- cytoplasm containing membrane-bound organelles
- so DNA enclosed in a nucleus
56
Describe structure of algal and fungal cells
similar to plant cells
57
Structure and function of cell-surface membrane
structure:
- hydrophilic phosphate head --> point to/ are attracted to water
- hydrophobic fatty acid tails --> point away/ repelled from water
function:
- selectively permeable --> enables control of passage on substances in/out of cell
- molecules/ receptors/ antigens on surface --> allow cell recognition/ signalling
58
Structure and function of nucleus
structure:
- nuclear envelope: double membrane, nuclear pores
- nucleoplasm
- nucleolus
- protein/histone-bound, linear DNA
function:
- holds/stores genetic info, which codes for polypeptides (proteins)
- site of DNA replication
- site of transcription (part of protein synthesis), producing mRNA
- nucleolus makes ribosomes/ rRNA
59
Structure and function of ribosome
structure:
- made of ribosomal RNA and protein (two subunits)
- not a membrane-bound organelle
function:
- site of protein synthesis (translation)
60
Structure and function of rough and smooth endoplasmic reticulum (rER and sER)
structure:
- system of membranes
- rER contains ribosomes
function:
rER:
- ribosomes on surface synthesise proteins
- proteins processed/ folded/ tranported inside rER
- proteins packaged into vesicles for transport, e.g. to Golgi apparatus
sER:
- synthesises and processes lipids
e.g. cholesterol and steroid hormones
61
Structure and function of golgi apparatus and golgi vesicles
structure:
- golgi apparatus = flattened membrane sacs
- golgi vesicle = small membrane sacs
function:
golgi apparatus:
- modifies proteins, e.g. adds carbohydrates to produce glycoproteins
- modifies lipids, e.g. adds carbohydrates to make glycolipids
- package proteins/lipids into golgi vesicles
- produces lysosomes (a type of golgi vescile)
golgi vesicles:
- transports proteins/ lipids to their required destination
-e.g. moves to and fuses with cell-surface membranes
62
Structure and function of lysosomes
structure:
- membrane
-hydrolytic enzymes
function:
- release hydrolytic enzymes (lysozynmes)
- to break down/ hydrolyse pathogens or worn-out cell components
63
Structure and function of mitochondria
structure:
- outer membrane
- cristae: inner membrane fold
- matrix, containing: small (70S) ribosomes and circular DNA
function:
- site of aerobic respiration
- to produce ATP for energy release
- e.g. for protein synthesis/ vesicle movement/ active transport
64
Structure and function of chloroplasts, in plants an algae
structure:
- double membrane
- stroma (the fluid stuff) containing: thylakoid membrane, small/70S ribosomes, circular DNA, starch granule/ lipid droplets
- lamella: thylakoid linking grana
- grana: stacks of thylakoid
function:
- absorbed light energy for photosynthesis
- to produce organic substances, e.g. carbohydrates/ lipids
65
Structure and function of cell wall, in plants and algae
structure:
- composed mainly of cellulose (a polysaccharide) in plants/ algae
- composed of chitin (a nitrogen- containing polysaccharide) in fungi
function:
- provide mechanical strength to cell
- so prevents cell changing shape or bursting, under pressure, due to osmosis
66
Structure and function of cell vacuole in plants
structure:
- tonoplast membrane
- cell sap
function:
- maintains turgor pressure in cell (stopping plant wilting)
- contains cell sap - stores sugars, amino acids, pigments and any waste chemicals
67
What are the distinguishing features of prokaryotic cells? (2)
- cytoplasm lacking membrane-bound organelles
- so genetic material not enclosed in nucleus
68
Examples of prokaryotic organisms?
bacteria and archaea (always unicellular)
69
The two different ways of naming the cell wall of prokaryotic cells?
murein
peptidoglycan
70
Describe the general structure of prokaryotic cells
always present:
- cell- surface membrane
- cell wall (contains murein - a glycoprotein)
- cytoplasm
- small ribosomes
- circular DNA (free in cytoplasm & not associated with proteins)
sometimes present:
- capsule
- plasmids (small rings of DNA)
- flagella
71
Compare and contrast the structure of eukaryotic and prokaryotic cells (7)
eukaryotic = membrane-bound organelles, but prokaryotic = doesn't
eukaryotic = has nucleus containing DNA, but prokaryotic = no nucleus, DNA is free in cytoplasm
eukaryotic = DNA is long & linear & associated with histone proteins, but prokaryotic = short & circular & not associated with proteins
eukaryotic = larger (80S) ribosomes (in cytoplasm), but prokaryotic = smaller (70S) ribosomes
eukaryotic = cell wall only in plants, algae and fungi, containing cellulose or chitin, but prokaryotic = all cells, containing murein - a glycoprotein
eukaryotic = plasmids/ capsule never present (sometimes flagella), but prokaryotic = plasmids, flagella and a capsule sometimes present
eukaryotic = larger overall size, but prokaryotic = much smaller overall size
72
Explain why viruses are described as acellular and non-living (2)
- acellular = not made of cells, no cell membrane/ cytoplasm/ organelles
- non-living = have no metabolism, cannot independently move/ respire/ replicate/ excrete
73
Describe the general structure of a virus particle
- nucleic acids surrounded by a capsid (protein coat)
- attachment proteins allow attachment of specific host cells
- no cytoplasm, ribosomes, cell wall, cell-surface membrane etc
- some also surrounded by a lipid envelope, e.g. HIV
74
suggest how you can apply your knowledge of cell features/ organelles to explain adaptations of eukaryotic cells?
general answer format:
- [named cell] has many [name organelle, e.g. ribosomes]
- to [link organelle function to cell function, e.g. increase rate of protein synthesis, making many antibodies]
75
describe how eukaryotic cells are organised in complex multicellular organisms?
in complex multicellular organisms, eukaryotic cells become specialised for specific functions
tissues = group of specialised cells with similar structure, working tg to perform a specific function, often with the same origin
organ = aggregations (groups) of tissues performing specific functions
organ system = grouo of organs working tg to perform specific functions
76
Describe the difference between magnification and resolution (2)
magnification = number of times greater image is than size of real (actual) object
magnification = size of image/ size of real object
resolution = the minimum distance apart 2 objects can be distinguished as separate objects
77
What does TEM stand for?
transmission electron microscope
78
What does SEM stand for?
scanning electron microscope
79
What do optical microscopes use to focus light?
glass lenses
80
In TEM and SEM what are the electrons focused using?
electromagnets
81
How is an image on an optical microscope produced?
light passes through specimen, different structures absorb different amounts & wavelengths
82
How is an image on an TEM produced?
electrons pass through specimen, denser parts absorb more and appear darker
83
How is an image on an SEM produced?
electrons deflected/ bounce off specimen surface
84
What type of image is produced by an optical microscope?
2D image of a cross-section
85
What type of image is produced by a TEM?
2D image of a cross-section
86
What type of image is produced by a SEM?
3D image of surface
87
Resolution of an optical microscope? And why?
low resolution due to long wavelength of light
88
Resolution of a TEM? And why?
very high resolution, due to short wavelength of electrons
89
Resolution of a SEM? And why?
high resolution due to short wavelength of electrons
90
Can you see internal structures with an optical microscope?
no
91
Can you see internal structures with a TEM?
yes, can see internal structures of organelles and ribosomes
92
Can you see internal structures with a SEM?
no
93
Requirement for specimen size for optical microscope?
thin
94
Requirement for specimen size for TEM?
very thin
95
Requirement for specimen size for SEM?
does NOT need to be thin
96
Magnification of an optical microscope? Exact maximum value too?
low magnification
x1500
97
Magnification of TEM? Exact maximum value too?
high magnification
x 1,000,000
98
Magnification of SEM? Exact maximum value too?
high magnification
x 1,000,000
99
What type of specimen can be used for optical microscopes?
living or dead
100
What type of specimen can be used for TEM?
dead/dehydrated only, as uses a vacuum
101
What type of specimen can be used for SEM?
dead/dehydrated only, as uses a vacuum
102
what type of prep is the preparation for an optical microscope slide?
simple
103
what type of prep is the preparation for TEM slide?
complex preparations, so artefacts often present
104
what type of prep is the preparation for SEM slide?
complex preparations, as artefacts often present
105
What microscopes can and cannot show colour?
can = optical
cannot = TEM/ SEM
106
Maximum resolution of an optical microscope?
200 nm
107
suggest how the scientific community distinguished between artef
108
Maximum resolution of TEM?
109
Maximum resolution of SEM?
110
What are some commonly used stains? What do they stain? What colour does the stain?
111
What are artefacts?
dust/ air bubbles that occur during preparation
112
How can scientists tell the difference between an artefact and cell organelles?
- scientists prepared specimens in different ways
- if an object was seen with one technique but not another, it was more likely to be an artefact, rather than an organelle
113
Magnification formula
I = A x M
size of image = size of object x magnification
114
Describe how to convert between different units (the timeline/numberline thing)
nm micrometer cm m
to the left = x1000
to the right = divide by 1000
mm to cm = divide by 10
cm to mm = x by 10
115
Describe how the size of an object viewed with an optical microscope can be measured [5]
1. Line up (scale of) eyepiece graticule with (scale of) stage micrometer
2. Calibrate eyepiece graticule - use stage micrometer to calculate size of divisions on eyepiece graticule
3. take stage micrometer away and use graticule to measure how many divisions make up the object
4. calculate the size of the object by multiplying number of divisions by size of division
5. recalibrate eyepiece graticule at different magnification
116
Describe and explain the principles of cell fractionation and ultracentrifugation as used to separate cell components
1. Homogenise tissue/ use a blender = disrupts cell membrane, breaking open cells to release contents/ organelles
2. Place in a cold, isotonic, buffered solution = cold to reduce enzyme activity, so organelles not broken down/ damaged
isotonic, so water doesn't move in or out of organelles by osmosis, so they don't burst
buffered to keep pH constant, so enzymes don't denature
3. Filter homogenate = to remove large, unwanted debris, e.g. whole cells, connective tissue
4. Ultracentrifugation - separates organelles in order of density/ mass = centrifuge homogenate in a tube at a low speed.
remove pellet of heaviest organelle and respin supernatant at a higher speed.
repeat at increasing speeds until separated out, each time the pellet is made of lighter organelles (nuclei -- chloroplasts/mitochondria -- lysosomes --rER/sER -- ribosomes)
117
What is the order of pellets based on
the dentisty/mass
118
What organelles are present in each pellet, in order?
1. nuclei
2. chlorplasts/ mitochondria
3. lysosomes
4. sER, rER
5. ribosomes
119
Why may [named organelle] not be visible in the TEM/optical microscope?
bc of the angle at which specimen cut/ viewed
120
Role of eyepiece graticule?
spans the full field of view, with no fixed units
can be used to measure cell/organelles, once calibrated
121
Role of a stage micrometer?
to calibrate the eyepiece graticule, at different magnification
122
What is a temporary mount?
a specimen that you prepared yourself
123
Describe the stages of the cell cycle in eukaryotic cells
Stage 1. Interphase:
- DNA replicates semi-conservatively (S phase)
- leading to 2 chromatids (identical copies) joined at a centromere
- number of organelles & volume of cytoplasm increases, protein synthesis (G1/G2)
Stage 2. Mitosis:
- nucleus divides
- to produce 2 nuclei with identical copies of DNA produced by parent cell
Stage 3. Cytokinesis:
- cytoplasm and cell membrane (normally) divide
- to form 2 new genetically identical daughter cells
124
Describe the behaviour of chromosomes & role of spindle fibres in mitosis
Prophase:
-chromosomes condese, becoming shorter/ thicker, so visible
- appear as 2 sister chromatids, joined by a centromere
- nuclear envelope breaks down
- centrioles move to opposite poled, forming spindle network
- spindle fibres start to attach to chromosomes, by their centromeres
Metaphase:
- spindle fibres attach to chromosomes, by their centromeres
- chromosomes align along equator
Anaphase:
- spindle fibres shorten/contract
- centromere divides
- pulling chromatides (from each pair) to opposite poles of cell
Telophase:
- chromosomes uncoil, becoming longer/ thinner
- nuclear envelope reforms - 2 nuclei
- spindle fibres/ centrioles break down
125
Why do some eukaryotic cells not undergo the cell cycle?
- within multicellular organisms, not all cells retain the ability to divide (e.g. neurons)
- only cells that do not retain this ability go through a cell cycle
126
Explain the importance of mitosis in the life of an organisms
parent cell divides to produce 2 genetically identical daughter cells for:
- growth of multicellular organisms by increasing cell number
- replacing cells to repair damaged tissues
- asexual reproduction
127
describe how tumours and cancers form
mitosis is a controlled process so:
- mutations in DNA/ genes controlling mitosis, can lead to uncontrolled cell division
- tumours formed if this results in mass of abnormal cells
128
What is a tumour? What are the types? Briefly describe the difference between the 2 types?
- tumours formed if this results in mass of abnormal cells
- malignant tumour = cancerous, can spread (metastasis)
- benign tumour = non-cancerous
129
Suggest how cancer treatments control the rate of cell division
Some disrupt spindle fibre activity / formation
○ So chromosomes can’t attach to spindle by their centromere
○ So chromatids can’t be separated to opposite poles (no anaphase)
○ So prevents / slows mitosis
Some prevent DNA replication during interphase
○ So can’t make 2 copies of each chromosome (chromatids)
○ So prevents / slows mitosis
130
Describe and name the process by which prokaryotic cells replicate
binary fission:
1. Replication of circular DNA
2. Replication of plasmids
3. Division of cytoplasm to produce 2 daughter cells
○ Single copy of circular DNA
○ Variable number of copies of plasmids
131
Why do viruses not undergo cell division?
bc they are non-living
132
Describe how viruses replicate
1. Attachment proteins attach to complementary receptors on host cell
2. Inject viral nucleic acid (DNA/RNA) into host cell
3. Infected host cell replicates virus particles:
a. Nucleic acid replicated
b. Cell produces viral protein / capsid / enzymes
c. Virus assembled then released
133
Difference in centromeres and centrioles?
Centromeres join sister chromatids, while centrioles are organelles involved in spindle formation.
134
What happens to centromeres, during anaphase? (1)
When sister chromatids are pulled
apart, the centromere holding them together divides.
135
Can cells undergo mitosis, without cytokinesis too? And why?
Some cells (eg. muscle cells) undergo mitosis (nuclear division) without cytokinesis (cytoplasmic division), so have multiple nuclei.
136
Describe how to prepare squashes of cells from plant root tips [5]
1. Cut a thin slice of root tip (5mm from end) using scalpel and mount onto a slide
2. Soak root tip in hydrochloric acid then rinse
3. Stain for DNA (eg. with toluidine blue)
4. Lower coverslip using a mounted needle at 45 degree angle, without trapping air bubbles
5. Squash by firmly pressing down on glass slip but do not push sideways
137
Why are root tips used? [1]
Where dividing cells are found / mitosis occurs
138
Why is a stain used? [1]
● To distinguish chromosomes
● Chromosomes not visible without stain
139
Why squash/press down on the cover slip? [1]
● (Spreads out cells) to create a single layer of cells
● So light passes through to make chromosomes visible
140
Why not push the cover slip sideways? [1]
Avoid rolling cells together / breaking chromosomes
141
Give two reasons why the roots in microscopy rqp should be soaked in acid [2]
● Separate cells / cell walls
● To allow stain to diffuse into cells
● To allow cells to be more easily squashed
● To stop mitosis
142
Describe how to set-up and use an optical microscope
1 Clip slide onto stage and turn on light
2 Select lowest power objective lens (usually x4)
3 a. Use coarse focusing dial to move stage close to lens
b. Turn coarse focusing dial to move stage away from
lens until image comes into focus
4 Adjust fine focusing dial to get clear image
5 Swap to higher power objective lens, then refocus
143
What are the rules of scientific drawings?
✓ Look similar to specimen / image - draw parts
to the same scale / relative size
✓ No sketching - only clear, continuous lines
✓ No shading / hatching
✓ Include a magnification scale (eg. x 400)
✓ Label with straight, uncrossed lines
144
How can the stage interphase be identified visually?
during interphase, chromosomes are not visible, but nuclei are
(however, in mitosis, chromosomes are visible)
145
Explain how the four stages of mitosis can be identified visually?
Prophase:
● Chromosomes visible / distinct → because condensing
● But randomly arranged → because no spindle activity / not attached to spindle fibre
Metaphase:
● Chromosomes lined up on equator → because attaching to spindle
Anaphase:
● Chromatids (in two groups) at poles of spindle
● Chromatids V shaped → because being pulled apart at their
centromeres by spindle fibres
Telophase:
● Chromosomes in two sets, one at each pole
146
What is a mitotic index (MI)?
● Proportion of cells undergoing mitosis (with visible chromosomes)
● Mitotic index = number of cells undergoing mitosis / total number of cells in sample
147
Explain how to determine a reliable mitotic index (MI) from observed squashed?
● Count cells in mitosis in field of view
● Count only whole cells / only cells on top and right edges → standardise counting
● Divide this by total number of cells in field of view
● Repeat with many / at least 5 fields of view selected randomly → representative sample
● Calculate a reliable mean
148
Suggest how to calculate the time cells are in a certain phase of mitosis
1. Identify proportion of cells in named phase at any one time
○ Number of cells in that phase / total number of cells observed
2. Multiply by length of cell cycle
149
Describe the fluid-mosaic model of membrane structure
● Molecules free to move laterally in phospholipid bilayer
● Many components - phospholipids, proteins,
glycoproteins and glycolipids
150
Describe the arrangement of the components of a cell membrane
● Phospholipids form a bilayer - fatty acid tails face inwards, phosphate heads face outwards
Proteins
○ Intrinsic / integral proteins span bilayer eg. channel and carrier proteins
○ Extrinsic / peripheral proteins on surface of membrane
● Glycolipids (lipids with polysaccharide chains attached) found on exterior surface
● Glycoproteins (proteins with polysaccharide chains attached) found on exterior surface
● Cholesterol (sometimes present) bonds to phospholipid hydrophobic fatty acid tails
151
Describe the arrangement of phospholipids in a cell membrane
● Bilayer, with water present on either side
● Hydrophobic fatty acid tails repelled from water so point away from water / to interior
● Hydrophilic phosphate heads attracted to water so point to water
152
Is cholesterol always present in the cell membranes?
no, it is only present sometimes
153
Explain the role of cholesterol in cell membranes
● Restricts movement of other molecules making up membrane
● So decreases fluidity (and permeability) / increases rigidity
154
Suggest how cell membranes are adapted for other functions
● Phospholipid bilayer is fluid → membrane can bend for vesicle formation / phagocytosis
● Glycoproteins / glycolipids act as receptors / antigens → involved in cell signalling / recognition
155
Describe how movement across membranes occurs by simple diffusion
● Lipid-soluble (non-polar) or very small substances eg. O2, steroid hormones
● Move from an area of higher concentration to an area of lower conc., down a conc. gradient
● Across phospholipid bilayer
● Passive - doesn’t require energy from ATP / respiration (only kinetic energy of substances)
156
Explain the limitations imposed by the nature of the phospholipid bilayer
● Restricts movement of water soluble (polar) & larger substances eg. Na+/ glucose
● Due to hydrophobic fatty acid tails in interior of bilayer
157
Describe how movement across membranes occurs by facilitated diffusion
● Water-soluble / polar / charged (or slightly larger) substances eg. glucose, amino acids
● Move down a concentration gradient
● Through specific channel / carrier proteins
● Passive - doesn’t require energy from ATP / respiration (only kinetic energy of substances)
158
Explain the role of carrier and channel proteins in facilitated diffusion
● Shape / charge of protein determines which substances move
● Channel proteins facilitate diffusion of water-soluble substances
○ Hydrophilic pore filled with water
○ May be gated - can open / close
● Carrier proteins facilitate diffusion of (slightly larger) substances
○ Complementary substance attaches to binding site
○ Protein changes shape to transport substance
159
Describe how movement across membranes occurs by osmosis
● Water diffuses / moves
● From an area of high to low water potential (ψ) / down a water potential gradient
● Through a partially permeable membrane
● Passive - doesn’t require energy from ATP / respiration (only kinetic energy of substances)
160
What is water potential?
Water potential is a measure of how likely water molecules are to move out of a solution
161
What is the water potential of pure (distilled) water?
pure (distilled) water has the maximum possible ψ (0 kPa)
162
What effect does increasing solute concentration have on water potential?
increasing solute concentration decreases ψ
163
describe how movement across membranes occurs by active transport
● Substances move from area of lower to higher concentration / against a concentration gradient
● Requiring hydrolysis of ATP and specific carrier proteins
164
Describe the role of carrier proteins and the importance of the hydrolysis of ATP in active transport
165
Describe how movement across a membranes occurs by co-transport
1 ● Na + actively transported from
epithelial cells to blood (by
Na+/K+ pump)
● Establishing a conc. gradient
of Na+ (higher in lumen than
epithelial cell)
2 ● Na+ enters epithelial cell down
its concentration gradient with
glucose against its
concentration gradient
● Via a co-transporter protein
3 ● Glucose moves down a conc.
gradient into blood via
facilitated diffusion
166
Describe an example that illustrates co-transport
absorption of sodium ions and glucose (or amino acids) by cells lining the mammalian ileum
167
What type of active transport is the movement of sodium ions and why?
The movement of sodium can be considered indirect / secondary active transport, as it is reliant on a
concentration gradient established by active transport
168
Explain the adaptations of some specialised cells in relation to the rate of transport, across their internal and external membranes
● Cell membrane folded eg. microvilli in ileum → increase in surface area
● More protein channels / carriers → for facilitated diffusion (or active transport - carrier proteins only)
● Large number of mitochondria → make more ATP by aerobic respiration for active transport
169
Only what type of molecules can move by simple diffusion, across membranes
small molecules
170
Active transport involves what types of proteins?
only carrier proteins
171
What does cholesterol do?
decreases fluidity/ increases rigidity
172
Describe how to calculate dilutions
C1 x V1 = C2 x V2
173
Describe how you would use a 0.5 mol dm-3 solution of sucrose (stock solution) to produce 30 cm3 of a 0.15 mol dm-3 sucrose solution.
1. Calculate dilution factor (desired concentration / stock concentration): 0.15 / 0.5 = 0.3
2. Calculate volume of stock solution (dilution factor x final volume): 0.3 x 30 cm3 = 9 cm3
3. Calculate volume of distilled water (final volume - stock solution volume): 30 cm3 - 9 cm3 = 21 cm3
174
Describe a method to produce a calibration curve with which to identify the water potential of plant tissue (e.g: potato) and mention the control variables at each stage too [6]
1. Create a series of dilutions using a 1 mol
dm-3 sucrose solution (0.0, 0.2, 0.4, 0.6, 0.8,
1.0 mol dm-3)
2. Use scalpel / cork borer to cut potato into
identical cylinders
3. Blot dry with a paper towel and measure /
record initial mass of each piece
4. Immerse one chip in each solution and
leave for a set time (20-30 mins) in a
water bath at 30 degrees C
5. Blot dry with a paper towel and measure /
record final mass of each piece
6. Repeat (3 or more times) at each conc
7. Calculate % change in mass = (final - initial mass)/ initial mass
8. Plot a graph with concentration on x axis and percentage change in mass
on y axis (calibration curve)
9. Identify concentration where line of best fit intercepts x axis (0% change)
10. Use a table in a textbook to find the water potential of that solution
175
Why calculate the % change in mass? [2]
● Enables comparison / shows proportional change
● As plant tissue samples had different initial masses
176
Why blot dry before weighing? [2]
● Solution on surface will add to mass (only want to measure water taken up or lost)
● Amount of solution on cube varies (so ensure same amount of solution on outside)
177
Explain why there is an increase in mass of plant tissue when placed in different concentrations of solute? [2]
● Water moved into cells by osmosis
● As water potential of solution higher than inside cells
178
Explain why there is a decrease in mass of plant tissue when placed in different concentrations of solute? [2]
● Water moved out of cells by osmosis
● As water potential of solution lower than inside cells
179
Explain why there is no change in mass of plant tissue when placed in different concentrations of solute? [2]
● No net gain/loss of water by osmosis
● As water potential of solution = water potential of cells
180
Describe a method to investigate the effect of a named variable (e.g: temperature) on the permeability of cell-surface membranes [6]
1. Cut equal sized / identical cubes of plant tissue (eg. beetroot) of same age / type using a scalpel
2. Rinse to remove pigment released during cutting or blot on paper towel
3. Add same number of cubes to 5 different test tubes containing same volume of water (eg. 5 cm3)
4. Place each test tube in a water bath at a different temperature (eg. 10, 20, 30, 40, 50
degrees C)
5. Leave for same length of time (eg. 20 minutes)
6. Remove plant tissue and measure pigment release by measuring intensity of colour or
concentration of surrounding solution semi-quantitatively or quantitatively
181
How are semi-quantitative results produced? [2]
● Use a known concentration of extract and distilled water to prepare a dilution series
● Compare results with these ‘colour standards’ to estimate concentration
182
How are quantitative results produced? [3]
● Measure absorbance (of light) of known concentrations using a colorimeter
● Draw a calibration curve → plot a graph of absorbance (y) against concentration of
extract (x) and draw a line / curve of best fit
● Read off sample absorbance value on curve to find associated concentration
183
What are the issues with comparing to a colour standard [2]
- subjective
- bias
184
Why wash the beetroot before placing it in water? [2]
● Wash off any pigment on surface
● To show that release is only due to [named variable]
185
Why regularly shake each test tube containing cubes of plant tissue? [2]
● To ensure all surfaces of cubes remain in contact with liquid
● To maintain a concentration gradient for diffusion
186
Why control the volume of water? [2]
● Too much water would dilute the pigment so solution will
appear lighter / more light passes through in colorimeter
than expected
● So results are comparable
187
How could you ensure that the beetroot cylinders were kept at the same temperature throughout the experiment? [2]
● Take readings in intervals throughout experiment of temperature in tube using a digital thermometer / temperature sensor
● Use corrective measure if temperature has fluctuated
188
What does a high absorbance suggest about the cell-membrane? [2]
● More permeable / damaged
● As more pigment leaks out making surrounding solution more concentrated (darker)
189
Explain how temperature affects permeability of cell-surface membranes [5]
● As temperature increases, cell membrane permeability increases
○ Phospholipids gain kinetic energy so fluidity increases
○ Transport proteins denature at high temperatures as hydrogen bonds break,
changing their tertiary structure
● At very low temperatures, cell membrane permeability increases
○ Ice crystals can form which pierce the cell membrane and increase permeability
190
Explain how pH affects permeability of cell-surface membranes [2]
● High or low pH increases cell membrane permeability
○ Transport proteins denature as H / ionic bonds break, changing tertiary structure
191
Explain how lipid-soluble solvents, e.g: alcohol affect permeability of cell-surface membranes
● As concentration increases, cell membrane permeability increases
● Ethanol (a lipid-soluble solvent) may dissolve phospholipid bilayer (creating gaps)
192
What is an antigen? [2]
● Foreign molecule / protein / glycoprotein / glycolipid
● That stimulates an immune response leading to production of antibody
193
How are cells identified by the immune system? [2]
● Each type of cell has specific molecules on its surface (cell-surface membrane / cell wall) that identify it
● Often proteins → have a specific tertiary structure (or glycoproteins / glycolipids)
194
What types of cells and molecules can the immune system identify? [4]
1. Pathogens (disease causing microorganisms) eg. viruses, fungi, bacteria
2. Cells from other organisms of the same species (eg. organ transplants)
3. Abnormal body cells eg. tumour cells or virus-infected cells
4. Toxins (poisons) released by some bacteria
195
Is phagocytosis a specific or non-specific immune response?
non-specific
196
Describe phagocytosis of pathogens [5]
1) Phagocyte attracted by chemicals / recognises (foreign) antigens on pathogen
2) Phagocyte engulfs pathogen by surrounding it with its cell membrane
3) Pathogen contained in vesicle / phagosome in cytoplasm of phagocyte
4) Lysosome fuses with phagosome and releases lysozymes (hydrolytic enzymes)
5) Lysozymes hydrolyse / digest pathogen
197
What does phagocytosis lead to? And what does this stimulate?
leads to presentation of antigens, where antigens are displayed on the phagocyte cell-surface membrane, stimulating the specific immune response (cellular and humoral response)
198
What type of response is carried out by T lymphocytes?
the cellular response
199
Describe the response of T lymphocytes to a foreign antigen [5]
T lymphocytes recognise antigen presenting cells eg. infected cells, phagocytes presenting antigens, transplanted cells, tumour cells etc.
Specific helper T cells with complementary receptors (on cell surface) bind to antigen on
antigen-presenting cell → activated and divide by mitosis to form clones which stimulate:
● Cytotoxic T cells → kill infected cells / tumour cells (by producing perforin)
● Specific B cells
● Phagocytes → engulf pathogens by phagocytosis
200
What type of response is carried out by B lymphocytes?
the humoral response
201
Describe the response of B lymphocytes to a foreign antigen [6]
B lymphocytes can recognise free antigens eg. in blood or tissues, not just antigen presenting cells.
1. Clonal selection:
○ Specific B lymphocyte with complementary receptor (antibody on cell surface) binds to antigen
○ This is then stimulated by helper T cells (which releases cytokines)
○ So divides (rapidly) by mitosis to form clones
2. Some differentiate into B plasma cells → secrete large amounts of (monoclonal) antibody
3. Some differentiate into B memory cells → remain in blood for secondary immune response
202
What are antibodies? [3]
● Quaternary structure proteins (4 polypeptide chains)
● Secreted by B lymphocytes eg. plasma cells in response to specific antigens
● Bind specifically to antigens forming antigen-antibody complexes
203
Explain how antibodies lead to the destruction of pathogens [5]
● Antibodies bind to antigens on pathogens forming an antigen-antibody complex
○ Specific tertiary structure so binding site / variable region binds to complementary antigen
● Each antibody binds to 2 pathogens at a time causing agglutination (clumping) of pathogens
● Antibodies attract phagocytes
● Phagocytes bind to the antibodies and phagocytose many pathogens at once
204
Explain the difference between the primary and secondary immune responses [7] and sketch a brief graph to illustrate it.
Primary - first exposure to antigen
○ Antibodies produced slowly & at a lower conc.
○ Takes time for specific B plasma cells to be
stimulated to produce specific antibodies
○ Memory cells produced
● Secondary - second exposure to antigen
○ Antibodies produced faster & at a higher conc.
○ B memory cells rapidly undergo mitosis to
produce many plasma cells which produce
specific antibodies
205
What is a vaccine? [2]
● Injection of antigens from attenuated (dead or weakened) pathogens
● Stimulating formation of memory cells
206
Explain how vaccines provide protection to individuals against disease [7]
1. Specific B lymphocyte with complementary receptor binds to antigen
2. Specific T helper cell binds to antigen-presenting cell and stimulates B cell
3. B lymphocyte divides by mitosis to form clones
4. Some differentiate into B plasma cells which release antibodies
5. Some differentiate into B memory cells
6. On secondary exposure to antigen, B memory cells rapidly divide by mitosis to produce B plasma cells
7. These release antibodies faster and at a higher concentration
207
Explain how vaccines provide protections for populations against disease [3]
● Herd immunity - large proportion of population vaccinated, reducing spread of pathogen
○ Large proportion of population immune so do not become ill from infection
○ Fewer infected people to pass pathogen on / unvaccinated people less likely to come in contact
with someone with disease
208
Describe the differences between active and passive immunity [5]
Active =
- initial exposure to antigen, e.g. vaccine or primary infection
- memory cells involved
- antibodies produced and secreted by B plasma cells
- slow; takes longer to develop
- long term immunity, as antibodies can be produced in response to specific antigen again
Passive =
- no exposure to antigen
- no memory cells involved
- antibody introduced from another organism, e.g. breast milk/ across placenta from mother
- faster acting
- short term immunity, as antibody hydrolysed (endo/exo/dipeptidases)
209
Explain the effect of antigen variability on disease and disease prevention [4] and give some examples of viruses that have this [1]
● Antigens on pathogens change shape / tertiary structure due to gene mutations (creating new strains)
● So no longer immune (from vaccine or prior infection)
○ B memory cell receptors cannot bind to / recognise changed antigen on secondary exposure
○ Specific antibodies not complementary / cannot bind to changed antigen
Example applications: yearly new flu vaccines developed, no vaccine for HIV, can catch a cold many times
210
Describe the replication of HIV in helper T cells [7]
1. HIV attachment proteins attach to receptors on helper T cell
2. Lipid envelope fuses with cell-surface membrane, releasing capsid into cell
3. Capsid uncoats, releasing RNA and reverse transcriptase
4. Reverse transcriptase converts viral RNA to DNA
5. Viral DNA inserted / incorporated into helper T cell DNA (may remain latent)
6. Viral protein / capsid / enzymes are produced
a. DNA transcribed into HIV mRNA
b. HIV mRNA translated into new HIV proteins
7. Virus particles assembled and released from cell (via budding)
211
What does AIDS stand for?
acquired immune deficiency syndrome
212
Explain how HIV causes the symptoms of acquired immune deficiency syndrome (AIDS)
● HIV infects and kills helper T cells (host cell) as it multiplies rapidly
○ So T helper cells can’t stimulate cytotoxic T cells, B cells and phagocytes
○ So B plasma cells can’t release as many antibodies for agglutination & destruction of pathogens
● Immune system deteriorates → more susceptible to (opportunistic) infections
● Pathogens reproduce, release toxins and damage cells
213
Explain why antibiotics are ineffective against viruses [3]
Viruses do not have structures / processes that antibiotics inhibit:
● Viruses do not have metabolic processes (eg. do not make protein) / ribosomes
● Viruses do not have bacterial enzymes / murein cell wall
214
What is a monoclonal antibody? [2]
● Antibody produced from genetically identical / cloned B lymphocytes / plasma cells
● So have same tertiary structure
215
Explain how monoclonal antibodies can be used in medical treatments [4]
● Monoclonal antibody has a specific tertiary structure / binding site / variable region
● Complementary to receptor / protein / antigen found only on a specific cell type (eg. cancer cell)
● Therapeutic drug attached to antibody
● Antibody binds to specific cell, forming antigen-antibody complex, delivering drug
216
Some monoclonal antibodies are also designed to do what? [1]
block antigens/ receptors on cells
217
Explain how monoclonal antibodies can be used in medical diagnosis [4] and give an example of this [1]
● Monoclonal antibody has a specific tertiary structure / binding site / variable region
● Complementary to receptor / protein / antigen found only on a specific cell type (eg. cancer cell)
● Therapeutic drug attached to antibody
● Antibody binds to specific cell, forming antigen-antibody complex, delivering drug
218
What does ELISA stand for?
enzyme- linked immunosorbent assay
219
What are the two types of ELISA test for antigens? [2]
direct and sandwich
220
Explain the use of antibodies in the ELISA (enzyme-linked immunosorbent assay) test to detect antigens (4 for one type & 5 for other type)
Direct ELISA:
1. Attach sample with potential antigens to well
2. Add complementary monoclonal antibodies with enzymes attached → bind to antigens if present
3. Wash well → remove unbound antibodies (to prevent false positive)
4. Add substrate → enzymes create products that cause a colour change (positive result)
Sandwich ELISA:
1. Attach specific monoclonal antibodies to well
2. Add sample with potential antigens, then wash well
3. Add complementary monoclonal antibodies with enzymes attached → bind to antigens if present
4. Wash well → remove unbound antibodies (to prevent false positive)
5. Add substrate → enzymes create products that cause a colour change (positive result)
221
What type of ELISA test is used for antibodies detection? [1]
indirect ELISA
222
Explain the use of antibodies in the ELISA test to detect antibodies [5]
1. Attach specific antigens to well
2. Add sample with potential antibodies, wash well
3. Add complementary monoclonal antibodies
with enzymes attached → bind to antibodies if
present
4. Wash well → remove unbound antibodies
5. Add substrate → enzymes create products that cause a colour change (positive result)
223
Suggest the purpose of a control well in the ELISA test [2]
● Compare to test to show only enzyme causes colour change
● Compare to test to show all unbound antibodies have been washed away
224
Discuss some general ethical issues associated with the use of vaccines and monoclonal antibodies [4]
● Pre-clinical testing on / use of animals - potential stress / harm / mistreatment
○ But animals not killed & helps produce new drugs to reduce human suffering
● Clinical trials on humans - potential harm / side-effects
● Vaccines - may continue high risk activities and still develop / pass on pathogen
● Use of drug - potentially dangerous side effects
225
Suggest some points to consider when evaluating methodology relating to the use of vaccines and monoclonal antibodies [5]
● Was the sample size large enough to be representative?
● Were participants diverse in terms of age, sex, ethnicity and health status?
● Were placebo / control groups used for comparison?
● Was the duration of the study long enough to show long-term effects?
● Was the trial double-blind (neither doctor / patient knew who was given drug or placebo) to reduce bias?
226
Suggest some points to consider when evaluating evidence and data relating to the use of vaccines and monoclonal antibodies [6]
● What side effects were observed, and how frequently did they occur?
● Was a statistical test used to see if there was a significant difference between start & final results?
● Was the standard deviation of final results large, showing some people did not benefit?
● Did standard deviations of start & final results overlap, showing there may not be a significant difference?
● What dosage was optimum? Does increasing dose increase effectiveness enough to justify extra cost?
● Was the cost of production & distribution low enough?
227
What is wrong with the statement ‘an antibody has an active site’?
An enzyme has an active site. An antibody has a binding site.
228
What is wrong with the statement ‘HIV replicates using the T helper cells machinery’?
This is too vague. Refer to specific processes, such
as transcription and translation.
229
What is wrong with the statement ‘a monoclonal antibody is a clone of an antibody’?
A monoclonal antibody by definition is produced by a clone of a
plasma cell. The antibody itself can't be considered a clone.
230
how does SA affect the rate of movement across cell membranes?
Increasing surface area of membrane increases rate of movement
231
how does number of carrier/channel proteins affect the rate of movement across cell membranes?
Increasing number of channel / carrier proteins increases rate of facilitated diffusion / active transport
232
how does diff in gradients of conc/water potential affect the rate of movement across cell membranes?
Increasing concentration gradient increases rate of simple diffusion
Increasing concentration gradient increases rate of facilitated diffusion
○ Until number of channel / carrier proteins becomes a limiting factor as all in use / saturated
● Increasing water potential gradient increases rate of osmosis
233
Describe the issues with comparing to
a colour standard. (2)
● Matching to colour standards is subjective
● Colour obtained may not match any of colour standards
234
Suggest why failure to thoroughly wash the well can result in a false positive
in the ELISA test (2)
● Antibody with enzyme remains / not washed out
● So substrate converted into colour product
235
what is a homologous pair of chromosomes? [1]
(two chromosomes that) cary the same genes
biology
flashcards
Decks in class (14)
# Cards
-
1. biological molecules161
-
2. cells235
-
3. exchange and mass transport202
-
4. genetic variation, protein synthesis and mutations259
-
5. energy transfers in & between organisms289
-
6. response to change to enviro264
-
7. genetics, populations, evolution and ecosystems1
-
8. control of gene expression1
-
estruch flashc213
-
a*38
-
required practicals21
-
maths, stats and equations36
-
essay2
-
kw sheets stuff1
