unit 2 Flashcards
1
Q
Eukaryotic (eg human) cells compared with Prokaryotic (bacterium) (7)
A
- Bacterial cell is much smaller than a human cell; (or human cell is much larger than a bacterial cell) 2. Bacterial cell has a cell wall but human cell does not;
- Bacterial cell lacks a nucleus but human cell has a nucleus;
- Bacterial cell lacks membrane-bound organelles but human cell has membrane-bound organelles;
- Bacterial ribosomes smaller than human ribosomes / bacteria have 70S ribosomes whereas humans have 80S
- Bacterial DNA is circular but human DNA is linear
- Bacterial DNA is ‘naked’ whereas human DNA is bound to histones/proteins
2
Q
Eukaryotic - Describe the structure and function of the nucleus.(4)
A
Any four from Structure Nuclear envelope/double membrane (Nuclear) pores (in the membrane) Chromosomes/chromatin/(linear) DNA with histones Nucleolus/nucleoli Function Holds/stores genetic information for production of proteins DNA replication OR interphase Production of mRNA/tRNA OR transcription Production of rRNA/ribosomes;;;;
3
Q
Eukaryotic - Describe the role of one named organelle in digesting these bacteria. (3)
A
- Lysosomes;
- Fuse with vesicle; Accept phagosome for vesicle
- (Releases) hydrolytic enzymes;
4
Q
Eukaryotic - Identify two organelles in cells that enable the production of glycoproteins (1)
A
Rough endoplasmic reticulum/ribosomes and Golgi (apparatus/vesicles);
5
Q
Eukaryotic - Give two structures found in all prokaryotic cells and in all eukaryotic cells. (2)
A
- Cell(-surface) membrane; 2. Ribosomes; Ignore 70S
- Cytoplasm;
- DNA;
6
Q
Eukaryotic – Give one feature of the chloroplast that allows protein to be synthesised inside the cell
A
Mark in pairs, 1 and 2 OR 3 and 4
1. DNA;
2. Is not associated with protein/histones but nuclear DNA is chloroplast and describe one difference between this feature in the chloroplast and a eukaryotic cell. (2) OR Is circular but nuclear DNA is linear OR Is shorter than nuclear DNA;
3. Ribosomes;
4. Are smaller than cytoplasmic ribosomes;
7
Q
Eukaryotic - Eukaryotic cells produce and release proteins. Outline the role of organelles in the production, transport and release of proteins from eukaryotic cells.(4)
A
- DNA in nucleus is code (for protein);
- Ribosomes/rough endoplasmic reticulum produce (protein); Accept rER for ‘rough endoplasmic reticulum’
- Mitochondria produce ATP (for protein synthesis); 4. Golgi apparatus package/modify; OR Carbohydrate added/glycoprotein produced by Golgi apparatus; Accept body for ‘apparatus’
- Vesicles transport OR Rough endoplasmic reticulum transports;
- (Vesicles) fuse with cell(-surface) membrane;
8
Q
Eukaryotic – state three differences between DNA in the nucleus of a plant cell and DNA in a prokaryotic cell.(3)
A
Plant v prokaryote
1. (Associated with) histones/proteins v no histones/proteins;
2. Linear v circular;
3. No plasmids v plasmids; Do not credit if suggestion that prokaryotic DNA only exists as plasmids.
4. Introns v no introns;
5. Long(er) v short(er);
9
Q
Eukaryotic – Name the main biological molecule in the cell membrane (1)
A
Phospholipids;
9
Q
Eukaryotic – Describe the role of mitochondria in secreting a protein (1)
A
(Many mitochondria) release energy / ATP for movement of vesicles / synthesis of protein / active transport;
10
Q
Eukaryotic – Describe the role of golgi apparatus in secreting a protein (1)
A
(Many Golgi) vesicles transport protein / glycoprotein / milk to cell membrane / out of cell;
11
Q
Eukaryotic – Descirbe the role of the golgi apparatus in lipid absorption
A
- Modifies / processes triglycerides;
- Combines triglycerides with proteins;
- Packaged for release / exocytosis OR Forms vesicles;
12
Q
Prokaryotic - Name the main biological molecule in a bacterial cell wall (1)
A
Murein / glycoprotein;
13
Q
Prokaryotic - Give two features of all prokaryotic cells that are not features of eukaryotic cells.
A
Cytoplasm with no membrane-bound organelles Single, Circular DNA DNA free in the cytoplasm DNA that is not associated with proteins/histones A cell wall that contains murein
14
Q
Viruses – Give 2 features of all viruses (2)
A
- attachments proteins
- capsid
- nucleic acid
15
Q
Microscopes - How to measure objects using an eyepiece graticule (3)
A
- Use eyepiece graticule to measure the object e.g. nucleus or capillary
- Calibrate eyepiece graticule against stage micrometer
- Take a number of measurements and calculate the mean
16
Q
Microscopes - Advantages and Limitations of Transmission Electron Microscope (TEM) (6)
A
Advantages:
1. Small objects can be seen; 2. TEM has high resolution as wavelength of electrons shorter;
Limitations:
1. Cannot look at living cells as cells must be in a vacuum;
2. Must be thin specimen;
3. Preparation may create artefact;
4. Does not produce colour image;
17
Q
Microscopes - Comparison of TEM and optical microscope (8)
A
- TEM use electrons and optical use light;
- TEM allows a greater resolution;
- (So with TEM) smaller organelles/named cell structure can be observed
- TEM view only dead/dehydrated specimens and optical (can) view live specimens;
- TEM does not show colour and optical (can);
- TEM requires thinner specimens;
- TEM requires a more complex/time consuming preparation;
- TEM focuses using magnets and optical uses (glass) lenses;
18
Q
Microscopes – Advantage of electron microscope over optical microscope (2)
A
- High resolution;
- Can see internal structure of organelles
19
Q
Microscopes - The resolution of an image obtained using an electron microscope is higher than the resolution of an image obtained using an optical microscope. Explain why. (2)
A
Shorter wavelength between electrons; OR Longer wavelength in light rays;
20
Q
Microscopes - Describe and explain one difference between TEM and SEM (2)
A
- 3D image (with SEM), not 2D image OR Lower resolution (with SEM) OR (Only) surface visible with SEM, but internal structures visible with TEM;
- (Because) electrons deflected/bounce off (using SEM) OR Electrons transmitted/pass through (using TEM);
20
Q
Homogenisation – Conditions required for cell homogenisation (3)
A
- Ice-cold – Slows/stops enzyme activity to prevent digestion of organelles/mitochondria;
- Buffered – Maintains pH so that enzymes/proteins are not denatured;
- Same water potential – Prevents osmosis so no lysis/shrinkage of organelles/mitochondria;
20
Q
Homogenisation & Ultracentrifugation – How to separate mitochondria? (4)
A
- Break open cells/homogenise/produce homogenate;
- Remove unbroken cells/larger debris by filtration;
- Centrifuge highest density organelle nuclei obtained as pellet at slowest speed
- Mitochondria in 2nd pellet as less dense than nucleus/organelle in first pellet;
21
Q
Suggest why scientists can use detergent to break open cells instead of homogenisation (2)
A
- Cell membranes made from phospholipid;
- (Detergent) dissolves membranes / phospholipid (bilayer);
21
Viruses - Describe viral replication.(4)
1. Attachment proteins attach to receptors; For ‘attachment protein’ accept gp41/gp120/ glycoprotein but ignore ‘receptor protein’. 2. Virus injects nucleic acid (into host cell); For this mp accept ‘genetic material’ for ‘nucleic acid’?
3. Host cell replicates viral nucleic acid; Accept ‘RNA/DNA’ for ‘nucleic acid’. 4. Host cell produces (viral) protein/capsid/enzymes;
5. Virus (particles) assembled and released (from cell);
22
Bacteria - Describe binary fission in bacteria. (3)
1. Replication of (circular) DNA; Accept nucleoid Reject chromosome Reject mitosis 2. Replication of plasmids;
3. Division of cytoplasm (to produce daughter cells);
22
Bacteria -Describe how bacteria divide.(2)
1. Binary fission;
2. Replication of (circular) DNA;
3. Division of cytoplasm to produce 2 daughter cells;
4. Each with single copy of (circular) DNA;
23
Eukaryotic division - What is a tumour? (2)
1. Mass of cells; Accept abnormal growth for ‘mass’ 2. Many cells in mitosis/dividing cells OR Uncontrolled cell division;
24
Eukaryotic division - Describe and explain the arrangement of the genetic material in prophase (2)
1. Chromosomes (are) becoming visible/distinct;
2. Because (still) condensing; OR Accept ‘chromosomes are condensed’ for 2 marks. Accept shorten or thicken for ‘condensed’
3. Chromosomes (arranged) at random/not lined up;
4. Because no spindle (activity); OR Because not attached to spindle fibres;
25
Eukaryotic division - Chromosome behaviour in all Stages (8)
(During prophase)
1. Chromosomes coil/condense/shorten/thicken/become visible;
2. (Chromosomes) appear as (two sister) chromatids joined at the centromere; (During metaphase)
3. Chromosomes line up on the equator/centre of the cell;
4. (Chromosomes) attached to spindle fibres;
5. By their centromere; (During anaphase)
6. The centromere splits/divides;
7. (Sister) chromatids/chromosomes are pulled to opposite poles/ends of the cell/separate;
(During telophase)
8.Chromatids/chromosomes uncoil/unwind/become longer/thinner;
26
Eukaryotic division - Describe the role of the spindle fibres and the behaviour of the chromosomes during mitosis (5)
1. (In) prophase, chromosomes condense; Accept chromatin for ‘chromosomes’ and for ‘condense’, shorten and thicken
2. (In) prophase OR metaphase, centromeres attach to spindle fibres;
3. (In) metaphase, chromosomes/pairs of chromatids at equator/centre of spindle/cell;
4. (In) anaphase, centromeres divide;
5. (In) anaphase, chromatids (from each pair) pulled to (opposite) poles/ends (of cell); Accept for ‘chromatids’, chromosomes but reject homologous chromosomes 6. (In) prophase/metaphase/anaphase, spindle fibres shorten;
27
Eukaryotic division – state name given to the division of cytoplasm during the cell cycle. (1)
cytokinesis
28
Eukaryotic division - Give two pieces of evidence that the cell was undergoing mitosis (2)
1. The (individual) chromosomes are visible because they have condensed;
2. (Each) chromosome is made up of two chromatids because DNA has replicated; 3. The chromosomes are not arranged in homologous pairs, which they would be if it was meiosis;
29
Eukaryotic division – Evidence for a cell in anaphase (2)
1. Chromosomes / chromatids are (in two groups) at poles of spindle / at ends of spindle; Do not accept ‘ends of cell’
2. V-shape shows that (sister) chromatids have been pulled apart at their centromeres / that centromeres of (sister) chromatids have been pulled apart.
30
Eukaryotic division – During the cell cycle, the amount of DNA in a cell changes. Explain how the behaviour of chromosomes causes these changes in the amount of DNA per cell (2)
(Increase)
1. Chromosomes / DNA replicates;
(First decrease)
2. Homologous chromosomes separate; (Second decrease)
3. Sister chromatids separate.
31
Eukaryotic division - Suggest why preventing the formation of spindle fibres stopped the cell cycle.
1.Chromosomes/centromeres cannot attach (to spindle) OR Chromosomes cannot line up (on spindle);
2. (So, no) metaphase; OR
3. Chromatids cannot separate (on spindle); Accept description of ‘cannot separate’ e.g cannot move to poles Ignore ‘split’ 4. (So, no) anaphase;
32
Eukaryotic division -– Req Prac 2 Suggest why the student soaked the root tips in hydrochloric acid
1. To break down links between/separate cell walls; 2. Allowing the stain to pass/diffuse into the cells OR
Allowing the cells to be (more easily) squashed;
33
Eukaryotic division - Suggest and explain how two environmental variables could be changed to increase the growth rate of cells. 4)
1. Increased (concentration of) glucose;
2. Increased respiration;
3. Increased (concentration of) oxygen;
4. Increased respiration;
5. Increased temperature;
6. Increased enzyme activity; 7. Increased (concentration of) phosphate;
8. Increased ATP/DNA/RNA; 9. Increased (concentration of) nucleotides;
10. Increased DNA synthesis;
34
Eukaryotic division – Describe the appearance of chromosomes in anaphase
(1)
Chromatids are being pulled to opposite poles/ends (of the cell) by spindles/spindle fibres;
35
Eukaryotic division -– Req Prac 2 Pressing the coverslip downwards enabled the student to observe the stages of mitosis clearly. Explain why.
1. To break down links between/separate cell walls; 2. Allowing the stain to pass/diffuse into the cells OR Allowing the cells to be (more easily) squashed;
36
Eukaryotic division -– Req Prac 2 using only the first 5 mm from the tip of an onion root.(1)
Where dividing cells are found / mitosis occurs;
OR
No dividing cells / mitosis in tissue further away / more than 5 mm from tip;
OR
To get (soft) tissue that will squash;
OR
Length that will fit under cover slip;
37
Eukaryotic division – Req Prac 2 -
Describe how you would determine a reliable mitotic index (MI) from tissue observed with an optical microscope.
Do not include details of how you would prepare the tissue observed with an optical microscope.
1. Count cells in mitosis in field of view;
2. Divide this by total number of cells in field of view;
3. Repeat many/> 10 times OR Select (fields of view) at random;
38
Eukaryotic division – Req Prac 2 -
Describe and explain what the student should have done when counting cells to make sure that the mitotic index he obtained for this root tip was accurate.
1. Examine large number of fields of view / many cells; Mark as pairs only Accept large number / 20 or more for many
2. To ensure representative sample; Accept typical / reliable OR
3. Repeat count;
4. To ensure figures are correct;
OR
5. Method to deal with part cells shown at edge /count only whole cells;
6. To standardise counting;
38
Eukaryotic division -The scientists measured the percentage change in tumour volume.
Suggest why they recorded both percentage change and tumour volume.(2)
Percentage change
1. To allow comparison as tumours may differ in volume/size (at the start of the investigation); Tumour volume
2. (As) tumours may differ in length/width/shape OR (As) volume is (best) indication of the number of cells in tumour;
39
Eukaryotic division – Req Prac 2 - suggest why different student may get a different mitotic index using the same methods (assume no errors) (2)
1. (Garlic) grown for different lengths of time OR (Garlic) grown in different conditions; Accept suitable descriptions of conditions, eg in different temperatures 2. The root tips from different (garlic) plants/roots/bulbs/species; 3. Single field of view is not representative of a root tip OR Different fields of view are different samples;
40
Membrane structure – Describe how proteins arrange themselves in the membrane (2)
1. Hydrophobic parts of helix/AP (to the outside) to sit within the (hydrophobic) fatty acid (tails) of the phospholipids;
2. Hydrophilic parts of helix/AP (to the inside) as ions are charged/polar/water soluble;
41
Membrane structure – Describe the role of cholesterol (1)
Cholesterol stabilises the membrane OR Cholesterol restricts the movement of molecules/phospholipids (making up the membrane);
42
Transport methods -
Name and describe five ways substances can move across the cell- surface membrane into a cell. (5)
1. (Simple) diffusion of small/non-polar molecules down a concentration gradient; If no reference to 'small/ non-polar' for
1. accept this idea from 'large/charged' given in description of 2.
2. Facilitated diffusion down a concentration gradient via protein carrier/channel; Reject if active rather than passive
3. Osmosis of water down a water potential gradient;
4. Active transport against a concentration gradient via protein carrier using ATP;
5. Co-transport of 2 different substances using a carrier protein;
43
Transport methods - The movement of substances across cell membranes is affected by membrane structure. Describe how. (5)
1. Phospholipid (bilayer) allows movement/diffusion of non-polar/lipid-soluble substances;
2. Phospholipid (bilayer) prevents movement/diffusion of polar/ charged/lipid-insoluble substances OR (Membrane) proteins allow polar/charged substances to cross the membrane/bilayer;
3. Carrier proteins allow active transport;
4. Channel/carrier proteins allow facilitated diffusion/co-transport;
5. Shape/charge of channel / carrier determines which substances move;
6. Number of channels/carriers determines how much movement;
7. Membrane surface area determines how much diffusion/movement;
8. Cholesterol affects fluidity/rigidity/permeability;
44
Transport methods - Give two similarities in the movement of substances by diffusion and by osmosis. (2)
1. (Movement) down a gradient / from high concentration to low concentration;
2. Passive / not active processes; OR Do not use energy from respiration / from ATP / from metabolism; OR Use energy from the solution;
45
Transport methods – What two factors affect the rate of facilitated diffusion (2)
1. (external) concentration
2. number of channel / carrier proteins
46
Transport methods - Suggest and explain two ways the cell-surface membranes of may be adapted to allow rapid transport of nutrients. (2)
1. Membrane folded so increased / large surface area; OR Membrane has increased / large surface area for (fast) diffusion / facilitated diffusion / active transport / co-transport;
2. Large number of protein channels / carriers (in membrane) for facilitated diffusion;
3. Large number of protein carriers (in membrane) for active transport;
4. Large number of protein (channels / carriers in membrane) for co-transport;
47
Transport methods - Describe how substances move across cell-surface membranes by facilitated diffusion. (3)
1. Carrier / channel protein; 2. (Protein) specific / complementary to substance;
3. Substance moves down concentration gradient;
48
Transport methods - Contrast the processes of facilitated diffusion and active transport. (3)
1. Facilitated diffusion involves channel or carrier proteins whereas active transport only involves carrier proteins;
2. Facilitated diffusion does not use ATP / is passive whereas active transport uses ATP;
3. Facilitated diffusion takes place down a concentration gradient whereas active transport can occur against a concentration gradient.
49
Transport methods - Why does inhibiting respiration/using cyanide prevent active transport? (4)
1. Oxygen is required for aerobic respiration which releases ATP
2. ATP is needed to change the shape of the protein carrier
3. Which would cause the release of the transported ion/molecule
4. So no ATP, no Active Transport
50
Req prac 3- How do we find water potential of plant tissue practically? (3)
1. Plot a graph with concentration on the x-axis and percentage change in mass on the y-axis;
2. Find concentration where curve crosses the x-axis/where percentage change is zero;
3. Use (another) resource to find water potential of sucrose concentration (where curve crosses x-axis);
51
Req prac 4 - Describe an experiment that you could do to investigate whether the mangrove root cells have a lower water potential than sea water.
You are given:
1.a piece of fresh mangrove root
2. sea water
3. access to laboratory equipment.
1. Record mass/length before and after;
2. Place in sea water for specified/equal time;
3. Remove surface water;
4. Increase in mass/length will show water has been absorbed by osmosis;
5. Repeat minimum of three times;
52
Req prac 4 - Give one way in which the student could ensure the first three beetroot cylinders were kept at 25 °C throughout her experiment. (1)
Measure temperature (in tube) at intervals and use appropriate corrective measure (if temperature has fluctuated);
53
Req prac 4 – How does a high temperature disrupt membranes (2)
(By) 70oC denaturing/altering membrane protein
OR (
By) 70oC increasing fluidity/permeability of membrane;
54
Req prac 4 - How does alcohol disrupt membranes (1)
(By) ethanol dissolving phospholipid bilayer
OR
(By acid) altering membrane protein;
55
Req prac 4 - Use your knowledge of membrane structure to explain how high temperature cause an increase in absorbance 1)
Higher absorbance indicates more pigment (released/in solution)
OR
Higher absorbance indicates more membrane damage/permeability
56
Req prac 4 - Explain why it is important to control the volume of water in each test tube (1).
1. (If) too much water the concentration of pigment (in solution) will be lower / solution will appear lighter / more light passes through (than expected);
OR
(If) too little water the concentration of pigment (in solution) will be greater / solution will appear darker / less light passes through (than expected);
2. So results (from different temperatures) are comparable;
57
Non-specific - Describe how a phagocyte destroys a pathogen present in the blood.(3)
1. Engulfs; Accept endocytosis OR Description Ignore ‘taken in’
2. Forming vesicle/phagosome and fuses with lysosome;
3. Enzymes digest/hydrolyse;
57
Non-specific - Phagocytosis (3
1. Phagosome/vesicle fuses with lysosome;
2. (pathogen) destroyed by lysozymes/hydrolytic enzymes;
3. Antigen (from pathogen) displayed on cell membrane (of phagocyte/antigen presenting cell);
58
Specific - Describe how presentation of a virus antigen leads to the secretion of an antibody against this virus antigen.
1. Helper T cell / TH cell binds to the antigen (on the antigen-presenting cell / phagocyte);
2. This helper T / TH cell stimulates a specific B cell; 3. B cell clones OR B cell divides by mitosis;
4. (Forms) plasma cells that release antibodies;
59
Specific - What is antigen? (2
1. Foreign protein;
2. (that) stimulates an immune response/production of antibody
60
Specific - What is antibody? (2)
1. A protein/immunoglobulin specific to an antigen;
2. Produced by B cells OR Secreted by plasma cells;
61
Specific - Antibody specificity (4)
1. Antibody has (specific) tertiary structure
2. Has binding site/ variable region which only binds to one antigen
3. Antigen is only found on this particular (pathogen/cell/tissue)
4. so antibody (only) binds to / forms antigen/antibody complex with these (pathogen/cell/tissue) destroying them
62
Specific - Antigen-Antibody
complex formation (4)
1. Antibody has 4 polypeptide chains and has a quaternary structure
2. Antibody has a variable region which has a specific amino acid sequence/primary structure 3. Shape of the binding site is complementary to the antigen
4. Forming an antigen-antibody complex
63
Specific - Humoral Response (6)
1. Antigen on surface of bacterium binds to surface protein / surface receptor on a (specific/single) B cell; 2. (Activated) B cell divides by mitosis / produces clone; 3. (Division) stimulated by cytokines / by T cells;
4. B cells/plasma cells release antibodies;
5. (Some) B cells become memory cells;
6. Memory cells produce plasma / antibodies faster;
64
Specific - Give two types of cell, other than pathogens, that can stimulate an immune response.(2)
1. (Cells from) other organisms/transplants;
2. Abnormal/cancer/tumour (cells);
3. (Cells) infected by virus;
4. Antigen presenting cells
65
Specific - Draw a labelled diagram of an antibody (3)
1. Y shape showing two long and two short (polypeptide) chains correctly positioned; 2. binding site labelled on the end of the branches of the Y of the antibody; Accept one or two being labelled, if two both must be correct.
3. Variable region labelled /Constant region labelled / Disulfide bridge/bond labelled;
66
Specific - Describe and explain the role of antibodies in stimulating
phagocytosis.
Do not include details about the process of phagocytosis.
1. Bind to antigen OR Are markers; Accept opsonin for ‘marker’ Accept form (antibody-antigen) complexes/are complementary to antigen 2. (Antibodies) cause clumping/agglutination OR Attract phagocytes;
67
Vaccines - Immunity – Compare Active and
Passive Immunity (6)
1. Active involves memory cells, passive does not;
2. Active involves production of antibody by plasma cells/memory cells;
3. Passive involves antibody introduced into body from outside/named source;
4. Active long term, because antibody produced in response to antigen;
5. Passive short term, because antibody (given) is broken down;
6. Active (can) take time to develop/work, passive fast acting;
68
Vaccines - Immunity – Compare Primary and Secondary Response (4)
1. Before vaccination no antibody released because patients not yet encountered vaccine/antigen/virus;
2. Primary response/after first dose) activation/clonal selection/expansion of B cells into plasma cells;
3. Plasma cells release antibodies;
4. Secondary response/after second dose) memory cells produce more antibodies/produce antibodies more quickly;
69
Vaccines - How a vaccine
produces an immune response (7)
1. Vaccine contains antigen from pathogen;
2. Macrophage presents antigen on its surface;
3. T cell with complementary receptor protein binds to antigen;
4. T cell stimulates B cell;
5. (With) complementary antibody on its surface;
6. B cell/plasma cell secretes large amounts of antibody; 7. B cell divides to form clone all secreting/producing same antibody;
70
Vaccines - Explain why giving children more than one vaccination develops good immunity (2)
1. (Production of more) memory cells; 2. (So) higher concentration of (circulating) antibodies in blood
OR
(So) rapid production of antibodies (on further infection)
71
Vaccines - Determining the genome of the viruses could allow scientists to develop a vaccine.
Explain how.(2)
1. (The scientists) could identify proteins (that derive from the genetic code)
OR
(The scientists) could identify the proteome;
2. (They) could (then) identify potential antigens (to use in the vaccine);
72
Vaccines - Describe how B lymphocytes would respond to vaccination
1. B cell (antibody) binds to (viral) specific/complementary receptor/antigen; Accept B cell forms antigen-antibody complex
2. B cell clones OR B cell divides by mitosis;
3. Plasma cells release/produce (monoclonal) antibodies (against the virus);
4. (B/plasma cells produce/develop) memory cells;
73
HIV - HIV treatment with anti-retroviral drug AZT (6)
1. Person (infected with HIV) has HIV DNA (in their DNA); 2. New HIV (particles) still made;
3. (AZT) inhibits reverse transcriptase;
4. (AZT) stops replication of HIV;
5. Stops destruction of more / newly infected T cells;
6. So immune system continues to work (and AIDS does not develop);
74
HIV - Describe how HIV is replicated (5)
1. Attachment proteins attach to receptors on helper T cell/lymphocyte;
2. Nucleic acid/RNA enters cell;
3. Reverse transcriptase converts RNA to DNA;
4. Viral protein/capsid/enzymes produced;
5. Virus (particles) assembled and released (from cell);
75
HIV - Describe how the human immunodeficiency virus (HIV) is replicated once inside helper T cells (TH cells). (4)
1. RNA converted into DNA using reverse transcriptase; Reject ‘messenger’ or ‘m’ before RNA
2. DNA incorporated/inserted into (helper T cell) DNA/chromosome/genome/nucleus;
3. DNA transcribed into (HIV m)RNA; Accept descriptions of transcription
4. (HIV mRNA) translated into (new) HIV/viral proteins (for assembly into viral particles);
76
HIV - Explain how HIV affects the production of antibodies when AIDS develops in a person. (3)
1. Less/no antibody produced;
2. (Because HIV) destroys helper T cells; Accept ‘reduces number’ for ‘destroys’
3. (So) few/no B cells activated / stimulated OR (So) few/no B cells undergo mitosis/differentiate/form plasma cells;
77
HIV - Describe the structure of the human immunodeficiency virus
(HIV).(4)
1. RNA (as genetic material); Reject nucleus/DNA/plasmids.
2. Reverse transcriptase;
3. (Protein) capsomeres/capsid; Reject capsule.
4. (Phospho)lipid (viral) envelope OR Envelope made of membrane; Reject if HIV has a cell membrane or a cell wall.
5. Attachment proteins;
78
MABs - What is a monoclonal antibody? (3)
1. Antibody specific/complementary to one antigen only
2. Antibodies all the same and from one original plasma cell
3. Derived from a hybridoma cell/fused B lymphocyte and cancer cell
79
MABs - Suggest monoclonal antibodies help scientists to identify target cells (4)
1. antigen in cell-surface membrane;
2. Antibody is complementary;
3. (So) binds/attaches to the ZO-1/protein;
4. (Cells identified with) dye/stain/fluorescent marker linked to antibody;
80
MABs – Suggest how one antibody can bind two different molecules (2)
1. have a similar shape/structure;
2. Antibody is complementary to both
OR
Antigen-binding site is complementary to both
OR
Antibody can form antigen-antibody complex with both
81
MABs - Explain why antibody will only bind to target cell
1. antibody has a (specific) tertiary structure;
2. Has binding site / variable region that only binds to / complementary to one antigen;
3. Antigen to this antibody (only) found on these nerve cells;
4. So, antibody (only) binds to / forms antigen-antibody complex with these cells
82
MABs - Describe the role of antibodies in producing a positive result in an ELISA test.(4)
1. (First) antibody binds/attaches /complementary (in shape) to antigen;
2. (Second) antibody with enzyme attached is added; 3. (Second) antibody attaches to antigen; Accept (second) antibody attaches to (first) antibody (indirect ELISA test).
4. (Substrate/solution added) and colour changes;
