Mark Scheme Answers Flashcards
What environmental factors can be changed to increase the rate of growth (5)
- Increased concentration of glucose increases the rate of respiration
- Increased rate of oxygen which increases rate of respiration
- Increased temperature which increases enzyme activity
- Increased concentration of phosphate which increases ATP concentration
- Increased protein synthesis
Describe binary fission in bacteria (3)
- Circular DNA is replicated
- Plasmids are replicated
- Cytoplasm divides
Why is the cover slip pressed firmly down (1)
So a thin layer of cells are spread out and light can pass through
When counting cells for the mitotic index, what should be done to ensure accuracy (3)
- Examine large number of field views to ensure representative sample
- Repeat count to ensure figures are correct
- Method to deal with part cells shown at edge to standardise counting
What is a homologous pair of chromosomes (1)
Two chromosomes that carry the same genes
Describe asceptic techniques used in transferring a sample of broth culture on to an agar plate (3)
- Keep lid on Petri dish/open lid of Petri dish as little as possible to prevent unwanted bacteria contaminating the dish
- Wear gloves to prevent contamination from bacteria on hands to prevent the spread of bacteria outside the lab
- Use sterile pipette or flame the loop or neck of the container of the culture to maintain a pure culture of bacteria
Why must the cover slip be pushed hard (1)
To squash/spread
How is ATP used in cells (2)
- Muscle contraction
- Phosphorylation: To add phosphate to other substances and make them more reactive
What is the function of the thylakoid and stroma in photosynthesis (1)
Thylakoid: Light dependent reaction
Stroma: carbon fixation
How is starch formed in plants (1)
Many glucose molecules joined together/ from glucose in a condensation
How are palisade cells adapted for photosynthesis (2)
- Elongated cells
- Absorbs light energy
Compare and contrast the structure and properties of triglycerides and phospholipids (7)
- Both contain ester bonds (between glycerol and fatty acid)
- Both contain glycerol
- Fatty acids on both may be saturated or unsaturated
- Both are insoluble in water
- Both contain C,H and O but phospholipids also contain P
- Triglycerides are hydrophobic/non-polar and phospholipids have hydrophilic and hydrophobic regions
- Phospholipids form mono layer/ micelle/ bilateral in water but triglycerides don’t
The movement of substances across cell membranes is affected by membrane structure. Describe how (7)
- Phospholipid bilayer allows movement/diffusion of non-polar/lipid soluble substances
- Phospholipid (bilayer) prevents movement/diffusion of polar/charged/lipid-insoluble substances
- Carrier proteins allow facilitated diffusion/co-transport
*Shape/charge of channel/carrier determines which substances move - Number of channels/carriers determines how much movement
- Membrane surface area determines how much diffusion/movement
- Cholesterol affects rigidity/fluidity/permeability
Suggest and explain a practical method to test for memory B cells (3)
- Add enzyme attached to (second) antibody against memory
- Colour change shows memory cell present
- Inject vaccine
What is a monoclonal antibody? (2)
- Antibodies with the same tertiary structure
- Clones/ identical B cells
Give one example of using monoclonal antibodies in a medical treatment (1)
- Targets/binds/carries drug/medicine to specific cells/antigens/receptors
A precipitate is produced in a positive result for reducing sugar in Benedict’s test. A precipitate is solid matter suspended in a solution.
Suggest a method, other than using a colorimeter, that a student could use to measure the quantity of reducing sugar in a solution. (2)
- Filter and dry the precipitate
- Find the mass/weight
Use of a colorimeter in an investigation will improve the repeatability of students results. Give reasons why? (3)
- Quantitative
- Colour change is subjective
- Standardises the method
Why must a homogenous solution be isotonic? (1)
For the same water potential/to prevent lysis/bursting of organelle
Describe how the structure of protein depends on the amino acids it contains (8)
- Structure is determined by (relative) position of amino acid/R group/interactions
- Primary structure is sequence/order of amino acids
- Secondary structure formed by hydrogen bonding (between amino acids)
- Tertiary structure formed by interactions (between R groups)
- Creates active site in enzymes
- Creates complementary/specific shapes in antibodies/carrier proteins/receptor (molecules)
- Quaternary structure contains >1 polypeptide chains
- Quaternary structure formed by interactions/bonds between polypeptides
A competitive inhibitor decreases the rate of an enzyme-controlled reaction. Explain how. (3)
- Inhibitor has a similar shape to substrate
- Fits/binds to active site
- Reduces/prevents enzyme substrate complexes from forming
Suggest appropriate units a student should use to compare the distribution of stomata on leaves (2)
- Stomata per mm2 or cm2
- Number per mm2 or cm2
Pieces of a leaf tissue that were examined were thin. Explain why this was important (2)
- Single/few layer of cells
- To allow light to pass through
Give two reasons why it is important that the student counted the number of stomata in several parts of each piece of leaf tissue (2)
- To produce reliable results
- So the distribution may not be uniform so it can be representative
HIV attaches to a specific protein receptor on helper T cells. A low percentage of people have a mutation of the CCR5 gene which codes for this protein receptor. This mutation results in a non-functional protein receptor.
Explain how this mutation can result in the production of a non-functional proteins receptor (4)
- Change in DNA base/nucleotide sequence
- Change in amino acid (sequence)/primary structure
- Alters (position of) hydrogen/ionic/disulphide bonds
- Change in tertiary structure of receptor
The frequency of the CCR5 mutation is highest in Europe. Scientists have collected data on the history and number of HIV infections in Europe. Using these data, scientists have concluded that the high frequency of the CCR5 mutation is not due to natural selection in response to HIV.
Suggest two reasons why scientists reached this conclusion (4)
- HIV has only been present for a short time period
- Mutation/CCR5 has been around for many years
- Mutation/CCR5 is advantageous for something else
Give the structure of HIV (5)
- RNA as genetic material
- Reverse transcriptase
- Capsid
- viral envelope
- Attachment proteins
Use your knowledge of ELISA test to suggest and explain how scientists identified the cells that have BrdU in their DNA (3)
- Add antibody (anti-BrdU with enzyme attached to cells/DNA
- Wash cells TO remove excess/unattached antibody
- Add SUBSTRATE to cause colour change
What is vaccination? (1)
An antigen
What is an antigen? (1)
an antigen is (usually a protein) presented on the cell surface membrane that can be recognized as self/non-self by the immune system. Non-self antigens can trigger an immune response
Define simple diffusion and co-transport (2)
- Simple diffusion: simple diffusion of small/non-polar molecules down a concentration gradient
- Co-transport: co-transport of 2 different substances using a carrier protein
Explain the function of ATP hydrolase in a carrier protein (2)
- Releases energy by the hydrolysis of ATP to form ADP to Pi
- Energy allows ions to be moved against a concentration gradient
Explain how the movement of Na+ out of the cell allows the absorption of glucose into the cell lining the ileum (knowledge) (3)
- Maintains/generates a concentration/diffusion gradient for Na+
- Na+ moving in by facilitated diffusion and brings glucose with it
- Na+ moving in by co-transport brings glucose with it
Give one similarity in the movement of substances by diffusion and by osmosis (2)
- Both are passive processes
- Does not require energy from ATP
Explain how a monoclonal antibody would prevent a protein from working (2)
- Monoclonal antibody has a specific tertiary structure complementary to the protein
- Binds to/ forms a complex with the protein
Describe how a control group can be treated (1)
Placebo injection
Changes to the protein coat of the influenza virus cause antigenic variability. Explain how antigenic variability has caused some people to become infected more than once with influenza viruses. (3)
- memory B / T cells do not recognise (new antigens);
- antibodies previously produced are not effective
- as shape not complementary to new antigen;
Describe the role of phagocytes in stimulating B lymphocytes (1)
Antigen in membrane is presented to lymphocytes
Explain the role of organelles in in the immune response (4)
- mitochondria provide (more) ATP / energy;
- (more) RER / ribosomes synthesise proteins;
- (more) Golgi body secretes / modifies or packages proteins /
- produces glycoproteins;
(B lymphocytes) produces antibodies;
What is an antigen (2)
- protein / glycoprotein / glycolipid / polysaccharide / molecule;
- on surface / membrane (of cell);
causes immune response / description / triggers antibody
production;
What is a monoclonal antibody (2)
- A protein / immunoglobulin specific to an antigen;
- Produced by B cells/ secreted by plasma cells
Explain why this test detects prostate cancer, but not any other disease. (antigen PSA) (2)
- antibodies specific / only binds to PSA;
- PSA only associated with prostate cancer / not with other
diseases;
Explain why there will not be a colour change if the blood sample does not contain PSA. (1)
- antibody with enzyme only attaches - - if PSA present / washed
away if no PSA;
no colour change without enzyme;
Describe how the complementary strand of HIV DNA is made. (6)
- DNA double stranded/double helix and RNA single-stranded;
Contrast requires both parts of the statement
- DNA (very) long and RNA short;
Accept ‛RNA shorter’ or ‛DNA bigger/longer’
- Thymine/T in DNA and uracil/U in RNA;
- Deoxyribose in DNA and ribose in RNA;
R Deoxyribonucleic/ ribonucleic acid
Ignore ref. to histones
Ignore ref. to helix and straight chain alone
- DNA has base pairing and RNA doesn’t/ DNA has hydrogen bonding and mRNA doesn’t;
- DNA has introns/non-coding sequences and RNA doesn’t;
Ignore ref to splicing
Explain why there is a significantly low number of antibodies after a first dose of vaccine (1)
- (Sample 2 / primary response / after first dose) activation / clonal selection / expansion of B cells into plasma cells;
Explain why there is a significantly higher number of antibodies after the second dose of a vaccine (2)
- Plasma cells release antibodies;
- (Sample 3 / secondary response / after second dose) memory cells produce more antibodies / produce antibodies more quickly;
People with AIDS die because they are unable to produce an immune response to pathogens (lines 2-4). (4)
Explain why this leads to death
- Infected by / susceptible to (other) pathogen(s) / named disease caused by a pathogen (from environment);
Context is where immune system cannot prevent or stop these events
Allow attack / kill
- Pathogen(s) reproduce / cause diease (in host);
MPs not given in context of HIV
- Damage cells / tissues / organs;
- Release toxins;
Explain why antigenic variability might make a vaccine not effective against HIV (2)
- Antigen (on HIV) changes;
Accept mutates
2. (Specific) antibody / receptor no longer binds to (new) antigen;
Describe how the control group should have been treated. (3)
- Injection with salt solution
- Accept inject placebo in salt solution
- Otherwise treated the same.
Changes to the protein coat of the influenza virus cause antigenic variability. Explain how antigenic variability has caused some people to become infected more than once
with influenza viruses. (2)
Memory B cells do not recognise new antigens;
Antibodies previously produced are not effective
Changes to the protein coat of the influenza virus causes antigenic variability. Explain how antigenic variability has caused some people to become infected more than once with influenza virus (2)
- Memory B cells do recognise new antigens
- Memory B cells are not effective
- Takes a long time to produce new antibodies to new antigen
What is a monoclonal antibody (1)
reference to hybrid cell from tumour / cancer and B-lymphocyte / hybridoma; antibodies all the same / from one type of plasma cell; specific to / complementary to / fits only one antigen
Explain why this test detects prostate cancer but not any other disease (2)
- Antibodies are specific
- PSA only associated with prostate cancer
How is complementary base pairing formed?
When nucleotide bases pair
What is an antibody (2)
- A protein
- produced from B cells
What is the function of a vaccine
- Triggers an immune response so that anitbodies are RELEASED
People with AIDs die because they are unable to produce an immune response to pathogens, explain why this leads to death (3)
1. Infected by / susceptible to (other) pathogen(s) / named disease caused by a pathogen (from environment);
Context is where immune system cannot prevent or stop these events
Allow attack / kill
2. Pathogen(s) reproduce / cause diease (in host);
MPs not given in context of HIV
3. Damage cells / tissues / organs;
4. Release toxins;
Explain why a vaccine might not be effective against HIV when HIV rapidly enters the host cell (2)
1. (HIV enters cells) before antibodies can bind to / destroy it;
1. and 2. Relate to antibodies
2. Antibodies cannot enter cells (to destroy HIV) / stay in blood;
Explain why a vaccine might not be effective against HIV when HIV shows a lot of antigen variability? (2)
1. Antigen (on HIV) changes;
Accept mutates
2. (Specific) antibody / receptor no longer binds to (new) antigen;
Ignore SAFETY comments
OR
3. Many different strains of HIV / many antigens present on HIV;
4. Not possible to make a vaccine for all antigens / vaccine may not stimulate an antibody for a particular antigen
A tick is a small animal that bites humans and feeds on their blood. This results in
proteins from the tick saliva entering the human body.
Scientists have suggested one hypothesis for the allergic reaction to alpha-gal in
red meat. They think that an earlier immune response to a tick bite can cause a
person to have an allergic reaction to alpha-gal in red meat.
Suggest how one antibody can be specific to tick protein and to alpha-gal. (2)
- (Part of tick protein and alpha-gal) have a similar
shape/structure; - Antibody is complementary to both (tick protein
and alpha-gal)
OR
Antigen-binding site is complementary to both
(tick protein and alpha-gal)
OR
Antibody can form antigen-antibody complex with
both (tick protein and alpha-gal)
