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Biology AS-LEVEL AQA 2017
Terms in this set (52)
Describe how you could use cell fractionation to isolate chloroplasts from leaf tissue.
1. How to break open cells and remove debris;
2. Solution is cold/isotonic/buffered;
3. Second pellet is chloroplast;
Name two structures in a eukaryotic cell that cannot be identified using an optical
Describe and explain the appearance of one of the chromosomes in cell X
1. Chromosome is formed of two chromatids;
2. (Because) DNA replication (has occurred);
3. (Sister) chromatids held together by
Describe what has happened during division 1 in Figure 3
1. Chromosomes in homologous pair;
2. One of each into daughter cells / haploid
Identify one event that occurred during division 2 but not during division 1.
Separation of (sister) chromatids / division of
Name two ways in which meiosis produces genetic variation.
1. Independent segregation (of homologous
2. Crossing over / formation of chiasmata;
What makes up a DNA molecule?
Phosphate, Base, Deoxyribose sugar.
Some populations of animals that have never been hunted show very low levels of
Other than hunting, suggest two reasons why populations might show very low levels
of genetic diversity
1. Population might have been very small/genetic
2. Population might have started with small
number of individuals / by one pregnant female
/ founder effect;
High blood pressure leads to an accumulation of tissue fluid. Explain how.
1. High blood pressure = high hydrostatic
2. Increases outward pressure from (arterial) end
of capillary/reduces inward pressure at (venule)
end of capillary;
3. (So) more tissue fluid formed /less tissue fluid is
Describe how you would test a piece of food for the presence of lipid.
1. Dissolve in alcohol, then add water;
2. White emulsion shows presence of lipid;
E. coli has no cholesterol in its cell-surface membrane. Despite this, the cell maintains
a constant shape. Explain why.
1. Cell unable to change shape;
2. (Because) cell has a cell wall;
3. (Wall is) rigid/made of peptidoglycan/murein;
A student investigated mitosis in the tissue from an onion root tip.
The student prepared a temporary mount of the onion tissue on a glass slide. She
covered the tissue with a cover slip. She was then given the following instruction.
"Push down hard on the cover slip, but do not push the cover slip sideways."
Explain why she was given this instruction.
1. Push hard - spread/squash tissue;
2. Not push sideways - avoid rolling cells
Aspartic acid and proline are both amino acids. Describe how two amino acids differ
from one another. You may use a diagram to help your description.
Have different R group;
Breathing out as hard as you can is called forced expiration.
Describe and explain the mechanism that causes forced expiration.
1. Contraction of internal intercostal muscles;
2. Relaxation of diaphragm muscles/of external
3. Causes decrease in volume of chest/thoracic
4. Air pushed down pressure gradient;
Newborn babies can be fed with breast milk or with formula milk. Both types of milk
contain carbohydrates, lipids and proteins.
• Human breast milk also contains a bile-activated lipase. This enzyme is thought to
be inactive in milk but activated by bile in the small intestine of the newborn baby.
• Formula milk does not contain a bile-activated lipase.
Scientists investigated the benefits of breast milk compared with formula milk.
The scientists used kittens (newborn cats) as model organisms in their laboratory
Other than ethical reasons, suggest two reasons why they chose to use cats as model
Two suitable suggestions;
1. (Are mammals so) likely to have same
physiology/reactions as humans;
2. Small enough to keep in laboratory / produce
enough milk to extract;
3. (Can use a) large number;
Before starting their experiments, the scientists confirmed that, like human breast milk,
cat's milk also contained bile-activated lipase.
To do this, they added bile to cat's milk and monitored the pH of the mixture.
Explain why monitoring the pH of the mixture could show whether the cat's milk
1. Hydrolysis of lipids produces fatty acids;
2. Which lower pH of mixture;
Suggest how a student would obtain data to give a more precise value for the index
of diversity of this habitat.
1. Take more samples and find mean;
2. Method for randomised samples described;
Explain why an antibody (A) attaches only to a protein found in species of Plasmodium (for example)
1. Antibody has tertiary structure;
2. Complementary to binding site on protein;
An Antibody B is important if this test shows a person is not infected with Plasmodium.
Explain why antibody B is important.
1. Prevents false negative results;
2. (Since) shows antibody A has moved up
strip/has not bound to any Plasmodium protein;
When a vaccine is given to a person, it leads to the production of antibodies against a
disease-causing organism. Describe how.
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 secretes large amounts of antibody;
7. B cell divides to form clone all
secreting/producing same antibody;
Describe the difference between active and passive immunity.
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
6. Active (can) take time to develop/work, passive
Some people cannot digest lactose when they are adult. They could digest lactose when they were children.Use your knowledge of water potential to explain why these adults get diarrhoea when they drink milk.
Low(er) water potential in lumen / intestine / gut; Water enters lumen / leaves (body) cells / by osmosis;
Describe how you could use the biuret test to distinguish a solution of the enzyme, lactase from a solution of lactose.
(Add Biuret reagent to both solutions) - no mark; Lactase / enzyme will give purple / lilac / mauve; OR Lactose / reducing sugar will not give purple / lilac / mauve / will remain blue;
Describe the path by which oxygen goes from an alveolus to the blood
Through alveolar epithelium; Through capillary epithelium/endothelium;
Explain why people with miner's lung have a lower concentration of oxygen in their blood.
(Thicker alveolar wall) - no mark (So) Longer diffusion pathway / slower diffusion;
In healthy lungs, a gradient is maintained between the concentration of oxygen in the alveoli and the concentration of oxygen in the lung capillaries. Describe how ventilation helps to maintain this difference in oxygen concentration
(alveolus) Brings in air containing a high(er) oxygen concentration;Removes air with a low(er) oxygen concentration;
Give one other way that helps to maintain the difference in oxygen concentration.
Circulation of blood / moving blood;
Explain how Mitochondrion help the cell to absorb the products of digestion
(Site of aerobic) respiration / ATP production / energy release; Active transport / transport against the concentration gradient;
Give two ways in which a pathogen may cause disease when it has entered the body
Produces toxins; Damages cells / tissues / example given e.g. cell lysis
Explain what is meant by antibodies that are referred to as monoclonal.
(Antibodies) produced from a single clone of B cells / plasma cells; OR (Antibodies) produced from the same B cell / plasma cell;
Tests using monoclonal antibodies are specific. Use your knowledge of protein structure to explain why.
(Specific) primary structure / order of amino acids; (Specific) tertiary / 3D structure; (So) Only binds to / fits / complementary to one antigen;
The tests using monoclonal antibodies allow vets to identify brucellosis while they are still on a farm. Explain the advantages of this.
(Rapid) treatment of carriers / infected cattle / disease; Can isolate / cull carriers / infected cattle; Infected (dairy) products not sold / consumed / tracked; Reduces spread of disease; No need to kill / prevents the death of non-infected animals;
The cardiac cycle is controlled by the sinoatrial node (SAN) and the atrioventricularnode (AVN). Describe how
1. SAN initiates heartbeat / acts as a pacemaker / myogenic; 2. (SAN) sends wave of electrical activity / impulses (across atria) causing atrial contraction; 3. AVN delays (electrical activity / impulses); 4. (Allowing) atria to empty before ventricles contract / ventricles to fill before they contract; 5. (AVN) sends wave of electrical activity / impulses down Bundle of His / Purkyne fibres; 6. (Causing) ventricles to contract (from base up) / ventricular systole;
What is atheroma and how may it cause myocardial infarction?
1. Cholesterol / plaque / lipoprotein / LDL / fatty material / cells; 2. In artery wall / under lining / endothelium of artery / blood vessel; 3. Atheroma linked to blood clot / thrombosis; 4. (Blocks) coronary artery / artery supplying heart muscle / tissue / cells; 5. Reduces oxygen / glucose supply (to heart muscle / tissues / cells); 6. (Heart muscle / tissue / cells) unable to respire / dies;
Give one advantage of using a TEM rather than a SEM.
Higher resolution / higher (maximum) magnification/ higher detail(of image);ORAllows internal details / structures within (cells) to be seen/ cross section to be taken;
Give one advantage of using a SEM rather than a TEM
Thin sections do not need to be prepared / shows surface of specimen / can have 3-D images;
Induced fit and lock and key are two models used to explain the action of enzymes. Describe the induced fit model of enzyme action
Active site/ enzyme not complementary;Active site changes(shape) / is flexible;(Change in enzyme allows) substrate to fit / E-S complex to form
Describe oneway that the lock and key model is different from the induced fit model.
Active site does not change (shape) / is fixed (shape)/is rigid/does not wrap around substrate / (already)fits the substrate / is complementary (before binding);
Explain, in terms of pressure, why the semilunar valves open.
Pressure is greater below valve/ in ventricle than (artery);
When a wave of electrical activity reaches the AVN, there is a short delay before a new wave leaves the AVN. Explain the importance of this short delay.
Allow atria to empty / contract / ventricles to fill; Before ventricles contract; OR Delays contraction of ventricles;Until after atria have contracted / ventricles have filled;
What is an unsaturated fatty acid?
Double bond(s);(Bonds) between carbon;
A student investigated the effect of putting cylinders cut from a potato into sodium chloride solutions of different concentration. He cut cylinders from a potato and weighed each cylinder. He then placed each cylinder in a test tube. Each test tube contained a different concentration of sodium chloride solution. The tubes were left overnight. He then removed the cylinders from the solutions and reweighed them. Before reweighing, the student blotted dry the outside of each cylinder. Explain why.
Water will affect the mass / only want to measure water taken up or lost;Amount of water on cylinders varies/ ensures same amount of water on outside;
The student calculated the percentage change in mass rather than the change in mass.Explain the advantage of this.
Allows comparison / shows proportional change;Idea that cylinders have different starting masses / weights;
The student carried out several repeats at each concentration of sodium chloride solution. Explain why the repeats were important.
(Allows) anomalies to be identified / ignored / effect of anomalies to be reduced/ effect of variation in data to be minimised; Makes the average / mean/ line of best fit more reliable/ allows concordant results;
HPV vaccine is offered to girls aged 12 to 13 Suggest why it is offered to this age group.
Girls are not sexually active / not likely to carry HPV / vaccine may not work if already infected/ few girls sexually active (at this age);
The vaccine is made from HPV types 16 and 18. Explain why this vaccine may not protect against other types of this virus.
Other (HPV) types have different antigens;No memory cells for other types / memory cells not activated;Antibodies cannot attach to antigen / correct antibodies not produced / antibodies are not complementary;
Three injections of the vaccine are given. Use your knowledge of immunity to suggest why.
More antigen;More memory cells;So more antibodies produced / antibodies produced quicker(if infected);
It will be many years before it can be shown that this vaccination programme has reduced cases of cervical cancer. Suggest two reasons why.
Cancer takes years to develop/ develops later in life;Takes time for females to become sexually active / females must become sexually active to obtain data;Few people / only teenagers vaccinated
Smear tests will continue to be offered to women, even if they have been vaccinated (lines 9 to 10). Suggest why women who have been vaccinated still need to be offered smear tests.
(Cervical cancer)can be caused by other types of HPV / other factors / example given;OR(Some) women may have been infected (with HPV) before receiving the vaccine;OR(As a precaution) in case vaccine does not work / a way of monitoring if the vaccine has worked
Suggest one reason why vaccinating a large number of people would reduce significantly the spread of HPV through the population
Virus cannot replicate / is destroyed / is not carried (in vaccinated people);Non-vaccinated people more likely to contact vaccinated people
Emphysema is another disease of the lungs. People with emphysema may feel weak and tired. Explain why
1Alveoli break down / collapse/ rupture / walls thicken; 2 Less surface area/ increases diffusion distance/ less diffusion; 3Loss of elastin / elastic tissue / elastase involved; 4(Alveoli/ lungs)cannot recoil / spring back / have reduced elasticity/ more difficult to expel air; 5Reduced diffusion gradient / air not replenished/ less air leaves lungs; 6Less oxygen enters blood/ tissues; 7Less respiration / less energy released / less ATP produced;
Pulmonary tuberculosis is a disease of the lungs.Describe the transmission and course of infection of pulmonary tuberculosis
1(Bacteria transmitted in) droplets/ aerosol;2(Bacteria) engulfed / ingested by phagocytes / macrophages; 3(Bacteria)encased in named structure e.g. wall / tubercle /granuloma /nodule;4 (Bacteria) are dormant /not active/ not replicating;5If immunosuppressed, bacteria activate / replicate/ released;6Bacteria destroy alveoli / capillary / epithelial cells;7(Leads to) fibrosis / scar tissue /cavities/calcification;8(Damage) leads to less diffusion /less surface area/ increases diffusion distance;9(Activation / damage allows bacteria) to enter blood / spreads(to other organs)
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