paper 1 Flashcards
Describe how a phagocyte destroys a pathogen present in the blood.
[3 marks]
- engulfs pathogen
- forms a phagosome and fuses with a lysosome
- hydrolytic enzymes (lysozymes) digest the pathogen
4 types of cells that stimulate an immune response?
- Pathogens
- Cells from other organisms/transplants
- Cells infected by a virus
- cancer cells
What is the role of the disulfide bridge in forming the quaternary structure of an antibody?
joins two different polypeptides
Give two advantages over using a TEM over a SEM
- higher resolution
- view internal structures
Statistical values that can be calculated from a set of data?
- Mean
- Median
- Mode
- Range
- Standard deviation
Null hypothesis for an experiment?
No significant difference between…
Statistical test to compare two mean values?
Students t-test
Order of highest to lowest blood pressure in blood vessels?
- Artery
- Arteriole
- Capillary
- Vein
Equation for cardiac output?
cardiac output = heart rate × stroke volume
Data evaluation questions
- does the data support/not support the statement?
- Negative/positive correlation?
- Correlation does not mean causation - other factors may be involved, for example…
- no statistical test?
- small sample size, so data may not be representative?
- Time frame?
- Unknown side effects?
- No control group?
- Initial conditions unknown?
- Only one species/size/gender tested, so data may not be representative?
The action of a carrier protein on the cell-surface membrane of the lining of the ileum that transports ions is linked to a membrane-bound ATP hydrolase enzyme.
Explain the function of this ATP hydrolase.
[2 marks]
- Converts ATP to ADP and Pi to release energy
- This energy is used for the active transport of ions
At X seconds, the pressure of the left ventricle is increasing, and the pressure in the aorta is higher than in the left ventricle. At X seconds, the rate of blood flow in the aorta has yet to increase - explain why.
[2 marks]
- Pressure is higher in the aorta than in the left ventricle
- So, the semi-lunar valve is closed
Method to investigate loss of pigment from a cell WITHOUT a colorimeter
[3 marks]
- Use known concentration of pigment solution
- Prepare dilution series
- Compare results with colour standards to give
concentrations
Describe the role of DNA polymerase in the semi-conservative replication of DNA.
[2 marks]
- Joins adjacent DNA nucleotides
- catalyses condensation reactions
- catalyses formation of phosphodiester bonds between adjacent nucleotides
Describe how an enzyme can be phosphorylated.
[2 marks]
- Attachment of inorganic phosphate
to the enzyme - Released from the hydrolysis of ATP
Why may a higher than normal concentration of cyclin D, an enzyme involved in activating DNA polymerase, result in the formation of a tumor?
[2 marks]
- DNA replication happens faster, shortening interphase
- Faster mitosis, which may lead to uncontrolled mitosis
- Results in mass of excessive cells
Labelled antibody
- Y shape - two long and two short chains
- binding site
- variable region/constant region/disulfide bridge labelled
Compare DNA in the nucleus of a plant cell with DNA in a prokaryotic cell, outlining 3 differences.
[3 marks]
Plant v prokaryote:
1. linear v circular
2. associated with histones v no histones
3. no plasmids v plasmids
4. introns v no introns
5. longer v shorter
Statistical test to determine whether or not X and Y are correlated?
Correlation coefficient
(e.g. Spearman’s rank)
Evaluating the use of a drug for the successful treatment of something
- What is the info/data showing?
- Dosage known?
- Clinical trials done?
- Effectiveness known?
- Side effects known?
- Are healthy cells affected?
- Is the test group representative (gender, sample size, etc.)?
Graph of oxygen affinity - curve is to the left
[2 marks]
- Higher affinity for oxygen (so haemoglobin dissociates oxygen less readily and more saturated at lower partial pressures of oxygen)
- Relate it to context of the question
e.g. allows aerobic respiration when diving in low partial pressures of oxygen
Purpose of a control experiment in an investigation?
[2 marks]
- As a baseline
- To show effect of…
Ways in which genetic diversity between species is measured?
- Comparing differences in the base sequence of DNA/mRNA
2.Compare observable characteristics - Compare primary structures of the same protein
Use the graph to explain how human mass at birth is affected by stabilising selection.
[3 marks]
- Most likely to be transferred to a special care unit are those under 2800g and over 4200g
- Extreme mass babies are least likely to survive and pass on their genes, so less likely to pass on their alleles
- Extreme mass at birth decrease in frequency in the population
Statistical test for comparing expected and observed data?
Chi-squared
Statistical test questions using given P values
[3 marks]
- The probability that the difference in …. is due to chance is more/less than 0.05
- So, reject (<0.05) /accept (>0.05) the null hypothesis
- … significantly affects …. (refer back to Q)
Use your knowledge of gas exchange in leaves to explain why plants grown in soil with very little water grow only slowly.
[2 marks]
- Stomata close
- Less carbon dioxide, so less photosynthesis, so less glucose production
Using graph of oxygen affinity - curve to the right
- Haemoglobin has a lower affinity for oxygen
- Relate it to context of the question
Why would a smaller organism have a higher metabolic rate?
[3 marks]
- Smaller, so larger surface area to volume ratio
- More heat loss
- Faster rate of respiration (to release heat)
General control variables?
- Temperature of…
- pH of …
- Size of…
- Species/age/organism/gender/health of….
Evidence and explanations from a diagram that a cell is undergoing mitosis
- Individual chromosomes are visible as they have condensed
- each chromosome is made up of two chromatids as DNA has replicated
- The chromosomes are not arranged in homologous pairs, which they would be if it was meiosis
The dark stain used on the chromosomes binds more to some areas of the chromosomes than others, giving the chromosomes a striped appearance.
Suggest one way the structure of the chromosome could differ along its length to result in the stain binding more in some areas.
- Differences in base sequences
- Differences in histone interactions
- Differences in condensation
What is a homologous pair of chromosomes?
Two chromosomes that carry the same genes (for the same characteristics at the same loci)
Formation of an enzyme-substrate complex increases the rate of reaction.
Explain how.
[2 marks]
- Reduces activation energy
- By bending bonds
Directional selection
[3 marks]
- Context of question - what extreme/specific thing has been selected?
- These (survive, reproduce and) pass on the alleles for…
- Frequency of the alleles for… increases in the population
Obtaining a more accurate estimate of a value of ___ to ___, given it has been found from an experiment that ___ was needed?
[2 marks]
- Test several values between __ and __
- Repetitions of each
Describe how to produce a calibration curve and how you would use it to find the concentration of ____ in _____ .
[3 marks]
- Produce known concentrations of ____
- Measure absorbance of each concentration
- Plot a graph of absorbance on the y-axis against concentration on the x-axis and draw a curve
- Use absorbance of sample to find ____ concentration from the curve
Explain why all body cells would have a genetic mutation.
[2 marks]
- Mutation in the gamete that formed the zygote
- All body cells derived from this zygote by mitosis
Give the two types of molecule from which a ribosome is made.
One of RNA, and one of ribosomal protein
Describe the structure of glycogen.
[2 marks]
- Polysaccharide of α-glucose
- Joined by glycosidic bonds
- Branched structure
Suggest how glycogen acts as a source of energy.
Do not include transport across membranes in your answer.
[2 marks]
- Hydrolysed to glucose
- Glucose used in respiration
Sodium ions from salt (sodium chloride) are absorbed by cells lining the gut. Some of these cells have membranes with a carrier protein called NHE3.
NHE3 actively transports one sodium ion into the cell in exchange for one proton (hydrogen ion) out of the cell.
Use your knowledge of transport across cell membranes to suggest how NHE3 does this.
[3 marks]
- Co-transport
- Uses the hydrolysis of ATP
- Sodium ion and proton bind to the protein
- Protein changes shape to move sodium ion and proton across the membrane
Mammals have some cells that produce extracellular proteases. They also have cells with membrane-bound dipeptidases.
Describe the action of these membrane-bound dipeptidases and explain their importance.
[2 marks]
- Hydrolyse peptide bonds to release amino acids
- Amino acids can cross the cell membrane
A new antibiotic against a bacteria is tested against the old antibiotic against the same bacteria. A bar chart is plotted, showing bars representing the number of bacteria alive for the control group, after treatment of the old antibiotic, and the new antibiotic.
Scientists suggested that both antibiotics should be used. Explain why.
- New/old bacteria does not kill all bacteria
- Resistant bacteria will reproduce to produce more resistant bacteria
- Use of both antibiotics is likely to kill most of the bacteria / unlikely that the bacteria is resistant to both the new and old antibiotic / one antibiotic will kill the bacteria resistant to the other antibiotic
3 comparisons of genetic diversity that would be used in order to generate a classification diagram based on genetic characteristics?
- Base sequence of DNA
- Base sequence of mRNA
- The amino acid sequence of proteins
Method to investigate the effect of a variable between two populations
- Use random samples from each population
- Use a large enough sample so they are representative of each population
- Something to standardise measured sample, e.g. use a quadrat, measure the masses, etc.
- Calculate a mean and standard deviation for each population
- Use the Student’s t-test
- Analyse whether there is a significant difference between the means of the two populations
Y is a protein. One function of Y is to transport cellulose molecules across the phospholipid bilayer.
Using information from Figure 3, describe the other function of Y.
[2 marks]
- Y is an enzyme
- That makes cellulose from β glucose
What is the evidence in Figure 3 that the phospholipid bilayer shown is part of the cell-surface membrane?
Cell wall forms outside the cell-surface membrane
Why may multiple samples taken in an experiment?
- So it is a representative sample
- To obtain a reliable mean
Suggest two precautions that should have been taken to ensure that a mean obtained from a sample of data was reliable.
[2 marks]
- Large sample size
- ____ chosen at random
- Repeat readings
Others, depending on context of Q:
1. Healthy individuals
2. Equal number of females and males/same sex
Cholesterol increases the stability of plasma membranes. Cholesterol does this by making membranes less flexible.
Suggest one advantage of the higher percentage of cholesterol in red blood cells compared with cells lining the ileum.
Red blood cells are free in the blood so cholesterol helps to maintain their shape
E. coli, a bacteria, has no cholesterol in its cell-surface membrane. Despite this, the cell maintains a constant shape. Explain why.
[2 marks]
The cell is unable to change shape as it has a rigid cell wall made of murein
What reducing sugar would you expect to be produced during chewing and why?
• Maltose
• Salivary amylase breaks down starch into maltose
Some cells lining the bronchi of the lungs secrete large amounts of mucus. Mucus contains protein.
Name one organelle that you would expect to find in large numbers in a mucus-secreting cell and describe its role in the production of mucus.
[2 marks]
• Golgi - packages proteins
• Ribosomes - site of protein synthesis
• Mitochondria - site of ATP synthesis
• Vesicles - transport of protein
Describe competitive and non-competitive inhibition of an enzyme.
[5 marks]
• Inhibitors prevent the formation of enzyme-substrate complexes
Competitive inhibitors…
• are a similar shape to the substrate, so bind to the active site of the enzyme
• Competitive inhibition can be overcome by adding more substrate
Non-competitive inhibitors…
• bind to a site on enzyme other than active site, changing the shape of the active site of the enzyme
• non-competitive inhibition cannot be overcome by adding more substrate
Explain how a decrease in the number of a specific organism may affect the genetic diversity of that organism.
[2 marks]
Smaller population, so decreased variety of alleles, so genetic diversity is decreased
Give two ways in which courtship behaviour increases the probability of successful mating.
- Attracts the same species
- Attracts the opposite sex
- Stimulates the release of gametes
- Indicates sexual maturity
- Formation of a pair bond between two organisms
Explain directional selection
• Extremes are favoured
• Extreme lower/higher than the mean is favoured (depends on context of Q)
Explain why the mixture is blended (homogenised) and filtered when carrying out ultracentrifugation.
• break cells open
• remove whole cells (and other debris)
Why may results be processed into percentages?
• makes results comparable
• initial ___ are different
(e.g. finding the water potential of potatoes using a sample of 5 potato cylinders and different concentrations of solutions - differences in final and initial masses would be recorded as percentage changes in mass)
What is the function of the coronary arteries?
[2 marks]
- Carry oxygen/glucose
- To heart muscle
The rise and fall in blood pressure in the aorta is greater than in the small arteries. Suggest why.
The aorta…
1. has a higher pressure (since it’s directly linked to the heart)
2. has elastic tissue
3. stretches and recoils
Although the speed of blood flow in an arteriole is greater than speed of blood flow in a capillary, blood does not accumulate in the arterioles.
Explain why.
- Many more capillaries than arterioles
- Cross-sectional area of capillaries is much greater than of arterioles
Other than causing slow blood flow, explain one advantage of capillaries being narrow.
[2 marks]
- Short distance between blood and outside of capillary
- Large surface area of blood in contact with walls of capillaries
- Fast diffusion
What factor limits the minimum internal diameter of the lumen of a capillary?
diameter of blood cell
How is pressure in the left ventricle related to blood flow into the aorta?
[2 marks]
- Ventricle pressure rises, then blood flows into the aorta, as the higher pressure causes the semilunar valve to open
- When ventricle pressure starts to fall, blood flow into the aorta starts to fall
How is the pressure in the left ventricle related to the thickness of the left ventricle wall?
[2 marks]
- Thickness of the wall increases because the ventricle wall contracts
- Contraction causes the increase in pressure
Describe and explain how centrifuging the culture allowed the scientists to obtain a cell-free liquid.
- Large / dense / heavy cells;
- Form pellet / move to bottom of tube (when centrifuged);
- Liquid / supernatant can be removed.
The scientists measured cell damage by measuring the activity of lysosomes. Give one function of lysosomes.
Break down toxins/
H. pylori cells produce an enzyme that neutralises acid.
Suggest one advantage to the H. pylori of producing this enzyme.
Is not damaged/destroyed by stomach acid
The scientists carried out a further investigation. They treated the liquid from strain A that releases toxins and neutralises stomach acid with a protein-digesting enzyme before adding it to a culture of human cells. No cell damage was recorded.
Suggest why there was no damage to the cells
Enzyme is broken down, so no toxin is produced, so toxin is a protein
The events that take place during interphase and mitosis lead to the production of two genetically identical cells. Explain how.
1.DNA replicated;
2. (Involving) specific / accurate / complementary base-pairing;
Accept: semi conservative replication
3. two identical / sister chromatids;
4. Each chromatid / moves / is separated to (opposite) poles / ends of cell.
Describe how you would use the student’s results of conc of sucrose and percentage change in mass of a potato to find the water potential of the potato tissue.
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).
Two ways pathogens cause disease
Release toxins
Kills cells
The same variety of barley was used in all the plots. Why was this important?
genetically similar not identical
3. (So) have similar salt tolerance / response to salt water / response to watering treatment;
4. (So) have similar yield / mass of seeds;
The scientists suggested that watering barley with diluted seawater might not be sustainable if repeated every year.
Do these data support this suggestion?
Data showed less yield with seawater
Irrigation with sea water / C / D increases concentration of salt in soil; Ignore reference to standard deviation / quality of the data.
2. Lower water potential in the soil linked to reduced uptake of water;
3. Salt concentration in the soil might / might not increase in the future;
4. Might decrease plant growth / yield in the future;
5. Less food / fewer seeds for future planting;
Push down hard on the cover slip, but do not push the cover slip sideways.” Explain why she was given this instruction
Push hard - Squashes tissue
Not sideways - Avoids cell rolling together
Explain why antibody B is important as a control in Elisa strip
Prevents false negative results
Shows antibody A moved up test strip
This gene is the 5 latency-associated transcript (LAT) gene that prevents programmed cell death of an infected nerve cell.
Scientists have found that transcription of the LAT gene produces a microRNA.
This microRNA binds to some of the nerve cell’s own mRNA molecules. These
mRNA molecules are involved in programmed cell death of nerve cells. The 10 scientists concluded that production of this microRNA allows HSV to remain in the
body for years.
The scientists concluded that production of this microRNA allows HSV to remain in the body for years (lines 10–12).
Explain how this microRNA allows HSV to remain in the body for years.
MicroRNA binds to cell’s mRNA (no mark)
1. (Binds) by specific base pairing;
2. (So) prevents mRNA being read by ribosomes; 3. (So) prevents translation / production of proteins; 4. (Proteins) that cause cell death.
Some cancer cells have a receptor protein in their cell-surface membrane that binds to a hormone called growth factor. This stimulates the cancer cells to divide.
Scientists have produced a monoclonal antibody that stops this stimulation.
Use your knowledge of monoclonal antibodies to suggest how this antibody stops the growth of a tumour.
- Antibody has specific tertiary structure / binding site / variable region;
Do not accept explanations involving undefined antigen
1 max - Complementary (shape / fit) to receptor protein / GF / binds to receptor protein / to GF;
Ignore: same shape as receptor protein / GF - Prevents GF binding (to receptor).
3
[6]
The percentage of the population vaccinated does not need to be 100% to be effective in preventing the spread of whooping cough.
Suggest why.
More people are immune / fewer people carry the pathogen;
So susceptible / unvaccinated people less likely to contact infected people.
When seals dive was does heart rate reduce for all organs except for the brain
Brain controls other organs so needs constant supply of oxygen
Lungs are used less as seal not breathing
Describe how oxygen in the air reaches capillaries surrounding alveoli in the lungs. Details of breathing are not required.
- Trachea and bronchi and bronchioles;
- Down pressure gradient;
- Down diffusion gradient;
- Across alveolar epithelium.
- Across capillary endothelium / epithelium.
During a TRANSLOCATION experiment, the scientists ensured that the rate of photosynthesis of their plants remained constant.
Explain why this was important.
Rate of photosynthesis related to rate of sucrose production; Rate of translocation higher when sucrose concentration is higher.
The people in group B were recovering from an asthma attack.
Explain how an asthma attack caused the drop in the mean Forces expiration
Muscle walls of bronchi / bronchioles contract; Walls of bronchi / bronchioles secrete more mucus; Diameter of airways reduced;
(Therefore) flow of air reduced.
High blood pressure leads to an accumulation of tissue fluid. Explain how.
- High blood pressure = high hydrostatic pressure;
- Increases outward pressure from (arterial) end of capillary / reduces
inward pressure at (venule) end of capillary; - (So) more tissue fluid formed / less tissue fluid is reabsorbed.
The volume of water passing over the gills increases if the temperature of the water increases. Suggest why.
Increased metabolism / respiration / enzyme activity
2. Less oxygen (dissolved in water);
The biologist concluded that there was a correlation between rate of ventilation of the gills and temperature of the water. A scatter diagram can be used to look for a
correlation but, in this investigation, it was not the appropriate graph for her data. Explain why.
There is only one dependent variable / there are not two dependent variables / water temperature is the independent variable / breathing rate is dependent on water temperature;
Water temperature plus breathing rate are not both properties of
fish
or
Describe how the scientists calculated the death rate from breast cancer for each country.
No. of deaths from breast cancer divided by total population × 100 000;
No. of deaths from breast cancer divided by all deaths × 100 000;
Sample and count deaths from breast cancer in 100 000 people;
Use the information provided to explain the effect that glycaemic load of the diet has on the risk of developing CHD.
Very high GL causes harmful lipids in the blood
Higher GL diets lead to) more (harmful) lipids (in blood), so greater risk of atheroma
Ignore reference to lipids in diet
2. Atheroma leads to blockage of coronary artery / increased risk of blood clot in coronary artery;
The rise and fall in blood pressure in the aorta is greater than in the small arteries.Suggest why
Aorta)
1. (is) close / directly linked to the heart / ventricle / pressure is higher / is
very high;
2. (Aorta has) elastic tissue;
Accept elasticity
Ignore reference to muscle
3. (Aorta has) stretch / recoil.
