Science Feedback — CID 0001

Q1(a) — Chemical tests for carbohydrates (6 marks, levels-based) 3/6 marks Level 2 Adequate

Student Answer

Starch iodine Btw orangey-brown -> bluish black Q1. (a) Describe the chemical tests that could be used to show the presence of the two types of carbohydrate in cake. Include a risk assessment in your answer. * Put a sample of the bread on a tray * Add a few drops of iodine * Put a sample of the bread in a test tube with distilled water * added a few drops of iodine solution and wait a few minutes. * If carbohydrate (starch) is present there will be a colour change from orangey-brown to bluish black. However it must be acknowledged that iodine is an irritant so wear gloves when using. Also the water may cause spillage which can lead to slips, therefore you should use the test tube rack to hold water in place. For the cake you should repeat the same test and do several times to remove anomalous results.

Strengths

Correctly described the chemical test for starch, including the reagent (iodine) and the positive colour change (orangey-brown to bluish-black).
Included a relevant risk assessment, identifying iodine as an irritant and spillage as a slip hazard, with appropriate precautions (wearing gloves, using a test tube rack).

Misconceptions

The student seems to have overlooked the requirement to test for a second type of carbohydrate (sugar).

Missing Points

The entire test for the second type of carbohydrate (sugar) is missing.
No mention of Benedict's reagent, the need for heating, or the positive colour change from blue to green/yellow/orange/red for the sugar test.

Examiner Feedback

This is a Level 2 answer. You have provided a clear and accurate method for testing for starch and included a good risk assessment. However, the question asks for tests for two types of carbohydrate. Because the test for sugar is completely missing, the method is incomplete and cannot achieve a higher level.

Model Answer (full marks)

To test for starch, add a few drops of iodine solution to a sample of cake. If starch is present, the iodine will change colour from orange-brown to blue-black. To test for sugar, crumble a sample of cake into a test tube with some water. Add Benedict's solution and heat the test tube in a water bath for a few minutes. If sugar is present, the solution will change colour from blue to green, yellow, orange, or brick-red. Risk assessment: Wear eye protection as Benedict's solution is an irritant and may spit upon heating. Use a water bath for even heating and to avoid burns from a hot test tube. Wear gloves as iodine is also an irritant.

Q1(b) — Dependent variable (1 mark) 0/1 marks Incorrect

Student Answer

how long it takes for the type of bread to break down by carbohydrase in mouth

Strengths

The student correctly identified that the variable being measured was related to time ('how long it takes').

Misconceptions

The student has confused the variable that was measured with the underlying biological process causing the result. They described the breakdown of bread by enzymes, not the perception of a sweet taste, which is what the experiment recorded.

Missing Points

The answer does not state that the time was measured until the bread tasted sweet, which is the specific requirement of the mark scheme.

Examiner Feedback

Your answer describes the biological process, but the dependent variable is what is measured in the experiment, which was the 'time taken for the bread to taste sweet'.

Model Answer (full marks)

The time taken for the bread to taste sweet

Q1(c) — Control variable (1 mark) 1/1 marks Correct

Student Answer

the size of the bread

Strengths

The student correctly identified a valid control variable that matches the mark scheme.

Examiner Feedback

The student correctly identified a valid control variable, which is the size of the bread.

Model Answer (full marks)

The size/mass of the piece of bread used each time

Q1(d) — Why bread tastes sweet (3 marks) 3/3 marks Excellent

Student Answer

the saliva glands release amylase. Amylase breaks down carbohydrates/starch (found in bread) into simple sugars. this is important as the sweet taste is the sugars which have been broken down from the starch.

Strengths

Correctly identifies that bread contains starch.
Correctly states that starch is broken down into simple sugars.
Correctly identifies the enzyme responsible as amylase and links it to saliva (via saliva glands).

Examiner Feedback

An excellent and complete explanation. You have correctly identified that amylase from saliva breaks down the starch in bread into sugars, which causes the sweet taste. You have earned all available marks.

Model Answer (full marks)

The bread contains starch. The starch is broken down into sugar (glucose/maltose) by amylase in the saliva. This sugar solution reaches the taste receptors on the tongue, which is why the bread tastes sweet.

Q1(e) — Why results not valid (1 mark) 1/1 marks Correct

Student Answer

The individual can not directly have the same amount of saliva at the same time. This is one not in control.

Strengths

The student correctly identified a key biological variable that affects the validity of the experiment, which is listed in the mark scheme.

Examiner Feedback

You have correctly identified that the amount of saliva produced is variable, which is a valid reason why the results may not be valid and is an accepted point on the mark scheme.

Model Answer (full marks)

The amount of saliva produced is variable.

Q2(a) — Two aseptic techniques (2 marks) 1/2 marks Partial

Student Answer

1. Wear gloves to or use antibacterial spray to stop the bacteria growing on your hands 2. Keep in a different petri dish so the salmonella/bacteria does not spread to food

Strengths

You correctly identified one valid aseptic technique: using antibacterial spray on hands, which is a method of disinfection.

Misconceptions

Your second point is not a recognised aseptic technique. Aseptic techniques are specific procedures to prevent unwanted microorganisms from contaminating the culture during the experiment, rather than general safety rules about containment.

Missing Points

You could have mentioned other techniques such as sterilising the Petri dish and agar before use, flaming the inoculating loop, or working near a Bunsen burner flame to create an updraft.

Examiner Feedback

You earned one mark for describing the use of antibacterial spray to disinfect hands. Your second point was not a valid aseptic technique for preventing contamination of the culture. To get the second mark, you could have described sterilising the equipment or working near a flame.

Model Answer (full marks)

1. Sterilise the Petri dish and culture medium before use. 2. Pass the inoculating loop or forceps through a flame before use.

Q2(b) — 37 degrees vs 25 degrees incubation (3 marks) 0/3 marks Needs Improvement

Student Answer

because the students can't culture the bacteria and the optimal temperature to do so is 25C but the scientists want to test the efficacy so they use at 37C to speed up rate of reaction

Misconceptions

The student incorrectly states that 25°C is the optimal temperature for bacteria.
The student does not understand the safety reason for using 25°C in schools.
The student uses the imprecise term 'rate of reaction' instead of 'rate of growth' or 'reproduction'.

Missing Points

37°C is human/body temperature.
Bacteria/Salmonella grow best/better at 37°C.
25°C is used to reduce/prevent the growth of harmful bacteria/pathogens (for safety).

Examiner Feedback

Your answer does not explain the reasons correctly. You need to state that 37°C is human body temperature, which is optimal for the growth of pathogens like Salmonella. The lower temperature of 25°C is used in schools as a safety measure to prevent the growth of these harmful bacteria.

Model Answer (full marks)

37C is human body temperature, and Salmonella/bacteria grow best at this temperature. Students use 25C instead because this is too low for human pathogens to grow well, reducing the risk of harmful bacteria growing in the school lab.

Q2(c) — Purpose of control disc (1 mark) 0/1 marks Incorrect

Student Answer

to indicate where the bacteria has or hasnt grown

Misconceptions

The student has described an observation (that you can see where bacteria has grown around the disc) rather than explaining the scientific purpose of the disc in the experiment.

Missing Points

The answer does not state that the disc is a 'control' or that it is used for 'comparison'.

Examiner Feedback

Your answer describes what is observed on the plate, but it does not explain the scientific purpose of including a disc with no antibiotic. This disc acts as a control to show that any inhibition of bacterial growth is due to the antibiotic and not the paper disc itself.

Model Answer (full marks)

It acts as a control, to show that the results are due to the antibiotic and not the paper disc itself.

Q2(d) — Why antibiotic A or B (1 mark) 0/1 marks Incorrect

Student Answer

as antibiotic kill bacteria and salmonella is a bacteria

Misconceptions

{'misconception': 'The student provided a general definition of what an antibiotic does rather than answering the specific question.', 'student_answer_extract': 'as antibiotic kill bacteria', 'explanation': 'The question asks why antibiotics A or B should be prescribed, which requires a comparison of their effectiveness against the other antibiotics tested. Simply stating that antibiotics kill bacteria does not explain why these particular ones were chosen.'}

Missing Points

{'point': 'The answer does not state that antibiotics A and B were the most effective.', 'suggestion': 'You needed to explain that A and B were chosen because they worked the best.'}
{'point': 'The answer does not refer to the evidence from the experiment (e.g., largest zone of inhibition or killing the most bacteria).', 'suggestion': 'You should have mentioned that these antibiotics killed the most bacteria or created the largest clear areas (zones of inhibition).'}

Examiner Feedback

Your answer explains what antibiotics do, but it does not explain why antibiotics A or B were the best choice in this experiment. You needed to state that they were the most effective because they killed the most bacteria, which is shown by the largest clear zones around them.

Model Answer (full marks)

Antibiotics A and B killed/prevented the growth of the most bacteria, shown by the largest zones of inhibition around their discs

Q3(a) — Two effects of anaerobic respiration (4 marks) 2/4 marks Adequate

Student Answer

1. increase in lactic acid is harmful the body so has to be removed through oxygenated blood / aerobic respiration 2. muscle fatigue increased blood circulation as the muscles are demanding more oxygenated blood but are not recieve as quickly or efficieny in comparison to anaerobic respiration.

Strengths

Correctly identified 'muscle fatigue' as an effect of anaerobic respiration.
Correctly identified 'increased blood circulation' as an effect of anaerobic respiration (accepted as equivalent to increased heart rate).

Misconceptions

The explanation provided describes the cause of anaerobic respiration (oxygen demand exceeding supply) rather than explaining the effects themselves.
The student does not link the build-up of lactic acid to muscle fatigue.
The student does not link the continued increased circulation to the need to break down lactic acid.

Missing Points

The reason for muscle fatigue, which is the build-up of lactic acid, was not stated in the explanation for that effect.
The reason for increased blood circulation, which is to provide oxygen to break down the built-up lactic acid, was not stated.

Examiner Feedback

You correctly identified two effects of anaerobic respiration: muscle fatigue and increased blood circulation, earning two marks. However, your explanations were incorrect. You needed to explain that muscle fatigue is caused by the build-up of lactic acid, and that the increased circulation is needed to transport oxygen to break down this lactic acid.

Model Answer (full marks)

1. Muscle fatigue/cramp occurs, caused by a build-up of lactic acid in the muscles. 2. Continued heavy/fast breathing occurs after exercise, to provide the oxygen needed to break down the built-up lactic acid (repay the oxygen debt).

Q3(b) — Type of cell from lymphocyte and tumour (1 mark) 1/1 marks Correct

Student Answer

Student ticked: Hybridoma

Strengths

Correctly identified that a hybridoma cell is formed from the fusion of a lymphocyte and a tumour cell.

Examiner Feedback

You have correctly identified the cell created as a hybridoma.

Model Answer (full marks)

Hybridoma

Q3(c) — Property of monoclonal antibody (1 mark) 1/1 marks Correct

Student Answer

Student ticked: A monoclonal antibody only binds to the anabolic steroid.

Strengths

The student correctly identified that the high specificity of monoclonal antibodies is the key property that makes them useful for diagnostic tests.

Examiner Feedback

You have correctly identified that the specificity of monoclonal antibodies, meaning they bind to only one specific molecule (the anabolic steroid in this case), is what makes them useful for this type of test.

Model Answer (full marks)

A monoclonal antibody only binds to the anabolic steroid.

Q3(d) — Purpose of control area in test strip (1 mark) 0/1 marks Incorrect

Student Answer

to see the dye move up/across colour change because the monoclonal antibodies are specific to one antigen the scientists can see if the antibodies also bind to the urine.

Misconceptions

The student has described an observation (a colour change) rather than explaining the purpose of the control line.
The student seems to confuse the purpose of a control with a general description of how the test works.

Missing Points

The answer does not state that the purpose of the control is to show that the test is working correctly.
The answer does not mention that the control prevents a false negative result.

Examiner Feedback

Your answer describes what happens at the control area (a colour change) but does not explain its purpose, which is to confirm that the test strip is working correctly.

Model Answer (full marks)

To show that the test is working correctly (and to prevent a false negative result).

Q4(e) — Calculate mass of chemical A (4 marks) 0/4 marks Needs Improvement

Student Answer

100g 60% = 1.2 6 parts = 1.2 1 part = 0.2 10 part = 2 ] 100g 2 x 2 = 4 g [A bar model is drawn showing 10 boxes, with 0.2 written in some. The first 6 boxes are bracketed and labelled 1.2] 4 / 1000 g ÷ 1000 Mass of chemical A = 0.004 mg

Misconceptions

{'description': "The student misinterpreted '60% of the mass shown' (which is 1.2g). Instead of calculating 0.6 x 1.2, they incorrectly assumed that 1.2g *is* 60% and then calculated what 100% would be.", 'student_work_evidence': '60% = 1.2\n6 parts = 1.2\n1 part = 0.2\n10 part = 2'}
{'description': 'The student used the wrong operation to convert from grams (g) to milligrams (mg). They divided by 1000 instead of multiplying by 1000.', 'student_work_evidence': '4 / 1000\ng ÷ 1000\nMass of chemical A = 0.004 mg'}

Missing Points

Did not correctly calculate the mass of chemical A in 100g of chlorotic leaves (0.6 x 1.2 = 0.72g).
Did not correctly calculate the mass of chemical A in 200g of chlorotic leaves (0.72g x 2 = 1.44g).
Did not correctly apply the conversion factor from grams to milligrams (multiply by 1000).
The final answer is incorrect.

Examiner Feedback

You have made errors at each stage of the calculation. First, you needed to find 60% of 1.2 g, which is 0.72 g. Second, this value should be doubled for 200 g of leaves, giving 1.44 g. Finally, to convert from grams to milligrams, you must multiply by 1000, not divide. The correct answer is 1440 mg.

Model Answer (full marks)

Mass in 100g of chlorotic leaves = 0.6 x 1.2 g = 0.72 g Mass in 200g of chlorotic leaves = 0.72 g x 2 = 1.44 g Mass in mg = 1.44 g x 1000 = 1440 mg Mass of chemical A = 1440 mg

Q5(a) — Meaning of limiting factor (1 mark) 0/1 marks Incorrect

Student Answer

Something which reduces the rate or amount of photosynthesis

Strengths

The student correctly identifies that a limiting factor is related to the rate of photosynthesis.

Misconceptions

The student uses the word 'reduces', which is incorrect. A limiting factor prevents the rate from increasing, it does not necessarily cause a reduction from a previous higher rate.
The student includes 'amount' of photosynthesis, but the definition of a limiting factor is specifically about the 'rate' of the reaction.

Missing Points

The core idea that the factor is preventing the rate from increasing is not clearly stated.
The alternative correct idea, that increasing the factor would increase the rate, is also not stated.

Examiner Feedback

Your answer is not precise enough. A limiting factor is something that prevents the rate of a reaction from increasing further, not something that 'reduces' the rate. The definition must refer to the 'rate' of the reaction.

Model Answer (full marks)

A factor that, if increased, would increase the rate of photosynthesis (or that currently prevents the rate from increasing further).

Q5(b) — Effect of temperature and CO2 on photosynthesis (4 marks) 1/4 marks Needs Improvement

Student Answer

as the carbon dioxide concentration increases the rate of photosynthesis also increases as the plant has more CO2 which is a necessary factor for the plant to perform photosynthesis. Also as the temperature increases from 15°C to 25°C the rate of photosynthesis also increases as it reaches its optimal temperature for rate of reaction.

Strengths

Correctly states that increasing carbon dioxide concentration increases the rate of photosynthesis.
Correctly states that increasing temperature from 15°C to 25°C increases the rate of photosynthesis.

Missing Points

The explanation for the effect of temperature does not mention increased kinetic energy of molecules or increased enzyme activity.
The explanation for the effect of carbon dioxide does not identify it as a substrate or reactant.
There is no mention or explanation of why the rate of photosynthesis plateaus.

Examiner Feedback

You correctly identified that increasing temperature or CO2 concentration increases the rate of photosynthesis, which earned one mark. However, your explanations lacked the required biological detail about enzymes, kinetic energy, or substrates, and you did not explain why the rate plateaus.

Model Answer (full marks)

Increasing temperature (with CO2 constant) increases the rate of photosynthesis, because it increases the rate of enzyme activity / kinetic energy of molecules. Increasing CO2 concentration increases the concentration of substrate/reactants available for photosynthesis. All the curves eventually plateau because another factor (such as chlorophyll) becomes limiting.

Q5(c) — Inverse square law MCQ (1 mark) 1/1 marks Correct/Incorrect

Student Answer

The student has ticked the box next to the formula: light intensity ∝ 1/distance².

Strengths

Correctly identified the mathematical relationship for the inverse square law.

Examiner Feedback

You have correctly identified the formula for the inverse square law.

Model Answer (full marks)

The correct box to tick is the one next to 'light intensity ∝ 1/distance²'.

Q6(a) — Time when insulin is high (1 mark) 1/1 marks Correct

Student Answer

Time = 1.7 hours

Strengths

The student has correctly identified a time from the (unseen) Figure 3 that falls within the acceptable range.

Examiner Feedback

Your answer of 1.7 hours is correct as it falls within the acceptable range of 1.1 to 2.0 hours.

Model Answer (full marks)

Any value between 1.1 and 2.0 hours, e.g. 1.5 hours

Q6(b) — Effect of high insulin on blood glucose (3 marks) 0/3 marks Needs Improvement

Student Answer

Effect: diabetes Explanation: if blood glucose concentration is too low and there is also too much insulin there will not be enough glucose for the body to function Margin notes: too much insulin. if glucagon -> glycogen into glucose

Misconceptions

{'student_error': "The effect of high insulin is 'diabetes'.", 'correction': 'Diabetes is a condition related to blood glucose regulation, not the direct effect of high insulin. The effect of high insulin is to lower blood glucose concentration.'}
{'student_error': "The explanation focuses on the consequences of low blood glucose ('not enough glucose for the body to function').", 'correction': 'The question asks for the mechanism by which insulin acts. Insulin causes glucose to be taken up by cells and converted into glycogen.'}
{'student_error': "The margin note 'glucagon -> glycogen into glucose' is incorrect.", 'correction': 'Insulin causes glucose to be converted into glycogen. Glucagon does the opposite, converting glycogen back into glucose.'}

Missing Points

{'point': 'The effect is that blood glucose concentration is lowered.', 'student_evidence': "The student wrote 'diabetes' and described blood glucose being 'too low' as a condition, not as the effect of insulin."}
{'point': 'The explanation is that glucose is taken in by cells OR converted to glycogen.', 'student_evidence': 'The student did not provide a correct mechanism. The margin note shows confusion between insulin and glucagon.'}
{'point': 'This process occurs in the cells/liver/muscles.', 'student_evidence': "The student mentioned 'the body', which is too general."}

Examiner Feedback

You have not correctly stated the effect of insulin on blood glucose. The effect is that the concentration is lowered. Your explanation describes the consequences of low blood sugar, not the mechanism by which insulin causes it. Insulin causes liver and muscle cells to take up glucose from the blood and convert it to glycogen for storage.

Model Answer (full marks)

Effect: blood glucose concentration is lowered. Explanation: glucose is taken in by cells and converted to glycogen for storage in the liver and muscles.

Q6(c) — Two ways to reduce Type 2 diabetes risk (2 marks) 2/2 marks Full marks

Student Answer

1. improve cardiovascular activity increase exercise 2. Reduce consumption of high cholesterol fatty sugary foods

Strengths

Correctly identified that increasing exercise is a way to reduce the risk of Type 2 diabetes.
Correctly identified that reducing the intake of sugary and fatty foods is a way to reduce the risk of Type 2 diabetes.

Examiner Feedback

Well done. You have correctly identified two distinct and valid ways to reduce the chance of developing Type 2 diabetes, earning full marks.

Model Answer (full marks)

1. Do more exercise. 2. Eat less carbohydrate/sugar (or a low-carbohydrate diet).

Q7(a) — Hormone from gland A (1 mark) 1/1 marks Correct

Student Answer

thyroxine

Strengths

Correctly identified the hormone produced by the thyroid gland (gland A).

Examiner Feedback

You have correctly named the hormone produced by gland A as thyroxine.

Model Answer (full marks)

Thyroxine

Q7(b) — Hormone from gland B (1 mark) 1/1 marks Correct

Student Answer

insulin

Strengths

Correctly identified a hormone produced by the pancreas.

Examiner Feedback

The student correctly named insulin as a hormone produced by the pancreas.

Model Answer (full marks)

Insulin (or glucagon)

Q7(c) — Hormonal contraception and infertility treatment (6 marks, levels-based) 1/6 marks Level 1 Needs Improvement

Student Answer

Main text: For in reproduction when the egg is matured by FSH and released by LH into the uterus. Oestrogen must rebuild the uterus lining to allow progesterone to maintain the lining. This is important so that the sperm cell can swim to the egg cell to fertilise the egg. However in the case of pregnancy the female may take pills with LH in it to stop the maturing of the egg (inhibits maturity of egg). Some infertile men may attempt to try sperm cell clinics if their sperm is infertile. Margin notes (left): -> Master gland, FSH ↓, LH ↓, { Oestrogen ↓, Progesterone ↓ Margin notes (bottom): hormonal contraception

Strengths

Identifies that 'pills' are used for contraception.
Correctly identifies the roles of FSH (maturing the egg) and LH (releasing the egg) in the normal menstrual cycle.

Misconceptions

States that contraceptive pills contain LH; they typically contain oestrogen and/or progesterone.
States that LH stops the maturing of the egg; LH actually triggers ovulation, while inhibiting FSH is what stops egg maturation.
The discussion of male infertility and sperm clinics is not relevant to the use of hormones for treatment as specified in the mark scheme.

Missing Points

A correct explanation of how hormonal contraceptives work (e.g., by inhibiting FSH and/or LH to prevent egg maturation and ovulation).
Any discussion of the use of hormones (FSH, LH, progesterone) to treat infertility (e.g., stimulating egg production for IVF).

Examiner Feedback

The answer is awarded a Level 1 mark as it identifies a method of hormonal contraception ('pills') but does not explain it correctly. The second part of the question, on the treatment of infertility using hormones, has not been addressed. The response mainly describes the normal menstrual cycle rather than how hormones are used to control it.

Model Answer (full marks)

Contraception: The pill contains oestrogen and/or progesterone, which inhibit the release of FSH and LH. Without FSH, eggs/follicles do not mature; without LH, ovulation does not occur - so there is no egg available to be fertilised. Infertility treatment: FSH is given to stimulate the maturation of several eggs/follicles, increasing the number of eggs available. LH is then given to trigger ovulation, allowing eggs to be collected for IVF, where they are fertilised outside the body and the embryo is implanted into the uterus. Progesterone may also be given to maintain the uterus lining and increase the chance of successful implantation.

Science Feedback Report

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