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Question 1

Read the passage below. Use the information in the passage and your own knowledge to answer the questions that follow.

Schistosomiasis

Schistosomiasis is an infection caused by a parasitic worm called a schistosome. The immature or larvae of the worm live in rivers and lakes in tropical parts of the world. The diagram shows the life cycle of the schistosome worm.

Some people in tropical parts of the world use water from these rivers and lakes for their daily lives. These people risk infection because the larvae burrow into their skin. The larvae are then transported to other parts of the body where they damage organs such as the kidneys, intestines, lungs and brain. The larvae develop into adult worms.

The adult worms lay eggs in the human body. Some of these eggs are destroyed by the immune system, but most eggs survive. These eggs can get into water if faeces or urine from infected people pass into rivers or lakes. In the water, the eggs develop into small larvae which grow inside freshwater snails. Larvae are released from the snails and infect any person they contact. These larvae develop into adult worms inside the human body.

Doctors diagnose schistosomiasis when they find eggs in the faeces or urine of infected people. Infected people also have blood cells in their urine and antibodies for the pathogen in their blood.

At present, the drug praziquantel is used to kill the worms. A dose of \(0.040\ \text{g}\) per kg of body mass is usually effective. With no treatment, affected organs can be permanently damaged, leading to death. It is estimated that 240 million people (in the world) have schistosomiasis. Every year \(8 \times 10^{-4}\) per cent of infected people die from the disease.

A vaccine is being developed using a plasmid. The plasmid has DNA inserted that makes a protein found on the body surface of the adult schistosome worm.

In one investigation, a vaccine made using the DNA plasmid was given to a group of infected people. The results showed a mean number of 21.53 worms per person in this group. In the control group, a mean number of 40.53 worms per person was found.

(a) Which process is affected if kidneys are damaged (line 8)?

A) digestion
B) mutation
C) ultrafiltration
D) vaccination

(b) Suggest three ways to reduce the risk of being infected by schistosomes.

(c) Name two different blood cells that would be found in the urine of infected people (line 17).

(d) An infected person has a body mass of \(120\ \text{kg}\). What dose of drugs would be effective for this person (lines 19 to 20)?

A) \(0.04\ \text{mg}\)
B) \(4.8\ \text{mg}\)
C) \(40\ \text{mg}\)
D) \(4800\ \text{mg}\)

(e) Using the estimated number of people in the world who have schistosomiasis (lines 21 to 22), calculate the number of people who die each year from schistosomiasis.

(f) Which of these is the correct description of a plasmid?

A) a circle of DNA
B) a circle of mRNA
C) a circle of protein
D) a circle of tRNA

(g) Explain how a vaccine could protect people from schistosomiasis (lines 24 to 25).

(h)(i) Suggest what is given to the control group (lines 27 to 29).

(ii) A scientist claims that the investigation proves the vaccine is effective against schistosomiasis (lines 27 to 29). Comment on this claim.

Most-appropriate topic codes (Edexcel IGCSE Biology):

• 2(h): Transport — parts (c) [Blood composition], (g), (h)(i) [Vaccination and immune response]
• 2(i): Excretion — part (a) [Kidney function]
• 1(b): Variety of living organisms / Pathogens — context of parasitic infection
• 5(c): Genetic modification — part (f) [Plasmids as vectors]
• Mathematical Skills (Appendix 3): — parts (d), (e) [Calculations]
• Experimental Skills & Evaluation (Section 4): — part (h)(ii) [Evaluating an investigation]
▶️ Answer/Explanation
Solution

(a) C (ultrafiltration)
A is incorrect because digestion is not a process in the kidneys.
B is incorrect because mutation is not a process in the kidneys.
D is incorrect because vaccination is not a process in the kidneys.

(b) An answer that makes reference to three of the following points:
• treat drinking water / boil water (before drinking) / do not drink water / drink bottled water / eq (1)
• sanitation / no faeces in water / no urine in water / eq (1)
• remove snails / eq (1)
• vaccination (1)
Additional guidance: Allow “do not go in infected rivers or lakes / cover skin when in water / avoid contact with affected water / only wash in clean water”.

(c) An answer that makes reference to two of the following points:
• red blood cells / rbc (1)
• white blood cells / wbc (1)
• lymphocytes (1)
• phagocytes / macrophages (1)

(d) D (4800 mg)
Calculation: \(120\ \text{kg} \times 0.040\ \text{g/kg} = 4.8\ \text{g} = 4800\ \text{mg}\)
A is incorrect because it is the wrong value.
B is incorrect because it is the wrong value.
C is incorrect because it is the wrong value.

(e) \(1920\) people
Working:
• \(8 \times 10^{-4}\% = 0.0008\%\)
• \(0.0008\% \text{ of } 240,000,000 = 0.000008 \times 240,000,000 = 1920\)
Allow 1 mark for: \(19200000 / 1920000 / 192000 / 192200 / 192 / 19.2 / 1.92 / 0.192 / 0.0192\)
Award full marks for correct numerical answer without working.

(f) A (a circle of DNA)
B is incorrect because it is not RNA.
C is incorrect because it is not a protein.
D is incorrect because it is not RNA.

(g) An explanation that makes reference to three of the following points:
• antigen (1)
• memory cells / lymphocytes (1)
• (secondary) immune response (1)
• more antibodies / antibodies made sooner / faster / faster immune response / eq (1)

(h)(i) • (a treatment with) no plasmid / no protein / only water / saline / eq (1)
Allow placebo vaccine / a placebo / plasmid with no gene / plasmid with no DNA / different DNA.

(h)(ii) An answer that makes reference to three of the following points:
• reduced numbers / eq (1)
• by 19 or by 47% / about 50% (1)
• schistosomes / worms, still present in body (1)
• no idea of group size / needs to be repeated (1)
• no idea of age / sex / health (1)
Additional Guidance:
Allow “reduces numbers of worms / worms decrease / lower number of worms after vaccine”.
Allow “more worms in control group”.
Allow “does not completely get rid of them”.
Allow “more testing / more people tested”.

Question 2

Blood clotting is an important process in humans. The process is controlled by enzymes.

(a) (i) Give two reasons why blood clotting is important. 

(ii) The optimum temperature for the enzymes involved in blood clotting is \(37^\circ C\). Sketch a graph to show how temperature affects the time taken for blood to clot.

(b) Some people cannot make the proteins needed for blood clotting. Cloning is used to produce large numbers of transgenic mammals. These transgenic mammals can make the human blood-clotting proteins. The human blood-clotting proteins can then be removed from the mammals’ milk and injected into people who cannot make the proteins.

(i) Explain why these mammals are described as transgenic. 
(ii) Describe how a mammal is cloned.

Most-appropriate topic codes (Edexcel IGCSE Biology):

• 2(h): Transport — Blood clotting (part a(i), a(ii))
• 2(c): Biological molecules — Enzymes (part a(ii))
• 5(c): Genetic modification (genetic engineering) — Transgenic organisms (part b(i))
• 5(d): Cloning — Cloning mammals (part b(ii))
▶️ Answer/Explanation
Solution

(a)(i) Two reasons from:

  • Prevent loss of blood / stops bleeding (1)
  • Prevent entry of pathogens / microbes / bacteria / viruses / fungi / prevent infections (1)

(a)(ii) Sketch graph showing a clear minimum (fastest clotting time) at \(37^\circ C\). The line should drop to a low point at \(37^\circ C\) and then rise on both sides.

(b)(i) An explanation that makes reference to:

  • (They have been given) genetic material / gene / allele / DNA / are genetically altered (1)
  • From human / a different species (1)

(b)(ii) An answer that makes reference to six of the following points:

  1. Use enucleated egg / empty egg / remove nucleus from egg / eq (1)
  2. Nucleus from body cell / diploid nucleus (placed into empty egg) / fuse adult cell with empty egg (1) (Ignore DNA)
  3. Use of electricity / shock (to fuse cells) (1)
  4. Cell division / mitosis (stimulated) (1)
  5. Embryo forms / develops (1)
  6. Embryo placed into uterus / womb (1)
  7. Surrogate mother (carries embryo to term) (1)

Award marks for any correct and relevant points describing the process of somatic cell nuclear transfer as used in cloning mammals (e.g., Dolly the sheep).

Question 3

The brain is part of the central nervous system.

(a) Name the other part of the central nervous system.

(b) Huntington’s disease (HD) is caused by a mutation in the gene for making a protein called huntingtin. This protein damages nerve cells in the brain. HD is caused by a dominant allele. A heterozygous parent and a homozygous recessive parent have a child.

(i) What is the probability of this child having HD? 

A) 0.0
B) 0.25
C) 0.5
D) 1.0

(ii) These parents have three more children. The key shows the possible sex and phenotype of the individuals with or without HD.

The family pedigree gives the predicted sex ratio and the predicted phenotype ratio for two of the children.

Complete the family pedigree by giving the predicted sex ratio and predicted phenotype ratio for the other two children.

(c) A drug can reduce the damage to nerve cells in the brains of people with HD. The drug binds to messenger RNA produced by the mutated gene for huntingtin protein. Suggest ways that this drug reduces damage to nerve cells in people with HD.

Most-appropriate topic codes (Edexcel IGCSE Biology):

• 2(j): Co-ordination and response — part (a)
• 3(b): Inheritance — parts (b)(i), (b)(ii), (c)
• 3(b): Protein synthesis — part (c)
• 2(j): Central nervous system — part (a)
▶️ Answer/Explanation
Solution

(a) spinal cord

(b)(i) C (0.5)
A is incorrect because 0.5 is the answer
B is incorrect because 0.5 is the answer
D is incorrect because 0.5 is the answer
Cross: Hh (heterozygous, HD) × hh (homozygous recessive, no HD). Probability of child inheriting H (HD) allele from heterozygous parent is \( \frac{1}{2} = 0.5 \).

(b)(ii) A diagram that makes reference to the following points:
• one circle and one square shown (1)
• two shapes unshaded (1)
For each of the two additional children, the predicted sex ratio is 1:1 (one male, one female). The predicted phenotype ratio for children from this cross is 1 with HD : 1 without HD. Therefore, for two more children, one is predicted to have HD and one without, with sexes not specified by probability.

(c) An explanation that makes reference to three of the following points:
• prevents translation / no translation (1)
• prevents ribosomes attaching (to mRNA) (1)
• prevents / no, codon binding to anticodon (1) Allow tRNA does not bind to mRNA
• prevents amino acids joining / amino acid chain not made (1)
• huntingtin / protein / polypeptide not made (1) Allow less huntingtin / protein made
The drug binds to the mutated mRNA, blocking the process of protein synthesis (translation). This prevents the formation of the harmful huntingtin protein, thereby reducing damage to nerve cells.

Question 4

A student investigates the effect of different colours of light on the rate of photosynthesis in a water plant.

This is the student’s method.

  • place a 1% sodium hydrogen carbonate solution in a boiling tube
  • cut a 5 cm length of pondweed and place it in the tube
  • place a lamp 10 cm from the tube containing the pondweed
  • leave the pondweed for 10 minutes until it starts to produce bubbles from the cut end
  • count the bubbles produced in one minute
  • count the bubbles for two more one minute periods

The student repeats the experiment three more times using filters in front of the lamp that let through either red light, blue light or green light.

These are the student’s results.

Colour of filterNumber of bubbles per minute
 Test 1Test 2Test 3Mean
no filter478480 
red48484246
blue55565054
green98109

(a) Write the balanced symbol equation for photosynthesis.

(b)(i) Anomalous results are not included in the calculation of the mean. Calculate the mean number of bubbles per minute for the lamp with no filter.
(ii) Explain the student’s results.
(iii) Give two abiotic variables that the student should control in her experiment.

(c)(i) Explain why measuring the rate of photosynthesis by counting bubbles may not be an accurate method to use.
(ii) Suggest an alternative method that the student could use to measure the rate of photosynthesis in her experiment.

Most-appropriate topic codes (Edexcel IGCSE Biology):

• 2(e): Nutrition in flowering plants — parts (a), (b)(ii)
• 2(g): Gas exchange in plants — part (c)(ii)
• 4 Assessment Information / Experimental Skills: — parts (b)(i), (b)(iii), (c)(i), (c)(ii)
• Appendix 3: Mathematical skills — part (b)(i)
▶️ Answer/Explanation
Solution

(a) 6CO2 + 6H2O → C6H12O6 + 6O2 (2)

(b)(i) 84 + 80 ÷ 2 = 82 (bubbles per minute) (2)

(b)(ii) An explanation that makes reference to four of the following points:

  • no filter has highest rate of photosynthesis / bubbling / oxygen (1)
  • (because) all light colours / wavelengths are present / has more light energy / most amount of light that can be absorbed (1)
  • green has low(est) rate of photosynthesis, because green light is not absorbed (1)
  • blue / red has a medium rate of photosynthesis because light is, absorbed / not reflected (1)
  • chlorophyll / chloroplast absorbs red / blue light / does not absorb green light (1)

(b)(iii) An answer that makes reference to two of the following points:

  • temperature (1)
  • carbon dioxide (1) Allow volume / amount / concentration of hydrogen carbonate
  • light intensity (1) Allow brightness of lamp / thickness of filter

(c)(i) An explanation that makes reference to two of the following points:

  • bubbles are different volumes / sizes (1)
  • O2 may dissolve in water (1)
  • bubbles may be CO2 not oxygen / may not be due to photosynthesis / other gases may be present (1) Allow bubbles may be due to respiration
  • easy to miscount / miss bubbles (1)
  • bubbles get trapped / stuck (1)

(c)(ii) An answer that makes reference to two of the following points:

    • use measuring cylinder / (gas) syringe / burette / graduated test tube (1)
    • (to measure) volume (1)

OR

  • use hydrogen carbonate indicator (1)
  • change colour (of hydrogen carbonate indicator) (1)
Question 5

(a) The table gives information about some hormones involved in the menstrual cycle.

Complete the table by giving the missing information.

HormoneName of structure that secretes hormoneFunctions of hormone
FSH……1 ……
2 stimulates oestrogen secretion
……pituitary1 ……
2 stimulates development of corpus luteum
……ovaries1 repairs lining of uterus
2 stimulates LH secretion
progesterone……1 maintains the lining of uterus
2 inhibits LH

(b) State what is meant by the term menstruation.

(c) A girl starts to ovulate at the age of 12 years and continues to ovulate until she reaches the age of 51 years.
[Assume her menstrual cycle is 28 days and she releases one egg per cycle.]
Estimate the maximum number of eggs she could release in her lifetime.
Give your answer to two significant figures.

(d) Give a reason why a female does not produce as many offspring as the number of eggs she releases.

Most-appropriate topic codes (Edexcel IGCSE Biology):

• 3(a): Reproduction — part (a), (b), (d)
• 4.10B: Roles of FSH and LH in the menstrual cycle — part (a)
• 4.9: Roles of oestrogen and progesterone in the menstrual cycle — part (a)
• 3.45B: Sources, roles and effects of hormones (ADH, FSH, LH) — part (a)
• Appendix 3: Mathematical skills — part (c)
▶️ Answer/Explanation
Solution

(a) Completed table:

HormoneName of structure that secretes hormoneFunctions of hormone
FSHpituitary1. stimulate follicle growth / mature eggs / develop eggs
2. stimulates oestrogen secretion
LH / Lutenising hormonepituitary1. cause ovulation / egg / ovum release / stimulate progesterone release
2. stimulates development of corpus luteum
oestrogen / estrogenovaries1. repairs lining of uterus
2. stimulates LH secretion
progesteroneovaries / corpus luteum / placenta1. maintains the lining of uterus
2. inhibits LH

(b) An answer that makes reference to one of the following points:
• blood loss once a month / monthly period
• breakdown of uterus lining / breakdown of endometrium
(Allow: passing out / shedding / loss of uterus lining / endometrium)

(c) Estimation of maximum number of eggs:
• Ovulating years: \( 51 – 12 = 39 \) years
• Days ovulating: \( 39 \times 365 = 14,235 \) days (or \( 39 \times 365.25 = 14,244.75 \))
• Number of cycles: \( \frac{14,235}{28} \approx 508.4 \)
• To 2 significant figures: \( \mathbf{510} \)
(Alternative method: \( \frac{365}{28} \approx 13.04\) cycles/year; \( 13.04 \times 39 \approx 508.6\); to 2 s.f. = 510)

(d) An answer that makes reference to one of the following points:
• not all eggs fertilised
• no sexual intercourse
• contraception
• no implantation
• miscarriages
• some eggs not fertile
(Allow: eggs fertilised by abnormal sperm)

Question 6

The diagram shows the path that the water takes when it is absorbed from the soil into the xylem of a plant.

(a) (i) Explain how root hair cells are adapted for efficient absorption of water. 
(ii) Explain how water is transported from the soil to the leaves. 

(b) Describe how you could determine the rate of water loss from a leafy shoot. 

Most-appropriate topic codes (Edexcel IGCSE Biology – Modular):

• 2(h): Transport — parts (a)(i), (a)(ii)
• 3.5B, 3.6B, 3.7B, 3.8B: Water absorption, transpiration, and factors affecting transpiration rate — parts (a)(i), (a)(ii), (b)
▶️ Answer/Explanation
Solution

(a)(i) An explanation that makes reference to two of the following points:

  • elongated / pointed / projections / extensions (1)
  • increase surface area (1)
  • thin wall for short diffusion path (1)
  • concentrated cell sap for osmosis (1)

(a)(ii) An explanation that makes reference to four of the following points:

  • water enters (root) by osmosis (1)
  • from dilute solution to more concentrated solution / from higher water potential to lower water potential (1)
  • (water) enters / moves up xylem (1)
  • water pulled up to leaf due to transpiration / pulled along transpiration stream (1)
  • (water vapour) exits through stomata (1)

(b) A description that makes reference to four of the following points:

  • use (bubble) / (weight) potometer (1)
  • cut shoot underwater / dry leaves / place mineral oil on surface of water (1)
  • measure distance moved by bubble (in cm) / mass lost / change in volume of water (1)
  • (in set) time (1)
  • repeat / calculate mean rate (1)
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