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Edexcel iGCSE Biology 4BI1 - Paper 1B -Excretion- Exam Style Questions- New Syllabus

Edexcel International GCSE in Biology Paper 1B - All Chapters
Question

Cystic fibrosis (CF) is a condition that affects the mucus produced in the lungs and in other organs.

The condition is caused by a recessive allele.

(a) State what is meant by a recessive allele.

(b) The diagram below shows a family pedigree. Some people in the family have CF.

(i) Use the pedigree to determine the genotypes of individuals A, B and C.
(ii) Individuals E and F have a third child.
Draw a genetic diagram to show the genotypes of E and F, the gametes they produce and the possible genotypes and phenotypes of the offspring.

(c) The gene for cystic fibrosis affects many different body systems including the digestive system and the reproductive system.

(i) The mucus that is produced in the pancreas is much thicker and blocks the pancreatic duct. Explain the effects this would have on human digestion.
(ii) Cystic fibrosis can result in the production of thick mucus which builds up in the cervix. Explain the effect this will have on reproduction.

Most-appropriate topic codes (Edexcel IGCSE Biology):

• 4(b): Inheritance — parts (a), (b)(i), (b)(ii)
• 2(e): Nutrition (Humans) — part (c)(i)
• 4(a): Reproduction (Humans) — part (c)(ii)
• 3(b): Excretion — part (c)(i) – context of digestion
▶️ Answer/Explanation
Solution

(a) An allele that is only expressed in the homozygote / only shown in phenotype if two copies are present / not expressed in the heterozygote / not expressed if a dominant allele is present. (1 mark)

(b)(i)
A: Ff (heterozygous) (1)
B: Ff (heterozygous) (1)
C: ff (homozygous recessive) (1)
(Total 3 marks)

(b)(ii) A genetic diagram showing:
• Parental genotypes: Ff and Ff (1)
• Gametes: F and f from each parent (1)
• Offspring genotypes and phenotypes: FF (unaffected), Ff (unaffected), Ff (unaffected), ff (affected) OR correct phenotype ratio (1)
(Total 3 marks)

(c)(i) An explanation that refers to three of the following:
• Pancreas produces/releases amylase/proteases/lipases. (1)
• No/less digestion of starch to maltose. (1)
• No/less digestion of proteins to amino acids. (1)
• No/less digestion of lipids to fatty acids and glycerol. (1)
• Less absorption of smaller/soluble molecules (e.g., amino acids, glucose, fatty acids). (1)
(Total 3 marks)

(c)(ii) An explanation that refers to two of the following:
• Reduces likelihood of pregnancy / less likely to conceive. (1)
• Sperm/semen cannot enter the fallopian tube/oviduct. (1)
• Fertilisation less likely / no fusion of gametes. (1)
(Total 2 marks)

Question

The diagram shows the human alimentary canal.

(a) (i) Explain how food passes down the oesophagus.

(ii) Which labelled structure produces bile?

  • A
  • B
  • C
  • D

(iii) Describe the role of bile in digestion.

(b) Lipase inhibitors are chemicals that bind to lipase enzymes.

To test the effect of a lipase inhibitor, equal masses of full fat milk are placed into two test tubes.

Lipase inhibitor is added to one test tube.

Lipase is added to both test tubes and the pH of each solution is measured every five minutes.

The results are shown in the table.

(i) Calculate the mean rate of pH change per minute of the solution without lipase inhibitor.

(ii) Explain the difference in the changes of pH of the solutions in the two test tubes during the 20-minute period.

(iii) Doctors use this method to investigate the use of lipase inhibitor as a treatment for obesity.

  • give three volunteers a tablet containing the lipase inhibitor
  • give another three volunteers a tablet with no lipase inhibitor
  • give all the volunteers 100 cm³ of olive oil to drink
  • measure the lipid concentrations in the blood of the volunteers after three hours

Some of the volunteers reported abdominal pains three hours after drinking the olive oil.

The table shows the doctors’ results.

Discuss the use of the lipase inhibitor as a treatment for obesity. Use the data from the table to support your answer.

Most-appropriate topic codes (Edexcel IGCSE Biology):

• 2(e): Nutrition — parts (a)(i), (a)(ii), (a)(iii), (b)(ii)
• 2(e): Digestive enzymes — parts (b)(i), (b)(ii), (b)(iii)
• 2(i): Excretion — part (a)(ii) (liver function)
• Appendix 4: Mathematical skills — part (b)(i)
• Appendix 5: Command words — parts (a)(i) (explain), (a)(iii) (describe), (b)(iii) (discuss)
▶️ Answer/Explanation
Solution

(a)(i) Peristalsis. Waves of muscular contractions.

Explanation: Food is moved down the oesophagus by a process called peristalsis. This involves rhythmic, wave-like contractions of the muscular walls of the oesophagus. These contractions squeeze the food bolus, pushing it along the digestive tract towards the stomach.

(a)(ii) C

Explanation: Bile is produced by the liver. In the diagram, structure C is labelled as the liver. The other structures are incorrect: A is the stomach, B is the pancreas, and D is the gall bladder (which stores and concentrates bile but does not produce it).

(a)(iii) Bile neutralises stomach acid and emulsifies fats.

Explanation: Bile has two main roles in digestion. First, it is alkaline and neutralises the hydrochloric acid from the stomach, creating the optimum alkaline pH for pancreatic enzymes to work in the small intestine. Second, bile salts emulsify lipids (fats). This means they break large fat globules into tiny droplets, massively increasing the surface area for the lipase enzymes to work on, which speeds up the digestion of fats.

(b)(i) 0.11 per minute

Explanation: The mean rate of pH change is calculated by finding the total change in pH and dividing it by the total time. The pH without inhibitor changed from 8.0 to 5.8, a total change of \(8.0 – 5.8 = 2.2\). This change happened over 20 minutes. Therefore, the mean rate is \(2.2 \div 20 = 0.11\) pH units per minute.

(b)(ii) The pH falls faster in the solution without the inhibitor because fats are broken down into fatty acids.

Explanation: Lipase enzymes break down lipids (fats) into fatty acids and glycerol. Fatty acids are acidic, so their production causes the pH of the solution to decrease. In the test tube without the inhibitor, lipase is active, leading to rapid fat digestion and a significant drop in pH. In the test tube with the inhibitor, the lipase enzyme is blocked from working effectively. Therefore, far fewer fatty acids are produced, and the pH remains much higher and changes more slowly.

(b)(iii) Discussion points include lower blood lipid levels with the inhibitor, potential side effects, and limitations of the study.

Explanation: The data suggests the lipase inhibitor could be a useful treatment for obesity. The blood lipid concentration increased much less in the volunteers who took the inhibitor (to 38, 42, 43 mg/dm³) compared to two of the three volunteers who did not take it (62, 64 mg/dm³). This indicates that the inhibitor successfully reduced the amount of fat absorbed from the olive oil into the bloodstream. Since less fat is absorbed, less fat would be stored in the body, potentially leading to weight loss.

However, there are significant drawbacks and limitations. Two out of the three volunteers taking the inhibitor reported abdominal pains, suggesting it may cause unpleasant side effects. It’s also important to note that one volunteer without the inhibitor also had a relatively low final lipid reading (45 mg/dm³), showing there can be natural variation.

The study itself is very small, with only three people in each group, so its results are not very reliable. Other factors like the volunteers’ age, sex, overall diet, and activity levels were not controlled, and these could all influence obesity. The experiment only measured short-term fat absorption after a single large dose of oil; it did not actually measure long-term weight loss, which is the ultimate goal of an obesity treatment.

In conclusion, while the inhibitor shows promise in reducing fat absorption, its side effects and the need for much more extensive, long-term research mean it cannot be confidently recommended as a treatment based on this data alone.

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