Organisation

• Explain the role of red blood cells in the circulatory system.

  (2 marks)

  • Red blood cells transport oxygen from the lungs to the tissues and carbon dioxide from the tissues to the lungs.
  • They contain hemoglobin, which binds to oxygen, allowing efficient gas transport.
• Describe how the structure of the heart is adapted to its function.

  (4 marks)

  • The heart has four chambers: two atria and two ventricles.
  • The left ventricle has thicker walls than the right because it needs to pump blood to the whole body at high pressure.
  • The right ventricle pumps blood to the lungs, so it only needs to exert lower pressure.
  • The heart has valves to ensure blood flows in one direction and prevent backflow.
• What is the function of platelets in the blood?

  (1 mark)

  • Platelets are involved in blood clotting to prevent excessive bleeding after injury.
• Explain the role of the coronary arteries in the heart.

  (2 marks)

  • The coronary arteries supply oxygen and nutrients to the heart muscle, enabling it to contract and pump blood efficiently.
  • Blockages in these arteries can lead to a heart attack due to reduced oxygen supply.
• Describe the process of digestion in the human body.

  (5 marks)

  • Mouth: Teeth break down food mechanically and saliva contains enzymes that begin starch digestion.
  • Esophagus: Muscular contractions (peristalsis) move the food to the stomach.
  • Stomach: Enzymes and hydrochloric acid break down proteins.
  • Small intestine: Digestion is completed with enzymes, and nutrients are absorbed through the villi.
  • Large intestine: Water is absorbed, and waste is formed into feces.
• What is the function of the villi in the small intestine?

  (2 marks)

  • The villi increase the surface area for absorption of nutrients like glucose and amino acids.
  • They contain capillaries to transport absorbed nutrients into the blood.
• Explain how the structure of the alveoli is adapted for gas exchange.

  (4 marks)

  • Alveoli have a large surface area, which increases the area available for gas exchange.
  • The walls are one cell thick, which shortens the distance for diffusion.
  • The capillaries surrounding the alveoli maintain a steep concentration gradient for efficient oxygen and carbon dioxide exchange.
• Describe the structure and function of the blood plasma.

  (3 marks)

  • Blood plasma is a yellowish liquid that makes up about 55% of blood volume.
  • It carries dissolved substances, such as glucose, hormones, carbon dioxide, and waste products like urea.
  • Plasma also helps in maintaining body temperature and balancing pH.
• Describe how the structure of the human heart is adapted to its function.

  (6 marks)

  • The heart has four chambers: two atria and two ventricles.
  • The left ventricle has thicker muscular walls compared to the right ventricle because it needs to pump blood to the whole body at high pressure, whereas the right ventricle only pumps blood to the lungs.
  • The heart has valves (e.g., tricuspid, bicuspid, and semilunar valves) that ensure blood flows in one direction and prevent backflow.
  • The coronary arteries supply oxygen and nutrients to the heart muscle.
  • The heart’s muscular walls (myocardium) contract rhythmically to pump blood.
  • The septum separates oxygenated and deoxygenated blood to ensure efficient circulation.
• Explain how the digestive system breaks down food and absorbs nutrients.

  (6 marks)

  • Mouth: Teeth break down food mechanically, and saliva, containing the enzyme amylase, begins breaking down starch into sugars.
  • Esophagus: Food moves down the esophagus through a process called peristalsis (muscular contractions).
  • Stomach: Hydrochloric acid and the enzyme pepsin begin breaking down proteins.
  • Small intestine: In the duodenum, enzymes (e.g., lipase, amylase, protease) break down fats, carbohydrates, and proteins. Nutrients are absorbed through the villi in the small intestine into the bloodstream.
  • Large intestine: Water is absorbed from undigested food, forming solid waste (feces).
  • The pancreas and liver release enzymes and bile, respectively, to aid digestion.
• Discuss how the structure of a red blood cell is related to its function.

  (6 marks)

  • Red blood cells are biconcave in shape, which increases the surface area for gas exchange.
  • They lack a nucleus, allowing more room to carry hemoglobin, the protein that binds to oxygen.
  • The flexible structure allows red blood cells to squeeze through tiny capillaries.
  • Hemoglobin binds to oxygen in the lungs and releases it in the tissues, aiding in oxygen transport throughout the body.
  • The thin membrane allows gases to diffuse efficiently in and out of the cell.
  • These adaptations enable red blood cells to efficiently transport oxygen to body tissues.
• Explain the role of enzymes in digestion and how they are adapted to their function.

  (6 marks)

  • Enzymes are biological catalysts that speed up chemical reactions, breaking down large food molecules into smaller, absorbable molecules.
  • Amylase breaks down starch into sugars in the mouth and small intestine.
  • Proteases (e.g., pepsin) break down proteins into amino acids in the stomach and small intestine.
  • Lipase breaks down fats into fatty acids and glycerol in the small intestine.
  • Each enzyme works best at a specific temperature and pH (e.g., pepsin works at a low pH in the stomach).
  • Enzymes are specific to their substrate, and their active site is shaped to fit the substrate molecule (like a lock and key).
  • The small intestine’s villi increase surface area, allowing more enzyme-substrate interactions and faster digestion.
• Describe the process of gas exchange in the lungs.

  (6 marks)

  • Oxygen from the air diffuses across the alveolar membrane into the blood in the capillaries.
  • The alveolar walls are one cell thick, reducing the diffusion distance for gases.
  • Carbon dioxide from the blood diffuses into the alveoli to be exhaled.
  • The alveoli have a large surface area due to their tiny size and the presence of many capillaries, which increases the rate of gas exchange.
  • The steep concentration gradient of oxygen in the alveoli and carbon dioxide in the blood allows efficient gas exchange.
  • The thin walls of the alveoli and capillaries allow gases to diffuse quickly between the blood and lungs.
• Discuss the structure and function of the human circulatory system.

  (6 marks)

  • The circulatory system consists of the heart, blood vessels (arteries, veins, capillaries), and blood.
  • The heart pumps blood through the body, maintaining blood flow.
  • Arteries carry oxygenated blood away from the heart at high pressure, with thick muscular walls to withstand the pressure.
  • Veins carry deoxygenated blood back to the heart at low pressure, with valves to prevent backflow.
  • Capillaries are tiny blood vessels where the exchange of gases (oxygen and carbon dioxide) and nutrients occurs between blood and tissues.
  • The double circulatory system ensures that oxygenated and deoxygenated blood are kept separate, improving the efficiency of gas exchange.
• Explain the causes and effects of coronary heart disease (CHD).

  (6 marks)

  • Causes of CHD include the buildup of fatty deposits (atherosclerosis) in the coronary arteries, which supply oxygen and nutrients to the heart muscle.
  • Risk factors include high cholesterol levels, smoking, poor diet, lack of exercise, and genetics.
  • The fatty deposits narrow the coronary arteries, reducing blood flow to the heart.
  • This can lead to a heart attack if the blood supply to part of the heart muscle is blocked.
  • Symptoms of CHD include chest pain (angina), breathlessness, and fatigue.
  • If left untreated, CHD can lead to heart failure or death. Treatment includes lifestyle changes, medication, and surgical procedures like bypass surgery or the use of stents to open blocked arteries.
• Describe how lifestyle factors can influence the risk of developing heart disease.

  (6 marks)

  • High-fat diet: A diet high in saturated fats can lead to increased levels of cholesterol, which may cause fatty deposits in the coronary arteries.
  • Smoking: Smoking damages the lining of blood vessels, promoting the buildup of fatty deposits, and increases the risk of blood clots, which can block arteries.
  • Lack of exercise: Regular physical activity helps maintain a healthy weight, lowers cholesterol, and strengthens the heart. Lack of exercise increases the risk of obesity, which is linked to heart disease.
  • High blood pressure: Stress, obesity, or excessive alcohol intake can increase blood pressure, putting extra strain on the heart and arteries. This increases the risk of a heart attack.
  • Alcohol consumption: Excessive drinking can lead to high blood pressure and heart rhythm problems, which can contribute to heart disease
• What are the differences between a heart attack and angina?

  (6 marks)

  • Angina is chest pain caused by reduced blood flow to the heart due to narrowed coronary arteries. It is typically triggered by physical activity or stress.
  • Angina is temporary and does not cause permanent damage to the heart.
  • Heart attack occurs when a blood clot completely blocks a coronary artery, cutting off the blood supply to a part of the heart muscle.
  • A heart attack causes permanent damage to the heart muscle and is often accompanied by severe chest pain, sweating, nausea, and shortness of breath.
  • Both conditions are related to atherosclerosis, but a heart attack is more severe and life-threatening.
• Describe how a stent is used to treat coronary heart disease.

  (6 marks)

  • A stent is a small mesh tube inserted into a narrowed coronary artery to open up the blockage and improve blood flow.
  • The stent is placed inside the artery during a procedure called angioplasty, where a balloon is used to push the artery open before the stent is inserted.
  • The stent is expanded and stays in place, keeping the artery open to allow oxygen-rich blood to flow to the heart muscle.
  • This reduces the risk of heart attacks and alleviates symptoms like chest pain (angina).
  • Stents can be made of metal or polymer materials and may be coated with drugs to prevent further narrowing of the artery.
  • Although stents are effective, they may require lifelong medication to prevent blood clots from forming around the stent.
• How can statins help in the treatment of coronary heart disease?

  (6 marks)

  • Statins are a type of medication that lower cholesterol levels in the blood.
  • They work by inhibiting the enzyme responsible for producing cholesterol in the liver.
  • Lowering cholesterol helps reduce the buildup of fatty deposits (plaque) in the coronary arteries, which narrows them and restricts blood flow.
  • By preventing further plaque buildup, statins reduce the risk of heart attacks and angina.
  • Statins may also reduce the risk of stroke and improve overall cardiovascular health.
  • Statins are often prescribed alongside lifestyle changes, such as a healthier diet and increased exercise.
• What is the role of enzymes in the digestive system?

  (2 marks)

  • Enzymes break down large, insoluble food molecules into small, soluble molecules that can be absorbed into the bloodstream.
  • They speed up the rate of digestion without being used up.
• Name the enzyme that breaks down starch and state where it is produced.

  (2 marks)

  • The enzyme is amylase.
  • It is produced in the salivary glands, pancreas, and small intestine.
• Describe the ‘lock and key’ model of enzyme action.

  (3 marks)

  • Enzymes have an active site with a specific shape.
  • Only the correct substrate fits into the active site, like a key fits into a lock.
  • This forms an enzyme-substrate complex, allowing the reaction to take place.
• What are the products when lipase breaks down lipids?

  (1 mark)

  • Fatty acids and glycerol.
• Explain how temperature affects enzyme activity.

  (4 marks)

  • As temperature increases, the rate of reaction increases because the molecules move faster.
  • The enzyme and substrate collide more often and with more energy.
  • The reaction rate reaches an optimum temperature.
  • Beyond this, the enzyme becomes denatured—its active site changes shape and the substrate no longer fits.
• A student investigates the effect of pH on amylase activity. Suggest a method they could use.

  (6 marks)

  • Add amylase and starch solution to a spotting tile or test tube.
  • Use iodine solution in the spotting tile to test for starch (turns blue-black if starch is present).
  • Add buffer solution at a specific pH to control the pH.
  • Mix the enzyme and starch, start a timer.
  • At regular intervals, use a pipette to take a drop and add it to the iodine.
  • Record how long it takes for the iodine to remain orange, indicating starch has been broken down.
• Describe and explain the effect of pH on enzyme action.

  (4 marks)

  • Enzymes work best at their optimum pH.
  • Changes in pH can alter the shape of the active site, slowing the reaction.
  • If the pH is too low or too high, the enzyme may become denatured.
  • A denatured enzyme no longer fits the substrate, so the reaction stops.
• Explain why enzymes are specific to one type of substrate.

  (3 marks)

  • Each enzyme has a unique active site.

  • Only the correct substrate can bind to the active site.

  • This ensures that enzymes only catalyse one type of reaction.
• What is the function of bile in the digestive system?

  (2 marks)

  • Bile neutralises stomach acid to provide the correct pH for enzymes in the small intestine.
  • It also emulsifies fats, breaking them into smaller droplets to increase surface area for lipase enzymes.
• Why is the wall of the left ventricle thicker than the right?

  (1 mark)

  • It needs to pump blood all around the body, so it must generate a higher pressure than the right ventricle, which only pumps to the lungs.
• Describe the structure of an artery and explain how it is adapted to its function.

  (3 marks)

  • Arteries have thick, muscular, and elastic walls to withstand and maintain high pressure.
  • The small lumen helps maintain pressure.
  • Elastic fibres allow the artery to stretch and recoil as the blood pulses through.
• Name the three types of blood vessels and state their functions.

  (3 marks)

  • Arteries: carry blood away from the heart.
  • Veins: carry blood towards the heart.
  • Capillaries: allow exchange of substances between the blood and tissues.
• How is the small intestine adapted for absorption?

  (3 marks)

  • It has villi that increase surface area.
  • Villi have thin walls for a short diffusion distance.
  • It has a rich blood supply to maintain a concentration gradient for diffusion and active transport.
• Explain how lifestyle and diet can increase the risk of developing non-communicable diseases.

  • A poor diet high in fat and sugar can lead to obesity, increasing the risk of heart disease and type 2 diabetes.
  • Lack of exercise reduces energy expenditure, leading to weight gain and high blood pressure.
  • Smoking introduces harmful chemicals (like carbon monoxide and tar), increasing the risk of lung disease, heart disease, and cancer.
  • Excessive alcohol damages the liver (cirrhosis) and can lead to brain and heart problems.
  • These lifestyle choices can increase the likelihood of non-communicable diseases which are not passed from person to person.
• What is cancer and how do benign and malignant tumours differ?

  (4 marks)

  • Cancer is caused by uncontrolled cell division.
  • Benign tumours stay in one place and do not invade other tissues.
  • Malignant tumours are cancerous, they invade surrounding tissues and can spread to other parts of the body through the blood (metastasis).
  • Malignant tumours are more dangerous and harder to treat.
• Describe how the lungs are adapted for gas exchange.

  • The lungs contain alveoli, which provide a large surface area for gas exchange.
  • The walls of the alveoli are one cell thick, allowing a short diffusion path.
  • They are surrounded by capillaries, which also have thin walls and carry blood close to the alveoli.
  • A high concentration gradient is maintained as oxygen diffuses into the blood and carbon dioxide diffuses out.
  • The breathing movements and blood flow maintain this gradient.
  • The alveoli are also moist, allowing gases to dissolve and diffuse more efficiently.
• Put the following in order of increasing complexity:

  Organ, cell, tissue, organ system

  Cell → Tissue → Organ → Organ system
• Define the term tissue.

  A tissue is a group of similar cells working together to perform a specific function.
• Give an example of an organ system and name two organs it includes.

  The digestive system includes the stomach and the small intestine.
• What happens to an enzyme when it is denatured?

  The shape of the enzyme’s active site changes, so the substrate no longer fits, and the enzyme can no longer catalyse the reaction.
• What is the optimum temperature for most human enzymes?

  37°C