option D

• Essential nutrients


  • cannot be synthesised
  • Minerals
  • Vitamins
  • Amino acids
  • Fatty acids
• Malnutrition


  Deficiency, imbalance or excess of specific nutrients in the diet
• Stomach acid secretion


  Controlled by a proton pump in parietal cells, exchanges protons from cytoplasm for potassium ions from stomach contents, mucus barrier protects stomach lining
• Sight or smell of food

  Stimulates the brain to send nerve impulses to parietal cells, causing secretion of hydrochloric acid and pepsin in gastric juice
• Lipoproteins


  Small droplets coated in phospholipid that transport cholesterol, low density carries it from liver to body tissues, high density does the opposite for removal
• Cardiac cycle


  1. SAN initiates the impulse, spreads in all directions through atria

  2. Impulse travels to AVN, which delays the signal before it goes to the ventricles meaning the atria can pump the blood down into the ventricles before they contract

  3. AVN to the purkinje fibres and bundle of his
• artificial pacemakers

  malfunctioning SAN or a block in the signal conduction pathway. Regulates heart rate, provides a continuous regular impulse or only when a heart beat is missed
• Energy sources in the diet


  • Carbohydrates
  • Lipids
  • Amino acids
• Energy sources


  • Can all be used in aerobic cell respiration as a source of energy
  • If the energy is insufficient, reserves of glycogen and fats are mobilised and used
• Conditions related to energy intake


  • Starvation
  • Anorexia
  • Obesity
• High levels of cholesterol in blood plasma


  Increased risk of coronary heart disease
• Vitamin D


  If there is insufficient vitamin D then calcium is not absorbed from food in the gut, leading to osteomalacia and rickets
• Vitamin C


  Needed for the synthesis of collagen fibres in many body tissues, deficiency leads to scurvy
• Stomach acid


  Helps to control pathogens and favours some hydrolysis reactions
• Pepsin


  Secreted by chief cells in the stomach in an inactive form of pepsinogen
• Deoxygenated blood flows through the hepatic portal veins, oxygenated blood flows through the hepatic artery in the liver
• Cardiac muscle cells

  • Have junctions called intercalated discs. cytoplasmic connections which allow movement of ions and rapid conduction of electrical signals
  • They are also branched
• Electrocardiogram (ECG)


  1. P wave is caused by atrial systole, QRS wave is caused by ventricular systole, T-wave occurs during ventricular diastole
• Phenylketonuria


  Genetic disease caused by a recessive allele, lack of phenylalanine hydroxylase enzyme leads to high levels of phenylalanine in the blood, tyrosine supplements may be needed