Biology AQA PAPER 1

• Pancreas and salivary gland

  Glands which produce digestive juices containing enzymes
• Large intestine


  Absorbs water from undigested food, producing faeces
• Enzymes


  Act as biological catalysts which speed up the rate of biological reactions (the breakdown of food) without being used up
• Enzyme shape


  Enzymes have a specific active site which is complementary to their substrate
• Metabolism


  The sum of all the reactions in a cell or an organism
• Types of metabolic reactions catalysed by enzymes

  • Building larger molecules from smaller molecules
  • Changing one molecule to another
  • Breaking down larger molecules into smaller molecules
• Temperature effect on enzymes

  Up to a certain point, increasing temperature increases enzyme action, as molecules have a higher kinetic energy. Above a certain temperature, the shape of the active site is altered and the enzyme becomes denatured, so it can no longer catalyse the reaction. The optimum temperature is around 37°
• pH effect on enzymes

  The optimum pH for most enzymes is 7 (apart from proteases in the stomach). If the pH is too extreme, the shape of the active site may be altered and the enzyme may no longer work
• Locations of digestive enzymes

  • Carbohydrases: amylase - salivary gland and pancreas; maltase - small intestine
  • Proteases: pepsin - stomach; others - pancreas and small intestine
  • Lipases: pancreas and small intestine
• Role of carbohydrases


  Break down carbohydrates into monosaccharides and disaccharides. Amylase breaks down starch into maltose, and maltase breaks down maltose into glucose
• Role of proteases


  Break down proteins into amino acids
• Role of lipases


  Break down lipids into fatty acids and glycerol
• Role of bile


  Neutralises the hydrochloric acid secreted by the stomach, and emulsifies lipids to form droplets - this increases the surface area for the lipase enzyme to work on
• Heart


  An organ that pumps blood around the body
• Double circulatory system


  1. One pathway carries blood from the heart to the lungs - where the gaseous exchange of oxygen and carbon dioxide takes place

  2. One pathway carries blood from the heart to the tissues
• Right ventricle


  Pumps blood to the lungs
• Left ventricle


  Pumps blood to the body tissues
• Heart chambers


  4 - right atrium, right ventricle, left atrium, left ventricle
• Main blood vessels associated with the heart

  • Aorta (left) - carries oxygenated blood from the heart to the body
  • Pulmonary vein (left) - carries oxygenated blood from the lungs to the heart
  • Vena cava (right) - carries deoxygenated blood from the body to the heart
  • Pulmonary artery (right) - carries deoxygenated blood from the heart to the lungs
• Purpose of heart valves

  Prevent the backflow of blood
• Blood flow through the heart

  1. Blood enters the right atrium via the vena cava, and the left atrium via the pulmonary vein

  2. The atria contract, forcing blood into the ventricles and causing valves to shut

  3. After the ventricles contract, blood in the right ventricle is pumped to the lungs, and blood in the left ventricle is pumped to the body
• Valves in the heart


  Prevent the backflow of blood
• Blood flow through the heart

  1. Blood enters the right atrium via the vena cava, and the left atrium via the pulmonary vein

  2. The atria contract, forcing blood into the ventricles and causing valves to shut

  3. After the ventricles contract, blood in the right ventricle enters the pulmonary artery (to the lungs) and blood in the left ventricle enters the aorta (to the body)
• The approximate value of the natural resting heart rate is 70 beats per minute
• Heart rate control


  Heart rate is controlled by a group of cells in the right atrium which act as a pacemaker. They release waves of electrical activity which cause the heart muscle to contract.
• Abnormal heart rhythm treatment

  Irregular heart rhythms can be treated using an artificial pacemaker, which sends out electrical signals to correct the heart's rhythm.
• Types of blood vessels

  • Arteries
  • Veins
  • Capillaries
• Arteries


  • Thick muscle layer - adds strength to resist high pressure
  • Thick elastic layer - allows arteries to stretch and recoil - in order to withstand high pressure
• Veins


  • Wide lumen - enables low pressure
  • Valves - prevent backflow of blood
• Blood flow rate calculation

  Volume of blood / number of minutes
• Lung ventilation by intercostal muscles

  1. Intercostal muscles contract

  2. Ribcage moves upwards and outwards

  3. Diaphragm flattens and volume of the chest increases

  4. Increased volume results in decreased pressure

  5. Air is drawn into lungs down pressure gradient
• Gas exchange at the alveoli

  1. Oxygen diffuses from the alveoli into the capillary bloodstream down its concentration gradient

  2. Carbon dioxide diffuses from the capillary into the alveoli down its concentration gradient
• Alveoli adaptations for gas exchange

  • Small and arranged in clusters - larger surface area
  • Rich blood supply - maintains concentration gradient
  • Thin alveolar wall - short diffusion pathway
• Breathing rate calculation


  Number of breaths / number of minutes
• Substances transported by plasma


  • Red blood cells
  • White blood cells
  • Platelets
  • Carbon dioxide
  • Urea
  • Products of digestion
• Plasma


  A yellow liquid within blood that transports substances around the body
• Red blood cell adaptations

  • Biconcave shape - increased surface area to volume ratio
  • No nucleus - more room for haemoglobin to bind to oxygen
  • Contain haemoglobin - binds to oxygen
• Purpose of white blood cells


  They form part of the immune system, which protects the body from invading pathogens
• White blood cell adaptations

  • Have a nucleus - contains DNA which codes for proteins
  • Can produce antibodies
  • Can produce antitoxins
  • Can engulf and digest pathogens (phagocytosis)
• Purpose of platelets


  Platelets are small cell fragments which aid the clotting of blood at the site of a wound