Paper 1 Biology

• Exchange surface


  Specialised surface that arises as the size of the organism, and its surface area to volume ratio increases
• Features of an efficient exchange surface

  • Large surface area
  • Thin to ensure short distance for substances to cross
  • Good blood supply/ventilation to maintain a steep gradient
• Ventilation in fish


  1. Fish opens mouth

  2. Lowers floor of buccal cavity to enable water flow in

  3. Closes mouth, raising buccal cavity floor to increase pressure

  4. Water forced over gill filaments by pressure difference between mouth and opercular cavities

  5. Operculum acts as valve and pump to let water out and pump it in
• Spiracles


  Small openings of tubes (trachea or tracheoles) that supply insects with gases
• Gas exchange in plants

  • Leaves have many small holes called stomata to allow gases to enter and exit
  • Air spaces in leaves allow gases to move around and come into contact with photosynthesising cells
• Mammalian gaseous exchange system

  • Lungs are lobed structures with large surface area in chest cavity
  • Rib cage protects lungs and lubricating substance prevents friction during inflation/deflation
  • Intercostal muscles and diaphragm control volume changes for ventilation
• Inspiration


  1. External intercostal muscles contract, diaphragm contracts and flattens

  2. Increases volume in thorax, decreases pressure, air forced into lungs
• Expiration


  1. Internal intercostal muscles contract, diaphragm relaxes

  2. Decreases volume in thorax, increases pressure, air forced out of lungs
• Spirometer


  Device used to measure lung volumes and breathing rate

  
• Lung volumes


  • Vital capacity
  • Tidal volume
  • Residual volume
  • Inspiratory reserve volume
  • Expiratory reserve volume
• Digestion


  Hydrolysis of large biological molecules into smaller molecules that can be absorbed
• Carbohydrate digestion


  1. Amylases in mouth digest larger polymers

  2. Maltases in ileum break down monosaccharides

  3. Sucrases and lactases break down disaccharides
• Lipid digestion


  1. Lipases hydrolyse ester bonds between monoglycerides and fatty acids

  2. Bile salts emulsify lipids to increase surface area
• Protein digestion


  1. Endopeptidases hydrolyse peptide bonds between specific amino acids

  2. Exopeptidases hydrolyse bonds at ends of polypeptides

  3. Dipeptidases break dipeptides into individual amino acids
• Absorption


  Products of digestion are absorbed by cells lining the ileum
• Haemoglobin


  Water soluble globular protein with haem groups that can bind and transport oxygen
• Partial pressure of oxygen

  Affects the affinity of haemoglobin for oxygen - higher partial pressure increases affinity

  
• Dissociation curves


  Illustrate the relationship between partial pressure of oxygen and oxygen binding to haemoglobin

  
• Haemoglobin


  A globular protein which consists of two beta polypeptide chains and two alpha helices. Each molecule forms a complex containing a haem group.
• Haemoglobin


  • It carries oxygen in the blood as oxygen can bind to the haem (Fe2+) group
  • Each molecule can carry four oxygen molecules

  
• Partial pressure of oxygen

  The greater the concentration of dissolved oxygen in cells, the greater the partial pressure

  
• Partial pressure of oxygen increases

  The affinity of haemoglobin for oxygen increases, oxygen binds to haemoglobin tightly

  
• Loading


  Oxygen binds to haemoglobin in the lungs
• Partial pressure of oxygen decreases


  The affinity of oxygen for haemoglobin decreases, oxygen is released in respiring tissues

  
• Unloading


  Oxygen is released in respiring tissues

  
• Haemoglobin returns to the lungs


  It binds to oxygen again

  
• Dissociation curves


  Illustrate the change in haemoglobin saturation as partial pressure changes

  
• Partial pressure is high


  Haemoglobin has high affinity for oxygen and is highly saturated

  
• Partial pressure is low


  Haemoglobin has low affinity for oxygen and is less saturated

  
• Haemoglobin binds to first oxygen molecule

  The affinity of haemoglobin for oxygen increases due to a change in shape, making it easier for other oxygen molecules to bind

  
• Positive cooperativity


  The steep increase in oxygen binding after the first molecule has bound

  
• Fetal haemoglobin


  Has a higher affinity for oxygen compared to adult haemoglobin, to better absorb oxygen at low partial pressure in the placenta

  
• Presence of carbon dioxide

  The affinity of haemoglobin for oxygen decreases, causing oxygen to be released

  
• Bohr effect


  Carbon dioxide creates slightly acidic conditions which change the shape of the haemoglobin protein, making it easier for oxygen to be released

  
• In large organisms, the surface area to volume ratio is not large enough for diffusion alone to supply substances like oxygen, glucose and other molecules to cells where they are needed
• Common features of a circulatory system

  • Suitable medium (blood)
  • Means of moving the medium (heart)
  • Mechanism to control flow around the body (valves)
  • Close system of vessels
• Closed double circulatory system

  The heart at the centre has two pumps - one pumps blood to the lungs to be oxygenated, the other pumps oxygenated blood around the body
• Atrium


  Thin walled and elastic, can stretch when filled with blood
• Ventricle


  Thick muscular wall to pump blood around the body or to the lungs
• Main vessels connecting the heart

  • Aorta
  • Pulmonary Artery
  • Pulmonary Vein
  • Vena Cava