Biology Topic 3

• Surface area to volume ratio

  The relationship between the size of an organism and the surface area available for exchange processes
• Importance of surface area to volume ratio in biology

  • Explains how many exchange surfaces organisms have and the adaptations to make transport across those surfaces more efficient
• Calculating surface area to volume ratio

  1. Calculate surface area of shape

  2. Calculate volume of shape

  3. Divide surface area by volume
• Larger objects

  Smaller surface area to volume ratio
• Smaller microscopic organisms have larger surface area to volume ratios
• Larger organisms cannot just diffuse gases across their surface, they need adaptations to increase surface area
• Adaptations in smaller organisms

  • Efficient diffusion across large surface area
  • Short diffusion distance to centre
• Adaptations in larger organisms

  • Increased surface area without reducing volume too much
  • Higher metabolic rates requiring more efficient exchange
• Adaptations to increase surface area

  • Villi and microvilli in digestive system
  • Alveoli and bronchioles in respiratory system
  • Spiracles and tracheal system in insects
  • Gill filaments and lamellae in fish
  • Broad thin leaves in plants
  • Capillary networks
• Digestion

  Large insoluble molecules hydrolyzed into smaller soluble molecules which can then be absorbed across cell membranes and into the bloodstream
• Molecules digested

  • Carbohydrates
  • Lipids
  • Proteins
• Amylases

  Enzymes that hydrolyze carbohydrates
• Carbohydrate digestion

  1. Amylases in saliva hydrolyze polysaccharides into disaccharides

  2. Disaccharidases in small intestine hydrolyze disaccharides into monosaccharides
• Protein digestion

  1. Endopeptidases hydrolyze peptide bonds within the protein chain

  2. Exopeptidases hydrolyze peptide bonds at the ends of the chain

  3. Dipeptidases hydrolyze dipeptides into amino acids
• Lipid digestion

  1. Lipase hydrolyzes triglycerides into fatty acids and glycerol

  2. Bile salts emulsify lipids to increase surface area for lipase
• Micelles

  Spheres made of fatty acids, monoglycerides, and bile salts that deliver lipids to epithelial cells
• Villi and microvilli

  • Increase surface area for absorption in small intestine
  • Contain capillary network to maintain concentration gradient
• Monosaccharide and amino acid absorption

  By co-transport (active transport)
• Lipid absorption

  • Fatty acids and monoglycerides diffuse into epithelial cells
  • Resynthesized into triglycerides and packaged into chylomicrons
  • Chylomicrons released by exocytosis and absorbed into lymphatic system
• Cardiac muscle

  The muscle that the heart is made of
• Cardiac muscle

  • It can contract and relax without any input from the nervous system or hormones
  • It does not fatigue as long as it has glucose and oxygen
• Coronary arteries

  The blood vessels that surround the heart and supply the cardiac muscle with oxygenated blood
• Blockages in coronary arteries

  Causes myocardial infarction (heart attack)
• Chambers of the heart

  • Left atrium
  • Right atrium
  • Left ventricle
  • Right ventricle
• Atria

  • Have thinner muscular walls
  • Can stretch as blood moves in
  • Only need to contract to push blood into ventricles
• Ventricles

  • Have thicker muscular walls
  • Need to contract with greater force to pump blood at higher pressure
• Right ventricle

  Pumps blood to the lungs at a lower pressure
• Left ventricle

  Pumps blood to the rest of the body at a higher pressure
• Major blood vessels

  • Aorta
  • Left pulmonary artery
  • Right pulmonary artery
  • Left pulmonary vein
  • Inferior vena cava
  • Superior vena cava
• Veins

  Bring blood into the heart
• Arteries

  Carry blood away from the heart
• Pulmonary

  Attached to the lungs
• Valves

  • Semilunar valves (in arteries)
  • Atrioventricular valves (between atria and ventricles)
• Valves

  Ensure blood flows in one direction
• Septum

  Separates the left and right sides of the heart to prevent oxygenated and deoxygenated blood from mixing
• Cardiac cycle

  1. Diastole

  2. Atrial systole

  3. Ventricular systole
• Diastole

  Relaxation of atria and ventricles
• Systole

  Contraction of atria or ventricles
• Atrial systole

  Atria contract, decreasing volume and increasing pressure
• Atrial systole

  Increases pressure behind atrioventricular valves, forcing them open