Organisms exchange substances with their environment

• Surface area to volume ratio

  Formula: Surface area / Volume. Relationship between organism size/shape and this ratio
• Small organisms


  • Have very large surface area compared to volume, so can meet needs through simple diffusion
• Larger organisms


  • Have smaller surface area compared to volume, so need adaptations for mass transport and efficient exchange
• Key adaptations for exchange surfaces

  • Villi and microvilli in small intestine
  • Alveoli and bronchioles for gas exchange
  • Spiracles and tracheae for insect gas exchange
  • Gill filaments and lamellae for fish gas exchange
  • Stomata on plant leaves
• Breathing


  Movement of air in and out of the lungs
• Ventilation


  The scientific term for breathing
• Gas exchange


  Diffusion of oxygen and carbon dioxide in and out of cells
• Key structures of human gas exchange system

  • Alveoli
  • Bronchioles
  • Bronchi
  • Trachea
  • Lungs
• Human ventilation


  1. Diaphragm muscle contracts, external intercostal muscles contract, rib cage moves out, air flows in

  2. Diaphragm relaxes, internal intercostal muscles contract, rib cage moves in, air flows out
• Pulmonary ventilation


  Total volume of air moved into the lungs per minute
• Alveolar epithelium


  • Very thin to minimize diffusion distance
  • Surrounded by capillary network to maintain concentration gradients
• Insect gas exchange system

  • Tracheal system with spiracles, trachea, and tracheoles
  • Gases can diffuse in, muscles can ventilate, and water loss is minimized
• Fish gills


  • Large surface area with gill filaments and lamellae
  • Short diffusion distance due to capillary network
  • Counter-current flow maintains concentration gradient
• Stomata


  Openings on plant leaves that allow gas exchange, close at night to reduce water loss
• Water and blood in opposite directions which means you should never actually have equilibrium and there will always be a higher concentration of oxygen in the water compared to the blood and that is why we maintain the concentration or the diffusion gradient across the entire gill lamellae
• Structures in the leaf

  • Palisade mesophyll
  • Spongy mesophyll
  • Stomata
• Palisade mesophyll


  Where photosynthesis mainly happens
• Spongy mesophyll


  Lots of air spaces
• Stomata


  Where gases diffuse in and out
• Oxygen diffuses out of stomata


  If not being used in respiration
• Carbon dioxide diffuses in through stomata


  Because it's needed for photosynthesis
• Stomata close at night

  To reduce water loss by evaporation
• Stomata open in the daytime


  When it's bright
• This is linked to the light-dependent reaction of photosynthesis
• Adaptations of xerophytic plants to minimise water loss

  • Leaves roll up
  • Stomata are deep and sunken in
  • Tiny hairs sticking out
  • Thicker cuticle
  • Longer root network
• Monomers

  Smaller units from which larger molecules are made
• Digestion of carbohydrates


  1. Amylase in mouth

  2. Amylase in duodenum

  3. Sucrase and lactase break down disaccharides
• Digestion of proteins


  1. Endopeptidases hydrolyze peptide bonds in middle of chain

  2. Exopeptidases hydrolyze peptide bonds at ends of chain

  3. Dipeptidase breaks down dipeptides
• Digestion of lipids


  1. Lipase hydrolyzes ester bonds in triglycerides

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


  Vesicle formed of fatty acids, glycerol, monoglycerides and bile salts
• Absorption of lipids


  1. Monoglycerides and fatty acids diffuse across cell membrane

  2. Reassembled into triglycerides in ER and Golgi

  3. Packaged into vesicles and released into lacteal
• Ileum


  • Covered in villi and microvilli to increase surface area
  • Thin walls for short diffusion distance
  • Network of capillaries to maintain concentration gradients
• Co-transport


  Monosaccharides and amino acids absorbed by active transport due to higher concentration in epithelial cells
• Hemoglobin


  Quaternary structure protein involved in oxygen transport
• Myoglobin


  Oxygen-binding protein found in muscle tissue and fetal hemoglobin
• Oxyhemoglobin dissociation curve


  Shows how hemoglobin binds and releases oxygen at different partial pressures
• Cooperative binding of oxygen to hemoglobin

  First oxygen binding makes it easier for subsequent oxygens to bind
• Bohr effect


  High CO2 concentration causes hemoglobin to release oxygen more readily
• Different animals have hemoglobin adapted to their needs and environments
• Fetal hemoglobin


  Has higher affinity for oxygen than adult hemoglobin