Exchange of Substances

• What is the reason for the need for specialized exchange surfaces in organisms?

  As the size of the organism and its surface area to volume ratio increases
• Why can single-celled organisms easily exchange substances?

  Because the distance that needs to be crossed is short
• What do multicellular organisms require for efficient gas exchange?

  Specialized exchange surfaces for carbon dioxide and oxygen
• What are the features of an efficient exchange surface?

  • Large surface area (e.g., root hair cells, folded membranes)
  • Thin structure to minimize distance for substance crossing
  • Good blood supply/ventilation to maintain a steep gradient
• What is the surface area to volume ratio like in fish?

  Fish have a small surface area to volume ratio for gas exchange
• Why can't gases diffuse through the skin of fish?

  Because fish have an impermeable membrane
• How many pairs of gills do bony fish have?

  Four pairs of gills
• What are gill filaments and lamellae responsible for?

  They participate in gas exchange
• How does blood and water flow across the lamellae in fish?

  In a counter current direction
• What is the significance of the counter current flow in fish gills?

  It maintains a steep diffusion gradient for oxygen
• What happens to gill projections when fish are out of water?

  They stick together and fish cannot survive long
• What initiates ventilation in fish?

  Opening the mouth and lowering the floor of the buccal cavity
• How does water flow over the gill filaments?

  By the difference in pressure between the mouth cavity and opercular cavity
• What do terrestrial insects lack that affects oxygen transport?

  A transport system
• How do insects transport oxygen to tissues?

  Through spiracles and trachea/tracheoles
• What mechanisms facilitate gas movement in insects?

  Diffusion, mass transport, and volume changes in tracheoles
• What are stomata in plants?

  Small holes that allow gases to enter and exit leaves
• How do air spaces in leaves aid gas exchange?

  They allow gases to move around and contact mesophyll cells
• What are the lungs in mammals?

  A pair of lobed structures with a large surface area
• What protects the lungs in mammals?

  The rib cage
• What is the role of the lubricating substance in the lungs?

  To prevent friction during inflation and deflation
• What muscles are involved in ventilation in mammals?

  External and internal intercostal muscles and diaphragm
• How does air enter the lungs?

  Through the nose, trachea, bronchi, and bronchioles
• Where does gaseous exchange occur in mammals?

  In the walls of alveoli
• What keeps the airways open in mammals?

  Rings of cartilage
• How do the trachea and bronchi differ?

  Bronchi are narrower than the trachea
• What is the composition of the wall of the trachea and bronchi?

  Several layers including cartilage, glandular tissue, elastic fibres, smooth muscle, and blood vessels
• What type of epithelium is found in the inner lining of the trachea and bronchi?

  Ciliated epithelium
• What is the function of goblet cells in the respiratory system?

  To secrete mucus that traps bacteria and dust
• How do smooth muscles contribute to the respiratory system?

  By controlling the diameter of the airway
• What role do elastic fibres play in the respiratory system?

  They stretch during exhalation and recoil during inhalation
• What are the stages of ventilation in mammals?

  • Inspiration: External intercostal muscles contract, diaphragm flattens, volume increases, pressure decreases, air enters lungs.
  • Expiration: Internal intercostal muscles contract, diaphragm relaxes, volume decreases, pressure increases, air exits lungs.
• What is a spirometer used for?

  To measure lung volume
• What is vital capacity?

  The maximum volume of air that can be inhaled or exhaled in a single breath
• What is tidal volume?

  The volume of air breathed in and out at rest
• How is breathing rate calculated using a spirometer?

  By counting the number of peaks or troughs in a minute
• What is residual volume?

  The volume of air always present in the lungs
• What is inspiratory reserve volume?

  The additional volume of air that can be inhaled beyond tidal volume
• What is expiratory reserve volume?

  The additional volume of air that can be exhaled beyond tidal volume
• What is digestion and absorption?

  • Digestion: Hydrolysis of large biological molecules into smaller molecules.
  • Absorption: Movement of digested molecules across cell membranes.