unit 3

• Things organisms need to exchange with their surroundings

  • Oxygen, carbon dioxide, water, ions
• As the organism gets bigger

  The SA:vol ratio decreases
• Thermoregulation

  Control of body temperature
• Organisms that maintain a constant internal body temperature

  • Mammals and birds
• Metabolic rate

  The amount of energy expended by an organism in a given time period
• Elephants have a small surface area to volume ratio
• Adaptations large animals have to lose heat

  • Large, flat ears / Sweating or panting / Vasodilation
• Being flat or hollow helps multicellular organisms exchange respiratory gases by increasing the surface area to volume ratio, allowing for faster rates of diffusion
• How insects reduce water loss

  Close their spiracles, waterproof exoskeleton
• Difference between tracheae and tracheoles

  Tracheae are larger and have rings of cartillage
• Insects close the spiracles to reduce water loss
• How some insects increase ventilation

  Abdominal pumping
• Water is more dense than air
• Water contains less oxygen than air
• Warm water contains less oxygen than cold water
• Diffusion of gases is slower in water than in air
• Water flow across the gills of fish

  Counter-current system
• Key components of the gill

  • Filament and lamellae
• Operculum

  Gill flap
• Gills

  • Large surface area as filaments at right angles with lamallae
• The countercurrent flow in fish gills maintains a concentration gradient along the whole length of the lamellae
• The countercurrent flow is important as it allows water to flow in the opposite direction to blood, maintaining the concentration gradient
• Leaf adaptations for gas exchange

  • Large surface area / Spongy mesophyl with air spaces to maintain concentration gradient
• The gas needed for leaves to photosynthesise is carbon dioxide
• The gas that will diffuse into the palisade mesophyll cells at night is oxygen
• Stomata

  Openings on the underside of leaves that allow gas exchange
• Stomata are sometimes closed to reduce water loss
• Xerophyte

  A plant adapted for dry environments
• Adaptations of xerophytic plants

  • Sunken stomata / Reduced surface area of leaves / Hairs at stomata / Thick waxy cuticle / Rolled leaves
• Path of oxygen from air to blood in mammals

  Into mouth/nasal passage, down trachea, into bronchi, into bronchioles, into alveoli, across epithelium and capillary endothelium into blood
• Ventilation

  Breathing - movement of ribs and muscles/diaphragm to increase air flow to lungs
• The rings of cartilage in the trachea prevent collapse
• Intercostal muscles

  They work in pairs with opposite motions of contraction and relaxation
• When the diaphragm contracts, the volume of the thorax increases
• The external intercostal muscles contract to pull the ribs up and out
• When the volume of the thorax increases, the pressure inside the thorax decreases
• Tidal volume

  Volume of air in/out of the lungs at rest with each breath
• How breathing rate is measured

  Spirometer - number of breaths per minute
• Pulmonary ventilation rate


  Calculated as tidal volume x breathing rate
• Fibrosis

  Thickening or scarring of tissue