Gas exchange

• Explain adaptations for gas exchange in insects

  Tracheoles - highly branched - larger SA

  Muscle contractions - increase tracheal pressure - ventilates system to maintain a large conc. gradient

  Tracheole end walls - thin - small diffusion pathway

  Tracheole end walls - permeable to oxygen and CO2
• What are the adaptations to reduce water loss in insects?

  Exoskeletons - waterproof waxy cuticle to reduce evaporation

  Hairs around spiracles - trap moist air

  Valves close spiracles - reduce evaporation
• Explain the adaptations for gas exchange in fish

  -The gill arch has many filaments and lamella for a large SA

  -Lamella capillaries have thin walls for a short diffusion pathway

  -Countercurrent flow means blood and water flow in opposite directions to maintain a diffusion gradient for oxygen across the entire length of a gill lamella

  -Ventilation replaces deoxygenated water with oxygenated to maintain a large diffusion gradient

  -Circulation replaces oxygenated blood with deoxygenated to maintain a large diffusion gradient
• Explain the adaptations for gas exchange in a leaf

  Mesophyll cells - arranged in flat layers - large SA

  CO2 - used in photosynthesis - maintains diffusion gradient in cells

  Air spaces - between cells - small diffusion pathway
• Explain adaptations to reduce water loss in xerophytes

  Hairs around the stomata, Sunken stomata, and Folded leaves -all trap moist air and reduce water potential gradient for evaporation

  Spine/needle leaves, Reduced stomatal density - both have a smaller SA:V for evaporation

  Thicker waxy cuticle - impermeable to water
• Define a xerophyte

  A species of plant adapted to live in environments with very minimal liquid water
• Why is gas exchange at the alveolar surface efficient?

  -Many alveoli = large SA

  -Squamous alveolar epithelium and capillary endothelium are made from a single layer of cells = small diffusion pathway

  -Ventilation of the thoracic cavity and circulation of blood = large conc. gradient for O2 between the alveoli and capillaries
• Explain the mechanism of breathing - inspiration

  -The volume of the thoracic cavity increases and the pressure decreases

  -Contraction and flattening of the diaphragm muscle

  -Contraction of external intercostal muscles

  -So the ribs are pulled upwards and outward
• What is used to calculate a pulmonary ventilation rate?

  A spirograph
• What is the equation to calculate the pulmonary ventilation rate and explain the components?

  Pulmonary ventilation rate = Tidal volume x Respiratory rate

  PVR: volume of air exchanged per minute Tidal volume: amount of air inhaled or exhaled in one breath Respiratory rate: number of breaths taken per minute