Gas Exchange

• How do gases move?

  By diffusion
• How does a single celled organism exchange gas from the environment

  Through cell membrane
• What are spiracles in insects?

  Openings on the insect’s body surface where air enters.
• At the end of each tracheole in an insect, what fluid lays there?

  Tracheal fluid
• What polymer forms the trachea and tracheoles

  Spirals of Chitin - Strong and flexible
• In order to cross the tips of the tracheoles, Oxygen must what to be in the tracheal fluid?

  Dissolve
• what adaptations increases the surface area for gas exchange in insects?

  Large number of tracheoles
• Describe the conditions that create a diffusion gradient for oxygen in the insect gas exchange system.

  Aerobic respiration in insect muscle tissue uses oxygen.This makes the oxygen concentration inside the insect lower than the oxygen concentration in the air.As a result, there is an oxygen concentration gradient from the air into the tissues.
• How have insects adapted to help reduce water loss?

  waterproof exoskeloton

  can close spiracles
• A genetic mutation causes some insects to have a thinner coating on their exoskeletons.How might this affect their survival in dry environments?

  A thinner waterproof coating on the exoskeleton may be less efficient at preventing water loss.
• In fish, gas exchange takes place in an organ called the…

  Gill fillaments
• What are the key parts of a fish

  Lamellae

  Gill fillaments

  Gill arch
• The blood in the lamella has a relatively high concentration of carbon dioxide. Why?

  Respiration in body tissues
• adaptations that enable efficient gas exchange in fish gills

  Large SA

  Countercurrent flow

  short diffusion pathway (lamella one cell thick)
• Describe how the structure of a gill is adapted to maximise surface area, to ensure efficient gas exchange.

  The gills of a fish have a large number of gill filaments and a large number of gill lamellae to maximise the surface area for diffusion.
• How does counter-current flow enable efficient gas exchange in fish?

  Counter-current flow maintains steep concentration gradients for carbon dioxide (and oxygen) across the lamella.
• What is countercurrent flow?

  Countercurrent flow is when two materials flow in opposite directions to maintain a concentration gradient. 
• • Counter-Current Flow Mechanism:
  • Water flows over gills in one direction, and blood flows in the opposite direction.
  • This maintains a steep oxygen gradient along the entire gill, maximizing oxygen uptake.

  Result:More oxygen diffuses into the blood.
• How many pairs of gills do fish have?

  4
• D. Plants (Leaves & Stomata) 🌿

  • Gas Exchange Structures:
  • Stomata: Small pores on the leaf surface (mainly underside) for gas exchange.
  • Guard cells control stomatal opening/closing.
  • Spongy mesophyll inside leaves allows gas diffusion.
• PLants:

  Gas Exchange Process:

  • CO₂ enters for photosynthesis; O₂ exits as a byproduct.
  • During the day, stomata open to allow gas exchange.
  • At night or in dry conditions, stomata close to prevent water loss.
• Where does gas exchange occur in the leaf?

  stomata
• Describe the structure of alveoli.

  Alveoli are tiny air sacs with a one-cell-thick layer of epithelial cells.
• Describe the structure of capillaries.

  Capillaries are blood vessels with a one-cell-thick layer of endothelial cells.
• How are alveoli adapted for efficient gas exchange?

  1. The alveolar epithelium is one cell thick, which creates a short diffusion distance for gas exchange. Note: in the exam, it is not enough to say the epithelium is ‘thin’. 
  2. The lungs contain a large number of alveoli. This provides a large surface area for gas exchange.  
  3. There is a steep concentration gradient for oxygen and carbon dioxide.
• How is a steep concentration gradient of oxygen and carbon dioxide maintained between the alveoli and capillaries?

  Ventilation is the process of moving air in and out of the lungs. This ensures a lot of oxygen enters the lungs and a lot of carbon dioxide exits the lungs.

   

  A good blood supply ensures that blood containing a lot of oxygen is quickly taken away from the lungs and blood containing a lot of carbon dioxide is taken towards the lungs.
• Humans (The Lungs & Alveoli) 🫁

  • Gas Exchange Structures:
  • Trachea → Bronchi → Bronchioles → Alveoli.
  • Alveoli: Tiny air sacs where gas exchange happens.
  • Adaptations of Alveoli:
  • Large surface area (millions of alveoli).
  • Thin walls (one-cell thick for short diffusion distance).
  • Rich blood supply maintains the oxygen gradient.
  • Moist lining helps dissolve gases for diffusion.
  • Ventilation:
  • Breathing movements ventilate the lungs, maintaining a steep concentration gradient for O₂ and CO₂.
• Whats tidal volume?

  The volume of air inhaled or exhaled in one normal breath (at rest).
• Whats respiration?

  A metabolic process where cells release energy from glucose.
• Whats lung capacity?

  • The total volume the lungs can hold.
  • Includes several volumes:
  • Vital Capacity (VC): The maximum amount of air a person can exhale after a deep breath (~4,800 cm³ in adults).
  • Total Lung Capacity (TLC): The total volume of the lungs after maximum inhalation (~6,000 cm³).
  • Residual Volume (RV): The air left in the lungs after maximum exhalation (~1,200 cm³).
• Whats breathing rate?

  The number of breaths taken per minute.