Gas exchange

• Gas Exchange in Plants


  1. Respiration: Oxygen diffuses into cells, carbon dioxide diffuses out.
  2. Photosynthesis: Carbon dioxide diffuses in, oxygen diffuses out.
  3. Diffusion: Movement from high to low concentration.
• Leaf Adaptations for Gas Exchange


  a

  • Thin & Flat: Short diffusion distance, large surface area.
  • Stomata: Open in sunlight to allow gas exchange; close in low water or light.
  • Internal Structure: Air spaces allow gas movement around cells.
• Stomata Function


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  • Opening: Guard cells absorb water, become turgid.
  • Closing: Guard cells lose water, become flaccid.
• Gas Exchange: Night vs Day


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  • Day: Net CO₂ intake and O₂ release due to photosynthesis.
  • Night: Only respiration; net O₂ intake and CO₂ release.
  • Low Light: Photosynthesis rate = Respiration rate; no net gas movement.
• Hydrogencarbonate Indicator


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  • Purple = Low CO₂ (high photosynthesis).
  • Yellow = High CO₂ (no photosynthesis).
  • Orange/Red = Atmospheric CO₂ levels.
• Structure of the Breathing System

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  • Components: Ribs, intercostal muscles, diaphragm, trachea, bronchi, bronchioles, alveoli.
  • Adaptations for Gas Exchange: Large surface area, thin walls, good ventilation and blood supply.
• Role of Intercostal Muscles & Diaphragm


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  • Inhalation: Diaphragm contracts (flattens), external intercostals lift ribs; air drawn in.
  • Exhalation: Diaphragm relaxes (domes), external intercostals relax; air forced out.
  • Forced Exhalation: Internal intercostals contract, rib cage lowers further.
• Alveoli: Adaptations for Gas Exchange


  a

  1. Large Surface Area: For faster diffusion.
  2. Thin Walls: Short distance for gas exchange.
  3. Moist Lining: Dissolves gases for easy movement.
  4. Good Blood Supply: Maintains high concentration gradient.
• Smoking & Gas Exchange


  a

  1. Damages Alveoli: Reduces surface area for gas exchange.
  2. Tar Accumulation: Increases risk of lung infections and diseases.
  3. Carbon Monoxide: Binds with hemoglobin, reducing oxygen transport.
• What are the key adaptations of alveoli for gas exchange?


  a

  • Large surface area to volume ratio.
  • Thin single layers of cells to minimize diffusion distance.
  • Ventilation maintains high oxygen and low carbon dioxide levels.
  • Good blood supply maintains concentration gradients.
  • Moist surface layer aids gas diffusion.
• What are the risks associated with smoking related to the gas exchange system?

  a

  • Nicotine: Narrows blood vessels, increases heart rate and blood pressure.
  • Carbon Monoxide: Binds to hemoglobin, reducing oxygen transport and increasing strain on breathing.
  • Tar: Carcinogen linked to cancer; contributes to chronic obstructive pulmonary disease (COPD).
• What is chronic bronchitis and how is it caused by smoking?


  • Tar stimulates mucus production, leading to blockage of bronchioles.
  • Mucus buildup damages cilia, preventing mucus removal.
  • Results in smoker's cough.
• How does smoking lead to emphysema?

  • Frequent lung infections lead to phagocytes releasing elastase.
  • Elastase breaks down elastic fibers in alveoli, reducing elasticity.
  • Alveoli burst, decreasing surface area for gas exchange, leading to breathlessness.
• How does exercise affect breathing rates?

  • Breathing rate increases to supply more oxygen and remove carbon dioxide.
  • Post-exercise, elevated breathing rate helps remove lactic acid, indicating "oxygen debt."
• What does breathing rate indicate about fitness?


  • Higher resting and exercise-induced breathing rates suggest lower fitness levels.
  • Longer recovery times indicate reduced fitness.
• What factors must be controlled in a practical investigation of breathing rates?


  • Similar age, gender, size, and fitness level of participants.
  • Controlled exercise type and intensity.
  • Rest breaks to reduce fatigue.