Edexcel iGCSE Biology-2.41 B gas exchange in relation to respiration and photosynthesis- Study Notes- New Syllabus

Gas Exchange in Plants – Link to Respiration & Photosynthesis

📝 Introduction

Plants carry out both respiration and photosynthesis.
Both processes involve oxygen (O₂) and carbon dioxide (CO₂).
Gas exchange = movement of these gases in and out of the leaf by diffusion.

🔄 Gas Exchange During Respiration

• Happens all the time (day & night).
• O₂ in → used for respiration.
• CO₂ out → waste product of respiration.
• Respiration does not depend on light → continuous process.

🌞 Gas Exchange During Photosynthesis

• Happens only in light (daytime).
• CO₂ in → used to make glucose.
• O₂ out → by-product of photosynthesis.
• Rate depends on light intensity, CO₂ availability, temperature.

⚖️ Balance Between Respiration & Photosynthesis

• Daytime (bright light):
  • Photosynthesis rate higher than respiration.
  • Net result:
    • CO₂ taken in (more for photosynthesis than released by respiration).
    • O₂ released (more from photosynthesis than used in respiration).
• Night (no light):
  • No photosynthesis (can’t happen without light).
  • Only respiration occurs.
  • Net result:
    • O₂ taken in.
    • CO₂ released.

🌟 Adaptations of Leaves for Gas Exchange

• Stomata (tiny pores) control entry/exit of gases.
• Air spaces inside leaf → allow gases to diffuse quickly.
• Thin leaf → short distance for diffusion.

📊 Summary Table – Gas Exchange in Plants

📌 Quick Recap 
Plants respire all the time (O₂ in, CO₂ out).
Photosynthesis only in light (CO₂ in, O₂ out).
Day: photosynthesis > respiration → net O₂ released.
Night: only respiration → net CO₂ released.
Stomata + leaf structure = efficient gas exchange.