Gas Exchange in Plants: Practical 7.9

Gas Exchange in Plants

• Green plants use photosynthesis to create food, consuming carbon dioxide and releasing oxygen.
• Respiration releases energy from consumed food, requiring oxygen and releasing carbon dioxide.
• The absorption and release of gases by plants changes throughout the day.
• Practical 7.9 explores carbon dioxide uptake or release in plants.

Practical 7.9: Studying Uptake or Release of Carbon Dioxide in Plants

• Aim: To observe how carbon dioxide levels change in tubes with leaves, under different light conditions.
• Apparatus and materials: boiling tubes, cotton thread, fresh green leaves, aluminium foil, test tubes rack, measuring cylinder (10 cm³), hydrogencarbonate indicator, table lamp.
• Procedure:
  • Add indicator to four tubes (A, B, C, D).
  • Note the initial indicator colour.
  • Put leaves in tubes A and C, then seal.
  • Seal tubes B and D. Cover tube C with foil.
  • Expose the set-ups to light for 5 hours.
  • Note the change in indicator colour in each tube.

Hydrogencarbonate Indicator

• Different colours correspond to different carbon dioxide levels.
• Purple = lower carbon dioxide levels.
• Red = normal levels in air (approximately 0.04%).
• Yellow = Higher carbon dioxide levels.

Results and Discussion

• Tube A (light, leaves): Indicator colour changes to purple, indicating carbon dioxide uptake.
• Tube B (light, no leaves): Indicator stays red, serving as a control.
• Tube C (dark, leaves): Indicator colour changes to yellow, suggesting carbon dioxide release.
• Tube D (dark, no leaves): Indicator remains red, serving as a control.
• These results show that plants take in carbon dioxide in light and release it in the dark.

Net Gas Exchange in Plants (Light and Dark)

• Light conditions: Plants take in more carbon dioxide in photosynthesis than they produce in respiration, resulting in a net uptake of carbon dioxide. Photosynthesis produces more oxygen than respiration uses, resulting in a net oxygen release.
• Dark conditions: Plants only carry out respiration (no photosynthesis). This leads to a net release of carbon dioxide and net oxygen uptake.

Gas Exchange Through Stomata

• Stomata are pores on leaf surfaces enabling gas exchange.
• They allow carbon dioxide and oxygen to enter and exit the leaf.

Observing Stomata

• Practical 7.11 demonstrates observing stomata under a microscope.
• Specific leaf epidermis, preparation, magnification (low and high) are important details.
• Drawings are essential; diagrams should include labelled drawings of stomata and surrounding cells.

Explore the mechanisms of gas exchange in plants through practical experiments. This quiz focuses on carbon dioxide uptake and release under varying light conditions, utilizing different apparatus and procedures. Understand the role of photosynthesis and respiration in plant biology.