Overview
This lecture explains key experiments demonstrating that plants use oxygen, produce carbon dioxide, and give off heat during respiration, including both aerobic and anaerobic processes.
Experiment: Oxygen Use in Plant Respiration
- Aim: To show that oxygen is used up during respiration in plants.
- Flask A contains germinating bean seeds; Flask B contains dead, boiled seeds (control).
- Both flasks have wet cotton; Flask B has antiseptic to prevent bacterial respiration.
- Soda lime in tubes absorbs carbon dioxide produced by seeds.
- After several days, water level rises in delivery tube of Flask A, indicating oxygen is used.
- Burning paper goes out in Flask A, showing oxygen has been depleted; it burns briefly in Flask B.
Experiment: Carbon Dioxide Production in Respiring Seeds
- Aim: To prove carbon dioxide is produced during germination.
- Flask A has germinating seeds; Flask B has boiled, dead seeds.
- Gases from each flask are tested with lime water; Flask A's gas turns lime water milky, indicating CO₂ production.
- Control flask (Flask B) shows no effect on lime water.
Experiment: Carbon Dioxide from Green Plants
- Small potted plant set up with apparatus to remove external CO₂ using soda lime.
- Incoming air is CO₂-free, confirmed with lime water.
- Air leaving plant turns lime water milky, proving plant releases CO₂ during respiration.
- Experiment must be done in the dark to prevent photosynthesis.
Experiment: Heat Production During Respiration
- Two thermos flasks: Flask A (germinating seeds), Flask B (dead seeds, antiseptic).
- Both flasks have thermometers and cotton plugs.
- Flask A shows increased temperature after hours, proving heat is released during respiration.
Experiment: Anaerobic Respiration in Plants
- Soaked, peeled seeds are introduced into a mercury-filled test tube.
- After two days, mercury level falls and CO₂ is detected.
- CO₂ presence is confirmed by introducing potassium hydroxide, which absorbs gas and raises mercury level.
- Control with sterilized seeds produces no gas.
- Seed coat is removed to speed up CO₂ diffusion.
Key Terms & Definitions
- Respiration — The process by which living organisms use oxygen to convert glucose into energy, releasing CO₂ and heat.
- Soda lime — A mixture of sodium hydroxide and slaked lime used to absorb carbon dioxide.
- Lime water — A solution of calcium hydroxide that turns milky in the presence of CO₂.
- Control — The setup in an experiment where the tested variable is absent, used for comparison.
- Anaerobic respiration — Respiration that occurs without oxygen, producing energy and CO₂.
Action Items / Next Steps
- Review each experiment's setup and outcomes.
- Understand the function of controls and variables in experiment design.
- Prepare for questions on the significance of each observation.