Muscle respiration
Demonstrate cellular respiration in muscle cells by measuring the gas exchange of a piece of beef in a sealed chamber with FizziQ Connect sensors.
Visão geral da atividade:
The student places fresh beef in a sealed chamber with CO₂ and O₂ sensors and observes the continuous production of CO₂ and water vapor by cellular respiration.
Nível:
Autor:
High school
Marie-Anne Dejoan
Duração (minutos):
25
O que os alunos farão:
- Demonstrate cellular respiration in animal (muscle) cells
- Measure the simultaneous evolution of CO₂, O₂, and humidity in a sealed chamber
- Interpret gas exchange in terms of the respiration equation
- Calculate CO₂ production rate and relate it to metabolic activity
- Understand why cellular respiration continues after death
Conceitos científicos:
- Aerobic cellular respiration
- Glycolysis
- Krebs cycle
- Electron transport chain
- ATP (adenosine triphosphate)
- Cellular metabolism
- Gas exchange
Sensores:
- SCD40 sensor (CO₂ in ppm, temperature, humidity)
- O₂ sensor
Materiais necessários:
- Smartphone or tablet with FizziQ Connect
- SCD40 sensor (CO₂, temperature, humidity)
- O₂ sensor
- M5 Stack module and multiport hub
- Small sealed chamber
- Fresh raw beef (about 50 g)
Procedimento experimental:
Connect the O₂ and SCD40 sensors to the I2C port of the M5 Stack module via the multiport hub.
Open FizziQ Connect on your smartphone or tablet and connect to the M5 Stack via Bluetooth.
Verify that three quantities are accessible: CO₂ concentration (ppm), O₂ concentration (%), and relative humidity (%).
Place the piece of fresh raw beef in the sealed chamber. Position the sensors so they are not in direct contact with the meat.
Start recording in FizziQ Connect with the chamber still open for 1-2 minutes to establish baseline values.
Seal the chamber and note the exact time of closure.
Record for 10 to 15 minutes without touching the setup. Observe the real-time evolution of the three measured quantities.
Observe the trends: CO₂ and humidity increase, O₂ decreases slightly.
Stop the recording. Open the chamber to ventilate and remove the meat.
Analyze the graphs in FizziQ Connect: identify the moment the chamber was sealed and calculate the rates of change for CO₂, O₂, and humidity.
Resultados esperados:
A clear increase in humidity (from about 52% to 67%) and CO₂ concentration (from 400-800 ppm to over 16,000 ppm) is observed once the chamber is sealed. The increase is nearly instantaneous after sealing, confirming active respiration. O₂ decreases slightly but the change may be within the sensor's precision limits.
Questões científicas:
- Why do muscle cells continue to respire after the animal's death?
- How can we explain that the humidity increase accompanies the CO₂ increase?
- What would happen if the chamber were left sealed for several hours?
- Why is the O₂ variation harder to detect than the CO₂ variation?
- At what point would the cells stop respiring? What would limit them?
- How does temperature affect the respiration rate of muscle cells?
Explicações científicas:
Cellular respiration is the process by which cells convert glucose into usable energy (ATP). The overall equation is: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy (ATP).
This process occurs in three successive stages. Glycolysis takes place in the cytoplasm: glucose (6 carbons) is split into two pyruvate molecules (3 carbons each), producing a small amount of ATP.
The Krebs cycle takes place in the mitochondrial matrix: pyruvates are oxidized, releasing CO₂ and reduced coenzymes (NADH, FADH₂) that carry electrons to the next stage.
The electron transport chain (or oxidative phosphorylation) occurs on the inner mitochondrial membrane: electrons are transferred through a series of protein complexes, driving ATP synthesis. Oxygen is the final electron acceptor.
Muscle cells are particularly metabolically active and contain a large number of mitochondria. Even after the animal's death, these mitochondria continue to function as long as substrates (glucose, oxygen) remain available.
The humidity increase in the chamber is explained by two factors: water production by cellular respiration and evaporation from the meat surface.
CO₂ concentration can reach very high values (over 16,000 ppm) in a small sealed chamber, far exceeding the normal atmospheric level of about 420 ppm.
Atividades de extensão:
- Why do muscle cells continue to respire after the animal's death?
- How can we explain that the humidity increase accompanies the CO₂ increase?
- What would happen if the chamber were left sealed for several hours?
- Why is the O₂ variation harder to detect than the CO₂ variation?
- At what point would the cells stop respiring? What would limit them?
- How does temperature affect the respiration rate of muscle cells?
Perguntas frequentes:
Q: Must the meat be raw or cooked?
R: The meat must be raw and fresh. Cooking denatures enzymes and destroys mitochondria, eliminating cellular respiration.
Q: How long should I record?
R: 10-15 minutes is sufficient for a clear demonstration. Longer recordings show higher CO₂ levels but the rate may slow as O₂ is depleted.
Q: The CO₂ seems very high. Is the sensor saturated?
R: The SCD40 measures up to 40,000 ppm. In a small sealed chamber with fresh meat, concentrations of 15,000-20,000 ppm are common and within the sensor's range.
Q: Is there a health risk from the CO₂ produced?
R: Not in a small sealed chamber. The total CO₂ produced is negligible compared to the room volume. Simply ventilate when opening the chamber.