🧫 Multi-Day Yeast Culture & Cellular Respiration Investigation
A comprehensive exploration of cellular respiration through yeast culture maintenance and experimental observation
📋 Lab Overview
In this multi-day investigation, you'll culture living yeast cells and observe their metabolic activity over time. You'll maintain yeast cultures for 5 days, making daily observations of their growth and respiration. Then, you'll conduct a controlled experiment to measure CO₂ production through balloon inflation. Finally, you'll connect your findings to photosynthesis and the carbon cycle.
Timeline
- Day 1 (Today): Set up yeast cultures in test tubes
- Days 2-5: Make daily observations (5 minutes per day)
- Day 6: Conduct balloon respiration experiment (40 minutes)
- Day 6 continued: Analysis and connections to photosynthesis
🧪 Materials (Per Group)
- 2 test tubes with caps or stoppers
- Test tube rack
- Active dry yeast (1 packet or ~7g)
- Warm water (35-40°C)
- Sugar (glucose or sucrose)
- Graduated cylinder or measuring spoons
- Permanent marker for labeling
- Thermometer
- Stirring rod or spoon
🔬 Procedure: Day 1 Setup
- Label two test tubes: "Sugar Water" and "Plain Water"
- Add approximately 10mL of warm water (35-40°C) to each test tube
- To the "Sugar Water" tube, add 1/2 teaspoon of sugar and stir until dissolved
- Add 1/4 teaspoon of active dry yeast to BOTH test tubes
- Gently swirl to mix (don't shake vigorously - yeast needs to acclimate)
- Cap or cover both tubes loosely (CO₂ needs to escape)
- Place both tubes in the test tube rack in a warm location (20-25°C)
- Record your initial observations below
📝 Day 1 Initial Observations
📸 Click to upload a photo of your setup
🔍 Daily Observations (Days 2-5)
Each day, spend 5 minutes observing your yeast cultures. Look for changes in:
- Turbidity: How cloudy is the liquid? (1=clear, 5=very cloudy)
- Bubbling: Are bubbles forming? How much activity?
- Smell: What does it smell like? (yeasty, alcoholic, sweet?)
- Sediment: Is yeast settling at the bottom?
- Visual changes: Any color changes or surface foam?
📅 Day 2 Observations
Sugar Water Tube:
Plain Water Tube:
📸 Click to upload Day 2 photo
📅 Day 3 Observations
Sugar Water Tube:
Plain Water Tube:
📸 Click to upload Day 3 photo
📅 Day 4 Observations
Sugar Water Tube:
Plain Water Tube:
📸 Click to upload Day 4 photo
📅 Day 5 Observations
Sugar Water Tube:
Plain Water Tube:
📸 Click to upload Day 5 photo
🎈 Day 6: Balloon Respiration Experiment
Today, you'll transfer your thriving yeast cultures to Erlenmeyer flasks and measure CO₂ production by balloon inflation. This experiment provides visible, measurable evidence of cellular respiration.
Additional Materials Needed
- 2 Erlenmeyer flasks (125-250mL)
- 2 balloons (same size and type)
- Warm sugar water solution (prepared fresh)
- Ruler or measuring tape
- Timer or stopwatch
🔬 Procedure: Balloon Experiment
- Label two Erlenmeyer flasks: "Sugar Water" and "Plain Water"
- Add 50mL of warm water to each flask
- Add 1 tablespoon of sugar to the "Sugar Water" flask and swirl to dissolve
- Transfer approximately 90% of your cultured yeast from each test tube to the corresponding flask (leave 10% behind - this is your seed culture for future experiments!)
- Swirl gently to mix the yeast with the fresh solution
- Stretch each balloon several times to make it easier to inflate
- Carefully place a balloon over the mouth of each flask, ensuring an airtight seal
- Place both flasks in a warm location and start your timer
- Measure balloon circumference at 10-minute intervals for 40 minutes
📊 Balloon Inflation Data
Measure the circumference of each balloon at 10-minute intervals. Use the widest part of the balloon.
| Time (minutes) | Sugar Water Balloon (cm) | Plain Water Balloon (cm) |
|---|---|---|
| 0 (start) | ||
| 10 | ||
| 20 | ||
| 30 | ||
| 40 |
📸 Click to upload photo of inflated balloons
🔗 Connecting Respiration to Photosynthesis
You've now observed cellular respiration in action through yeast cultures. Let's connect this back to photosynthesis and understand how these two processes are intimately linked in the carbon cycle.
The Opposite Processes
Photosynthesis and cellular respiration are essentially opposite chemical reactions. Look at their equations:
6 CO₂ + 6 H₂O + light energy → C₆H₁₂O₆ + 6 O₂
C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O + ATP energy
The Carbon-Oxygen Cycle
Notice how photosynthesis consumes the products of respiration (CO₂ and H₂O), and respiration consumes the products of photosynthesis (glucose and O₂). This creates a continuous cycle that sustains life on Earth.
| Characteristic | Photosynthesis | Cellular Respiration |
|---|---|---|
| Location | Chloroplasts (plants, algae, some bacteria) | Mitochondria (all eukaryotes) |
| Energy Flow | Stores energy (light → chemical) | Releases energy (chemical → ATP) |
| Input Molecules | CO₂ + H₂O | Glucose + O₂ |
| Output Molecules | Glucose + O₂ | CO₂ + H₂O |
| Energy Source | Sunlight (photons) | Glucose (chemical bonds) |
| Organisms | Autotrophs (producers) | All organisms (including plants!) |
🧬 Yeast and the Carbon Cycle
In your experiment, yeast cells broke down glucose (C₆H₁₂O₆) to produce CO₂, which inflated the balloons. This glucose originally came from plants through photosynthesis. The CO₂ your yeast produced can be used by plants to make more glucose, completing the cycle.
Thinking About Your Green Onion Photosynthesis Experiment
Remember when you observed green onions producing oxygen bubbles in the light? Those O₂ molecules came from water splitting during photosynthesis. That same oxygen is what aerobic organisms (including yeast and your own cells) use during cellular respiration to break down glucose efficiently.