Investigating the Rate of Photosynthesis: How Fast Can Plants Make Food?

Photosynthesis is the process plants use to make their food, and its rate can change based on light, temperature, and carbon dioxide $(CO_2)$ levels.

 

What is the Rate of Photosynthesis?

The rate of photosynthesis is how quickly plants produce glucose and oxygen. Scientists measure this rate by observing:

• Oxygen production (e.g., bubbles from aquatic plants).
• $CO_2$ uptake (e.g., using a pH indicator).

 

 

Key Factors Affecting Photosynthesis

1. Light Intensity:

   • More light = faster photosynthesis (up to a point).
   • No light = no photosynthesis.

2. Carbon Dioxide Concentration:

   • More $CO_2$ = faster photosynthesis (up to a point).
   • Low $CO_2$ slows the rate.

3. Temperature:

   • Enzymes involved in photosynthesis work fastest at an optimum temperature.
   • Too cold = slow reactions. Too hot = enzymes denature.

 

 

How to Investigate the Rate of Photosynthesis

Equipment Needed:

• Aquatic plant (e.g., Elodea or Cabomba)
• Beaker of water
• Sodium bicarbonate (for $CO_2$)
• Lamp (light source)
• Ruler (to measure light distance)
• Stopwatch

 

 

Method:

1. Measure Oxygen Production

• Place the aquatic plant in a beaker filled with water and a pinch of sodium bicarbonate (to ensure $CO_2$ availibility) 
• Position the plant under a lamp and measure the distance between the lamp and the beaker.
• Start the stopwatch and count the number of oxygen bubbles produced in 1 minute.

 

2. Test Light Intensity

• Repeat the experiment by moving the lamp to different distances (e.g., 10 cm, 20 cm, 30 cm).
• Record the bubble count for each distance.

 

3. Test $CO_2$ Concentration

• Add different amounts of sodium bicarbonate to the water (e.g., 1g, 2g, 3g).
• Count the bubbles for each level of $CO_2$

 

4. Test Temperature

• Place the beaker in water baths at different temperatures (e.g., 10°C, 20°C, 30°C, 40°C).
• Measure the bubbles at each temperature.

 

 

Expected Results

1. Light Intensity:

   • Closer light = more bubbles (faster photosynthesis).
   • Beyond a certain point, increasing light intensity won’t increase the rate (other factors become limiting).

2. CO₂ Concentration:

   • More CO₂ = more bubbles.
   • Beyond a certain point, increasing $CO_2$ won’t increase the rate.

3. Temperature:

   • Photosynthesis increases as temperature rises to the optimum temperature.
   • Beyond this, the rate decreases as enzymes denature.