Biology
Photosynthesis
Photosynthesis is the process of converting CO₂ and H₂O into glucose and O₂.
It is the opposite of respiration, which converts glucose and O₂ into CO₂ and H₂O.
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂Several factors can impact photosynthesis, including:
- ☆ Light intensity (or the amount of light reaching the plant)
- ☆ CO₂ concentration (or the amount of CO₂ in the atmosphere
- ☆ Temperature
Limiting Factors
These factors are known as Limiting Factors, which affect rates of photosynthesis on their own right. For light intensity and CO₂ concentration, the graph for the rate of photosynthesis increases, then levels off/plateaus as other factors become limiting.
The graph for temperature, however, is different. The graph shows an increase as temperature reaches the optimum (for the enzymes that perform photosynthesis), then a peak and decrease as enzymes start to denature.
Required Practical
Students should use pondweed submerged in a calcium carbonate solution to maintain a constant CO₂ level, and then follow these steps:
- ☆ Put the pondweed into the beaker with CaCO₃ solution.
- ☆ Put a light source 40cm away from the beaker.
- ☆ Start a timer for 1 minute and observe any bubbles.
- ☆ Repeat for reliability.
- ☆ Move the light source closer, and repeat the experiment.
To write this practical on paper, remember VVVVVR: (control) variable, (control) variable, (control) variable, (independent) variable, (dependent) variable, repeat (for reliability).
Respiration
The opposite of photosynthesis is respiration, or the usage of the glucose to release energy.
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂OThat is the formula for aerobic respiration, where the cell is fueled with enough oxygen to keep it going.
For anaerobic respiration, the breakdown of glucose is incomplete, leading to the buildup of lactic acid.
Lactic acid causes muscle fatigue, which feels like cramps.
C₆H₁₂O₆ → 2C₃H₆O₃After exercise, the buildup of lactic acid must be oxidised by the liver to get rid of it. This is called oxygen debt.