In the leaf disk assay, what is the purpose of adding baking soda to the water?

To provide a source of carbon dioxide for the leaves.

Why is it important to use a consistent wattage light source when comparing photosynthetic rates in different experimental setups?

To ensure that light intensity is not a variable affecting the rate of photosynthesis.

I can relate changes in BTB color to the rate of photosynthesis.

1
Photosynthesis is the process where plants use energy from the sun to convert water and carbon dioxide into sugars, releasing oxygen in the process.
2
In the leaf disk assay, leaves are infiltrated with water under a vacuum to make them sink, and then the rate at which they float again due to oxygen production is measured to estimate photosynthetic rate.
3
A control group without carbon dioxide is used to compare against the experimental group with carbon dioxide, ensuring that any observed flotation is due to photosynthesis.