Question

2. Briefly propose a simple experiment that would demonstrate the rate of photosynthesis by examining the "first stage."

Answer 1

Photosynthesis involves converting light energy into chemical energy. The formula for photosynthesis is the following: 6C02 + 6H2O -- (light energy) --> C6H12O6 + 6O2 If we take a look at the different components of the equation, we can quickly determine a few ways of measuring the rate of photosynthesis. Since carbon dioxide is used up during the process, and oxygen produced, the rate of photosynthesis can be measured directly, by measuring either the production of oxygen or the uptake of carbon dioxide. For instance, aquatic plants (plants in water) release oxygen bubbles during photosynthesis which can be measured. The easiest way to measure photosynthesis rate in this manner is to measure carbon dioxide or oxygen levels using a data logger. We can also measure the rate of photosynthesis by measuring an increase in the plant's biomass (weight). If you harvest batches of plants at a series of different times and you calculate the biomass of these batches, the increase in biomass will give you an indirect measure of the rate of photosynthesis in the plants! Different conditions will affect the rate of photosynthesis. I will focus on 3: (1) Temperature: Photosynthesis is controlled by enzymes (biological catalysts), and enzymes are sensisitve to changes in temperature. As temperature increases, the rate of photosynthesis increases because reactants have more kinetic energy and so more collision will happen. The rate will increase until the optimal temperature is reached. If temperature keeps increasing past this point, enzymes will denature and thus the rate of photosynthesis will drop. (2) Light intensity: Light is absored by chlorophyll in plants, which convert light energy into chemical energy or ATP. As light intensity increases, the rate of photosynthesis increases until a certain point when all the available chlorophyll become saturated with light (they are working at maximum capacity). At this point, the photosynthetic rate will plateau. (3) Carbon dioxide concentration: Carbon dioxide is involved in the fixation of carbon to make organic molecules. As carbon dioxide concentration increases, so does the rate of photosynthesis, since more organic molecules are able to be produced. At a certain concentration, the rate of photosynthesis will plateau because the enzymes responsible for carbon fixation are working at full capacity.