In 3-5 sentences, explain how the rate of photosynthesis or cellular respiration can be measured using products or reactants.

There are a few key methods to calculate the rate of photosynthesis. These include:

1) Measuring the uptake of CO2

2) Measuring the production of O2

3) Measuring the production of carbohydrates

4) Measuring the increase in dry mass

As the equation for respiration is almost the reverse of the one for photosynthesis, you will need to think whether these methods measure photosynthesis alone or whether they are measuring the balance between photosynthesis and respiration.

Explanation: There would be no biology without photosynthesis. Plant biomass is the food and fuel for all animals. Plants are the primary producers. These amazing organisms are capable of capturing the energy of sunlight and fixing it in the form of potential chemical energy in organic compounds. The organic compounds are constructed from two principle raw materials; carbon dioxide and water (which is a source of hydrogen). These compounds are stable and can be stored until required for life processes. Hence animals, fungi and non-photosynthetic bacteria depend on these for the maintenance of life.

But how can we measure the rates at which photosynthesis takes place?

The quantities are mind boggling. A hectare (e.g. a field 100 m by 100 m) of wheat can convert as much as 10,000 kg of carbon from carbon dioxide into the carbon of sugar in a year, giving a total yield of 25,000 kg of sugar per year.

There is a total of 7000 x 109 tonnes of carbon dioxide in the atmosphere and photosynthesis fixes 100 x 109 tonnes per year. So 15% of the total carbon dioxide in the atmosphere moves into photosynthetic organisms each year.

6CO2+6H2O>C6H12O6+6O2

based on O2 (product)

Photosynthesis can be measured by the O2 that is being released. You can introduce an algae in a test tube with water and measure the rate of photosynthesis based on the number of bubbles released.

based on CO2(reactant)

To prove that this gas is O2 you can introduce a match that is barely lit in the tube and it will light up.The photosynthesis can be measured by the consumption of CO2. If an algae is introduced in water that has boiled for a few minutes the CO2 is eliminated so the plant won't release any bubbles. If sodium carbonate is introduced in the water the bubble release will begin.

based on glucides (product)

A leaf that has been exposed to light can be boiled in ethanol and marked with Lugol solution. The more intense the coloration the more starch there is.