Photosynthesis

Photosynthesis is the conversion of light energy to chemical energy which is then

stored in the form of glucose or other organic compounds. Photosynthesis occurs in

plants, algae and certain prokaryotes. Photosynthesis is generally the opposite of

respiration where photosynthesis starts with CO2, light energy, and water to yield glucose,

water and oxygen. This is the general equation for photosynthesis: 6CO2 + light energy +

12H2O = C6H12O6 + 6O2 + 6H2O.

In plants photosynthesis occurs in the thylakoid membrane. There are two

reactions in the thylakoid membrane: the light dependent reactions, and the light

independent reactions. In the light dependent reactions, light excites an electron into a

higher energy state. This electron is then captured by an electron acceptor and the energy

released during it’s fall back down to ground state is harvested to create ATP. In the light

independent reactions, the energy made from the light dependent reactions is used to make

glucose, a six carbon sugar. The carbon comes form the break down of CO2 and the

oxygen is released into the air.

However, there are imperfections. Sometimes the light independent reactions uses

O2 instead of CO2 which produces a two carbon compound. This compound is useless to

the plant and it uses more energy to break it back down to CO2. The process where O2 is

used instead of CO2 is called photorespiration. Plants which have a lot of photorespiration

are known as C3 plants and are very slow growing. Fast growing plants, plants that have

little photorespiration, are known as C4 plants.

This experiment tested how much CO2 is consumed in C3 plants versus C4 plants.

The null hypothesis is that in C3 plants will consume as much CO2 as C4 plants. The

alternate hypothesis is that C4 plants will consume more CO2 because photorespiration is

very little.

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