Photosynthesis

Biology 1-2

Photosynthesis

Photosynthesis-the process of using light energy, carbon dioxide and water to make sugar and other food molecules. Light energy is stored in the bonds of

glucose. Done by plants, some protists and some

bacteria. 6CO2 + 6 H2O + light ---> Glucose + 6O2

The Chloroplast

Photosynthesis takes place in the chloroplast. In the chloroplast is the pigment chlorophyll.

• A pigment is a molecule that absorbs some colors of light and reflects others.

• Chlorophyll absorbs red and blue and reflects green.

Photosynthesis cont’d

Photosynthesis is divided into two parts: The light reactions

• Uses light energy and water.• Makes oxygen.

The Calvin Cycle• Uses carbon dioxide.• Makes glucose (sugar).• Does not require light energy.

The Light Reactions

Photosynthesis begins when chlorophyll absorbs light energy. Chlorophyll releases electrons. The energy in the electrons is used to make

ATP. Water is split, releasing two electrons and

oxygen.• The electrons replace the ones used to make

ATP.

The Calvin Cycle

The Calvin cycle turns carbon dioxide into glucose. Carbon dioxide enters the plant through the

leaves. ATP provides energy for the Calvin Cycle.

• The light reactions makes ATP needed for the Calvin Cycle.

The Calvin Cycle cont’d

Glucose made during the Calvin Cycle has many uses. Cellular respiration (in the mitochondrion)

• Produces more ATP than the light reactions. Making cell walls (for growth). Making starch (for energy storage). Making other organic compounds.

• Growth and maintenance.