Photosynthesis

Photo = Light Synthesis = the making of something

Photosynthesis is a process that uses light energy to make food. Organisms that make their own food are called autotrophs.

Photosynthetic Autotrophs include: Algae (including seaweed) Most plants (a few are parasites or saprophytes) Some protists Some bacteria (cyanobacteria)

Animals can not do photosynthesis. Animals are not autotrophs. Animals are heterotrophs. ( heterotrophs need to eat other organisms to get energy.)

Animals eat autotrophs either directly or indirectly through the food chain. Animals get their energy from autotrophs. Autotrophs get their energy from the sun. Therefore animals get their energy from the sun (but indirectly).

Photosynthesis converts light energy into chemical energy. (Food is chemicals and the chemicals contain energy) Photosynthesis is divided into two parts. Part one is the Light Reactions. Part two is the Calvin Cycle.

In plants, both parts of photosynthesis take place in the chloroplast. The chloroplast contains sacks called thylakoids. Stacks of thylakoids are called grana The area of the chloroplast surrounding the thylakoids is called the stroma.

The light reactions take place in the thylakoid membranes. The Calvin cycle takes place in the stroma. Notice that both are in the chloroplast.

The purpose of the light reactions is to capture energy from sunlight and convert it to chemical energy. This energy is used to run the Calvin cycle. The purpose of the Calvin cycle is to make organic compounds such as carbohydrates. These compounds are the plants food. ( People sometimes call fertilizer plant food, but this isn’t really correct.)

The light reactions: involve chlorophyll a involve accessory pigments which absorb wavelengths that chlorophyll a can’t absorb involve an electron transport chain

Electron Transport Chain (Where is this chain?)

The Light Reactions: Require sunlight Require water Do not use carbon dioxide Do not make food Release oxygen( by splitting water)

The Calvin Cycle: Requires carbon dioxide Does not require light But will not run without energy from the light reactions( ATP and NADPH) Does not produce oxygen Produces food by carbon fixation

Relationship between the light reactions and the Calvin cycle

How does the plant get the carbon dioxide? How does the plant release oxygen?

The leaf has breathing holes.

The breathing holes are called stomata and they are opened and closed by pairs of guard cells. One opening is called a stomate or stoma. Be careful not to confuse this with the stroma. Where is the stroma? Where are the stomata?

Stomata are in the epidermis of the leaf.

Why would the plant need to open and close stomata? Which surface of the leaf would be likely to have the most stomata? Why?