What is photosynthesis?
- Photosynthesis is the process of converting light energy into chemical energy, and storing it in sugar. All plants and some algae use photosynthesis to get energy from light.
- Light energy (for example, the sun), carbon dioxide, and water.
- In plants’ chloroplasts, primarily in the leaves.
Click image to be taken to the source. What do different parts of the leaf do?
- Upper and lower epidermis: protection for most of the leaf
- Stomas: air exchange; they let in carbon dioxide and let out oxygen
- Veins (or vascular bundles): move water and nutrients around the plant
- Mesophyll cells: contains chloroplasts, which means photosynthesis occurs here
Chloroplasts and Chlorophyll
- Chloroplasts are tiny cells that begin the whole photosynthetic process.
- Chloroplast contain chlorophyll, which are responsible for the green pigmentation of most plants
- Chlorophyll isn’t actually green; it’s the green light that is not absorbed by the chlorophyll that reaches our eyes and makes it appear green
- Blue and red light is absorbed by chlorophyll and is used in photosynthesis
The Photosynthetic Process
Photosynthesis Equation
Click image to be taken to the source.
Click image to be taken to the source.
There are actually two stages to photosynthesis: the light reactions and the dark reactions (or the Calvin cycle).
Light Reactions: light energy --> chemical energy
Light Reactions: light energy --> chemical energy
- Chlorophyll absorbs light
- The light energizes electrons to a transport chain in the thylakoid membrane.
- As the chain progresses, the electrons drop to a lower energy state and produces ATP and NADPH.
- The chlorophyll molecules replace their lost electrons with a hydrogen from water—this splits the water molecule and cause oxygen to be a by-product.
Click image to be taken to the source.
Dark Reactions (the Calvin cycle): chemical energy --> sugars
- Energy produced from the ATP and NADPH in the light reactions creates a chemical pathway, using carbon drawn from carbon dioxide in the air. This carbon is used to create a 3-carbon sugar, G3P (glyceraldehyde-3-phosphate).
- Using G3P, the cells build other sugars, such as glucose.
- These sugars are transported to other parts of the cell, where they are broken down to be used as energy.
Khanacademy has an overview of the photosynthetic process in the YouTube video below. (x)
