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Photosynthesis is a metabolic process by which an autotroph combines carbon dioxide and water by harnessing sunlight, producing glucose and oxygen gas. To understand this process, we must first understand light.
Light is electromagnetic radiation that travels in waves in photons. The wavelength (λ) is inversely proportional to energy (--> The shorter the wavelength, the higher the energy!). To the right is the Electromagnetic Radiation Spectrum, which shows that visible light actually is a very small range within the entire spectrum. Red light has a longer wavelength than purple, so it has less energy than purple.
Recall: If something is a specific colour (ex. Red) it is reflecting that colour and absorbing all others.
Pigment molecules have colour because they are reflecting that colour, and absorbing other colours.
An absorption spectrum shows which wavelengths of light are being absorbed by a pigment. The one to the left shows how chlorophyll (the pigment found in chloroplasts) absorbs blue and red light, but has low absorbance of green light. This means that the green light is reflected, which is why chloroplasts and plant leaves in general are green!
Chlorophyll and Accessory Pigments
Chlorophyll and Accessory Pigments
Chlorophyll is a green pigment that absorbs light energy to drive the initial stages of photosynthesis. It actually has two different types: chlorophyll a and chlorophyll b. Each has unique absorption spectrum. Chlorophyll a is the only pigment that can transfer the energy of light for carbon fixaton, while Chlorophyll b is an accessory pigment.
Other accessory pigments include (but are not limited to):
- Carotenoids – energy absorbing molecules to protect tissue from excessive light energy (photoprotection).
- Xanthophylls (appear yellow) – in thylakoid along with chlorophyll a and b, but masked by green of chlorophyll. Visible in fall leaves.
- Anthocyanin (appear red, violet, blue) – in vacuoles to provide colour to fruit and leaves.
Photosynthesis is broken up into two stages:
- The Light Reactions, where sunlight is captured by chlorophyll, creating ATP and NADPH (an alternate energy carrier found in plants)
- The Dark Reactions, where glucose is made from CO2 using the Calvin cycle (Carbon fixation)
Textbook Practice
Textbook Practice
Read p.212-217
Questions: Click on the link to the right to access questions that go along with your textbook --> Intro to Photosynthesis
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