Photosynthesis Topic E: 3.8 & 8.2

What is Photosynthesis? A) The production of carbon compounds in cells using light energy B) The opposite of respiration C) A reaction only carried out by plants D) The production of light energy by plants cells

Done by plants and some bacteria, and some protists

Photosynthesis  The equation is almost the opposite of respiration  6CO 2 + 6H 2 O + light  C 6 H 12 O 6 + 6O 2  Low energy molecules become a high energy molecule

Photosynthesis has 2 stages  Photosynthesis has 2 stages:  1) Light-dependent reactions:  Require continual supply of light  produce compounds used in…  2) Light-independent reactions:  Can run in darkness until above compounds are used up.  Produce glucose, amino acids and other organics.

So the process requires light… But not all light is equal

Light  Spectrum: range of wavelengths of radiation.  Short = blue; medium = green/yellow; long = orange/red.  The efficiency of photosynthesis depends on the wavelength.  Action Spectrum: the percent of light of a wavelength that is used in photosynthesis.

Action Spectrum of Photosynthesis  The shorter and longer wavelengths are used most efficiently.  These colours are red and blue light  Explained by different photosynthetic pigments.  Main pigments are chlorophyll a & b  Compare Action Spectrum to

Absorption Spectrum VVVVery similar to action spectrum. AAAAbsorption Spectrum: the percent of light of a wavelength that is absorbed by the pigments. IIIIf light is not absorbed it is reflected or transmitted. CCCChlorophyll absorbs red and blue light most effectively and reflects green light more than other colours WWWWhy leaves appear green.