Providing an in-depth, complete, and well-written description of IB biology topic 2.9, including all the mechanisms to thoroughly understand photosynthesis. It includes diagrams, and annotated pictures, and all important key words are highlighted.
Photosynthesis
Photosynthesis involves the use of light energy to synthesise organic compounds from inorganic molecules as
B G R
wavelength
of
light (nm)
Light Spectrum
↑
Visible light has a range of wavelengths (~ 400 – 700 nm) • Violet has the shortest wavelength, red has the longest
0
Violet
·
is the shortest chlorophyll absorbs Blue, and violet the best.
Indigo
wavelength.
>Absorption spectrum: shows how effective
specificwavelengths
is at
pigment absorbing a a
Light Absorption
Pigments are required for the conversion of light energy into chemical energy in photosynthetic organisms Chlorophyll is the main photosynthetic
pigment, although other accessory pigments also exist (e.g. carotenoids)
• Chlorophyll absorbs red light and blue light most effectively and reflects green light more than other colours
An absorption spectrum (left) indicates the wavelengths of light absorbed by each photosynthetic pigment (e.g. chlorophyll
I
An action spectrum (right) indicates the overall rate of photosynthetic activity at each wavelength of light
Light energy is converted into chemical energy Carbon compounds are made from the chemical energy • ATP and hydrogen are fixed
• Light is absorbed by chlorophyll to produce ATP with carbon dioxide
• The photolysis of water forms oxygen and hydrogen • This results in the formation of organic molecules
Limiting Factors
When a process depends on more than one condition, the rate will be limited by the factor nearest its minimum value
Limiting factors in photosynthesis include:
• Temperature (influences photosynthetic enzymes)
• Light intensity (required for chlorophyll photoactivation)
• Carbon dioxide concentrations (CO2 is a core substrate)
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