Photosynthetic Activity

The light receiving photosynthetic pigments in the plant are at the thylakoid membrane in the chloroplasts. The most common pigment in his quantity and is present in all green plants and alga is ‘Chlorophyll a’. Other pigments are called secondary pigments and include ‘Chlorophyll b’ and carotenoids. To every photosynthetic pigment a typical absorption spectrum, meaning a different absorption ability of light in different wavelengths.

• Chlorophyll a – 420nm, 663nm
• Chlorophyll b – 453nm, 645nm
• Carotenoids – 420nm-480nm

The light receiving pigments array constructs a type of antenna that is used to transfer light energy to the reaction center (Chlorophyll a), which drives the light process in Photosynthesis. The quantitative ratio of different chlorophylls varies in different plants, organs at the same plant, different exterior conditions and different periods.

The absorption by the chlorophyll is mainly obvious in the red and blue-violet area, although absorption lines in other areas do exist. Chlorophylls a and b are separated by the wavelength at which maximum absorption occurs. The absorption lines of Chlorophyll a at both the blue and red ends of the spectrum are farther away than the absorption lines of Chlorophyll b. Chlorophyll quantities in a green leaf vary between 0.05%-0.2% of the fresh weight. The ratio between Chlorophyll a and Chlorophyll b is 2.5/1=a/b, although it is not permanent because Chlorophyll a is more easily destroyed, meaning the quantitative ratio varies under different conditions.

Types of Plants

Sun and shade plants differ by various leaf qualities due to the amounts of light reaching them. Shade plants allocate more resources to harvest light than CO2 fixation. This is why in shade plants the secondary pigments are produced in greater quantities – more Chlorophyll and less RuBisCO*.

* Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), is an enzyme that is used in the Calvin cycle to catalyze the first major step of carbon fixation, a process by which the atoms of atmospheric carbon dioxide are made available to organisms in the form of energy-rich molecules such as sucrose.

See Also:
Light & Plants Part I - The Basics
Artificial Light