13.1.4—Chloroplast pigments in light absorption

Chloroplasts contain several photosynthetic pigments in the thylakoid membranes. Because different pigments absorb different wavelengths, the pigment mixture broadens the light that can be captured and transferred into photosynthetic reactions.

• Chlorophylls: chlorophyll a and chlorophyll b are located in the thylakoid membrane system. They absorb mainly in the blue-violet and red regions, while reflected green light contributes to the green appearance of plants.
• Carotenoids: β-carotene and xanthophyll are accessory pigments in the thylakoid system. Their different absorption range, mainly including blue-violet light, adds to the wavelengths available for light capture.
• Energy transfer: pigment molecules are organised in photosystems. Absorbed light excites pigment electrons, and the captured energy is transferred through the photosystem towards the reaction centre for the light-dependent stage.
• Functional consequence: a mixture of pigments absorbs a broader range of usable wavelengths than one pigment alone, helping the chloroplast capture light energy under varied illumination. This card establishes the pigment-to-light-capture link; it does not interpret absorption/action spectra or separate pigments by chromatography.

Do not confuse the colour a pigment reflects with the wavelengths it absorbs, place pigments in the stroma, or treat accessory pigments as a replacement for the reaction centre. Detailed spectrum graphs, chromatography and the full light-dependent pathway belong to neighbouring cards.