Photosynthesis

Englemanns experiment

• experiment to determine which wavelengths of light most effective in photosynthesis
• using green alga in aerobic bacteria evenly distributed
• exposed alga to range of wavelengths 
• bacteria found to cluster at blue and red wavelengths 
• these had increased rates of photosynthesis 

structure and role of chloroplasts

• organelles surrounded by a double membrane 
• grana are stacks of disc like thylakoids with photosynthetic pigments
• stroma is the fluid interior

photosynthetic pigments

• light energy trapped 
• different wavelengths trapped by different pigments
• chlorophylls absorb in the red and blue regions 
• carotenoids absorb from just the blue region
• two main types of carotenoids are carotenes and xanthophylls which act as accessory pigments 

absorption and action spectra

• absorption spectrum represents as a graph indicating how much light a particular pigment absorbs at each wavelength
• action spectrum is a graph showing the rate of photosynthesis at different wavelengths
• there is a close correlation between absorption spectrum and action spectrum
• pigments are responsible for absorbing light used in photosynthesis

light harvesting

• chlorophylls and accessory pigments in thylakoid membranes of chloroplast are grouped in clusters called antenna complex
• proteins associated aid funneling photons of light so the pigments pass absorbed light energy from one to the next
• tranferred until they reach chlorophyll a, a primary pigment molecule known as the reaction centre
• photosystem 1 has absorption peak of 700nm
• photosystem 2 has absorption peak of 680nm

light dependant stage of photosynthesis

• occurs in thylakoid membranes
• photolysis is the splitting of water by light producting H+ and e-
• ATP is synthesised from ADP and Pi in photophosphorylation
• H+ reduces NADP to NADPH
• as electrons flow through chain of carriers…