Summary WJEC (England) Eduqas A-Level Biology - 1. Energy For Life - 2. Photosynthesis

a. light trapping adaptations
leaf
 large SA: capture max light
 thin: light penetrates through
 stomata & air spaces: CO2 diffuse in to photosynthesising cells
 transparent cuticle & epidermis: light penetrates through

palisade cell
 large vacuoles: chloroplasts form single layer at cell periphery – don’t shade each other
 more chloroplasts than spongy mesophyll – near top of cell = more exposed to light: capture max light

chloroplast
 thylakoid large SA
 move within cell: max light absorption (top) / protect pigments from bleaching (bottom)
 rotate within cell
 pigments in single layer along thylakoid membrane



b. chloroplasts = transducers: convert light photon energy to chemical energy (ATP)
Photosynthetic pigments – absorb photons at great range of wavelengths of light
Chlorophyll – absorb red & blue-violet Carotenoids – absorb blue-violet
chlorophyll a: yellow-green beta-carotene: orange
chlorophyll b: blue-green xanthophylls: yellow



c. light harvesting by antenna complex to reaction centre to emit e -
Absorption spectra of pigment: how much light absorbed at different wavelengths
Action spectra: rate of photosynthesis at different wavelengths



d. Photosystem 1 (P700) & 2 (P680) – thylakoid membrane: absorb light at range of wavelengths
antenna complex – contains pigments & proteins: energy passed through pigments to reaction centre
reaction centre – 2 chlorophyll a: energy from absorbed light boosts electrons to excited state = emit high-energy e -