PHOTOSYNTHESIS

OXIDATION

• the loss of hydrogen atoms or electrons
• the gain of oxygen

REDUCTION

• the gain of hydrogen atoms or electrons
• the loss of oxygen

STRUCTURE OF THE LEAF

• large surface area that absorbs as much sunlight as possible
• arrangement of leaves that minimises overlapping
• thin to keep diffusion pathway short
• transparent cuticle + epidermis to let light through to mesophyll cells
• long narrow upper mesophyll cells packed with chloroplasts
• numerous stomata so each cell is only a short diffusion pathway from one
• stomata that open and close in response to changes in light intensity
• air spaces in lower mesophyll later to allow rapid diffusion in gas phase
• network of xylem and phloem for transport

STRUCTURE OF THE CHLOROPLASTS

GRANA

• stacks of thylakoids where light-dependent stage takes place
• thylakoids contain photosynthetic pigment chloropyll
• thylakoids may have tubular extensions that join with thylakoids in adjacent grana (inter-granal lamellae)

STROMA

• fluid-filled matrix where the light independent stage takes place
• contains starch grains etc

THE LIGHT DEPENDENT REACTIONS

1. ABSORPTION OF LIGHT ENERGY

• chlorophyll absorbs light energy
• electrons are excited to higher energy levels
• electrons taken up by electron acceptor molecule on the thylakoid membrane

2. PHOTOPHOSPHORYLATION

• electrons move across electron transport chain via electron carriers
• lose energy as they do so
• energy used to synthesise…