BY4.3 Photosynthesis

Photosynthesis

green plants using light to synthesise nutrients

• found in the mesophyll cells and the guard cells
• energy from sunlight is trapped by the chlorophyll pigment

• biochemical process divided into 2 parts:
  • light dependent stage
  • light independent stage/ calvin cycle

Light harvesting

• chlorophylls and accessory pigments are found in the thylakoid membrane
• grouped into several clusters of hundreds of moleucles - form the antenna complex
• special proteins assocaited with pigments help to funnel photons of light energy enetering the chlorophylls
  • pigment moleules pass absorbed light energy from one molecule to the next
• photons of light are passed on until they reach a primary pigemtn molecule known as the reaction centre
  • usually chlorophyll a

light strikes a molecule at the reaction centre and an electron is raised to a higher energy level

it can:

• move to another atom and form a bond
• be emitted and go around a ciriuit
• fall back to a lower energy level and emit light
• fall back to a lower energy level and pass energy to another substance

there are 2 types of reaction centres :

• PSI - arranged around a chlorophyll a molecule with a peak absorbance of 700nm (P700)
• PSII - arranged around a chlorophyll a molecule with a peak absorbance of 680nm (P680)

Light Dependent Stage:

occurs in the thylakoids:

• water is split by photolysis to form protons and electrons
• ATP is synthesised through photophosporylation
• NADP is reduced into NADPH2

ATP can be synthesised through cyclic and non cyclic photophosphorylaton

Non-cyclic photophsophorylation

• photons of light are absorbed by PSII and passed to chlorophyll a in the reaction centre
• 2 electrons are rasied to a igher energy level, are displaced and…