Photosynthesis

• There are 3 main stages of photosynthesis: Light harvesting, Light dependant stage and Light independant stage
• leaf structure

  A) waxy cuticle

  B) upper epidermis

  C) Palisade mesophyll layer

  D) spongy mesophyll layer

  E) xylem vesssel

  F) stoma

  G) lower epidermis

  H) guard cells

  
• chloroplast structure

  A) outer membrane

  B) inner membrane

  C) chloroplast envelope

  D) one granum

  E) stroma

  F) intergranal lamella

  G) starch grain

  H) lipid droplet

  I) ribosomes

  
• Pigments:

  •Chlorophyll a and b:–Absorbs light in the blue-violet and red regions of the spectrum (appear green).

  •Carotenoids: B-carotene (carrots)–Absorbs light in the blue-violet range (appear orange).
• A photosystem is a collection of pigment molecules designed to channel energy through a specific chlorophyll molecule. Both Photosystem I (PSI) and Photosystem II (PSII) comprise primary pigments (variants of chlorophyll a) and accessory pigments (including other forms of chlorophyll a, chlorophyll b, and carotenoids). These pigments form clusters known as antenna complexes, with each complex constituting a photosystem.
• Chlorophyll a is situated at the base of the antenna complex within the reaction center. The accessory pigments play a crucial role in capturing light energy and transmitting it to chlorophyll a, the primary pigment.
• Light dependant stage

  A) 2H+

  B) Photosystem II

  C) 2e-

  D) Electron acceptor

  E) ADP

  F) ATP

  G) Photosystem I

  H) 2e-

  I) Electron acceptor

  J) 2e-

  K) NADP+

  L) NADPH + H+

  M) Z scheme

  
• Light independant stage aka Calvin cycle

  A) Carbon dioxide

  B) ATP

  C) ADP + Pi

  D) NADPH + H+

  E) NADP+

  F) Triose phosphate

  G) ATP

  H) ADP + Pi

  I) Ribulose biphosphate

  J) Glycerate phosphate

  K) Fixation of carbon dioxide

  L) reduction of glycerate phosphate

  M) regeneration of ribulose biphosphate

  N) product synthesis

  
• When the light is removed (the plant is in darkness) the light dependent reaction stops. Consequently ATP and NADPH will no longer be made and be available for the light independent reaction. This means that glycerate phosphate cannot be converted into triose phosphate, leading to a buildup of glycerate phosphate and a reduction in ribulose bisphosphate (as the ribulose bisphosphate present in the stroma fixes CO2 to form glycerate phosphate and no more can be regenerated from triose phosphate). The concentrations of each level off as the cycle grinds to a halt.

  
• When CO2is no longer available it cannot be ‘fixed' and combine with ribulose bisphosphate therefore glycerate phosphate cannot be formed. The ribulose bisphosphate therefore builds up and the glycerate phosphate already in the system gets converted to triose phosphate, leading to its rapid fall. As before the concentrations of each level off as the cycle stops.