Higher Biology - Photolysis, Carbon Fixation

what do chloroplasts contain?

structures called thylakoids

photosynthesis stage 1

photolysis; the light-dependent reaction

photosynthesis stage 2

carbon fixation (calvin cycle)

step 1 light-dependent reaction

absorbed light energy excites electrons in the pigment molecule

step 2 light-dependent reaction

The transfer of these electrons through the electron transport chain releases energy to generate ATP by ATP synthase

step 3 light-dependent reaction

Energy is also used for photolysis, in which water is split into oxygen, which is evolved, and hydrogen ions, which are transferred to the coenzyme NADP

what do light reactions produce?

ATP, NADPH, oxygen – diffuses out of the chloroplast, out of the mesophyll cell then out through the stoma

step 1 carbon fixation

enzyme RuBisCO fixes carbon dioxide by attaching it to ribulose bisphosphate (RuBP), producing 3-phosphoglycerate (3PG)

step 2 carbon fixation

The 3-phosphoglycerate (3PG) is phosphorylated by ATP and combined with hydrogen ions from NADPH to form glyceraldehyde-3- phosphate (G3P)

step 3 carbon fixation

Glyceraldehyde-3- phosphate (G3P) is used to regenerate RuBP and for the synthesis of glucose

step 4 carbon fixation

Glucose may be used as a respiratory substrate, synthesised into starch or cellulose or passed to other biosynthetic pathways

step 5 carbon fixation

These biosynthetic pathways can lead to the formation of a variety of metabolites such as DNA, protein and fat