Fig. 10.1. 3 Stages of Photosynthesis. Capturing light energy Using this energy to make ATP to split H2O molecules and use (H+) to reduce NADP+ to NADPH Both 1&2 need light and are known as the LIGHT REACTIONS
Both 1&2 need light and are known as the LIGHT REACTIONS
3. The power of ATP and NADPH is used to synthesize organic molecules (glucose) from CO2 in the air (carbon fixation)
Carbon fixation can happen without light and is called THE CALVIN CYCLE
- each pigment molecule of a photosystem is capable of capturing PHOTONS (packets of electromagnetic energy) that boost the pigment’s atoms to a higher energy level.
- a protein lattice holds the pigments in close contact with one another and the energy gained in each pigment molecule is transferred from one chlorophyll molecule to another in the thylakoid until it reaches a key protein that transfers the excited electrons of energy to a series of proteins that make NADPH+ and ATP to make glucose in the stroma.
- leaves absorb mostly blue and red light and the green if reflected (that is why we SEE it)
Phase #1: Carbon Fixation
CO2 is incorporated in to a five-carbon molecule called ribulose biphosphate (RuBP) catalyzed by the enzyme rubisco (RuBP carboxylase). The product of this reaction is six carbon molecule which is very unstable and splits in ½ to make two 3-carbon molecules of 3-phosphoglycerate.
Phase #2: Reduction
ATP and NADPH (light reactions) are used to convert the 3 carbon molecules into glyceraldehyde 3-phosphate (G3P) which is a 3-carbon precursor to glucose.
Phase #3: Regeneration
More ATP is used to convert some of the product of #2 back to RuBP (acceptor of CO2).
Net Output: 3 molecules of CO2 yields one molecule of G3P
Used by some tropical plants to cut down on photorespiration %.
These plants switch the time of day when stomata are open. Open at NIGHT when cooler to avoid heat of day that normally increases CO2 loss.