PHOTOSYNTHESIS:
- Photosynthesis only occurs in autotrophs such as plants, algae, and cyanobacteria.
- Photosynthesis is a two-step process:
- 1. The "light reactions" use solar energy and chlorophyll to split water molecules into hydrogen and oxygen (the "Hill reaction").
Oxygen gas is released as a waste product. The hydrogen combines with NADP to make NADPH.
Energy is used to combine ADP + phosphate and synthesize ATP; this energy is used to drive the dark reactions.
- 2. The "dark reactions" (Calvin cycle): In a series of reactions, atmospheric CO2 combines with NADPH and is "fixed" (initially) into carbohydrate compounds such as glucose. Water is released.
- OVERALL REACTION:
12 H2O + 6 CO2 ——> C6H12O6 + 6 H2O + 6 O2
water carbon dioxide glucose new water oxygen gas
CELLULAR RESPIRATION:
- Respiration occurs in all organisms, both autotrophs (in the dark) and heterotrophs (all the time).
- Chemically, respiration is the opposite of photosynthesis:
C6H12O6 + 6 O2
glucose oxygen
| respiration
————>
<————
photosynthesis
| 6 H2O + 6 CO2
water carbon dioxide
|
GLOBALLY, Photosynthesis takes CO2 from the atmosphere and releases oxygen;
respiration takes oxygen from the atmosphere and releases CO2.
|