Megan Petterborg
Biology 1010
Final Paper
Photosynthesis and Respiration
Photosynthesis converts solar energy into the chemical energy of a carbohydrate.
Photosynthesis powers almost all trophic chains and food webs in the world. It only
occurs in the presence of sunlight. Photosynthesis is the production of food while
respiration is the breakdown of food. The simple meaning of the equation for
photosynthesis means that carbon dioxide from the air and water combine in the
presence of sunlight to form sugars and oxygen is released. The producers of
photosynthesis are autotrophs and the consumers are heterotrophs. Two sets of
reactions in photosynthesis include light reactions and the Calvin cycle reactions. Light
reactions only occur when solar energy is available while the Calvin cycle reactions can
happen during the daytime or the nighttime. Oxidation and reduction both occur in
photosynthesis. Oxidation is when a molecule loses electrons (hydrogen atoms),
reduction is when a molecule gains electrons (hydrogen atoms). This is called the
redox reaction. Pigments absorb solar energy. These pigments absorb red, blue, and
violet light. They don’t absorb green light, which is why leaves appear green to us.
There are two types of photosystems called photosystem 1 and photosystem 2. The
electron transport chain or ETC is a series of membrane-bound electron carriers. An
electron acceptor sends electrons down the ETC. As they are passed between different
carriers they give up energy. Carriers use this energy to pump hydrogen across the
membrane. When these ions go down their electrochemical gradient, ATP forms.
Cellular respiration is a redox reaction that requires oxygen. Unlike
photosynthesis cellular respiration occurs at all times. Cellular respiration has four
phases: Glycolysis, The Preparatory Reaction, The Krebs Cycle, and The Electron
Transport Chain. Glycolysis is the first phase. It breaks down glucose to two molecules
of pyruvate. The second step is The Preparatory Reaction, which takes place in the
matrix of the mitochondria. The end product of this phase is a 2-carbon acetyl group.
The third step is The Krebs Cycle. It also takes place in the matrix of the mitochondria
like The Preparatory Reaction. The Krebs cycle produces two ATP per glucose
molecule. The Krebs cycle generates lots of NADH. The electron transport chain is a
series of electron carries in the cristae of the mitochondria. When oxygen is not
available fermentation produces two ATP per glucose molecule. It only provides a
energy for a short term activity. Lactate or alcohol buildup is toxic to cells. In humans
lactate buildup makes a person oxygen debt because oxygen is needed to completely
metabolize it.