Volcanic and impact theories of dinosaur extinction and atmospheric darkness

Photosynthesis is critical for the survival of all life on earth. The process of photosynthesis within plants consists of two processes, one which begins with energy from the sun in the form of visible light, and another which is light-independent and capture carbon dioxide for glucose production (Audesirk, Audesirk, & Byers, 2008).

Plants are green because they absorb the red and blue wavelengths of visible light, thereby reflecting the color green (University of Idaho, 2008). In the light-dependent phase of photosynthesis, oxidative phosphorylation occurs when light pigments are absorbed by plant chloroplasts and converted into ATP and NADPH in the thylakoid membranes (University of Idaho, 2008; Audesirk, Audesirk, & Byers, 2008). The light-independent phase, also known as the carbon fixation reactions, uses the ADP and NADPH to produce glucose from fixed and reduced carbon dioxide and the enzyme RuBisCo (University of Idaho, 2008; Audesirk, Audesirk, & Byers, 2008). Water is necessary to keep the electrons moving through the plant system, and oxygen is released into the atmosphere as a result of photosynthesis.

Aerobic respiration in living creatures is also dependent upon water, carbon dioxide, glucose, and oxygen (Audesirk, Audesirk, & Byers, 2008). During aerobic respiration, oxygen is the catalyst for glucose to be broken down into carbon dioxide and water, releasing ATP for cellular energy (IUPUI Dept of Biology, 2004). The most basic premise of respiration is that oxygen must be taken in and carbon dioxide waste released; this is a perfect complement (reverse reaction) to the photosynthesis of plants, which takes in carbon dioxide and releases oxygen (Audesirk, Audesirk, & Byers, 2008). In addition, plants produce the glucose that is necessary to fuel the respiration of aerobic organisms, and humans can control the amount and type of plants produced by forcing photosynthesis through horticulture and agriculture. These complementary processes are the key factor in the survival of all life on earth (University of Idaho, 2008).

Without oxygen, energy can still be produced from glucose by some living organisms, but this energy production requires an entirely different process involving glycolysis and fermentation (Audesirk, Audesirk, & Byers, 2008). During fermentation, the two pyruvates produced from glucose in glycolysis are combined with NADH electrons to produce ATP in the form of either alcohol or lactate (Gregory, 2010). This process is also dependent upon the energy from the sun; without the sun, photosynthesis could not occur to produce glucose, and glucose is necessary for glycolysis and fermentation to produce energy in the absence of oxygen (Cohn, 2008).

In addition to the enzyme RuBisCo (the most abundant enzyme on earth), many other enzymes are necessary to catalyze chemical reactions that support life (Cohn, 2008). Enzymes decrease the chemical energy needed for a reaction to take place, thereby speeding up the process (Audesirk, Audesirk, & Byers, 2008). This occurs when the enzyme (usually a protein) attaches to one or more substrates involved in the reaction, forming an enzyme-substrate complex (Audesirk, Audesirk, & Byers, 2008). The enzyme substrate complex then interacts to produce the enzyme product (Cohn, 2008). In the final stage of enzymatic reactions, the enzyme product detaches from the enzyme, freeing the enzyme to be used again if needed (Audesirk, Audesirk, & Byers, 2008).