AP BIOLOGY

Detailed explanation-1: -Glycolysis can take place without oxygen in a process called fermentation. The other three stages of cellular respiration-pyruvate oxidation, the citric acid cycle, and oxidative phosphorylation-require oxygen in order to occur.

Detailed explanation-2: -Glycolysis, which is the first step in all types of cellular respiration is anaerobic and does not require oxygen. If oxygen is present, the pathway will continue on to the Krebs cycle and oxidative phosphorylation. However, if oxygen is not present, some organisms can undergo fermentation to continually produce ATP.

Detailed explanation-3: -When oxygen is not present, pyruvate will undergo a process called fermentation. In the process of fermentation the NADH + H+ from glycolysis will be recycled back to NAD+ so that glycolysis can continue. In the process of glycolysis, NAD+ is reduced to form NADH + H+.

Detailed explanation-4: -Cellular respiration always begins with glycolysis, which can occur either in the absence or presence of oxygen. Cellular respiration that proceeds in the absence of oxygen is anaerobic respiration.

Detailed explanation-5: -If oxygen is available, glycolysis is followed by two processes in the mitochondria–the Krebs cycle and oxidative phosphorylation, respectively–that further increase ATP yield.