1. why is the ability to perform lactic acid fermentation important to an animal cell when oxygen is scarce?

Fermentation is important can keep obtaining energy from glycolysis.

Explanation:

In the presence of oxygen, cells will use aerobic respiration to obtain energy in the form of ATP. In these conditions, it can produce up to 36 ATP molecules.

This process has three steps: glycolysis, citric acid cycle and electron transport chain.

During glycolysis, a glucose molecule is broken down into two pyruvate molecules, releasing electrons that are taken up by NAD+ which is converted into NADH, and producing a net total of 2 ATP molecules. The NADH produced during glycolysis and the citric acid cycle will go to the mitochondria and give away the electrons to start the electron transport chain that has Oxygen as the last electrons acceptor, and the NAD+ used to continue glycolysis is regenerated in the process.

In anaerobic conditions (no oxygen), the last electron acceptor is scarce, so the NADH can't give away its electrons and the NAD+ cannot be regenerated, so glycolysis stops, eventually causing cell death due to lack of ATP. To avoid this, cells perform lactic acid fermentation, where the NADH gives the electrons to pyruvate which is then converted into lactic acid. This regenerates the NAD+ necessary to continue glycolysis and keep obtaining some energy to survive until oxygen levels increase.

not necessarily. higher fitness requires the organism to be reproductive successful. for example, an organism at age 10 with 15 offspring is much more fit than an organism at age 15 with only 5 offspring.

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