Exam Answers - A Level Biology

1) Respiration is a biochemical process that occurs within every living cell of the body, and is used as a means of producing energy.

2) There are several stages Glycolysis, the link reaction Kreb's cycle and oxidative phosphorylation.

Two molecules of ATP are used initially to phosphorylated the Glucose molecule and start to break it down. 4 molecules of ATP are produced from glycolysis, however as 2 are used initially it only gives you a net gain of 2 ATP units. Two molecules of NAD are reduced to NADH these can be fed into the mitochondrion to yield 6 ATP later on if sufficient oxygen is available. Glycolysis occurs in the cytoplasm of the cell. The next stage in the process is the link reaction, this occurs in the mitochrondrial matrix. Here the pyruvate is converted via a series of steps into acetyl, it is then combined with co enzyme A to form acetyl co enzyme A.

Following from the link reaction is the Kreb's Cycle. However please remember that from 1 molecule of glucose you produce two molecules of pyruvate and therefore you will form two lots of acetyl co-enzyme A. This means that for every 1 molecule of glucose you will get two turns of the krebs cycle.

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