Question

A runner uses all available oxygen for respiration. She then notices that her legs are becoming sore. Which of these statements is most representative of respiration?

A) She has been running too long.
B) Her body is producing lactic acid as a result of doing anaerobic respiration.
c) Her body is producing lactic acid because she is breathing too hard.
D) Her body is producing lactic acid as a result of doing aerobic respiration.

Answer 1

Production of lactic acid as a result of anaerobic respiration.

Explanation: When oxygen is running low, as is the case during exercise due to increased energy demand and oxygen consumption, the body resorts to energy production via the anaerobic pathway;

Aerobic respiration consists of 4 parts or stages:

1. Glycolysis

2. Link reaction

3. Krebs or tricarboxylic acid (TCA) cycle

4. Electron transport chain (ETC)

A key point to note is the availability of NAD+, which is a necessary oxidising agent throughout the entire respiration process;

It is reduced to NADH in several reactions in glycolysis and other stages and needs to be oxidised back to NAD+ to sustain respiration;

In aerobic respiration, this oxidation will occur in the ETC;

The ETC requires oxygen however so when oxygen is inadequately available, it cannot proceed and NADH cannot be oxidised back to NAD+;

Restoration of the NAD+ thus occurs via an alternative route;

After glycolysis, pyruvate is reduced to lactate, facilitated by oxidation of NADH back to NAD+