A researcher studies two muscles of an animal…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A researcher studies two muscles of an animal. Muscle X is deep red. It has much myoglobin, many mitochondria and little sarcoplasmic reticulum. Muscle Y is pale. It has little myoglobin, few mitochondria and much sarcoplasmic reticulum.
- Which muscle is a red muscle?
- Which muscle can work for a long time without tiring? Why?
- Which muscle would build up lactic acid sooner in a hard burst of work? Why?
Need a reminder? The key ideaShow
Repeated contraction makes lactic acid from the anaerobic breakdown of glycogen, and this causes fatigue. Red fibres have much myoglobin, plenty of mitochondria and work with oxygen. White fibres have little myoglobin, fewer mitochondria and much sarcoplasmic reticulum, and they depend on anaerobic breakdown.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Given. The features of X and of Y.
Plan. Match each set of features with the red or the white fibres.
Step 1. (a) X has much myoglobin and many mitochondria. It is the red muscle.
Step 2. (b) X. Its mitochondria use the oxygen that the myoglobin stores to make ATP, so it works aerobically and tires slowly.
Step 3. (c) Y. It has little myoglobin and few mitochondria, so it depends on the anaerobic breakdown of glycogen, which makes lactic acid.
Answer: (a) X; (b) X, because it works with oxygen; (c) Y, because it depends on anaerobic breakdown.
Check. The pale muscle with much sarcoplasmic reticulum matches the description of the white fibres.
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