IMAT 2011 Q49 [Muscle Cells]

During vigorous exercise, a variety of products will be generated in muscle cells.
Which answer correctly lists some of the products?

A. water, lactic acid, heat and carbon dioxide

B. water, sweat, heat and lactic acid

C. usable energy (ATP), carbon dioxide and oxygen

D. carbon dioxide, lactic acid and ethanol

E. useable energy (ATP), heat, glycogen and carbon dioxide

In my opinion, this is a pretty good practice question to analyze, as it gives you a better understanding of the concept.

When I studied for the IMAT a few years back I analyzed every question and answer but let’s first understand what we were asked to answer and figure out are, then we will go through each and each answer to quickly understand why it was false or true.

The facts we are given in the question:

  • a vigorous exercise
  • a variety of products will be generated (not consumed, produced, it is important!)
  • in muscle cells.

At this point, after learning muscle physiology you should have a clearer picture of what to expect.

Let’s go through each one of the answers and try to figure out if it is a product of a muscle cell of someone who is doing vigorous exercise.

Water – The end product of the electron transport chain, the combination of low energy electrons with the oxygen at the end making water (in vigorous exercise, or sleeping, it is making the water as a product nonstop.

It’s confusing because most people would think that you only consume water during exercise.

Lactic acid – you should know the lactic acid pathway, which refers to the metabolic pathway in which lactate produced by anaerobic glycolysis in the muscles is transported to the liver and is converted to glucose, which then returns to the muscles and is cyclically metabolized back to lactate. Or in other simple words, too much pyruvate accumulates in the muscle cell because the Krebs cycle and the electron transport chain can’t hold to the high production rate of pyruvate, which is eventually being turned into lactic acid. During intense exercise, there may not be enough oxygen available to complete the process, so a substance called lactate is made . Your body can convert this lactate to energy without using oxygen. But this lactate or lactic acid can build up in your bloodstream faster than you can burn it off.

Heat – a form of energy, is always being produced by our body, especially from a working muscle cell, the catabolic pathways (breaking of the larger molecule into smaller ones to produce energy) are producing heat by themselves, not to mention the movement of the muscle fibers and plenty more reasons!

Carbon dioxide – a product of our kreb׳s cycle, always making carbon dioxide that we exhale, even without vigorous exercise, and especially while one.
We also constantly release carbon dioxide from other pathways.

Sweat – While being a by-product of heavy exercise, it is not a by-product of a muscle cell.

Oxygen – Is not a product, we consume it, not generate it.

Ethanol – Ethanol fermentation regenerates NAD from NADH by releasing CO2 from pyruvate and reducing the two-carbon acetaldehyde molecule to ethanol . … Fermentation reactions occur in the cytoplasm of both prokaryotic and eukaryotic cells . In the absence of oxygen, pyruvate does not enter the mitochondria in eukaryotic cells .

Glycogen – is being consumed by the muscle cell; it is not a product!

The right answer must be A