Use models to describe how cellular respiration converts the chemical energy in glucose into ATP, comparing aerobic and anaerobic respiration (North Carolina Standard Course of Study, Biology, LS.Bio.3).

What this topic is asking

North Carolina LS.Bio.3 asks you to model how cellular respiration converts the energy in glucose into ATP. For the Biology EOC you need the equation, the role of the mitochondrion, and the difference between aerobic respiration (with oxygen, lots of ATP) and anaerobic respiration or fermentation (without oxygen, little ATP). Items often ask you to compare the two or to spot the products.

The equation and the mitochondrion

The balanced equation is the reverse of photosynthesis:

In words: glucose plus oxygen produces carbon dioxide plus water plus energy (ATP). The reactants are glucose and oxygen; the products are carbon dioxide, water, and ATP. A small amount of ATP is made in the cytoplasm (in glycolysis), but most of it is made inside the mitochondrion. The mitochondrion's inner membrane is folded into cristae, increasing the surface area for the reactions, which is why cells that need a lot of energy have many mitochondria.

Respiration happens in all living cells, all the time, including plant cells. Plants photosynthesise in the light and respire constantly, so do not assume only animals respire.

Aerobic versus anaerobic respiration

Anaerobic respiration takes two common forms:

• In animal cells (lactic acid fermentation). During hard exercise, muscle cells run low on oxygen and produce lactic acid, which builds up and contributes to muscle fatigue and soreness. When oxygen returns, the lactic acid is broken down.
• In yeast and some microbes (alcoholic fermentation). Yeast produces ethanol and carbon dioxide. This is the basis of bread rising (carbon dioxide) and brewing (ethanol).

Both forms release far less ATP than aerobic respiration, which is why anaerobic respiration is a short-term backup rather than a long-term solution.

Try this

Q1. Write the word equation for aerobic cellular respiration. [2]

• Cue. Glucose plus oxygen produces carbon dioxide plus water plus energy (ATP).

Q2. State two differences between aerobic and anaerobic respiration. [2]

• Cue. Aerobic uses oxygen and yields a lot of ATP; anaerobic uses no oxygen and yields little ATP (and produces lactic acid, or ethanol and carbon dioxide).