Identify the reactants, products, and basic functions of aerobic and anaerobic cellular respiration (NGSSS SC.912.L.18.8; Reporting Category 1, Molecular and Cellular Biology).

What this topic is asking

The NGSSS benchmark SC.912.L.18.8 asks you to identify the reactants, products, and basic functions of aerobic and anaerobic cellular respiration. For the Florida Biology 1 EOC you need the inputs and outputs of aerobic respiration, the role of the mitochondrion and ATP, and the difference between aerobic respiration and the two kinds of anaerobic respiration (fermentation). Items test the inputs and outputs and the comparison of energy yields.

What cellular respiration does

The released energy in ATP powers everything the cell does: building molecules, moving substances by active transport, contracting muscles, and so on.

Aerobic respiration

A balanced chemical version is $\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + \text{energy (ATP)}$. Notice this is the reverse of photosynthesis, which is the link the next topic explores.

Anaerobic respiration (fermentation)

When oxygen is not available, cells can release energy by anaerobic respiration, also called fermentation. It produces far less ATP than aerobic respiration (because glucose is only partly broken down), and it produces different waste products depending on the organism:

• Lactic acid fermentation (in human and animal muscle cells). When muscles run low on oxygen during hard exercise, they make lactic acid, which builds up and contributes to muscle fatigue and soreness. Once oxygen returns, the lactic acid is cleared.
• Alcoholic fermentation (in yeast and some microbes). Yeast breaks glucose down without oxygen to make alcohol (ethanol) and carbon dioxide. This is used to make bread rise (the carbon dioxide) and to brew beer and wine (the alcohol).

How it connects

Respiration links to many topics: the mitochondrion (the organelle that carries it out), ATP (the energy currency), glucose (a carbohydrate from food or photosynthesis), and the carbon cycle (respiration returns carbon dioxide to the air). It is the mirror image of photosynthesis.

Try this

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

• Cue. Glucose + oxygen gives carbon dioxide + water + energy (ATP).

Q2. State what human muscle cells produce during anaerobic respiration and how the energy yield compares with aerobic respiration. [2]

• Cue. They produce lactic acid, and the energy yield is much lower than in aerobic respiration.