Science

Common mistakes in respiration

6 mistakes learners make with respiration, each one named and explained.

All common mistakes

Respiration releases energy from glucose in every living cell, all the time.

A product of respiration misremembered

What it looks like

Glucose or carbon dioxide alone is given where the question asks for a different product.

Why it happens

The same handful of substances appears on both sides of the equations, so which side is not fixed.

A worked example

Question. What anaerobic respiration in muscle produces

A common answer. glucose

The answer. lactic acid

Why. Glucose is what goes in, so it cannot be what comes out.

Put the two side by side

Reactants are what you start with.
Products are what you are left with.

Write the arrow first. Then nothing on the left can appear as an answer on the right.

Breathing and respiration treated as one

What it looks like

You define respiration as breathing in and out, or say the two words mean the same thing.

Why it happens

Outside science lessons, respiration really is used to mean breathing.

A worked example

Question. A difference between breathing and respiration

A common answer. there is no difference

The answer. breathing moves air; respiration is a reaction inside cells

Why. A plant respires and has no lungs at all.

Put the two side by side

Breathing happens in the chest, a few times a minute.
Respiration happens in every cell, constantly.

One is a movement of air. The other is a chemical reaction.

Respiration and photosynthesis swapped

What it looks like

The photosynthesis equation is given for respiration, or respiration is described as making glucose.

Why it happens

The two equations are near mirror images, and they are always taught side by side.

A worked example

Question. The word equation for aerobic respiration

A common answer. carbon dioxide + water gives glucose + oxygen

The answer. glucose + oxygen gives carbon dioxide + water

Why. Respiration uses glucose to release energy; photosynthesis uses energy to build glucose.

Put the two side by side

Photosynthesis builds glucose, in the light, in plants only.
Respiration breaks glucose down, all the time, in every living thing.

One builds and one breaks down. Ask which way the energy is going.

Respiration given the wrong purpose

What it looks like

Respiration is described as digesting food or cooling the body rather than releasing energy.

Why it happens

All of those happen inside a body, so any of them sounds plausible for a bodily process.

A worked example

Question. The main purpose of respiration

A common answer. to digest food

The answer. to release energy from glucose

Why. Digestion happens in the gut; respiration happens inside every cell.

Put the two side by side

Digestion breaks food into small molecules.
Respiration releases the energy from one of them.

Digestion prepares the fuel. Respiration burns it.

The anaerobic equation given for the aerobic one

What it looks like

Glucose to lactic acid is offered as the equation for aerobic respiration.

Why it happens

Both are respiration and both start with glucose, so the difference is easy to lose.

A worked example

Question. Aerobic respiration

A common answer. glucose gives lactic acid

The answer. glucose + oxygen gives carbon dioxide + water

Why. Aerobic means with oxygen, so oxygen has to appear in the equation.

Put the two side by side

Aerobic uses oxygen and releases much more energy.
Anaerobic runs without oxygen and leaves lactic acid behind.

Look for oxygen in the equation. Its presence is what the word aerobic means.

The yeast product given for muscles

What it looks like

Ethanol is given as the product of anaerobic respiration in human muscle.

Why it happens

Both are anaerobic respiration and both are taught in the same lesson.

A worked example

Question. Anaerobic respiration in human muscle

A common answer. ethanol and carbon dioxide

The answer. lactic acid

Why. Ethanol is what yeast produces, which is why it is useful for brewing and not for people.

Put the two side by side

Yeast: glucose gives ethanol and carbon dioxide.
Human muscle: glucose gives lactic acid.

Ask whose cells. The organism decides the product.

WAJD spots these patterns in your child's answers and names the one behind their wrong answers, instead of just marking them wrong.

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