Science

Common mistakes in cells

4 mistakes learners make with cells, each one named and explained.

All common mistakes

Each part of a cell has one job, and the job explains the shape.

A bacterium given a nucleus

What it looks like

The genetic material of a bacterial cell is placed inside a true nucleus.

Why it happens

Every cell diagram you have ever drawn had a nucleus in the middle of it.

A worked example

Question. Where is the DNA in a bacterial cell

A common answer. in the nucleus

The answer. in a single loop, free in the cytoplasm

Why. Prokaryote means before the nucleus, which is exactly what the word is telling you.

Put the two side by side

Eukaryotes keep DNA inside a nucleus.
Prokaryotes have no nucleus at all.

The name of the group is the answer. Pro-karyote: no proper nucleus.

Membrane-bound organelles given to a bacterium

What it looks like

A bacterium is described as keeping its DNA in the mitochondria or a chloroplast.

Why it happens

Those are the organelles most recently learned, so they are the ones that come to mind.

A worked example

Question. Where is bacterial DNA

A common answer. inside the mitochondria

The answer. free in the cytoplasm

Why. Bacteria have none of the membrane-bound organelles.

Put the two side by side

Animal and plant cells have organelles inside membranes.
Bacteria have ribosomes and a cell wall, and little else.

If it has a membrane around it and is inside a cell, a bacterium does not have it.

Plant and animal cell parts mixed up

What it looks like

A part both cells share, such as the cell membrane or a mitochondrion, is given as plant only.

Why it happens

The plant cell diagram is drawn with more labels, so every label on it looks like a plant feature.

A worked example

Question. Which part is in a plant cell but not an animal cell

A common answer. the cell membrane

The answer. the cell wall

Why. Animal cells have membranes too. Only the wall, the chloroplasts and the large vacuole are extra.

Put the two side by side

Both cells: membrane, cytoplasm, nucleus, mitochondria, ribosomes.
Plant only: cell wall, chloroplasts, large permanent vacuole.

Learn the short list of three extras rather than the long list of everything.

The right part, the wrong job

What it looks like

A cell part is named correctly but paired with another part's job, such as the nucleus controlling what enters the cell.

Why it happens

The parts are learned as a labelled diagram, and a diagram shows where things are, not what they do.

A worked example

Question. Which part controls what enters and leaves the cell

A common answer. the nucleus

The answer. the cell membrane

Why. The membrane is the only part that surrounds the cell, so it is the only one that can control the boundary.

Put the two side by side

The nucleus holds the instructions.
The membrane is the border.

Learn each part by the one job only it can do, and its position stops being the thing you remember.

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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