Biology 5090/11 — October/November 2011

Walkthrough

We are comparing an animal cell (cheek) and a plant cell (spongy mesophyll). Both cell types share the basic structures: a cell membrane surrounds the cell, cytoplasm fills the space inside, and the nucleus controls the cell's activities. The key difference is that a plant cell has an extra cell wall outside the cell membrane, as well as chloroplasts and a large permanent vacuole, which animal cells do not have.

The question asks which structures are seen in BOTH cells. The cell wall is only present in the plant cell, so any option that includes "cell wall" cannot be correct — this rules out B, C and D at once. Option A lists exactly the three structures common to both cell types: cell membrane, nucleus and cytoplasm.

Key Takeaways

• An animal cell contains a cell membrane, cytoplasm and a nucleus, but no cell wall, no chloroplasts and no permanent vacuole.
• A plant cell contains a cell membrane, cytoplasm and a nucleus, plus a cell wall, chloroplasts (in photosynthetic tissues) and a permanent vacuole.
• In a "which structures are in both" question, list the shared structures first, then check each option against that list.

Common Mistakes

• Choosing an option that contains "cell wall" (B, C or D) because the plant cell has one, while forgetting that the animal cell does not — the question asks for structures present in both cells.
• Confusing the cell wall with the cell membrane. The cell membrane is present in all cells; the cell wall is an extra plant (and bacterial/fungal) structure.
• Including chloroplasts or a vacuole in the answer, as these are also plant-only features and would not be seen in the cheek cell.

Things to Be Careful About

• Read "in both cells" carefully — the mark is awarded for the shared set, not for the plant cell's distinctive features.
• The cell wall is found in plant, bacterial and fungal cells, but never in animal cells.
• A cheek cell is an animal cell, so it has no cell wall; if the stem named a plant cell and an animal cell, any option with "cell wall" is automatically wrong.