Biology 5090/12 — October/November 2011

Walkthrough

The question asks which structures are found in both a human cheek cell and a spongy mesophyll cell from a leaf. This is a direct comparison of an animal cell and a plant cell.

A cheek cell is a typical animal cell: it is bounded by a cell membrane, has cytoplasm filling the cell, and has a nucleus that controls the cell's activities. It does not have a cell wall, chloroplasts or a large permanent vacuole.

A spongy mesophyll cell is a plant cell found in the leaf. It has a cell wall made of cellulose outside the cell membrane, a cell membrane, cytoplasm, a nucleus, chloroplasts (which carry out photosynthesis) and a large permanent vacuole.

So the structures common to both are the cell membrane, the nucleus and the cytoplasm. Only option A lists exactly these three, so A is correct.

The other options each include the cell wall, which is present only in the plant cell and not in the animal cheek cell, so they cannot be correct.

Key Takeaways

• Animal cells have a cell membrane, cytoplasm, nucleus, and (in many cases) small temporary vacuoles, mitochondria and ribosomes.
• Plant cells have all of the above PLUS a cellulose cell wall, chloroplasts and a large permanent vacuole.
• The cell wall, chloroplasts and large permanent vacuole are the structures that distinguish a plant cell from an animal cell.
• When comparing cells, the presence or absence of the cell wall is often the quickest way to tell an animal cell from a plant cell.

Common Mistakes

• Choosing an option that includes the cell wall: the cell wall is present only in the plant cell (the spongy mesophyll cell), not in the animal cheek cell.
• Confusing the cell wall with the cell membrane: every cell, animal or plant, has a cell membrane, but only plant cells have a cell wall outside it.
• Forgetting that a cheek cell is an animal cell and has no chloroplasts or permanent vacuole.

Things to Be Careful About

• Read the question exactly: it asks for structures seen in BOTH cells, so any structure unique to one cell type (the cell wall) must be excluded.
• Note the wording "cell membrane" rather than just "membrane" — the mark depends on the precise term.
• Check each option systematically: option A lists cell membrane, nucleus and cytoplasm, all present in both cell types, so it is the correct choice.