Biology 5090/12 — October/November 2016

Walkthrough

First, identify each numbered structure on the plant cell diagram. The outermost thick layer is the cell wall (5); just inside it is the thin cell membrane (2); the dark oval body is the nucleus (3); the stippled material filling the cell around the organelles is the cytoplasm (4); and the large clear space taking up most of the cell's volume is the central vacuole (1).

Now compare this list with an animal cell. An animal cell has a cell membrane, cytoplasm and a nucleus — so structures 2, 3 and 4 are shared by both cell types. What it lacks are the two features that give plant cells their box-like shape and firmness: the cellulose cell wall and the large central vacuole full of cell sap. These correspond to structures 5 and 1, so the option pairing them together is A.

Key Takeaways

• Plant cells uniquely possess a cellulose cell wall and a large central vacuole containing cell sap; animal cells never have these.
• Both plant and animal cells share a cell membrane, cytoplasm and nucleus.
• The cell wall gives plant cells a fixed, regular shape; the vacuole keeps cells turgid by osmosis.

Common Mistakes

• Confusing the cell wall with the cell membrane: the wall is the outermost, thicker line; the membrane lies immediately inside it and is present in ALL cells.
• Thinking animal cells have no vacuole at all — small temporary vacuoles may occur, but the large central vacuole is plant-specific, which is what the question tests.
• Misreading the label lines: check exactly where each pointer line ends before matching numbers to options.

Things to Be Careful About

• The mark scheme gives only the letter, so your identification of each numbered structure must be right for the letter to follow.
• If asked to name rather than select, use the exact terms "cell wall" and "(permanent) vacuole" — "cell sap" alone names the contents, not the structure.