Biology 5090/11 — October/November 2016

Walkthrough

This question tests two facts about two structures: what each does, and where it is found.

1. Cell membrane: every living cell — plant or animal — is surrounded by a cell membrane. It is partially permeable, meaning it lets some substances through and holds others back, so it controls the passage of substances into and out of cells. That matches option A exactly.
2. Cell wall: found only around plant cells (and fungal/bacterial cells, never animal cells). It is a fully permeable layer of cellulose that gives mechanical support; together with the vacuole pressing against it, it helps the cell stay turgid. So 'maintains turgor' belongs with the cell wall/vacuole system of a plant cell — not with the cell membrane (B), and not in animal cells at all (D).
3. Option C gives the cell wall the membrane's job ('controls the passage of substances'), which is wrong because the cellulose wall is freely permeable — it does not select what passes.

Only option A pairs the correct structure, function and location.

Key Takeaways

• The cell membrane controls entry and exit of substances because it is partially permeable; it is in all cells.
• The cell wall is fully permeable, provides support, and exists only in plant cells (not animals).
• Turgor depends on the plant cell's vacuole pressing on the cell wall — an animal cell cannot be turgid.

Common Mistakes

• Choosing B: confusing the roles of the membrane and the wall/vacuole — the membrane does not maintain turgor.
• Choosing C: assuming the cell wall controls passage of substances; it is fully permeable, so it cannot.
• Choosing D: placing a cell wall in an animal cell — animal cells have no cell wall.
• Writing 'controls what goes in and out' without naming the structure's key property, partially permeable.

Things to Be Careful About

• In option tables like this, check all three columns before answering — one correct column alone often eliminates two options, but only a row correct in all three scores.
• Remember the exact wording: the membrane controls the passage of substances; the wall supports the cell.