Biology 5090/12 — October/November 2020

Walkthrough

1. The question asks to identify the part of a plant cell that controls the entry of substances.
2. Recall the functions of plant cell structures: the cell wall is fully permeable and provides structural support; the cell membrane is partially permeable and controls what enters and leaves the cell; chloroplasts are the site of photosynthesis; the cytoplasm is the site of metabolic reactions.
3. Examine the diagram to match labels to structures. Label C points to the thin line just inside the thicker outer cell wall, which is the cell membrane. (Label D points to the cell wall, A to a chloroplast, and B to the cytoplasm).
4. Since the cell membrane is partially permeable, it controls the entry of substances. Thus, C is the correct answer.

Key Takeaways

• The cell membrane is partially permeable and controls the movement of substances in and out of the cell.
• The cell wall is fully permeable and provides support and shape to the plant cell.
• Carefully reading diagram labels is essential, as automated descriptions may sometimes misassign labels or misidentify lines.

Common Mistakes

• Confusing the cell wall with the cell membrane. The cell wall is fully permeable and does not control entry; the cell membrane is partially permeable and does.
• Selecting the label for the cell wall (which is fully permeable) instead of the cell membrane.
• Misreading the diagram labels, especially when multiple lines are close together (e.g., confusing C and D).

Things to Be Careful About

• Always verify the label lines against the structures. In this diagram, C points to the cell membrane (the inner line), not the cell wall (the outer line, D).
• Remember that 5090 requires precise terminology: "partially permeable" for the cell membrane, not "selectively permeable" (though both are understood, "partially permeable" is the standard 5090 term).
• The cell wall is fully permeable, allowing all substances to pass through freely without control.