BIOLOGY WITH HAMZA · MDCAT REVISION
Cell Structure & Function
Name: ____________________ Date: ______________
Recall first. Check second. Return to the ideas you missed.
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Learning targets
- Relate major organelles to their roles in cell metabolism.
- Distinguish diffusion, osmosis, facilitated diffusion and active transport.
- Predict water movement using water-potential reasoning.
Core notes
- Organelles create specialised reaction environments.
- Membrane proteins produce selectivity beyond the phospholipid bilayer.
- Passive transport moves down a gradient; active transport can move against it.
- Osmosis describes water movement according to water potential.
Read, cover and redraw
Blocks most ions and large polar solutes.
Provides a selective hydrophilic pore.
Binds a solute and changes conformation.
Uses energy to move solutes against a gradient.
Written recall
1. Why can facilitated diffusion become saturated while simple diffusion through the bilayer does not saturate in the same way?
2. What prevents a plant cell in dilute solution from continuing to expand indefinitely?
Apply the idea
1. A cell image is 36 mm long. The actual cell is 60 μm long. What is the magnification?
- ×600
- ×60
- ×2,160
- ×6,000
My answer: _____ Reason: ____________________________________
2. A cubic cell doubles its side length. How does its surface-area-to-volume ratio change?
- It doubles
- It halves
- It quadruples
- It is unchanged
My answer: _____ Reason: ____________________________________
3. A labelled amino acid becomes part of a protein that is secreted from an animal cell. Which route is most consistent with this observation?
- Free ribosome → nucleus → lysosome
- Smooth ER → mitochondrion → Golgi apparatus
- Rough ER → Golgi apparatus → secretory vesicle
- Golgi apparatus → nucleolus → peroxisome
My answer: _____ Reason: ____________________________________
Answer key
Cover this section while attempting the questions.
Written recall
1. Facilitated diffusion depends on a finite number of channels or carriers, whereas simple diffusion is not limited by transport-protein binding sites.
2. The rigid cell wall develops an opposing pressure as the cell becomes turgid, reducing further net water entry.
Applied questions
1. A — Convert 36 mm to 36,000 μm, then divide image size by actual size: 36,000 ÷ 60 = 600.
2. B — Surface area scales with length squared but volume with length cubed. Doubling length gives four times the area and eight times the volume, halving their ratio.
3. C — Proteins entering the secretory pathway are synthesized into rough ER, modified and sorted through the Golgi, then carried in vesicles to the plasma membrane.