Membranes, Transport and Cell Division
The fluid-mosaic membrane, passive and active transport, osmosis, the cell cycle, mitosis, differentiation and loss of cell-cycle control.
How to study A-level Biology
Move between scales deliberately: identify the biological process, trace matter or information, use quantitative evidence, then evaluate the method and conclusion.
Core concepts
Concept 1
The phospholipid bilayer, proteins, cholesterol and surface carbohydrates create selective permeability, signalling and recognition.
Exam cue: State the direction of movement relative to concentration or water-potential gradients.
Concept 2
Diffusion, facilitated diffusion, osmosis, active transport, endocytosis and exocytosis differ in route and energy requirement.
Exam cue: Name the membrane component responsible for the transport or signalling function.
Concept 3
DNA replication and mitosis preserve genetic information, while checkpoints and regulated differentiation support growth and repair.
Exam cue: Distinguish chromosome, chromatid and DNA molecule at the stated cell-cycle stage.
Risk pitfalls and guardrails
Defining osmosis as movement of water from a concentrated to a dilute solution.
Guardrail: Do not replace a mechanism with a vague purpose statement, or infer causation from an association without experimental support.
Assuming facilitated diffusion requires ATP because it uses a protein.
Guardrail: Do not replace a mechanism with a vague purpose statement, or infer causation from an association without experimental support.
Saying mitosis creates genetic variation as its normal outcome.
Guardrail: Do not replace a mechanism with a vague purpose statement, or infer causation from an association without experimental support.
Memory anchors
Fluid Mosaic
Membrane components move laterally in a phospholipid bilayer containing varied proteins.
Osmosis
Osmosis is net water movement through a partially permeable membrane from higher to lower water potential.
Active Transport
Active transport uses energy and carrier proteins to move substances against a gradient.
Mitosis
Mitosis normally produces nuclei with genetically identical chromosome sets.
Differentiation
Differentiation creates specialised cells through controlled gene expression.
Checkpoint rule
Do the check-up only after you can summarize each concept in one sentence and identify one dangerous pitfall from memory.
Knowledge Check (after reading)
Short check-up to confirm understanding of this module.
Check-up Questions
Which description matches the fluid-mosaic model?
Why does the phospholipid bilayer restrict passage of ions?
Answer all questions to submit.
Next step personalized recommendations
Continue learning
Move forward only after this module is stable.
What is Pass Harbor?
Completely free exam prep for 247 UK exams.
- Practice questions
- Flashcards
- Study guides
- Mock exams
- No registration
- No paywall
- Start instantly
“No more expensive exam prep. Quality study tools should be accessible to everyone.”