Lecture Notes: Biological Membranes (OCR Specification A)

Overview

• Topic: Biological Membranes (2.1.5) per the OCR specification.
• Focus: Roles of membranes within cells and the cell surface.
• Key Points:
  • Partially permeable barriers
  • Compartmentalization within organelles
  • Membranes as sites of chemical reactions
  • Cell communication and signaling

Partially Permeable Barriers

• Definition: Membranes that allow certain substances to pass while blocking others.
• Functions: Act as gatekeepers (analogy: bouncers in a club).
• Examples: Movement of molecules through the cell membrane (osmosis, active transport, facilitated diffusion, diffusion).

Compartmentalization within Organelles

• Importance: Separates contents of organelles from the cytoplasm.
  • Example: Lysosomes contain hydrolytic enzymes; separation prevents digestion of cell components.
• Function: Controls what enters and leaves the organelle.

Membrane Roles within Organelles

• Example: Mitochondria
  • Inner membrane establishes and maintains concentration gradients.
  • Houses ATP synthase enzyme.
  • Sites of various chemical reactions (detailed in respiration at A2 level).

Membranes as Sites of Chemical Reactions

• Discussion: Membranes can host chemical reactions essential to cellular processes.
  • Example: Reactions in mitochondria (covered in A2 respiration).

Cell Communication and Signaling

• Importance: Essential for cells to communicate and respond to signals (e.g., hormones).
• Mechanism: Detection via specific, complementary receptors on cell surface membranes.

Key Definitions

• Cell Signaling: Communication between cells, involving cell recognition and triggering responses inside cells.

Application in Exams

• Be prepared to apply knowledge of cell membranes, receptors, and signaling to unfamiliar contexts (e.g., new drugs or hormones).
• Examples:
  • Insulin: Hormone signaling.
  • Beta Blockers: Medicinal drug applications.

Exam Tips

• Avoid vague terms like "it's," "they," "amount," or "size"; use precise scientific terminology for higher marks.
• Review all points and relate them to practical examples where possible.

Summary

• Understand the multifaceted roles of biological membranes, their importance in cell compartmentalization, and their function in chemical reactions and communication.
• Apply knowledge effectively in exam scenarios, using appropriate scientific language.