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Cambridge AS Level Biology Overview

May 14, 2025

AS Cambridge International Year 12 Biology Summary

Lecture Overview

  • Comprehensive review of Year 12 Biology for AS Cambridge International.
  • Focus on topics 1 to 4: Cell Structure, Biological Molecules, Enzymes, and Cell Membranes and Transport.
  • Includes theory aligned with specifications to aid in achieving high grades.
  • Encourages use of additional notes with key marking points, terms, and examiner tips.

Cell Structure

Microscopes

  • Types: Light, Transmission Electron, Scanning Electron.
  • Light Microscopes: Poorer resolution than electron due to longer light wavelengths, can view living samples and provide color images.
  • Electron Microscopes: Higher resolution, shorter electron wavelengths, transmission views internal structures, scanning provides 3D images.

Key Definitions

  • Resolution: Minimum distance between distinguishable objects.
  • Magnification: Image size compared to actual object.

Scientific Drawings

  • Use pencil, provide a title with specimen name, state magnification, annotate components, no sketches or color.

Cell Measurements

  • Use eyepiece graticule and stage micrometer to measure and calibrate.

Cell Components

  • Eukaryotic Organelles: Nucleus, mitochondria, ribosomes, endoplasmic reticulum (rough and smooth), Golgi apparatus, lysosomes, chloroplasts, cell wall, vacuoles.
  • Prokaryotic Differences: Smaller, no membrane-bound organelles, 70s ribosomes, cell wall of murein.
  • Viruses: Non-living, nucleic acid core, protein capsid, replication within host cells.

Biological Molecules

Testing for Molecules

  • Starch: Iodine test - blue-black color if present.
  • Reducing Sugars: Benedict’s test - red, orange, yellow, green color change.
  • Non-reducing Sugars: Acid boil, neutralize, Benedict’s test.
  • Proteins: Biuret test - purple/lilac if present.
  • Lipids: Ethanol and water - white emulsion.

Carbohydrates

  • Monomers: Glucose (α and β), galactose, fructose.
  • Disaccharides: Maltose, lactose, sucrose.
  • Polysaccharides: Starch (plants), glycogen (animals), cellulose.

Lipids

  • Types: Triglycerides, phospholipids.
  • Properties: Hydrophobic, insoluble in water.

Proteins

  • Structure Levels: Primary (amino acid sequence), Secondary (α-helix, β-pleated sheet), Tertiary (3D shape), Quaternary (multiple polypeptides).
  • Fibrous vs. Globular: Structural (e.g., collagen) vs. functional (e.g., enzymes).

Water

  • Properties: Solvent, high specific heat capacity, cohesion, adhesion, surface tension.

Enzymes

Characteristics

  • Nature: Biological catalysts, specific active sites.
  • Models: Lock and Key, Induced Fit.

Catalytic Action

  • Lower activation energy.
  • Enzyme-substrate complex formation.

Factors Affecting Activity

  • Temperature, pH, enzyme concentration, substrate concentration.

Inhibition

  • Competitive: Bind to active site, reversible.
  • Non-competitive: Bind elsewhere, change enzyme shape.

Applications

  • Immobilized enzymes in industry.

Cell Membranes and Transport

Fluid Mosaic Model

  • Structure: Phospholipid bilayer, proteins, cholesterol, glycoproteins/glycolipids.

Transport Mechanisms

  • Passive: Diffusion, facilitated diffusion, osmosis.
  • Active: Active transport, endocytosis, exocytosis.

Surface Area to Volume Ratio

  • Impacts rate of transport, adaptations in multicellular organisms for efficient exchange.

Mitotic Cell Cycle

Cell Division

  • Eukaryotic: Mitosis and meiosis.
  • Stages: Interphase (G1, S, G2), Mitosis (prophase, metaphase, anaphase, telophase), Cytokinesis.

Replication

  • DNA Replication: Semi-conservative, enzymes involved (DNA helicase, polymerase).
  • Stem Cells: Totipotent, pluripotent, multipotent, unipotent.
  • Cancer: Uncontrolled mitosis, tumor formation.

Nucleic Acids and Protein Synthesis

DNA and RNA

  • Structure: Nucleotides, double helix, base pairing (A-T, G-C).
  • Replication: Enzymatic process, importance in cell division.

Protein Synthesis

  • Transcription: DNA to mRNA in nucleus.
  • Translation: mRNA to protein in ribosomes.

Mutations

  • Types: Substitutions, insertions, deletions.

Transport in Plants

Structures

  • Tissues: Xylem (water transport), Phloem (translocation of nutrients).

Mechanisms

  • Transpiration: Water movement, cohesion-tension theory.
  • Adaptations: Xerophytes conserve water, importance of guard cells.

Circulatory System

Blood Vessels

  • Types: Arteries, veins, capillaries.
  • Functions: Transport oxygen, nutrients, remove waste.

Heart Function

  • Cycle: Diastole, atrial systole, ventricular systole.
  • Control: Sinoatrial node, atrioventricular node.

Gas Exchange

Human System

  • Pathway: Nasal cavity, trachea, bronchi, bronchioles, alveoli.
  • Adaptations: Large surface area, thin walls, maintained concentration gradient.

Infectious Disease

Pathogens and Immunity

  • Types: Bacteria (e.g., tuberculosis, cholera), Viruses (e.g., HIV/AIDS), Protoctista (e.g., malaria).
  • Treatment: Antibiotics for bacteria, challenges of resistance.

Immunity

  • Types: Innate (phagocytosis), Adaptive (lymphocytes: T and B cells).
  • Vaccination: Active artificial immunity, herd immunity concepts.

This summary captures the main elements and concepts covered in the lecture on Cambridge International AS Level Biology. Each section is intended to provide a quick reference and overview of important topics and processes essential for understanding the subject matter.

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