Lecture Notes: AQA A-Level Biology

Introduction

• Lecture on AQA A-Level Biology
• Multiple presenters, including Dr. Edward Langley
• Covers all content for AQA A-Level Biology exams
• Provides resources for exam preparation on Dr. Edward's website

Biological Molecules

Types of Bonding

• Covalent Bonding: Sharing of electrons between non-metals.
• Ionic Bonding: Transfer of electrons from metal to non-metal, forming positive and negative ions.
• Hydrogen Bonding: Weak attraction between opposite dipoles (e.g., water molecules).

Monomers and Polymers

• Monomer: Single building block (e.g., amino acids, nucleotides, glucose).
• Polymer: Chain of monomers (e.g., proteins, DNA, polysaccharides).
• Macromolecules: Large molecules like proteins.

Reactions

• Hydrolysis: Breaking chemical bonds using water (e.g., breaking down peptides, lipids, nucleic acids).
• Condensation: Joining molecules by eliminating a molecule (e.g., forming polypeptides, polysaccharides).

Carbohydrates

• Monosaccharides: Simplest form of sugars (e.g., glucose, galactose, fructose).
• Disaccharides: Formed by two monosaccharides (e.g., maltose, sucrose).
• Polysaccharides: Long chains of monosaccharides (e.g., starch, glycogen, cellulose).

Lipids

• Triglycerides and Phospholipids: Types of lipids.
• Functions: Energy storage, insulation, protective coatings.
• Test for Lipids: Ethanol test.

Proteins

• Made of amino acids.
• Structure: Primary, secondary, tertiary, quaternary.
• Test for Proteins: Biuret test.

Enzymes

• Biological catalysts that lower activation energy.
• Specificity: Active site specific to substrate.
• Models: Induced fit model (current understanding).

Nucleic Acids

DNA and RNA

• DNA: Deoxyribonucleic acid, double helix.
• RNA: Ribonucleic acid, single-stranded.
• Base Pairing: A-T, C-G in DNA; A-U, C-G in RNA.

DNA Replication

• Semi-conservative process.
• Enzymes: DNA helicase, DNA polymerase.

ATP

• Adenosine triphosphate, energy currency of cells.
• Hydrolysis releases energy.

Water and Inorganic Ions

Properties of Water

• Polarity: Creates hydrogen bonding.
• Functions: Metabolic reactions, temperature buffering, solvent.

Inorganic Ions

• Essential for various biological processes (e.g., Na⁺, K⁺, Ca²⁺).

Cells

Eukaryotic Cells

• Organelles: Nucleus, mitochondria, ribosomes, ER, Golgi apparatus, lysosomes.
• Plant cells have additional structures: Chloroplasts, cell wall, vacuole.

Prokaryotic Cells

• Simple structure: No nucleus, plasmids, flagella.
• Viruses: Non-living, require host cells to replicate.

Microscopy

Types of Microscopes

• Optical Microscopes: Use light, limited resolution.
• Electron Microscopes: Higher resolution, use electron beams.

Measuring Cells

• Magnification Calculations: Size of image/actual size.
• Units: Millimeters, micrometers, nanometers.

Cell Cycle and Division

Mitosis

• Produces two identical daughter cells.
• Phases: Prophase, metaphase, anaphase, telophase, cytokinesis.

Meiosis

• Produces four non-identical haploid cells (gametes).
• Processes: Crossing over, independent assortment.

Cancer

• Uncontrolled cell division.
• Causes: Mutations in genes controlling cell cycle.

Transport Across Membranes

Plasma Membrane Structure

• Fluid mosaic model: Phospholipid bilayer with proteins.

Transport Mechanisms

• Diffusion: Passive movement down concentration gradient.
• Facilitated Diffusion: Via channel proteins.
• Active Transport: Requires energy, against concentration gradient.
• Osmosis: Movement of water across partially permeable membrane.
• Co-transport: Coupled transport (e.g., glucose and sodium in intestines).

Gas Exchange

Plants

• Occurs in leaves through stomata.
• Xerophytes: Adaptations to reduce water loss.

Animals

• Insects: Tracheal system.
• Fish: Gills with counter-current exchange.
• Humans: Respiratory system with alveoli.

Genetics

Mendelian Genetics

• Monohybrid Crosses: Single gene inheritance.
• Dihybrid Crosses: Two genes inheritance.
• Co-dominance: Both alleles expressed.
• Sex Linkage: Genes located on sex chromosomes.

Genetic Variation

• Sources: Mutations, meiosis, random fertilization.
• Natural Selection: Differential survival and reproduction.

Genetic Engineering

• Recombinant DNA Technology: Gene cloning, transformation, gene therapy.

Ecology

Ecosystems and Biodiversity

• Ecosystems: Interactions between organisms and environment.
• Biodiversity: Variety of life, importance for ecosystem stability.

Conservation

• Conservation Techniques: Protecting endangered species, maintaining habitats.
• Human Impact: Pollution, habitat destruction, overexploitation.

Conclusion

• Comprehensive coverage of AQA A-Level Biology topics.
• Emphasis on understanding key concepts and their applications.
• Resources available for further study and exam preparation.