A-Level Biology Complete Guide

Jul 9, 2024

Lecture Notes: A-Level Biology Paper 1 Overview

Introduction

  • Lecture by Miss Estrick
  • Comprehensive review for AQA A-Level Biology Paper 1
  • Tips: Use 2x speed to save time, use time codes, and refer to additional resources in the description

Basic Concepts: Monomers and Polymers

  • Monomers: Smaller units that can create larger molecules
    • Examples: Glucose, amino acids, nucleotides (RNA & DNA)
  • Polymers: Made from monomers bonded together
    • Examples: Starch, cellulose, glycogen, proteins, DNA, and RNA
  • Reactions: Condensation and Hydrolysis
    • Condensation Reaction: Joins two molecules, creating a chemical bond and removing water (3 marks in exams)
    • Hydrolysis Reaction: Breaks chemical bonds using water (3 marks in exams)

Carbohydrates

  • Monosaccharides: 1 sugar unit
    • Examples: Glucose, fructose, galactose
  • Disaccharides: 2 sugar units
    • Examples: Sucrose, maltose, lactose
  • Polysaccharides: Many sugar units
    • Examples: Starch, cellulose, glycogen
  • Alpha and Beta Glucose Structures:
    • Alpha glucose: C6H12O6, H on top, OH on bottom (carbon 1)
    • Beta glucose: OH on top, H on bottom (carbon 1)
  • Glycosidic Bonds: Formed between monosaccharides via condensation reactions
  • Polysaccharide Function and Structure:
    • Starch: Energy store in plants (alpha glucose)
    • Cellulose: Structural strength in plant cell walls (beta glucose)
    • Glycogen: Energy store in animals, particularly liver and muscle cells (alpha glucose)

Lipids

  • Types: Triglycerides and phospholipids
  • Structure: Both have glycerol; triglycerides have 3 fatty acids, phospholipids have 2 fatty acids and a phosphate group
  • Formation: Condensation reactions forming ester bonds
  • Fatty Acids: Saturated (no double bonds) vs. unsaturated (one or more double bonds)
  • Functions:
    • Energy store (high carbon to hydrogen bond ratio)
    • Metabolic water source
    • Do not affect water potential due to insolubility
    • Light mass, useful for storage

Proteins

  • Amino Acids: Monomers that make up proteins
    • Structure: Central carbon, hydrogen atom, R group, amino group (NH2), and carboxyl group (COOH)
  • Protein Synthesis:
    • Primary Structure: Order of amino acids
    • Secondary Structure: Folding into alpha helices or beta sheets (hydrogen bonds)
    • Tertiary Structure: Further folding into 3D shapes (ionic, hydrogen, disulfide bonds)
    • Quaternary Structure: Multiple polypeptide chains

Enzymes

  • Function: Catalyze reactions by lowering activation energy
  • Specificity: Due to unique active site shape
  • Models: Induced fit model (accepted model)
  • Factors Affecting Rate: Temperature, pH, substrate concentration, enzyme concentration, inhibitors

Biochemical Tests

  • Starch: Add iodine -> blue-black
  • Reducing Sugars: Add Benedict’s reagent + heat -> green/yellow/orange/red
  • Non-Reducing Sugars: Add acid, boil, neutralize, add Benedict’s + heat -> orange/red
  • Proteins: Add Biuret solution -> purple
  • Lipids: Dissolve in ethanol, add water -> white emulsion

DNA and RNA

  • DNA: Contains genetic code
    • Structure: Double helix, complementary base pairs (A-T, C-G)
    • Replication: Semi-conservative, involving helicase and polymerase
  • RNA: Almost identical to DNA but single-stranded and shorter
    • Types: mRNA, tRNA, rRNA
  • ATP: Immediate energy source, composed of adenine, ribose, and three phosphates
    • Hydrolysis releases energy

Water Properties

  • Metabolite: Involved in reactions
  • Solvent: Due to polarity
  • High Heat Capacity: Buffers temperature
  • Large Latent Heat of Vaporization: Cooling effect
  • Cohesion: Due to hydrogen bonds, important for transport in plants

Organelles and Their Functions

  • Nucleus: Contains DNA, site of replication and transcription
  • Endoplasmic Reticulum: Protein (rough ER) and lipid (smooth ER) synthesis
  • Golgi Apparatus: Modifies and packages proteins
  • Lysosomes: Contain digestive enzymes
  • Mitochondria: Site of aerobic respiration (ATP production)
  • Ribosomes: Protein synthesis
  • Vacuole (Plants): Storage and turgidity maintenance
  • Chloroplasts: Site of photosynthesis
  • Cell Wall: Provides strength and prevents bursting in plants
  • Plasma Membrane: Controls entry and exit
  • Prokaryotic vs. Eukaryotic Cells: Key differences and structure

Cell Division and Microscopy

  • Mitosis: Nuclear division producing two genetically identical diploid cells
  • Meiosis: Produces four genetically different haploid gametes
  • Binary Fission: Prokaryotic cell division
  • Microscopy: Types (optical, SEM, TEM) and comparisons (resolution, magnification)
  • Cell Fractionation: Isolating organelles through homogenization and ultracentrifugation

Immunity

  • Self vs. Non-Self: Lymphocytes distinguish cells
  • Phagocytosis: Non-specific response, macrophages engulf pathogens
  • T and B Cells: Specific responses, including cell-mediated (T-cells) and humoral (B-cells)
  • Antibodies: Structure and function in immune response
  • Vaccines: Introducing antigens to create memory cells for immunity
  • HIV Structure & Replication: Impact on the immune system
  • Monoclonal Antibodies: Uses in treatment and diagnostics

Gas Exchange

  • Human System: Alveoli structure and gas exchange
  • Insects and Fish: Tracheal system and gills
  • Plants: Gas exchange through stomata

Digestion and Absorption

  • Carbohydrates: Enzymes like amylase break down into monosaccharides
  • Proteins: Broken down by endopeptidases, exopeptidases, and dipeptidases
  • Lipids: Digested by lipase and bile salts
  • Absorption: Villi and microvilli increase absorption in intestine
  • Co-Transport: Mechanism for glucose and amino acids

Transport in Plants and Animals

  • Transpiration: Water movement and evaporation in plants
  • Xylem and Phloem: Transport water and nutrients (cohesion-tension theory, translocation)
  • Cardiovascular System: Heart structure, blood vessels, and blood flow
  • Hemoglobin: Oxygen transport and dissociation curves

Biodiversity and Classification

  • Genetic Diversity: Importance for species survival and adaptation
  • Natural Selection: Mechanisms and types (directional, stabilizing)
  • Species and Taxonomy: Organization and classification (hierarchy, binomial system)
  • Measuring Biodiversity: Index of diversity, impact of human activities