IB Biology HL Complete Study Guide

THEME A: UNITY AND DIVERSITY

A1: Water

Properties of Water

Structure

  • Water is a polar molecule

  • Oxygen is more electronegative than hydrogen

  • Bent molecular shape causes uneven charge distribution

Hydrogen Bonding

  • Attraction between slightly positive hydrogen and slightly negative oxygen

  • Weaker than covalent bonds but essential for life

Properties Caused by Hydrogen Bonding

Cohesion

  • Water molecules stick together

  • Important for transport in xylem

Adhesion

  • Water sticks to other surfaces

  • Helps capillary action

Thermal Properties

  • High specific heat capacity

  • High latent heat of vaporization

  • Stabilizes temperatures

Solvent Properties

  • Polar and ionic substances dissolve in water

  • Important for cytoplasm and blood plasma

Metabolism and Water

  • Condensation reactions remove water

  • Hydrolysis reactions add water

A2: Nucleic Acids

DNA Structure

  • Double helix

  • Antiparallel strands

  • Nucleotides contain:

    • Phosphate

    • Deoxyribose sugar

    • Nitrogenous base

Base Pairing

  • Adenine pairs with thymine

  • Cytosine pairs with guanine

RNA Structure

  • Single stranded

  • Ribose sugar

  • Uracil replaces thymine

DNA Replication

Semi-conservative replication

  • Each new DNA molecule contains one old and one new strand

Enzymes

  • Helicase unzips DNA

  • DNA polymerase adds nucleotides

  • Ligase joins fragments

Transcription

  • DNA → mRNA

  • Occurs in nucleus

  • RNA polymerase involved

Translation

  • mRNA read by ribosomes

  • tRNA brings amino acids

  • Codons determine amino acid sequence

Mutations

Types

  • Substitution

  • Insertion

  • Deletion

Effects

  • Silent

  • Missense

  • Nonsense

  • Frameshift

Genetic Engineering

  • PCR

  • Gel electrophoresis

  • DNA sequencing

  • CRISPR-Cas9

A3: Classification and Biodiversity

Taxonomy

Hierarchy

  • Domain

  • Kingdom

  • Phylum

  • Class

  • Order

  • Family

  • Genus

  • Species

Binomial Nomenclature

  • Genus capitalized

  • Species lowercase

  • Italicized

Domains of Life

Archaea

  • Prokaryotic

  • Unique membrane lipids

Bacteria

  • Prokaryotic

  • Peptidoglycan cell walls

Eukarya

  • Membrane-bound organelles

Evidence for Evolution

  • Fossils

  • Comparative anatomy

  • Molecular evidence

  • Selective breeding

Natural Selection

Requirements

  • Variation

  • Heritability

  • Competition

  • Differential survival/reproduction

Speciation

Allopatric speciation

  • Geographic isolation

Sympatric speciation

  • Reproductive isolation without geographic separation

Biodiversity

Importance

  • Ecosystem stability

  • Genetic variation

  • Resources for medicine/agriculture

Threats

  • Habitat destruction

  • Climate change

  • Pollution

  • Invasive species

B1: Carbohydrates and Lipids

Carbohydrates

Monosaccharides

  • Glucose

  • Fructose

  • Galactose

Disaccharides

  • Maltose

  • Sucrose

  • Lactose

Polysaccharides

Starch

  • Energy storage in plants

Glycogen

  • Energy storage in animals

Cellulose

  • Structural component of plant cell walls

Functions of Carbohydrates

  • Energy source

  • Energy storage

  • Structural support

Lipids

Triglycerides

  • Glycerol + 3 fatty acids

Saturated vs Unsaturated Fats

  • Saturated: no double bonds

  • Unsaturated: one or more double bonds

Phospholipids

  • Hydrophilic phosphate head

  • Hydrophobic fatty acid tails

  • Form bilayers in membranes

Steroids

  • Cholesterol

  • Hormones

Functions of Lipids

  • Long-term energy storage

  • Insulation

  • Hormone production

  • Membrane structure

B2: Proteins

Amino Acids

General Structure

  • Amino group

  • Carboxyl group

  • Variable R group

Peptide Bonds

  • Formed by condensation reactions

Protein Structure

Primary

  • Amino acid sequence

Secondary

  • Alpha helices

  • Beta pleated sheets

Tertiary

  • 3D folding

Quaternary

  • Multiple polypeptide chains

Enzymes

Properties

  • Biological catalysts

  • Lower activation energy

  • Specific active site

Factors Affecting Enzyme Activity

  • Temperature

  • pH

  • Substrate concentration

Enzyme Inhibition

Competitive

  • Competes for active site

Noncompetitive

  • Binds elsewhere and changes shape

Denaturation

  • Loss of protein shape/function

B3: Membranes and Transport

Fluid Mosaic Model

  • Phospholipid bilayer

  • Embedded proteins

  • Cholesterol

  • Glycoproteins

Membrane Properties

  • Selectively permeable

Passive Transport

Diffusion

  • Movement from high to low concentration

Osmosis

  • Movement of water through partially permeable membrane

Facilitated Diffusion

  • Uses channel or carrier proteins

Active Transport

  • Requires ATP

  • Moves substances against concentration gradient

Bulk Transport

Endocytosis

  • Material enters cell

Exocytosis

  • Material exits cell

C1: Cell Structure and Function

Cell Theory

  • All organisms made of cells

  • Cells are basic unit of life

  • Cells arise from preexisting cells

Prokaryotes vs Eukaryotes

Prokaryotes

  • No nucleus

  • Circular DNA

  • Smaller ribosomes

Eukaryotes

  • Membrane-bound organelles

  • Linear chromosomes

Organelles and Functions

Nucleus

  • Stores DNA

Ribosomes

  • Protein synthesis

Mitochondria

  • Aerobic respiration

  • ATP production

Chloroplasts

  • Photosynthesis

Rough ER

  • Protein modification

Smooth ER

  • Lipid synthesis

Golgi Apparatus

  • Packaging and secretion

Lysosomes

  • Digestion

Vacuoles

  • Storage

Stem Cells

Potency

  • Totipotent

  • Pluripotent

  • Multipotent

Therapeutic Uses

  • Tissue repair

  • Disease treatment

C2: Cell Division

Cell Cycle

  • Interphase

  • Mitosis

  • Cytokinesis

Mitosis Stages

Prophase

  • Chromosomes condense

Metaphase

  • Chromosomes align

Anaphase

  • Sister chromatids separate

Telophase

  • Nuclear membranes reform

Cancer

  • Uncontrolled cell division

  • Tumors may be benign or malignant

Meiosis

Purpose

  • Produces haploid gametes

Variation Mechanisms

  • Crossing over

  • Independent assortment

  • Random fertilization

Chromosome Number

  • Diploid (2n)

  • Haploid (n)

D1: DNA Replication and Protein Synthesis

Central Dogma

DNA → RNA → Protein

Genetic Code

  • Triplet code

  • Degenerate

  • Universal

  • Non-overlapping

Transcription Details

  • Template strand used

  • mRNA complementary to DNA

Translation Details

  • Ribosomes read codons

  • Start codon: AUG

  • Stop codons terminate translation

Gene Regulation

Operons in Prokaryotes

  • lac operon

Epigenetics

  • DNA methylation

  • Histone modification

D2: Biotechnology and Bioinformatics

PCR

Steps

  • Denaturation

  • Annealing

  • Extension

Gel Electrophoresis

  • Separates DNA fragments by size

DNA Profiling

  • Forensics

  • Paternity testing

Genetic Modification

Uses

  • Agriculture

  • Medicine

Cloning

Reproductive cloning

Therapeutic cloning

Bioinformatics

  • Genome databases

  • Sequence comparison

E1: Metabolism and Cellular Respiration

ATP

  • Adenosine triphosphate

  • Immediate energy source

Metabolism

  • Sum of all chemical reactions

Cellular Respiration Equation

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Glycolysis

  • Occurs in cytoplasm

  • Produces pyruvate

  • Net gain of 2 ATP

Link Reaction

  • Pyruvate converted to acetyl-CoA

Krebs Cycle

  • Occurs in mitochondrial matrix

  • Produces NADH and FADH2

Electron Transport Chain

  • Inner mitochondrial membrane

  • Oxidative phosphorylation

  • Produces most ATP

Anaerobic Respiration

Lactic acid fermentation

Alcoholic fermentation

E2: Photosynthesis

Photosynthesis Equation

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Chloroplast Structure

  • Thylakoids

  • Grana

  • Stroma

Light-Dependent Reactions

  • Occur in thylakoids

  • Produce ATP and NADPH

  • Photolysis of water

Calvin Cycle

  • Occurs in stroma

  • Carbon fixation

  • Produces sugars

Factors Affecting Photosynthesis

  • Light intensity

  • Temperature

  • Carbon dioxide concentration

F1: Homeostasis

Homeostasis Definition

  • Maintenance of stable internal conditions

Negative Feedback

  • Reverses changes from set point

Positive Feedback

  • Amplifies changes

Blood Glucose Regulation

Insulin

  • Lowers blood glucose

Glucagon

  • Raises blood glucose

Thermoregulation

Vasodilation

Vasoconstriction

Sweating

Shivering

Osmoregulation

  • Kidney function

  • Water balance

F2: Nervous and Hormonal Control

Neurons

Structure

  • Dendrites

  • Cell body

  • Axon

  • Myelin sheath

Resting Potential

  • Sodium-potassium pump

Action Potential

  • Depolarization

  • Repolarization

Synapses

  • Neurotransmitters cross synaptic cleft

Endocrine System

  • Hormones transported in blood

Hormones to Know

  • Insulin

  • Glucagon

  • Adrenaline

  • Estrogen

  • Testosterone

  • Progesterone

G1: Evolution

Darwin’s Theory

  • Descent with modification

  • Natural selection

Artificial Selection

  • Human-directed breeding

Evidence for Evolution

  • Fossils

  • Homologous structures

  • DNA evidence

Hardy-Weinberg Principle

Conditions

  • No mutation

  • No migration

  • Large population

  • Random mating

  • No selection

Speciation Mechanisms

  • Isolation

  • Divergence

G2: Ecology and Conservation

Ecosystems

  • Community + abiotic environment

Food Chains and Webs

  • Producers

  • Consumers

  • Decomposers

Energy Transfer

  • Energy lost as heat between trophic levels

Carbon Cycle

  • Photosynthesis

  • Respiration

  • Combustion

  • Decomposition

Nitrogen Cycle

  • Nitrogen fixation

  • Nitrification

  • Denitrification

Population Growth

Exponential growth

Logistic growth

Carrying Capacity

  • Maximum sustainable population size

Conservation

In situ conservation

Ex situ conservation

H1: Human Physiology

Digestion

Mechanical digestion

Chemical digestion

Digestive Enzymes

  • Amylase

  • Protease

  • Lipase

Gas Exchange

Alveoli adaptations

  • Large surface area

  • Thin walls

  • Rich blood supply

Circulatory System

Heart chambers

  • Left/right atria

  • Left/right ventricles

Blood Vessels

Arteries

Veins

Capillaries

Immune System

Innate immunity

Adaptive immunity

Antibodies

  • Produced by B cells

Vaccination

  • Produces memory cells

H2: Plant Biology

Plant Structure

  • Roots

  • Stems

  • Leaves

Xylem

  • Water transport

Phloem

  • Sugar transport

Transpiration

  • Water loss through stomata

Translocation

  • Movement of sucrose in phloem

Plant Hormones

Auxins

  • Cell elongation

Gibberellins

  • Stem growth

Abscisic Acid

  • Stress responses

Reproduction in Flowering Plants

Pollination

Fertilization

Seed dispersal

Experimental Skills and Data Analysis

Variables

Independent variable

Dependent variable

Controlled variables

Reliability vs Accuracy

  • Reliability = consistency

  • Accuracy = closeness to true value

Graphing Skills

Line graphs

  • Continuous data

Bar graphs

  • Categorical data

Statistical Tests

Standard deviation

Chi-square test

t-test

Evaluating Experiments

Sources of error

Limitations

Improvements

Important Command Terms

Analyze

Break down and explain relationships

Compare

Give similarities and differences

Contrast

Give differences only

Describe

Provide detailed account

Discuss

Give balanced review with evidence

Evaluate

Judge strengths and weaknesses

Explain

Give reasons/mechanisms

Outline

Brief summary

Common IB Biology HL Essay Topics

  • Natural selection and evolution

  • Enzyme action

  • Membrane transport

  • Photosynthesis vs respiration

  • DNA replication and protein synthesis

  • Homeostasis

  • Ecology and nutrient cycles

  • Cell division

  • Human impacts on ecosystems

  • Gene technology ethics

Most Important Processes to Memorize

Cellular Respiration

  • Glycolysis

  • Krebs cycle

  • Electron transport chain

Photosynthesis

  • Light-dependent reactions

  • Calvin cycle

DNA Processes

  • Replication

  • Transcription

  • Translation

Cell Division

  • Mitosis

  • Meiosis

Transport

  • Osmosis

  • Diffusion

  • Active transport

High-Yield Exam Tips

Multiple Choice

  • Read all answer choices carefully

  • Eliminate clearly incorrect answers first

  • Watch for qualifiers like “always” and “only”

Data Analysis Questions

  • Look for trends before explaining

  • Include units and evidence from graphs/tables

  • Correlation does not always equal causation

Extended Response Questions

  • Use biological vocabulary

  • Organize answers clearly

  • Include examples where possible

  • Answer exactly what the question asks

Memorization Strategies

  • Draw diagrams repeatedly

  • Use flashcards for terminology

  • Practice past papers

  • Teach concepts aloud

Essential Vocabulary

Allele

Alternative form of a gene

Antigen

Substance that triggers immune response

ATP

Main energy carrier in cells

Codon

Three-base sequence on mRNA

Enzyme

Biological catalyst

Gene

DNA sequence coding for a product

Homeostasis

Stable internal conditions

Osmosis

Movement of water across membrane

Species

Organisms able to interbreed and produce fertile offspring

Stem Cell

Undifferentiated cell capable of specialization

Final Review Checklist

Before the exam, make sure you can:

  • Explain all major cycles and pathways

  • Label cell organelles and structures

  • Compare mitosis and meiosis

  • Describe enzyme function and inhibition

  • Explain transport mechanisms

  • Interpret graphs and data

  • Apply genetics concepts to crosses/problems

  • Explain ecological relationships

  • Describe human body systems

  • Evaluate experiments scientifically

  • Use IB command terms correctly