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IB Diploma Biology HL revision notes

Short notes for every spec point. Pick a topic, then a note.

A1

Molecules (Unity and diversity)

2 subtopics · 12 notes

Water
  1. Subtopic overview: questions, flashcards and PDFs
  2. Water as the medium for life and hydrogen bonding
  3. Cohesion and adhesion
  4. Solvent properties of water
  5. Physical properties of water and aquatic animals
  6. Origin of water on Earth and the search for life HL only
Nucleic acids
  1. Subtopic overview: questions, flashcards and PDFs
  2. DNA as the genetic material and nucleotides
  3. RNA polymers and the DNA double helix
  4. Differences between DNA and RNA
  5. Base pairing, information storage and the genetic code
  6. Directionality and purine–pyrimidine pairing HL only
  7. Structure of a nucleosome HL only
  8. Hershey–Chase experiment and Chargaff's data HL only
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A2

Cells (Unity and diversity)

3 subtopics · 16 notes

Origins of cellsHL only
  1. Subtopic overview: questions, flashcards and PDFs
  2. Early Earth and the first carbon compounds
  3. Living and non-living, and the challenge of the first cells
  4. Vesicles and RNA as the first genetic material
  5. The last universal common ancestor
Cell structure
  1. Subtopic overview: questions, flashcards and PDFs
  2. Cell theory and structures common to all cells
  3. Microscopy skills
  4. Developments in microscopy
  5. Prokaryote and eukaryote cell structure
  6. Processes of life in unicellular organisms
  7. Animal, fungal and plant cells, and atypical cells
  8. Micrographs, drawing and annotation
  9. Origin of eukaryotic cells by endosymbiosis HL only
  10. Cell differentiation and the evolution of multicellularity HL only
VirusesHL only
  1. Subtopic overview: questions, flashcards and PDFs
  2. Structure and diversity of viruses
  3. Lytic and lysogenic cycles
  4. Origins and rapid evolution of viruses
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A3

Organisms (Unity and diversity)

2 subtopics · 11 notes

Diversity of organisms
  1. Subtopic overview: questions, flashcards and PDFs
  2. Variation, species and binomial names
  3. The biological species concept and speciation
  4. Chromosome numbers and karyograms
  5. Unity and diversity of genomes
  6. Whole genome sequencing
  7. Limits of the biological species concept HL only
  8. Dichotomous keys and environmental DNA HL only
Classification and cladisticsHL only
  1. Subtopic overview: questions, flashcards and PDFs
  2. Why classify, and problems with the traditional hierarchy
  3. Clades and the molecular clock
  4. Constructing and analysing cladograms
  5. Testing classifications and the three domains
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A4

Ecosystems (Unity and diversity)

2 subtopics · 10 notes

Evolution and speciation
  1. Subtopic overview: questions, flashcards and PDFs
  2. Evolution as change in heritable characteristics
  3. Evidence from sequences and selective breeding
  4. Homologous and analogous structures
  5. Speciation, reproductive isolation and differential selection
  6. Allopatric and sympatric speciation, and adaptive radiation HL only
  7. Barriers to hybridization and abrupt speciation by polyploidy HL only
Conservation of biodiversity
  1. Subtopic overview: questions, flashcards and PDFs
  2. Biodiversity and the number of species
  3. Anthropogenic species extinction and ecosystem loss
  4. Evidence for and causes of the biodiversity crisis
  5. Approaches to conservation and the EDGE of Existence programme
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B1

Molecules (Form and function)

2 subtopics · 16 notes

Carbohydrates and lipids
  1. Subtopic overview: questions, flashcards and PDFs
  2. Carbon atoms and the diversity of carbon compounds
  3. Condensation and hydrolysis reactions
  4. Monosaccharides: form and function
  5. Starch, glycogen and cellulose
  6. Glycoproteins and cell–cell recognition
  7. Lipids: hydrophobic properties, triglycerides and phospholipids
  8. Fatty acids, energy storage and insulation
  9. Phospholipid bilayers and steroids
Proteins
  1. Subtopic overview: questions, flashcards and PDFs
  2. Amino acids and peptide bonds
  3. Dietary amino acids and the variety of peptide chains
  4. Effect of pH and temperature on protein structure
  5. R-groups and primary structure HL only
  6. Secondary structure: alpha helices and beta-pleated sheets HL only
  7. Tertiary structure and the effect of polar and non-polar amino acids HL only
  8. Quaternary structure: non-conjugated and conjugated proteins HL only
  9. Form and function in globular and fibrous proteins HL only
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B2

Cells (Form and function)

3 subtopics · 15 notes

Membranes and membrane transport
  1. Subtopic overview: questions, flashcards and PDFs
  2. Lipid bilayers, barriers and simple diffusion
  3. Osmosis, channel proteins and pump proteins
  4. Membrane proteins, glycoproteins and the fluid mosaic model
  5. Membrane fluidity, cholesterol and vesicles HL only
  6. Gated ion channels, sodium–potassium pumps and cotransporters HL only
  7. Adhesion of cells to form tissues HL only
Organelles and compartmentalization
  1. Subtopic overview: questions, flashcards and PDFs
  2. Organelles, the nucleus and compartments
  3. Adaptations of mitochondria and chloroplasts HL only
  4. The nucleus, free ribosomes and rough ER HL only
  5. The Golgi apparatus and vesicles HL only
Cell specialization
  1. Subtopic overview: questions, flashcards and PDFs
  2. Differentiation and stem cells
  3. Cell size and surface area-to-volume ratio
  4. Surface area adaptations and pneumocytes HL only
  5. Cardiac muscle cells and striated muscle fibres HL only
  6. Adaptations of sperm and egg cells HL only
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B3

Organisms (Form and function)

3 subtopics · 21 notes

Gas exchange
  1. Subtopic overview: questions, flashcards and PDFs
  2. Gas exchange and exchange surfaces
  3. Adaptations of mammalian lungs
  4. Ventilation and lung volumes
  5. Gas exchange in leaves
  6. Transpiration and stomatal density
  7. Haemoglobin, the Bohr shift and oxygen dissociation curves HL only
Transport
  1. Subtopic overview: questions, flashcards and PDFs
  2. Adaptations of capillaries
  3. Structure and adaptations of arteries and veins
  4. Pulse rates and occlusion of the coronary arteries
  5. Water transport in xylem
  6. Tissues in dicotyledonous stems and roots
  7. Tissue fluid and lymph HL only
  8. Single and double circulation and the mammalian heart HL only
  9. Stages in the cardiac cycle HL only
  10. Root pressure and phloem transport HL only
Muscle and motilityHL only
  1. Subtopic overview: questions, flashcards and PDFs
  2. Movement and reasons for locomotion
  3. Sliding filament model of muscle contraction
  4. Titin, antagonistic muscles and the intercostal muscles
  5. Motor units in skeletal muscle
  6. Skeletons, the hip joint and range of motion
  7. Adaptations for swimming in marine mammals
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B4

Ecosystems (Form and function)

2 subtopics · 12 notes

Adaptation to environment
  1. Subtopic overview: questions, flashcards and PDFs
  2. Habitats and adaptations to the abiotic environment
  3. Abiotic variables and range of tolerance
  4. Conditions required for coral reef formation
  5. Terrestrial biomes
  6. Adaptations to hot deserts and tropical rainforest
Ecological niches
  1. Subtopic overview: questions, flashcards and PDFs
  2. Ecological niche and tolerance of oxygen
  3. Photosynthesis and mixotrophic nutrition
  4. Holozoic and saprotrophic nutrition, and archaea
  5. Dentition and diet in the Hominidae
  6. Adaptations for herbivory and predation
  7. Adaptations of plant form for harvesting light
  8. Fundamental and realized niches, and competitive exclusion
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C1

Molecules (Interaction and interdependence)

3 subtopics · 24 notes

Enzymes and metabolism
  1. Subtopic overview: questions, flashcards and PDFs
  2. Enzymes as catalysts and their role in metabolism
  3. Active sites, induced fit, collisions and denaturation
  4. Effects of temperature, pH and substrate concentration
  5. Effect of enzymes on activation energy
  6. Intracellular and extracellular reactions, heat and metabolic pathways HL only
  7. Non-competitive and competitive inhibition HL only
  8. Feedback inhibition and mechanism-based inhibition HL only
Cell respiration
  1. Subtopic overview: questions, flashcards and PDFs
  2. ATP: the molecule that distributes energy
  3. Cell respiration: aerobic and anaerobic
  4. Variables affecting the rate of cell respiration
  5. NAD, oxidation and glycolysis HL only
  6. Anaerobic respiration: lactate and yeast HL only
  7. The link reaction and the Krebs cycle HL only
  8. Electron transport chain, chemiosmosis and oxygen HL only
  9. Lipids and carbohydrates as respiratory substrates HL only
Photosynthesis
  1. Subtopic overview: questions, flashcards and PDFs
  2. Photosynthesis: energy, carbon dioxide, water and oxygen
  3. Separating photosynthetic pigments by chromatography
  4. Absorption of light, absorption spectra and action spectra
  5. Investigating limiting factors on photosynthesis
  6. Carbon dioxide enrichment experiments
  7. Photosystems and the photolysis of water HL only
  8. Chemiosmosis, reduction of NADP and thylakoids HL only
  9. The Calvin cycle: carbon fixation, triose phosphate and RuBP HL only
  10. Making other carbon compounds and interdependence of the reactions HL only
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C2

Cells (Interaction and interdependence)

2 subtopics · 14 notes

Chemical signallingHL only
  1. Subtopic overview: questions, flashcards and PDFs
  2. Receptors, ligands and quorum sensing HL only
  3. Types of signalling chemicals HL only
  4. Transmembrane and intracellular receptors HL only
  5. Ion channel receptors and G protein-coupled receptors HL only
  6. Tyrosine kinase receptors: insulin HL only
  7. Intracellular receptors and steroid hormones HL only
  8. Positive and negative feedback in cell signalling HL only
Neural signalling
  1. Subtopic overview: questions, flashcards and PDFs
  2. Neurons and the resting potential
  3. Nerve impulses as action potentials
  4. Depolarization, repolarization and oscilloscope traces HL only
  5. Speed of nerve impulses
  6. Synapses and excitatory postsynaptic potentials
  7. Exogenous chemicals, inhibition and summation HL only
  8. Pain perception and consciousness HL only
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C3

Organisms (Interaction and interdependence)

2 subtopics · 17 notes

Integration of body systems
  1. Subtopic overview: questions, flashcards and PDFs
  2. System integration and the hierarchy of subsystems
  3. The brain, spinal cord, neurons and nerves
  4. Pain reflex arcs and the cerebellum
  5. Melatonin, epinephrine and control by the hypothalamus and pituitary
  6. Feedback control of heart rate and ventilation rate
  7. Control of peristalsis by the CNS and enteric nervous system
  8. Tropic responses in seedlings and positive phototropism HL only
  9. Phytohormones, auxin efflux carriers and cell growth HL only
  10. Auxin and cytokinin interactions, and ethylene in fruit ripening HL only
Defence against disease
  1. Subtopic overview: questions, flashcards and PDFs
  2. Pathogens as the cause of infectious diseases
  3. Skin, mucous membranes and blood clotting
  4. Innate and adaptive immunity, and phagocytes
  5. Lymphocytes, antigens and antibody production
  6. Immunity, vaccines and herd immunity
  7. HIV transmission and AIDS
  8. Antibiotics and antibiotic resistance
  9. Zoonoses and evaluating COVID-19 data
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C4

Ecosystems (Interaction and interdependence)

2 subtopics · 18 notes

Populations and communities
  1. Subtopic overview: questions, flashcards and PDFs
  2. Populations and random sampling
  3. Capture–mark–release–recapture and the Lincoln index
  4. Carrying capacity and density-dependent factors
  5. Population growth curves
  6. Intraspecific and interspecific relationships
  7. Mutualism
  8. Invasive species and testing for competition
  9. Predator–prey relationships and control of populations
  10. Allelopathy and secretion of antibiotics
Transfers of energy and matter
  1. Subtopic overview: questions, flashcards and PDFs
  2. Ecosystems as open systems and the source of energy
  3. Food chains, food webs and decomposers
  4. Autotrophs and heterotrophs
  5. Trophic levels and energy pyramids
  6. Energy losses between trophic levels
  7. Primary and secondary production
  8. The carbon cycle, carbon sinks and combustion
  9. The Keeling Curve
  10. Interdependence of autotrophs and heterotrophs and recycling of elements
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D1

Molecules (Continuity and change)

3 subtopics · 20 notes

DNA replication
  1. Subtopic overview: questions, flashcards and PDFs
  2. Exact copies by semi-conservative replication
  3. Roles of helicase and DNA polymerase
  4. PCR and gel electrophoresis
  5. Applications of PCR and gel electrophoresis
  6. Directionality: leading and lagging strands HL only
  7. Replication enzymes and DNA proofreading HL only
Protein synthesis
  1. Subtopic overview: questions, flashcards and PDFs
  2. Transcription and gene expression
  3. Translation at the ribosome
  4. The genetic code
  5. Mutations that change protein structure
  6. Directionality and initiation at the promoter HL only
  7. Non-coding DNA, mRNA processing and alternative splicing HL only
  8. Initiation of translation and the A, P and E sites HL only
  9. Modification of polypeptides and proteasomes HL only
Mutation and gene editing
  1. Subtopic overview: questions, flashcards and PDFs
  2. Substitutions, insertions and deletions
  3. Causes of mutation and randomness
  4. Germ and somatic cells, and mutation as a source of variation
  5. Gene knockout HL only
  6. CRISPR–Cas9 gene editing HL only
  7. Conserved and highly conserved sequences HL only
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D2

Cells (Continuity and change)

3 subtopics · 14 notes

Cell and nuclear division
  1. Subtopic overview: questions, flashcards and PDFs
  2. Cell division and cytokinesis
  3. Mitosis, meiosis and chromosome movement
  4. Phases of mitosis
  5. Meiosis, non-disjunction and variation
  6. Cell proliferation and the cell cycle HL only
  7. Mutations, tumours and the mitotic index HL only
Gene expressionHL only
  1. Subtopic overview: questions, flashcards and PDFs
  2. Gene expression and its regulation
  3. Epigenesis, the transcriptome and epigenetic tags
  4. Epigenetic inheritance and the environment
  5. External factors and gene expression
Water potential
  1. Subtopic overview: questions, flashcards and PDFs
  2. Solvation and osmosis
  3. Osmosis in plant tissue: the practical
  4. Water movement in cells with and without walls
  5. Water potential HL only
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D3

Organisms (Continuity and change)

3 subtopics · 28 notes

Reproduction
  1. Subtopic overview: questions, flashcards and PDFs
  2. Sexual and asexual reproduction
  3. Male and female sexes and human reproductive systems
  4. Ovarian and uterine cycles and their hormones
  5. Fertilization in humans and hormones in IVF
  6. Sexual reproduction in flowering plants and insect-pollinated flowers
  7. Cross-pollination and self-incompatibility
  8. Seed dispersal and germination
  9. Puberty, spermatogenesis and oogenesis HL only
  10. Preventing polyspermy, the blastocyst and implantation HL only
  11. Pregnancy testing and the placenta HL only
  12. Hormones in pregnancy and childbirth, and HRT HL only
Inheritance
  1. Subtopic overview: questions, flashcards and PDFs
  2. Haploid gametes, diploid zygotes and genetic crosses in plants
  3. Genotype, phenotype, dominance and phenotypic plasticity
  4. Phenylketonuria, SNPs, multiple alleles and ABO blood groups
  5. Incomplete dominance and codominance
  6. Sex determination, sex linkage and haemophilia
  7. Pedigree charts
  8. Continuous variation and box-and-whisker plots
  9. Segregation, independent assortment and dihybrid crosses HL only
  10. Gene loci, autosomal linkage and recombinants HL only
  11. Chi-squared test on dihybrid cross data HL only
Homeostasis
  1. Subtopic overview: questions, flashcards and PDFs
  2. Homeostasis and negative feedback
  3. Regulation of blood glucose
  4. Type 1 and type 2 diabetes
  5. Thermoregulation
  6. The kidney: excretion, ultrafiltration and reabsorption HL only
  7. Loop of Henle and osmoregulation in the collecting ducts HL only
  8. Changes in blood supply to organs with activity HL only
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D4

Ecosystems (Continuity and change)

3 subtopics · 24 notes

Natural selection
  1. Subtopic overview: questions, flashcards and PDFs
  2. Natural selection as the mechanism of evolution
  3. Mutation and sexual reproduction as sources of variation
  4. Overproduction, competition and selection pressures
  5. Sexual selection and Endler's guppies
  6. Gene pools and allele frequencies HL only
  7. Directional, disruptive and stabilizing selection; artificial selection HL only
  8. The Hardy–Weinberg equation and its conditions HL only
Stability and change
  1. Subtopic overview: questions, flashcards and PDFs
  2. Stability of natural ecosystems
  3. Amazon deforestation as a possible tipping point
  4. Mesocosms and keystone species
  5. Sustainable harvesting and agriculture
  6. Eutrophication
  7. Biomagnification of pollutants
  8. Microplastic and macroplastic pollution of the oceans
  9. Rewilding
  10. Ecological succession and primary succession HL only
  11. Cyclical succession, climax communities and arrested succession HL only
Climate change
  1. Subtopic overview: questions, flashcards and PDFs
  2. Anthropogenic causes and positive feedback
  3. Boreal forest tipping point and polar habitat change
  4. Nutrient upwelling and threats to coral reefs
  5. Poleward and upslope range shifts
  6. Afforestation, forest regeneration and peatland restoration
  7. Phenology and disrupted synchrony HL only
  8. Insect life cycles and evolution due to climate change HL only
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