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IB Biology Topic A - Unity and Diversity (SL/HL) covers syllabus content. Use these Notes, Questionbank, Videos, Flashcards, and Lessons to review the topic, practise exam questions, and move between notes, videos, flashcards, and lessons where available.
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A1.1.1 Water as the medium for life
A1.1.2 Hydrogen bonds as a consequence of the polar covalent bonds within water molecules
A1.1.3 Cohesion of water molecules due to hydrogen bonding and consequences for organisms
A1.1.4 Adhesion of water to materials that are polar or charged and impacts for organisms
A1.1.5 Solvent properties of water as a medium for metabolism and transport
A1.1.6 Physical properties of water and the consequences for animals in aquatic habitats
A1.1.7 Extraplanetary origin of water on Earth and reasons for its retention (HL only)
A1.1.8 Relationship between the search for extraterrestrial life and the presence of water (HL only)
A1.2.1 DNA as the genetic material of all living organisms
A1.2.2 Components of a nucleotide
A1.2.3 Sugar–phosphate bonding and the sugar–phosphate “backbone” of DNA and RNA
A1.2.4 Bases in each nucleic acid that form the basis of a code
A1.2.5 RNA as a polymer formed by condensation of nucleotide monomers
A1.2.6 DNA as a double helix linked by hydrogen bonding between complementary base pairs
A1.2.7 Differences between DNA and RNA
A1.2.8 Complementary base pairing in allowing genetic information to be replicated and expressed
A1.2.9 Diversity of possible DNA base sequences and its capacity for storing information
A1.2.10 Conservation of the genetic code as evidence of universal common ancestry
A1.2.11 Directionality of RNA and DNA (HL only)
A1.2.12 Purine-to-pyrimidine bonding as a component of DNA helix stability (HL only)
A1.2.13 Structure of a nucleosome (HL only)
A1.2.14 Evidence from the Hershey–Chase experiment for DNA as the genetic material (HL only)
A1.2.15 Chargaff’s data on pyrimidine and purine bases across diverse life forms (HL only)
A2.1.1 Conditions on early Earth and the pre-biotic formation of carbon compounds (HL only)
A2.1.2 Cells as the smallest units of self-sustaining life (HL only)
A2.1.3 Challenge of explaining the spontaneous origin of cells
A2.1.4 Evidence for the origin of carbon compounds
A2.1.5 Spontaneous formation of vesicles by coalescence of fatty acids into spherical bilayers
A2.1.6 RNA as a presumed first genetic material
A2.1.7 Evidence for a last universal common ancestor
A2.1.8 Approaches used to estimate dates of the first living cells
A2.1.9 Evidence for the evolution of the last universal common ancestor
A2.2.1 Cells as the basic structural unit of all living organisms
A2.2.2 Microscopy skills
A2.2.3 Developments in microscopy
A2.2.4 Structures common to cells in all living organisms
A2.2.5 Prokaryote cell structure
A2.2.6 Eukaryote cell structure
A2.2.7 Processes of life in unicellular organisms
A2.2.8 Differences in eukaryotic cell structure between animals, fungi, and plants
A2.2.9 Atypical cell structure in eukaryotes
A2.2.10 Cell types and cell structures viewed in light and electron micrographs
A2.2.11 Drawing and annotation based on electron micrographs
A2.2.12 Origin of eukaryotic cells by endosymbiosis (HL)
A2.2.13 Cell differentiation (HL)
A2.2.14 Evolution of multicellularity (HL)
A3.1.1 Variation between organisms as a defining feature of life
A3.1.2 Species as groups of organisms with shared traits
A3.1.3 Binomial system for naming organisms
A3.1.4 Biological species concept
A3.1.5 Difficulties distinguishing between populations and species
A3.1.6 Diversity in chromosome numbers of plant and animal species
A3.1.7 Karyotyping and karyograms
A3.1.8 Unity and diversity of genomes within species
A3.1.9 Diversity of eukaryote genomes
A3.1.10 Comparison of genome sizes
A3.1.11 Current and potential future uses of whole genome sequencing
A3.1.12 Difficulties applying the biological species concept (HL)
A3.1.13 Chromosome number as a shared trait within a species (HL)
A3.1.14 Engagement with local plant or animal species to develop a dichotomous key (HL)
A3.1.15 Identification of species from environmental DNA in a habitat using barcodes (HL)
A3.2.1 Need for classification of organisms (HL)
A3.2.2 Difficulties classifying organisms into the traditional hierarchy of taxa (HL)
A3.2.3 Advantages of classification corresponding to evolutionary relationships (HL)
A3.2.4 Clades as groups of organisms with common ancestry and shared characteristics (HL)
A3.2.5 Gradual accumulation of sequence differences (HL)
A3.2.6 Base sequences of genes or amino acid sequences of proteins (HL)
A3.2.7 Analysing cladograms (HL)
A3.2.8 Using cladistics to investigate evolutionary relationships (HL)
A3.2.9 Classification of all organisms using evidence from rRNA base sequences (HL)
A4.1.1 Evolution as change in the heritable characteristics of a population
A4.1.2 Evidence for evolution from base sequences in DNA or RNA and amino acid sequences
A4.1.3 Evidence for evolution from selective breeding of domesticated animals and crop plants
A4.1.4 Evidence for evolution from homologous structures
A4.1.5 Convergent evolution as the origin of analogous structures
A4.1.6 Speciation by splitting of pre-existing species
A4.1.7 Roles of reproductive isolation and differential selection in speciation
A4.1.8 Differences and similarities between sympatric and allopatric speciation (HL)
A4.1.9 Adaptive radiation as a source of biodiversity (HL)
A4.1.10 Barriers to hybridization and sterility of interspecific hybrids (HL)
A4.1.11 Abrupt speciation in plants by hybridization and polyploidy (HL)
A4.2.1 Biodiversity as the variety of life in all its forms, levels and combinations
A4.2.2 Comparisons between current number of species on Earth and past levels of biodiversity
A4.2.3 Causes of anthropogenic species extinction
A4.2.4 Causes of ecosystem loss
A4.2.5 Evidence for a biodiversity crisis
A4.2.6 Causes of the current biodiversity crisis
A4.2.7 Need for several approaches to conservation of biodiversity
A4.2.8 Evolutionarily distinct and globally endangered species in conservation prioritization