Variation between organisms as a defining feature of life

Whether you're a current IB Biology student looking to get a deeper grasp of the syllabus or a prospective IB student weighing your science options, this post will be your guide. We'll break down the IB Biology syllabus to give you a clear understanding of what to expect in the course.

The IB Biology syllabus is divided into four themes:

Each theme consists of a variety of topic, but at the core of them all is the study of molecules, cells, organisms, and ecosystems, which serve as the foundation of the entire course.

Biology

In this theme, you will explore the following topics:

Unity and diversity

Hydrogen bonds as a consequence of the polar covalent bonds within water molecules

Cohesion of water molecules due to hydrogen bonding and consequences for organisms

Adhesion of water to materials that are polar or charged and impacts for organisms

Solvent properties of water linked to its role as a medium for metabolism and for transport in plants and animals

Physical properties of water and the consequences for animals in aquatic habitats

Extraplanetary origin of water on Earth and reasons for its retention

Relationship between the search for extraterrestrial life and the presence of water

Water

DNA as the genetic material of all living organisms

Sugar–phosphate bonding and the sugar–phosphate “backbone” of DNA and RNA

Bases in each nucleic acid that form the basis of a code

RNA as a polymer formed by condensation of nucleotide monomers

DNA as a double helix made of two antiparallel strands of nucleotides with two strands linked by hydrogen bonding between complementary base pairs

Role of complementary base pairing in allowing genetic information to be replicated and expressed

Diversity of possible DNA base sequences and the limitless capacity of DNA for storing information

Conservation of the genetic code across all life forms as evidence of universal common ancestry

Purine-to-pyrimidine bonding as a component of DNA helix stability

Evidence from the Hershey–Chase experiment for DNA as the genetic material

Chargaff’s data on the relative amounts of pyrimidine and purine bases across diverse life forms

Nucleic acids

Conditions on early Earth and the pre-biotic formation of carbon compounds

Cells as the smallest units of self-sustaining life

Challenge of explaining the spontaneous origin of cells

Evidence for the origin of carbon compounds

Spontaneous formation of vesicles by coalescence of fatty acids into spherical bilayers

Evidence for a last universal common ancestor

Approaches used to estimate dates of the first living cells and the last universal common ancestor

Evidence for the evolution of the last universal common ancestor in the vicinity of hydrothermal vents

Origins of cells

Cells as the basic structural unit of all living organisms

Structures common to cells in all living organisms

Processes of life in unicellular organisms

Differences in eukaryotic cell structure between animals, fungi and plants

Cell types and cell structures viewed in light and electron micrographs

Drawing and annotation based on electron micrographs

Origin of eukaryotic cells by endosymbiosis

Cell differentiation as the process for developing specialized tissues in multicellular organisms

Cell structure

Evidence for several origins of viruses from other organisms

Viruses

Species as groups of organisms with shared traits

Difficulties distinguishing between populations and species due to divergence of non- interbreeding populations during speciation

Diversity in chromosome numbers of plant and animal species

Unity and diversity of genomes within species

Current and potential future uses of whole genome sequencing

Difficulties applying the biological species concept to asexually reproducing species and to bacteria that have horizontal gene transfer

Chromosome number as a shared trait within a species

Engagement with local plant or animal species to develop a dichotomous key

Identification of species from environmental DNA in a habitat using barcodes

Diversity of organisms

Difficulties classifying organisms into the traditional hierarchy of taxa

Advantages of classification corresponding to evolutionary relationships

Clades as groups of organisms with common ancestry and shared characteristics

Gradual accumulation of sequence differences as the basis for estimates of when clades diverged from a common ancestor

Base sequences of genes or amino acid sequences of proteins as the basis for constructing cladograms

Using cladistics to investigate whether the classification of groups corresponds to evolutionary relationships

Classification of all organisms into three domains using evidence from rRNA base sequences

Classification and cladistics

Evolution as change in the heritable characteristics of a population

Evidence for evolution from base sequences in DNA or RNA and amino acid sequences in proteins

Evidence for evolution from selective breeding of domesticated animals and crop plants

Evidence for evolution from homologous structures

Convergent evolution as the origin of analogous structures

Speciation by splitting of pre-existing species

Roles of reproductive isolation and differential selection in speciation

Differences and similarities between sympatric and allopatric speciation

Adaptive radiation as a source of biodiversity

Barriers to hybridization and sterility of interspecific hybrids as mechanisms for of preventing the mixing of alleles between species

Abrupt speciation in plants by hybridization and polyploidy

Evolution and speciation

Biodiversity as the variety of life in all its forms, levels and combinations

Comparisons between current number of species on Earth and past levels of biodiversity

Causes of anthropogenic species extinction

Causes of the current biodiversity crisis

Need for several approaches to conservation of biodiversity

Selection of evolutionarily distinct and globally endangered species for conservation prioritization in the EDGE of Existence programme

Conservation of biodiversity

Form and function

Cell

Chemical properties of a carbon atom allowing for the formation of diverse compounds upon which life is based

Production of macromolecules by condensation reactions that link monomers to form a polymer

Digestion of polymers into monomers by hydrolysis reactions

Polysaccharides as energy storage compounds

Structure of cellulose related to its function as a structural polysaccharide in plants

Role of glycoproteins in cell–cell recognition

Formation of triglycerides and phospholipids by condensation reactions

Difference between saturated, monounsaturated and polyunsaturated fatty acids

Triglycerides in adipose tissues for energy storage and thermal insulation

Formation of phospholipid bilayers as a consequence of the hydrophobic and hydrophilic regions

Ability of non-polar steroids to pass through the phospholipid bilayer

Carbohydrates and lipids

Condensation reactions forming dipeptides and longer chains of amino acids

Infinite variety of possible peptide chains

Effect of pH and temperature on protein structure

Chemical diversity in the R-groups of amino acids as a basis for the immense diversity in protein form and function

Impact of primary structure on the conformation of proteins

Pleating and coiling of secondary structure of proteins

Dependence of tertiary structure on hydrogen bonds, ionic bonds, disulfide covalent bonds and hydrophobic interactions

Effect of polar and non-polar amino acids on tertiary structure of proteins

Quaternary structure of non-conjugated and conjugated proteins

Relationship of form and function in globular and fibrous proteins

Proteins

Lipid bilayers as the basis of cell membranes

Integral and peripheral proteins in membranes

Movement of water molecules across membranes by osmosis and the role of aquaporins

Channel proteins for facilitated diffusion

Relationships between fatty acid composition of lipid bilayers and their fluidity

Cholesterol and membrane fluidity in animal cells

Membrane fluidity and the fusion and formation of vesicles

Sodium–potassium pumps as an example of exchange transporters

Sodium-dependent glucose cotransporters as an example of indirect active transport

Membranes and membrane transport

Organelles as discrete subunits of cells that are adapted to perform specific functions

Advantage of the separation of the nucleus and cytoplasm into separate compartments

Advantages of compartmentalization in the cytoplasm of cells

Adaptations of the mitochondrion for production of ATP by aerobic cell respiration

Adaptations of the chloroplast for photosynthesis

Functional benefits of the double membrane of the nucleus

Structure and function of free ribosomes and of the rough endoplasmic reticulum

Structure and function of the Golgi apparatus

Structure and function of vesicles in cells

Organelles and compartmentalization

Gas exchange as a vital function in all organisms

Maintenance of concentration gradients at exchange surfaces in animals

Adaptations of mammalian lungs for gas exchange

Transpiration as a consequence of gas exchange in a leaf

Adaptations of foetal and adult haemoglobin for the transport of oxygen

Oxygen dissociation curves as a means of representing the affinity of haemoglobin for oxygen at different oxygen concentrations

Gas exchange

Adaptations of capillaries for exchange of materials between blood and the internal or external environment

Adaptations of arteries for the transport of blood away from the heart

Adaptations of veins for the return of blood to the heart

Causes and consequences of occlusion of the coronary arteries

Transport of water from roots to leaves during transpiration

Adaptations of xylem vessels for transport of water

Distribution of tissues in a transverse section of the stem of a dicotyledonous plant

Distribution of tissues in a transverse section of the root of a dicotyledonous plant

Release and reuptake of tissue fluid in capillaries

Exchange of substances between tissue fluid and cells in tissues

Drainage of excess tissue fluid into lymph ducts

Differences between the single circulation of bony fish and the double circulation of mammals

Adaptations of the mammalian heart for delivering pressurized blood to the arteries

Generation of root pressure in xylem vessels by active transport of mineral ions

Adaptations of phloem sieve tubes and companion cells for translocation of sap

Transport

Adaptations for movement as a universal feature of living organisms

Sliding filament model of muscle contraction

Role of the protein titin and antagonistic muscles in muscle relaxation

Structure and function of motor units in skeletal muscle

Roles of skeletons as anchorage for muscles and as levers

Internal and external intercostal muscles as an example of antagonistic muscle action to facilitate internal body movements

Adaptations for swimming in marine mammals

Muscle and motility

Habitat as the place in which a community, species, population or organism lives

Adaptations of organisms to the abiotic environment of their habitat

Abiotic variables affecting species distribution

Conditions required for coral reef formation

Abiotic factors as the determinants of terrestrial biome distribution

Biomes as groups of ecosystems with similar communities due to similar abiotic conditions and convergent evolution

Adaptations to life in hot deserts and tropical rainforest

Adaptation to environment

Ecological niche as the role of a species in an ecosystem

Differences between organisms that are obligate anaerobes, facultative anaerobes and obligate aerobes

Photosynthesis as the mode of nutrition in plants, algae and several groups of photosynthetic prokaryotes

Saprotrophic nutrition in some fungi and bacteria

Relationship between dentition and the diet of omnivorous and herbivorous representative members of the family Hominidae

Adaptations of herbivores for feeding on plants and of plants for resisting herbivory

Adaptations of predators for finding, catching and killing prey and of prey animals for resisting predation

Adaptations of plant form for harvesting light

Competitive exclusion and the uniqueness of ecological niches

Ecological niches

Interaction and interdependence

Enzymes as globular proteins with an active site for catalysis

Interactions between substrate and active site to allow induced-fit binding

Role of molecular motion and substrate-active site collisions in enzyme catalysis

Relationships between the structure of the active site, enzyme–substrate specificity and denaturation

Effects of temperature, pH and substrate concentration on the rate of enzyme activity

Measurements in enzyme-catalysed reactions

Intracellular and extracellular enzyme-catalysed reactions

Generation of heat energy by the reactions of metabolism

Cyclical and linear pathways in metabolism

Allosteric sites and non-competitive inhibition

Competitive inhibition as a consequence of an inhibitor binding reversibly to an active site

Regulation of metabolic pathways by feedback inhibition

Mechanism-based inhibition as a consequence of chemical changes to the active site caused by the irreversible binding of an inhibitor

Enzymes and metabolism

ATP as the molecule that distributes energy within cells

Life processes within cells that ATP supplies with energy

Energy transfers during interconversions between ATP and ADP

Cell respiration as a system for producing ATP within the cell using energy released from carbon compounds

Differences between anaerobic and aerobic cell respiration in humans

Variables affecting the rate of cell respiration

Role of NAD as a carrier of hydrogen and oxidation by removal of hydrogen during cell respiration

Conversion of glucose to pyruvate by stepwise reactions in glycolysis with a net yield of ATP and reduced NAD

Collections

Physics

Biology

Chemistry

Diversity of organisms

Syllabus concepts to know

Study & practice A3.1 Diversity of organisms

Practice A3.1 in Question Bank

Read Notes for A3.1

Review A3.1 Flashcards