1 - Cells

This section of the IB biology syllabus explores the cells found within all
living organisms. It covers cell ultrastructure, origin, and cycles, as well
as membrane structure and transport. It builds the fundamental
understanding required for later topics in the IB biology syllabus.
Subtopic
Understanding
Application

1.1: Introduction to cells

According to the cell theory, living organisms are composed of cells

Organisms consisting of only one cell carry out all functions of life in
that cell

Surface area to volume ratio is important in the limitation of cell size

Multicellular organisms have properties that emerge from the

interaction of their cellular components

Specialized tissues can develop by cell differentiation in multicellular

organisms

Differentiation involves the expression of some genes and not others in

a cell’s genome

The capacity of stem cells to divide and differentiate along different

pathways is necessary in embryonic development, and makes stem
cells suitable for therapeutic uses

Questioning the cell theory using atypical examples, including striated

muscle, giant algae and aseptate fungal hyphae

Investigation of functions of life in Paramecium and one named

photosynthetic unicellular organism
Use of stem cells to treat Stargardt’s disease and one other named
condition

Ethics of the therapeutic use of stem cells from specially created

embryos, from the umbilical cord blood of a new-born baby and from
an adult’s own tissues

Use of a light microscope to investigate the structure of cells and

tissues, with drawing of cells. Calculation of the magnification of
drawings and the actual size of structures and ultrastructures shown in
drawings or micrographs (Practical 1)

1.2: Ultrastructure of cells

Prokaryotes have a simple cell structure without compartmentalization

Eukaryotes have a compartmentalized cell structure

Electron microscopes have a much higher resolution than light

microscopes

Structure and function of organelles within exocrine gland cells of the

pancreas and within palisade mesophyll cells of the leaf

Prokaryotes divide by binary fission

Drawing of the ultrastructure of prokaryotic cells based on electron

micrographs

Drawing of the ultrastructure of eukaryotic cells based on electron

micrographs

Interpretation of electron micrographs to identify organelles and

deduce the function of specialized cells

1.3: Membrane structure

Membrane proteins are diverse in terms of structure, position in the
membrane and function

Phospholipids form bilayers in water due to the amphipathic properties

of phospholipid molecules

Cholesterol is a component of animal cell membranes

Cholesterol in mammalian membranes reduces membrane fluidity and

permeability to some solutes

Drawing of the fluid mosaic model

Analysis of evidence from electron microscopy that led to the proposal

of the Davson-Danielli model

Analysis of the falsification of the Davson- Danielli model that led to

the Singer-Nicolson model

1.4: Membrane transport

Particles move across membranes by simple diffusion, facilitated

diffusion, osmosis, and active transport

The fluidity of membranes allows materials to be taken into cells by

endocytosis or released by exocytosis. Vesicles move materials within
cells

Structure and function of sodium– potassium pumps for active

transport and potassium channels for facilitated diffusion in axons

Tissues or organs to be used in medical procedures must be bathed in

a solution with the same osmolarity as the cytoplasm to prevent
osmosis
Estimation of osmolarity in tissues by bathing samples in hypotonic
and hypertonic solutions (Practical 2)

1.5: Origin of cells

Cells can only be formed by division of pre-existing cells

The first cells must have arisen from non-living material

The origin of eukaryotic cells can be explained by the endosymbiotic

theory

Evidence from Pasteur’s experiments that spontaneous generation of

cells and organisms does not now occur on Earth

1.6: The Cell Cycle

Mitosis is division of the nucleus into two genetically identical daughter

nuclei

Chromosomes condense by supercoiling during mitosis

Cytokinesis occurs after mitosis and is different in plant and animal

cells

Interphase is a very active phase of the cell cycle with many processes
occurring in the nucleus and cytoplasm

Cyclins are involved in the control of the cell cycle

Mutagens, oncogenes, and metastasis are involved in the development

of primary and secondary tumours

The correlation between smoking and incidence of cancers

Identification of phases of mitosis in cells viewed with a microscope or
in a micrograph

Determination of a mitotic index from a micrograph

2 - Molecules

This section of the IB biology syllabus explores the molecules and

components found within cells. It covers the features of carbon
compounds, water, and proteins as well as the structure and behavior
of DNA & RNA. The fundamentals of respiration and photosynthesis are
also introduced. It links to the content covered in topic 1 of the IB
biology syllabus.
Subtopic
Understanding
Application

2.1: Molecules to metabolism

Molecular biology explains living processes in terms of the chemical

substances involved

Carbon atoms can form four covalent bonds allowing a diversity of

stable compounds to exist

Life is based on carbon compounds including carbohydrates, lipids,

proteins, and nucleic acids

Metabolism is the web of all the enzyme-catalysed reactions in a cell or

organism

Anabolism is the synthesis of complex molecules from simpler

molecules including the formation of macromolecules from monomers
by condensation reactions

Catabolism is the breakdown of complex molecules into simpler

molecules including the hydrolysis of macromolecules into monomers
Urea as an example of a compound that is produced by living
organisms but can also be artificially synthesized

Drawing molecular diagrams of glucose, ribose, a saturated fatty acid,

and a generalized amino acid

Identification of biochemicals such as sugars, lipids, or amino acids

from molecular diagrams

2.2: Water

Water molecules are polar and hydrogen bonds form between them

Substances can be hydrophilic or hydrophobic

Hydrogen bonding and dipolarity explain the cohesive, adhesive,

thermal and solvent properties of water

The solvent properties of water and its role as a medium for

metabolism and for transport in plants and animals.

The physical properties of water and the consequences for animals in

aquatic habitats, including: buoyancy, viscosity, thermal conductivity
and specific heat capacity.

Comparison of the thermal properties of water with those of methane

Use of water as a coolant in sweat

Modes of transport of glucose, amino acids, cholesterol, fats, oxygen,

and sodium chloride in blood in relation to their solubility in water

2.3: Carbohydrates & lipids

Monosaccharide monomers are linked together by condensation

reactions to form disaccharides and polysaccharide polymers
Fatty acids can be saturated, monounsaturated, or polyunsaturated

Unsaturated fatty acids can be cis or trans isomers

Triglycerides are formed by condensation from three fatty acids and

one glycerol

Structure and function of cellulose and starch in plants and glycogen in

humans

Scientific evidence for health risks of trans fats and saturated fatty
acids

Lipids are more suitable for long-term energy storage in humans than
carbohydrates

Evaluation of evidence and the methods used to obtain the evidence

for health claims made about lipids

Use of molecular visualization software to compare cellulose, starch,

and glycogen

Determination of body mass index by calculation or use of a

nomogram

2.4: Proteins

There are 20 different amino acids in polypeptides synthesized on

ribosomes

Amino acids are linked together by condensation to form polypeptides

Amino acids can be linked together in any sequence giving a huge

range of possible amino acids
The amino acid sequence of polypeptides is coded for by genes

A protein may consist of a single polypeptide, or more than one

polypeptide linked together

The amino acid sequence determines the three-dimensional

conformation of a protein

Living organisms synthesize many different proteins with a wide range

of functions

Every individual has a unique proteome

Rubisco, insulin, immunoglobulins, rhodopsin, collagen, and spider silk

as examples of the range of protein functions

Drawing molecular diagrams to show the formation of a peptide bond

Denaturation of proteins by heat or by deviation of pH from the

optimum

2.5: Enzymes

Enzymes have an active site to which specific substrates bind

Enzyme catalysis involves molecular motion and the collision of

substrates with the active site

Temperature, pH, and substrate concentration affect the rate of

activity of enzymes

Enzymes can be denatured

Immobilized enzymes are widely used in industry

Methods of production of lactose-free milk and its advantages

Design of experiments to test the effect of temperature, pH, and

substrate concentration on the activity of enzymes

Experimental investigation of a factor affecting enzyme activity

(Practical 3)

2.6: Structure of DNA & RNA

DNA differs from RNA in the number of strands present, the base
composition, and the type of pentose

The nucleic acids DNA and RNA are polymers of nucleotides

DNA is a double helix made of two antiparallel strands of nucleotides

linked by hydrogen bonding between complementary base pairs

Crick and Watson’s elucidation of the structure of DNA using model

making

Drawing simple diagrams of the structure of single nucleotides of DNA

and RNA, using circles, pentagons, and rectangles to represent
phosphates, pentoses and bases

2.7: Replication, transcription & translation

The replication of DNA is semi- conservative and depends on

complementary base pairing

Helicase unwinds the double helix and separates the two strands by
breaking hydrogen bonds

DNA polymerase links nucleotides together to form a new strand, using

the pre-existing strand as a template
The amino acid sequence of polypeptides is determined by mRNA
according to the genetic code

Translation is the synthesis of polypeptides on ribosomes

Transcription is the synthesis of mRNA copied from the DNA base

sequences by RNA polymerase

Codons of three bases on mRNA correspond to one amino acid in a

polypeptide

Translation depends on complementary base pairing between codons

on mRNA and anticodons on tRNA

Use of Taq DNA polymerase to produce multiple copies of DNA rapidly

by the polymerase chain reaction (PCR)

Production of human insulin in bacteria as an example of the

universality of the genetic code allowing gene transfer between
species

Use a table of the genetic code to deduce which codon corresponds to

(s)

which amino acid

2.8: Respiration

Cell respiration is the controlled release of energy from organic

compounds to produce ATP

ATP from cell respiration is immediately available as a source of energy

in the cell

Anaerobic cell respiration gives a small yield of ATP from glucose

Aerobic cell respiration requires oxygen and gives a large yield of ATP
from glucose
Use of anaerobic cell respiration in yeasts to produce ethanol and
carbon dioxide in baking

Analysis of results from experiments involving measurement of

respiration rates in germinating seeds or invertebrates using a
respirometer

Lactate production in humans when anaerobic respiration is used to

maximize the power of muscle contractions

2.9: Photosynthesis

Photosynthesis is the production of carbon compounds in cells using

light energy

Visible light has a range of wavelengths with violet the shortest

wavelength and red the longest

Chlorophyll absorbs red and blue light most effectively and reflects
green light more than other colours

Oxygen is produced in photosynthesis from the photolysis of water

Temperature, light intensity, and carbon dioxide concentration are

possible limiting factors on the rate of photosynthesis

Energy is needed to produce carbohydrates and other carbon

compounds from carbon dioxide

Changes to the Earth’s atmosphere, oceans, and rock deposition due

to photosynthesis

Drawing an absorption spectrum for chlorophyll and an action

spectrum for photosynthesis
Separation of photosynthetic pigments by chromatograph (Practical 4)

Design of experiments to investigate the effect of limiting factors on

photosynthesis
3 - Genetics

This section of the IB biology syllabus focuses on the genetic

information present within all living organisms. It covers genes,
chromosomes, meiosis, and inheritance as well as the fundamentals of
genetic modification mechanisms. It provides understanding necessary
for the later topics in the IB biology syllabus.
Subtopic
Understanding
Application

3.1: Genes

A gene is a heritable factor that consists of a length of DNA and

influences a specific characteristic

The various specific forms of a gene are alleles

A gene occupies a specific position on a chromosome

Alleles differ from each other by one or only a few bases

The genome is the whole of the genetic information of an organism

New alleles are formed by mutation.

The entire base sequence of human genes was sequenced in the

Human Genome Project

Comparison of the number of genes in humans with other species

The causes of sickle cell anaemia, including a base substitution
mutation, a change to the base sequence of mRNA transcribed from it
and a change to the sequence of a polypeptide in haemoglobin

Use of a database to determine differences in the base sequence of a

gene in two species

3.2: Chromosomes

Prokaryotes have one chromosome consisting of a circular DNA

molecule

Some prokaryotes also have plasmids, but eukaryotes do not

Eukaryote chromosomes are linear DNA molecules associated with

histone proteins

In a eukaryote species there are different chromosomes that carry

different genes

Diploid nuclei have pairs of homologous chromosomes

Homologous chromosomes carry the same sequence of genes but not

necessarily the same alleles of those genes

Haploid nuclei have one chromosome of each pair

The number of chromosomes is a characteristic feature of members of

a species

A karyogram shows the chromosomes of an organism in homologous

pairs of decreasing length

Sex is determined by sex chromosomes and autosomes are

chromosomes that do not determine sex
Cairns’ technique for measuring the length of DNA molecules by
autoradiography

Use of karyograms to deduce sex and diagnose Down syndrome in

humans

Comparison of genome size in T2 phage, Escherichia coli, Drosophila

melanogaster, Homo sapiens and Paris japonica

Comparison of diploid chromosome numbers of Homo sapiens, Pan

troglodytes, Canis familiaris, Oryza sativa, Parascaris equorum

Use of databases to identify the locus of a human gene and its

polypeptide product

3.3: Meiosis

One diploid nucleus divides by meiosis to produce four haploid nuclei

The halving of the chromosome number allows a sexual life cycle with
fusion of gametes

The early stages of meiosis involve pairing of homologous

chromosomes and crossing over followed by condensation

Orientation of pairs of homologous chromosomes prior to separation is

random

Crossing over and random orientation promotes genetic variation

Separation of pairs of homologous chromosomes in the first division of

meiosis halves the chromosome number

Fusion of gametes from different parents promotes genetic variation

DNA is replicated before meiosis so that all chromosomes consist of
two sister chromatids

Non-disjunction can cause Down syndrome and other chromosome

abnormalities

Studies showing age of parents influences chances of non- disjunction

Description of methods used to obtain cells for karyotype analysis e.g.,

chorionic villus sampling and amniocentesis and the associated risks

Drawing diagrams to show the stages of meiosis resulting in the

formation of four haploid cells

3.4: Inheritance

Mendel discovered the principles of inheritance with experiments in

which large numbers of pea plants were crossed

Gametes are haploid so contain only one allele of each gene

Fusion of gametes results in diploid zygotes with two alleles of each

gene that may be the same allele or different alleles

The two alleles of each gene separate into different haploid daughter
nuclei during meiosis

Dominant alleles mask the effects of recessive alleles, but co-dominant

alleles have joint effects

Many genetic diseases in humans are due to recessive alleles of

autosomal genes, although some genetic diseases are due to dominant
or co-dominant alleles
Some genetic diseases are sex-linked. The pattern of inheritance is
different with sex-linked genes due to their location on sex
chromosomes

Many genetic diseases have been identified in humans, but most are
very rare

Radiation and mutagenic chemicals increase the mutation rate and can
cause genetic diseases and cancer

Inheritance of ABO blood groups

Red-green colour blindness and haemophilia as examples of sex-

linked inheritance

Inheritance of cystic fibrosis and Huntington’s disease

Consequences of radiation after nuclear bombing of Hiroshima and

accident at Chernobyl

Construction of Punnett grids for predicting the outcomes of

monohybrid genetic crosses

Comparison of predicted and actual outcomes of genetic crosses using

real data

Analysis of pedigree charts to deduce the pattern of inheritance of

genetic diseases

3.5: Genetic modification & biotechnology

Gel electrophoresis is used to separate proteins or fragments of DNA

according to size

PCR can be used to amplify small amounts of DNA

DNA profiling involves comparison of DNA

Genetic modification is carried out by gene transfer between species

Clones are groups of genetically identical organisms, derived from a

single original parent cell

Animals can be cloned at the embryo stage by breaking up the embryo

into more than one group of cells

Many plant species and some animal species have natural methods of
cloning

Methods have been developed for cloning adult animals using

differentiated cells

Use of DNA profiling in paternity and forensic investigations

Gene transfer to bacteria using plasmids makes use of restriction

endonucleases and DNA ligase

Assessment of the potential risks and benefits associated with genetic

modification of crops

Design of an experiment to assess one factor affecting the rooting of

stem-cuttings

Production of cloned embryos produced by somatic-cell nuclear

transfer

Analysis of examples of DNA profiles

Analysis of data on risks to monarch butterflies of Bt crops

4 - Ecology
This section of the IB biology syllabus discusses the organisms and
their interaction with the natural environment that surrounds them. It
covers organism hierarchy, energy flow, carbon cycling, and climate
change. These terms are also used elsewhere in the IB biology
syllabus.
Subtopic
Understanding
Application

4.1: Species, communities, & ecosystems

Species are groups of organisms that can potentially interbreed to

produce fertile offspring

Members of a species may be reproductively isolated in separate

populations

Species have either an autotrophic or heterotrophic method of

nutrition (a few species have both methods)

Consumers are heterotrophs that feed on living organisms by ingestion

Detritivores are heterotrophs that obtain organic nutrients from

detritus by internal digestion

Saprotrophs are heterotrophs that obtain organic nutrients from dead

organisms by external digestion

A community is formed by populations of different species living

together and interacting with each other

A community forms an ecosystem by its interactions with the abiotic

environment

Autotrophs obtain inorganic nutrients from the abiotic environment

The supply of inorganic nutrients is maintained by nutrient cycling

Ecosystems have the potential to be sustainable over long periods of
time

Classifying species as autotrophs, consumers, detritivores, or

saprotrophs from a knowledge of their mode of nutrition

Setting up sealed mesocosms to try to establish sustainability

(Practical 5)

Recognizing and interpreting statistical significance

Testing for association between two species using the chi-squared test
with data obtained by quadrat sampling

4.2: Energy flow

Most ecosystems rely on a supply of energy from sunlight

Light energy is converted to chemical energy in carbon compounds by

photosynthesis

Chemical energy in carbon compounds flows through food chains by

means of feeding

Energy released from carbon compounds by respiration is used in

living organisms and converted to heat

Living organisms cannot convert heat to other forms of energy

Energy losses between trophic levels restrict the length of food chains
and the biomass of higher trophic levels

Heat is lost from ecosystems

Quantitative representations of energy flow using pyramids of energy

4.3: Carbon cycling

Autotrophs convert carbon dioxide into carbohydrates and other

carbon compounds

In aquatic ecosystems carbon is present as dissolved carbon dioxide

and hydrogen carbonate ions

Carbon dioxide diffuses from the atmosphere or water into autotrophs

Carbon dioxide is produced by respiration and diffuses out of

organisms into water or the atmosphere

Methane is produced from organic matter in anaerobic conditions by

methanogenic archaeans and some diffuses into the atmosphere or
accumulates in the ground

Methane is oxidized to carbon dioxide and water in the atmosphere

Peat forms when organic matter is not fully decomposed because of

acidic and/or anaerobic conditions in waterlogged soils

Partially decomposed organic matter from past geological eras was

converted either into coal or into oil and gas that accumulate in porous
rocks

Carbon dioxide is produced by the combustion of biomass and

fossilized organic matter

Animals such as reef-building corals and mollusca have hard parts that
are composed of calcium carbonate and can become fossilized in
limestone

Estimation of carbon fluxes due to processes in the carbon cycle

Construct a diagram of the carbon cycle

Analysis of data from air monitoring stations to explain annual

fluctuations

4.4: Climate change

Carbon dioxide and water vapour are the most significant greenhouse
gases

Other gases including methane and nitrogen oxides have less impact

The impact of a gas depends on its ability to absorb long wave

radiation as well as on its concentration in the atmosphere

Longer wave radiation is absorbed by greenhouse gases that retain the

heat in the atmosphere

The warmed Earth emits longer wavelength radiation (heat)

There is a correlation between rising atmospheric concentrations of

carbon dioxide since the start of the industrial revolution 200 years
ago and average global temperatures

Global temperatures and climate patterns are influenced by

concentrations of greenhouse gases

Recent increases in atmospheric carbon dioxide are largely due to

increases in the combustion of fossilized organic matter

Threats to coral reefs from increasing concentrations of dissolved

carbon dioxide

Correlations between global temperatures and carbon dioxide

concentrations on Earth
Evaluating claims that human activities are not causing climate change
5 - Evolution & Biodiversity

This section of the IB biology syllabus discusses the existence and

emergence of life on planet Earth. It covers evolutionary evidence,
natural selection, classification, and cladistics. This content is unique to
this topic of the IB biology syllabus.
Subtopic
Understanding
Application

5.1: Evidence for evolution

The fossil record provides evidence for evolution

Evolution occurs when heritable characteristics of a species change

Evolution of homologous structures by adaptive radiation explains

similarities in structure when there are differences in function

Selective breeding of domesticated animals shows that artificial

selection can cause evolution

Populations of a species can gradually diverge into separate species by

evolution

Continuous variation across the geographical range of related

populations matches the concept of gradual divergence

Development of melanistic insects in polluted areas

Comparison of the pentadactyl limb of mammals, birds, amphibians,

and reptiles with different methods of locomotion

5.2: Natural selection

Natural selection can only occur if there is variation among members

of the same species
Mutation, meiosis, and sexual reproduction cause variation between
individuals in a species

Species tend to produce more offspring than the environment can

support

Adaptations are characteristics that make an individual suited to its

environment and way of life

Individuals that are better adapted tend to survive and produce more
offspring while the less well adapted tend to die or produce fewer
offspring

Individuals that reproduce pass on characteristics to their offspring

Natural selection increases the frequency of characteristics that make

individuals better adapted and decreases the frequency of other
characteristics leading to changes within the species

Changes in beaks of finches on Daphne Major

Evolution of antibiotic resistance in bacteria

5.3: Classification of biodiversity

The binomial system of names for species is universal among biologists

and has been agreed and developed at a series of congresses

When species are discovered, they are given scientific names using the
binomial system

All organisms are classified into three domains

Taxonomists classify species using a hierarchy of taxa

The principal taxa for classifying eukaryotes are kingdom, phylum,
class, order, family, genus, and species

Taxonomists sometimes reclassify groups of species when new

evidence shows that a previous taxon contains species that have
evolved from different ancestral species

In a natural classification, the genus and accompanying higher taxa

consist of all the species that have evolved from one common
ancestral species

Natural classifications help in identification of species and allow the

prediction of characteristics shared by species within a group

Classification of one plant and one animal species from domain to

species level

Recognition features of bryophyta, filicinophyta, coniferophyta and

angiospermophyta

Recognition features of porifera, cnidaria, platylhelmintha, annelida,

mollusca, arthropoda and chordata

Recognition of features of birds, mammals, amphibians, reptiles, and

fish

Construction of dichotomous keys for use in identifying specimens

5.4: Cladistics

A clade is a group of organisms that have evolved from a common

ancestor

Evidence for which species are part of a clade can be obtained from
the base sequences of a gene or the corresponding amino acid
sequence of a protein
Sequence differences accumulate gradually so there is a positive
correlation between the number of differences between two species
and the time since they diverged from a common ancestor

Traits can be analogous or homologous

Evidence from cladistics has shown that classifications of some groups

based on structure did not correspond with the evolutionary origins of
a group or species

Cladograms are tree diagrams that show the most probable sequence
of divergence in clades

Reclassification of the figwort family using evidence from cladistics

Cladograms including humans and other primates

Analysis of cladograms to deduce evolutionary relationships

6 - Human Physiology

This section of the IB biology syllabus explores the physiological

processes occurring within humans. It covers digestion, circulation, the
immune response, gas exchange, neural transmission, homeostasis,
and reproduction. This content builds on the fundamentals established
by earlier topics of the IB biology syllabus.
Subtopic
Understanding
Application

6.1: Digestion and absorption

The contraction of circular and longitudinal muscle of the small

intestine mixes the food with enzymes and moves it along the gut

The pancreas secretes enzymes into the lumen of the small intestine
Enzymes digest most macromolecules in food into monomers in the
small intestine

Villi increase the surface area of epithelium over which absorption is

carried out

Villi absorb monomers formed by digestion as well as mineral ions and

vitamins

Different methods of membrane transport are required to absorb

different nutrients

Processes occurring in the small intestine that result in the digestion of

starch and transport of the products of digestion to the liver

Use of dialysis tubing to model absorption of digested food in the

intestine

Production of an annotated diagram of the digestive system

Identification of tissue layers in transverse sections of the small

intestine viewed with a microscope or in a micrograph

6.2: Circulation & blood

Arteries convey blood at high pressure from the ventricles to the

tissues of the body

Arteries have muscle cells and elastic fibres in their walls

The muscle and elastic fibres assist in maintaining blood pressure

between pump cycles

Blood flows through tissues in capillaries. Capillaries have permeable

walls that allow exchange of materials between cells in the tissue and
the blood in the capillary
Valves in veins and the heart ensure circulation of blood by preventing
backflow

Veins collect blood at low pressure from the tissues of the body and
return it to the atria of the heart

There is a separate circulation for the lungs

The heart beat is initiated by a group of specialized muscle cells in the

right atrium called the sinoatrial node

The sinoatrial node acts as a pacemaker

The sinoatrial node sends out an electrical signal that stimulates

contraction as it is propagated through the walls of the atria and then
the walls of the ventricles

Epinephrine increases the heart rate to prepare for vigorous physical

activity

The heart rate can be increased or decreased by impulses brought to

the heart through two nerves from the medulla of the brain

William Harvey’s discovery of the circulation of the blood with the

heart acting as the pump

Pressure changes in the left atrium, left ventricle, and aorta during the
cardiac cycle

Causes and consequences of occlusion of the coronary arteries

Recognition of the chambers and valves of the heart and the blood
vessels connected to it in dissected hearts or in diagrams of heart
structure
Identification of blood vessels as arteries, capillaries, or veins from the
structure of their walls

6.3: Defence against infectious disease

Cuts in the skin are sealed by blood clotting

The skin and mucous membranes form a primary defence against

pathogens that cause infectious disease

Clotting factors are released from platelets

The cascade results in the rapid conversion of fibrinogen to fibrin by

thrombin

Ingestion of pathogens by phagocytic white blood cells gives non-

specific immunity to diseases

Production of antibodies by lymphocytes in response to particular

pathogens gives specific immunity

Antibiotics block processes that occur in prokaryotic cells but not in

eukaryotic cells

Viruses lack a metabolism and cannot therefore be treated with

antibiotics. Some strains of bacteria have evolved with genes that
confer resistance to antibiotics and some strains of bacteria have
multiple resistance

Causes and consequences of blood clot formation in coronary arteries

Florey and Chain’s experiments to test penicillin on bacterial infections

in mice

Effects of HIV on the immune system and methods of transmission

6.4: Gas exchange

Ventilation maintains concentration gradients of oxygen and carbon

dioxide between air in alveoli and blood flowing in adjacent capillaries

Type I pneumocytes are extremely thin alveolar cells that are adapted
to carry out gas exchange

Type II pneumocytes secrete a solution containing surfactant that

creates a moist surface inside the alveoli to prevent the sides of the
alveolus adhering to each other by reducing surface tension

Air is carried to the lungs in the trachea and bronchi and then to the
alveoli in bronchioles

Muscle contractions cause the pressure changes inside the thorax that
force air in and out of the lungs to ventilate them

Different muscles are required for inspiration and expiration because

muscles only do work when they contract

Causes and consequences of lung cancer

Causes and consequences of emphysema

External and internal intercostal muscles, and diaphragm and

abdominal muscles as examples of antagonistic muscle action

Monitoring of ventilation in humans at rest and after mild and vigorous

exercise (Practical 6)

6.5: Neurones & synapses

Neurons transmit electrical impulses

Neurons pump sodium and potassium ions across their membranes to
generate a resting potential

The myelination of nerve fibres allows for saltatory conduction

An action potential consists of depolarization and repolarization of the

neuron

Nerve impulses are action potentials propagated along the axons of

neurons

Propagation of nerve impulses is the result of local currents that cause

each successive part of the axon to reach the threshold potential

Synapses are junctions between neurons and between neurons and

receptor or effector cells

When presynaptic neurons are depolarized they release a

neurotransmitter into the synapse

A nerve impulse is only initiated if the threshold potential is reached

Secretion and reabsorption of acetylcholine by neurons at synapses

Blocking of synaptic transmission at cholinergic synapses in insects by

binding of neonicotinoid pesticides to acetylcholine receptors

Analysis of oscilloscope traces showing resting potentials and action

potentials

6.6: Hormones, homeostasis & reproduction

Insulin and glucagon are secreted by β and α cells of the pancreas

respectively to control blood glucose concentration
Thyroxin is secreted by the thyroid gland to regulate the metabolic
rate and help control body temperature

Leptin is secreted by cells in adipose tissue and acts on the

hypothalamus of the brain to inhibit appetite

Melatonin is secreted by the pineal gland to control circadian rhythms

Testosterone causes pre-natal development of male genitalia and both

sperm production and development of male secondary sexual
characteristics during puberty

A gene on the Y chromosome causes embryonic gonads to develop as

testes and secrete testosterone

Estrogen and progesterone cause pre-natal development of female

reproductive organs and female secondary sexual characteristics
during puberty

The menstrual cycle is controlled by negative and positive feedback

mechanisms involving ovarian and pituitary hormones

Causes and treatment of Type I and Type II diabetes

Testing of leptin on patients with clinical obesity and reasons for the
failure to control the disease

The use in IVF of drugs to suspend the normal secretion of hormones,

followed by the use of artificial doses of hormones to induce
superovulation and establish a pregnancy

Causes of jet lag and use of melatonin to alleviate it

William Harvey’s investigation of sexual reproduction in deer

Annotate diagrams of the male and female reproductive system to
show names of structures and their functions
7 - Nucleic Acids

This section of the IB biology syllabus explores the processes of DNA

handling in great depth. It covers DNA replication, transcription, and
translation. It builds on the material included earlier in topic 2 of the IB
biology syllabus.
Subtopic
Understanding
Application

7.1: DNA structure & replication (HL)

Nucleosomes help to supercoil the DNA

DNA polymerases can only add nucleotides to the 3’ end of a primer

DNA replication is continuous on the leading strand and discontinuous

on the lagging strand

DNA replication is carried out by a complex system of enzymes

DNA structure suggested a mechanism for DNA replication

Some regions of DNA do not code for proteins but have other
important functions

Analysis of results of the Hershey and Chase experiment providing

evidence that DNA is the genetic material

Tandem repeats are used in DNA profiling

Use of nucleotides containing dideoxyribonucleic acid to stop DNA

replication in preparation of samples for base sequencing
Utilization of molecular visualization software to analyse the
association between protein and DNA within a nucleosome

Rosalind Franklin’s and Maurice Wilkins’ investigation of DNA structure

by X-ray diffraction

7.2: Transcription & gene expression (HL)

Transcription occurs in a 5’ to 3’ direction

Nucleosomes help to regulate transcription in eukaryotes

Eukaryotic cells modify mRNA after transcription

Splicing of mRNA increases the number of different proteins an

organism can produce

Gene expression is regulated by proteins that bind to specific base

sequences in DNA

The environment of a cell and of an organism has an impact on gene

expression

Analysis of changes in the DNA methylation patterns

The promoter as an example of non- coding DNA with a function

7.3: Translation (HL)

Initiation of translation involves assembly of the components that carry

out the process

Synthesis of the polypeptide involves a repeated cycle of events

Disassembly of the components follows termination of translation

Free ribosomes synthesize proteins for use primarily within the cell

Bound ribosomes synthesize proteins primarily for secretion or for use

in lysosomes

The sequence and number of amino acids in the polypeptide is the

primary structure

Translation can occur immediately after transcription in prokaryotes

due to the absence of a nuclear membrane

The secondary structure is the formation of alpha helices and beta

pleated sheets stabilized by hydrogen bonding

The tertiary structure is the further folding of the polypeptide stabilized

by interactions between R groups

The quaternary structure exists in proteins with more than one

polypeptide chain

tRNA-activating enzymes illustrate enzyme–substrate specificity and

the role of phosphorylation

The use of molecular visualization software to analyse the structure of

eukaryotic ribosomes and a tRNA molecule

Identification of polysomes in electron micrographs of prokaryotes and

eukaryotes
8 - Respiration & Photosynthesis

This section of the IB biology syllabus explores the two major

metabolic reactions that occur in living organisms. It covers
metabolism, respiration, and photosynthesis. It builds on the material
included earlier in topic 2 of the IB biology syllabus.
Subtopic
Understanding
Application

8.1: Metabolism (HL)

Metabolic pathways consist of chains and cycles of enzyme-catalysed

reactions

Enzymes lower the activation energy of the chemical reactions that

they catalyse

Enzyme inhibitors can be competitive or non-competitive

Metabolic pathways can be controlled by end-product inhibition

Use of databases to identify potential new anti-malarial drugs

End-product inhibition of the pathway that converts threonine to

isoleucine

Calculating and plotting rates of reaction from raw experimental

results

Distinguishing different types of inhibition from graphs at specified

substrate concentration

8.2: Further respiration (HL)

Light-dependent reactions take place in the intermembrane space of

the thylakoids

Light-independent reactions take place in the stroma

Reduced NADP and ATP are produced in the light-dependent reactions

Absorption of light by photosystems generates excited electrons

Photolysis of water generates electrons for use in the light-dependent
reactions

Excited electrons from Photosystem II are used to contribute to

generate a proton gradient

Transfer of excited electrons occurs between carriers in thylakoid

membranes

ATP synthase in thylakoids generates ATP using the proton gradient

Excited electrons from Photosystem I are used to reduce NADP

In the light-independent reactions a carboxylase catalyses the

carboxylation of ribulose bisphosphate

Glycerate 3-phosphate is reduced to triose phosphate using reduced

NADP and ATP

Triose phosphate is used to regenerate RuBP and produce

carbohydrates

The structure of the chloroplast is adapted to its function in

photosynthesis

Ribulose bisphosphate is reformed using ATP

Calvin’s experiment to elucidate the carboxylation of RuBP

Annotation of a diagram to indicate the adaptations of a chloroplast to

its function

8.3: Further photosynthesis (HL)

Cell respiration involves the oxidation and reduction of electron

carriers
Phosphorylation of molecules makes them less stable

In glycolysis, glucose is converted to pyruvate in the cytoplasm

Glycolysis gives a small net gain of ATP without the use of oxygen

In aerobic cell respiration pyruvate is decarboxylated and oxidized and

converted into acetyl compound and attached to coenzyme A to form
acetyl coenzyme A in the link reaction

In the Krebs cycle, the oxidation of acetyl groups is coupled to the

reduction of hydrogen carriers, liberating carbon dioxide

Energy released by oxidation reactions is carried to the cristae of the

mitochondria by reduced NAD and FAD

Transfer of electrons between carriers in the electron transport chain in

the membrane of the cristae is coupled to proton pumping

In chemiosmosis protons diffuse through ATP synthase to generate ATP

The structure of the mitochondrion is adapted to the function it

performs

Oxygen is needed to bind with the free protons to maintain the

hydrogen gradient, resulting in the formation of waterE

Electron tomography used to produce images of active mitochondria

Analysis of diagrams of the pathways of aerobic respiration to deduce

where decarboxylation and oxidation reactions occur

Annotation of a diagram of a mitochondrion to indicate the adaptations

to its function
9 - Plants

This section of the IB biology syllabus explores the structures,

functions, and processes of plants on earth. It covers plant transport,
growth, and reproduction. The material within this topic is not covered
elsewhere on the IB biology syllabus.
Subtopic
Understanding
Application

9.1: Transport in the Xylem (HL)

Transpiration is the inevitable consequence of gas exchange in the leaf

Plants transport water from the roots to the leaves to replace losses
from transpiration

The cohesive property of water and the structure of the xylem vessels
allow transport under tension

The adhesive property of water and evaporation generate tension

forces in leaf cell walls

Active uptake of mineral ions in the roots causes absorption of water

by osmosis

Adaptations of plants in deserts and in saline soils for water

conservation

Models of water transport in xylem using simple apparatus including

blotting or filter paper, porous pots, and capillary tubing

Drawing the structure of primary xylem vessels in sections of stems

based on microscope images

Measurement of transpiration rates using potometers (Practical 7)

Design of an experiment to test hypotheses about the effect of
temperature or humidity on transpiration rates

9.2: Transport in the Phloem (HL)

Plants transport organic compounds from sources to sinks

Incompressibility of water allows transport along hydrostatic pressure

gradients

Active transport is used to load organic compounds into phloem sieve

tubes at the source

Raised hydrostatic pressure causes the contents of the phloem to flow

towards sinks

High concentrations of solutes in the phloem at the source lead to

water uptake by osmosis

Structure–function relationships of phloem sieve tubes

Identification of xylem and phloem in microscope images of stem and

root

Analysis of data from experiments measuring phloem transport rates

using aphid stylets and radioactively labelled carbon dioxide

9.3: Growth in plants (HL)

Mitosis and cell division in the shoot apex provide cells needed for
extension of the stem and development of leaves

Undifferentiated cells in the meristems of plants allow indeterminate

growth

Plant hormones control growth in the shoot apex

Plant shoots respond to the environment by tropisms

Auxin efflux pumps can set up concentration gradients of auxin in plant

tissue

Auxin influences cell growth rates by changing the pattern of gene

expression

Micropropagation of plants using tissue from the shoot apex, nutrient

agar gels and growth hormones

Use of micropropagation for rapid bulking up of new varieties,

production of virus-free strains of existing varieties and propagation of
orchids and other rare species

9.4: Reproduction in plants (HL)

Flowering involves a change in gene expression in the shoot apex

The switch to flowering is a response to the length of light and dark

periods in many plants

Success in plant reproduction depends on pollination, fertilization, and

seed dispersal

Most flowering plants use mutualistic relationships with pollinators in

sexual reproduction

Methods used to induce short-day plants to flower out of season

Drawing internal structure of seeds

Drawing of half-views of animal-pollinated flowers

Design of experiments to test hypotheses about factors affecting
germination
10 - Genetics & Evolution

This section of the IB biology syllabus further details the processes

associated with the genetic code during reproduction. It covers
meiosis, inheritance, and speciation. It builds on the material included
earlier in topic 3 of the IB biology syllabus.
Subtopic
Understanding
Application

10.1: Further meiosis (HL)

Crossing over is the exchange of DNA material between non-sister

homologous chromatids

Chromosomes replicate in interphase before meiosis

Chiasmata formation between non-sister chromatids can result in an

exchange of alleles

Crossing over produces new combinations of alleles on the

chromosomes of the haploid cells

Homologous chromosomes separate in meiosis I

Sister chromatids separate in meiosis II

Independent assortment of genes is due to random orientation of pairs

of homologous chromosomes in meiosis I

Drawing diagrams to show chiasmata formed by crossing over

10.2: Further inheritance (HL)

Gene loci are said to be linked if on the same chromosome

Unlinked genes segregate independently as a result of meiosis

Variation can be discrete or continuous

The phenotypes of polygenic characteristics tend to show continuous

variation

Chi-squared tests are used to determine whether the difference

between an observed and expected frequency distribution is
statistically significant

Morgan’s discovery of non-Mendelian ratios in Drosophila

Completion and analysis of Punnett squares for dihybrid traits

Calculation of the predicted genotypic and phenotypic ratio of offspring

of dihybrid crosses involving unlinked autosomal genes

Polygenic traits such as human height may also be influenced by

environmental factors

Identification of recombinants in crosses involving two linked genes

Use of a chi-squared test on data from dihybrid crosses

10.3: Gene pools & speciation (HL)

A gene pool consists of all the genes and their different alleles, present
in an interbreeding population

Evolution requires that allele frequencies change with time in

populations

Speciation due to divergence of isolated populations can be gradual

Reproductive isolation of populations can be temporal, behavioural, or
geographic

Speciation can occur abruptly

Comparison of allele frequencies of geographically isolated populations

Identifying examples of directional, stabilizing, and disruptive selection

Speciation in the genus Allium by polyploidy

11 - Animal Physiology

This section of the IB biology syllabus spans the physiological

processes that occur in animals. It covers antibody production,
movement, kidney function, and sexual reproduction. It discusses
linked but unique themes to earlier topics in the IB biology syllabus.
Subtopic
Understanding
Application

11.1: Antibody production & vaccination (HL)

Every organism has unique molecules on the surface of its cells

Pathogens can be species-specific although others can cross species

barriers

B lymphocytes are activated by T lymphocytes in mammals

Activated B cells multiply to form clones of plasma cells and memory

cells

Plasma cells secrete antibodies

Antibodies aid the destruction of pathogens

Histamines cause allergic symptoms

White cells release histamine in response to allergens

Immunity depends upon the persistence of memory cells

Vaccines contain antigens that trigger immunity but do not cause the
disease

Fusion of a tumour cell with an antibody-producing plasma cell creates

a hybridoma cell

Monoclonal antibodies are produced by hybridoma cells

Smallpox was the first infectious disease of humans to have been

eradicated by vaccination

Antigens on the surface of red blood cells stimulate antibody

production in a person with a different blood group

Monoclonal antibodies to hCG are used in pregnancy test kits

Analysis of epidemiological data related to vaccination programmes

11.2: Movement & muscle contraction (HL)

Synovial joints allow certain movements but not others

Bones and exoskeletons provide anchorage for muscles and act as

levers

Movement of the body requires muscles to work in antagonistic pairs

Skeletal muscle fibres are multinucleate and contain specialized

endoplasmic reticulum
Muscle fibres contain many myofibrils

Each myofibril is made up of contractile sarcomeres

ATP hydrolysis and cross bridge formation are necessary for the
filaments to slide

The contraction of the skeletal muscle is achieved by the sliding of

actin and myosin filaments

Calcium ions and the proteins tropomyosin and troponin control muscle
contractions

Antagonistic pairs of muscles in an insect leg

Annotation of a diagram of the human elbow

Drawing labelled diagrams of the structure of a sarcomere

Analysis of electron micrographs to find the state of contraction of

muscle fibres

11.3: The Kidneys & osmoregulation (HL)

Animals are either osmoregulators or osmoconformers

The Malpighian tubule system in insects and the kidney carry out
osmoregulation and removal of nitrogenous wastes

The proximal convoluted tubule selectively reabsorbs useful

substances by active transport

The ultrastructure of the glomerulus and Bowman’s capsule facilitate

ultrafiltration
The composition of blood in the renal artery is different from that in the
renal vein

ADH controls reabsorption of water in the collecting duct

The loop of Henle maintains hypertonic conditions in the medulla

The length of the loop of Henle is positively correlated with the need
for water conservation in animals

The type of nitrogenous waste in animals is correlated with

evolutionary history and habitat

Consequences of dehydration and overhydration

Treatment of kidney failure by haemodialysis or kidney transplant

Blood cells, glucose, proteins, and drugs are detected in urinary tests

Drawing and labelling a diagram of the human kidney

Annotation of diagrams of the nephron

11.4: Sexual reproduction (HL)

Spermatogenesis and oogenesis both involve mitosis, cell growth, two

divisions of meiosis and differentiation

Processes in spermatogenesis and oogenesis result in different

numbers of gametes with different amounts of cytoplasm

Fertilization involves mechanisms that prevent polyspermy

Fertilization in animals can be internal or external

Implantation of the blastocyst in the endometrium is essential for the
continuation of pregnancy

HCG stimulates the ovary to secrete progesterone during early

pregnancy

The placenta facilitates the exchange of materials between the mother

and fetus

Estrogen and progesterone are secreted by the placenta once it has

formed

Birth is mediated by positive feedback involving estrogen and oxytocin

Annotation of diagrams of seminiferous tubule and ovary to show the

stages of gametogenesis

The average 38-week pregnancy in humans can be positioned on a

graph showing the correlation between animal size and the
development of the young at birth for other mammals

Annotation of diagrams of mature sperm and egg to indicate functions