You are currently viewing Comprehensive IB Biology SL & HL Syllabus

Comprehensive IB Biology SL & HL Syllabus

Chapter 1: Cell

Topic Number Subtopic Key points
1 1.1 Introduction to cells
  • Cell is the smallest collective functional unit a living organism can own.
  • Surface area to volume relativity ratio limits the size of the cell
1.2 Ultrastructure of cells
  • Two types of cells exist; prokaryotic and eukaryotic.
  • Cell wall: Prokaryotic cell wall is made up of peptidoglycan which is a carbohydrate-protein complex.
1.3 Membrane structure
  • The Cell membrane is a continuous and constituent structure of phospholipids and the embedded proteins.
  • Two distinctive areas of bilayer are termed as hydrophilic (water-loving) and hydrophobic (water-fearing)
  • Two types of cellular transport are found; passive and active transport
1.4 Cell division
  • A cell cycle describes the growth and division phase of the cells. It occurs mainly in 2 parts; Interphase and M phase (mitosis).
  • An uncontrolled division of cells causes a cluster of unwanted cells in an area called a tumour.


Chapter 2: Molecular Biology

Topic Number Subtopic Key points
2 2.1 Molecules to metabolism
  • There are four biochemical molecules; Carbohydrates, lipids, proteins and nucleic acids. These four molecules interact to carry out metabolism.
2.2 Water
  • Water is a covalently bonded structure involving one Oxygen and two Hydrogen atoms.
2.3 Carbohydrates and lipids
  • Carbohydrate is a kind of sugar. Monosaccharides (single sugar units) combined by condensation reactions to form disaccharides and polysaccharides.
  • When a hydrocarbon long chain has a carboxyl group at one end and a methyl group at the other, it is called saturated fatty acids.
2.4 Proteins
  • Amino acids are linked together by condensation to form polypeptides, by the process called translation.
2.5 Enzymes
  • Enzymes are solely proteins that act as catalysts in the metabolic reactions that occur inside the cells.
2.6 DNA replication, transcription and translation
  • DNA Replication occurs during the cell division in which the DNA content is doubled.
  • Transcription is the synthesis of mRNA copied from the DNA base sequences by RNA polymerase.
  • Translation is the synthesis of polypeptides on ribosomes.
2.7 Cell respiration
  • A variety of biochemical pathways that can be used to metabolize glucose in a cell is called cell respiration.
  • Yeast (single-celled fungus) is used when oxygen is not present.
2.8 Photosynthesis
  • The conversion of in the light energy into the chemical energy is called photosynthesis.


Chapter 3: Genetics

Topic Number Subtopic Key points
3 3.1 Genes
  • Genetics: The study of genes, variation and heredity.
  • Red blood cells changed their shape from biconcave to sickle-shaped. It reduces their oxygen carrying capacity and causes severe anaemia and therefore it is also known as sickle cell anaemia.
  • The complete set of organism’s base sequences of DNA is called its genome.
3.2 Chromosomes
  • The nucleoid region of prokaryotes like bacteria and archaea contains single, long, continuous, circular thread of DNA.
  • Some prokaryotes like Escherichia coli contains small circular loops of DNA called plasmids. 
3.3 Meiosis
  • Meiosis is a special type of cell division which reduces the chromosomal content of a cell into exactly half of the original after its division, also called reduction division.
  • Down’s syndrome is one of the disorders and caused by additional copy of chromosome number 21 i.e. when 21st chromosome fails to separate during Anaphase I, creating trisomy of 21st chromosomes in the offspring.
3.4 Inheritance
  • Concept of inheritance was first put forward by Gregor Mendel in 1865.
  • There are two kinds of genetic diseases in humans: Autosomal genetic and sex-linked. 
3.5 Genetic modification and biotechnology
  • Gene transfer is the technique of transferring a gene of interest from one organism (donor organism) to other organisms (host organism) to modify them in search of availing more benefits.


Chapter 4: Ecology

Topic Number Subtopic Key points
4 4.1 Species, communities and ecosystems
  • Habitat: A natural environment in which an organism live.
  • Ecosystem: Sum total of biotic and abiotic components of a particular geographical area being integrated through exchange of energy and nutrient cycling.
  • Decomposers are the organisms which help in breakdown of the organic waste material and dead animal and plant matter into inorganic useful material.
4.2 Energy flow
  • Every that position which is occupied by certain organism in the food chain is called it’s trophic level.
  • The interlinking of two or many food chains is called food web.
  • Autotrophs absorb the sunlight and take up inorganic nutrients from the soil to make organic food for the rest of the food chain.
4.3 Carbon Cycling
  • In the carbon cycle, the producers takes up the carbon in the form of CO2 and coverts it into and organic carbohydrate, glucose (C6H12O12 )
  • Methanogens (members of Archaea) produces methane (CH4) as a waste gas while metabolizing its food.
  • Peat is a dark coloured, waterlogged soil mixture of dead organic matter, found in wetlands.
4.4 Climate Change
  • Greenhouse effect refers to the ability of a planet to use its atmosphere to retain heat and warm even when no sunlight is hitting the surface.


Chapter 5: Evolution and Biodiversity

Topic Number Subtopic Key points
5 5.1  Evidence for evolution
  • Speciation: A process by which one or more species arise for previously existing species.
  • Evolution is defined the cumulative gradual or sudden change in the heritable characteristic of a population.
  • Adaptive Radiation refers development of different functional structures from a common ancestral form.
  • In asexual reproduction, the offspring is produced from a single parent and therefore there is a slight chance of variation to occur but in sexual reproduction two individual parents are involved and the gamete from each parentis united to form a zygote and therefore variation occurs.
5.2 Natural selection
  • Alfred Wallace and Charles Darwin support this idea as a mechanism of evolution in species over time.
  • The organism that is well adapted to its environment has better chances of survival than the one which is less adapted.
5.3 Classification of biodiversity
  • The system of naming and organism using two names always, is called binomial nomenclature.
  • All the organism exist or existed (with the exception of viruses because they are considered as non-living) are classified into three domains namely; Archaea domain, Eubacteria domain and Eukaryote domain.
5.4 Cladistics
  • Cladistics is an example of natural classification which classifies taxa together according to the characteristics that have evolved more recently.


Chapter 6: Human Physiology

Topic Number Subtopic Key points
6 6.1 Digestion and Absorption
  • Digestion is a series of events takes place for the breakdown of ingested food into smaller molecular forms, with the help of enzymes.
  • The Liver is the largest organ in the human body.
  • The Pancreas produces two hormones named insulin and glucagon which metabolise glucose and pancreatic juice which is constituent of enzymes; lipase (for digestion of lipids), amylase (for digestion of starch) and endopeptidase (for protein digestion).
6.2 The Blood System
  • The heart is a double pump organ which pumps blood to every organ in the body with the help of arteries and veins.
  • Cardiac cycle is occupied by the pressure changes in the chambers of the heart in order to supply and receive the blood.
6.3 Defence against infectious diseases
  • Primary defence: Pathogens are the most likely threat to humans and to prevent them from entering into our body primary defence comes into action.
  • Secondary defence: When the pathogens somehow pass through these primary physical barriers then it comes into action.
  • Antibodies are the Y-shaped protein molecules which help in fighting against the invading foreign cells.
6.4 Gas exchnage
  • The process of taking in the oxygen and giving off the CO2 is called cell respiration, which ultimately results in ATP formation.
  • Lungs move by surrounding muscles (external and internal intercostal muscles) and diaphragm.
6.5 Neurons and synapses
  • Neurons are the fundamental cells of the brain and nervous system, designed to transmit information in the form of electrical impulses to other nerve cells.
  • Action potential is the nerve impulse and consists of depolarization and repolarization.
6.6 Hormones, homeostasis and reproduction
  • Homeostasis is the tendency of human body to maintain a stable equilibrium of certain physiological variables like blood pH, body temperature, blood-glucose concentration, blood-CO2 concentration and osmotic balance within tissues.
  • Hormones are the non-nutrient chemical messengers which are produces in trace amounts.
  • Human Reproduction involves the fusion of male gamete (sperm) and female gamete (egg) to form a zygote.


Chapter 7: Nucleic Acids

Topic Number Subtopic Key points
7 7.1 DNA structure and replication


  • DNA was confirmed as the genetic material by Alfred Hershey and Martha Chase in 1952, in their experiment using radioisotopes
  • DNA is a double stranded structure, with each strand consists of alternating deoxyribose sugar and phosphate molecules as a backbone.
  • DNA Replication occurs during the cell division in which the DNA content is doubled.
  • Slicing is the post-transcription process for removal of non-coding sequence called introns from the pre-mRNA, so that only exons remain.
7.2 Transcription and gene expression


  • Transcription is the synthesis of mRNA copied from the DNA base sequences by RNA polymerase.
  • Two or more polypeptides bond together to perform a particular function, together they are considered as protein.
7.3 Translation


  • Translation is the synthesis of polypeptides on ribosomes.



Chapter 8: Metabolism, Cell respiration and photosynthesis

Topic Number Subtopic Key points
8 8.1 Metabolism (HL ONLY)
  • Metabolism is the sum of all the chemical reactions taking place inside a living organism, most of which are enzyme-mediated reactions.
  • The inhibition of an enzymatic activity occurs due to change in certain factors including pH, temperature and substrate concentration. The alteration in shape of active site or the occupying of a foreign molecule on active site may also cause inhibition.
8.2 Cell respiration (HL ONLY)
  • Cell respiration is a catabolic pathway.
  • Glycolysis: In this process of glucose breakdown, 4 molecules of ATP are generated and two are used in the process to conduct.
8.3 Photosynthesis (HL ONLY)
  • The conversion of the light energy into the chemical energy is called photosynthesis.
  • Types of photosystem; Photosystem I and Photosystem II.


Chapter 9: Plant Biology

Topic Number Subtopic Key points
9 9.1 Transport in the xylem and phloem of plants (HL ONLY)
  • Cohesion: It is the force of attraction between the molecules of the same substance like in water.
  • Adhesion: It is the force of attraction between the molecules of different substances.
  • Xylem is involved in supporting the plant and act as water conducting tissue of terrestrial plants.
  • Phloem is made of living cells and helps in transport of the organic molecules.
9.2 Growth in plants (HL ONLY)
  • Plants show indeterminate growth pattern i.e. they grow throughout their lifetime (with exceptions in some).
  • The growth of the plant in response to light is called phototropism.
9.3 Reproduction in plants (HL ONLY)
  • Flower bearing plants are called angiosperms. Flowers are the reproductive organs of the plants.
  • Flower bearing plants are called angiosperms. Flowers are the reproductive organs of the plants.
  • Pollination is the process by which pollen grains from the anther lands on the stigma of the same or another flower by means of wind, insects, water, birds etc.
  • Fertilization is the process of union of male and female sex cells to form a unit called zygote.


Chapter 10: Genetics and Evolution

Topic Number Subtopic Key points
10 10.1 Meiosis (HL ONLY)
  • Replication of chromosome and joining of two copies of chromosomes with each other by centromere.
10.2 Inheritance (HL ONLY)
  • Law of Segregation: It states that during the formation of the gametes the pair of alleles for a specific trait separates such that the offspring receive one allele from each parent. This law is one of the conclusions of dihybrid cross.
  • When two genes are found on the same chromosome i.e. really close to each other then they are called linked.
  • Two types: Continuous and discrete or discontinuous variation.
10.3 Gene pools and speciation (HL ONLY)
  • Gene pool can be defined as all the genetic information present in the reproducing members of a population at a given time.
  • Gradualism: The changes happen are small, continuous and occur at a very rate. This idea was adopted by Charles Darwin while purposing his ideas about natural selection.


Chapter 11: Animal Physiology

Topic Number Subtopic Key points
11 11.1 Antibody production and vaccination (HL ONLY)
  • Immune system recognizes any foreign cell through antigens.
  • Monoclonal antibodies are specific antibodies for only one type of antigens
11.2 Movement (HL ONLY)
  • Bones together make up a structure called skeleton, it can be made up of bones or chitin.
  • Muscles work antagonistically in pairs to contract and relax at the same time, causing movement of the bone.
  • Muscle is composed of thousands if cells called muscle fibre. They are multinucleated and have specialized endoplasmic reticulum.
11.3 The kidney and osmoregulation (HL ONLY)
  • The animals which are having different solute concentrations compares with that of environment are called osmoregulators.
11.4 Sexual reproduction (HL ONLY)
  • The process of formation of spermatozoa (sperm cells) is called spermatogenesis.
  • The process of formation of ovum is called oogenesis.
  • The fusion of male and female gamete is called fertilization.


Chapter 12: Biotechnology and Bioinformatics

Topic Number Subtopic Key points
12 12.1 Microbiology: organisms in industry
  • Microorganisms are small, have fast growth rate and metabolically diverse.
  • There are two types of fermentation; fed-batch and continuous fermentation.
  • It is a method of differentiating two groups of bacteria named; gram-negative and gram-positive bacteria. These two groups are different based on their structure of cell wall.
12.2 Biotechnology in agriculture
  • The technique of biotechnology makes it possible to have genetically modified crops (GM crops).
12.3 Bioremediation
  • Bioremediation is the process of using organisms, especially microorganisms to eradicate pollutants.
  • A biofilm is a film of aggregates of microorganism that sticks to the surface due to cooperation between individual cells.
  • Polymerase Chain Reaction is the most prominent tool in biotechnology to amplify any strand of DNA. Thereby found its place in detecting markers as well
  • Gene therapy – using viral vectors.
12.4 Biopharming
  • The idea of biopharming was that, if the edible vaccines could be produced (like vaccine in crop) then the antigens would be produced which could stimulate the release of antibiotics and thus provided immunity.
12.5 Bioinformatics
  • Bioinformatics is prominent in genomics. It uses information technology and computer to help us understand biological process.


Chapter 13: Neurobiology and behavior

Topic Number Subtopic Key points
13 13.1 Neurobiology
  • Neurobiology: The study of the complex information processing system that includes the brain and the nervous system is called neurobiology.
  • Embryogenesis: The study of process of development of embryo into a newborn.
  • The process of formation or synthesis of neuron by differentiation of the neuroblast cell is called neurogenesis.
  • When a person shows no movements of extremities like legs and arms, no eye movement, absence of corneal reflex, absence of pupil reflex, absence of gag reflex, no respiration then the person is considered to be brain dead.
13.3 The human eye
  • The human eye is a complex structure in the body that enables the vision in an organism.
13.4 Memory
  • Memory is the process of encoding the information, storing it and then accessing it while putting into use.
13.5  Psychoactive drugs
  • Psychoactive drugs affect the post-synaptic transmission and thereby alter the functioning of these synapses.
  • Anaesthetics are the molecules that can block the sensory reception and causes loss of sensation in any part or the whole body.
  • The study of animal behaviour in natural conditions is called ethology.


Chapter 14: Ecology and Conservation

Topic Number Subtopic Key points
14 14.1 Species and Communities
  • The group of organisms living in a habitat, comprising related features and are capable of interbreeding belongs is called species.
  • Abiotic and biotic factors sometimes act as limiting factors which results in distribution of the species according to their tolerance of limiting factors.
  • All the parameters in which an organism lives, including its habitat, its feeding, its interaction with other organisms is called its niche.
  • Parasitism: In this interaction, one organism is host and the other is a parasite that lives in or on the body of the host.
  • Mutualism: In this relationship, two species live in a close association and both of them benefit each other.
  • Commensalism: In this interaction, one organism benefits from the other which is neither harmed nor benefitted in any way.
14.2 Communities and ecosystems
  • Pyramids of energy show the available energy at each trophic level.
  • The process of inhabiting living organism with their abiotic factors in an area is called succession.
14.3 Biomagnification
  • Any introduced species by humans in an area of endemic species (native species) is called alien species.
  • Biomagnification is the process of accumulation of chemical substances in higher trophic levels
  • Two kinds of plastics found in the ocean that are considered extremely harmful for marine populations; Microscopic plastic and macroscopic plastic.
14.4 Biodiversity
  • Biodiversity – It is defined as the degree of variation of life forms in an ecosystem. It can be described by its two components; richness (number of different species present) and evenness (the closeness or relatedness of the species with each other).
14.5 Population
  • Population of a certain area depends on the four factors: Natality, mortality, Immigration, Emigration.
  • When a habitat has limited supply of resources then S-shaped (sigmoid) curve graph in shown by the population. It is also called logistic growth curve.
14.6 Nitrogen and phosphorus cycles
  • It is mainly regulated by certain bacteria in the following ways:
  • Nitrogen fixing bacteria fixes atmospheric nitrogen. Ex – Rhizobium (symbiotic) and Azotobacter (free living).
  • Another type of bacteria performs nitrification in which ammonia is converted into nitrites. Ex – Nitrosomonas.


Chapter 15: Human Physiology

Topic Number Subtopic Key points
15 15.1 Human Nutrition
  • If the necessary nutrients are synthesised in our bodies by metabolism, then they are called non-essential nutrients and if some nutrients are not getting synthesised in the body but need to be taken as a part of our diet, those are called essential nutrients.
  • Malnutrition is the result of intake of unbalanced or improper diet.
15.2 Digestion
  • Secretions through exocrine glands are necessary for digestion.
  • There are three glandular secretions; HCl, pepsin and mucus which are produced by three glandular cells present in the gastric pits.
  • Absorption of the digested food occurs in small intestine lined by villi.
15.3 Functions of the liver
  • Two major blood vessels; hepatic portal vein and hepatic artery, flow blood in the liver which exits by only one (hepatic vein).
  • Hepatocytes extract toxin from blood plasma, modifies them to weaker molecules and make them water soluble so that they can be eliminated by kidney.
15.4 The heart
  • Heart is wholly made up of muscles known as cardiac muscles.
  • When the heart stopped working (cardiac arrest) or is no longer in sequence with the set of electrical impulse of a cardiac cycle (arrhythmia), defibrillators could be used.
15.5 Hormones and metabolism
  • Endocrine system: the hormones are secreted directly into the bloodstream which is accepted by the receptor molecules of the target cells
15.6 Transport of respiratory gases
  • Each haemoglobin molecule inside the each erythrocyte cell can occupy four oxygen molecules at most and one CO2 molecule.
  • Bohr Shift: It is observed when the partial pressure of CO2 (pCO2) increased above the pO2. In this condition the haemoglobin release oxygen molecules for cell respiration and thus a shift is observed in the curves.
  • Ventilation rate is controlled by respiratory centre in medulla oblongata.

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