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Comprehensive IB Biology SL & HL Syllabus

Comprehensive IB Biology SL & HL Syllabus

Unit 1: Cell


In this comprehensive IB Biology syllabus Unit 1, we’ll explore the characteristics of living things and why cells are so important. We’ll look at the differences between prokaryotic and eukaryotic cells, how they’re built, and what they do. Additionally, we’ll explore cell membranes and how things move in and out of cells.

Subtopic Subtopic Number IB Points to Understand
Introduction to cell 1.1 Cell is the smallest collective functional unit a living organism can own.

Surface area to volume relativity ratio limits the size of the cell – More the surface area, more will be the movement of the materials in/out of the cell.

Specific genes are involved in the production of certain types of cells, with each cell having the complete genetic information of the organism.

Stem cells are the origin cells, from where the cell division starts and also they retain their ability to differentiate into various cell types. Different types of stem cells

Ultrastructure of cells 1.2 Two types of cells exist; prokaryotic and eukaryotic.

Structural parts of a prokaryotic:

  • Cell wall and plasma membrane
  • Pili and Flagella
  • Ribosomes
  • Nucleoid Region

 and eukaryotic cells:

  • Cell wall
  • Cytoplasm
  • Ribosomes
  • Endoplasmic Reticulum
  • Golgi Apparatus
  • Lysosomes
  • Mitochondria
  • Nucleus
  • Chloroplasts
  • Centrosomes
  • Vacuoles

Eukaryotic cells in animals and plants

Membrane Structure 1.3 Phospholipid is made up of glycerol (3-C compound), which further includes fatty acids and alcohol group with phosphate.

Cholesterol molecules are not present in the plant cells but in animal cells.

Two distinctive areas of Phospholipid bilayers are termed as hydrophilic (water-loving) and hydrophobic (water-fearing)

Membrane Transport 1.4 Active membrane transport: This transportation of molecules or substances requires energy which is provided in the form of ATP, because movement in this is against the concentration gradient.

  • Sodium-potassium pump

Passive membrane transport: Does not require energy

  • Diffusion – Movement of substance occurs from an area of higher concentration
    to lower concentration across a membrane
  • Facilitated diffusion – Involves the membrane bound proteins to aid movement of substance across the membrane. The protein acts as a “carrier protein”
  • Osmosis It involves the movement across the partially permeable membrane due to concentration gradient

Endocytosis and exocytosis: Endocytosis allows the molecules to enter the cell while exocytosis allows them to leave the cell. Fluidity (provided by bilayer structure) of the membrane is essential for these processes.

The origin of cells 1.5 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.

Cell division 1.6 ​​A cell cycle describes the growth and division phase of the cells. It occurs mainly in 2 parts; Interphase & M phase

Mitosis is the division of the nucleus into two genetically identical daughter nuclei.

The division of cytoplasm into two daughter cytoplasmic cells is called cytokinesis.

Cyclins mediate the cell cycle by binding to cyclin-dependent protein kinases (CDKs). Cyclins are involved in the control of the cell cycle.

  • Interphase
  • Mitosis
  • Prophase
  • Metaphase
  • Anaphase
  • TeloPhase
  • Cytokinesis

An uncontrolled division of cells causes a cluster of unwanted cells in an area called tumour. Two types are found; primary tumour and secondary tumour.

Mutagens, oncogenes and metastasis are involved in the development of primary and secondary tumours.

Unit 2: Molecular Biology

Molecular Biology

In Unit 2 of IB Biology, you’ll get to study Molecular Biology, covering areas like how molecules are involved in metabolism, the characteristics of water, carbohydrates and lipids, proteins, enzymes, the structures of DNA and RNA, and the four most commonly found elements in living organisms.

Subtopic Subtopic Number IB Points to Understand
Molecules to metabolism 2.1 There are four biochemical molecules; Carbohydrates, lipids, proteins and nucleic acids. These four molecules interact to carry out metabolism.

Metabolism: Inside a cell, in an aqueous medium many molecular collisions occur, these collisions provide energy for the reactants to undergo chemical reactions.

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.

Water 2.2 Water is a covalently bonded structure involving one Oxygen and two Hydrogen atoms.

Properties: Cohesive, adhesive, thermal, solvent, and  high boiling point

Water works on the principle “like dissolves like” and dissolves only polar solutes, being polar molecules. These polar solutes are called hydrophilic.

Hydrophobic (water-fearing) solutes like methane (CH4) do not dissolve in the water because they are non-polar.

Carbohydrates and Lipids 2.3 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.

If one double bond exists in the chain of hydrocarbons, the fatty acid is then called monounsaturated fatty acids.

When two or more double bonds are present, then it is called polyunsaturated fatty acids.

Lipids get hydrolysed into two carbon segments which ultimately fulfil the energy requirements by the production of ATP through cellular respiration.

Proteins 2.4 Amino acids are linked together by condensation to form polypeptides, by the process called translation.

There are 20 different types of amino acids out of which 16 are polar and 4 are non-polar

Ribosomes link these amino acids together and form polypeptides which can be of huge numbers.

Two or more polypeptides bond together to perform a particular function, together they are considered as protein.

Structure of proteins goes from the simple primary to the globular quaternary.

Examples of proteins: Insulin, Collagen, Rubisco, Haemoglobin, etc

Enzymes 2.5 Enzymes are solely proteins that act as catalysts in the metabolic reactions that occur inside the cells.

They have an active site on which the substrate binds. Substrates and their active sites are specific for each other.

Factors affecting enzymatic reactions:

  • Temperature
  • pH
  • Substrate concentration

Immobilised enzyme: These enzymes are trapped in tiny pores on beads of calcium alginate.

Immobilised enzymes are used for the production of lactose-free milk.

Structure of RNA and DNA 2.6 Three types of nucleic acids are found in nature namely; adenosine triphosphate (ATP), deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).

DNA contains deoxyribose pentose sugar while RNA contains Ribose pentose sugar.

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

DNA replication, transcription and translation 2.7 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 Process of synthesis of polypeptide with the help of cell organelle, ribosome.

  • Three types of RNA are used in this process namely;
      mRNa: Has genetic information for the formation of polypeptide
      rRNA: Makes up the ribosomal protein and support the formation of polypeptides
      tRNA: It has an anticodon loop that has bases complementary to the code. These are specific for each amino acid.
Cell Respiration 2.8 A variety of biochemical pathways that can be used to metabolise glucose in a cell is called cell respiration.

Glycolysis is the method of slow oxidation of the glucose using various enzymes.

Fermentation is of two types; alcoholic fermentation and lactic acid fermentation

Aerobic pathway of cell respiration: It involves complete oxidation of glucose into water + CO2 + ATPs.

Photosynthesis 2.9 The conversion of the light energy into chemical energy is called photosynthesis.

In the leaves of the plants, there is a presence of green colour organelle called chloroplast which contains the light absorbing pigment chlorophyll in it

Photosynthesis gives off the oxygen and in the cellular respiration oxygen is taken in.

Photosynthetic rate is affected by many external factors like light, temperature and CO2 concentrations. These are also called the limiting factors of the photosynthesis

Unit 3: Genetics


In this IB Biology Guide you’ll find out , Genetics involves the fundamental units of heredity, genes, which are composed of specific sequences of DNA bases carrying instructions for protein synthesis. Human DNA comprises roughly three billion bases, with over 99 percent being identical across all individuals. The Human Genome Project estimates humans possess between 20,000 and 25,000 genes, each person inheriting two copies, one from each parent.

Subtopic Subtopic Number IB Points to Understand
Genes 3.1 Gene: A heritable factor that consists of a DNA sequence and influences a specific character or trait in an individual.

Alleles: These are the versions or a form of gene, differs with only one or few bases.

Mutation: It is a sudden random change in the genetic material.

The complete set of an organism’s base sequences of DNA is called its genome.

The Human Genome Project was begun in 1990, with the aim to find all the base sequences of the human genome.

Chromosomes 3.2 The nucleoid region of prokaryotes like bacteria and archaea contains a single, long, continuous, circular thread of DNA.

When the cell is not dividing, the chromosomes (condensed form) are not visible, but the chromatin is there in the nucleus.

Two chromosomes with the same kind of genes like in 23 pairs of human cell chromosomes.

Ploidy is the number of sets of chromosomes that exist in a cell:

  1. Haploid (n); having only one set of chromosomes
  2. Diploid (2n); having two sets of chromosomes
  3. Triploid (3n); having three sets of chromosomes

Karyotype is the picture of the chromosome of an individual and karyogram is the standard representation of the chromosomes in the order, according to shapes and sizes.

The 23rd pair of chromosome is sex chromosome, as it determines the sex of the individual.

Meiosis 3.3 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.

Meiosis I and II

Down’s syndrome is one of the disorders and caused by an additional copy of chromosome number 21 i.e. when the 21st chromosome fails to separate during Anaphase I, creating trisomy of 21st chromosomes in the offspring.

Inheritance 3.4 Concept of inheritance was first put forward by Gregor Mendel in 1865.

Gametes receive one of the two alleles of a specific gene. And this allele could be dominant or recessive with respect to the other allele.

  • Dominant alleles: These alleles always express themselves in the phenotype over the other.
  • Recessive alleles: These are the alleles which get masked by the dominant allele i.e. can’t express themselves in the presence of dominant allele.

There are two kinds of genetic diseases in humans:

  • Autosomal genetic: The disease caused by alteration in genetic material of autosomal cells rather than sex cells
  • Sex-linked: The disease caused by alteration in an allele found on either of the sex chromosomes X or Y
Genetic modification and biotechnology 3.5 Gel Electrophoresis: This technique is used to separate DNA fragments (chopped out of long DNA strands by the action of enzymes), according to their sizes.

Polymerase chain reaction: This technique is used to amplify the gene of interest obtained from gel electrophoresis, using a thermocycler.

DNA Profiling: This is the process for matching an unknown sample of DNA with a known sample to see if they correspond.

The technique of transferring a gene of interest from one organism (donor organism) to other organism (host organism) to modify them in search of availing more benefits, also called as recombinant DNA technology.

Clones: These are the exact copy of the individuals already exist, made by using genetic techniques

Genetically Modified Organisms (GMOs) are called transgenic plants or transgenic animals

Unit 4: Ecology


Ecology explores the interactions between organisms and their surroundings, encompassing the distribution and abundance of organisms, energy flow, and nutrient cycling.

Subtopic Subtopic Number IB Points to Understand
Species, communities and ecosystems 4.1 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.

Species: It is a group of organisms that can interbreed and produce fertile offspring

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.

Energy flow 4.2 Every position which is occupied by certain organisms in the food chain is called its 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.

This loss of the energy is in the form of heat which can’t be used ever again but then contributes to global warming.

Carbon Cycling 4.3 In the carbon cycle, the producers takes up the carbon in the form of CO2 and converts it into and organic carbohydrate, glucose

Methanogens (members of Archaea) produce methane (CH4) as a waste gas while metabolizing its food.

Methane is found in natural gas and its oxidation produces CO2

Peat is a dark coloured, waterlogged soil mixture of dead organic matter, found in wetlands.

Limestone: Many organisms in the oceans takes up the dissolved CO2 from the water and form their carbonated shells and coral polyps takes up the carbonate ions and calcium which combines to form calcium carbonate

Climate Change 4.4 Greenhouse effect refers to the ability of a planet to use its atmosphere to retain heat and warmth even when no sunlight is hitting the surface.

Greenhouse gases (GHGs) include water vapour, CO2, CH4, nitrous oxide (NO2) etc
Light-colored objects absorb much less of the sunlight and reflect it back but dark coloured objects absorb much of the sunlight and get more warmer than light coloured objects.

Unit 5: Evolution and Biodiversity

Evolution and Biodiversity

Evolution, the process of life’s transformation over generations, leads to the incredible diversity of organisms present today. Biodiversity encompasses the variety of life on Earth, including species diversity, genetic diversity, and ecosystem diversity.

Subtopic Subtopic Number IB Points to Understand
Evidence for evolution 5.1 Evolution: It is defined as the cumulative gradual or sudden change in the heritable characteristic of a population.

Fossils are the petrified remains or traces of animals and plants and the accumulated evidence from these remains are called fossil record.

Adaptive Radiation refers to the development of different functional structures from a common ancestral form.

Animal Breeding: The breeding of animals and plants is done artificially by selecting the best individual with the desired traits and crossing them to get the product with the desired trait.

Homologous structures: The structures which are anatomically the same but perform different functions and focus on common ancestors.

Adaptive radiation: It refers to the development of different functional structures from a common ancestral form.

Natural Selection 5.2 Alfred Wallace and Charles Darwin support this idea as a mechanism of evolution in species over time.

Sudden drastic change in the DNA sequence due to external or internal factors which produces variation in an organism is called mutation.

Meiosis: Random orientation of the chromosomes at metaphase offers variation every time the gamete forms.

The organism that is well adapted to its environment has better chances of survival than the one which is less adapted.

Classification of biodiversity 5.3 The system of naming an organism using two names is called binomial nomenclature.

All the organisms that 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.

Further classification occurs by classification of the organism into seven different taxa: Kingdom, Phylum, Class, Order, Family, Genus and Species

Plant and Animal Phyla

Vertebrates are classified into class: Fish, Amphibians, Reptiles, Birds and Mammals

Cladistics 5.4 Cladistics is an example of natural classification which classifies taxa together according to the characteristics that have evolved more recently. And a clade is the group of organisms that have evolved from the common ancestor.

Two types of traits: Plesiomorphic and Apomorphic traits

Mutations in organisms occur roughly at the same rate and therefore the number of differences in sequence can be used to deduce how long ago species split from a common ancestor. This is how it works as an evolutionary or molecular clock.

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

Unit 6: Human Physiology

Human Physiology

Human physiology investigates the functioning of the human body, including its systems and processes that maintain balance (homeostasis) and support survival.

Subtopic Subtopic Number IB Points to Understand
Digestion and Absorption 6.1 Digestion: It is a series of events takes place for the breakdown of ingested food into smaller molecular forms, with the help of enzymes

Pancreas: It is a Multipurpose organ which produces two hormones named insulin and glucagon which metabolise glucose and pancreatic juice.

Liver: It is the largest organ in the human body. The hepatic lobules are the structural and functional units of liver, from where bile juice is secreted into the small intestine for digestion purposes.

Small Intestine: It is a four-layered tubular structure with the lumen and villi (facing lumen) on the innermost layer mucosa.

Each villus contains a capillary bed for absorbing and transport of digested monomers.

The blood system 6.2 Arteries: These are the blood vessels that take blood away from the heart to supply the different organs of the body.

Veins: These blood vessels take blood from different organs of the body towards the heart.

Capillaries are single-celled thick therefore the blood cells enter the capillaries at the rate of one cell at a time.

Right side of the heart offers pulmonary circulation and the left side of the heart offers systemic circulation.

A specialized tissue called sinoatrial node (SA node) is present in the right atrium, it is also known as pacemaker. SA node has the properties of both muscles and nervous system.

Atrial systole: The sinoatrial node generates the signals and both the atria go into contraction

Ventricular systole: The atria relaxes (atrial diastole) but the ventricles now contract

The lub and dub sound (heart beat), the heart makes comes from the closure of the atrioventricular valves and the semilunar valves respectively.

Defence against infectious disease 6.3 Pathogens are the most likely threat to humans and to prevent them from entering into our body primary defence comes into action.

Skin and mucous membranes offers the major primary defence towards the

Secondary defence: When the pathogens somehow pass through these primary physical barriers then it comes into action.

Leucocytes (WBC) are the cells that tackles pathogens provides immunity against them

Antibodies are the Y-shaped protein molecules which help in fighting against the invading foreign cells

Antibiotics: It disfigures the biochemistry of the bacterial cell wall and deactivates them in such a way to stop their metabolism in many ways without harming the human eukaryotic cells which lack a cell wall.

Gas Exchange 6.4 The process of taking in the oxygen and giving off the CO2 is called cell respiration

The filling and expiration of the air in and from the lungs is called ventilation.

Inspiration: While breathing in diaphragm contracts, external intercostal muscles with abdominal muscle raise the rib cage to increase the volume of thorax.

Journey of air: Trachea → Left and right primary bronchi → smaller branches of bronchi → bronchioles → alveoli.

Type I pneumocytes: Thin, large membrane surface area, capable of diffusion and if damaged cannot be replaced due to incapability of performing mitosis.

Type II pneumocytes: Thick, cuboidal, have smaller membrane surface area. They produce surfactants which prevents alveolus membrane from sticking together.

Neurons and Synapses 6.5 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.

The highly developed nervous system has neurons with myelin sheath around axons, called myelinated neurons. And other kind does not have myelin sheath around axons and are called non-myelinated neuron

When a voltage or potential difference is maintained across the membrane and the neuron is not transmitting any impulse then it is called resting potential of that neuron.

Action potential is the nerve impulse and consists of depolarization and repolarization.

Repolarization: It is the change from positive to negative by opening of the potassium ions and closing of the sodium ions at the same time.

Hormones, Homeostasis and reproduction 6.6 Homeostasis: It is the tendency of the 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 produced in trace amounts.

Thyroxin: Produced and secreted by butterfly-shaped thyroid gland.

Leptin (appetite-controlling hormone): Produced by adipose tissue in the body. More fat, the more the secretion of leptin into the blood.

Melatonin: Produced by pineal gland present in the brain and helps to maintain the 24-hour cycle of activity called the circadian rhythm.

Insulin and Glucagon: Produced and secreted by pancreas and regulates blood sugar levels.

Human Reproduction: It involves the fusion of male gamete (sperm) and female gamete (egg) to form a zygote

Sex determination: Male has XY pair and female has XX pair of chromosome.

Menstrual Cycle: It is the hormonal cycle that begins after hitting puberty in human females. Each cycle lasts for approximately 28 days however, it differs from person to person.

  • Hormones involved:
      FSH and LH: They increase the production of estrogen
      Progesterone: After ovulation, corpus luteum secretes progesterone which helps in thickening of the endometrium.
      Oestrogen: The oestrogen is released as to provide a negative feedback by signalling hypothalamus to stop secretion of GnRH

In vitro fertilisation: It is a method of artificial reproduction in which egg and sperm are fertilised in vitro

Unit 7: Nucleic Acids

Nucleic Acids

Nucleic acids like DNA and RNA store and transmit genetic information. DNA is composed of four chemical bases—adenine (A), cytosine (C), guanine (G), and thymine (T)—arranged in specific sequences, analogous to letters forming words, sentences, and paragraphs.

Subtopic Subtopic Number IB Points to Understand
DNA structure and replication 7.1 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 consisting of alternating deoxyribose sugar and phosphate molecules as a backbone.

There are 4 nitrogenous bases: Adenine and Guanine (Purines) and Cytosine and Thymine (Pyrimidines)

The negatively charged DNA wrapped around the positively charged histones to make a bead-like structure called the nucleosome.

DNA Replication: This process occurs during the cell division in which the DNA content is doubled. This is also an enzyme catalysed process involves helicase and DNA polymerase

Transcription and gene expression 7.2 One of the two major sets of reactions leading to protein synthesis, other is translation.

Genes are present on the DNA inside the nucleus and the protein synthesis occurs outside the nucleus in the cytoplasm. Therefore the mRNA (messenger RNA) acts as the intermediary molecule to transfer the information for protein synthesis from nucleoplasm to cytoplasm.

The strand which has the same base sequence as that of mRNA (while having uracil in the place of thymine) is called sense strand. And the other template which has a complementary base sequence is called antisense DNA strand.

Slicing: This is post-transcription process for removal of non-coding sequence called introns
from the pre-mRNA, so that only exons remain.

Methylation of any gene expression could prevent transcription

Translation 7.3 Translation: Process of synthesis of polypeptide with the help of cell organelle, ribosome.

Process: Initiation, Elongation, Translocation and then repeats

Two or more polypeptides bond together to perform a particular function, together they are considered as protein.

All the organisms are found to be genetically different due to specific DNA sequences called the genome and so their proteome.

Structure of proteins goes from the simple primary to the globular quaternary. It possesses a three-dimensional shape (specific shape for the particular function).

Unit 8: Metabolism, Cell respiration and photosynthesis

Metabolism, Cell respiration and photosynthesis

Metabolism encompasses the chemical reactions occurring in living organisms to sustain life, including cell respiration and photosynthesis.

Subtopic Subtopic Number IB Points to Understand
Metabolism 8.1
  • Metabolism is the sum of all the chemical reactions taking place inside a living organism, most of which are enzyme-mediated reactions.
  • Catabolism and Anabolism
  • Enzymes lower the activation energy of the reaction, without altering the reactant or product proportions.
  • The inhibition of an enzymatic activity occurs due to change in certain factors including pH, temperature and substrate concentration. Types: Competitive and Non-competitive
  • End product inhibition: Many metabolic reactions occur in an assembly-line type of process with each step catalysed by an enzyme to achieve the end product.
Cell Respiration 8.2 Cell respiration is a catabolic pathway.

The reduced molecule has much more potential energy than the oxidised form of molecule, therefore the energy is released when the glucose gets oxidised.

Glycolysis is the method of slow oxidation of the glucose using various enzymes

If no oxygen is available, the pyruvate molecules enter the anaerobic pathway followed by fermentation.

There is a direct transfer of a phosphate group from a phosphate bearing molecule (phosphoenolpyruvate) to ADP in order to make ATP. The process is called substrate-level phosphorylation.

Krebs cycle

Electron Transport Chain – It is the series of protein complexes called cytochromes and organic molecules to pass on the electrons from one member of the chain to another in a series of redox reactions.

The coenzymes NADH and FADH2 released in previous cycles act as the sources of electrons. NADH allows the production of three ATPs and FADH2 allows the production of 2 ATP molecules.

Chemiosmosis is the process in which movement of protons occurs to provide energy for phosphorylation.

An enzyme called ATP synthase is embedded in the inner membranes of the mitochondria which facilitates ions across.

Photosynthesis 8.3 The conversion of the light energy into chemical energy is called photosynthesis.

Light Dependent reactions:

  • It is a non-cyclic reaction that occurs in thylakoids and the stack of thylakoids is called granum.
  • Presence of pigments like chlorophyll, xanthophyll and carotenoids
  • The organized structure of these pigments in the thylakoid membrane is called a photosystem.
  • Photosystem contains even more complex structures within which is the reaction centre.
  • Photosystem I and Photosystem II

Light Independent reactions:

  • It happens at night and occurs in the stroma of the chloroplast.

18 molecules of ATP and 12 molecules of NADPH are necessary to produce one molecule of glucose.

Unit 9: Plant Biology

Plant Biology

Plant biology concentrates on the study of plants, including their structure, growth, reproduction, and adaptation to their environment.

Subtopic Subtopic Number IB Points to Understand
Transport in the xylem of the plants 9.1 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: It is involved in supporting the plant and act as water conducting tissue of terrestrial plants.

Stomatal Activity: Stomatal pores open and close by change in the turgor pressure in the guard cells

Cohesion-tension theory: This theory explains the movement of fluid in plants. It takes into account the concentration gradients, cohesion between the water molecules, adhesion between the water molecules and walls of the xylem and tension created by all these phenomena.

Roots absorb water and mineral ions necessary for plant growth which can be done passively, actively or by the action of fungal hyphae.

Transport in the phloem of plants 9.2 Phloem is made of living cells and helps in transport of the organic molecules. The main composing cells are sieve tubes and companion cells.

Phloem translocates molecules in various directions inside the plant but follows the principle of source to sink flow.

Sugar is loaded in the sieve tube from the source (leaves). The formation of concentration gradients forces water from surrounding cells to enter the sieve tube as well.

Water uptake inside the sieve tube creates hydrostatic pressure which helps in flowing of the sugar to the sink (any fruit or root).

Growth in plants 9.3 Plants show indeterminate growth pattern

Meristematic tissue composed of cells which have the ability to divide on its own by keeping one cell as its origin.

Apical meristems: These are the primary meristems occurring at the tips of roots and stems. The developing tip tissue with apical meristem collectively called as shoot apex.

Lateral meristems: These are responsible for secondary growth which allows growth in the thickness of plants.

Hormones are the chemical messengers and in plants they are released in response to an environmental stimulus.

Auxins are the group of plant hormones that can be produced artificially but produced naturally at apices of stems and roots. They influence the tropism of the plant.

The growth of the plant in response to light is called phototropism.

Reproduction in plants 9.4 Flower bearing plants are called angiosperms. Flowers are the reproductive organs of the plants.

Monocots and Dicots

Four basic flower parts: Sepals, Petals, Stamen and Carpel

Pollination: It 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: It is the process of union of male and female sex cells to form a unit called zygote.

Seeds: These are the structures that keep the embryo functional and protected.

Plants react to the sunlight as they grow. This reaction to light features three types of flowering: Long-day plants, Short-day plants, Day-neutral plants

Phytochrome is the pigment in the plants to offer control by light.

Unit 10: Genetics and Evolution

Genetics and Evolution

Genetics and evolution are intertwined disciplines; genetic variation serves as the basis for evolution, and genetic studies enhance our comprehension of evolutionary processes.

Subtopic Subtopic Number IB Points to Understand
Meiosis 10.1 Meiosis: Replication of chromosome and joining of two copies of chromosomes with each other by centromere.

Crossing over: Exchange in DNA material between non-sister chromatids. It is an enzyme-mediated process and the enzyme involved is recombinase.

Chiasma forms while crossing over. It is a point of adherence of two non-sister chromatids for efficient exchange of genetic material.

Crossing over produces new combinations of alleles on the chromosomes of the haploid cells.

Law of independent assortment: It states that the separation of one pair of alleles between the daughter cells is independent of another pair of alleles.

Inheritance 10.2 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.

When two genes are found on the same chromosome they are called linked. The tendency of these genes to pass on to the next generation together is called linkage.

Continuous variation deals with the spectrum of phenotypes and shows an unbroken range of phenotypes of a particular character.

While discontinuous variation deals with few phenotypes and can show two or more forms of a particular character.

Chi squared tests: These are the tests done to actually check the accuracy of possible ratios come by crossing.

Gene pools and speciation 10.3 Gene pool: All the genetic information present in the reproducing members of a population at a given time.

Change in the allele frequency leads to evolution.

Hardy-Weinberg equation; It is the equation to calculate the allele frequency, genotypes or phenotypes within a population.

Variation in allelic frequency by natural factors leads to different types of selection of equilibrium: Directional, Stabilising, Disruptive

Some factors cause the hindrance in a major proportion which fall apart the populations and causes barrier in reproducing together: Geographical, Temporal and Behavioural

All the reproductive isolation factors lead to speciation

The rate of speciation can be judge by two ways: Gradualism and punctuated equilibrium

Unit 11: Animal Physiology

Animal Physiology

Animal physiology explores how animal bodies function, including the myriad systems and processes responsible for maintaining equilibrium (homeostasis) and ensuring survival.

Subtopic Subtopic Number IB Points to Understand
Antibody production and vaccination 11.1 Immune system recognizes any foreign cell through antigens.

Antigens are polysaccharide and proteins, present on the surface of the cell.

Immune response:

  • Macrophages: These are massive leukocyte cells, which engulfs the pathogen by the process called phagocytosis
  • T lymphocytes recognise the antigen presentation and become activated
  • T lymphocytes bind to B lymphocytes and simulate them to produce specific antibodies

B cells are less in number while initiating the response but they clone themselves (undergo mitosis) to produce large amounts of antibodies.

Histamines are the chemical which causes allergy symptoms like sneezing, congestion, itching, red skin etc. i.e. histamines are the cause of allergy.

Memory cells stream in blood vessels but remain inactive until the pathogen it is specific to, attacks again.

Vaccine: A vaccine contains attenuated or killed pathogens or their derivatives to generate the primary response in human’s body against the pathogen

Monoclonal antibodies are specific antibodies for only one type of antigens i.e. they are exactly the same.

B cells are fused with cancer cells called myeloma cells so that the leukocytes remain alive for a long time. The fusion of B cells and myeloma cells makes up hybridoma cells (hybrids of antibody producing cells and are