Comprehensive IB Biology SL & HL Syllabus

• Cells are the basic structural unit of all living organisms.
• 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
• Electron micrographs.
• homeostasis, metabolism, nutrition, movement, excretion, growth, response to stimuli, and reproduction- functions of life in living organisms.

• Phospholipid is made up of glycerol (3-C compound), which further includes fatty acids and alcohol groups with phosphate.
• Two distinctive areas of Phospholipid bilayers are termed as hydrophilic (water-loving) and hydrophobic (water-fearing).
• 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.
• Cholesterol inhibits membrane permeability.
• Draw the fluid mosaic model.

• Organelles are distinctive units of cells that perform specific functions.
• Recall the organelles of eukaryotic cells.
• Advantages of compartmentalisation in the cytoplasm of cells.

• 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- Embryonic, adult, and cord blood stem cells.
• Totipotent Stem Cells – Can become all cell types, including extra-embryonic tissues.
• Pluripotent Stem Cells – Can become almost all cell types except extra-embryonic tissues.
• Multipotent Stem Cells – Can become multiple cell types within a specific tissue or lineage.
• 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.
• Cells are unspecialised following fertilization, but become specialized as they age.

• 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 the 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.
• Release of neurotransmitters from a presynaptic membrane.
• Explain the generation of an excitatory postsynaptic potential using acetylcholine as an example.

• 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

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

• Water contains hydrogen bonding, making it a polar compound, and only dissolves polar compounds.
• Recall adhesive and cohesive properties of water.
• Osmosis – It involves the movement across the partially permeable membrane due to concentration gradient
• Hypotonic Solution:
  • The solution outside the cell has a lower solute concentration than inside the cell.
  • Water moves into the cell, causing it to swell and potentially burst (lyse) if too much water enters.
• Hypertonic Solution:
  • The solution outside the cell has a higher solute concentration than inside the cell.
  • Water moves out of the cell, causing it to shrink (crenate).
• Isotonic Solution:
  • The solute concentration outside the cell is equal to the concentration inside the cell.
  • Water moves in and out of the cell at equal rates, resulting in no net movement of water, maintaining normal cell shape.
• Medical applications of isotonic solutions.
• Describe the effects of water movement on cells with a cell wall, including use of the terms “turgor” and “plasmolysis”.

• Species: It is a group of organisms that can interbreed and produce fertile offspring.
• 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.
• 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.
• Analyze the evidence for the hypothesis that chromosome 2 in humans arose from the fusion of chromosomes 12 and 13 with a shared primate ancestor.
• State the difficulties distinguishing between populations and species due to divergence of non- interbreeding populations during speciation.
• Genome sequencing.

• 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.
• Understand measurement of lung volumes, including: tidal volume, vital capacity, and inspiratory and expiratory reserves.
• Gas exchange in leaves with the assistance of diagrams.
• Leaf cast micrographs.

• Capillaries are single-celled thick therefore the blood cells enter the capillaries at the rate of one cell at a time.
• 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.
• 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.
• Structural differences between veins and arteries-
• Wall Thickness:
  • Arteries: Thick walls.
  • Veins: Thin walls.
• Lumen Size:
  • Arteries: Narrow lumen.
  • Veins: Wide lumen.
• Elasticity:
  • Arteries: Highly elastic.
  • Veins: Less elastic.
• Valves:
  • Arteries: No valves.
  • Veins: Have valves to prevent backflow.
• Pressure:
  • Arteries: High pressure.
  • Veins: Low pressure.
• Blood Flow Direction:
  • Arteries: Away from the heart.
  • Veins: Toward the heart.
• Occlusion of coronary arteries (epidemiology).
• Explain the transport of water from roots to leaves during transpiration due to cohesion.
• Recall the adaptations of xylem vessels for the transport of water.
• Draw and identify the distribution of tissues in a transverse section of the stem of a dicotyledonous plant.
• Draw and identify the distribution of tissues in a transverse section of the root of a dicotyledonous plant.

• Hierarchy of subsystems that are integrated in a multicellular living organism.
• Difference between the nervous and endocrine systems in sending messages.
• The human brain controls and produces every emotion, thought, feeling, memory. Also the involuntary actions like cardiac heart-beat, peristalsis etc. are controlled by it.
• The neural tube has two ends; Anterior end and Posterior end, which develop into the forebrain and rest of the other parts of the brain, respectively.
• Different parts of the brain constitutes to different functions
• Brain and spinal cord are parts of the CNS (Central Nervous System), the other parts are covered by PNS (Peripheral Nervous System).
• ANS is further divided into sympathetic and parasympathetic systems.
• 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.
• The cerebral cortex covers the largest part of the mature brain i.e. cerebrum, formed from the front part of the neural tube.
• The left cerebral hemisphere receives sensory input and controls muscle contraction.

• Pathogens are the most likely threat to humans and to prevent them from entering into our body primary defense comes into action.
• Skin and mucous membranes offers the major primary defense towards the
• Secondary defense: 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.
• Define zoonoses as infectious diseases that can transfer from other species to humans, including the examples of tuberculosis, rabies and Japanese encephalitis, and COVID-19.
• Explain vaccines and the process of immunization.
• Describe herd immunity and the prevention of epidemics.
• Evaluate data related to the COVID-19 pandemic
• HIV aids transmission and consequences.

• 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 chromosomes.
• 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.
    ○ Estrogen: The estrogen is released as to provide a negative feedback by signaling hypothalamus to stop secretion of GnRH
• In vitro fertilization: It is a method of artificial reproduction in which egg and sperm are fertilized in vitro.
• Drawing the male and female reproductive systems. Explain sexual reproduction in flowering plants, including: production of gametes, pollination, pollen development and fertilization.
• Draw and identify the features of an insect-pollinated flower.
• Recall the methods of promoting cross-pollination.
• Understand self-incompatibility mechanisms to increase genetic variation within a species.

• 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.
• Recall ABO blood groups as an example of multiple alleles and use IA, IB and i to denote the alleles.
• Phenylketonuria (PKU) is an example of a human disease due to a recessive allele.
• Box and whisker plots.

• 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.
• Insulin and Glucagon: Produced and secreted by pancreas and regulates blood sugar levels.
• Negative feedback loops are a part of homeostasis- peripheral thermoreceptors, the hypothalamus, pituitary gland, thyroxine and muscle and adipose tissue as effectors.
• Thermoregulation mechanisms-

Vasodilation:

• Purpose: Release excess heat.
• Action: Blood vessels widen.
• Effect: More blood flows to the skin, cooling the body.

Vasoconstriction:

• Purpose: Conserve heat.
• Action: Blood vessels narrow.
• Effect: Less blood flows to the skin, retaining heat.

Shivering:

• Purpose: Generate heat.
• Action: Rapid muscle contractions.
• Effect: Increases heat production.

Sweating:

• Purpose: Cool the body.
• Action: Sweat glands release fluid.
• Effect: Evaporation of sweat cools the skin.

Uncoupled Respiration in Brown Adipose Tissue:

• Purpose: Generate heat.
• Action: Mitochondria produce heat instead of ATP.
• Effect: Increases body warmth.

Hair Erection (Piloerection):

• Purpose: Insulate the body.
• Action: Hair stands up due to tiny muscle contractions.
• Effect: Traps air for insulation, reducing heat loss.

• 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.
• Selective breeding.

• Biodiversity is the variety of life in all its forms, levels and combinations. Define ecosystem diversity, species diversity and genetic diversity.

Causes of Anthropogenic Species Extinction-

• Habitat Destruction: Deforestation, urbanization, and agriculture reduce natural habitats.
• Pollution: Contaminants like chemicals, plastics, and oil spills harm species and ecosystems.
• Overexploitation: Overfishing, hunting, and poaching reduce species populations.
• Climate Change: Alters habitats and ecosystems, leading to species’ inability to adapt.
• Invasive Species: Non-native species introduced by humans outcompete or prey on native species.
• Land Use Change: Conversion of natural landscapes for agriculture, mining, and development disrupts ecosystems.

• Habitat- the place in which a community, species, population or organism lives.
• Organisms have the ability to adapt to their abiotic environment.
• Use transect data to correlate the distribution of plant or animal species with an abiotic variable.
• Recall the conditions required for coral reef formation, including: water depth, pH, salinity, clarity, and temperature.
• Biomes- groups of ecosystems with similar communities due to similar abiotic conditions and convergent evolution.
• Explain adaptations to life in hot deserts and tropical rainforests, including examples in named species of plants, example (cactus), and animals, example (Camels).
• Recall two case studies of the causes of ecosystem loss,including the loss of mixed dipterocarp forest in Southeast Asia.
• Recall evidence for a biodiversity crisis through examples.
• Recall human population growth as a major cause of the current biodiversity crisis, as well as: hunting, urbanization, deforestation, pollution, diseases and invasive alien species.
• Appreciate the need for several approaches to the conservation of biodiversity.
• Appreciate the selection of evolutionarily distinct and globally endangered species for conservation prioritization in the EDGE of Existence programme.

• Ecological niche is the role of a species in an ecosystem, and the interactions that influence growth, survival and reproduction.
• State differences between organisms that are obligate anaerobes, facultative anaerobes and obligate aerobes.
• Photosynthesis is the mode of nutrition in plants, algae, and photosynthetic prokaryotes.
• Saprotrophic Nutrition is a mode of nutrition in which organisms obtain nutrients by breaking down dead and decaying organic matter.
• Organisms: Fungi, some bacteria, and certain protists.

1. Phototrophic Archaea

• Mechanism: Utilize light as an energy source.
• Example: Halobacterium species use a pigment called bacteriorhodopsin to capture light and generate ATP, but they do not perform photosynthesis like plants.

2. Chemotrophic Archaea

• Mechanism: Obtain energy by oxidizing inorganic or organic compounds.
• Types:
  • Lithotrophic Archaea: Use inorganic molecules (e.g., hydrogen, sulfur, or ammonia) as energy sources.
    • Example: Sulfolobus species oxidize sulfur or iron.
  • Organotrophic Archaea: Use organic compounds as energy sources.
    • Example: Some methanogens metabolize organic compounds like acetate.

3. Methanogenic Archaea

• Mechanism: Produce methane (CH₄) as a byproduct of anaerobic respiration.
• Example: Methanobrevibacter species in the digestive systems of ruminants convert carbon dioxide and hydrogen into methane.

4. Halophilic Archaea

• Mechanism: Thrive in high-salt environments and often rely on organic molecules or light (via bacteriorhodopsin) for energy.
• Example: Halobacterium species, which live in environments like salt lakes.

5. Thermoacidophilic Archaea

• Mechanism: Survive in hot, acidic environments, often using sulfur compounds as energy sources.
• Example: Sulfolobus species that oxidize sulfur or sulfur compounds in hot springs.

6. Anaerobic Archaea

• Mechanism: Live in environments without oxygen, using various anaerobic processes for energy.
• Example: Methanococcus species, which thrive in deep-sea hydrothermal vents using hydrogen as an energy source and producing methane.
• Adaptations of plants for harvesting light.

• Populations as interacting groups of organisms of the same species living in an area.
• Interspecific interactions:
• Herbivory: An interaction between plants and animals
• Predation: One is predator and the other is prey
• Parasitism: One organism is host and the other is a parasite that lives in or on the body of the host
• Mutualism: Two species live in a close association and both of them benefit each other.
• Commensalism: One organism benefits from the other which is neither harmed nor benefitted in any way.
• Transect is a method of sampling a population of plants or animals along a longitudinal section of an ecosystem.
• Chi squared tests: These are the tests done to actually check the accuracy of possible ratios come by crossing.
• Understand allelopathy and secretion of antibiotics, including one specific example of each.
• Estimate population size by random sampling.

• Ecosystems- open systems in which both energy and matter can enter and exit.
• Pyramid of energy shows the available energy at each trophic level.
• This available energy at each level is called net production.
• 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.
• In a closed ecosystem, energy can be exchanged but not the matter.
• Carbon cycle diagrams.
• Outline ecosystems as carbon sinks and carbon sources.
• 19: Explain the release of carbon dioxide into the atmosphere during combustion of biomass, peat, coal, oil and natural gas.
• 20: Analyse the Keeling Curve in terms of photosynthesis, respiration and combustion.
• 21: Explain the dependence of aerobic respiration on atmospheric oxygen produced by photosynthesis, and of photosynthesis on atmospheric carbon dioxide produced by respiration.
• 22: Understand the recycling of all chemical elements required by living organisms in ecosystems

• Natural selection is the mechanism driving evolutionary change.
• 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.
• Examples of evolution include the plumage of birds of paradise

• Illustrate stability as a property of natural ecosystems.
• Recall the requirements for stability in ecosystems including: the supply of energy, recycling of nutrients, genetic diversity and climatic variables remaining within tolerance levels.
• Recall the deforestation of the Amazon rainforest as an example of a possible tipping point in ecosystem stability. Understand the importance of transpiration, cooling, air flows and rainfall to global sustainability.
• Understand the use of a Mesocosm model to investigate the effect of variables on ecosystem stability.
• Understand the role of keystone species in the stability of ecosystems.
• Assess the sustainability of resource harvesting from natural ecosystems including one terrestrial plant species and one species of marine fish as examples.
• Factors affecting the sustainability of agriculture-
  • Soil erosion
  • Leaching of nutrients
  • Supply of fertilizers
  • Pollution due to agrochemicals
  • Carbon footprint.
• Eutrophication of aquatic bodies.
• Biological Oxygen Demand (BOD) is a measure of the amount of oxygen required by microorganisms to break down organic matter in water over a specific period, usually five days at 20°C. It is an important indicator of water quality, particularly in terms of pollution levels.
• Microplastic are contaminating Oceans, and entering living organisms in the Oceans.

• Anthropogenic Causes of Climate Change
• Carbon Dioxide (CO₂)
  • Fossil Fuel Combustion: Power plants, vehicles, industry.
  • Deforestation: Fewer trees to absorb CO₂.
  • Cement Production: Releases CO₂ during manufacturing.
• Methane (CH₄)
  • Agriculture: Livestock digestion (ruminants), rice paddies.
  • Landfills: Decomposition of organic waste produces CH₄.
  • Fossil Fuel Extraction: Natural gas leaks, coal mining.
• Melting of landfast ice and sea ice are examples of polar habitat change.
• Depletion of coral reefs is a representation of potential ecosystem collapse.

Approaches to Carbon Sequestration

• Afforestation
  • Definition: Planting new forests on lands that were not previously forested.
  • Benefit: Absorbs CO₂ as trees grow, storing carbon in biomass.
• Forest Regeneration
  • Definition: Allowing or encouraging natural recovery of degraded forests.
  • Benefit: Enhances CO₂ absorption as forests recover and mature.
• Restoration of Peat-Forming Wetlands
  • Definition: Rehabilitating degraded wetlands that form peat, a carbon-rich material.
• Benefit: Traps and stores large amounts of carbon in waterlogged soils, reducing CO₂ emissions.