Author: Admin

📌Definition Table

Term	Definition
Phospholipid bilayer	Double layer of phospholipids forming the fundamental structure of membranes, with hydrophilic heads facing outwards and hydrophobic tails facing inwards.
Amphipathic	A molecule containing both hydrophilic (water-attracting) and hydrophobic (water-repelling) regions.
Fluid mosaic model	Describes membranes as flexible, with lipids and proteins moving laterally while maintaining overall structure.
Integral proteins	Proteins embedded within the lipid bilayer, often spanning the membrane.
Peripheral proteins	Proteins loosely attached to membrane surfaces or integral proteins, not embedded in the hydrophobic core.
Cholesterol	A lipid molecule interspersed within membranes that regulates fluidity and permeability.

📌Introduction

Biological membranes form the boundary between the cell and its environment, and between internal compartments within eukaryotic cells. Their structure ensures selective exchange of materials, compartmentalization, signaling, and energy transduction. The fluid mosaic model, proposed by Singer and Nicolson in 1972, remains the central framework for understanding membrane organization. According to this model, membranes are dynamic, with proteins “floating” in a sea of phospholipids, giving them both flexibility and specificity. The interplay between lipids, proteins, and carbohydrates results in membranes that are not merely passive barriers but active regulators of cellular life.

📌 Phospholipids and Amphipathic Nature

• Phospholipids are amphipathic molecules with a hydrophilic phosphate head and hydrophobic fatty acid tails.
• In aqueous environments, phospholipids self-assemble into bilayers, with heads facing water and tails shielded inside.
• This bilayer arrangement produces a hydrophobic core, preventing free passage of polar molecules and ions.
• The amphipathic nature underpins selective permeability — small, non-polar molecules diffuse easily, while charged or large molecules require transport proteins.

🧠 Examiner Tip: When drawing the bilayer, always show hydrophilic heads facing outwards toward aqueous environments and hydrophobic tails inwards. Label integral vs peripheral proteins clearly, as this is a common diagram question.

📌 Membrane Proteins and the Fluid Mosaic Model

• Integral proteins penetrate the hydrophobic core; some span the bilayer (transmembrane proteins). They function as channels, carriers, pumps, or receptors.
• Peripheral proteins attach loosely to surfaces, playing roles in signaling and anchoring.
• Membranes are described as “fluid” because phospholipids and proteins move laterally, allowing flexibility, endocytosis, and dynamic interactions.
• They are “mosaics” because of the irregular distribution of proteins, glycoproteins, and glycolipids scattered across the bilayer.

🧬 IA Tips & Guidance: Osmosis experiments using dialysis tubing (as an artificial membrane) can illustrate selective permeability. More advanced setups include investigating the effect of detergents or alcohol on beetroot cell membranes by measuring pigment leakage.

📌 Cholesterol and Membrane Stability

• Cholesterol inserts between phospholipids, affecting fluidity and permeability.
• At low temperatures, it prevents phospholipids from packing too tightly, maintaining flexibility.
• At high temperatures, it holds fatty acid tails together, preventing excessive fluidity and leakage.
• Cholesterol reduces permeability to small water-soluble molecules, stabilizing the bilayer.

🌐 EE Focus: An EE could investigate how membrane fluidity changes with lipid composition — e.g., the role of unsaturated fatty acids in cold-adapted organisms. Another route is analyzing how drugs or alcohol disrupt membrane permeability in model systems.

📌 Specialized Membrane Components

• Glycoproteins and glycolipids extend from the cell surface, serving as receptors and recognition markers (e.g., blood group antigens).
• These molecules mediate cell-cell communication, immune recognition, and adhesion.
• Specialized domains such as lipid rafts concentrate signaling molecules, showing that membranes are not uniform but compartmentalized within themselves.

❤️ CAS Link: Students could create interactive models showing how detergents, alcohol, or temperature changes affect membrane permeability, linking classroom biology to public health campaigns on alcohol effects or frostbite.

📌 Applications of Membrane Structure

• Explains how endocytosis and exocytosis transport large molecules.
• Provides the framework for selective transport, signaling pathways, and compartmentalization.
• Variations in lipid and protein composition reflect cell specialization — e.g., myelin membranes are rich in lipids for insulation.

🔍 TOK Perspective: The fluid mosaic model is itself a scientific model — a simplification of reality. TOK reflection: How reliable are models in explaining dynamic biological systems, and what happens when evidence requires us to revise them?

📝 Paper 2: Be ready to draw and label the fluid mosaic model, explain amphipathic phospholipid behavior, describe cholesterol’s role, and distinguish integral vs peripheral proteins. Questions may also ask how membrane composition varies across organelles or cell types

📌Definition Table

Term	Definition
Enzyme	A biological catalyst, usually a globular protein, that speeds up reactions by lowering activation energy.
Hormone	A signaling molecule, often protein-based (e.g., insulin), that regulates physiological processes.
Antibody	A protein (immunoglobulin) produced by B cells that binds specifically to antigens to defend against pathogens.
Hemoglobin	A transport protein in red blood cells that binds and carries oxygen.
Collagen	A fibrous protein forming connective tissue, providing strength and elasticity.
Motor protein	Protein such as actin or myosin that produces movement within cells or tissues.

📌Introduction

While all proteins share the same fundamental building blocks, their folding, interactions, and specializations give rise to functions as diverse as catalysis, transport, defense, and movement. Specialized proteins are finely tuned to perform particular biological roles essential for survival. From enzymes that sustain metabolism to antibodies that protect against infection, the diversity of protein function illustrates the central role proteins play in all forms of life.

📌 Enzymes as Specialized Proteins

• Enzymes are highly specific globular proteins that accelerate metabolic reactions by lowering the activation energy required.
• The active site of an enzyme is complementary in shape to its substrate, ensuring specificity. Substrate binding often involves hydrogen bonds, ionic bonds, and hydrophobic interactions.
• Enzymes work under mild conditions of temperature and pH, making them ideal for biological processes.
• Examples include catalase (decomposes hydrogen peroxide), amylase (breaks down starch), and DNA polymerase (synthesizes DNA).
• Enzyme activity is regulated by inhibitors, activators, and environmental conditions, reflecting the need for precise cellular control.

🧠 Examiner Tip: When describing enzyme function, always connect structure to specificity — the shape of the active site determines which substrate is bound and what reaction occurs. Avoid vague statements like “enzymes speed up reactions” without mechanistic explanation.

📌 Transport and Regulatory Proteins

• Hemoglobin is a globular protein with four polypeptide subunits, each containing a heme group with an iron atom that binds oxygen. Its quaternary structure allows cooperative binding, enabling efficient oxygen uptake and release.
• Insulin is a protein hormone secreted by the pancreas that regulates blood glucose by promoting uptake into cells and stimulating glycogen synthesis. Deficiency or resistance leads to diabetes mellitus.
• Membrane proteins act as channels, pumps, and receptors, controlling what enters and exits cells, ensuring homeostasis.

🧬 IA Tips & Guidance: Practical investigations could involve testing enzyme activity at different temperatures or pH levels. More advanced projects could model hemoglobin’s oxygen dissociation curve or simulate the effect of enzyme inhibitors.

📌 Defense Proteins

• Antibodies (immunoglobulins) are Y-shaped proteins produced by B cells, each with highly variable regions that specifically bind to unique antigens.
• They neutralize pathogens by marking them for destruction, blocking toxins, or activating complement proteins.
• Their enormous diversity arises from rearrangements in DNA, allowing the immune system to recognize millions of potential antigens.
• Specialized defense proteins highlight the adaptability of protein structure to external challenges.

🌐 EE Focus: An EE could examine how structural differences in antibodies influence antigen binding, or how protein engineering is used to design therapeutic antibodies for cancer and infectious diseases.

📌 Structural and Motor Proteins

• Collagen is a fibrous protein forming triple-helical fibers with enormous tensile strength, making it critical in connective tissue, tendons, skin, and cartilage.
• Keratin provides mechanical strength in hair, nails, and feathers, protecting organisms from physical damage.
• Actin and myosin are motor proteins that interact to generate muscle contraction and enable movement at both cellular and organismal levels.
• Specialized structural proteins ensure that organisms maintain form, mobility, and resilience.

❤️ CAS Link: Students could design a fitness and health awareness project explaining the roles of proteins in muscle function and nutrition, highlighting how exercise and diet influence protein needs.

📌 Functional Significance of Protein Diversity

• Proteins carry out most essential life processes, from catalysis and transport to immunity and movement.
• Their diversity is a direct result of amino acid sequence variation, folding patterns, and the ability to form complex quaternary structures.
• Specialized proteins illustrate how a single class of biomolecules can be adapted to virtually every role in biology, underpinning the complexity and adaptability of life.

🔍 TOK Perspective: Specialized proteins raise questions about the relationship between structure and function. TOK reflection: If protein structure determines function, to what extent can we predict function from structure alone, and how does uncertainty shape our scientific knowledge?

📝 Paper 2: Be ready to give examples of specialized proteins (enzymes, antibodies, hemoglobin, collagen), explain how their structure relates to function, and describe experimental investigations into enzyme activity or the role of hemoglobin in oxygen transport.

📌Definition Table

Term	Definition
Primary structure	Linear sequence of amino acids in a polypeptide, determined by DNA.
Secondary structure	Local folding of the polypeptide into α-helices or β-pleated sheets, stabilized by hydrogen bonds.
Tertiary structure	Overall 3D shape of a polypeptide, formed by interactions between R groups (hydrophobic, ionic, hydrogen bonds, disulfide bridges).
Quaternary structure	Association of multiple polypeptide chains to form a functional protein (e.g., hemoglobin).
Denaturation	Loss of protein’s native structure due to heat, pH, or chemicals, leading to loss of function.
Fibrous protein	Structural proteins with long, elongated shapes (e.g., collagen, keratin).
Globular protein	Compact, spherical proteins that are soluble and functional (e.g., enzymes, hormones).

📌Introduction

The function of a protein depends critically on its structure. Although all proteins are made from the same 20 amino acids, their folding and organization result in immense structural diversity. The four levels of protein structure — primary, secondary, tertiary, and quaternary — provide increasing complexity and specificity. Proteins can be fibrous and structural, globular and functional, or even combine features of both. Their unique properties, such as solubility, flexibility, or tensile strength, arise from chemical interactions between amino acid R groups, making protein folding one of the most fascinating aspects of molecular biology.

📌 Primary and Secondary Structure

• The primary structure of a protein is its amino acid sequence, coded by DNA and assembled by ribosomes. Even a single change in sequence can dramatically alter function (e.g., sickle-cell hemoglobin caused by one substitution).
• Secondary structures arise when polypeptide chains coil or fold locally:
  • α-helices: right-handed coils stabilized by hydrogen bonds every fourth amino acid.
  • β-pleated sheets: parallel or antiparallel strands held by hydrogen bonds, forming rigid structures.
• These recurring motifs provide the backbone of many proteins, contributing to stability and mechanical properties.

🧠 Examiner Tip: When describing secondary structure, explicitly mention hydrogen bonds between backbone atoms (C=O and N–H), not between R groups — this is a common mistake in IB exams.

📌 Tertiary Structure

• The tertiary structure is the unique 3D conformation of a polypeptide, formed by interactions among R groups.
• Key interactions include:
  • Hydrogen bonds between polar side chains.
  • Ionic bonds between charged R groups.
  • Hydrophobic interactions driving nonpolar R groups inward, away from aqueous environments.
  • Disulfide bridges, covalent bonds between cysteine residues, providing strong stability.
• Tertiary structure determines the protein’s active site, specificity, and overall function.
• Denaturation disrupts these interactions, causing irreversible loss of shape and function.

🧬 IA Tips & Guidance: Experiments on enzyme activity at different pH or temperatures highlight the effect of tertiary structure disruption. For instance, heating catalase destroys its active site by denaturation, visibly reducing its ability to break down hydrogen peroxide.

📌 Quaternary Structure

• Proteins with multiple polypeptides form quaternary structures, where subunits interact to create a functional protein.
• Example: Hemoglobin, composed of four subunits, each with a heme group that binds oxygen cooperatively.
• Other examples include antibodies (four polypeptide chains) and ion channels made of multiple protein subunits.
• Quaternary structures often enable regulation, stability, and complex functionality not possible with single polypeptides.

🌐 EE Focus: An EE could explore the structural basis of enzyme specificity, or how mutations affecting quaternary structure impair function, such as in sickle-cell anemia or prion diseases.

📌 Fibrous vs Globular Proteins

• Fibrous proteins: elongated, insoluble, structural roles. Examples:
  • Collagen → provides tensile strength in skin, ligaments, and tendons.
  • Keratin → strong protein in hair, nails, and feathers.
  • Silk fibroin → provides lightweight tensile strength in spider webs.
• Globular proteins: compact, soluble, functional roles. Examples:
  • Enzymes like catalase → catalyze metabolic reactions.
  • Hemoglobin → transports oxygen.
  • Insulin → regulates blood sugar.
• The contrast between fibrous and globular proteins demonstrates how structure underlies biological roles.

❤️ CAS Link: Students could organize an educational outreach project using 3D models to show how protein folding leads to different properties, raising awareness of protein denaturation in food (e.g., cooking egg white) or health.

📌 Protein Properties and Functions

• Solubility, elasticity, and stability all depend on protein structure.
• Denaturation alters these properties, often irreversibly.
• Specificity of enzymes arises from precise active site geometry.
• Structural rigidity of fibrous proteins ensures support and protection.
• Flexibility of globular proteins allows them to act as dynamic regulators and catalysts.

🔍 TOK Perspective: Proteins highlight the role of models in science. Structural diagrams, ribbon models, and molecular simulations each reveal different aspects of protein folding. TOK reflection: How do different visual models influence our perception of something as complex and dynamic as protein structure?

📝 Paper 2: Be ready to describe the four levels of protein structure, explain differences between fibrous and globular proteins, give examples such as collagen, hemoglobin, and enzymes, and analyze how pH and temperature affect protein properties.

📌Definition Table

Term	Definition
Amino acid	Monomer of proteins; contains an amine group (–NH₂), a carboxyl group (–COOH), a hydrogen, and an R group around a central carbon.
Peptide bond	Covalent bond between amino acids formed by condensation (between –COOH and –NH₂ groups).
Dipeptide	Molecule formed when two amino acids join via a peptide bond.
Polypeptide	Chain of three or more amino acids joined by peptide bonds.
Essential amino acids	Amino acids that must be obtained from diet because humans cannot synthesize them.
Non-essential amino acids	Amino acids that can be synthesized by the body.

📌Introduction

Proteins are macromolecules essential for nearly every cellular process, from catalyzing reactions to providing structural support. They are polymers of amino acids, assembled by ribosomes under the genetic instructions encoded in DNA. The immense variety of proteins arises from the 20 amino acids that can be combined in almost infinite sequences, leading to structural and functional diversity.

📌 Formation of Polypeptides

• Amino acids link together through condensation reactions, where the carboxyl group (–COOH) of one amino acid reacts with the amine group (–NH₂) of another, releasing a molecule of water and forming a peptide bond.
• The resulting bond is strong and stable, allowing long chains of amino acids (polypeptides) to form. A short chain of two amino acids is a dipeptide, while chains of many amino acids make up polypeptides, which fold into proteins.
• Proteins are synthesized by ribosomes during translation, where mRNA provides the instructions and tRNA delivers the appropriate amino acids.
• The vast number of possible sequences — even a short chain of 50 amino acids allows trillions of combinations — explains the extraordinary diversity of protein structures and functions.
• Hydrolysis reactions, catalyzed by protease enzymes, can break peptide bonds by adding water, returning proteins to their amino acid monomers.

🧠 Examiner Tip: When drawing peptide bond formation, always show the loss of water (–OH from carboxyl, –H from amine) and highlight the C–N bond that results. Make sure to note that the R group is not directly involved in bond formation but is responsible for diversity.

📌 Essential and Non-Essential Amino Acids

• Of the 20 amino acids used in protein synthesis, humans can synthesize 11, known as non-essential amino acids, because they can be made from other compounds within the body.
• The other 9 are essential amino acids, which must be obtained from the diet because humans lack the metabolic pathways to produce them.
• Animal-derived foods (such as meat, eggs, and dairy) are considered “complete proteins” because they contain all essential amino acids in sufficient quantities.
• Plant-based foods often lack one or more essential amino acids, but by combining different plant sources (e.g., legumes with grains), vegetarians and vegans can obtain all essentials.
• Protein deficiency, particularly a lack of essential amino acids, can lead to health conditions such as kwashiorkor, highlighting the importance of dietary variety.

🧬 IA Tips & Guidance: A simple lab experiment could involve the Biuret test, which detects peptide bonds by producing a violet color. More advanced IAs could test the action of proteases on protein-rich foods (e.g., egg white hydrolyzed into amino acids). Linking visible experimental outcomes back to molecular processes of peptide bond hydrolysis strengthens analysis.

📌 Variety of Proteins

• Protein variety is determined by the sequence, number, and type of amino acids that form each polypeptide. Even small changes in sequence can drastically alter a protein’s structure and function.
• The genetic code in DNA ultimately determines this sequence, with codons specifying which amino acids are assembled during protein synthesis.
• Proteins can be short peptides with fewer than 100 amino acids, or enormous complexes with thousands of subunits, reflecting their versatility.
• The 20 amino acids differ by their R groups, which may be hydrophobic, hydrophilic, acidic, or basic. This chemical diversity influences folding, interactions, and ultimately protein function.
• As a result, proteins can act as enzymes, transporters, receptors, structural fibers, storage molecules, hormones, or antibodies, making them indispensable to life.

🌐 EE Focus: An EE could explore how mutations in DNA alter amino acid sequence and protein function, for example in diseases like sickle-cell anemia. Another avenue would be investigating how synthetic biology manipulates amino acid sequences to create novel proteins for biotechnology.

📌 Examples of Protein Diversity

• Rubisco: The enzyme central to carbon fixation in photosynthesis; considered one of the most abundant proteins on Earth.
• Insulin: A small protein hormone secreted by the pancreas that regulates blood glucose by promoting uptake into cells.
• Immunoglobulins: Antibodies that recognize and bind to a vast range of antigens due to highly variable regions in their amino acid sequences.
• Rhodopsin: A light-sensitive receptor protein in the retina that allows vision in dim light.
• Collagen: A fibrous protein with a triple-helix structure that provides tensile strength in connective tissues, ligaments, and skin.
• Spider silk: A protein fiber produced by spiders that is both lightweight and stronger than steel, with potential for industrial and biomedical applications.

❤️ CAS Link: Students could design a nutrition awareness project comparing plant-based and animal-based diets, explaining how different protein sources provide essential amino acids and how combinations of foods can ensure balanced intake.

📌 Applications in Biology

• Proteins function as enzymes, speeding up biochemical reactions that sustain life.
• As hormones, proteins such as insulin and glucagon regulate physiological processes.
• Antibodies defend organisms against pathogens by specifically binding to foreign molecules.
• Structural proteins like keratin and collagen provide mechanical support in tissues and organs.
• Transport proteins such as hemoglobin carry oxygen in the blood, while membrane channels regulate ion and nutrient movement.

🔍 TOK Perspective: The sheer diversity of proteins raises the question of reductionism in science. Although proteins are built from just 20 amino acids, predicting their three-dimensional folding and function remains one of biology’s great challenges. TOK reflection: To what extent can complex biological phenomena be fully explained by the sum of their chemical parts?

📝 Paper 2: Be ready to draw and label amino acids, show peptide bond formation and hydrolysis, explain the difference between essential and non-essential amino acids, and give examples of protein diversity such as enzymes, hormones, structural proteins, and antibodies.

📌Definition Table

Term	Definition
Lipid	Hydrophobic organic molecule composed mostly of carbon and hydrogen with some oxygen; not true polymers.
Triglyceride	A lipid formed from glycerol and three fatty acids linked by ester bonds; main form of energy storage.
Fatty acid	Long hydrocarbon chain with a carboxyl group at one end; can be saturated or unsaturated.
Saturated fatty acid	Fatty acid with no double bonds; solid at room temperature (e.g., animal fats).
Unsaturated fatty acid	Fatty acid with one or more C=C double bonds; liquid at room temperature (e.g., plant oils).
Phospholipid	Lipid with glycerol, two fatty acids, and a phosphate group; forms bilayers in cell membranes.
Steroid	Lipid with four fused carbon rings; includes hormones like testosterone, estrogen, and cholesterol.

📌Introduction

Lipids are a diverse group of hydrophobic molecules that perform crucial roles in energy storage, insulation, cell signaling, and membrane structure. Unlike carbohydrates and proteins, lipids are not true polymers, but their structural variations allow for wide functional diversity. They are formed mainly through condensation reactions between glycerol and fatty acids (esterification) and can store more than twice the energy of carbohydrates. Lipids are essential in both cellular biology and human health, making them one of the most important classes of biomolecules.

📌 Triglycerides and Energy Storage

• Composed of glycerol + 3 fatty acids linked by ester bonds.
• Store large amounts of chemical energy in C–H bonds.
• Hydrophobic → stored without water, making them more compact than glycogen.
• Used for long-term energy storage, thermal insulation, and protection of organs.

🧠 Examiner Tip: Always contrast lipid energy storage with carbohydrates — lipids store more energy per gram but are slower to mobilize than glycogen.

📌 Phospholipids and Membrane Structure

• Structure: glycerol + 2 fatty acids + phosphate group.
• Amphipathic: hydrophilic phosphate head + hydrophobic fatty acid tails.
• Self-assemble into bilayers in aqueous environments → basis of cell membranes.
• Allow selective permeability and membrane fluidity.

🧬 IA Tips & Guidance: Simple experiments with oil–water mixtures or soap micelles can demonstrate lipid hydrophobicity and amphipathic behavior. For HL, cholesterol’s effect on membrane permeability can be modeled.

📌 Saturated vs Unsaturated Fatty Acids

• Saturated: no double bonds, straight chains, pack tightly → solid fats.
• Unsaturated: one or more C=C double bonds, kinks prevent tight packing → oils.
• Trans fats: unsaturated fats artificially hydrogenated; associated with cardiovascular disease.

🌐 EE Focus: An EE could explore the health impacts of different dietary lipids (saturated, unsaturated, trans fats) or investigate how lipid structure affects membrane permeability.

📌 Steroids and Other Lipid Functions

• Steroids: cholesterol, testosterone, estrogen, cortisol.
• Waxes: protective coatings in plants and animals.
• Pigments and vitamins: fat-soluble vitamins (A, D, E, K) derived from lipids.
• Signaling molecules: steroid hormones regulate metabolism, reproduction, stress responses.

❤️ CAS Link: Students could organize a health campaign on the role of dietary fats, comparing “good” vs “bad” lipids, and promoting balanced nutrition in their community.

📌 Lipid Functions in Biology

• Long-term energy storage (triglycerides).
• Thermal insulation and shock absorption.
• Structural (phospholipids in membranes, cholesterol regulating fluidity).
• Hormonal signaling (steroid hormones).
• Waterproofing (waxes on leaves, feathers).

🔍 TOK Perspective: Lipids raise knowledge questions in nutrition science — for decades fats were considered harmful, but now “good fats” are recognized as essential. TOK reflection: How does evolving scientific evidence reshape long-standing societal beliefs?

📝 Paper 2: Be ready to draw triglycerides and phospholipids, compare saturated vs unsaturated fatty acids, explain why lipids store more energy per gram than carbohydrates, and describe their structural and signaling roles.

📌Definition Table

Term	Definition
Monosaccharide	Simplest carbohydrate monomer (e.g., glucose, fructose, galactose).
Disaccharide	Carbohydrate formed when two monosaccharides join via a glycosidic bond (e.g., maltose, sucrose, lactose).
Polysaccharide	Large carbohydrate polymer made of many monosaccharides (e.g., starch, glycogen, cellulose).
Glycosidic bond	Covalent bond formed between monosaccharides in condensation reactions.
Isomer	Molecules with the same molecular formula but different structural arrangements (e.g., α-glucose vs β-glucose).
Cellulose	Structural polysaccharide made of β-glucose, found in plant cell walls.
Glycogen	Highly branched polysaccharide of α-glucose used for energy storage in animals.

📌Introduction

Carbohydrates are one of the four main classes of biological macromolecules and serve as a primary energy source, storage material, and structural component in living organisms. They are composed of carbon, hydrogen, and oxygen, usually in the ratio C:H:O = 1:2:1. Their variety arises from different monomers (monosaccharides), linkages (glycosidic bonds), and structures (branched, straight, helical, or fibrous). This structural diversity underpins their multiple roles in metabolism, storage, and biological architecture.

📌 Monosaccharides

• General formula: CₙH₂ₙOₙ.
• Classified by number of carbon atoms:
  • Trioses (3C) → glyceraldehyde.
  • Pentoses (5C) → ribose (in RNA), deoxyribose (in DNA).
  • Hexoses (6C) → glucose, galactose, fructose.
• Glucose is the most important hexose, existing in two isomers: α-glucose and β-glucose.
• Structural differences between α- and β-glucose affect the properties of their polymers.

🧠 Examiner Tip: You must be able to draw and label both α-glucose and β-glucose and identify the difference at carbon 1.

📌 Disaccharides

• Formed by condensation reactions between two monosaccharides.
• Examples:
  • Maltose = glucose + glucose.
  • Sucrose = glucose + fructose.
  • Lactose = glucose + galactose.
• Hydrolyzed back into monosaccharides by enzymes.

🧬 IA Tips & Guidance: Food testing experiments (e.g., Benedict’s test for reducing sugars, using lactase to hydrolyze lactose) provide simple but effective investigations into carbohydrate chemistry.

📌 Polysaccharides: Storage and Structure

• Starch: α-glucose storage in plants, composed of amylose (helix, compact) and amylopectin (branched).
• Glycogen: α-glucose storage in animals, highly branched, enabling rapid glucose release.
• Cellulose: β-glucose chains, alternating monomers invert, hydrogen bonds form microfibrils → strong plant cell walls.

🌐 EE Focus: An EE could compare the digestibility of starch vs cellulose in different organisms, or investigate enzyme specificity for α- and β-linked glucose polymers.

📌 Role of Glycoproteins

• Carbohydrates attached to proteins in membranes form glycoproteins.
• Functions include:
  • Cell recognition and signaling.
  • Immune responses (ABO blood group antigens).
  • Hormone and neurotransmitter receptor activity.

❤️ CAS Link: Students could run a health awareness campaign by testing food samples for carbohydrate types and linking results to dietary energy intake.

📌 Applications of Carbohydrates in Biology

• Medicine: Glycoprotein antigens determine blood type.
• Agriculture: Crop yield and storage rely on carbohydrate content.
• Biotechnology: Carbohydrate-based nanomaterials used in drug delivery.
• Food industry: Modified starches act as thickeners and stabilizers.

🔍 TOK Perspective: Carbohydrates demonstrate how small structural changes (α vs β glucose) create entirely different biological roles. TOK reflection: Does knowledge depend more on molecular detail or on functional context when classifying biological molecules?

📝 Paper 2: Be ready to draw α- and β-glucose, identify disaccharides and polysaccharides, describe starch, glycogen, and cellulose, and explain the role of glycoproteins in cell recognition.

📌Definition Table

Term	Definition
Carbon	Element with atomic number 6; tetravalent (forms 4 covalent bonds) allowing structural diversity in organic compounds.
Covalent bond	Strong bond formed when atoms share electron pairs.
Monomer	Small basic unit that can join with others to form polymers (e.g., glucose, amino acids).
Polymer	Large molecule made of repeating monomer units (e.g., starch, proteins, DNA).
Macromolecule	Very large biological molecule (proteins, nucleic acids, polysaccharides, lipids).
Condensation reaction	Reaction where covalent bonds form between monomers, releasing water.
Hydrolysis	Breaking of covalent bonds in polymers by adding water, releasing monomers.
Functional groups	Specific groups of atoms (–OH, –COOH, –NH₂, –PO₄³⁻) that determine chemical reactivity.

📌Introduction

Carbon is the chemical foundation of all life on Earth, forming the backbone of carbohydrates, lipids, proteins, and nucleic acids. Its unique ability to form four covalent bonds allows it to build an almost limitless variety of stable yet versatile molecules, from simple chains to complex rings and branched structures. These carbon-based macromolecules are essential for storing energy, transmitting genetic information, catalyzing reactions, and building cell structures. Understanding carbon’s bonding properties and the formation of macromolecules provides the basis for molecular biology, biochemistry, and biotechnology.

📌 Chemical Properties of Carbon

• Tetravalent: can form 4 covalent bonds → stable, complex structures.
• Can bond to itself → chains, branched molecules, and rings.
• Can form single, double, or triple bonds with C and other atoms.
• Functional groups provide specific chemical properties (e.g., hydroxyl makes molecules polar).
• Carbon compounds can adopt 3D tetrahedral shapes, influencing biological function.

🧠 Examiner Tip: Always emphasize that it is carbon’s tetravalency that makes life possible — this is a frequent IB marking point.

📌 Formation and Breakdown of Macromolecules

• Condensation Reactions:
  • Monomers join to form polymers.
  • Water is released.
  • Examples:
    • Monosaccharides → Polysaccharides (glycosidic bonds).
    • Amino acids → Polypeptides (peptide bonds).
    • Nucleotides → Nucleic acids (phosphodiester bonds).
    • Glycerol + fatty acids → Triglycerides (ester bonds).
• Hydrolysis Reactions:
  • Polymers broken into monomers.
  • Water is used to break covalent bonds.
  • Essential in digestion and recycling of biomolecules.

🧬 IA Tips & Guidance: Enzyme experiments (e.g., amylase breaking starch → maltose) are excellent demonstrations of hydrolysis. Ensure you connect reaction type (condensation/hydrolysis) to observed outcomes.:

📌 Major Biological Macromolecules

• Carbohydrates: Monosaccharides joined by glycosidic bonds → energy storage (starch, glycogen) and structure (cellulose).
• Proteins: Amino acids joined by peptide bonds → enzymes, hormones, structural support.
• Nucleic acids: Nucleotides joined by phosphodiester bonds → store and transmit genetic information (DNA, RNA).
• Lipids: Not true polymers; formed by glycerol + fatty acids → long-term energy storage, membranes, hormones.

🌐 EE Focus: An EE could investigate how condensation and hydrolysis reactions are catalyzed by enzymes, or how structural diversity in carbon-based molecules enables biochemical specialization.

📌 Digestion and Metabolism of Macromolecules

• Hydrolysis of polysaccharides → monosaccharides for respiration.
• Hydrolysis of polypeptides → amino acids for protein synthesis.
• Hydrolysis of triglycerides → fatty acids and glycerol for energy storage or metabolic water.
• Hydrolysis of nucleic acids → nucleotides for DNA/RNA synthesis.

❤️ CAS Link: Students can design educational models showing how food macromolecules (bread, eggs, oils) break down into their basic units, linking classroom biology to nutrition and health awareness.

📌 Applications of Macromolecules in Biology

• Medicine: Protein-based drugs (e.g., insulin) and nucleic acid therapies (mRNA vaccines).
• Food industry: Enzymes used to hydrolyze starch into simple sugars for sweeteners.
• Agriculture: Knowledge of macromolecules aids in creating nutrient-rich animal feed.
• Biotechnology: Genetic engineering relies on manipulating nucleic acids and proteins.

🔍 TOK Perspective: Models of macromolecules (ball-and-stick, Fischer projections, space-filling diagrams) are simplifications of reality. TOK reflection: To what extent do different representations of molecules shape the way we perceive biological processes?

📝 Paper 2: Be ready to draw and label glucose, amino acids, and fatty acids; distinguish condensation from hydrolysis reactions; identify bonds (glycosidic, peptide, phosphodiester, ester); and link monomer structure to polymer function in digestion and metabolism.

📌Definition Table

Term	Definition
In-situ Conservation	Protecting species in their natural habitat.
Ex-situ Conservation	Conserving species outside their natural habitat, such as in zoos or botanical gardens.
Protected Area	A designated region managed to conserve biodiversity and natural resources.
Restoration Ecology	The process of assisting the recovery of degraded ecosystems.
Sustainable Use	Using biological resources in a way that does not lead to long-term decline.

📌Introduction

Conservation strategies aim to protect biodiversity, maintain ecosystem services, and ensure the sustainable use of natural resources. These strategies operate at global, national, and local levels, and include both proactive measures to prevent biodiversity loss and reactive measures to restore degraded ecosystems. Effective conservation requires a combination of in-situ and ex-situ methods, legal protection, community involvement, and integration with sustainable development goals.

📌 In-situ Conservation Strategies

• Establishment of national parks, wildlife reserves, and marine protected areas.
• Legal enforcement against poaching, logging, and illegal fishing.
• Habitat restoration to support natural populations.
• Community-based conservation projects involving local stakeholders.
• Ecological corridors to connect fragmented habitats.
• Control of invasive species within protected areas.

🧠 Examiner Tip: Always highlight that in-situ conservation maintains natural ecological processes and species interactions.

📌 Ex-situ Conservation Strategies

• Zoos and aquaria for captive breeding and reintroduction programmes.
• Botanical gardens and seed banks preserving plant genetic diversity.
• Cryopreservation of gametes and embryos for rare species.
• Gene banks for agricultural crops and livestock.
• Rescue and rehabilitation centres for injured wildlife.
• Ensures survival when in-situ conservation is not possible.

🧬 IA Tips & Guidance: An IA could assess germination rates of seeds stored under different conditions to model seed bank viability.

📌 Legal and Policy Measures

• National biodiversity strategies aligned with the Convention on Biological Diversity (CBD).
• Endangered Species Acts and wildlife protection laws.
• CITES regulating international trade in endangered species.
• Environmental impact assessments before development projects.
• Integration of biodiversity conservation into land-use planning.
• Enforcement mechanisms and penalties for violations.

🌐 EE Focus: An EE could compare the effectiveness of protected areas in two different countries or ecosystems.

📌 Restoration and Sustainable Use

• Reforestation and afforestation projects.
• Wetland restoration to improve water quality and biodiversity.
• Sustainable forestry and fisheries management practices.
• Agroforestry combining agriculture with biodiversity benefits.
• Ecotourism generating revenue while conserving habitats.
• Payment for ecosystem services to incentivise conservation.

❤️ CAS Link: A CAS project could involve volunteering in a local habitat restoration programme or running a biodiversity awareness campaign.

📌 Community and International Collaboration

• Indigenous knowledge integrated into conservation planning.
• Local communities trained as wildlife monitors or eco-guides.
• Cross-border conservation initiatives for migratory species.
• Partnerships between governments, NGOs, and private sector.
• Public awareness campaigns and environmental education.
• Citizen science projects for biodiversity monitoring.

🔍 TOK Perspective: Conservation decisions often involve balancing scientific recommendations with cultural, economic, and political considerations.

📝 Paper 2: Be prepared to compare in-situ and ex-situ methods, give examples of conservation strategies, and evaluate their effectiveness.

📌Definition Table

Term	Definition
Habitat Loss	The destruction, fragmentation, or degradation of natural habitats, reducing their ability to support species.
Overexploitation	The unsustainable harvesting of species for food, trade, or other purposes.
Invasive Species	Non-native species that outcompete, prey on, or otherwise harm native species and ecosystems.
Pollution	The introduction of harmful substances or energy into the environment, adversely affecting biodiversity.
Climate Change	Long-term alteration of global or regional climate patterns, impacting ecosystems and species survival.

📌Introduction

Biodiversity faces unprecedented threats from human activities, leading to what many scientists call the sixth mass extinction. These threats operate at multiple scales — from local habitat destruction to global climate change — and often act synergistically, accelerating biodiversity loss. Understanding these threats is essential for developing effective conservation strategies and policies to protect life on Earth.

📌 Habitat Loss and Fragmentation

• Caused by agriculture, urbanisation, mining, and infrastructure development.
• Leads to smaller, isolated populations more vulnerable to extinction.
• Reduces available food, shelter, and breeding sites.
• Alters ecological processes such as pollination and nutrient cycling.
• Creates edge effects that change microclimates and species interactions.
• Particularly devastating for species with large home ranges or specialised habitats.

🧠 Examiner Tip: Always specify the driver behind habitat loss in examples — e.g., deforestation for soybean farming in the Amazon.

📌 Overexploitation

• Includes overfishing, overhunting, and overharvesting of plants.
• Depletes populations faster than they can reproduce.
• Can cause collapse of fisheries and wildlife populations.
• Often driven by high market demand and illegal trade.
• Selective harvesting can alter genetic diversity.
• Example: overharvesting of medicinal plants leading to extinction risk.

🧬 IA Tips & Guidance: An IA could assess the impact of human harvesting on population sizes of a local plant or animal species.

📌 Invasive Species

• Outcompete native species for resources.
• May introduce diseases to which natives have no immunity.
• Can alter ecosystem structure and function.
• Often spread through global trade and travel.
• Particularly harmful to island ecosystems.
• Example: introduction of brown tree snakes to Guam leading to bird extinctions.

🌐 EE Focus: An EE could investigate the ecological and economic impacts of a specific invasive species in a local area.

📌 Pollution

• Chemical: pesticides, heavy metals, and industrial waste harming organisms directly.
• Plastic: ingestion and entanglement affecting marine life.
• Nutrient: fertiliser runoff causing eutrophication and dead zones.
• Light and noise: disrupting animal behaviours such as migration and reproduction.
• Pollution can act synergistically with other threats.
• Persistent pollutants can bioaccumulate in food chains.

❤️ CAS Link: A CAS project could involve organising a community clean-up and awareness campaign on pollution impacts on biodiversity.

📌 Climate Change

• Alters temperature and precipitation patterns.
• Shifts species ranges and disrupts migration timing.
• Causes coral bleaching and loss of polar ice habitats.
• Increases frequency of extreme weather events.
• Forces rapid adaptation or migration, which many species cannot achieve.
• Contributes to ocean acidification, harming marine biodiversity.

🔍 TOK Perspective: Decisions on prioritising biodiversity threats involve value judgments, as resources are limited and trade-offs must be made between economic and environmental goals.

📝 Paper 2: Expect to discuss major threats to biodiversity, give examples, and explain how these threats interact to accelerate species loss.

📌Definition Table

Term	Definition
Biodiversity	The variety of life in all its forms, levels, and combinations, including genetic, species, and ecosystem diversity.
Genetic Diversity	The variation of genes within a species, providing the raw material for adaptation and evolution.
Species Diversity	The number of different species and their relative abundance in an area.
Ecosystem Diversity	The variety of ecosystems and ecological processes within the biosphere.
Endemic Species	Species found only in a specific geographic location.

📌Introduction

Biodiversity is the foundation of ecosystem stability, resilience, and productivity. It is essential for maintaining ecological balance and supporting human well-being through ecosystem services such as food production, water purification, climate regulation, and cultural enrichment. Biodiversity exists at multiple levels — from genetic diversity within species to the variety of ecosystems across landscapes — and is the result of millions of years of evolutionary processes. Its preservation is vital for sustaining life on Earth and adapting to environmental changes.

📌 Levels of Biodiversity

• Genetic diversity ensures populations can adapt to changing environments.
• Species diversity maintains ecosystem balance and resilience.
• Ecosystem diversity supports a wide range of ecological processes.
• All levels are interconnected and influence each other.
• Loss at one level often impacts the others.
• Measurement uses indices such as Shannon-Wiener or Simpson’s index.

🧠 Examiner Tip: When describing biodiversity, always specify the level (genetic, species, or ecosystem) and give an example.

📌 Importance to Ecosystem Functioning

• Enhances ecosystem productivity through niche differentiation.
• Increases stability against environmental fluctuations.
• Supports nutrient cycling and energy flow.
• Provides habitat for a variety of organisms.
• Ensures pollination and seed dispersal.
• Promotes resilience to invasive species and disease outbreaks.

🧬 IA Tips & Guidance: An IA could investigate species diversity in different habitats using a quadrat or transect sampling method.

📌 Importance to Humans

• Provisioning services: food, water, raw materials, medicines.
• Regulating services: climate regulation, flood control, disease regulation.
• Cultural services: recreation, spiritual value, education.
• Supporting services: soil formation, primary production.
• Acts as a genetic resource for crop and livestock improvement.
• Provides economic benefits through tourism and ecosystem products.

🌐 EE Focus: An EE could explore the relationship between biodiversity and crop productivity, analysing how species richness affects yields.

📌 Indicator of Environmental Health

• Healthy ecosystems usually have high biodiversity.
• Sudden biodiversity loss signals environmental degradation.
• Bioindicator species can signal changes in ecosystem quality.
• Monitoring biodiversity helps track climate change impacts.
• Protecting biodiversity protects ecosystem services.
• Restoration ecology aims to recover biodiversity in degraded areas.

❤️ CAS Link: A CAS project could involve organising a biodiversity survey in a local park and presenting results to raise community awareness.

📌 Global Biodiversity Patterns

• Biodiversity is highest in tropical regions and decreases toward the poles.
• Hotspots are regions with high species richness and high threat levels.
• Island ecosystems often have high endemism but are vulnerable to disturbances.
• Mountain regions offer diverse microhabitats increasing species diversity.
• Marine biodiversity is concentrated in coral reefs and coastal zones.
• Climate, geography, and evolutionary history shape biodiversity patterns.

🔍 TOK Perspective: Biodiversity valuation involves subjective decisions about which species and ecosystems are most important, reflecting human perspectives and cultural values.

📝 Paper 2: Be ready to define biodiversity at different levels, explain its importance to ecosystems and humans, and give examples of biodiversity hotspots.