00-Introduction
How to Use This Detailed HTML Book
This version is designed to be followed directly in the browser. Do not only read the paragraphs. For each chapter, look at the diagram first, then read the topic explanations, then return to the diagram and explain it aloud as if teaching another student.
The IMAT Biology section often uses short questions, but students miss them because they confuse location, direction, sequence or vocabulary. This book therefore repeats those distinctions visually: cytoplasm versus matrix, codon versus anticodon, mitosis versus meiosis, insulin versus glucagon, energy flow versus nutrient cycling.
About image sources and copyright safety
This edition uses newly drawn original educational diagrams embedded directly in the HTML. General Google Image search results are not automatically safe to reuse in a commercial or educational book. To avoid licensing problems, the visuals here are custom-made schematic diagrams for VerityPrep/Veritas IMAT teaching.
01-Chemistry of Life and Biomolecules
Water, polarity and hydrogen bonding
Water is polar because oxygen is more electronegative than hydrogen, producing partial charges within the molecule. This polarity allows water molecules to form hydrogen bonds with one another and with other polar substances.
Hydrogen bonding explains many biological properties: high specific heat helps organisms resist rapid temperature change; cohesion allows water columns to move in xylem; adhesion helps water interact with surfaces; and solvent ability allows ions and polar molecules to dissolve in cytoplasm and blood plasma.
In IMAT, the trap is usually the distinction between covalent bonds inside a water molecule and hydrogen bonds between water molecules. The O-H bonds inside water are covalent; the attraction between different water molecules is hydrogen bonding.
- Explain why water can dissolve NaCl but oil does not dissolve well in water.
- Predict what happens to body temperature stability if water had very low specific heat.
- Classify hydrogen bonding as intra- or intermolecular in liquid water.
Carbohydrates
Carbohydrates are built from monosaccharides. Glucose is a hexose sugar and a central fuel molecule in cellular respiration. Disaccharides form by condensation reactions, and polysaccharides form when many monosaccharides join.
Starch is a plant storage polysaccharide, glycogen is an animal storage polysaccharide, and cellulose is a plant structural polysaccharide. These molecules may all be made from glucose units, but their bond patterns and branching make their functions different.
Medical students must understand carbohydrates because blood glucose regulation, diabetes, glycogen storage and energy metabolism are all built on this chemistry.
- Why is glycogen more highly branched than starch useful in animals?
- Which carbohydrate is structural in plant cell walls?
- Why can humans digest starch more easily than cellulose?
Lipids
Lipids are mostly hydrophobic. Triglycerides store large amounts of energy because their hydrocarbon chains are highly reduced. Phospholipids form cell membranes because they are amphipathic: hydrophilic head and hydrophobic tails.
Steroids such as cholesterol have ring structures. Cholesterol stabilises animal membranes and is a precursor for steroid hormones. This makes lipid chemistry central to cell biology and endocrinology.
IMAT may test lipids through membrane structure, energy storage, hormone type or solubility. A steroid hormone can cross membranes more easily than a peptide hormone, while insulin must bind to a membrane receptor.
- Distinguish triglycerides and phospholipids structurally.
- Explain why lipids provide more energy per gram than carbohydrates.
- Identify why cholesterol is important in animal membranes.
Proteins and amino acids
Proteins are polymers of amino acids joined by peptide bonds. Each amino acid has an amino group, a carboxyl group, a hydrogen atom and a variable R group attached to the alpha carbon.
Protein structure has levels: primary sequence, secondary alpha helices/beta sheets, tertiary 3D folding and quaternary association of multiple subunits. Protein function depends strongly on shape.
Enzymes, antibodies, membrane channels, receptors, collagen and haemoglobin are all proteins. A mutation changing one amino acid can alter folding, binding or activity.
- What bond joins amino acids?
- Why can high fever affect enzyme function?
- Explain how a change in primary structure can affect tertiary structure.
Nucleic acids
DNA and RNA are polymers of nucleotides. Each nucleotide contains a sugar, phosphate and nitrogenous base. DNA contains deoxyribose and thymine; RNA contains ribose and uracil.
DNA stores genetic information in base sequence. RNA acts as messenger, adapter or structural/catalytic molecule. mRNA carries codons, tRNA carries anticodons and amino acids, and rRNA forms part of ribosomes.
IMAT frequently tests base pairing. In DNA, A pairs with T and C pairs with G. During transcription, RNA uses U instead of T.
- Write the complementary DNA strand to ATGCC.
- Explain why RNA contains uracil instead of thymine.
- Distinguish codon and anticodon.
Additional visual explanations
Additional original visual — Nucleotide structure
Additional original visual — Protein structure levels02-Cell Theory, Prokaryotes, Eukaryotes and Organelles
Chapter visual — Cell Theory, Prokaryotes, Eukaryotes and OrganellesCell theory and cell size
Cell theory states that all living organisms are made of cells, the cell is the basic unit of life, and new cells arise from pre-existing cells. This principle distinguishes cellular life from non-cellular infectious agents such as viruses.
Cell size is limited by surface area-to-volume ratio. As a cell grows, volume increases faster than surface area, making exchange of nutrients, gases and waste more difficult. Small cells exchange materials more efficiently.
Visual learners should imagine a cube: doubling side length increases surface area by four times but volume by eight times. This is why large organisms are multicellular rather than made of one enormous cell.
- Why are cells usually microscopic?
- What happens to surface area-to-volume ratio as a cell gets larger?
- Why are villi and alveoli highly folded?
Prokaryotic cells
Prokaryotes include bacteria and archaea. They lack a nucleus and membrane-bound organelles. Their DNA is usually circular and located in the nucleoid region, and they may contain plasmids.
Prokaryotes have ribosomes, cytoplasm, plasma membrane and often a cell wall. Bacterial cell walls usually contain peptidoglycan. Some bacteria have capsules, pili or flagella.
In medical biology, prokaryotes matter because bacterial structure determines antibiotic targets. For example, some antibiotics target bacterial ribosomes or cell-wall synthesis.
- List three structures found in bacteria.
- Why can an antibiotic target bacteria without damaging human cells as strongly?
- What is a plasmid?
Eukaryotic cells
Eukaryotes include animals, plants, fungi and protists. Their DNA is enclosed in a nucleus. They contain membrane-bound organelles that separate incompatible reactions and increase efficiency.
Compartmentalisation allows different conditions in different organelles. Lysosomes can be acidic, mitochondria can maintain proton gradients, and the nucleus can regulate gene expression separately from translation.
Plant cells have chloroplasts, a large central vacuole and a cellulose cell wall. Animal cells lack chloroplasts and cellulose walls but often have centrioles and lysosomes.
- Compare animal and plant cells.
- Why is compartmentalisation an advantage?
- Which organelles contain their own DNA?
Organelles and their functions
The nucleus stores DNA and controls gene expression. The nucleolus produces ribosomal RNA and assembles ribosomal subunits. Ribosomes synthesize proteins.
Rough ER is associated with ribosomes and processes proteins for secretion or membranes. Smooth ER synthesizes lipids, detoxifies substances and stores calcium in muscle cells.
The Golgi apparatus modifies, sorts and packages proteins. Lysosomes digest macromolecules. Mitochondria carry out aerobic respiration. Chloroplasts perform photosynthesis in plants and algae.
- Which organelle packages secreted proteins?
- Where does aerobic respiration mainly occur?
- Which organelle contains hydrolytic enzymes?
Viruses
Viruses are acellular infectious particles. They contain genetic material, either DNA or RNA, surrounded by a protein capsid; some also have a lipid envelope.
Viruses cannot reproduce independently. They must infect host cells and use host machinery to replicate. Because they lack ribosomes and metabolism, they are not considered cells.
IMAT questions may ask whether viruses are prokaryotes. They are not. Prokaryotes are cells; viruses are non-cellular.
- Why are viruses not considered cells?
- Do viruses have ribosomes?
- Why do antibiotics not work directly against viruses?
03-Cell Membranes, Transport and Osmosis
Chapter visual — Cell Membranes, Transport and OsmosisFluid mosaic model
The cell membrane is a phospholipid bilayer. Phospholipids have hydrophilic heads and hydrophobic tails. In water, they arrange so heads face the aqueous environment and tails point inward.
Proteins float within or attach to the bilayer. Integral proteins may form channels, carriers or receptors. Peripheral proteins may support structure or signalling. Cholesterol in animal membranes adjusts fluidity.
The membrane is called fluid because lipids and some proteins move laterally. It is called mosaic because different proteins are embedded in the phospholipid background.
- Explain why phospholipids form bilayers.
- What is the role of cholesterol?
- Distinguish integral and peripheral proteins.
Simple diffusion and facilitated diffusion
Simple diffusion is movement from high to low concentration without a transport protein. Small nonpolar molecules such as oxygen and carbon dioxide cross membranes easily.
Facilitated diffusion also moves down a gradient, but it requires membrane proteins. Channels provide hydrophilic pathways for ions; carriers change shape to move molecules such as glucose.
Both forms are passive. Neither directly uses ATP. The presence of a protein does not automatically mean active transport.
- Why does oxygen diffuse through the membrane?
- Why do ions need channels?
- Does facilitated diffusion use ATP directly?
Active transport
Active transport moves substances against their concentration or electrochemical gradient. This requires energy, often from ATP hydrolysis. Pumps maintain gradients essential for nerve impulses, nutrient uptake and cell volume.
The sodium-potassium pump moves Na+ out of cells and K+ into cells. This creates electrochemical gradients and contributes to resting membrane potential.
Secondary active transport uses an existing gradient to drive another molecule uphill. For example, sodium gradients can power glucose uptake in intestinal cells.
- What does against the gradient mean?
- Why is ATP required?
- How can one gradient power transport of another molecule?
Osmosis and tonicity
Osmosis is diffusion of water across a selectively permeable membrane. Water moves toward the side with higher effective solute concentration.
In a hypotonic solution, animal cells gain water and may burst. In a hypertonic solution, animal cells lose water and shrink. In an isotonic solution, there is no net water movement.
Plant cells behave differently because their cell wall resists bursting. In hypotonic solution, plant cells become turgid; in hypertonic solution, the membrane can pull away from the wall, called plasmolysis.
- Predict what happens to red blood cells in distilled water.
- Why do plant cells not burst as easily as animal cells?
- What is plasmolysis?
Endocytosis and exocytosis
Large particles and macromolecules cross membranes by vesicular transport. Endocytosis brings material into the cell by forming vesicles from the plasma membrane.
Phagocytosis is cell eating; pinocytosis is cell drinking; receptor-mediated endocytosis is specific uptake using receptors.
Exocytosis releases material from the cell when vesicles fuse with the plasma membrane. Neurotransmitter release and hormone secretion often use exocytosis.
- Which process releases neurotransmitters?
- Why can proteins not simply diffuse through the lipid bilayer?
- What is receptor-mediated endocytosis?
Additional visual explanations
Additional original visual — Osmosis and tonicity04-Enzymes and Metabolic Regulation
Activation energy and catalysis
Chemical reactions require reactants to reach a transition state. The energy needed is activation energy. Enzymes lower activation energy by stabilising the transition state or positioning substrates correctly.
Enzymes do not make impossible reactions possible; they speed up reactions that are thermodynamically possible. They do not change ΔG, equilibrium constant or final equilibrium position.
Because enzymes are not consumed, one enzyme molecule can catalyse many reactions. However, enzyme activity can be affected by conditions and inhibitors.
- What does an enzyme change in an energy diagram?
- Does an enzyme change equilibrium?
- Why can a small amount of enzyme have a large effect?
Active site and specificity
The active site is the region where substrate binds and reaction occurs. Specificity arises from shape, charge, polarity and chemical interactions.
The induced-fit model states that enzyme and substrate adjust shape during binding. This helps explain why enzymes are specific but flexible.
Mutation or denaturation can change active-site shape, reducing activity. This is why protein structure is central to enzyme function.
- Why is active-site shape important?
- What is induced fit?
- How can a mutation affect enzyme activity?
Temperature and pH
Increasing temperature usually increases reaction rate at first because molecules collide more often and with more energy. Above an optimum, enzymes denature and activity falls sharply.
pH affects charges on amino acid side chains. Extreme pH can disrupt ionic bonds and hydrogen bonds, changing enzyme shape.
Different enzymes have different optimum pH values. Pepsin works best in acidic stomach conditions; many cytoplasmic enzymes work near neutral pH.
- Why does high fever affect enzymes?
- Why does pepsin work in stomach acid?
- What happens to enzyme shape at extreme pH?
Competitive and non-competitive inhibition
Competitive inhibitors bind to the active site. They often resemble the substrate. Increasing substrate concentration can reduce their effect because substrate competes more successfully.
Non-competitive inhibitors bind away from the active site. They alter enzyme shape or catalytic function. Increasing substrate concentration usually cannot fully overcome them.
Many drugs work by enzyme inhibition. Understanding inhibition helps medical students connect biochemistry with pharmacology.
- How can competitive inhibition be overcome?
- Where does a non-competitive inhibitor bind?
- Why are inhibitors useful as drugs?
Additional visual explanations
Additional original visual — Enzyme action and inhibition05-Cellular Respiration and Bioenergetics
Chapter visual — Cellular Respiration and BioenergeticsGlycolysis
Glycolysis occurs in the cytoplasm and does not require oxygen directly. One glucose molecule is split into two pyruvate molecules.
The energy investment phase uses ATP; the payoff phase produces ATP and NADH. The net yield per glucose is 2 ATP and 2 NADH.
No carbon dioxide is released in glycolysis. This is a common IMAT distractor because CO2 is released later during pyruvate oxidation and the Krebs cycle.
- Where does glycolysis occur?
- What is the net ATP yield?
- Is CO2 released in glycolysis?
Pyruvate oxidation
If oxygen is available, pyruvate enters the mitochondrion. It is converted into acetyl-CoA, producing CO2 and NADH.
This step links glycolysis to the Krebs cycle. It is not part of glycolysis and not technically part of the Krebs cycle.
Acetyl-CoA carries a two-carbon acetyl group into the Krebs cycle. Coenzyme A acts as a carrier.
- What molecule enters Krebs cycle?
- How many carbons are lost from pyruvate during oxidation?
- Which reduced coenzyme is produced?
Krebs cycle
The Krebs cycle occurs in the mitochondrial matrix. Each acetyl-CoA produces 3 NADH, 1 FADH2, 1 GTP/ATP and 2 CO2.
The cycle completes oxidation of the acetyl group. Most energy is not captured directly as ATP but as reduced coenzymes NADH and FADH2.
Because one glucose produces two acetyl-CoA molecules, the per-glucose Krebs yield is double the per-acetyl-CoA yield.
- State the yield per acetyl-CoA.
- Why is NADH important?
- How many turns per glucose?
Oxidative phosphorylation
The electron transport chain is located in the inner mitochondrial membrane. NADH and FADH2 donate electrons. Energy from electron transfer pumps protons into the intermembrane space.
The proton gradient stores potential energy. Protons flow back through ATP synthase, driving ATP production. This is chemiosmosis.
Oxygen is the final electron acceptor. Without oxygen, electron flow stops, NADH cannot be efficiently reoxidised, and ATP production by oxidative phosphorylation collapses.
- Why is oxygen essential?
- Where is ATP synthase located?
- What creates the proton gradient?
Fermentation
When oxygen is unavailable, cells may regenerate NAD+ by fermentation. In lactic fermentation, pyruvate is reduced to lactate. In alcoholic fermentation, pyruvate is converted to ethanol and CO2.
The main purpose of fermentation is not to produce large amounts of ATP; it allows glycolysis to continue by regenerating NAD+.
Human muscle can produce lactate during intense exercise when oxygen delivery is insufficient for full aerobic respiration.
- Why is NAD+ regeneration important?
- What is pyruvate reduced to in lactic fermentation?
- Does fermentation use the electron transport chain?
Additional visual explanations
Additional original visual — Krebs cycle yield
Additional original visual — Electron transport chain06-Photosynthesis and Plant Biology
Chapter visual — Photosynthesis and Plant BiologyChloroplast structure
Chloroplasts are plant and algal organelles surrounded by double membranes. Inside, thylakoid membranes form stacks called grana, surrounded by stroma.
Photosynthetic pigments such as chlorophyll are embedded in thylakoid membranes. This location allows light energy to drive electron transport.
Chloroplasts contain their own DNA and ribosomes, like mitochondria. This supports the endosymbiotic origin of these organelles.
- Where are thylakoids?
- What is stroma?
- Why do chloroplasts support endosymbiotic theory?
Light-dependent reactions
Light reactions occur in thylakoid membranes. Light excites electrons in photosystems. Water is split to replace lost electrons, releasing oxygen.
Electron transport produces a proton gradient across the thylakoid membrane. ATP synthase uses this gradient to produce ATP. Electrons ultimately reduce NADP+ to NADPH.
The key products are ATP, NADPH and O2. ATP and NADPH are then used by the Calvin cycle.
- Where is oxygen produced?
- What is NADPH used for?
- What drives ATP synthase in chloroplasts?
Calvin cycle
The Calvin cycle occurs in the stroma. It fixes carbon dioxide into organic molecules using ATP and NADPH from light reactions.
Rubisco catalyses CO2 fixation. The cycle produces triose phosphate molecules that can be used to make glucose and other carbohydrates.
The Calvin cycle does not directly require light, but it depends on ATP and NADPH produced by light reactions. Therefore it usually slows in darkness.
- Where does carbon fixation occur?
- What enzyme fixes CO2?
- Why does Calvin cycle depend on light reactions?
Plant transport and gas exchange
Plants exchange gases through stomata. Guard cells regulate stomatal opening and closing. Opening allows CO2 entry but also increases water loss.
Xylem transports water and minerals upward. Phloem transports sugars from sources such as leaves to sinks such as roots, fruits or growing tissues.
Transpiration creates tension that helps pull water upward through xylem. Cohesion between water molecules and adhesion to xylem walls support this movement.
- What do stomata regulate?
- Which tissue transports sugars?
- Why does transpiration help water movement?
07-DNA, RNA, Protein Synthesis and Gene Regulation
Chapter visual — DNA, RNA, Protein Synthesis and Gene RegulationDNA structure
DNA is a double helix with antiparallel strands. The sugar-phosphate backbone is on the outside, and nitrogenous bases pair inside.
Adenine pairs with thymine through two hydrogen bonds; cytosine pairs with guanine through three hydrogen bonds. Complementary pairing allows accurate replication and transcription.
DNA sequence stores information. A gene is a DNA sequence that contributes to a functional product, often a protein or functional RNA.
- What does antiparallel mean?
- Which base pairs with guanine?
- Why is complementary base pairing important?
DNA replication
DNA replication is semi-conservative: each daughter DNA molecule contains one parental strand and one newly synthesized strand.
Helicase separates strands. DNA polymerase adds nucleotides using a template. DNA ligase joins fragments on the lagging strand.
Replication occurs before cell division so that each daughter cell receives a complete genome.
- What does semi-conservative mean?
- What enzyme adds DNA nucleotides?
- What does ligase do in replication?
Transcription
Transcription produces RNA from a DNA template. RNA polymerase binds near a gene, separates DNA locally and synthesizes RNA complementary to the template strand.
In eukaryotes, pre-mRNA is processed by adding a cap, poly-A tail and removing introns through splicing. Mature mRNA then exits the nucleus.
RNA uses uracil instead of thymine. If DNA template has A, RNA gets U; if template has T, RNA gets A.
- Where does transcription occur in eukaryotes?
- What enzyme makes RNA?
- What is splicing?
Translation
Translation occurs at ribosomes. mRNA codons are read in groups of three. tRNA molecules carry amino acids and have anticodons complementary to mRNA codons.
The ribosome forms peptide bonds between amino acids. Translation begins at a start codon and ends at a stop codon.
A mutation can alter codons and therefore amino acid sequence. Silent mutations do not change amino acid; missense mutations change one amino acid; nonsense mutations create stop codons.
- Where is the codon?
- Where is the anticodon?
- What is a nonsense mutation?
Gene regulation
Cells do not express all genes all the time. Gene regulation allows cell specialisation and response to environment.
In prokaryotes, operons coordinate expression of functionally related genes. In eukaryotes, gene expression can be controlled through chromatin structure, transcription factors, RNA processing and translation control.
Medical relevance is high: cancer often involves abnormal gene regulation, and many diseases result from altered protein expression.
- What is an operon?
- Why do liver and nerve cells express different genes?
- How can gene regulation relate to cancer?
Additional visual explanations
Additional original visual — DNA base pairing
Additional original visual — Transcription vs translation
Additional original visual — Lac operon08-Cell Cycle, Mitosis, Meiosis and Reproduction
Chapter visual — Cell Cycle, Mitosis, Meiosis and ReproductionCell cycle overview
The cell cycle includes interphase and division. Interphase consists of G1, S and G2. During G1 the cell grows; during S DNA replicates; during G2 the cell prepares for division.
Checkpoints monitor cell size, DNA damage and spindle attachment. These checkpoints prevent damaged DNA from being passed on.
When checkpoint control fails, cells may divide uncontrollably. This is a major principle in cancer biology.
- When is DNA replicated?
- What does the G2 checkpoint check?
- Why are checkpoints medically important?
Mitosis
Mitosis divides the nucleus to produce two genetically identical daughter nuclei. It includes prophase, metaphase, anaphase and telophase.
In metaphase, chromosomes align at the cell equator. In anaphase, sister chromatids separate. Cytokinesis divides the cytoplasm.
Mitosis preserves chromosome number: diploid parent cells produce diploid daughter cells in humans.
- What separates in anaphase of mitosis?
- Does mitosis produce genetic variation?
- What is cytokinesis?
Meiosis
Meiosis produces gametes. It consists of two divisions after one round of DNA replication. Meiosis I separates homologous chromosomes; meiosis II separates sister chromatids.
Crossing over occurs in prophase I and exchanges DNA between homologous chromosomes. Independent assortment during metaphase I also increases variation.
Meiosis halves chromosome number, producing haploid cells. Fertilisation restores diploid number.
- What separates in meiosis I?
- When does crossing over occur?
- Why are gametes haploid?
Asexual and sexual reproduction
Asexual reproduction produces genetically identical or very similar offspring and is efficient in stable environments. Sexual reproduction produces genetic variation through meiosis and fertilisation.
Variation is important for evolution because natural selection requires heritable differences among individuals.
IMAT may connect meiosis with inheritance patterns and evolution, especially variation from crossing over and independent assortment.
- Why does sexual reproduction increase variation?
- What is the advantage of asexual reproduction?
- How does meiosis support evolution?
Additional visual explanations
Additional original visual — Chromosome, chromatid and homologous pair09-Mendelian Genetics, Human Genetics and Evolution
Chapter visual — Mendelian Genetics, Human Genetics and EvolutionAlleles, genotype and phenotype
A gene is a DNA sequence that affects a trait. An allele is an alternative form of a gene. Genotype is the allele combination; phenotype is the observable trait.
In simple dominance, one dominant allele is enough to express the dominant phenotype. A recessive phenotype appears only when both alleles are recessive.
Homozygous individuals have two identical alleles; heterozygous individuals have two different alleles.
- Define allele.
- Distinguish genotype and phenotype.
- What is a heterozygote?
Monohybrid crosses
Punnett squares show possible gamete combinations. In Aa × Aa, genotypes are AA, Aa, Aa and aa, giving a 1:2:1 genotype ratio.
If A is dominant, the phenotype ratio is 3 dominant to 1 recessive. For autosomal recessive disease, aa is affected and Aa is carrier.
Be careful with conditional probability. Among all children of two carriers, probability of unaffected carrier is 1/2. Among unaffected children only, probability of carrier is 2/3.
- Aa × Aa: probability of aa?
- Aa × Aa: probability of carrier among all children?
- Among unaffected children, probability of carrier?
Human inheritance
Autosomal dominant diseases can appear in every generation. Affected heterozygous individuals have a 1/2 chance of passing the disease allele to each child.
Autosomal recessive diseases may skip generations and often appear in children of unaffected carrier parents.
X-linked recessive disorders are more common in males because males have one X chromosome. A male with the mutant allele on his X chromosome expresses the trait.
- Why are X-linked recessive diseases more common in males?
- How can unaffected parents have an affected child?
- What pattern suggests autosomal dominant inheritance?
Evolution
Evolution is change in allele frequencies over generations. Mutation creates new alleles, recombination reshuffles alleles, and natural selection changes frequencies based on reproductive success.
Genetic drift is random change, especially strong in small populations. Gene flow occurs when migration moves alleles between populations.
Natural selection acts on phenotype but changes genotype frequencies over time.
- What does natural selection act on directly?
- How does mutation contribute to evolution?
- What is genetic drift?
Hardy-Weinberg equilibrium
The Hardy-Weinberg model predicts allele and genotype frequencies in a non-evolving population. It requires large population size, random mating, no mutation, no migration and no selection.
For two alleles, p + q = 1 and p² + 2pq + q² = 1. Here p and q are allele frequencies; p², 2pq and q² are genotype frequencies.
IMAT may use simple numbers, especially recessive disease frequency q². If q² is known, q is the square root, and p = 1 - q.
- What does q² represent?
- If recessive disease frequency is 1/100, what is q?
- List one condition for Hardy-Weinberg equilibrium.
Additional visual explanations
Additional original visual — Pedigree symbols
Additional original visual — Hardy-Weinberg visual10-Human Physiology for Future Medical Students
Chapter visual — Human Physiology for Future Medical StudentsHomeostasis and feedback
Homeostasis maintains internal conditions within narrow limits. Variables include blood glucose, temperature, water balance, blood pH and ion concentrations.
Negative feedback reverses change. If a variable rises, responses lower it; if it falls, responses raise it. This stabilises the internal environment.
Positive feedback amplifies change and is less common. Examples include blood clotting and oxytocin during childbirth.
- Why is negative feedback stabilising?
- Give one example of positive feedback.
- What variable is controlled in blood glucose homeostasis?
Insulin and glucagon
Insulin is released by pancreatic beta cells when blood glucose rises. It promotes glucose uptake in muscle and adipose tissue and glycogen synthesis in liver and muscle.
Glucagon is released by pancreatic alpha cells when blood glucose falls. It stimulates glycogen breakdown and gluconeogenesis in the liver.
Insulin and glucagon are antagonistic hormones. Their balance maintains blood glucose within a safe range.
- Which hormone lowers blood glucose?
- Which hormone promotes glycogen breakdown?
- Why is insulin not a steroid hormone?
Respiration and gas transport
Haemoglobin in red blood cells carries oxygen. Each haemoglobin molecule can bind oxygen reversibly. Oxygen loading occurs in lungs; oxygen unloading occurs in tissues.
The Bohr effect describes reduced haemoglobin oxygen affinity when CO2 is high and pH is lower. This helps active tissues receive oxygen.
Carbon dioxide is transported in blood mainly as bicarbonate ions, with smaller amounts bound to haemoglobin or dissolved in plasma.
- Why does active muscle receive more oxygen?
- What causes the Bohr effect?
- How is most CO2 transported?
Kidney and water balance
The nephron is the functional unit of the kidney. Filtration occurs in the glomerulus. Useful substances are reabsorbed in tubules; wastes are secreted or excreted.
ADH increases water reabsorption in the collecting duct by increasing water permeability. This produces more concentrated urine.
Kidneys also help regulate blood pressure, ion balance and pH.
- Where does filtration occur?
- What does ADH do?
- Why are kidneys important for pH balance?
Additional visual explanations
Additional original visual — Neuron structure
Additional original visual — Chemical synapse
Additional original visual — Blood components
Additional original visual — Heart circulation
Additional original visual — Nephron processes11-Immunology and Disease Biology
Chapter visual — Immunology and Disease BiologyInnate immunity
Innate immunity is immediate and non-specific. It includes skin, mucous membranes, stomach acid, inflammation, phagocytes, complement and natural killer cells.
Phagocytes engulf pathogens and digest them. Inflammation increases blood flow and vessel permeability, helping immune cells reach affected tissue.
Innate immunity recognises broad pathogen-associated patterns rather than unique antigens.
- Why is skin an immune barrier?
- What do phagocytes do?
- Why is innate immunity fast?
Adaptive immunity
Adaptive immunity is specific and slower on first exposure. It depends on lymphocytes. B cells can become plasma cells that secrete antibodies. T helper cells coordinate responses; cytotoxic T cells kill infected cells.
Antibodies bind specific antigens. They can neutralise toxins, block viral entry, promote phagocytosis or activate complement.
After infection or vaccination, memory cells remain. A second exposure produces a faster and stronger response.
- Which cells produce antibodies?
- What is immune memory?
- What do cytotoxic T cells kill?
Vaccination
Vaccines expose the immune system to antigens without causing severe disease. This generates memory B and T cells.
A vaccine is preventive rather than usually curative. It prepares the immune system for future infection.
Population-level vaccination can reduce transmission and protect vulnerable individuals through herd immunity.
- Why are booster doses sometimes needed?
- Why is a vaccine not the same as an antibiotic?
- What is herd immunity?
Pathogens and antibiotics
Bacteria are cellular prokaryotes. Viruses are acellular and require host cells for replication. Fungi and protozoa are eukaryotic pathogens.
Antibiotics target bacterial structures or processes, such as cell wall synthesis or bacterial ribosomes. They do not directly kill viruses.
Antibiotic resistance can evolve through mutation and selection. Misuse of antibiotics increases selection pressure for resistant strains.
- Why do antibiotics not treat viral infections directly?
- How can resistance evolve?
- What bacterial structure is often targeted by antibiotics?
12-Muscle, Skeleton and Movement
Chapter visual — Muscle, Skeleton and MovementSarcomere structure
A sarcomere is the functional contractile unit of skeletal muscle. It extends from one Z line to the next. Thin filaments are mostly actin; thick filaments are mostly myosin.
The A band corresponds to the length of thick filaments. The I band contains thin filaments only. The H zone contains thick filaments only.
During contraction, filaments slide past each other; they do not significantly shorten themselves.
- What are thin filaments made of?
- What are thick filaments made of?
- What happens to the sarcomere during contraction?
Sliding filament mechanism
An action potential leads to calcium release from the sarcoplasmic reticulum. Calcium binds troponin, causing tropomyosin to move away from myosin-binding sites on actin.
Myosin heads bind actin, perform a power stroke and pull thin filaments inward. ATP binding causes myosin to detach; ATP hydrolysis re-energises the myosin head.
Without ATP, myosin cannot detach properly. This explains rigor mortis after death when ATP production stops.
- What does calcium bind?
- What causes myosin detachment?
- Why is ATP needed for relaxation?
Bone tissue
Bone is living tissue. Osteoblasts build bone matrix; osteoclasts break it down. Balance between these cells remodels bone.
Collagen gives tensile strength and flexibility. Calcium phosphate minerals give hardness and compression resistance.
Bone also stores minerals and contains marrow, where blood cells are produced.
- Which cells build bone?
- Which protein gives tensile strength?
- Why is bone not simply a mineral?
Connective tissue and collagen
Collagen is an extracellular structural protein. It is abundant in tendons, ligaments, skin, bone and cartilage.
Collagen fibres resist stretching. This is different from actin and myosin, which are intracellular muscle proteins involved in contraction.
IMAT often tests collagen as extracellular, not intracellular, not nuclear and not part of thick muscle filaments.
- Where is collagen found?
- How is collagen different from myosin?
- Why is vitamin C deficiency linked to weak connective tissue?
13-Biotechnology and Recombinant DNA Technology
Chapter visual — Biotechnology and Recombinant DNA TechnologyRecombinant DNA
Recombinant DNA combines DNA from different sources. A human gene can be inserted into a bacterial plasmid and expressed in bacteria.
A plasmid is a small circular DNA molecule that can replicate independently in bacteria. It can act as a vector carrying a gene of interest.
Recombinant insulin production works because the genetic code is nearly universal, so bacteria can interpret human coding sequences after transcription and translation.
- What is a vector?
- Why are plasmids useful?
- Why can bacteria produce human insulin?
Restriction enzymes and ligase
Restriction enzymes cut DNA at specific recognition sequences. Some cuts create sticky ends, which can base-pair with complementary sticky ends.
DNA ligase joins DNA fragments by sealing the sugar-phosphate backbone. This produces stable recombinant DNA.
Using the same restriction enzyme on plasmid and target DNA can create compatible ends.
- What cuts DNA?
- What joins DNA?
- Why use the same restriction enzyme?
PCR
PCR amplifies a target DNA sequence. It requires DNA template, primers, thermostable DNA polymerase, free nucleotides and temperature cycling.
Denaturation separates DNA strands. Annealing allows primers to bind. Extension allows DNA polymerase to synthesize new DNA.
PCR copies DNA exponentially. It is used in genetic testing, infection detection, forensics and research.
- What happens during annealing?
- Why use thermostable polymerase?
- Does PCR require ribosomes?
Gel electrophoresis
Gel electrophoresis separates DNA fragments by size. DNA is negatively charged because of its phosphate backbone and moves toward the positive electrode.
Smaller fragments move farther through the gel because they pass more easily through pores. Larger fragments remain closer to wells.
Gel patterns can compare DNA samples, check PCR products or detect genetic differences.
- Which fragments travel farthest?
- Why does DNA move to positive electrode?
- What can gel electrophoresis compare?
Gene therapy and CRISPR
Gene therapy aims to treat disease by adding, replacing, silencing or editing genetic material. Somatic gene therapy affects body cells and is not inherited.
CRISPR-Cas9 uses guide RNA to target a DNA sequence and Cas9 nuclease to cut DNA. Repair mechanisms can then disrupt or alter the gene.
Germline editing affects gametes or embryos and raises major ethical concerns because changes may be inherited.
- What is somatic gene therapy?
- What does guide RNA do?
- Why is germline editing ethically sensitive?
14-Ecology, Ecosystems and Human Impact
Chapter visual — Ecology, Ecosystems and Human ImpactEcological organization
An individual organism belongs to a population. Different populations living together form a community. A community plus abiotic factors forms an ecosystem.
Abiotic factors include light, temperature, water, oxygen, salinity and soil composition. Biotic factors include predators, competitors, parasites and food sources.
IMAT may ask whether a community includes abiotic factors. It does not; an ecosystem does.
- Define population.
- Define community.
- Define ecosystem.
Food chains and trophic levels
Producers convert inorganic carbon into organic molecules, usually through photosynthesis. Primary consumers eat producers. Secondary consumers eat primary consumers. Decomposers recycle nutrients from dead material.
Food webs are more realistic than simple chains because organisms often eat multiple food sources.
Arrows in food chains show direction of energy transfer, from food to consumer.
- What is a primary consumer?
- What do arrows show?
- Why are food webs more realistic?
Energy flow
Energy enters most ecosystems as sunlight. Producers convert some light energy into chemical energy. Consumers obtain energy by eating other organisms.
At each transfer, much energy is lost as heat through respiration and metabolism. Therefore only a small fraction reaches the next trophic level.
This explains why food chains are limited in length and why top predators are relatively few.
- Why are top predators rare?
- Is energy recycled?
- Why is the energy pyramid upright?
Biogeochemical cycles
Matter is recycled. The carbon cycle includes photosynthesis, respiration, decomposition and combustion. Human fossil fuel combustion increases atmospheric CO2.
The nitrogen cycle includes nitrogen fixation, nitrification, assimilation and denitrification. Plants generally absorb nitrogen as nitrate or ammonium, not directly as atmospheric N2.
The water cycle includes evaporation, condensation, precipitation, runoff and transpiration.
- How do plants obtain nitrogen?
- Which process removes CO2?
- Which process returns nitrogen gas to atmosphere?
Population growth and carrying capacity
Exponential growth can occur when resources are abundant. Logistic growth occurs when growth slows as population approaches carrying capacity.
Carrying capacity is the maximum population size that an environment can support sustainably. It can change with resources, disease, climate and human activity.
Density-dependent factors become stronger as population density increases, such as competition, disease and predation.
- What is carrying capacity?
- What is a density-dependent factor?
- Why does logistic growth slow?
Human impact
Human activities affect ecosystems through habitat destruction, pollution, climate change, overharvesting and invasive species.
Eutrophication occurs when excess nitrates or phosphates enter water, causing algal blooms. Decomposition of dead algae consumes oxygen, creating hypoxic conditions.
Persistent toxins can bioaccumulate in organisms and biomagnify at higher trophic levels.
- What causes eutrophication?
- What is biomagnification?
- How can biodiversity loss affect humans?
Additional visual explanations
Additional original visual — Carbon and nitrogen cycle shortcuts15-Visual Appendix
Cell Cycle Checkpoints
Use this diagram to distinguish G1, S, G2 and M phase. IMAT questions often ask where DNA replication occurs or why checkpoint failure is relevant to cancer.Nephron Overview
Use this diagram to connect filtration, reabsorption, secretion and water balance. For IMAT, the nephron is most useful as a homeostasis example.16-Practice Questions
The following questions match the concise style of IMAT Biology while reinforcing the visual explanations in this book.
- Nucleus
- Ribosome
- DNA
- Cell membrane
- Cytoplasm
- two pyruvate molecules
- two acetyl-CoA molecules directly
- carbon dioxide and water only
- oxygen and glucose
- urea and ammonia
- mRNA
- tRNA
- DNA polymerase
- rRNA gene only
- a phospholipid
- active site
- mitochondrial matrix
- ribosome exit tunnel
- DNA promoter
- cell membrane cholesterol
- Golgi apparatus
- Lysosome
- Nucleolus
- Centriole
- Peroxisome
- lose water and shrink
- gain water and swell
- remain unchanged
- build a cell wall
- stop osmosis completely
- Mitosis
- Meiosis
- Binary fission in all eukaryotes
- DNA replication alone
- Transcription
- 3 NADH, 1 FADH2, 1 GTP and 2 CO2
- 1 NADH, 3 FADH2, 1 GTP and 2 CO2
- 2 NADH, 2 FADH2, 2 GTP and 1 CO2
- 4 ATP and no CO2
- 2 pyruvate molecules
- raises blood glucose
- stimulates glucose uptake in muscle and adipose tissue
- is secreted by the adrenal cortex
- is a steroid hormone
- breaks down haemoglobin
- three nucleotides
- three amino acids
- one fatty acid
- two phospholipids
- one enzyme active site
- ATP
- DNA
- Collagen
- Glycogen
- Cholesterol
- increases haemoglobin oxygen affinity
- reduces haemoglobin oxygen affinity
- prevents oxygen transport
- turns haemoglobin into myosin
- blocks capillaries
- cut DNA at specific sequences
- join amino acids
- copy proteins
- digest lipids
- make ATP
- a negative phosphate backbone
- a positive sugar backbone
- no charge
- only hydrophobic bases
- many peptide bonds
- Population
- Community
- Ecosystem
- Species
- Organ system
- Final electron acceptor
- Initial glucose donor
- Product of glycolysis
- Enzyme inhibitor
- Source of carbon dioxide
- 1/4
- 1/2
- 3/4
- 1/3
- 2/3
- stroma
- thylakoid membranes
- mitochondrial matrix
- nucleus
- Golgi apparatus
- DNA ligase
- helicase
- amylase
- ATP synthase
- pepsin
- energy is lost at each trophic transfer
- producers are always animals
- biomass always increases upward
- energy is recycled
- decomposers do not respire
17-Final Visual Revision Checklist
- ☐ Draw an animal cell and label nucleus, mitochondria, ER, Golgi, ribosomes and lysosomes.
- ☐ Draw the membrane and distinguish simple diffusion, facilitated diffusion and active transport.
- ☐ Trace glucose through glycolysis, pyruvate oxidation, Krebs cycle and oxidative phosphorylation.
- ☐ Explain why oxygen is the final electron acceptor.
- ☐ Draw DNA → mRNA → protein and distinguish codon from anticodon.
- ☐ Compare mitosis and meiosis without notes.
- ☐ Solve a simple Punnett square and identify carrier probability.
- ☐ Explain insulin and glucagon as a negative feedback system.
- ☐ Label actin, myosin, troponin and calcium in muscle contraction.
- ☐ Explain PCR, gel electrophoresis and recombinant DNA technology.
- ☐ Draw an energy pyramid and explain why energy is not recycled.