In PMDC MDCAT Biology (Transport & Immunity), trace the electrical conduction system of the human heart and distinguish between Active vs. Passive (Natural & Artificial) Immunity.

Cardiac conduction pathway: Sinoatrial (SA) node (pacemaker in upper wall of right atrium) -> Internodal pathways -> Atrioventricular (AV) node (0.15 sec delay allowing atrial contraction to finish before ventricular contraction) -> Bundle of His (AV bundle) -> Right & Left Bundle Branches -> Purkinje fibres in ventricular walls. Active Immunity: host's own B/T lymphocytes produce antibodies/memory cells in response to antigen—Natural Active (recovering from clinical infection) or Artificial Active (Vaccination). Passive Immunity: ready-made antibodies transferred to host (immediate, short-lived, no memory)—Natural Passive (IgG across placenta, IgA in colostrum/breast milk) or Artificial Passive (antivenom, anti-tetanus serum, rabies immunoglobulin).

In PMDC MDCAT Biology (Gaseous Exchange), state the percentage of Oxygen and Carbon Dioxide transported in each form in human blood, and list the factors that shift the Oxygen-Haemoglobin Dissociation Curve to the RIGHT (Bohr Effect).

Oxygen transport: ~97% as Oxyhaemoglobin (HbO2) in RBCs and ~3% dissolved in plasma. Carbon Dioxide transport: ~70% as Bicarbonate ions (HCO3⁻, catalyzed by Carbonic Anhydrase inside RBCs with the Chloride Shift / Hamburger phenomenon), ~20–23% as Carbaminohaemoglobin (bound to amino groups of globin), and ~5–7% dissolved in plasma. Factors shifting the Hb-O2 curve to the RIGHT (decreasing Hb affinity for O2 so more O2 is unloaded to active tissues): increased pCO2, decreased pH (increased H⁺), increased Temperature, and increased 2,3-BPG.

In PMDC MDCAT Biology (Respiration Volumes), define Tidal Volume (TV), Inspiratory Reserve Volume (IRV), Expiratory Reserve Volume (ERV), Residual Volume (RV), Vital Capacity (VC), and Total Lung Capacity (TLC) in a healthy adult.

Tidal Volume (TV): air inspired/expired during normal quiet breathing (~500 mL). Inspiratory Reserve Volume (IRV): extra air forcibly inspired above TV (~3,000 mL). Expiratory Reserve Volume (ERV): extra air forcibly expired after normal expiration (~1,100 mL). Residual Volume (RV): air remaining in lungs after maximal forced expiration (~1,200–1,500 mL, prevents lung collapse). Vital Capacity (VC = TV + IRV + ERV ≈ 4,600 mL). Total Lung Capacity (TLC = VC + RV ≈ 5,000–6,000 mL).

In PMDC MDCAT Biology (Support & Movement - Sliding Filament Model), describe the A-band, I-band, H-zone, Z-line, and M-line of a skeletal muscle Sarcomere, and state how each changes during muscle contraction.

A Sarcomere is the contractile unit between two successive Z-lines: I-band (isotropic, light band) contains ONLY thin (actin) filaments and is bisected by the Z-line; A-band (anisotropic, dark band) contains the entire length of thick (myosin) filaments plus overlapping actin; H-zone is the central lighter region of the A-band containing ONLY myosin (bisected by the M-line). During contraction (Huxley's Sliding Filament Model): the Sarcomere shortens, Z-lines move closer together, the I-band shortens, the H-zone narrows or disappears, while the length of the A-band remains CONSTANT!

In PMDC MDCAT Biology (Biological Molecules), why does water have a high Specific Heat Capacity and Heat of Vaporization, and what glycosidic linkages exist in Maltose, Sucrose, Lactose, Amylose, Amylopectin, Glycogen, and Cellulose?

Extensive intermolecular Hydrogen Bonding gives water high specific heat capacity (thermal stabilizer) and high heat of vaporization (574 kcal/kg, evaporative cooling). Linkages: Maltose (α-1,4 between two glucoses); Sucrose (α-1,2 between glucose and fructose—non-reducing sugar!); Lactose (β-1,4 between galactose and glucose); Amylose (unbranched α-1,4); Amylopectin & Glycogen (α-1,4 chains with α-1,6 branches—glycogen is more extensively branched and gives red colour with iodine); Cellulose (unbranched β-1,4 linkage—gives no colour with iodine).

In PMDC MDCAT Biology (Cell Organelles), compare Peroxisomes and Glyoxysomes, and state which storage diseases (Tay-Sachs and Glycogenosis Type II) result from congenital deficiency of Lysosomal enzymes.

Peroxisomes (in both plant and animal cells, abundant in liver): contain oxidative enzymes (catalase, peroxidase, glycolate oxidase) that form and decompose toxic H2O2 (involved in photorespiration). Glyoxysomes (present ONLY in lipid-rich plant seeds like castor bean and soya bean during germination): contain enzymes of the Glyoxylate Cycle that convert stored fatty acids into succinate/carbohydrates. Tay-Sachs disease results from absence of a lipid-digesting lysosomal enzyme (hexosaminidase A), causing toxic lipid accumulation in brain cells; Glycogenosis Type II (Pompe disease) fills liver and muscle cells with undigested glycogen.

In PMDC MDCAT Biology (Biodiversity / Acellular Life), classify Bacteriophages, HIV, Poliovirus, Influenza virus, and Hepatitis viruses (HAV, HBV, HCV) by genome type (DNA vs. RNA, single vs. double-stranded) and capsid symmetry.

Bacteriophages (T4): dsDNA, icosahedral head + helical tail (tadpole-shaped). HIV (Retrovirus): ssRNA enveloped (2 identical RNA strands + Reverse Transcriptase enzyme, spherical/conical capsid). Poliovirus: ssRNA non-enveloped, spherical/icosahedral. Influenza virus: enveloped segmented ssRNA. Hepatitis B (HBV): enveloped partially dsDNA virus; HAV & HEV: non-enveloped ssRNA (fecal-oral); HCV: enveloped ssRNA (parenteral/blood).

In PMDC MDCAT Biology (Muscle Contraction), what is the exact role of Calcium ions (Ca²⁺), Tropomyosin, Troponin, and ATP in skeletal muscle contraction and Rigor Mortis?

At rest, Tropomyosin blocks the myosin-binding sites on actin. When a nerve impulse arrives at the neuromuscular junction (releasing Acetylcholine), action potentials travel down T-tubules and trigger the Sarcoplasmic Reticulum to release Ca²⁺ ions into the sarcoplasm. Ca²⁺ binds to the Troponin complex (Troponin-C), displacing Tropomyosin and exposing the binding sites on actin so Myosin heads can form cross-bridges and perform the power stroke. ATP binding is required to DETACH the myosin head from actin and cock it back; after death, ATP depletion prevents cross-bridge detachment, causing Rigor Mortis.

In PMDC MDCAT Biology (Plant Water Potential), write the equation relating Water Potential (Ψ_w), Solute Potential (Ψ_s), and Pressure Potential (Ψ_p), and state the water potential of pure water at atmospheric pressure.

Ψ_w = Ψ_s + Ψ_p. Pure water at standard atmospheric pressure has a Water Potential (Ψ_w) of ZERO (0 kPa/MPa)—the maximum possible value. Adding solutes always lowers water potential, so Solute Potential (Ψ_s, osmotic potential) is ALWAYS NEGATIVE, while Pressure Potential (Ψ_p, turgor pressure) in turgid plant cells is POSITIVE. Water always moves by osmosis from HIGHER (less negative) water potential to LOWER (more negative) water potential.

In PMDC MDCAT Biology (Evolution & Hardy-Weinberg Equilibrium), state the Hardy-Weinberg equations and the 5 conditions that must be met for allele frequencies to remain constant.

Allele frequency equation: p + q = 1; Genotype frequency equation: p² + 2pq + q² = 1 (where p² = homozygous dominant, 2pq = heterozygous carriers, q² = homozygous recessive). Five conditions for no evolution (Hardy-Weinberg equilibrium): 1. Infinitely large population size (no genetic drift), 2. Random mating, 3. No mutation, 4. No migration (no gene flow), and 5. No natural selection.

In PMDC MDCAT Biology (Immunity & Antibodies), describe the polypeptide structure of an Immunoglobulin (Antibody) molecule and list the 5 classes of human antibodies with their functions.

An antibody (Ig) consists of 4 polypeptide chains linked by disulfide bridges in a Y-shape: 2 identical Heavy (H) chains and 2 identical Light (L) chains, each having a Constant (C) region and a Variable (V) antigen-binding site (paratope). Five classes (GAMED): IgG (most abundant ~75–80%, only class that crosses the human placenta), IgA (secretory dimer in breast milk, saliva, tears, gut/respiratory mucus), IgM (pentamer—first antibody produced in primary immune response), IgE (binds mast cells & basophils, mediates Type I allergic/anaphylactic reactions and anti-parasitic defense), and IgD (B-cell surface receptor).

In PMDC MDCAT Biology (Variation & Genetics), what are the modified Mendelian F2 phenotypic ratios for Incomplete Dominance, Epistasis (Bombay Phenotype), and X-Linked Recessive Haemophilia?

Incomplete Dominance (e.g., 4 o'clock plant Mirabilis jalapa): both genotypic and phenotypic F2 ratios are 1:2:1 (1 Red : 2 Pink : 1 White). Bombay Phenotype (recessive epistasis where hh masks IA/IB expression because H substance precursor is absent): phenotypic ratio is modified from 9:3:3:1. Haemophilia A (Factor VIII deficiency) and B (Factor IX deficiency) are X-linked recessive, whereas Haemophilia C (Factor XI deficiency) is autosomal.

In PMDC MDCAT Biology (Evolution), distinguish between Homologous Organs (Divergent Evolution) and Analogous Organs (Convergent Evolution) with textbook examples.

Homologous organs have the SAME fundamental anatomical structure and embryonic origin but perform DIFFERENT functions due to adaptation to different habitats (Divergent Evolution)—e.g., the pentadactyl forelimbs of a human, bat wing, whale flipper, horse leg, and mole paw. Analogous organs have DIFFERENT anatomical structures and embryonic origins but perform the SAME function (Convergent Evolution)—e.g., wings of insects/butterflies vs. wings of birds/bats.

In PMDC MDCAT Biology (C4 Photosynthesis / Kranz Anatomy), how do C4 plants (sugarcane, maize, sorghum) minimize Photorespiration in hot, dry climates?

C4 leaves exhibit Kranz Anatomy (spatial separation between outer Mesophyll cells and inner Bundle-Sheath cells surrounding vascular bundles). In Mesophyll cells, PEP Carboxylase (which has high affinity for CO2/HCO3⁻ and NO affinity for O2) fixes CO2 into 4-carbon Oxaloacetate -> Malate. Malate is pumped into Bundle-Sheath cells where it is decarboxylated to release a high concentration of CO2 directly around RuBisCO for the Calvin Cycle, preventing RuBisCO from binding O2 (photorespiration).

In PMDC MDCAT Biology (Cell Structure & Function), distinguish between 70S Prokaryotic Ribosomes and 80S Eukaryotic Ribosomes, and state which ion controls the attachment of the two ribosomal subunits.

70S ribosomes (found in prokaryotes, mitochondria, and chloroplasts) consist of a 50S large subunit and a 30S small subunit. 80S ribosomes (eukaryotic cytoplasm/RER) consist of a 60S large subunit and a 40S small subunit. Magnesium ions (Mg²⁺) control the attachment of the two ribosomal subunits during translation.

In PMDC MDCAT Biology (Excretion & Thermoregulation in Animals), compare Ammonotelic, Ureotelic, and Uricotelic nitrogenous waste excretion in terms of toxicity and water requirement per gram of nitrogen removed.

1. Ammonia (Ammonotelic—bony fishes, aquatic invertebrates): highly toxic, requires ~500 mL of water to excrete 1 g of nitrogen. 2. Urea (Ureotelic—mammals, adult amphibians, sharks/cartilaginous fishes, synthesized in the liver via the Ornithine/Urea Cycle where Citrulline + Aspartate -> Argininosuccinate -> Arginine -> Urea + Ornithine): moderately toxic, requires ~50 mL of water per 1 g of nitrogen. 3. Uric Acid (Uricotelic—birds, reptiles, insects, land snails): least toxic, requires only ~1 mL of water per 1 g of nitrogen.

In PMDC MDCAT Biology (Cartilage & Bone Cells), compare Hyaline, Elastic, and Fibrocartilage, and state the functions of Osteoblasts, Osteocytes, and Osteoclasts.

Cartilage is avascular (no blood vessels penetrate it; nourished by diffusion) and contains chondrocytes in lacunae: Hyaline cartilage (most abundant—articular surfaces of movable joints, trachea, larynx, epiphyseal plates, nose), Elastic cartilage (epiglottis, external ear pinna), Fibrocartilage (strongest—intervertebral discs, pubic symphysis). Bone cells: Osteoblasts (bone-forming cells that synthesize collagen matrix), Osteocytes (mature bone cells trapped in lacunae), and Osteoclasts (multinucleated giant bone-resorbing/dissolving cells derived from monocytes).

In PMDC MDCAT Biology (Human Digestive Hormones), compare the site of secretion, stimulus, and physiological action of Gastrin, Secretin, and Cholecystokinin (CCK).

Gastrin (secreted by pyloric mucosa G-cells in response to protein/peptides in stomach): stimulates parietal and chief cells to secrete gastric juice. Secretin (first hormone discovered by Bayliss & Starling; secreted by duodenal S-cells in response to acidic chyme): stimulates the pancreas to secrete watery Bicarbonate-rich (NaHCO3) pancreatic juice and stimulates hepatic bile production while inhibiting gastric secretion. Cholecystokinin / CCK (secreted by duodenal I-cells in response to fatty acids and amino acids): stimulates contraction of the gallbladder to release bile and stimulates pancreatic acinar cells to secrete enzyme-rich pancreatic juice.

In PMDC MDCAT Biology (Digestive System), match the gastric mucosal cells of the human stomach (Mucous, Parietal/Oxyntic, Chief/Zymogen, and G-cells) to their secretions and functions.

1. Mucous (Goblet) cells: secrete thick alkaline mucus to protect the stomach wall from autodigestion. 2. Parietal (Oxyntic) cells: secrete concentrated Hydrochloric Acid (HCl—adjusts pH to 1.5–2.5, kills microbes, and activates pepsinogen to pepsin) AND Intrinsic Factor (essential for Vitamin B12 absorption in the ileum). 3. Chief (Zymogen) cells: secrete inactive enzyme precursor Pepsinogen. 4. Endocrine G-cells (in pyloric antrum): secrete the hormone Gastrin into the bloodstream to stimulate further gastric juice secretion.

In PMDC MDCAT Biology (Bioenergetics - Photosynthesis), compare Non-Cyclic Photophosphorylation (Z-Scheme) with Cyclic Photophosphorylation, and identify the primary CO2 acceptor and first stable product of the Calvin Cycle (C3).

Non-Cyclic Photophosphorylation involves BOTH Photosystem II (P680) and Photosystem I (P700), photolysis of water, evolution of O2, and generation of BOTH ATP and NADPH. Cyclic Photophosphorylation involves ONLY Photosystem I (P700) when NADP⁺ is scarce or ATP demand is high—producing ONLY ATP (no NADPH and no O2 released). In the Calvin Cycle, the 5-carbon primary CO2 acceptor is RuBP (Ribulose-1,5-bisphosphate, catalyzed by RuBisCO), and the first stable 3-carbon product is 3-PGA (3-Phosphoglycerate).

In PMDC MDCAT Biology (Proteins & Nucleic Acids), how many polypeptide chains and amino acids are present in Human Insulin and Haemoglobin, and what is the difference between a Nucleoside and a Nucleotide?

Human Insulin (sequenced by Frederick Sanger): 51 amino acids in 2 chains—Alpha chain (21 amino acids) and Beta chain (30 amino acids) linked by disulfide bridges. Adult Haemoglobin (HbA): 574 amino acids in 4 chains—2 Alpha chains (141 amino acids each = 282) and 2 Beta chains (146 amino acids each = 292). A Nucleoside = Nitrogenous Base + Pentose Sugar; a Nucleotide = Nucleoside + Phosphate group(s) esterified at the 5' carbon.

In PMDC MDCAT Biology (Plant Photoperiodism & Vernalization), distinguish between Short-Day Plants (Long-Night Plants), Long-Day Plants (Short-Night Plants), and the role of Phytochrome (P_r vs. P_fr).

Flowering is controlled primarily by the length of uninterrupted DARKNESS (critical night length): Short-Day / Long-Night Plants (e.g., tobacco, soybean, cocklebur, chrysanthemum) flower when uninterrupted darkness EXCEEDS a critical length. Long-Day / Short-Night Plants (e.g., wheat, radish, spinach, cabbage, henbane) flower when darkness is SHORTER than a critical length. Phytochrome exists in two interconvertible forms: P_r (absorbs red light at 660 nm -> converts to biologically active P_fr) and P_fr (absorbs far-red light at 730 nm or slowly reverts to P_r in darkness). Vernalization is the promotion of flowering by exposure to low-temperature chilling.

In PMDC MDCAT Biology (Enzymes), compare the Lock-and-Key Model (Emil Fischer, 1890) with the Induced-Fit Model (Daniel Koshland, 1959), and contrast Competitive vs. Non-Competitive Enzyme Inhibition.

Lock-and-Key: active site is a rigid, pre-shaped structure admitting only a specific substrate without conformational change. Induced-Fit: active site is flexible and moulds itself around the substrate upon binding to achieve catalytic conformation. Competitive Inhibition (e.g., Malonate inhibiting Succinate dehydrogenase): inhibitor resembles substrate and competes for the ACTIVE SITE—can be overcome by increasing substrate concentration (V_max unchanged, K_m increases). Non-Competitive Inhibition (e.g., Cyanide on Cytochrome oxidase, heavy metals): binds to an ALLOSTERIC site, altering active site shape—cannot be overcome by adding extra substrate (V_max decreases).

In PMDC MDCAT Biology (Endocrine Glands), distinguish the hormones of the Anterior Pituitary (Adenohypophysis) from the Posterior Pituitary (Neurohypophysis).

Anterior Pituitary synthesizes and secretes 6 tropic/direct hormones: Somatotropin (GH/STH), Thyroid-Stimulating Hormone (TSH), Adrenocorticotropic Hormone (ACTH), Follicle-Stimulating Hormone (FSH), Luteinizing Hormone (LH / ICSH in males), and Prolactin (LTH). Median Lobe secretes MSH (Melanocyte-Stimulating Hormone). Posterior Pituitary does NOT synthesize hormones—it stores and releases 2 neurohormones synthesized in the Hypothalamus: Antidiuretic Hormone (ADH / Vasopressin) and Oxytocin.

In PMDC MDCAT Biology (Human Brain Divisions), classify the structures of the Forebrain (Prosencephalon), Midbrain (Mesencephalon), and Hindbrain (Rhombencephalon), and state the role of the Limbic System (Hippocampus & Amygdala).

Forebrain: Telencephalon (Cerebrum & Limbic system) + Diencephalon (Thalamus—sensory relay station except smell; Hypothalamus—thermoregulation, osmoregulation, hunger/thirst, sleep-wake, pituitary control). Limbic System: Amygdala controls rage, fear, pleasure, and emotional responses; Hippocampus converts short-term memory into long-term memory. Midbrain: reticular formation (screens sensory input) and auditory/visual reflex integration. Hindbrain: Pons (controls rate/pattern of breathing and sleep-wake transition), Cerebellum (precise motor coordination and posture), and Medulla Oblongata (autonomic vital centers: heartbeat, breathing, BP, swallowing, vomiting).

In PMDC MDCAT Biology (Coordination & Control - Nerve Impulse), state the Resting Membrane Potential (RMP) vs. Action Potential Spike values of a neuron, and how the Na⁺/K⁺ Pump maintains the resting gradient.

Resting Membrane Potential (polarized state): -70 mV (inside of axon is negative relative to outside; K⁺ is 30× higher inside, Na⁺ is 10× higher outside, maintained by the ATP-driven Na⁺/K⁺ pump which pumps 3 Na⁺ OUT for every 2 K⁺ pumped IN). Depolarization (Action Potential): threshold stimulus opens voltage-gated Na⁺ channels -> rapid Na⁺ influx reverses potential to +50 mV (or +30 to +50 mV). Repolarization: Na⁺ channels close and voltage-gated K⁺ channels open -> K⁺ efflux restores negative inside potential (briefly hyperpolarizing to -75/-90 mV).

In PMDC MDCAT Biology (Syllabus Weightage & Structure), how many total MCQs are on the PMDC MDCAT exam, what is Biology's percentage weightage, and is there negative marking?

The PMDC MDCAT consists of 200 MCQs completed in 3.5 hours (210 minutes) with NO negative marking: Biology has the highest weightage at 34% (68 MCQs), Chemistry 27% (54 MCQs), Physics 27% (54 MCQs), English 9% (18 MCQs), and Logical Reasoning 3% (6 MCQs).

In PMDC MDCAT Biology (Human Reproduction & STIs), compare Spermatogenesis and Oogenesis in humans, and match the causative organisms of Gonorrhoea, Syphilis, Genital Herpes, and AIDS.

Spermatogenesis is continuous from puberty onward in the seminiferous tubules (stimulated by FSH on Sertoli cells and LH/ICSH on Leydig cells to secrete testosterone), yielding 4 motile haploid spermatozoa per primary spermatocyte. Oogenesis begins before birth (arrested in Prophase I as primary oocytes), resumes at puberty, and yields ONLY 1 large functional haploid ovum plus polar bodies per primary oocyte (arrested at Metaphase II until fertilization). STIs: Gonorrhoea = Neisseria gonorrhoeae (Gram-negative diplococcus); Syphilis = Treponema pallidum (spirochete); Genital Herpes = HSV Type 2 (DNA virus); AIDS = HIV (retrovirus).

In PMDC MDCAT Biology (Gene Linkage & Crossing Over), how is Recombination Frequency calculated, and how does it relate to Map Distance on a chromosome?

Recombination Frequency (RF) = (Number of Recombinant Offspring ÷ Total Number of Offspring) × 100%. One percent (1%) recombination frequency equals 1 Map Unit (1 centiMorgan, cM) of distance between two linked genes on the same chromosome. Because independent assortment produces a maximum of 50% recombinants, the maximum recombination frequency between any two genes is 50%.

In PMDC MDCAT Biology (Biotechnology & PCR), what are the three thermal steps of Each Cycle of the Polymerase Chain Reaction (PCR, invented by Kary Mullis), and why is Taq Polymerase used?

1. Denaturation (94°C–95°C for ~1 min): heat breaks hydrogen bonds to separate dsDNA into single strands. 2. Primer Annealing / Renaturation (50°C–60°C for ~1–2 min): forward and reverse DNA primers bind to complementary 3' flanking sequences. 3. Extension / Polymerization (72°C for ~1.5 min): Taq DNA polymerase (isolated from the thermophilic bacterium Thermus aquaticus, which is heat-stable and does not denature at 95°C) synthesizes new complementary DNA strands in the 5' -> 3' direction.

In PMDC MDCAT Biology (Bioenergetics - Cellular Respiration), trace the exact cellular locations and net yields of ATP, NADH, FADH2, and CO2 across Glycolysis, Pyruvate Oxidation (Link Reaction), and the Krebs Cycle per molecule of Glucose.

Per 1 Glucose (C6): 1. Glycolysis (in cytosol): 2 ATP net (4 formed - 2 used) + 2 NADH (0 CO2). 2. Pyruvate Oxidation / Link Reaction (in mitochondrial matrix, for 2 pyruvates): 2 NADH + 2 CO2 (forming 2 Acetyl-CoA). 3. Krebs / Citric Acid Cycle (in mitochondrial matrix, 2 turns): 2 ATP (GTP) + 6 NADH + 2 FADH2 + 4 CO2. Total before ETC: 4 ATP (substrate-level), 10 NADH, 2 FADH2, and 6 CO2.

In PMDC MDCAT Biology (Prokaryotes / Bacteria), classify bacteria based on Flagellar Arrangement (Atrichous, Monotrichous, Lophotrichous, Amphitrichous, Peritrichous) and Gram Staining cell wall composition.

Flagellar types: Atrichous (no flagella), Monotrichous (single polar flagellum), Lophotrichous (tuft of flagella at one pole), Amphitrichous (flagellum/tuft at both poles), Peritrichous (flagella surrounding the entire cell surface, e.g., E. coli, Salmonella). Gram-Positive bacteria: thick peptidoglycan layer (50% of dry weight), teichoic and lipoteichoic acids, no outer lipid membrane, minimal periplasmic space (stain purple/violet). Gram-Negative bacteria: thin peptidoglycan layer (10%), thick outer lipopolysaccharide/lipoprotein membrane with porins, periplasmic space present (stain pink/red with safranin).

Pakistan PMDC MDCAT Biology: Bioenergetics, Biological Molecules, Enzymes, Cell Structure, Coordination, Reproduction, Variation & Genetics

Covers the official PMDC National MDCAT Biology syllabus (FSc Pre-Medical Part 1 & 2 across Punjab, Federal, Sindh, KPK & Balochistan boards): Biodiversity/Viruses, Bioenergetics, Biological Molecules, Cell Structure, Coordination & Control, Enzymes, Evolution, Reproduction, Support & Movement, Immunity, and Variation & Genetics.

Level: basic
Languages: en → en
Cards: 32
Markdown: Pakistan PMDC MDCAT Biology: Bioenergetics, Biological Molecules, Enzymes, Cell Structure, Coordination, Reproduction, Variation & Genetics (.md)

Flashcards (32)

#	Front (Term / Question)	Back (Definition / Answer)
1	In PMDC MDCAT Biology (Transport & Immunity), trace the electrical conduction system of the human heart and distinguish between Active vs. Passive (Natural & Artificial) Immunity.	Cardiac conduction pathway: Sinoatrial (SA) node (pacemaker in upper wall of right atrium) -> Internodal pathways -> Atrioventricular (AV) node (0.15 sec delay allowing atrial contraction to finish before ventricular contraction) -> Bundle of His (AV bundle) -> Right & Left Bundle Branches -> Purkinje fibres in ventricular walls. Active Immunity: host's own B/T lymphocytes produce antibodies/memory cells in response to antigen—Natural Active (recovering from clinical infection) or Artificial Active (Vaccination). Passive Immunity: ready-made antibodies transferred to host (immediate, short-lived, no memory)—Natural Passive (IgG across placenta, IgA in colostrum/breast milk) or Artificial Passive (antivenom, anti-tetanus serum, rabies immunoglobulin).
2	In PMDC MDCAT Biology (Gaseous Exchange), state the percentage of Oxygen and Carbon Dioxide transported in each form in human blood, and list the factors that shift the Oxygen-Haemoglobin Dissociation Curve to the RIGHT (Bohr Effect).	Oxygen transport: ~97% as Oxyhaemoglobin (HbO2) in RBCs and ~3% dissolved in plasma. Carbon Dioxide transport: ~70% as Bicarbonate ions (HCO3⁻, catalyzed by Carbonic Anhydrase inside RBCs with the Chloride Shift / Hamburger phenomenon), ~20–23% as Carbaminohaemoglobin (bound to amino groups of globin), and ~5–7% dissolved in plasma. Factors shifting the Hb-O2 curve to the RIGHT (decreasing Hb affinity for O2 so more O2 is unloaded to active tissues): increased pCO2, decreased pH (increased H⁺), increased Temperature, and increased 2,3-BPG.
3	In PMDC MDCAT Biology (Respiration Volumes), define Tidal Volume (TV), Inspiratory Reserve Volume (IRV), Expiratory Reserve Volume (ERV), Residual Volume (RV), Vital Capacity (VC), and Total Lung Capacity (TLC) in a healthy adult.	Tidal Volume (TV): air inspired/expired during normal quiet breathing (~500 mL). Inspiratory Reserve Volume (IRV): extra air forcibly inspired above TV (~3,000 mL). Expiratory Reserve Volume (ERV): extra air forcibly expired after normal expiration (~1,100 mL). Residual Volume (RV): air remaining in lungs after maximal forced expiration (~1,200–1,500 mL, prevents lung collapse). Vital Capacity (VC = TV + IRV + ERV ≈ 4,600 mL). Total Lung Capacity (TLC = VC + RV ≈ 5,000–6,000 mL).
4	In PMDC MDCAT Biology (Support & Movement - Sliding Filament Model), describe the A-band, I-band, H-zone, Z-line, and M-line of a skeletal muscle Sarcomere, and state how each changes during muscle contraction.	A Sarcomere is the contractile unit between two successive Z-lines: I-band (isotropic, light band) contains ONLY thin (actin) filaments and is bisected by the Z-line; A-band (anisotropic, dark band) contains the entire length of thick (myosin) filaments plus overlapping actin; H-zone is the central lighter region of the A-band containing ONLY myosin (bisected by the M-line). During contraction (Huxley's Sliding Filament Model): the Sarcomere shortens, Z-lines move closer together, the I-band shortens, the H-zone narrows or disappears, while the length of the A-band remains CONSTANT!
5	In PMDC MDCAT Biology (Biological Molecules), why does water have a high Specific Heat Capacity and Heat of Vaporization, and what glycosidic linkages exist in Maltose, Sucrose, Lactose, Amylose, Amylopectin, Glycogen, and Cellulose?	Extensive intermolecular Hydrogen Bonding gives water high specific heat capacity (thermal stabilizer) and high heat of vaporization (574 kcal/kg, evaporative cooling). Linkages: Maltose (α-1,4 between two glucoses); Sucrose (α-1,2 between glucose and fructose—non-reducing sugar!); Lactose (β-1,4 between galactose and glucose); Amylose (unbranched α-1,4); Amylopectin & Glycogen (α-1,4 chains with α-1,6 branches—glycogen is more extensively branched and gives red colour with iodine); Cellulose (unbranched β-1,4 linkage—gives no colour with iodine).
6	In PMDC MDCAT Biology (Cell Organelles), compare Peroxisomes and Glyoxysomes, and state which storage diseases (Tay-Sachs and Glycogenosis Type II) result from congenital deficiency of Lysosomal enzymes.	Peroxisomes (in both plant and animal cells, abundant in liver): contain oxidative enzymes (catalase, peroxidase, glycolate oxidase) that form and decompose toxic H2O2 (involved in photorespiration). Glyoxysomes (present ONLY in lipid-rich plant seeds like castor bean and soya bean during germination): contain enzymes of the Glyoxylate Cycle that convert stored fatty acids into succinate/carbohydrates. Tay-Sachs disease results from absence of a lipid-digesting lysosomal enzyme (hexosaminidase A), causing toxic lipid accumulation in brain cells; Glycogenosis Type II (Pompe disease) fills liver and muscle cells with undigested glycogen.
7	In PMDC MDCAT Biology (Biodiversity / Acellular Life), classify Bacteriophages, HIV, Poliovirus, Influenza virus, and Hepatitis viruses (HAV, HBV, HCV) by genome type (DNA vs. RNA, single vs. double-stranded) and capsid symmetry.	Bacteriophages (T4): dsDNA, icosahedral head + helical tail (tadpole-shaped). HIV (Retrovirus): ssRNA enveloped (2 identical RNA strands + Reverse Transcriptase enzyme, spherical/conical capsid). Poliovirus: ssRNA non-enveloped, spherical/icosahedral. Influenza virus: enveloped segmented ssRNA. Hepatitis B (HBV): enveloped partially dsDNA virus; HAV & HEV: non-enveloped ssRNA (fecal-oral); HCV: enveloped ssRNA (parenteral/blood).
8	In PMDC MDCAT Biology (Muscle Contraction), what is the exact role of Calcium ions (Ca²⁺), Tropomyosin, Troponin, and ATP in skeletal muscle contraction and Rigor Mortis?	At rest, Tropomyosin blocks the myosin-binding sites on actin. When a nerve impulse arrives at the neuromuscular junction (releasing Acetylcholine), action potentials travel down T-tubules and trigger the Sarcoplasmic Reticulum to release Ca²⁺ ions into the sarcoplasm. Ca²⁺ binds to the Troponin complex (Troponin-C), displacing Tropomyosin and exposing the binding sites on actin so Myosin heads can form cross-bridges and perform the power stroke. ATP binding is required to DETACH the myosin head from actin and cock it back; after death, ATP depletion prevents cross-bridge detachment, causing Rigor Mortis.
9	In PMDC MDCAT Biology (Plant Water Potential), write the equation relating Water Potential (Ψ_w), Solute Potential (Ψ_s), and Pressure Potential (Ψ_p), and state the water potential of pure water at atmospheric pressure.	Ψ_w = Ψ_s + Ψ_p. Pure water at standard atmospheric pressure has a Water Potential (Ψ_w) of ZERO (0 kPa/MPa)—the maximum possible value. Adding solutes always lowers water potential, so Solute Potential (Ψ_s, osmotic potential) is ALWAYS NEGATIVE, while Pressure Potential (Ψ_p, turgor pressure) in turgid plant cells is POSITIVE. Water always moves by osmosis from HIGHER (less negative) water potential to LOWER (more negative) water potential.
10	In PMDC MDCAT Biology (Evolution & Hardy-Weinberg Equilibrium), state the Hardy-Weinberg equations and the 5 conditions that must be met for allele frequencies to remain constant.	Allele frequency equation: p + q = 1; Genotype frequency equation: p² + 2pq + q² = 1 (where p² = homozygous dominant, 2pq = heterozygous carriers, q² = homozygous recessive). Five conditions for no evolution (Hardy-Weinberg equilibrium): 1. Infinitely large population size (no genetic drift), 2. Random mating, 3. No mutation, 4. No migration (no gene flow), and 5. No natural selection.
11	In PMDC MDCAT Biology (Immunity & Antibodies), describe the polypeptide structure of an Immunoglobulin (Antibody) molecule and list the 5 classes of human antibodies with their functions.	An antibody (Ig) consists of 4 polypeptide chains linked by disulfide bridges in a Y-shape: 2 identical Heavy (H) chains and 2 identical Light (L) chains, each having a Constant (C) region and a Variable (V) antigen-binding site (paratope). Five classes (GAMED): IgG (most abundant ~75–80%, only class that crosses the human placenta), IgA (secretory dimer in breast milk, saliva, tears, gut/respiratory mucus), IgM (pentamer—first antibody produced in primary immune response), IgE (binds mast cells & basophils, mediates Type I allergic/anaphylactic reactions and anti-parasitic defense), and IgD (B-cell surface receptor).
12	In PMDC MDCAT Biology (Variation & Genetics), what are the modified Mendelian F2 phenotypic ratios for Incomplete Dominance, Epistasis (Bombay Phenotype), and X-Linked Recessive Haemophilia?	Incomplete Dominance (e.g., 4 o'clock plant Mirabilis jalapa): both genotypic and phenotypic F2 ratios are 1:2:1 (1 Red : 2 Pink : 1 White). Bombay Phenotype (recessive epistasis where hh masks IA/IB expression because H substance precursor is absent): phenotypic ratio is modified from 9:3:3:1. Haemophilia A (Factor VIII deficiency) and B (Factor IX deficiency) are X-linked recessive, whereas Haemophilia C (Factor XI deficiency) is autosomal.
13	In PMDC MDCAT Biology (Evolution), distinguish between Homologous Organs (Divergent Evolution) and Analogous Organs (Convergent Evolution) with textbook examples.	Homologous organs have the SAME fundamental anatomical structure and embryonic origin but perform DIFFERENT functions due to adaptation to different habitats (Divergent Evolution)—e.g., the pentadactyl forelimbs of a human, bat wing, whale flipper, horse leg, and mole paw. Analogous organs have DIFFERENT anatomical structures and embryonic origins but perform the SAME function (Convergent Evolution)—e.g., wings of insects/butterflies vs. wings of birds/bats.
14	In PMDC MDCAT Biology (C4 Photosynthesis / Kranz Anatomy), how do C4 plants (sugarcane, maize, sorghum) minimize Photorespiration in hot, dry climates?	C4 leaves exhibit Kranz Anatomy (spatial separation between outer Mesophyll cells and inner Bundle-Sheath cells surrounding vascular bundles). In Mesophyll cells, PEP Carboxylase (which has high affinity for CO2/HCO3⁻ and NO affinity for O2) fixes CO2 into 4-carbon Oxaloacetate -> Malate. Malate is pumped into Bundle-Sheath cells where it is decarboxylated to release a high concentration of CO2 directly around RuBisCO for the Calvin Cycle, preventing RuBisCO from binding O2 (photorespiration).
15	In PMDC MDCAT Biology (Cell Structure & Function), distinguish between 70S Prokaryotic Ribosomes and 80S Eukaryotic Ribosomes, and state which ion controls the attachment of the two ribosomal subunits.	70S ribosomes (found in prokaryotes, mitochondria, and chloroplasts) consist of a 50S large subunit and a 30S small subunit. 80S ribosomes (eukaryotic cytoplasm/RER) consist of a 60S large subunit and a 40S small subunit. Magnesium ions (Mg²⁺) control the attachment of the two ribosomal subunits during translation.
16	In PMDC MDCAT Biology (Excretion & Thermoregulation in Animals), compare Ammonotelic, Ureotelic, and Uricotelic nitrogenous waste excretion in terms of toxicity and water requirement per gram of nitrogen removed.	1. Ammonia (Ammonotelic—bony fishes, aquatic invertebrates): highly toxic, requires ~500 mL of water to excrete 1 g of nitrogen. 2. Urea (Ureotelic—mammals, adult amphibians, sharks/cartilaginous fishes, synthesized in the liver via the Ornithine/Urea Cycle where Citrulline + Aspartate -> Argininosuccinate -> Arginine -> Urea + Ornithine): moderately toxic, requires ~50 mL of water per 1 g of nitrogen. 3. Uric Acid (Uricotelic—birds, reptiles, insects, land snails): least toxic, requires only ~1 mL of water per 1 g of nitrogen.
17	In PMDC MDCAT Biology (Cartilage & Bone Cells), compare Hyaline, Elastic, and Fibrocartilage, and state the functions of Osteoblasts, Osteocytes, and Osteoclasts.	Cartilage is avascular (no blood vessels penetrate it; nourished by diffusion) and contains chondrocytes in lacunae: Hyaline cartilage (most abundant—articular surfaces of movable joints, trachea, larynx, epiphyseal plates, nose), Elastic cartilage (epiglottis, external ear pinna), Fibrocartilage (strongest—intervertebral discs, pubic symphysis). Bone cells: Osteoblasts (bone-forming cells that synthesize collagen matrix), Osteocytes (mature bone cells trapped in lacunae), and Osteoclasts (multinucleated giant bone-resorbing/dissolving cells derived from monocytes).
18	In PMDC MDCAT Biology (Human Digestive Hormones), compare the site of secretion, stimulus, and physiological action of Gastrin, Secretin, and Cholecystokinin (CCK).	Gastrin (secreted by pyloric mucosa G-cells in response to protein/peptides in stomach): stimulates parietal and chief cells to secrete gastric juice. Secretin (first hormone discovered by Bayliss & Starling; secreted by duodenal S-cells in response to acidic chyme): stimulates the pancreas to secrete watery Bicarbonate-rich (NaHCO3) pancreatic juice and stimulates hepatic bile production while inhibiting gastric secretion. Cholecystokinin / CCK (secreted by duodenal I-cells in response to fatty acids and amino acids): stimulates contraction of the gallbladder to release bile and stimulates pancreatic acinar cells to secrete enzyme-rich pancreatic juice.
19	In PMDC MDCAT Biology (Digestive System), match the gastric mucosal cells of the human stomach (Mucous, Parietal/Oxyntic, Chief/Zymogen, and G-cells) to their secretions and functions.	1. Mucous (Goblet) cells: secrete thick alkaline mucus to protect the stomach wall from autodigestion. 2. Parietal (Oxyntic) cells: secrete concentrated Hydrochloric Acid (HCl—adjusts pH to 1.5–2.5, kills microbes, and activates pepsinogen to pepsin) AND Intrinsic Factor (essential for Vitamin B12 absorption in the ileum). 3. Chief (Zymogen) cells: secrete inactive enzyme precursor Pepsinogen. 4. Endocrine G-cells (in pyloric antrum): secrete the hormone Gastrin into the bloodstream to stimulate further gastric juice secretion.
20	In PMDC MDCAT Biology (Bioenergetics - Photosynthesis), compare Non-Cyclic Photophosphorylation (Z-Scheme) with Cyclic Photophosphorylation, and identify the primary CO2 acceptor and first stable product of the Calvin Cycle (C3).	Non-Cyclic Photophosphorylation involves BOTH Photosystem II (P680) and Photosystem I (P700), photolysis of water, evolution of O2, and generation of BOTH ATP and NADPH. Cyclic Photophosphorylation involves ONLY Photosystem I (P700) when NADP⁺ is scarce or ATP demand is high—producing ONLY ATP (no NADPH and no O2 released). In the Calvin Cycle, the 5-carbon primary CO2 acceptor is RuBP (Ribulose-1,5-bisphosphate, catalyzed by RuBisCO), and the first stable 3-carbon product is 3-PGA (3-Phosphoglycerate).
21	In PMDC MDCAT Biology (Proteins & Nucleic Acids), how many polypeptide chains and amino acids are present in Human Insulin and Haemoglobin, and what is the difference between a Nucleoside and a Nucleotide?	Human Insulin (sequenced by Frederick Sanger): 51 amino acids in 2 chains—Alpha chain (21 amino acids) and Beta chain (30 amino acids) linked by disulfide bridges. Adult Haemoglobin (HbA): 574 amino acids in 4 chains—2 Alpha chains (141 amino acids each = 282) and 2 Beta chains (146 amino acids each = 292). A Nucleoside = Nitrogenous Base + Pentose Sugar; a Nucleotide = Nucleoside + Phosphate group(s) esterified at the 5' carbon.
22	In PMDC MDCAT Biology (Plant Photoperiodism & Vernalization), distinguish between Short-Day Plants (Long-Night Plants), Long-Day Plants (Short-Night Plants), and the role of Phytochrome (P_r vs. P_fr).	Flowering is controlled primarily by the length of uninterrupted DARKNESS (critical night length): Short-Day / Long-Night Plants (e.g., tobacco, soybean, cocklebur, chrysanthemum) flower when uninterrupted darkness EXCEEDS a critical length. Long-Day / Short-Night Plants (e.g., wheat, radish, spinach, cabbage, henbane) flower when darkness is SHORTER than a critical length. Phytochrome exists in two interconvertible forms: P_r (absorbs red light at 660 nm -> converts to biologically active P_fr) and P_fr (absorbs far-red light at 730 nm or slowly reverts to P_r in darkness). Vernalization is the promotion of flowering by exposure to low-temperature chilling.
23	In PMDC MDCAT Biology (Enzymes), compare the Lock-and-Key Model (Emil Fischer, 1890) with the Induced-Fit Model (Daniel Koshland, 1959), and contrast Competitive vs. Non-Competitive Enzyme Inhibition.	Lock-and-Key: active site is a rigid, pre-shaped structure admitting only a specific substrate without conformational change. Induced-Fit: active site is flexible and moulds itself around the substrate upon binding to achieve catalytic conformation. Competitive Inhibition (e.g., Malonate inhibiting Succinate dehydrogenase): inhibitor resembles substrate and competes for the ACTIVE SITE—can be overcome by increasing substrate concentration (V_max unchanged, K_m increases). Non-Competitive Inhibition (e.g., Cyanide on Cytochrome oxidase, heavy metals): binds to an ALLOSTERIC site, altering active site shape—cannot be overcome by adding extra substrate (V_max decreases).
24	In PMDC MDCAT Biology (Endocrine Glands), distinguish the hormones of the Anterior Pituitary (Adenohypophysis) from the Posterior Pituitary (Neurohypophysis).	Anterior Pituitary synthesizes and secretes 6 tropic/direct hormones: Somatotropin (GH/STH), Thyroid-Stimulating Hormone (TSH), Adrenocorticotropic Hormone (ACTH), Follicle-Stimulating Hormone (FSH), Luteinizing Hormone (LH / ICSH in males), and Prolactin (LTH). Median Lobe secretes MSH (Melanocyte-Stimulating Hormone). Posterior Pituitary does NOT synthesize hormones—it stores and releases 2 neurohormones synthesized in the Hypothalamus: Antidiuretic Hormone (ADH / Vasopressin) and Oxytocin.
25	In PMDC MDCAT Biology (Human Brain Divisions), classify the structures of the Forebrain (Prosencephalon), Midbrain (Mesencephalon), and Hindbrain (Rhombencephalon), and state the role of the Limbic System (Hippocampus & Amygdala).	Forebrain: Telencephalon (Cerebrum & Limbic system) + Diencephalon (Thalamus—sensory relay station except smell; Hypothalamus—thermoregulation, osmoregulation, hunger/thirst, sleep-wake, pituitary control). Limbic System: Amygdala controls rage, fear, pleasure, and emotional responses; Hippocampus converts short-term memory into long-term memory. Midbrain: reticular formation (screens sensory input) and auditory/visual reflex integration. Hindbrain: Pons (controls rate/pattern of breathing and sleep-wake transition), Cerebellum (precise motor coordination and posture), and Medulla Oblongata (autonomic vital centers: heartbeat, breathing, BP, swallowing, vomiting).
26	In PMDC MDCAT Biology (Coordination & Control - Nerve Impulse), state the Resting Membrane Potential (RMP) vs. Action Potential Spike values of a neuron, and how the Na⁺/K⁺ Pump maintains the resting gradient.	Resting Membrane Potential (polarized state): -70 mV (inside of axon is negative relative to outside; K⁺ is 30× higher inside, Na⁺ is 10× higher outside, maintained by the ATP-driven Na⁺/K⁺ pump which pumps 3 Na⁺ OUT for every 2 K⁺ pumped IN). Depolarization (Action Potential): threshold stimulus opens voltage-gated Na⁺ channels -> rapid Na⁺ influx reverses potential to +50 mV (or +30 to +50 mV). Repolarization: Na⁺ channels close and voltage-gated K⁺ channels open -> K⁺ efflux restores negative inside potential (briefly hyperpolarizing to -75/-90 mV).
27	In PMDC MDCAT Biology (Syllabus Weightage & Structure), how many total MCQs are on the PMDC MDCAT exam, what is Biology's percentage weightage, and is there negative marking?	The PMDC MDCAT consists of 200 MCQs completed in 3.5 hours (210 minutes) with NO negative marking: Biology has the highest weightage at 34% (68 MCQs), Chemistry 27% (54 MCQs), Physics 27% (54 MCQs), English 9% (18 MCQs), and Logical Reasoning 3% (6 MCQs).
28	In PMDC MDCAT Biology (Human Reproduction & STIs), compare Spermatogenesis and Oogenesis in humans, and match the causative organisms of Gonorrhoea, Syphilis, Genital Herpes, and AIDS.	Spermatogenesis is continuous from puberty onward in the seminiferous tubules (stimulated by FSH on Sertoli cells and LH/ICSH on Leydig cells to secrete testosterone), yielding 4 motile haploid spermatozoa per primary spermatocyte. Oogenesis begins before birth (arrested in Prophase I as primary oocytes), resumes at puberty, and yields ONLY 1 large functional haploid ovum plus polar bodies per primary oocyte (arrested at Metaphase II until fertilization). STIs: Gonorrhoea = Neisseria gonorrhoeae (Gram-negative diplococcus); Syphilis = Treponema pallidum (spirochete); Genital Herpes = HSV Type 2 (DNA virus); AIDS = HIV (retrovirus).
29	In PMDC MDCAT Biology (Gene Linkage & Crossing Over), how is Recombination Frequency calculated, and how does it relate to Map Distance on a chromosome?	Recombination Frequency (RF) = (Number of Recombinant Offspring ÷ Total Number of Offspring) × 100%. One percent (1%) recombination frequency equals 1 Map Unit (1 centiMorgan, cM) of distance between two linked genes on the same chromosome. Because independent assortment produces a maximum of 50% recombinants, the maximum recombination frequency between any two genes is 50%.
30	In PMDC MDCAT Biology (Biotechnology & PCR), what are the three thermal steps of Each Cycle of the Polymerase Chain Reaction (PCR, invented by Kary Mullis), and why is Taq Polymerase used?	1. Denaturation (94°C–95°C for ~1 min): heat breaks hydrogen bonds to separate dsDNA into single strands. 2. Primer Annealing / Renaturation (50°C–60°C for ~1–2 min): forward and reverse DNA primers bind to complementary 3' flanking sequences. 3. Extension / Polymerization (72°C for ~1.5 min): Taq DNA polymerase (isolated from the thermophilic bacterium Thermus aquaticus, which is heat-stable and does not denature at 95°C) synthesizes new complementary DNA strands in the 5' -> 3' direction.
31	In PMDC MDCAT Biology (Bioenergetics - Cellular Respiration), trace the exact cellular locations and net yields of ATP, NADH, FADH2, and CO2 across Glycolysis, Pyruvate Oxidation (Link Reaction), and the Krebs Cycle per molecule of Glucose.	Per 1 Glucose (C6): 1. Glycolysis (in cytosol): 2 ATP net (4 formed - 2 used) + 2 NADH (0 CO2). 2. Pyruvate Oxidation / Link Reaction (in mitochondrial matrix, for 2 pyruvates): 2 NADH + 2 CO2 (forming 2 Acetyl-CoA). 3. Krebs / Citric Acid Cycle (in mitochondrial matrix, 2 turns): 2 ATP (GTP) + 6 NADH + 2 FADH2 + 4 CO2. Total before ETC: 4 ATP (substrate-level), 10 NADH, 2 FADH2, and 6 CO2.
32	In PMDC MDCAT Biology (Prokaryotes / Bacteria), classify bacteria based on Flagellar Arrangement (Atrichous, Monotrichous, Lophotrichous, Amphitrichous, Peritrichous) and Gram Staining cell wall composition.	Flagellar types: Atrichous (no flagella), Monotrichous (single polar flagellum), Lophotrichous (tuft of flagella at one pole), Amphitrichous (flagellum/tuft at both poles), Peritrichous (flagella surrounding the entire cell surface, e.g., E. coli, Salmonella). Gram-Positive bacteria: thick peptidoglycan layer (50% of dry weight), teichoic and lipoteichoic acids, no outer lipid membrane, minimal periplasmic space (stain purple/violet). Gram-Negative bacteria: thin peptidoglycan layer (10%), thick outer lipopolysaccharide/lipoprotein membrane with porins, periplasmic space present (stain pink/red with safranin).