FOUNDATION – 2022

Red blood cells (RBCs) respond to the osmolarity of their surrounding solution:

1. Isotonic solution (0.9% NaCl): No net movement of water; RBCs maintain their shape.
2. Hypotonic solution (<0.9% NaCl): Water moves into the cells, causing them to swell and potentially burst.
3. Hypertonic solution (>0.9% NaCl): Water moves out of the cells, causing them to shrink (crenate).

A 1.0% NaCl solution is hypertonic compared to the intracellular fluid of RBCs, leading to water loss and cell shrinkage.

The prime mover (agonist) is the muscle primarily responsible for a specific movement. In the case of lifting the leg (hip flexion), the prime mover is the iliopsoas muscle. If this muscle is weakened, the patient would have difficulty performing the movement.

Other muscle roles include:

• Extensor: A muscle that extends a joint (e.g., gluteus maximus for hip extension).
• Flexor: A muscle that flexes a joint (e.g., iliopsoas for hip flexion).
• Antagonist: A muscle that opposes the action of the prime mover (e.g., gluteus maximus opposes iliopsoas during hip flexion).
• Synergist: A muscle that assists the prime mover (e.g., rectus femoris assists iliopsoas in hip flexion).

Chronic alcohol abuse is a common cause of fatty liver (steatosis), which is characterized by the accumulation of large lipid droplets within hepatocytes. This occurs due to impaired metabolism of fatty acids and increased synthesis of triglycerides in the liver. In the early stages, fatty liver may not cause significant symptoms or laboratory abnormalities, as described in this patient.

The other options are incorrect:

• Nuclear changes (karyolysis, pyknosis, karyorrhexis): These are signs of cell death (necrosis), which are not typically seen in early-stage fatty liver.
• Complete destruction of liver architecture: This occurs in advanced liver disease (e.g., cirrhosis), not in early-stage fatty liver.
• Detachment of polysomes: This is a cellular change seen in certain toxic injuries but is not specific to fatty liver.
• Hypertrophy of smooth endoplasmic reticulum: This is a microscopic change associated with chronic drug or toxin exposure but is not a hallmark of fatty liver.

Ammonia (NH₃) is highly toxic to cells, especially in the brain. To safely transport and store ammonia, it is converted into glutamine via the enzyme glutamine synthetase. Key points:

1. Glutamine: A non-toxic amino acid that serves as a carrier of ammonia in the blood.
2. Glutamate: Acts as a precursor for glutamine synthesis but is not the final product.
3. Asparagine, histidine, and aspartate: These amino acids are not directly involved in ammonia detoxification.

Reposition is the movement that returns the thumb (and sometimes the fingers) to their original anatomical position after opposition. Opposition is the movement where the thumb touches the tips of the fingers, allowing for precision grip (e.g., picking up a pen). Reposition reverses this action, bringing the thumb back to its neutral position.

The other options are incorrect:

• Circular motion of the thumb: This describes circumduction, not reposition.
• Flexion of the arm: This is unrelated to reposition.
• Thumb touches the tips of fingers: This describes opposition, not reposition.
• Flexion of the wrist: This is a separate movement and unrelated to reposition.

Excessive use of antibiotics can disrupt the normal flora of the gut, creating an opportunity for pathogenic bacteria to overgrow. Clostridium difficile is a gram-positive, spore-forming bacterium that can cause pseudomembranous colitis, a severe inflammation of the colon characterized by the formation of a pseudo-membrane composed of necrotic tissue, fibrin, and inflammatory cells. This condition is often associated with antibiotic use, particularly broad-spectrum antibiotics like clindamycin, ampicillin, and cephalosporins.

The other organisms are incorrect:

• Escherichia coli: Can cause diarrhea but not pseudo-membranous colitis.
• Streptococci: Not associated with pseudo-membrane formation in the GIT.
• Staphylococci: Can cause food poisoning but not pseudo-membranous colitis.
• Balantidium coli: A protozoan parasite that causes dysentery, not pseudo-membranous colitis.

The correct statement is: BAX and BAK are pro-apoptotic proteins.  

Here’s a breakdown of why:

• BAX and BAK are members of the Bcl-2 protein family. They are pro-apoptotic, meaning they promote apoptosis (programmed cell death). They can trigger the release of cytochrome c from mitochondria, which then activates caspases, leading to cell death.  

Why the other statements are incorrect:

• Apoptosis involves the activation of caspases, not their inactivation. Caspases are a family of proteases (enzymes that cut proteins) that play a central role in apoptosis. They are activated in a cascade, ultimately leading to the dismantling of the cell.  

• The intrinsic pathway is also known as the mitochondrial pathway, not the death receptor pathway. It’s triggered by internal cellular stress, such as DNA damage or growth factor deprivation, and involves the mitochondria.  

• Caspase 8 (and 9 in the intrinsic pathway) are initiator caspases, not caspase 3 and 6. Initiator caspases activate the executioner caspases, such as caspase 3 and 6, which then carry out the actual cell destruction.  

• The extrinsic pathway is also known as the death receptor pathway, not the mitochondrial pathway. It’s triggered by the binding of death ligands to death receptors on the cell surface.

The answer is Shivering of skeletal muscles.

Here’s why:

When exposed to cold temperatures, the body’s primary goal is to generate heat and conserve the heat it has. Shivering is a rapid, involuntary contraction of skeletal muscles. This muscle activity generates heat, helping to raise the body’s core temperature.

Why the other options are incorrect:

• Increased sweating: Sweating is a mechanism for cooling the body, not warming it. It would be counterproductive in a cold environment.

• Vasodilation: Vasodilation is the widening of blood vessels. While it can increase blood flow to the skin, it also increases heat loss. In a cold environment, the body would primarily use vasoconstriction (narrowing of blood vessels) to conserve heat.

• Relaxation of piloerector muscles: Piloerector muscles are the small muscles attached to hair follicles. Their contraction causes “goosebumps.” While this can trap a thin layer of air for slight insulation, it’s a minor effect compared to shivering. Relaxation of these muscles would have the opposite effect – making you colder.

• Relaxation of skeletal muscles: Muscle relaxation would decrease heat production. This is the opposite of what the body needs in a cold environment.

Colonization resistance refers to the ability of normal flora to prevent pathogenic bacteria from establishing themselves in the body. One of the key mechanisms is competitive exclusion, where resident bacteria occupy binding sites on mucosal surfaces, leaving fewer available sites for pathogens to attach. This prevents pathogens from colonizing and causing infection.

The other options describe related concepts but do not explain colonization resistance:

• Malnourished patients develop vitamin deficiencies due to reduced flora: This highlights a consequence of disrupted normal flora but does not describe the mechanism of colonization resistance.
• Intestinal bacteria provide vitamins B and K: This is a benefit of normal flora but unrelated to colonization resistance.
• Normal flora causes disease in immunocompromised patients: This describes opportunistic infections, not colonization resistance.
• Excessive use of antibiotics suppresses normal flora: This explains how colonization resistance can be disrupted but does not describe the mechanism itself.

Glycosidic bonds are the specific type of covalent bond that links two monosaccharide (simple sugar) units together to form a disaccharide (like sucrose or lactose) or a polysaccharide (like starch or cellulose). Think of it as the “glue” that holds the sugar building blocks together.  

Why the other options are incorrect:

• Ionic bond: Ionic bonds involve the electrostatic attraction between oppositely charged ions. They are important in many biological molecules, but not the primary linkage between sugar monomers.  

• Ether bond: While glycosidic bonds are technically a type of ether bond, “glycosidic bond” is the more specific and correct term in this context. Using the general term “ether bond” wouldn’t be precise enough.

• Ester bond: Ester bonds are formed between an alcohol and a carboxylic acid. They are important in lipids (fats and oils), but not in carbohydrates.  

• Peptide bond: Peptide bonds link amino acids together to form proteins.

  They are not found in carbohydrates.  

Phase I reactions in drug metabolism primarily involve oxidation, reduction, hydrolysis, and sometimes dehydrogenation. These reactions modify the drug molecule, often making it more polar. They prepare the drug for Phase II reactions.  

Conjugation is a Phase II reaction. In Phase II, the products of Phase I reactions are conjugated (joined) with other molecules, such as glucuronic acid, sulfate, or glutathione. This usually makes the drug much more water-soluble and easier to excrete.   

The periosteum is a dense layer of connective tissue that covers the outer surface of bones, except at joint surfaces. It has the following characteristics:

1. Outer fibrous layer: Composed of dense irregular connective tissue containing type I collagen.
2. Inner cellular layer: Contains osteoprogenitor cells (which can differentiate into osteoblasts) and osteoblasts (bone-forming cells).
3. Vascularity: The periosteum is highly vascular, providing blood supply to the underlying bone and aiding in bone repair and remodeling.

Thus, the statement claiming the periosteum is avascular is incorrect.

During DNA replication, the two strands of the double helix are replicated differently due to the antiparallel nature of DNA and the 5′-3′ directionality of DNA polymerase:

1. The leading strand is synthesized continuously in the 5′-3′ direction.
2. The lagging strand is synthesized discontinuously in the 5′-3′ direction as short segments called Okazaki fragments. These fragments are later joined by DNA ligase.

The lagging strand is synthesized in the opposite direction of the replication fork movement, requiring the formation of Okazaki fragments.

The pKa value is a measure of the strength of an acid in solution. It is the pH at which half of the acid molecules are dissociated. The relationship between pKa and acid strength is as follows:

• Low pKa: Indicates a strong acid (readily donates protons, highly dissociated).
• High pKa: Indicates a weak acid (less readily donates protons, less dissociated).

The other options are unrelated to pKa:

• Cation: A positively charged ion.
• Zwitterion: A molecule with both positive and negative charges but an overall neutral charge (e.g., amino acids at physiological pH).
• Amphoteric ion: A molecule that can act as both an acid and a base.

H&E staining is a common histological technique where:

1. Hematoxylin stains acidic (negatively charged) structures blue or purple. These structures are called basophilic (e.g., DNA in the nucleus, RNA in ribosomes).
2. Eosin stains basic (positively charged) structures pink or red. These structures are called acidophilic (e.g., cytoplasmic proteins, collagen).

If the tissue appears blue, it indicates the presence of basophilic components, such as nucleic acids or acidic proteins.

The other options are incorrect:

• Hydrophobic or hydrophilic: Refers to water-repelling or water-attracting properties, not staining characteristics.
• Acidophilic: Would stain pink or red with eosin.
• Carbohydrate-rich: Carbohydrates are typically stained with periodic acid-Schiff (PAS), not H&E.

Neural crest cells give rise to a diverse set of structures in the body, including Schwann cells, melanocytes, and glial cells. However, neurons are not derived from neural crest cells, except for specific populations of peripheral neurons.

Derivatives of Neural Crest Cells:

✅ Peripheral nervous system (PNS) components:

• Schwann cells (myelinate peripheral nerves)
• Dorsal root ganglia neurons
• Autonomic ganglia neurons
  ✅ Pigment-producing cells:
• Melanocytes
  ✅ Facial structures & connective tissue:
• Odontoblasts (form dentin of teeth)
  ✅ Other structures:
• Adrenal medulla cells (chromaffin cells)
• Glial cells (except microglia, which are derived from mesoderm)

Why are Neurons Not the Correct Answer?

• Neurons in the central nervous system (CNS) (e.g., cerebral and spinal cord neurons) arise from the neuroectoderm (neural tube), not the neural crest.
• Only certain peripheral neurons (e.g., autonomic and sensory neurons) arise from the neural crest.

Why not the other options?

• Odontoblasts → Derived from neural crest cells, form dentin.
• Schwann cells → Myelinate PNS axons, neural crest-derived.
• Melanocytes → Produce pigment (melanin) in skin, neural crest-derived.
• Glial cells → Most PNS glial cells (Schwann cells, satellite cells) come from neural crest, but CNS glial cells (astrocytes, oligodendrocytes) come from neuroectoderm.

Thus, the correct answer is “Neurons,” as most neurons in the CNS arise from the neural tube, not neural crest cells.

Inversion is a movement of the foot that involves turning the sole of the foot inward (toward the midline of the body). This motion occurs primarily at the subtalar and transverse tarsal joints.

The other terms describe different movements:

• Eversion: Turning the sole of the foot outward (away from the midline).
• Dorsiflexion: Lifting the foot upward toward the shin (decreasing the angle between the foot and the leg).
• Plantarflexion: Pointing the foot downward (increasing the angle between the foot and the leg).

Explanation:
Chorionic villi are finger-like projections of the placenta that play a crucial role in fetal-maternal exchange. They develop in stages:

1. Primary villi: Solid outgrowths of cytotrophoblast cells.
2. Secondary villi: Contain a core of extraembryonic mesoderm.
3. Tertiary villi: Contain fetal blood vessels within the mesodermal core.
4. Free terminal villi: These are the final, highly vascularized structures that facilitate the exchange of nutrients, gases, and wastes between maternal and fetal blood.

The other types of villi serve different functions:

• Anchoring villi: Attach the placenta to the decidua basalis.
• Primary, secondary, and tertiary villi: Represent earlier developmental stages and are not directly involved in exchange.

A bruise (contusion) results from trauma causing rupture of blood vessels, leading to extravasation of blood into tissues. The color changes seen in a bruise occur due to the breakdown of hemoglobin in RBCs over time.

Color Progression of a Bruise & Role of Hemosiderin:

1. Initial purple/blue color → Due to deoxygenated hemoglobin in extravasated blood.
2. Greenish color (days 3-5) → Due to biliverdin, a breakdown product of hemoglobin.
3. Yellow-brown color (days 10-16) → Due to hemosiderin, an iron-storage complex formed from degraded ferritin and hemoglobin.

Why is Hemosiderin the Correct Answer?

✅ Hemosiderin is an iron-containing pigment that accumulates in macrophages after RBC breakdown.
✅ It is responsible for the yellow-brown color of resolving bruises seen 16 days after injury.
✅ Seen in chronic hemorrhage sites and conditions like hemosiderosis and hemochromatosis.

Why not the other options?

• Melanin → Found in skin, hair, and eyes, not in bruises.
• Bilirubin → A breakdown product of heme metabolism, contributes to yellow discoloration, but it is seen more in systemic conditions (e.g., jaundice), not localized bruises.
• Lipofuscin → An aging pigment seen in old cells, not involved in bruise resolution.
• Glycogen → Involved in energy storage, not in bruise formation or color changes.

Thus, the correct answer is “Hemosiderin,” as it is the pigment responsible for the yellow-brown color seen in bruises during the later stages of healing.

Bacterial flagella arrangements are classified based on their number and distribution:

1. Lophotrichous: A cluster of flagella at one or both poles of the cell.
2. Monotrichous: A single flagellum at one pole.
3. Amphitrichous: A single flagellum at both poles.
4. Peritrichous: Flagella distributed all over the cell surface.
5. Bipolar flagella: This term is not commonly used in microbiology.

The term lophotrichous specifically describes the arrangement where multiple flagella are grouped together at one end of the bacterium, resembling a tuft.

Fat is primarily stored in the body as triglycerides (triacylglycerols) within adipose tissue. Triglycerides serve as the main energy reserve for the body and are broken down into fatty acids and glycerol when energy is needed.

Key Features of Triglycerides as Fat Storage:

✅ Composed of one glycerol molecule and three fatty acid chains.
✅ Stored in adipocytes (fat cells) in adipose tissue.
✅ Most energy-dense macronutrient, providing 9 kcal per gram.
✅ Broken down by lipase enzymes during fasting or energy demand.

Why not the other options?

• Fatty acids → Incorrect; fatty acids are released from triglycerides during metabolism but are not the primary stored form of fat.
• Ghee → Incorrect; ghee is clarified butter, a dietary fat but not the storage form in the body.
• Wax → Incorrect; waxes are structural lipids found in the skin and other tissues, not a major energy reserve.
• Cholesterol → Incorrect; cholesterol is a component of cell membranes and precursor for steroid hormones, not an energy storage molecule.

Thus, the correct answer is “Triglycerides,” as they are the primary form of stored fat in the body.

The isoelectric point (pI) of an amino acid (or protein) is the pH at which it has a net charge of zero. At this pH, the number of positive charges on the molecule equals the number of negative charges. The amino acid exists as a zwitterion, a molecule with both positive and negative charges, but the overall net charge is zero.

Why the other options aren’t the correct term:

• Dissociation point: This is a more general term referring to the point at which a molecule dissociates into ions in solution. While related to the concept of charge, it’s not specific to the point of zero net charge for an amino acid.

• Solubility point: This refers to the concentration of a solute at which it will dissolve in a given solvent at a specific temperature. It’s not related to the charge of an amino acid.

• Ionization point: Similar to dissociation point, this is a general term for when a molecule gains or loses electrons and becomes ionized. It’s not specific to the zero net charge condition.

• Neutral point: While it sounds close, “isoelectric point” is the established scientific term for the pH at which an amino acid has a net charge of zero.

The primitive streak is a critical structure in early embryonic development that establishes the craniocaudal (head-to-tail) axis of the embryo. It forms during the third week of development and is essential for:

1. Gastrulation: The process by which the three germ layers (ectoderm, mesoderm, and endoderm) are formed.
2. Axis formation: The primitive streak defines the cranial (head) and caudal (tail) ends of the embryo.

Without the primitive streak, the embryo lacks a clear craniocaudal axis, making it difficult to distinguish orientation during imaging.

The other options are incorrect:

• Formation of trophoblast: Involved in implantation and placental development, not axis formation.
• Formation of notochord: Occurs after the primitive streak and is involved in signaling for neural tube formation.
• Formation of syncytiotrophoblast: Part of the trophoblast involved in placental function.
• Formation of epiblast: The epiblast gives rise to the three germ layers but does not establish the craniocaudal axis directly.

Vomiting causes the loss of gastric contents, which are rich in hydrochloric acid (HCl). This leads to:

1. Loss of hydrogen ions (H⁺) and chloride ions (Cl⁻), resulting in metabolic alkalosis.
2. The kidneys attempt to compensate by excreting bicarbonate (HCO₃⁻) and retaining sodium (Na⁺) and potassium (K⁺).
3. However, prolonged vomiting can also lead to volume depletion, triggering the release of antidiuretic hormone (ADH). ADH promotes water retention, which dilutes the remaining sodium in the extracellular fluid, causing hyponatremia.

The other options are incorrect:

• Hypoglycemia: Not directly caused by vomiting.
• Hypernatremia: Vomiting typically leads to sodium loss, not excess.
• Hyperkalemia: Vomiting causes potassium loss (hypokalemia), not excess.

Dipalmitoyl lecithin (Diplamitoylphosphatidylcholine, DPPC) is a major component of pulmonary surfactant, which reduces alveolar surface tension and prevents lung collapse.

Role of Dipalmitoyl Lecithin in Respiratory Distress Syndrome (RDS):

✅ Produced by type II alveolar cells in the lungs.
✅ Surfactant production begins around week 24 of gestation but reaches sufficient levels only after week 35.
✅ Deficiency in preterm infants leads to neonatal respiratory distress syndrome (NRDS) → alveoli collapse due to increased surface tension, leading to hypoxia and respiratory failure.
✅ Treatment → Exogenous surfactant therapy & corticosteroids (betamethasone) to stimulate fetal lung maturity.

Why Not the Other Options?

• Cephalin (Phosphatidylethanolamine) → Component of cell membranes, but not a major surfactant component.
• Phosphatidyl inositol → Involved in cell signaling and membrane structure, but not in lung surfactant function.
• Phosphatidyl serine → Important in apoptosis and cell signaling, but not in surfactant production.
• Sphingomyelin → Present in cell membranes and used in fetal lung maturity tests (Lecithin/Sphingomyelin ratio) but not a major surfactant.

Thus, the correct answer is “Dipalmitoyl lecithin,” as it is the primary lipid responsible for surfactant function, preventing neonatal respiratory distress syndrome (NRDS) in preterm infants.

Skeletal muscles are characterized by the following properties:

1. Striated appearance: Due to the organized arrangement of actin and myosin filaments.
2. Voluntary control: Skeletal muscles are under conscious control.
3. Multinucleated cells: Each muscle fiber contains multiple nuclei.
4. No gap junctions: Skeletal muscle cells do not communicate via gap junctions (unlike cardiac muscle).

Other properties listed are incorrect:

• Involuntary muscle: Refers to smooth and cardiac muscles.
• Fusiform shape: Characteristic of smooth muscle fibers.
• Single nucleus: Found in smooth and cardiac muscle cells.
• Gap junctions: Present in cardiac and smooth muscles for synchronized contractions.

Sodium is the most abundant cation in the extracellular fluid and plays a critical role in maintaining osmotic pressure, fluid balance, and nerve impulse transmission. The concentration of sodium in ECF is approximately 135-145 mEq/L, which is much higher than its concentration inside cells.

The other cations are either less abundant or primarily located intracellularly:

• Potassium (K⁺): The major intracellular cation.
• Calcium (Ca²⁺): Important for bone health and signaling but present in lower concentrations in ECF.
• Magnesium (Mg²⁺): Primarily intracellular and involved in enzymatic reactions.
• Iron (Fe²⁺/Fe³⁺): Not a significant cation in ECF; mainly involved in hemoglobin and cellular processes.

Glycogen is a polysaccharide that functions as the primary storage form of glucose in animals. Key features include:

1. It is stored mainly in the liver and muscles.
2. It can be rapidly broken down into glucose to meet energy demands.

Other carbohydrates:

• Glucose: The primary energy source for cells, but not a storage form.
• Galactose and mannose: Monosaccharides that are not stored in large amounts.
• Sucrose: A disaccharide (glucose + fructose) found in plants, not animals.

Beta-glucans are a type of soluble dietary fiber. They form a viscous gel in the intestines. This gel can interfere with the absorption of fats and cholesterol, leading to reduced lipid absorption. This is one of the reasons beta-glucans are associated with heart health benefits.  

Why the other options are less directly involved in modifying lipid absorption in the way beta-glucans do:

• Alpha glucan: This is a general term for polysaccharides made of glucose linked by alpha glycosidic bonds. Starch is a prominent example. While starches are a source of energy, they don’t have the same viscous gel-forming properties as beta-glucans and don’t affect lipid absorption in the same way.  

• Glucose: Glucose is a simple sugar. It’s absorbed directly into the bloodstream and doesn’t directly modify the absorption of other lipids.  

• Starch: As mentioned above, starch is a polysaccharide made of glucose. It is a source of energy, but does not have a significant impact on lipid absorption.  

• Cellulose: Cellulose is another type of dietary fiber, but it’s insoluble fiber. It adds bulk to the stool and aids in digestion, but it doesn’t form a viscous gel like beta-glucan and therefore doesn’t have the same effect on lipid absorption.  

Lipoproteins are particles that transport lipids (including TAG, cholesterol, and phospholipids) in the bloodstream. Their composition varies:

1. Chylomicrons: These are the largest and least dense lipoproteins, carrying the highest percentage of TAG (about 90%). They transport dietary lipids from the intestine to tissues.
2. Very low-density lipoproteins (VLDL): Contain about 55% TAG and transport endogenous lipids from the liver to tissues.
3. Low-density lipoproteins (LDL): Contain mostly cholesterol and are involved in delivering cholesterol to tissues.
4. High-density lipoproteins (HDL): Contain the least TAG and are involved in reverse cholesterol transport.
5. Apolipoproteins: Protein components of lipoproteins, not carriers of TAG themselves.

Normal flora, or microbiota, refers to the community of microorganisms (bacteria, fungi, and viruses) that permanently reside on or within the human body. These organisms establish a stable relationship with the host and are typically harmless or even beneficial. Colonization refers to the establishment and persistence of these microorganisms in specific body sites, such as the skin, mouth, colon, and vagina.

The other options describe aspects of normal flora but do not specifically define colonization:

• Certain bacteria and fungi which are always present in mouth, colon, and vagina: This describes the composition of normal flora but not the process of colonization.
• They provide essential vitamins: This is a benefit of normal flora (e.g., vitamin K production by gut bacteria) but not a definition of colonization.
• They inhibit pathogenic organisms from binding to epithelial surfaces: This describes the protective role of normal flora (competitive exclusion) but not colonization itself.
• This is the acquisition of new organisms: This describes transient flora or infection, not colonization by permanent residents.

Tendons are composed of densely packed collagen fibers that are arranged in parallel to provide high tensile strength and resistance to unidirectional forces. This organization is characteristic of dense regular connective tissue, which is specialized for transmitting mechanical forces, such as those generated by muscle contraction.

The other options are incorrect:

• Dense irregular connective tissue: Has collagen fibers arranged in multiple directions, providing strength in many directions (e.g., dermis of the skin).
• Areolar connective tissue and loose connective tissue: Contain loosely arranged fibers and are not specialized for high tensile strength.
• Adipose tissue: Composed of fat cells and serves as energy storage and insulation, not for mechanical strength.

Zonula occludens, or tight junctions, are specialized cell junctions that form a nearly impermeable barrier between adjacent cells. They prevent the passage of extracellular fluid and molecules through the paracellular route (between cells). Tight junctions are commonly found in epithelial tissues, such as the lining of the intestines or blood-brain barrier, where control over substance movement is critical.

The other options allow some form of communication or structural connection:

• Desmosomes and macula adherens: These are anchoring junctions that provide mechanical strength but do not restrict paracellular movement.
• Hemidesmosomes: Anchor cells to the basement membrane but do not affect paracellular transport.
• Gap junctions: Allow direct communication between cells via the passage of ions and small molecules, but they are not involved in paracellular transport.

The anatomical position is a standardized reference position used in anatomy and medicine to describe the location and orientation of body structures. It is defined as follows:

1. The body is standing upright.
2. The face is facing forward.
3. The arms are at the sides with the palms facing forward.
4. The feet are parallel and close together.

This position ensures consistency in anatomical descriptions and allows for clear communication about the body’s structures.

The described dense connective tissue is dense regular connective tissue, which consists of:

✅ Bundles of collagen fibers running parallel → Provides high tensile strength in one direction.
✅ Fibroblast cells with flattened nuclei in between → These produce and maintain collagen fibers.
✅ Minimal ground substance → Helps maintain a compact and strong structure.

Where is this type of tissue found?

• Tendons → Connect muscle to bone, allowing force transmission for movement.
• Ligaments → Connect bone to bone, stabilizing joints.
• Aponeuroses → Broad, sheet-like tendinous structures aiding muscle attachment.

Why is “Tendon” the correct answer?

Tendons exclusively consist of dense regular connective tissue, designed for high tensile strength to endure the pulling forces generated by muscle contractions.

Why not the other options?

• Capsule → Made of dense irregular connective tissue, which resists stress in multiple directions.
• Adipose tissue → Composed mainly of fat cells (adipocytes), not collagen fibers.
• Ligament → Also dense regular connective tissue, but ligaments contain more elastin fibers than tendons, making them more flexible.
• Aponeurosis → Similar to tendons but flattened and sheet-like, whereas the question describes bundles running parallel, typical of tendons.

Thus, the correct answer is “Tendon,” as it consists of parallel collagen bundles with fibroblasts in between.

The sodium-potassium pump (Na⁺/K⁺-ATPase) is an essential membrane protein that maintains cellular homeostasis by performing the following functions:

1. Maintaining electrochemical gradients: It transports 3 Na⁺ ions out of the cell and 2 K⁺ ions into the cell, using energy from ATP hydrolysis. This creates a negative intracellular environment, which is critical for nerve impulse transmission and muscle contraction.
2. Controlling cell volume: By regulating ion concentrations, the pump helps prevent osmotic swelling or shrinkage of the cell.
3. Indirect transport of glucose: The pump establishes a sodium gradient that drives the secondary active transport of glucose (e.g., via SGLT transporters).

The other options are incorrect:

• Decreasing heat production: The pump generates heat as a byproduct of ATP hydrolysis.
• Synthesis of ATP: The pump hydrolyzes ATP, it does not synthesize it.
• Increasing electropositive character inside the cell: The pump actually increases the electronegative character inside the cell by exporting more positive charges (Na⁺) than it imports (K⁺).

The sagittal plane divides the body into left and right halves. Movements in this plane include:

1. Flexion: Decreasing the angle between two body parts (e.g., bending the knee).
2. Extension: Increasing the angle between two body parts (e.g., straightening the knee).

Other planes:

• Frontal (coronal) plane: Divides the body into front and back halves; movements include abduction and adduction.
• Transverse plane: Divides the body into upper and lower halves; movements include rotation.
• Median plane: A specific sagittal plane that runs exactly through the midline of the body.

Smooth muscle is found in the walls of blood vessels (among other structures like the digestive tract and airways). It is responsible for vasodilation (widening of blood vessels) and vasoconstriction (narrowing of blood vessels), which regulate blood flow and pressure. Smooth muscle is involuntary and controlled by the autonomic nervous system.

The other options are incorrect:

• Cardiac muscle: Found only in the heart and responsible for pumping blood, not controlling blood vessel diameter.
• Skeletal muscle: Attached to bones and responsible for voluntary movement, not involved in blood vessel regulation.

The joint between a tooth and its root in the alveolar socket is called a gomphosis, which is a type of fibrous joint.

Key Features of a Gomphosis (Fibrous Joint):

✅ A specialized type of fibrous joint that connects the tooth root to the alveolar bone.
✅ The periodontal ligament (PDL) anchors the tooth in place.
✅ Allows very minimal movement, mainly for shock absorption during chewing.
✅ Unique because it is the only joint that does not connect bone to bone but rather bone to a structure (tooth).

Why not the other options?

• Ball-and-socket → Incorrect; seen in hip (femur-acetabulum) and shoulder (humerus-glenoid) joints, allowing wide movement, unlike tooth joints.
• Synchondrosis → Incorrect; a cartilaginous joint with hyaline cartilage, seen in epiphyseal plates and costochondral joints.
• Hyaline → Incorrect; hyaline cartilage is present in synovial joints, not in tooth sockets.
• Cartilaginous → Incorrect; gomphosis is a fibrous joint, not cartilaginous.

Thus, the correct answer is “Fibrous,” as gomphosis is a type of fibrous joint anchoring the tooth to the jawbone.

The epiphyseal plate (growth plate) is a hyaline cartilage structure located between the epiphysis and diaphysis of long bones in children and adolescents. It allows for longitudinal bone growth. Once growth is complete, the epiphyseal plate ossifies, and the epiphysis fuses with the diaphysis. This type of joint is classified as a primary cartilaginous joint (synchondrosis), where bones are joined by hyaline cartilage.

The other options are incorrect:

• Symphysis: A secondary cartilaginous joint where bones are joined by fibrocartilage (e.g., intervertebral discs).
• Synovial joint: A freely movable joint with a synovial cavity (e.g., knee joint).
• Syndesmosis: A fibrous joint where bones are connected by ligaments (e.g., distal tibiofibular joint).
• Secondary cartilaginous joint: Another term for symphysis, involving fibrocartilage.

Carbohydrates are organic molecules that contain a polyhydroxy aldehyde (-CHO) or a polyhydroxy ketone (C=O) functional group in their structure.

Key Features of Carbohydrates:

✅ Classified based on their functional group:

• Aldoses → Contain an aldehyde (-CHO) group (e.g., glucose).
• Ketoses → Contain a ketone (C=O) group (e.g., fructose).
  ✅ Composed of carbon (C), hydrogen (H), and oxygen (O) in a general formula:
• Cn(H2O)nC_n(H_2O)_nCn​(H2​O)n​ (e.g., glucose: C6H12O6C_6H_{12}O_6C6​H12​O6​).
  ✅ Types of Carbohydrates:
• Monosaccharides → Glucose, fructose, galactose.
• Disaccharides → Sucrose, lactose, maltose.
• Polysaccharides → Starch, glycogen, cellulose.

Why Not the Other Options?

• Proteins → Made of amino acids, do not contain polyhydroxy aldehydes or ketones.
• Nucleic acids → Made of nucleotides (DNA, RNA), contain sugars but are not themselves carbohydrates.
• Lipids → Include fatty acids, triglycerides, phospholipids, which lack polyhydroxy functional groups.
• Steroids → Derived from cholesterol, have a characteristic four-ring structure, not polyhydroxy aldehydes or ketones.

Thus, the correct answer is “Carbohydrates,” as they contain either a polyhydroxy aldehyde or ketone group in their structure.

In competitive inhibition:

1. The inhibitor closely resembles the substrate and competes for binding to the active site of the enzyme.
2. This type of inhibition can be overcome by increasing the substrate concentration.
3. The Vmax (maximum reaction rate) remains unchanged, but the Km (substrate affinity) increases.

Other types of inhibition:

• Allosteric inhibition: The inhibitor binds to a site other than the active site, altering the enzyme’s shape and function.
• Irreversible inhibition: The inhibitor permanently inactivates the enzyme, often by covalent bonding.
• Feedback inhibition: The end product of a metabolic pathway inhibits an earlier enzyme in the pathway.
• Non-competitive inhibition: The inhibitor binds to a site other than the active site, reducing Vmax without affecting Km.

Flagella are long, whip-like appendages that protrude from the surface of bacterial cells. Their primary function is to enable movement (locomotion) by rotating like propellers, allowing bacteria to swim through liquid environments. This movement is crucial for bacteria to seek nutrients, escape harmful substances, or reach favorable environments.

The other options describe functions of other bacterial structures:

• Acts as sex pili: This is the function of pili, specifically the F-pilus, which facilitates conjugation (transfer of genetic material).
• To obtain nutrient in agar medium: Bacteria obtain nutrients through diffusion or secretion of enzymes, not flagella.
• Reproduction: Bacteria reproduce through binary fission, not flagella.
• Adherence to tissue surface: This is the function of adhesins or fimbriae, not flagella.

The steps in preparing a tissue for light microscopy are as follows:

1. Fixation: Preserves the tissue structure using fixatives like formaldehyde.
2. Dehydration: Removes water from the tissue using a series of alcohol solutions.
3. Clearing: Replaces alcohol with a solvent like xylene to make the tissue transparent.
4. Embedding: Infuses the tissue with paraffin wax to provide support for sectioning.
5. Sectioning: Cuts the tissue into thin slices using a microtome.
6. Staining: Adds dyes to highlight cellular structures.

After fixation, the next step is dehydration, which prepares the tissue for embedding.

The WHO’s Healthy Cities initiative is a global movement aimed at promoting health and well-being in urban environments. Its primary objectives include:

1. Addressing health inequalities and improving access to healthcare.
2. Enhancing the physical, social, and environmental conditions of urban areas.
3. Encouraging community participation and intersectoral collaboration to create healthier living conditions.

While the other options (income generation, economic development, social support networks, and community partnerships) may be components of the initiative, the overarching goal is to improve the health and quality of life of urban populations.

Keratan sulfate is a type of glycosaminoglycan (GAG) found in various tissues. It is particularly abundant in the cornea, where it plays a critical role in maintaining transparency and hydration. Keratan sulfate is also present in cartilage but in lower amounts compared to other GAGs like chondroitin sulfate.

The other options are incorrect:

• Extracellular membrane: Contains various GAGs but not specifically keratan sulfate in abundance.
• Cardiac muscle and hepatocyte: Do not contain significant amounts of keratan sulfate.
• Cartilage: Contains keratan sulfate but in smaller quantities compared to the cornea.

ACE inhibitors, such as captopril or enalapril, typically work by binding to the angiotensin-converting enzyme at a site other than the active site, reducing its activity. This is characteristic of non-competitive inhibition, where:

1. The inhibitor binds to an allosteric site, causing a conformational change in the enzyme.
2. The Vmax (maximum reaction rate) is reduced because the enzyme’s catalytic efficiency is decreased.
3. The Km (substrate concentration at half Vmax) remains unchanged because the substrate can still bind to the active site.

The other options are incorrect:

• Competitive inhibition: The inhibitor competes with the substrate for the active site, increasing Km but not affecting Vmax.
• Allosteric inhibition: A type of non-competitive inhibition, but the term is less specific.
• Full agonist and partial agonist: These terms describe drugs that activate receptors, not inhibit enzymes.

Enantiomers are a type of stereoisomer that are non-superimposable mirror images of each other. They have the same chemical formula and sequence of bonded atoms but differ in their three-dimensional orientation. Key points about enantiomers:

1. They rotate plane-polarized light in opposite directions (one is dextrorotatory, and the other is levorotatory).
2. They have identical physical and chemical properties except for their interaction with plane-polarized light and other chiral molecules.

The other terms describe different types of isomers:

• Diastereoisomers: Stereoisomers that are not mirror images of each other.
• Isomers: Compounds with the same molecular formula but different structures.
• Stereoisomers: Isomers with the same molecular formula and sequence of bonded atoms but different spatial arrangements.
• Epimer: A type of diastereomer that differs in configuration at only one chiral center.

Dorsiflexion refers to the movement at the ankle joint where the foot is pulled upwards towards the shin (tibia). This action decreases the angle between the dorsum (top) of the foot and the leg. It is the opposite of plantarflexion, where the foot points downward (e.g., standing on tiptoes).

The other terms describe different movements:

• Inversion: Turning the sole of the foot inward.
• Eversion: Turning the sole of the foot outward.
• Plantarflexion: Pointing the foot downward (away from the shin).
• Extension: A general term for straightening a joint, but not specific to the ankle.

The bacterial capsule is a polysaccharide or polypeptide layer outside the cell wall that serves as a virulence factor by protecting the bacterium from phagocytosis and immune recognition. Capsules exhibit significant antigenic variability due to differences in their chemical composition and structure among bacterial species and even strains. This variability allows bacteria to evade the host immune system.

The other options are less variable:

• Spore: Highly resistant structures formed by some bacteria, but not highly antigenically variable.
• Peptidoglycan: A rigid layer in the bacterial cell wall with a conserved structure.
• Slime: A less organized extracellular matrix with limited antigenic variability.
• Lipid A of endotoxin: A component of lipopolysaccharide (LPS) in Gram-negative bacteria, which is relatively conserved.

The Graafian follicle is a mature ovarian follicle that is ready for ovulation. It contains the following components:

1. Secondary oocyte: The mature egg cell arrested in metaphase II of meiosis.
2. Granulosa cells: Surround the oocyte and provide nourishment.
3. Cumulus oophorus: A cluster of granulosa cells that anchors the oocyte to the follicle wall.
4. Zona pellucida: A glycoprotein layer surrounding the oocyte.

The primary oocyte is present in earlier stages of follicular development (primordial and primary follicles) but undergoes meiosis I to become a secondary oocyte in the Graafian follicle.

Liquefactive necrosis typically occurs in the brain due to ischemic injury or bacterial infection. Key features include:

1. Brain tissue: The brain contains high amounts of hydrolytic enzymes and lipids, which lead to rapid digestion of dead tissue, resulting in a soft, liquefied area.
2. Cerebral infarction: Occlusion of a cerebral artery (as in this case) causes ischemia, leading to liquefactive necrosis.

Other types of necrosis:

• Coagulative necrosis: Seen in solid organs like the heart, kidney, and liver due to ischemia.
• Caseous necrosis: Characteristic of tuberculosis; has a cheese-like appearance.
• Fat necrosis: Occurs in adipose tissue, often due to trauma or pancreatitis.
• Gangrenous necrosis: Typically affects limbs (dry gangrene) or internal organs (wet gangrene).

Amino acids are classified as either essential or non-essential:

1. Essential amino acids: Cannot be synthesized by the body and must be obtained from the diet. Examples include phenylalanine, valine, and leucine.
2. Non-essential amino acids: Can be synthesized by the body. Examples include glutamine, glycine, alanine, and arginine.

Phenylalanine is an essential amino acid, meaning it must be consumed through dietary sources. The other options (glutamine, glycine, alanine, and arginine) are non-essential and can be synthesized by the body.

Ribozymes are RNA molecules that can catalyze specific biochemical reactions, similar to how protein enzymes function. They are unique because they combine the genetic information-carrying capability of RNA with the catalytic activity typically associated with proteins. Examples of ribozymes include the peptidyl transferase activity of the ribosome (during protein synthesis) and self-splicing introns.

The other options are incorrect:

• Ribonuclease: A protein enzyme that degrades RNA, not an RNA molecule itself.
• Ribosome: A complex of RNA and proteins that facilitates protein synthesis, but the catalytic activity is attributed to its RNA component (a ribozyme).
• Ribonucleotide: A building block of RNA, not a catalytic molecule.
• mRNA: Messenger RNA carries genetic information from DNA to the ribosome but does not have catalytic activity.

Gangliosides are a type of glycosphingolipid that are predominantly found in the neuronal cell membranes of the central nervous system (CNS). They play an essential role in cell signaling, neurodevelopment, and synaptic transmission.

Key Features of Gangliosides in Neurons:

✅ Mainly located in the outer leaflet of neuronal plasma membranes.
✅ Involved in synaptic transmission and signal transduction.
✅ Rich in sialic acid residues, which contribute to electrical conductivity and intercellular communication.
✅ Abnormal metabolism of gangliosides leads to lysosomal storage disorders, such as Tay-Sachs disease and Sandhoff disease.

Why Not the Other Options?

• Oligodendrocytes → Responsible for myelination in the CNS, but do not primarily contain gangliosides.
• Ganglion cells of the central nervous system (CNS) → Gangliosides are found in the CNS, but they are most concentrated in neurons, not just ganglion cells.
• All cells of the body → Incorrect; gangliosides are not found in all cells, but predominantly in neurons.
• Ganglion cells of the peripheral nervous system (PNS) → Present in PNS ganglia, but neurons in the CNS have a much higher concentration of gangliosides.

Thus, the correct answer is “Neurons,” as gangliosides are highly concentrated in neuronal membranes, especially in the CNS.

Somites are blocks of paraxial mesoderm that form during embryonic development and give rise to important structures such as the axial skeleton, skeletal muscles, and dermis of the skin. Key facts about somites include:

1. Rate of formation: Somites form at a rate of approximately 3 pairs per day during the embryonic period.
2. Total number: A total of 42-44 pairs of somites are formed during fetal life, not 44-47 pairs.
3. Function: Somites are involved in the development of the axial skeleton and are used to estimate the age of the embryo during the fetal period.
4. Origin: They are derived from blocks of paraxial mesoderm.

Thus, the statement claiming 44-47 pairs of somites is incorrect.

Structural isomers, also known as constitutional isomers, have the same molecular formula but differ in the way their atoms are connected. This leads to different arrangements of functional groups and the carbon skeleton itself. Think of it like having the same Lego bricks but building completely different structures with them.

Here’s why the other options aren’t the best fit:

• Optical isomers (Enantiomers): These are stereoisomers (same connectivity, different spatial arrangement) that are non-superimposable mirror images of each other, like your left and right hands. They arise due to chirality, often around a carbon atom bonded to four different groups. While they are isomers, the question specifically asks about differences due to functional group arrangement, not just spatial arrangement.

• Chain isomers: These are a specific type of structural isomer where the difference is in the branching of the carbon chain. While they are structural isomers, the question is asking about the broader category.

• Epimers: These are stereoisomers that differ in the configuration at only one chiral center. Again, while they are isomers, they are a more specific type of stereoisomer, and the question asks about functional group arrangement, not just spatial arrangement.

Synovial joints are characterized by the following features:

1. High mobility: They allow for a wide range of movements.
2. Synovial cavity: Filled with synovial fluid, which lubricates the joint.
3. Articular cartilage: Hyaline cartilage covers the articulating surfaces.
4. Ligaments: Intra-capsular and extra-capsular ligaments provide stability.
5. Fibrous tissue: Forms the joint capsule.

The statement that synovial joints are “immobile” is incorrect because synovial joints are specifically designed for movement.

Obligate anaerobes cannot survive in the presence of oxygen because they lack the enzymes necessary to neutralize toxic reactive oxygen species (ROS).

Why Can’t Obligate Anaerobes Tolerate Oxygen?

✅ Oxygen generates toxic byproducts, such as superoxide radicals (O₂⁻) and hydrogen peroxide (H₂O₂), which can damage cellular components.
✅ Obligate anaerobes lack key detoxifying enzymes:

• Superoxide dismutase (SOD) → Converts superoxide radicals into hydrogen peroxide (H₂O₂).
• Catalase or peroxidase → Breaks down H₂O₂ into water and oxygen.
  ✅ Without these enzymes, oxygen leads to lethal oxidative damage in anaerobes.

Examples of Obligate Anaerobes:

• Clostridium species (e.g., Clostridium tetani, Clostridium botulinum)
• Bacteroides species
• Fusobacterium species

Why Not the Other Options?

• “They possess defences to make aerobic life possible” → Incorrect; they do not have protective enzymes, which is why they die in oxygen.
• “They require oxygen for ATP generation” → Incorrect; they use anaerobic respiration or fermentation, not oxidative phosphorylation.
• “They cannot use the fermentation pathway for ATP generation” → Incorrect; obligate anaerobes rely on fermentation or anaerobic respiration.
• “They need ATP produced by host cells for survival” → Incorrect; this describes obligate intracellular parasites, not obligate anaerobes.

Thus, the correct answer is “They lack superoxide dismutase and catalase,” as this explains why oxygen is toxic to obligate anaerobes.

Posttranscriptional modification of mRNA includes several key steps:

1. 5′ capping: Addition of a 7-methylguanosine cap at the 5′ end.
2. 3′ polyadenylation: Addition of a poly-A tail (a stretch of adenine nucleotides) at the 3′ end. The poly-A tail stabilizes the mRNA and aids in its export from the nucleus and translation in the cytoplasm.
3. Splicing: Removal of introns and joining of exons.

The other options are incorrect:

• Poly-U tail: Not added during mRNA processing.
• Primer: Used in DNA replication, not mRNA processing.
• 7-methylguanosine: Added at the 5′ end, not the 3′ end.
• GTP-cap: Not a term used in mRNA processing; the 5′ cap is a 7-methylguanosine cap.

The anatomical position is the standard reference position for describing the human body. It ensures consistency in anatomical terminology.

Key Features of the Anatomical Position:

✅ Body standing upright (erect posture).
✅ Face forward (eyes looking straight ahead).
✅ Arms by the side with palms facing forward (supinated).
✅ Feet together, pointing forward.

This standardized position allows for consistent reference when describing anatomical structures and movements.

Why not the other options?

• Squatting position, both arms by the side, and both feet inverted → Incorrect; anatomical position requires standing upright, not squatting.
• Standing straight, both arms abducted, both feet together → Incorrect; in anatomical position, arms are by the side, not abducted.
• Standing straight, face forward, arms by the side and flexed → Incorrect; the arms should not be flexed, they remain extended by the side.
• Standing straight, both arms by the side and feet everted → Incorrect; in anatomical position, feet are pointing forward, not everted.

Thus, the correct answer is “Standing straight, both arms by the side, and both feet together,” as this is the universally accepted anatomical position.

Membrane potential is the difference in electrical charge across a cell membrane, primarily maintained by the sodium-potassium pump (Na⁺/K⁺-ATPase). This pump actively transports:

1. 3 Na⁺ ions out of the cell.
2. 2 K⁺ ions into the cell.

This creates an electrochemical gradient, with sodium playing a key role in depolarization and action potentials. Other minerals like calcium, magnesium, and chlorine are important for cellular functions but are not directly responsible for maintaining the membrane potential.

Chromosomes are composed of chromatin, which is a complex of DNA and proteins. The primary proteins associated with DNA in chromosomes are histones. DNA wraps around histone proteins to form nucleosomes, which are the fundamental units of chromatin. This structure allows for the efficient packaging of DNA within the nucleus.

The other options are incorrect:

• Nucleotides: The building blocks of DNA and RNA, but not conjugated with proteins in chromosomes.
• Ribonucleic acid (RNA): Not a structural component of chromosomes.
• Nucleosides: Consist of a sugar and a base but are not conjugated with proteins in chromosomes.

The clinical description of red skin with painful blisters suggests a second-degree (partial-thickness) burn, which affects both the epidermis and the superficial part of the dermis.

Key Features of Second-Degree Burns:

✅ Involves both the epidermis and superficial dermis.
✅ Blister formation due to fluid accumulation between the damaged epidermis and dermis.
✅ Painful because nerve endings are still intact.
✅ Redness, swelling, and moist appearance due to inflammation and capillary damage.

Why Not the Other Options?

• Epidermis and deep dermis → Incorrect; deep dermal burns (deep partial-thickness burns) involve more extensive damage, often appearing white and dry with reduced pain due to nerve damage.
• Only dermis → Incorrect; the dermis is never affected without also involving the epidermis.
• Epidermis → Incorrect; first-degree burns (e.g., sunburns) affect only the epidermis and do not cause blistering.
• Epidermis and entire dermis → Incorrect; this describes third-degree (full-thickness) burns, which appear white or charred, are painless (due to nerve destruction), and require grafting.

Thus, the correct answer is “Epidermis and superficial dermis,” as second-degree burns affect these layers and cause blisters, redness, and pain.

Normal flora, also known as commensal microbiota, are microorganisms (mostly bacteria) that live in or on the human body without normally causing disease. They colonize various sites, including the skin, throat, small intestine, and large intestine. These areas provide a suitable environment for these microorganisms to thrive.

However, blood is normally sterile. The presence of microorganisms in the bloodstream indicates a serious infection (bacteremia or septicemia), not normal flora. The body has robust defense mechanisms to prevent microbial growth in the blood.

Irreversible injury, also known as cell death, is characterized by specific morphological changes. The most definitive hallmark is the loss of the nucleus, which can occur through:

1. Karyolysis: Dissolution of the nucleus.
2. Pyknosis: Shrinkage and condensation of the nucleus.
3. Karyorrhexis: Fragmentation of the nucleus.

Other features of irreversible injury include:

• Eosinophilia: Increased staining of the cytoplasm with eosin due to denatured proteins.
• Cellular swelling: Early change in reversible injury, not specific to irreversible injury.
• Cellular blebbing: Formation of membrane protrusions, seen in both reversible and irreversible injury.
• Loss of proteins: Occurs in cell death but is not a definitive hallmark.

The semi-conservative model of DNA replication, proposed by Watson and Crick and experimentally proven by Meselson and Stahl, describes the process as follows:

1. The parental DNA double helix unwinds, and each strand serves as a template for the synthesis of a new complementary strand.
2. Each daughter DNA molecule consists of one parental (old) strand and one newly synthesized strand.

This ensures genetic continuity while allowing for replication and repair. The other options describe incorrect or alternative models of DNA replication:

• Fragments of both new and old strand are dispersed: This describes the dispersive model.
• Parental strands stay together as new DNA is formed: This describes the conservative model.
• Two entirely new daughter DNA are formed: This is incorrect, as the parental strands are not preserved.
• No new strand is formed: This is incorrect, as replication involves the synthesis of new strands.

The term prone refers to a body position where the individual is lying face down. During push-ups, the athlete’s chest and abdomen face the ground, which aligns with the definition of the prone position.

Other anatomical positions include:

• Recumbent: Lying down in any position (general term).
• Supine: Lying face up.
• Lateral: Lying on the side.
• Medial: A directional term referring to structures closer to the midline of the body, not a body position.

The decidua is the specialized endometrium of the uterus during pregnancy. It is divided into three regions based on its relationship to the implanted embryo:

1. Decidua basalis: The portion directly beneath the embryo, where the placenta forms.
2. Decidua capsularis: The thin layer overlying the embryo, separating it from the uterine cavity.
3. Decidua parietalis: The remaining decidua lining the rest of the uterine cavity.

The decidua basalis is critical for placental development and maternal-fetal exchange. The other options are incorrect because:

• Fused parietalis and basalis: This does not describe a specific decidual region.
• Decidua parietalis: This lines the non-implantation side of the uterus.
• Decidua capsularis: This covers the embryo but does not lie beneath it.
• Fused parietalis and capsularis: This is not a recognized term in embryology.

Tyrosine is an amino acid that serves as the precursor for the synthesis of several important hormones:

1. Epinephrine (adrenaline) and norepinephrine (noradrenaline): These catecholamines are synthesized in the adrenal medulla and play key roles in the “fight or flight” response.
2. Thyroxine (T4): A thyroid hormone involved in regulating metabolism, growth, and development.

The other amino acids listed are not involved in the synthesis of these hormones:

• Valine: A branched-chain amino acid.
• Tryptophan: Precursor for serotonin and melatonin.
• Ornithine: Intermediate in the urea cycle.
• Glycine: Involved in the synthesis of proteins, purines, and heme.

The B-complex vitamins (e.g., B1, B2, B3, B5, B6, B7, B9, and B12) are essential coenzymes in various metabolic pathways. Examples include:

1. Vitamin B1 (Thiamine): Coenzyme in carbohydrate metabolism.
2. Vitamin B2 (Riboflavin): Precursor for FAD and FMN, involved in redox reactions.
3. Vitamin B3 (Niacin): Precursor for NAD⁺ and NADP⁺, involved in energy production.
4. Vitamin B12 (Cobalamin): Coenzyme in amino acid and fatty acid metabolism.

Other vitamins:

• Vitamin D: Acts as a hormone, regulating calcium and phosphate metabolism.
• Vitamin E: An antioxidant, not a coenzyme.
• Vitamin A: Involved in vision and immune function, not a coenzyme.

Isosmotic volume contraction refers to a loss of fluid from the body that is isotonic (same osmolarity as plasma), leading to a decrease in extracellular fluid volume without a change in osmolarity. This occurs in conditions where both water and electrolytes are lost in equal proportions.

• Diarrhea: Results in the loss of isotonic fluid from the gastrointestinal tract, causing isosmotic volume contraction.
• Increased antidiuretic hormone (ADH) secretion: Leads to water retention and hyponatremia, not isosmotic volume contraction.
• Increased absorption of salts from the intestine: Does not typically cause volume contraction.
• Excessive blood loss: Causes hypovolemia but is not necessarily isosmotic, as it involves loss of both plasma and cells.

Cerebrosides are a type of glycosphingolipid, which are lipids containing a sphingosine backbone. Their structure includes:

1. Sphingosine: A long-chain amino alcohol.
2. Fatty acid: Attached to the amino group of sphingosine, forming ceramide.
3. Galactose or glucose: A single sugar molecule attached to the ceramide.

Thus, cerebrosides are composed of sphingosine, a fatty acid, and a sugar (galactose or glucose), forming ceramide as an intermediate.

The other options are incorrect:

• Sphingosine, ceramide, and phosphate: Describes sphingomyelin, not cerebrosides.
• Fatty acids and ceramide only: Incomplete, as cerebrosides also contain a sugar molecule.
• Sphingosine, phosphate, and fatty acid: Describes phosphosphingolipids, not cerebrosides.
• Ceramides only: Ceramides are intermediates in cerebroside synthesis but lack the sugar component.

Essential fatty acids (EFAs) are those that cannot be synthesized by the body and must be obtained from the diet. They include:

1. Linoleic acid (LA): An omega-6 fatty acid.
2. Alpha-linolenic acid (ALA): An omega-3 fatty acid.
3. Arachidonic acid (AA): Derived from linoleic acid and also considered essential in certain conditions.

The other options are incorrect:

• Palmitic acid and palmitoleic acid: Non-essential fatty acids.
• Oleic acid: A non-essential monounsaturated fatty acid.
• Acetic acid, butyric acid, and capric acid: Short-chain fatty acids, not essential.

Secondary cartilaginous joints, also called symphyses, are characterized by:

1. Midline location: Found in the midline of the body (e.g., pubic symphysis, intervertebral discs).
2. Fibrocartilage: The bones are united by fibrocartilage, which provides strength and flexibility.
3. Slight mobility: These joints allow limited movement, such as during childbirth or spinal flexion.

However, they are not covered by a synovial membrane, which is a feature of synovial joints (e.g., knee, shoulder). Synovial membranes produce synovial fluid to lubricate the joint, but secondary cartilaginous joints lack this structure.

MicroRNAs (miRNAs) are small, non-coding RNA molecules that play a crucial role in the regulation of gene expression by binding to messenger RNA (mRNA) and either blocking translation or inducing degradation.

Key Features of miRNA in Gene Regulation:

✅ Binds to complementary sequences on mRNA (usually in the 3’ UTR region).
✅ Inhibits translation by preventing ribosome attachment.
✅ Leads to mRNA degradation if the binding is highly complementary.
✅ Regulates numerous biological processes, including cell differentiation, proliferation, and apoptosis.
✅ Dysregulation of miRNA is linked to diseases, such as cancer and neurodegenerative disorders.

Why not the other options?

• ssRNA (Single-stranded RNA) → Not specific for gene regulation; miRNA is a functional type of ssRNA.
• rRNA (Ribosomal RNA) → Involved in protein synthesis, not gene regulation.
• mRNA (Messenger RNA) → Carries genetic information for protein synthesis, but does not regulate gene expression.
• tRNA (Transfer RNA) → Functions in protein translation, not gene regulation.

Thus, the correct answer is “miRNA,” as it directly regulates gene expression by targeting mRNA.

Chromatin is the complex of DNA and histone proteins that make up the genetic material within the nucleus. It exists in two forms:

1. Euchromatin: Loosely packed and transcriptionally active.
2. Heterochromatin: Tightly packed and transcriptionally inactive.

The other parts of the nucleus have different functions:

• Nuclear pore: Allows transport of molecules between the nucleus and cytoplasm.
• Nucleolus: Site of ribosomal RNA synthesis and ribosome assembly.
• Nuclear envelope: Double membrane that encloses the nucleus.
• Nucleoplasm: The gel-like substance within the nucleus, excluding the nucleolus and chromatin.

The skin over the elbow is covered by stratified squamous keratinized epithelium, which provides protection against mechanical stress, dehydration, and pathogens. However, the inner lining of the mouth, esophagus, and other moist surfaces is covered by stratified squamous non-keratinized epithelium. Since the question specifies bleeding from an injury (likely involving the skin), the damaged epithelium is stratified squamous keratinized.

The other options are incorrect:

• Simple squamous: Found in areas like the alveoli of the lungs and blood vessels, not the skin.
• Pseudostratified: Found in the respiratory tract (e.g., trachea).
• Simple cuboidal: Found in glands and kidney tubules, not the skin.

Fingerprinting is one of the most reliable methods of personal identification because fingerprints are unique to each individual and remain unchanged throughout life.

Key Advantages of Fingerprinting:

✅ Absolute Identification → No two people have the same fingerprints, making it the gold standard for forensic and legal identification.
✅ Permanent and Stable → Fingerprint patterns do not change with age or external conditions.
✅ Used in Law Enforcement → Helps in criminal investigations, border security, and forensic science.

Why not the other options?

• No special training required → Incorrect; fingerprint collection and analysis require trained personnel in forensic science.
• It is applicable for all people → Incorrect; individuals with fingerprint anomalies (e.g., genetic disorders like adermatoglyphia) may not have usable fingerprints.
• It is applicable for all age groups → Incorrect; newborns may have underdeveloped ridge patterns, making fingerprinting difficult.
• It does not require any special and expensive instruments → Incorrect; advanced automated fingerprint identification systems (AFIS) and digital scanners are used, which can be costly.

Thus, the correct answer is “It enables absolute identification of an individual,” as fingerprinting provides a unique and reliable method for personal identification.

Cleavage lines (also known as Langer’s lines) are natural orientation patterns of collagen fibers in the dermis. These lines are clinically significant because:

1. They indicate the direction of least tension in the skin.
2. Surgical incisions made parallel to these lines heal with less scarring.

Other fibers in the skin:

• Elastic fibers: Provide elasticity and resilience to the skin.
• Reticular fibers: Thin collagen fibers that form a supportive network in connective tissues.
• Fibronectin fibers: Glycoproteins involved in cell adhesion and migration.
• Muscle fibers: Found in muscles, not directly related to skin cleavage lines.

Phosphate is the primary intracellular anion and plays a crucial role in energy metabolism (e.g., ATP), buffering, and nucleic acid synthesis. Its concentration is much higher inside cells than in extracellular fluid.

The other anions are either less abundant or primarily located extracellularly:

• Chloride (Cl⁻): The major extracellular anion.
• Bicarbonate (HCO₃⁻): Important for buffering in blood but less abundant intracellularly.
• Sulphates (SO₄²⁻): Present in small amounts and not a major intracellular anion.
• Magnesium (Mg²⁺): A cation, not an anion.

Hypertrophy refers to an increase in the size of cells, leading to an increase in the size of the affected organ. In long-standing hypertension, the heart (particularly the left ventricle) undergoes hypertrophy to compensate for the increased workload required to pump blood against elevated pressure. This is known as left ventricular hypertrophy (LVH).

The other options are incorrect:

• Hyperplasia: An increase in the number of cells, which is not the primary response in hypertension.
• Atrophy: A decrease in cell size or number, which is not associated with hypertension.
• Dysplasia: Abnormal cell growth or development, often a precursor to cancer, unrelated to hypertension.
• Metaplasia: The replacement of one cell type with another, which is not a response to hypertension.