General Physiology Practice Questions

Q: Diffusion is inversely related to which of the following parameters?

Molecular size. This question is based on **Graham’s Law of Diffusion** and **Fick’s Law of Diffusion**, which describe the factors influencing the movement of substances across biological membranes [1]. ### Why Molecular Size is Correct According to Graham’s Law, the rate of diffusion of a gas (or solute) is **inversely proportional** to the square root of its **molecular weight (size)**. Larger molecules move more slowly due to increased resistance and lower kinetic velocity at a given temperature. Therefore, as molecular size increases, the rate of diffusion decreases. ### Why Other Options are Incorrect * **B. Area:** According to Fick’s Law, the rate of diffusion is **directly proportional** to the surface area available. A larger surface area (e.g., alveolar membrane in lungs) facilitates faster diffusion. * **C. Concentration Gradient:** Diffusion is **directly proportional** to the concentration (or partial pressure) gradient. A steeper gradient provides a stronger driving force for molecules to move from high to low concentration [2]. * **D. Solubility:** The rate of diffusion is **directly proportional** to the lipid solubility of the substance. For example, $CO_2$ is much more soluble than $O_2$, allowing it to diffuse across the respiratory membrane significantly faster despite being a larger molecule. ### High-Yield NEET-PG Pearls * **Fick’s Law Equation:** $Rate \propto \frac{Area \times Concentration\ Gradient \times Solubility}{Thickness \times \sqrt{Molecular\ Weight}}$ * **Membrane Thickness:** Diffusion is **inversely proportional** to the thickness of the membrane. This is clinically relevant in **Interstitial Lung Disease (ILD)**, where thickened membranes impair gas exchange. * **Clinical Application:** In the blood-brain barrier (BBB), highly lipid-soluble drugs (like thiopentone) diffuse rapidly, whereas large, polar molecules (like most antibiotics) require specific transporters or have poor penetration.

Q: Which of the following statements about Histamine is true?

All of the above. **Explanation:** Histamine is a biogenic amine that acts as a potent chemical mediator in various physiological and pathological processes. * **Option A (Mast Cells):** Histamine is primarily synthesized and stored in the granules of **mast cells** and **basophils**. Upon IgE-mediated stimulation (Type I Hypersensitivity), these cells degranulate, releasing histamine into the surrounding tissue. * **Option B (Gastric Acid):** In the stomach, histamine is released by **Enterochromaffin-like (ECL) cells**. It binds to **H2 receptors** on gastric parietal cells, activating the proton pump via the cAMP pathway to increase gastric acid secretion. This is the physiological basis for using H2-blockers (e.g., Ranitidine) in peptic ulcer disease. * **Option C (Arousal and BP):** In the CNS, histaminergic neurons originate in the **tuberomammillary nucleus** of the hypothalamus and are essential for maintaining **wakefulness/arousal** (which is why first-generation antihistamines cause sedation). Peripherally, histamine causes significant **vasodilation** (via H1 and H2 receptors), which can lead to a fall in blood pressure, most notably during anaphylaxis. **Clinical Pearls for NEET-PG:** * **Triple Response of Lewis:** Characterized by Red spot (capillary dilation), Flare (arteriolar dilation), and Wheal (exudation/edema) upon intradermal histamine injection. * **Receptors:** H1 (Allergy/Gq), H2 (Gastric acid/Gs), H3 (Presynaptic/Gi), H4 (Chemotaxis). * **Histamine Synthesis:** Derived from the amino acid **L-histidine** via the enzyme histidine decarboxylase.

Q: Which of the following is NOT an ATP-dependent transporter?

Na+ Ca2+ exchanger. ### Explanation The core concept here is distinguishing between **Primary Active Transport** and **Secondary Active Transport**. **Why Option D is Correct:** The **Na⁺-Ca²⁺ Exchanger (NCX)** is a classic example of **Secondary Active Transport** (specifically an antiport). It does not utilize ATP directly. Instead, it harnesses the potential energy created by the sodium concentration gradient (maintained by the Na⁺-K⁺ ATPase) to move one Calcium ion out of the cell against its gradient in exchange for three Sodium ions moving into the cell. **Why the other options are incorrect:** * **A. Na⁺-K⁺ ATPase:** This is the prototypical **Primary Active Transport** pump. It directly hydrolyzes ATP to move 3 Na⁺ out and 2 K⁺ into the cell. * **B. H⁺ ATPase:** Found in the intercalated cells of the renal collecting ducts and gastric parietal cells (as H⁺-K⁺ ATPase), these pumps directly use ATP to transport protons against steep concentration gradients. * **C. CFTR:** Although it functions as a Chloride channel, CFTR is a member of the **ABC (ATP-Binding Cassette) transporter family**. It requires ATP binding and hydrolysis to "gate" or open the channel. Therefore, it is ATP-dependent. ### High-Yield Clinical Pearls for NEET-PG: 1. **Digitalis Mechanism:** Digoxin inhibits the Na⁺-K⁺ ATPase. This increases intracellular Na⁺, which subsequently slows down the **Na⁺-Ca²⁺ exchanger**. The resulting increase in intracellular Ca²⁺ leads to increased cardiac contractility (positive inotropy). 2. **CFTR Mutation:** The most common mutation in Cystic Fibrosis is **ΔF508**, leading to misfolding of the protein in the endoplasmic reticulum. 3. **SGLT-1/2:** These are other high-yield examples of Secondary Active Transport (Symporters) that use the Na⁺ gradient rather than direct ATP.

Q: Adenylyl cyclase is associated with which of the following?

Seven transmembrane domain receptors or GPCR. **Explanation:** **1. Why the Correct Answer is Right:** Adenylyl cyclase (AC) is a key effector enzyme in the **G-protein coupled receptor (GPCR)** signaling pathway. GPCRs are also known as **Seven Transmembrane (7-TM) Domain receptors** or Serpentine receptors because they cross the cell membrane seven times. When a ligand binds to a GPCR, it activates a heterotrimeric G-protein. If the **Gs (stimulatory)** subunit is activated, it stimulates Adenylyl cyclase to convert ATP into **cyclic AMP (cAMP)**, which acts as a second messenger to activate Protein Kinase A (PKA). Conversely, the **Gi (inhibitory)** subunit inhibits this enzyme. **2. Why the Incorrect Options are Wrong:** * **GABA-A and Glycine Receptors:** These are **Ionotropic receptors** (ligand-gated ion channels). Specifically, they are pentameric structures that act as chloride channels. Binding of the neurotransmitter leads to an immediate influx of $Cl^-$ ions, causing hyperpolarization, rather than activating enzymatic cascades like Adenylyl cyclase. * **Cholinergic Receptors:** This is a broad category. While **Muscarinic** receptors (M1-M5) are GPCRs, **Nicotinic** receptors (N1, N2) are ionotropic (sodium channels). Since the question asks what Adenylyl cyclase is fundamentally associated with, the structural definition of "GPCR/7-TM" is the most accurate and universal answer. **3. High-Yield Facts for NEET-PG:** * **Second Messengers:** cAMP (via Adenylyl cyclase), $IP_3/DAG$ (via Phospholipase C), and cGMP (via Guanylyl cyclase). * **Toxins:** *Vibrio cholerae* toxin causes permanent activation of Gs (increasing cAMP), while *Pertussis* toxin inhibits Gi (also leading to increased cAMP). * **GPCR Examples:** Most hormones (ACTH, Glucagon, TSH) and sensory receptors (Rhodopsin, Olfactory receptors) are 7-TM receptors.

Q: What is the osmotic pressure of 1 mol of an ideal solute relative to pure water?

22.4 atm. ### Explanation **1. Why the Correct Answer is Right (The Concept)** The osmotic pressure of a solution is determined by the number of solute particles present, as described by **van't Hoff’s Law**. According to the Ideal Gas Law ($PV = nRT$), at standard temperature and pressure (STP, 0°C or 273 K), one mole of an ideal gas occupies a volume of 22.4 liters at 1 atmosphere of pressure. In the context of solutions, if **1 mole** of an ideal (non-dissociating) solute is dissolved in **1 liter** of water at 0°C, it exerts an osmotic pressure of **22.4 atmospheres (atm)**. This is a fundamental constant in physiology used to calculate the tonicity of body fluids. **2. Why the Incorrect Options are Wrong** * **Option A (6.5 atm):** This value is incorrect. However, it is worth noting that the total osmotic pressure of human plasma is approximately 7.3 atm (5500-5600 mmHg), which is much lower than 22.4 atm because plasma is not a 1-molar solution. * **Options C & D (4 atm and 2 atm):** These are arbitrary values that do not correspond to any standard physical constants related to molarity and osmotic pressure at STP. **3. Clinical Pearls & High-Yield Facts for NEET-PG** * **Osmolarity vs. Osmolality:** In clinical practice, we use **Osmolality** (mOsm/kg of water) because it is independent of temperature, whereas Osmolarity (mOsm/L) changes with temperature. * **Plasma Osmolality:** Normal range is **280–295 mOsm/kg**. It is primarily determined by Sodium ($Na^+$), Glucose, and BUN. * **Formula:** $Calculated\ Osmolality = 2[Na^+] + \frac{Glucose}{18} + \frac{BUN}{2.8}$. * **Oncotic Pressure:** While the total osmotic pressure of plasma is high (~5500 mmHg), the **Colloid Osmotic Pressure (Oncotic Pressure)** exerted by proteins (mainly albumin) is only about **25–28 mmHg**. This small fraction is crucial for preventing edema.

Q: Steroids are transported inside the cell using which mechanism?

Simple diffusion. **Explanation:** **1. Why Simple Diffusion is Correct:** Steroid hormones (such as cortisol, aldosterone, estrogen, and testosterone) are derivatives of **cholesterol**, making them highly **lipophilic (lipid-soluble)**. The cell membrane is composed of a phospholipid bilayer. Because "like dissolves like," steroid hormones can easily dissolve in the lipid matrix of the plasma membrane and cross it without the need for carrier proteins or energy. They move down their concentration gradient directly into the cytosol or nucleus to bind with intracellular receptors. **2. Why Other Options are Incorrect:** * **Facilitated Diffusion:** This requires specific transmembrane carrier proteins or channels (e.g., GLUT transporters for glucose). Steroids do not require these because they are not blocked by the lipid bilayer. * **Active Transport:** This process moves molecules against a concentration gradient using ATP (e.g., Na+/K+ ATPase pump). Steroid transport is a passive process driven by concentration gradients. * **Osmosis:** This specifically refers to the movement of **water** molecules across a semi-permeable membrane. **3. NEET-PG High-Yield Pearls:** * **Intracellular Receptors:** Most steroid hormones bind to receptors in the cytoplasm (Type I) or nucleus (Type II), acting as transcription factors to alter gene expression. * **Exception:** While steroids cross the *cell membrane* via simple diffusion, they are poorly soluble in *blood* and must be transported in the plasma bound to specific carrier proteins (e.g., Sex Hormone Binding Globulin, Albumin). * **Thyroid Hormones (T3/T4):** Like steroids, they are lipophilic and have intracellular receptors, but they often utilize specialized membrane transporters (facilitated diffusion) to enter cells more efficiently.

Q: What happens to the resting membrane potential when extracellular potassium is increased from 4 meq/L to 10 meq/L?

Increase in potassium conductance.. **Explanation:** The resting membrane potential (RMP) is primarily determined by the permeability of the cell membrane to potassium ions ($K^+$) via **inward rectifier potassium channels ($K_{ir}$)**. **Why Option C is Correct:** According to the **Goldman-Hodgkin-Katz equation**, membrane conductance (permeability) for an ion is influenced by its extracellular concentration. When extracellular $K^+$ increases (hyperkalemia), it causes a conformational change in potassium channels that **increases their conductance**. Additionally, the increased extracellular $K^+$ reduces the concentration gradient, causing the RMP to become **less negative (depolarization)**. This depolarization moves the membrane potential closer to the threshold, initially increasing excitability. **Analysis of Incorrect Options:** * **Option A:** Increasing extracellular $K^+$ decreases the efflux of $K^+$, making the RMP **less negative** (depolarization), not more negative (hyperpolarization). * **Option B:** Sodium conductance is primarily regulated by voltage-gated sodium channels during the action potential, not by changes in extracellular potassium at rest. * **Option D:** $Na^+/K^+$ ATPase activity is actually **stimulated** by an increase in extracellular potassium, as it works harder to pump the excess $K^+$ back into the cell to maintain homeostasis. **High-Yield Clinical Pearls for NEET-PG:** * **Hyperkalemia Paradox:** While mild hyperkalemia increases excitability (depolarization), severe hyperkalemia leads to **"depolarization block"** because sodium channels remain in an inactivated state, leading to cardiac arrest in diastole. * **ECG Changes:** Tall tented T-waves, PR prolongation, and widened QRS complexes are classic signs of hyperkalemia. * **Nernst Equation:** Used to calculate the equilibrium potential for a single ion; for $K^+$, it is approximately -94 mV.

Q: What does the Golgi tendon organ primarily detect?

Muscle tension. **Explanation:** The **Golgi Tendon Organ (GTO)** is a high-threshold mechanoreceptor located in the tendons of skeletal muscles, arranged in **series** with the muscle fibers. Its primary function is to monitor and respond to **muscle tension** (force of contraction). When a muscle contracts, it pulls on the tendon, compressing the nerve endings within the GTO. This triggers an inhibitory signal via **Ib afferent fibers** to the spinal cord, causing the muscle to relax (the **Inverse Stretch Reflex**). This mechanism protects the muscle and tendon from damage due to excessive force. **Analysis of Options:** * **Option A & D (Static and Dynamic Muscle Length):** These are detected by **Muscle Spindles**, which are arranged in **parallel** with muscle fibers. Nuclear chain fibers detect static length, while nuclear bag fibers detect dynamic changes in length (velocity). * **Option B (Muscle Action):** This is a general term. While GTOs are active during muscle action, their specific physiological stimulus is the resulting tension, not the action itself. **High-Yield Clinical Pearls for NEET-PG:** * **Location:** GTO is in **series**; Muscle Spindle is in **parallel**. * **Afferent Nerve:** GTO uses **Type Ib** fibers; Muscle Spindle uses **Type Ia** (primary) and **Type II** (secondary) fibers. * **Reflex:** GTO mediates the **Autogenic Inhibition** (Inverse Stretch Reflex), whereas the Muscle Spindle mediates the **Stretch Reflex** (DTRs). * **Function:** GTO prevents avulsion injuries; Muscle Spindles maintain muscle tone and posture.

Q: Which of the following statements is true about Nissl granules?

Involves in protein synthesis. **Explanation:** **Nissl granules** (also known as Nissl bodies) are large, granular structures found in the cytoplasm of neurons. They are composed of **Rough Endoplasmic Reticulum (RER)** and associated **free ribosomes**. 1. **Why Option C is correct:** The primary function of ribosomes and RER is translation. Therefore, Nissl granules are the primary sites of **protein synthesis** in the neuron, producing proteins required for intracellular transmission and the renewal of structural components. 2. **Why other options are incorrect:** * **Option A:** RNA synthesis (transcription) occurs within the **nucleus** (specifically the nucleolus for rRNA), not in the Nissl granules. * **Option B:** Nissl granules are found in the **cyton (cell body)** and **dendrites**, but they are characteristically **absent in the axon** and the **axon hillock**. This is a classic anatomical landmark used to identify the start of an axon. * **Option D:** While they contain RER, stating they are "structurally endoplasmic reticulum" is incomplete. They are a complex of **RER plus free ribosomes**. (Note: In many competitive exams, "Protein Synthesis" is the more functional and definitive answer). **High-Yield Clinical Pearls for NEET-PG:** * **Chromatolysis:** When a neuron is injured (axonal injury), Nissl granules undergo hypertrophy, fragment, and disperse. This process is called chromatolysis, indicating an active attempt at protein synthesis for regeneration. * **Staining:** They are highly basophilic and are best visualized using basic dyes like **Cresyl Violet** or **Methylene Blue**. * **Location Tip:** Always remember: **D**endrites have them, **A**xons do not (**D** yes, **A** no).

Q: In which organs can the whole range of cyclooxygenase (COX) products be synthesized?

Spleen and Lung. **Explanation:** The synthesis of eicosanoids (prostaglandins, thromboxanes, and prostacyclins) via the **Cyclooxygenase (COX) pathway** is tissue-specific. While most cells possess the COX enzyme, they usually lack the downstream isomerases required to produce all types of prostanoids. For instance, platelets primarily produce Thromboxane $A_2$ ($TXA_2$), while endothelial cells primarily produce Prostacyclin ($PGI_2$). **Why Spleen and Lung are correct:** The **Spleen and Lungs** are unique because they possess a comprehensive array of terminal enzymes (isomerases and reductases). Consequently, they are the only organs capable of synthesizing the **entire spectrum** of COX products, including $PGE_2$, $PGF_{2\alpha}$, $PGD_2$, $PGI_2$, and $TXA_2$. This is a high-yield physiological fact often tested in competitive exams. **Analysis of Incorrect Options:** * **Liver:** While metabolically active, the liver primarily focuses on the degradation and conjugation of eicosanoids rather than the synthesis of the full range. * **Blood Vessels:** Vascular endothelium is specialized. It predominantly produces **Prostacyclin ($PGI_2$)**, which acts as a potent vasodilator and inhibitor of platelet aggregation. It does not synthesize the full range of COX products. **NEET-PG High-Yield Pearls:** * **Rate-limiting step:** The release of Arachidonic acid from membrane phospholipids by **Phospholipase $A_2$**. * **COX-1 vs. COX-2:** COX-1 is constitutive (housekeeping), while COX-2 is inducible (inflammatory). * **Aspirin:** Irreversibly inhibits COX by acetylation, leading to a prolonged anti-platelet effect because platelets cannot synthesize new enzymes.

Question 1

Diffusion is inversely related to which of the following parameters?

Accepted Answer

Molecular size

Answer

Area

Answer

Concentration gradient

Answer

Solubility

Question 2

Which of the following statements about Histamine is true?

Accepted Answer

All of the above

Answer

Is found in mast cells

Answer

Increases gastric acid secretion

Answer

Related to arousal and blood pressure

Question 3

Which of the following is NOT an ATP-dependent transporter?

Accepted Answer

Na+ Ca2+ exchanger

Answer

Na+ K+ ATPase

Answer

H+ ATPase

Answer

Cystic Fibrosis Transmembrane Regulator (CFTR)

Question 4

Adenylyl cyclase is associated with which of the following?

Accepted Answer

Seven transmembrane domain receptors or GPCR

Answer

GABA-a receptor

Answer

Cholinergic receptor

Answer

Glycine receptor

Question 5

What is the osmotic pressure of 1 mol of an ideal solute relative to pure water?

Accepted Answer

22.4 atm

Answer

6.5 atm

Answer

4 atm

Answer

2 atm

Question 6

Steroids are transported inside the cell using which mechanism?

Accepted Answer

Simple diffusion

Answer

Facilitated diffusion

Answer

Active transport

Answer

Osmosis

Question 7

What happens to the resting membrane potential when extracellular potassium is increased from 4 meq/L to 10 meq/L?

Accepted Answer

Increase in potassium conductance.

Answer

Resting membrane potential becomes more negative.

Answer

Increase in sodium conductance.

Answer

Na+/K+ ATPase activity will be inhibited.

Question 8

What does the Golgi tendon organ primarily detect?

Accepted Answer

Muscle tension

Answer

Static muscle length

Answer

Muscle action

Answer

Dynamic muscle length

Question 9

Which of the following statements is true about Nissl granules?

Accepted Answer

Involves in protein synthesis

Answer

Involves in RNA synthesis

Answer

Present in the axon

Answer

Structurally, they are endoplasmic reticulum

Question 10

In which organs can the whole range of cyclooxygenase (COX) products be synthesized?

Accepted Answer

Spleen and Lung

Answer

Spleen and Liver

Answer

Lung and Liver

Answer

Spleen and Blood vessel

General Physiology — MCQs

General Physiology — MCQs

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