General Physiology Practice Questions

Q: Which substance is most accurate for the measurement of extracellular fluid (ECF) volume?

Inulin. **Explanation:** The measurement of body fluid compartments is based on the **Indicator Dilution Principle** ($Volume = Amount / Concentration$). To measure a specific compartment, the substance used must be able to distribute evenly throughout that compartment but not cross into others. **Why Inulin is the Correct Answer:** **Inulin** is a polysaccharide that is ideal for measuring **Extracellular Fluid (ECF) volume**. It is small enough to pass through capillary pores into the interstitial space but too large and polar to cross cell membranes into the intracellular fluid (ICF). Other substances used for ECF measurement include **Mannitol, Sucrose, and Thiosulfate**. **Analysis of Incorrect Options:** * **A. Deuterium oxide ($D_2O$):** Also known as "Heavy Water," it distributes across all water-containing compartments (ECF + ICF). Therefore, it is used to measure **Total Body Water (TBW)**. * **B. Cr-51 labeled RBC:** These stay strictly within the vascular system. They are used to measure **Total Blood Volume**. * **C. Albumin (Radio-iodinated):** Albumin remains primarily in the intravascular space. It is used to measure **Plasma Volume**. **High-Yield Clinical Pearls for NEET-PG:** * **Intracellular Fluid (ICF):** Cannot be measured directly. It is calculated as $TBW - ECF$. * **Interstitial Fluid:** Cannot be measured directly. It is calculated as $ECF - Plasma\ Volume$. * **Inulin's Dual Role:** Inulin is the "Gold Standard" for measuring both **ECF volume** and **Glomerular Filtration Rate (GFR)** because it is freely filtered but neither reabsorbed nor secreted by the renal tubules.

Q: The titin protein present in the muscle fibre binds?

The tail ends of myosin filaments to the Z disc. ### Explanation **1. Why Option B is Correct:** Titin (also known as connectin) is the largest known protein in the human body. It acts as a molecular spring that maintains the structural integrity of the sarcomere. One end of the titin molecule is anchored to the **Z-disc**, while the other end extends to the **M-line**. Crucially, the portion of titin between the Z-disc and the beginning of the thick filament is elastic, while the remainder is bound to the **thick (myosin) filament**. Thus, titin serves as a scaffold that anchors the tail ends of myosin filaments to the Z-disc, ensuring they remain centered during contraction and relaxation. **2. Analysis of Incorrect Options:** * **Option A:** Actin filaments are anchored to the Z-disc by **alpha-actinin**, not titin. * **Option C:** While titin does extend to the M-line, its primary functional role in providing "passive elasticity" and structural alignment is defined by its connection between the **myosin filament and the Z-disc**. * **Option D:** The protein responsible for linking myofibrils to each other and to the sarcolemma (cell membrane) is **Desmin** (an intermediate filament) and the **Dystrophin-Glycoprotein Complex**. **3. NEET-PG High-Yield Pearls:** * **Largest Protein:** Titin is the largest single polypeptide chain (approx. 3,800 kDa). * **Passive Tension:** Titin is responsible for the "resting" or passive tension of a muscle when it is stretched. * **Nebulin:** Often confused with titin, Nebulin acts as a "molecular ruler" to regulate the length of **actin** (thin) filaments. * **Clinical Correlation:** Mutations in the titin gene (*TTN*) are a leading cause of **Dilated Cardiomyopathy (DCM)**.

Q: The Donnan effect of ion movement across the capillary wall is due to which of the following?

Proteins. **Explanation:** The **Gibbs-Donnan Effect** describes the behavior of charged particles near a semi-permeable membrane when one of the ions is **non-diffusible**. In the context of the capillary wall, **plasma proteins** (primarily albumin) act as these non-diffusible anions because they are too large to pass through the capillary pores. 1. **Why Proteins are correct:** Plasma proteins carry a net negative charge. Because they cannot cross the capillary wall, they exert an electrostatic pull on diffusible cations (like $Na^+$) to maintain electroneutrality and repel diffusible anions (like $Cl^-$). This results in a higher concentration of cations and a higher osmotic pressure (oncotic pressure) inside the capillary compared to the interstitial fluid. 2. **Why other options are incorrect:** * **Cations (A) and Anions (C):** Most small ions like $Na^+$, $K^+$, and $Cl^-$ are freely diffusible across the capillary wall. The Donnan effect is not *caused* by them, but rather *affects* their distribution due to the presence of the non-diffusible proteins. * **Albumin (D):** While albumin is the most abundant plasma protein contributing to this effect, the term **"Proteins"** is the more comprehensive and standard physiological answer, as globulins and other plasma proteins also contribute to the total non-diffusible anionic charge. **High-Yield Clinical Pearls for NEET-PG:** * **Donnan Factor:** In plasma, the concentration of cations is about **5% higher** than in the interstitial fluid due to this effect. * **Osmotic Implications:** The Donnan effect increases the total osmotic pressure of plasma by approximately **6-7 mmHg** more than what would be exerted by proteins alone. * **Formula:** At equilibrium, the product of diffusible ions on one side equals the product on the other: $[Na^+]_{in} \times [Cl^-]_{in} = [Na^+]_{out} \times [Cl^-]_{out}$.

Q: On changing position from lying down to standing, there is a drop in blood pressure of 10 mm Hg. Immediately, the blood pressure recovers by 8 mm Hg, leaving behind a drop of 2 mm Hg. What is the gain for the baroreceptor system in the control of blood pressure?

4 mm Hg. ### Explanation The concept of **Feedback Gain** is a measure of the effectiveness of a control system (like the baroreceptor reflex) in maintaining homeostasis. It is calculated using the following formula: $$\text{Gain} = \frac{\text{Correction}}{\text{Residual Error}}$$ **1. Why Option B is Correct:** In this scenario: * **Initial Change (Disturbance):** 10 mm Hg (The drop that would occur without compensation). * **Correction:** 8 mm Hg (The amount the baroreceptor reflex successfully restored). * **Residual Error:** 2 mm Hg (The remaining deviation from the original baseline). Applying the formula: $$\text{Gain} = \frac{8\text{ mm Hg}}{2\text{ mm Hg}} = 4$$ Therefore, the gain of the baroreceptor system in this individual is **4**. **2. Why Other Options are Incorrect:** * **Option A (2 mm Hg):** This represents the **Residual Error**, not the gain. * **Option C (8 mm Hg):** This represents the **Correction** achieved by the system. * **Option D (10 mm Hg):** This is the total **Initial Disturbance** caused by the change in posture. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Definition of Gain:** A higher gain indicates a more efficient regulatory system. * **Negative Feedback:** Most physiological systems (e.g., BP control, body temperature, hormone regulation) operate via negative feedback. The gain for negative feedback systems is technically a negative value (e.g., -4), but in exams, the absolute value is typically used. * **Baroreceptor Reflex:** This is a **short-term** regulator of BP. It is most sensitive at pressures near the normal mean arterial pressure (approx. 95–100 mm Hg). * **Highest Gain System:** The **Renal-Body Fluid System** for long-term blood pressure control has an "infinite gain," meaning it can eventually return the pressure exactly to the starting point (zero residual error).

Q: Which of the following are force-generating proteins?

Dynein and kinesin. **Explanation:** The question focuses on **molecular motors**, which are specialized proteins that convert chemical energy (ATP) into mechanical work to generate force and movement within cells. **Why Option B is Correct:** **Dynein and Kinesin** are the primary microtubule-based motor proteins. * **Kinesins** generally move cargo (organelles, vesicles) toward the **plus-end** of microtubules (anterograde transport, e.g., from the cell body to the axon terminal). * **Dyneins** move cargo toward the **minus-end** (retrograde transport) and are also responsible for the beating of cilia and flagella. * *Note:* **Myosin** is also a force-generating protein (actin-based), but it is paired incorrectly in Option A. **Why Other Options are Incorrect:** * **Option A:** While Myosin is a motor protein, **Myoglobin** is an iron-containing protein found in muscle cells that functions solely for oxygen storage, not force generation. * **Option C:** **Calmodulin** is a calcium-binding messenger protein that regulates various enzymatic activities (like MLCK). **G proteins** are molecular switches involved in signal transduction. Neither generates mechanical force. * **Option D:** **Troponin** is a regulatory protein complex (consisting of Troponin C, I, and T) that controls the interaction between actin and myosin. It acts as a "switch" but does not generate force itself. **High-Yield Clinical Pearls for NEET-PG:** * **Kartagener Syndrome:** Caused by a defect in **dynein arms**, leading to immotile cilia, bronchiectasis, and situs inversus. * **Axonal Transport:** Fast axonal transport (400 mm/day) utilizes kinesin and dynein, whereas slow transport (0.5–10 mm/day) carries structural proteins like tubulin. * **Myosin II** is the specific type of myosin responsible for muscle contraction.

Q: Antibody specificity is determined by the amino acid sequence within which region?

Variable region. **Explanation:** The specificity of an antibody (Immunoglobulin) is determined by its ability to bind to a specific antigen. This binding occurs at the **Variable (V) region**, located at the tips of the "Y" shaped molecule. 1. **Why the Variable Region is Correct:** The variable regions of both the heavy (VH) and light (VL) chains contain **Hypervariable regions** or **Complementarity-Determining Regions (CDRs)**. The unique amino acid sequences in these CDRs create a specific three-dimensional shape that is complementary to a specific epitope on an antigen, much like a lock and key. This sequence diversity is generated through V(D)J recombination during B-cell development. 2. **Why other options are incorrect:** * **Constant (C) region:** This region has a stable amino acid sequence within a particular class of antibody. It determines the **isotype** (IgG, IgM, etc.) and the biological effector function, not antigen specificity. * **Fc region (Fragment crystallizable):** This is the tail region of an antibody formed by the constant domains of the heavy chains. it mediates functions like complement activation and binding to cell surface receptors. * **Fc receptors:** These are proteins found on the surface of certain immune cells (like macrophages and NK cells) that bind to the Fc portion of antibodies; they are not part of the antibody's primary structure. **High-Yield Clinical Pearls for NEET-PG:** * **Fab fragment:** Contains one constant and one variable domain of each of the heavy and light chains; it is the part that binds to the antigen. * **Papain digestion:** Cleaves an antibody into **two Fab** fragments and **one Fc** fragment. * **Pepsin digestion:** Cleaves an antibody into **one F(ab')2** fragment (divalent) and degraded Fc fragments. * **Isotype switching:** Changes the Constant region (e.g., IgM to IgG) but keeps the Variable region (specificity) the same.

Q: Which of the following muscles has the maximum density of white muscle fibers?

Extraocular muscles. **Explanation:** The classification of muscle fibers into **Red (Type I)** and **White (Type II)** is based on their metabolic profile and contraction speed. White muscle fibers (Type II) are characterized by high myosin ATPase activity, low myoglobin content, and a reliance on anaerobic glycolysis. They are designed for **rapid, short bursts of activity** but fatigue easily. **Why Extraocular Muscles are correct:** The extraocular muscles (EOMs) require the fastest contraction speeds in the human body to perform saccadic eye movements. Consequently, they possess the highest density of **Type II (White) fibers**. These muscles are specialized for precision and extreme velocity rather than sustained weight-bearing or posture, making them the classic example of white muscle predominance. **Analysis of Incorrect Options:** * **Calf Muscle (Gastrocnemius/Soleus):** The Soleus is a classic "Red" muscle (Type I) used for maintaining standing posture. While the Gastrocnemius has mixed fibers, it does not match the white fiber density of the EOMs. * **Back Muscles (Erector Spinae):** These are "Antigravity" muscles. They consist predominantly of Type I (Red) fibers because they must remain contracted for long periods to maintain posture without fatiguing. * **Hip Muscles (Gluteus Maximus):** These are large, powerful muscles used for locomotion and posture. They contain a high proportion of Type I fibers to support sustained activity. **High-Yield Clinical Pearls for NEET-PG:** * **Type I (Red):** "One Slow Red Ox" — Type **I**, **Slow**-twitch, **Red** (high myoglobin), **Ox**idative phosphorylation (high mitochondria). Found in marathon runners. * **Type II (White):** Fast-twitch, glycolytic, low mitochondria. Found in sprinters and extraocular muscles. * **Laryngeal muscles** also have a high density of fast-twitch fibers, second only to extraocular muscles.

Q: Which of the following is NOT a component of the thin filament?

Myosin. ### Explanation The sarcomere, the functional unit of skeletal muscle, is composed of thick and thin filaments. Understanding their molecular composition is fundamental to the sliding filament theory of muscle contraction. **Why Myosin is the Correct Answer:** **Myosin** is the primary constituent of the **thick filament**, not the thin filament. A myosin molecule consists of two heavy chains (forming the tail and heads) and four light chains. The myosin heads contain ATPase activity and binding sites for actin, which are essential for cross-bridge formation. **Analysis of Incorrect Options (Components of the Thin Filament):** * **Actin (Option A):** This is the backbone of the thin filament. It exists as globular (G-actin) monomers that polymerize to form filamentous (F-actin) double-helical strands. * **Troponin (Option B):** A complex of three regulatory proteins: **Troponin T** (binds to tropomyosin), **Troponin I** (inhibits actin-myosin binding), and **Troponin C** (binds calcium ions). * **Tropomyosin (Option D):** A regulatory protein that wraps around the actin helix. In a resting state, it physically covers the active sites on actin, preventing interaction with myosin heads. **High-Yield NEET-PG Pearls:** * **Regulatory Proteins:** Troponin and Tropomyosin are termed "regulatory proteins" because they control the "on/off" switch for contraction. * **Contractile Proteins:** Actin and Myosin are the "contractile proteins." * **Structural Proteins:** **Titin** (the largest known protein) anchors myosin to the Z-discs, while **Nebulin** acts as a molecular ruler for actin length. * **Clinical Correlation:** **Troponin I and T** are highly specific cardiac biomarkers used in the diagnosis of Myocardial Infarction (MI).

Question 1

Which substance is most accurate for the measurement of extracellular fluid (ECF) volume?

Accepted Answer

Inulin

Answer

Deuterium oxide

Answer

Cr-51 labeled RBC

Answer

Albumin

Question 2

The titin protein present in the muscle fibre binds?

Accepted Answer

The tail ends of myosin filaments to the Z disc

Answer

The tail ends of actin filaments to Z disc

Answer

The tail end of myosin filaments to M disc

Answer

The myofibrils to each other, and also to the cell membrane

Question 3

The Donnan effect of ion movement across the capillary wall is due to which of the following?

Accepted Answer

Proteins

Answer

Cations

Answer

Anions

Answer

Albumin

Question 4

Which statement is true about the lipid bilayer of a cell membrane?

Accepted Answer

It has an asymmetrical arrangement of membrane components.

Answer

It allows for the lateral diffusion of ions.

Answer

It has a symmetrical arrangement of membrane components.

Answer

It is not made up of amphipathic lipids.

Question 5

On changing position from lying down to standing, there is a drop in blood pressure of 10 mm Hg. Immediately, the blood pressure recovers by 8 mm Hg, leaving behind a drop of 2 mm Hg. What is the gain for the baroreceptor system in the control of blood pressure?

Accepted Answer

4 mm Hg

Answer

2 mm Hg

Answer

8 mm Hg

Answer

10 mm Hg

Question 6

Which of the following are force-generating proteins?

Accepted Answer

Dynein and kinesin

Answer

Myosin and myoglobin

Answer

Calmodulin and G protein

Answer

Troponin

Question 7

Antibody specificity is determined by the amino acid sequence within which region?

Accepted Answer

Variable region

Answer

Fc region

Answer

Constant region

Answer

Fc receptors

Question 8

Which of the following muscles has the maximum density of white muscle fibers?

Accepted Answer

Extraocular muscles

Answer

Calf muscle

Answer

Back muscles

Answer

Hip muscles

Question 9

How is an electrical synapse different from a chemical synapse?

Accepted Answer

Connexons are involved in the structure of an electrical synapse.

Answer

There is no cytoplasmic continuity between presynaptic and postsynaptic neurons.

Answer

The direction of impulse transmission is unidirectional.

Answer

Electrical synapses have a longer latent period than chemical synapses.

Question 10

Which of the following is NOT a component of the thin filament?

Accepted Answer

Myosin

Answer

Actin

Answer

Troponin

Answer

Tropomyosin

General Physiology — MCQs

General Physiology — MCQs

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