Cellular Physiology Practice Questions

Q: Which cell junction allows the exchange of cytoplasmic molecules?

Gap junction. **Explanation:** **Gap junctions** (also known as nexus junctions) are specialized intercellular connections that directly link the cytoplasm of two cells. They are composed of transmembrane proteins called **connexins**, six of which assemble to form a hemichannel called a **connexon**. When connexons of adjacent cells align, they create a continuous aqueous channel. This allows the rapid, bidirectional exchange of ions (like $Ca^{2+}$), small metabolites, and second messengers (like cAMP), facilitating **electrical and metabolic coupling**. **Why other options are incorrect:** * **Tight Junctions (Zonula Occludens):** These act as a "barrier" or "seal" rather than a bridge. They fuse the outer layers of plasma membranes to prevent the paracellular leakage of water and solutes, maintaining cell polarity. * **Anchoring Junctions:** These provide mechanical stability. Examples include **Desmosomes** (cell-to-cell) and **Hemidesmosomes** (cell-to-matrix). They link the cytoskeletons of adjacent cells but do not allow the exchange of cytoplasmic molecules. **High-Yield Clinical Pearls for NEET-PG:** * **Cardiac Physiology:** Gap junctions are a key component of **intercalated discs**, allowing the heart to function as a functional syncytium for coordinated contraction. * **Smooth Muscle:** They are abundant in "unitary" (single-unit) smooth muscles, such as the uterus and GI tract. * **Clinical Correlation:** Mutations in connexin genes are linked to specific pathologies, such as **Connexin 26** mutations causing congenital non-syndromic deafness and **Connexin 32** mutations linked to X-linked Charcot-Marie-Tooth disease.

Q: What is the mechanism of secretion of macromolecules by a cell through fusion with a vesicle?

Phagocytosis. ### Explanation The correct mechanism for the secretion of macromolecules through vesicle fusion is **Exocytosis**. *(Note: There appears to be a discrepancy in the provided key; while Phagocytosis involves vesicles, it is an ingestive process. Exocytosis is the specific mechanism for secretion/export.)* #### 1. Why Exocytosis is the Correct Mechanism **Exocytosis** is the process by which a cell directs the contents of secretory vesicles out of the cell membrane. These membrane-bound vesicles move to the cell surface, fuse with the plasma membrane, and release their macromolecular contents (such as hormones, enzymes, or neurotransmitters) into the extracellular space. This process is often triggered by an increase in intracellular calcium ($Ca^{2+}$). #### 2. Analysis of Incorrect Options * **Phagocytosis (Option A):** Known as "cell eating," this is a form of **endocytosis** where the cell engulfs large solid particles (e.g., bacteria) into an internal vesicle called a phagosome. It is an intake mechanism, not a secretory one. * **Pinocytosis (Option B):** Known as "cell drinking," this involves the non-specific intake of extracellular fluid and small solutes via small vesicles. * **Endocytosis (Option D):** This is a general term for the transport of macromolecules **into** the cell. It encompasses phagocytosis, pinocytosis, and receptor-mediated endocytosis. #### 3. NEET-PG High-Yield Pearls * **SNARE Proteins:** The fusion of the vesicle with the plasma membrane is mediated by **v-SNAREs** (on the vesicle) and **t-SNAREs** (on the target membrane). * **Clathrin-Coated Pits:** Essential for receptor-mediated endocytosis (e.g., LDL cholesterol uptake). * **Transcytosis:** A combination of endocytosis and exocytosis used to move macromolecules across an entire cell layer (e.g., IgA secretion into breast milk). * **ATP Dependency:** All forms of vesicular transport (Exo/Endocytosis) are **active processes** requiring energy.

Q: The sodium-potassium pump is an example of which type of cellular transport?

Active transport. **Explanation:** The **Sodium-Potassium Pump (Na⁺/K⁺-ATPase)** is the classic example of **Primary Active Transport**. It is "active" because it moves ions against their electrochemical gradients—pumping 3 Na⁺ ions out of the cell and 2 K⁺ ions into the cell. This process requires the direct hydrolysis of **ATP** to provide the necessary energy. It is "electrogenic" as it creates a net charge imbalance across the membrane, contributing to the resting membrane potential. **Analysis of Incorrect Options:** * **Passive Transport:** This involves the movement of substances down their concentration gradient without the expenditure of energy. * **Facilitated Diffusion:** A form of passive transport that uses carrier proteins or channels (e.g., GLUT transporters) to move molecules down a gradient. It does not require ATP. * **Osmosis:** The specific passive movement of water molecules across a semi-permeable membrane from an area of low solute concentration to high solute concentration. **Clinical Pearls & High-Yield Facts for NEET-PG:** 1. **Stoichiometry:** 3 Na⁺ out, 2 K⁺ in. Remember: **"K-IN"** (Potassium goes in). 2. **Inhibition:** The pump is specifically inhibited by **Cardiac Glycosides** (e.g., **Digoxin** and Ouabain). This inhibition increases intracellular Na⁺, which subsequently slows the Na⁺/Ca²⁺ exchanger, increasing intracellular Ca²⁺ and myocardial contractility. 3. **Energy Consumption:** In a resting state, this pump can consume up to 30-40% of a cell's total ATP production (even more in neurons). 4. **Function:** It is essential for maintaining cell volume; if the pump fails, the cell swells and bursts (hydropic swelling).

Q: Cellular and flagellar movement is carried out by all of the following except?

Intermediate filaments. **Explanation:** The cytoskeleton of a cell consists of three primary components: **Microtubules (Tubulin)**, **Microfilaments (Actin/Myosin)**, and **Intermediate Filaments**. The key to this question lies in distinguishing between structural support and active motility. **1. Why Intermediate Filaments (Correct Answer) are the exception:** Intermediate filaments (e.g., Keratin, Vimentin, Desmin, Neurofilaments, and Lamins) are primarily **structural** in nature. They provide mechanical strength to cells and tissues, helping them withstand shearing forces. Unlike microtubules and microfilaments, intermediate filaments are **non-polar** and lack associated "motor proteins." Therefore, they do not participate in cellular or flagellar movement. **2. Why the other options are involved in movement:** * **Tubulin (Microtubules):** These are the structural units of **cilia and flagella** (arranged in a 9+2 pattern). Movement is generated by the motor protein **Dynein**, which slides microtubules against each other. * **Actin & Myosin:** These are responsible for **amoeboid movement**, muscle contraction, and cytokinesis (cell cleavage). Actin (microfilaments) interacts with Myosin (motor protein) to generate contractile forces required for cellular locomotion. **Clinical Pearls & High-Yield Facts for NEET-PG:** * **Kartagener Syndrome:** Caused by a defect in **Dynein arms** within microtubules, leading to immotile cilia, situs inversus, and infertility. * **Colchicine & Vinca Alkaloids:** These drugs act by inhibiting **Tubulin** polymerization, arresting cell division. * **Diagnostic Marker:** Intermediate filaments are tissue-specific and used in pathology to identify tumor origins (e.g., **Cytokeratin** for Carcinomas, **Vimentin** for Sarcomas, **PSA** is not an IF, but **Desmin** is for myogenic tumors). * **Smallest to Largest:** Microfilaments (7nm) < Intermediate Filaments (10nm) < Microtubules (25nm).

Q: Peripheral cell membrane proteins are involved in which of the following functions?

Cellular adhesion. **Explanation:** Cell membrane proteins are classified into two main types based on their association with the lipid bilayer: **Integral (Transmembrane)** and **Peripheral** proteins. **Why Cellular Adhesion is Correct:** Peripheral proteins do not penetrate the lipid bilayer; instead, they are loosely attached to the inner or outer surfaces of the membrane via electrostatic interactions. On the extracellular surface, peripheral proteins (often as part of the glycocalyx) play a critical role in **cellular adhesion** and cell-to-cell recognition. They act as "anchors" or "linkers" that connect the cell membrane to the extracellular matrix or to the internal cytoskeleton (e.g., Spectrin and Ankyrin in RBCs). **Analysis of Incorrect Options:** * **A & B (Active transport pumps and Ion channels):** These functions require a continuous pathway across the hydrophobic lipid bilayer. Therefore, they are exclusively performed by **Integral/Transmembrane proteins**, which span the entire thickness of the membrane. * **D (Enzymatic activity):** While some peripheral proteins have enzymatic roles, this is not their primary defining function in the context of membrane structural organization compared to adhesion. Furthermore, most major membrane-bound signaling enzymes (like Adenylyl Cyclase) are integral proteins. **High-Yield Clinical Pearls for NEET-PG:** * **Spectrin & Ankyrin:** These are classic examples of peripheral proteins on the inner membrane of RBCs. A deficiency in these proteins leads to **Hereditary Spherocytosis**. * **Integral Proteins:** These can only be removed by disrupting the bilayer with detergents, whereas peripheral proteins can be removed using high-salt solutions or pH changes. * **Fluid Mosaic Model:** Remember that proteins provide the "mosaic" pattern, while lipids provide the "fluidity."

Q: Which of the following is NOT a characteristic of facilitated diffusion?

Uphill transport. ### Explanation **Facilitated diffusion** is a form of carrier-mediated transport that allows molecules to move across the cell membrane along their electrochemical gradient. **Why "Uphill transport" is the correct answer:** Facilitated diffusion is a **passive process**, meaning it does not require metabolic energy (ATP). It follows the concentration gradient (from high to low concentration), which is known as **downhill transport**. "Uphill transport" refers to movement against a gradient, which is the hallmark of **Active Transport** (Primary or Secondary). **Analysis of Incorrect Options:** Since facilitated diffusion relies on specific **carrier proteins**, it exhibits the following kinetics: * **Specificity (C):** Carrier proteins have binding sites that recognize only specific molecules or isomers (e.g., GLUT transporters are specific for D-glucose, not L-glucose). * **Saturability (B):** There are a finite number of carriers. Once all binding sites are occupied, the transport rate reaches a maximum ($V_{max}$), showing a plateau phase. * **Inhibition (A):** Because it involves protein binding, the process can be inhibited by competitive molecules that structurally resemble the substrate. **NEET-PG High-Yield Pearls:** * **Classic Example:** Transport of glucose into skeletal muscle and adipose tissue via **GLUT-4** (insulin-dependent). * **Kinetics:** Facilitated diffusion follows **Michaelis-Menten kinetics**, similar to enzyme-substrate interactions. * **Comparison:** Simple diffusion is the only transport mechanism that is **not** saturable (it is linear and does not show $V_{max}$). * **Key Distinction:** Both facilitated diffusion and active transport are carrier-mediated, but only active transport can achieve a "Target-to-Source" ratio greater than 1 (uphill).

Q: In dividing cells, the spindle is formed by which of the following components?

Tubulin. **Explanation:** The correct answer is **Tubulin (Option B)**. The mitotic spindle is a complex structure composed of **microtubules**, which are essential for segregating chromosomes during cell division (mitosis and meiosis). Microtubules are polymers made of globular protein subunits called **$\alpha$ and $\beta$-tubulin**. During the M-phase of the cell cycle, these tubulin dimers polymerize to form spindle fibers that attach to the kinetochores of chromosomes, facilitating their movement to opposite poles. **Analysis of Incorrect Options:** * **Ubiquitin (A):** This is a small regulatory protein involved in the degradation of defective or unneeded proteins via the **Ubiquitin-Proteasome Pathway**. It does not have a structural role in the spindle. * **Laminin (C):** This is a major glycoprotein component of the **basal lamina** (extracellular matrix). It helps in cell adhesion and signaling, not intracellular division. * **Keratin (D):** This is a type of **intermediate filament** found primarily in epithelial cells, providing mechanical strength to tissues (e.g., skin, hair, nails). **Clinical Pearls for NEET-PG:** * **Drug Link:** Several anti-cancer drugs target tubulin to inhibit the spindle. **Vinca alkaloids** (Vincristine/Vinblastine) inhibit tubulin polymerization, while **Taxanes** (Paclitaxel) inhibit depolymerization (stabilize microtubules). * **Colchicine:** Used in Gout, it also works by inhibiting tubulin polymerization, thereby interfering with neutrophil migration. * **Structure:** Microtubules follow a **"9+2" arrangement** in cilia/flagella and a **"9+0" arrangement** in centrioles.

Q: Which of the following statements regarding Nitric oxide (NO) is true?

NO is synthesized from arginine.. **Explanation:** Nitric Oxide (NO), formerly known as Endothelium-Derived Relaxing Factor (EDRF), is a key gaseous signaling molecule in cellular physiology. **1. Why Option A is Correct:** NO is synthesized through the enzymatic conversion of the amino acid **L-arginine** into **L-citrulline**. This reaction is catalyzed by the enzyme **Nitric Oxide Synthase (NOS)** in the presence of oxygen and several cofactors (NADPH, FAD, FMN, and Tetrahydrobiopterin/BH4). **2. Why Incorrect Options are Wrong:** * **Option B:** NO is a highly reactive gas with a short half-life (seconds). It is synthesized enzymatically on demand, not spontaneously from NO2. * **Option C:** NO is a potent **vasodilator**. It diffuses into vascular smooth muscle cells, activates **soluble Guanylyl Cyclase (sGC)**, increases **cGMP** levels, and leads to smooth muscle relaxation. * **Option D:** NO is primarily synthesized in the **cytoplasm** (by eNOS in endothelial cells or nNOS in neurons) or is associated with the plasma membrane, rather than being a mitochondrial release product. **High-Yield Clinical Pearls for NEET-PG:** * **Isoforms of NOS:** There are three types: **nNOS** (Type 1, Neuronal), **iNOS** (Type 2, Inducible/Macrophage-related), and **eNOS** (Type 3, Endothelial). * **Mechanism of Action:** NO → ↑ cGMP → Protein Kinase G (PKG) activation → Dephosphorylation of Myosin Light Chain → Vasodilation. * **Therapeutic Link:** Nitroglycerin works by releasing NO to treat angina. Sildenafil (Viagra) inhibits Phosphodiesterase-5 (PDE-5), preventing the breakdown of cGMP, thereby prolonging NO-mediated vasodilation.

Q: What is the approximate ratio of the concentration of sodium ions inside a typical mammalian cell to the concentration of sodium ions outside the cell?

0.1. **Explanation:** The concentration gradient of ions across the cell membrane is a fundamental concept in cellular physiology. In a typical mammalian cell, sodium ($Na^+$) is the primary extracellular cation, while potassium ($K^+$) is the primary intracellular cation. **1. Why Option C is Correct:** The typical concentration of sodium ions **inside** the cell (Intracellular Fluid - ICF) is approximately **10–15 mEq/L**, whereas the concentration **outside** the cell (Extracellular Fluid - ECF) is approximately **140–145 mEq/L**. * **Ratio Calculation:** $14 / 140 = 0.1$. This steep gradient is actively maintained by the **$Na^+$-$K^+$ ATPase pump**, which pumps 3 $Na^+$ ions out and 2 $K^+$ ions in per ATP molecule hydrolyzed. **2. Why Other Options are Incorrect:** * **Options A (0.5) and B (0.3):** These values suggest a much higher intracellular sodium concentration than what exists physiologically. Such ratios would imply a failure of the $Na^+$-$K^+$ pump, leading to cellular swelling and death. * **Option D (0.01):** This would imply an intracellular concentration of only 1.4 mEq/L, which is too low. While the gradient is steep, it is not a 100-fold difference (unlike Calcium, where the ratio is closer to 0.0001). **High-Yield Clinical Pearls for NEET-PG:** * **Resting Membrane Potential (RMP):** The $Na^+$ gradient contributes to the RMP, but the membrane is much more permeable to $K^+$ at rest. * **Action Potential:** The rapid upstroke (depolarization) of an action potential is caused by the sudden influx of $Na^+$ ions down this concentration gradient via voltage-gated channels. * **Secondary Active Transport:** This $Na^+$ gradient provides the driving force for the transport of other substances, such as glucose (SGLT) and amino acids. * **Ouabain/Digoxin:** These drugs inhibit the $Na^+$-$K^+$ ATPase, increasing intracellular $Na^+$, which subsequently affects the $Na^+$-$Ca^{2+}$ exchanger.

Question 1

Which cell junction allows the exchange of cytoplasmic molecules?

Accepted Answer

Gap junction

Answer

Tight junction

Answer

Anchoring junction

Answer

None of the above

Question 2

A muscle cell has an intracellular sodium concentration of 14 mM and an extracellular sodium concentration of 140 mM. Assuming that 2.3 RT/F = 60 mV, what would the membrane potential be if the muscle cell membrane were permeable only to Na+?

Accepted Answer

+60 mV

Answer

+80 mV

Answer

-60 mV

Answer

-80 mV

Question 3

What is the mechanism of secretion of macromolecules by a cell through fusion with a vesicle?

Accepted Answer

Phagocytosis

Answer

Pinocytosis

Answer

Exocytosis

Answer

Endocytosis

Question 4

The sodium-potassium pump is an example of which type of cellular transport?

Accepted Answer

Active transport

Answer

Passive transport

Answer

Facilitated diffusion

Answer

Osmosis

Question 5

Cellular and flagellar movement is carried out by all of the following except?

Accepted Answer

Intermediate filaments

Answer

Actin

Answer

Tubulin

Answer

Myosin

Question 6

Peripheral cell membrane proteins are involved in which of the following functions?

Accepted Answer

Cellular adhesion

Answer

Active transport pumps

Answer

Ion channels

Answer

Enzymatic activity at the cell surface

Question 7

Which of the following is NOT a characteristic of facilitated diffusion?

Accepted Answer

Uphill transport

Answer

Inhibition

Answer

Saturability

Answer

Specificity

Question 8

In dividing cells, the spindle is formed by which of the following components?

Accepted Answer

Tubulin

Answer

Ubiquitin

Answer

Laminin

Answer

Keratin

Question 9

Which of the following statements regarding Nitric oxide (NO) is true?

Accepted Answer

NO is synthesized from arginine.

Answer

NO is spontaneously produced from NO2.

Answer

NO causes vasoconstriction.

Answer

NO is released from mitochondria.

Question 10

What is the approximate ratio of the concentration of sodium ions inside a typical mammalian cell to the concentration of sodium ions outside the cell?

Accepted Answer

0.1

Answer

0.5

Answer

0.3

Answer

0.01

Cellular Physiology — MCQs

Cellular Physiology — MCQs

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