Cellular Physiology — MCQs

Cellular Physiology Indian Medical PG Practice Questions and MCQs

Question 301: Which of the following organelles is primarily responsible for cellular respiration?

A. Mitochondria (Correct Answer)
B. Endoplasmic Reticulum
C. Lysosome
D. Nucleus

Explanation: ***Mitochondria*** - This organelle is often referred to as the "**powerhouse of the cell**" because it is the primary site of **ATP synthesis** through aerobic respiration. - Cellular respiration involves a series of metabolic reactions that convert nutrients into **adenosine triphosphate (ATP)**, providing energy for cellular functions. *Endoplasmic Reticulum* - The **endoplasmic reticulum** is primarily involved in **protein synthesis** (rough ER) and **lipid synthesis** and detoxification (smooth ER). - It does not play a direct role in the production of bulk cellular energy via cellular respiration. *Lysosome* - **Lysosomes** are responsible for **waste breakdown**, recycling cellular debris, and degrading foreign substances through their digestive enzymes. - They are not involved in the processes of cellular respiration or energy production. *Nucleus* - The **nucleus** contains the cell's **genetic material** (DNA) and controls cell growth, metabolism, and reproduction by regulating gene expression. - While it controls cellular processes, it does not directly perform cellular respiration.

Question 302: What is the typical resolving power of an electron microscope?

A. 1-5 mm
B. 1-5 µm
C. 1-5 nm
D. 1-5 Å (Correct Answer)

Explanation: ***1-5 Å*** - Electron microscopes utilize a **beam of electrons** which have much shorter wavelengths than visible light, allowing for significantly higher resolving power. - A resolving power of 1-5 Å (Angstroms) means they can distinguish between objects that are less than a **nanometer** apart, revealing subcellular structures and even atomic details. *1-5 mm* - This range represents a resolution visible to the **unaided human eye** or with very low-power magnification, dramatically less precise than an electron microscope. - It would not allow for the observation of **cellular details** or organelles, which are the primary targets of electron microscopy. *1-5 µm* - This resolution is typical of a **conventional light microscope**, which uses visible light to magnify samples. - While sufficient for observing cells and larger organelles like mitochondria, it is insufficient to visualize **viruses** or intracellular structures at high detail. *1-5 nm* - While 1-5 nanometers (nm) is a very high resolution, a typical electron microscope, especially a **transmission electron microscope (TEM)**, can achieve even finer details, down to the Angstrom scale. - This range is a good approximation for the resolution limit of very advanced **scanning electron microscopes (SEM)** but not the ultimate capability across all electron microscopy.

Question 303: Which of the following statements is true regarding heterophilic interactions?

A. Involved in cell adhesion (Correct Answer)
B. Bind to the same ligand or hormone
C. Involved in immune response signaling
D. Involved in binding of growth hormone (GH) to specific receptors on the cell membrane

Explanation: ***Involved in cell adhesion*** - Heterophilic interactions refer to binding between **two different types of molecules** or cells. - This type of binding is fundamental to **cell-to-cell adhesion**, where dissimilar molecules on adjacent cell surfaces interact to form stable connections. - Examples include **integrins binding to ECM proteins** (fibronectin, laminin), and **selectins binding to carbohydrate ligands**. - This is the **primary and most general defining feature** of heterophilic interactions. *Bind to the same ligand or hormone* - This describes **homophilic interactions** or typical specific receptor-ligand binding. - Heterophilic interactions involve **dissimilar binding partners**, not identical ones. *Involved in immune response signaling* - While this statement is actually true (heterophilic interactions are crucial in immune responses like T cell receptor-MHC binding, CD28-B7 interactions, and selectin-mediated leukocyte rolling), it represents a **specific application** rather than the fundamental defining characteristic. - **Cell adhesion is the more general and primary function** that encompasses immune and non-immune contexts. *Involved in binding of growth hormone (GH) to specific receptors on the cell membrane* - This is an example of a specific **ligand-receptor interaction** with high specificity. - It does not represent the broader concept of heterophilic interactions as a general mechanism of binding between dissimilar molecular entities.

Question 304: Which of the following factors does the Nernst equation not depend on?

A. Concentration gradient
B. Electric gradient
C. Presence of non-ionic solutions (Correct Answer)
D. Concentration difference across the membrane

Explanation: ***Presence of non-ionic solutions*** - The **Nernst equation** calculates the **equilibrium potential** for an ion based on its concentration gradient and charge. - It does not consider the presence or effect of **non-ionic solutions** as they do not contribute to the electrochemical gradient of charged particles. *Concentration gradient* - The Nernst equation directly incorporates the **ratio of ion concentrations** inside and outside the cell. - This **concentration difference** is a primary determinant of the chemical driving force for ion movement. *Electric gradient* - The Nernst equation calculates the **electrical potential** (voltage) required to perfectly balance the chemical concentration gradient for a specific ion. - Therefore, the **electric gradient** is what the Nernst equation is designed to determine for a given ion. *Concentration difference across the membrane* - This is synonymous with the **concentration gradient**, which is a crucial component of the Nernst equation. - The formula explicitly uses the **logarithm of the ratio of extracellular to intracellular ion concentrations**.

Question 305: What is the equilibrium potential for potassium (K+) given an extracellular fluid (ECF) concentration of 4 mEq/L and an intracellular fluid (ICF) concentration of 140 mEq/L?

A. +60 mV
B. -60 mV
C. +90 mV
D. -90 mV (Correct Answer)

Explanation: **-90 mV** - The **Nernst equation** is used to calculate the equilibrium potential: E = (61/z) * log([ion]out/[ion]in). For potassium, the charge (z) is +1. - Plugging in the values: E = 61 * log(4/140) = 61 * log(0.02857) = 61 * (-1.544) ≈ **-94.2 mV**, which is closest to -90 mV. *+60 mV* - This value is close to the **equilibrium potential for sodium**, which has a much higher extracellular concentration and a positive equilibrium potential. - It does not reflect the significant concentration gradient of potassium, where the intracellular concentration is much higher. *-60 mV* - While negative, this potential is **not negative enough** to accurately represent the equilibrium potential for potassium with the given concentrations. - A potential of -60 mV falls between the typical resting membrane potential and the potassium equilibrium potential, indicating other ion influences. *+90 mV* - A positive equilibrium potential for potassium would imply that the **extracellular concentration is significantly higher** than the intracellular concentration, which is incorrect. - This value contradicts the physiological reality of potassium distribution across cell membranes.

Question 306: Which phase of meiosis includes the stages Leptotene and Pachytene?

A. Prophase I (Correct Answer)
B. Metaphase I
C. Anaphase II
D. Telophase II

Explanation: ***Prophase I*** - **Leptotene** is the first stage of Prophase I, where chromosomes begin to condense and become visible. - **Pachytene** is a later stage of Prophase I, characterized by the tight pairing of homologous chromosomes and the occurrence of **crossing over** (recombination). *Metaphase I* - During Metaphase I, **homologous chromosome pairs** align at the metaphase plate, not individual chromosomes in various stages of condensation. - This phase follows Prophase I and does not include the substages of synapsis and crossing-over. *Anaphase II* - In Anaphase II, **sister chromatids** separate and move to opposite poles of the cell, which is fundamentally different from the events of homologous chromosome pairing and exchange. - This phase occurs much later in meiosis, after meiosis I has completed. *Telophase II* - Telophase II is the final stage of meiosis, where nuclear envelopes reform around the separated chromatids, and the cells divide, resulting in four haploid cells. - It does not involve the initial condensation and pairing of homologous chromosomes seen in Leptotene and Pachytene.

Question 307: What is the most common mechanism for transport into the cell?

A. Diffusion (Correct Answer)
B. Primary active transport
C. Antiport
D. Cotransport

Explanation: ***Diffusion*** - **Diffusion** is the most common mechanism as it allows small, lipid-soluble molecules like **oxygen, carbon dioxide**, and other gases to passively move across the cell membrane down their **concentration gradients** without energy expenditure. - Many essential nutrients and waste products rely on this process for cellular entry and exit, making it a fundamental and widespread transport method. *Primary active transport* - **Primary active transport** directly uses **ATP hydrolysis** to move ions or molecules against their **concentration gradients**, such as the **Na+/K+ ATPase pump**. - While critical for maintaining gradients, it is an energy-intensive process and thus not as broadly utilized for general substance movement as passive diffusion. *Antiport* - **Antiport** is a type of **secondary active transport** where two different ions or molecules are transported across the membrane in **opposite directions**, with one moving down its electrochemical gradient to power the other's uphill movement. - This mechanism is specific to certain molecules and gradients, making it less ubiquitous than simple diffusion for overall cellular transport. *Cotransport* - **Cotransport** (also known as symport) is another form of **secondary active transport** where two substances move in the **same direction** across the membrane, with one moving down its electrochemical gradient to drive the other against its gradient. - Like antiport, it is a specialized, energy-dependent process that is not as universally applied as passive diffusion for cell transport.

Question 308: Which of the following statements about the Nernst equation is true?

A. All of the options are correct.
B. It can be calculated for non-ionic solutions.
C. It is used to calculate the equilibrium potential for ions. (Correct Answer)
D. The Nernst potential for Cl- is always constant regardless of concentration.

Explanation: ***It is used to calculate the equilibrium potential for ions.*** - The **Nernst equation** specifically determines the **equilibrium potential** (or reversal potential) for an **ion** across a semipermeable membrane, where net movement of that ion ceases. - This potential represents the **electrochemical gradient** required to perfectly balance the concentration gradient of a specific ion. - Formula: **E = (RT/zF) × ln([ion]outside/[ion]inside)**, where E is the equilibrium potential, R is the gas constant, T is temperature, z is the ionic charge, and F is Faraday's constant. *It can be calculated for non-ionic solutions.* - The Nernst equation fundamentally relies on the **charge of ions** and their **concentration gradients** across a membrane. - It describes the electrical potential generated by the movement of **charged species**, making it inapplicable to non-ionic solutions. *All of the options are correct.* - Since some of the other statements are incorrect, this option is invalid. - The Nernst equation has specific applications related to **ionic movement** across membranes. *The Nernst potential for Cl- is always constant regardless of concentration.* - The Nernst potential is directly dependent on the **ion's concentration gradient** across the membrane, as well as its charge and temperature. - Therefore, changes in the **extracellular or intracellular concentrations** of Cl- will indeed alter its Nernst potential.

Question 309: Which of the following is the MOST important feature of simple diffusion?

A. Easy for non-polar substance
B. Does not require carrier protein (Correct Answer)
C. Moves against a concentration gradient
D. More effective in thin membranes

Explanation: ***Does not require carrier protein*** - **Simple diffusion** directly involves the movement of substances across the lipid bilayer without the need for a **carrier protein** or channel. - This characteristic distinguishes it from **facilitated diffusion** and **active transport**, which both utilize proteins for transport. *Moves against a concentration gradient* - Movement against a **concentration gradient** (from low to high concentration) is characteristic of **active transport**, not simple diffusion. - **Simple diffusion** always occurs down a concentration gradient, from an area of higher concentration to an area of lower concentration. *Easy for non-polar substance* - While simple diffusion is indeed easier for **non-polar substances** due to the lipid nature of the cell membrane, this is a factor influencing the *rate* and *permeability*, not the *most important defining feature* of the process itself. - The fundamental aspect of simple diffusion is the absence of protein involvement, regardless of the substance's polarity. *More effective in thin membranes* - A **thinner membrane** would indeed allow for a faster rate of simple diffusion, following Fick's Law of Diffusion. - However, this describes a condition that *enhances* diffusion rather than being the defining characteristic of the process itself.

Question 310: What generates intracellular signals when cells are subjected to shear stress?

A. Focal adhesion molecules
B. Integrins (Correct Answer)
C. Cadherins
D. Selectins

Explanation: ***Integrins*** - **Integrins** are transmembrane receptors that link the extracellular matrix to the cytoskeleton, acting as mechanosensors. - When cells experience **shear stress**, integrins undergo conformational changes that activate intracellular signaling pathways, mediating cellular responses. - They are the **primary mechanotransducers** that directly sense and convert mechanical forces into biochemical signals. *Cadherins* - **Cadherins** are primarily involved in cell-to-cell adhesion, especially in epithelial tissues, forming adherens junctions. - While they contribute to tissue integrity, their primary role is not in sensing and transducing **shear stress** signals. *Selectins* - **Selectins** are a family of cell adhesion molecules involved in initial leukocyte rolling and adhesion to endothelial cells during inflammation. - They bind to carbohydrates on other cells but are not directly involved in the intracellular signaling response to **shear stress**. *Focal adhesion molecules* - **Focal adhesion molecules** are a complex of proteins that includes integrins along with intracellular adaptor proteins like talin, vinculin, and paxillin. - While focal adhesions are important for mechanotransduction, they represent the **downstream signaling complex** rather than the primary receptor that generates the initial signal. - **Integrins** are the specific transmembrane component that directly senses shear stress and initiates the cascade.

Practice by Chapter

Cell Membrane Structure and Function

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Membrane Transport Proteins

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Cellular Energetics and Metabolism

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Mitochondrial Function

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Cell Volume Regulation

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Cellular Responses to Stress

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Calcium Signaling

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Cell Cycle and Regulation

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Cellular Aging

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Apoptosis and Cell Death

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