Cellular Physiology — MCQs

Cellular Physiology Indian Medical PG Practice Questions and MCQs

Question 281: Equilibrium potential for an ion is calculated by:

A. Gibbs Donnan Equilibrium
B. Nernst Equation (Correct Answer)
C. Goldman Equation
D. None of the options

Explanation: ***Nernst Equation*** - The **Nernst equation** is used to calculate the **equilibrium potential** for a **single ion** across a semi-permeable membrane. - It considers the **charge of the ion**, the **temperature**, and the **concentration gradient** of the ion across the membrane. *Gibbs Donnan Equilibrium* - The **Gibbs-Donnan equilibrium** describes the distribution of **permeable ions** when there is a **non-permeable charged molecule** on one side of a membrane. - It focuses on the **overall distribution of ions** and water, rather than the equilibrium potential of a *single* ion. *Goldman Equation* - The **Goldman-Hodgkin-Katz (GHK) equation**, often referred to as the **Goldman equation**, calculates the **resting membrane potential** of a cell. - It accounts for the **permeability and concentration gradients** of *multiple* ions (e.g., Na+, K+, Cl-) that contribute to the membrane potential. *None of the options* - This option is incorrect because the **Nernst Equation** is specifically designed for calculating the equilibrium potential of a single ion.

Question 282: Resolution power of light microscope is

A. 2000 nm
B. 200 nm (Correct Answer)
C. 20 nm
D. 2 nm

Explanation: ***200 nm*** - The **resolution power** of a standard light microscope is approximately **0.2 micrometers** or **200 nanometers**. - This limit is due to the **wavelength of visible light** and the **diffraction limit**, which prevents distinguishing objects closer than half the wavelength of light used. *2000 nm* - A resolution of **2000 nm (2 micrometers)** would indicate a much **lower resolving power** than what a typical light microscope can achieve. - This value would not allow for visualization of fine cellular details or many bacteria. *20 nm* - A resolution of **20 nm** is beyond the capabilities of a standard light microscope and is typically achieved by **electron microscopes**. - Electron microscopes use a beam of electrons, which have a much **shorter wavelength** than visible light, to achieve higher resolution. *2nm* - A resolution of **2 nm** is an extremely high resolution, characteristic of advanced **electron microscopes**, such as **transmission electron microscopes (TEM)** and **scanning electron microscopes (SEM)**. - This level of detail allows for the visualization of **sub-cellular structures** and even **individual molecules**.

Question 283: Most metabolically active part in bone is

A. Endosteal surface
B. Cortical bone
C. Cancellous bone (Correct Answer)
D. Periosteal surface

Explanation: ***Cancellous bone*** - **Cancellous bone** (trabecular/spongy bone) is the **most metabolically active** part of bone due to its **large surface area-to-volume ratio** (approximately 10 times greater than cortical bone). - It has a **high rate of bone turnover** and remodeling, being 8-10 times more active than cortical bone. - Contains abundant **osteoblasts** and **osteoclasts** on trabecular surfaces, making it the primary site for **calcium homeostasis** and rapid response to metabolic demands. - Metabolic bone diseases like **osteoporosis** and **hyperparathyroidism** predominantly affect cancellous bone first due to its high metabolic activity. *Endosteal surface* - The **endosteal surface** (inner lining of cortical bone and trabecular surfaces) is metabolically active with osteoblasts and osteoclasts. - While technically the trabecular surfaces are endosteal surfaces, in clinical teaching, **cancellous bone as a whole** is recognized as the most metabolically active component. - This option represents an anatomical subdivision rather than the structural answer expected in standard physiology. *Cortical bone* - **Cortical bone** (compact bone) is dense and provides structural strength but has **lower metabolic activity** due to its compact structure and smaller surface area. - Remodeling rate is significantly slower (about 1/10th) compared to cancellous bone. - Makes up 80% of skeletal mass but contributes less to metabolic bone turnover. *Periosteal surface* - The **periosteal surface** (outer bone covering) is involved in bone growth in width and fracture repair. - Has osteoblasts and osteoclasts but accounts for a **smaller proportion** of total bone remodeling compared to the extensive trabecular surfaces. - Less metabolically active than cancellous bone overall.

Question 284: Equilibrium potential of calcium is

A. +130mV (Correct Answer)
B. -32mV
C. +65mV
D. -95mV

Explanation: ***+130mV*** - The **equilibrium potential** for an ion is the **membrane potential** at which the net movement of that ion across the membrane is zero, even if there is a concentration gradient. - Due to the significantly higher extracellular concentration of **calcium ions (Ca2+)** relative to the intracellular concentration, a large positive membrane potential is required to prevent Ca2+ influx. *-32mV* - This value does not represent the typical **equilibrium potential** for any major physiological ion like sodium, potassium, chloride, or calcium in mammalian cells. - Equilibrium potentials are highly dependent on the **concentration gradients** of the specific ion. *+65mV* - This value is close to the typical **equilibrium potential for sodium (Na+)**, which is approximately +60 to +70 mV in many cells, due to its outward concentration gradient. - **Calcium's equilibrium potential** is much more positive than sodium's due to its larger concentration gradient and its divalent charge. *-95mV* - This value is close to the typical **equilibrium potential for potassium (K+)**, which is approximately -90 to -95 mV, reflecting the movement of potassium out of the cell. - The **equilibrium potential for calcium** is highly positive, whereas this negative value suggests an inward current for a positively charged ion.

Question 285: Which of the following is most essential for wound healing?

A. Zinc
B. Vitamin A
C. Selenium
D. Ascorbic acid (Correct Answer)

Explanation: ***Ascorbic acid*** - **Ascorbic acid** (Vitamin C) is crucial for **collagen synthesis** and cross-linking, which are fundamental processes in wound healing. - It acts as a **cofactor** for enzymes like **prolyl hydroxylase**, essential for stabilizing collagen structure, and is a potent **antioxidant** reducing oxidative stress. *Zinc* - While important for cell proliferation and immune function, **zinc** deficiency primarily leads to delayed healing and impaired immune response, not the primary facilitator. - Zinc is a component of many enzymes involved in wound healing, but its role is secondary to the direct collagen synthesis facilitated by Vitamin C. *Vitamin A* - **Vitamin A** supports epithelial cell differentiation and immune response, which are beneficial for wound healing. - However, its primary role is not directly in collagen production or fibroblast function in the same way as ascorbic acid. *Selenium* - **Selenium** is a trace element with antioxidant properties, important for protecting cells from damage. - Its direct involvement in the fundamental processes of collagen synthesis and wound closure is less pronounced compared to ascorbic acid.

Question 286: The Nernst potential of K+ is (in mV):

A. -10
B. -61
C. -94
D. -90 (Correct Answer)

Explanation: ***-90*** - The **Nernst potential** for K+ is approximately -90 mV, the standard textbook value used in medical education, calculated using the Nernst equation with typical intracellular (140 mEq/L) and extracellular (4 mEq/L) concentrations of K+. - This value represents the **equilibrium potential** at which there is no net movement of potassium ions across the cell membrane. - This rounded value is consistently cited in standard physiology texts (Ganong, Guyton) and is the expected answer for medical examinations. *-10* - This value is significantly less negative than the actual Nernst potential for K+ and does not reflect the typical concentration gradient of potassium. - An equilibrium potential of -10 mV would imply a much smaller concentration gradient or a different ion species. *-61* - This value is close to the typical **resting membrane potential** of many excitable cells (around -70 mV), but not the Nernst potential for K+ specifically. - The resting membrane potential is a weighted average of the Nernst potentials of several ions, with K+ being a major contributor due to its high permeability. *-94* - While this represents a more precise calculation using the Nernst equation, **-90 mV is the standard textbook value** taught in medical physiology and expected in examinations. - The difference between -90 and -94 mV reflects rounding conventions; -90 mV is universally accepted in clinical and academic contexts.

Question 287: Epidermal turnover time in healthy adults is

A. 2 weeks
B. 6 weeks
C. 4 weeks (Correct Answer)
D. 8 weeks

Explanation: ***4 weeks*** - The **epidermal turnover time** refers to the period it takes for cells produced in the stratum basale to migrate to the stratum corneum and be shed. - In healthy adults, this process generally takes about **28 to 30 days**, which is approximately 4 weeks. *2 weeks* - A turnover time of 2 weeks would indicate a significantly **accelerated epidermal proliferation**, typically seen in conditions like **psoriasis**. - This rapid turnover does not allow for proper keratinization and leads to incomplete differentiation of keratinocytes. *6 weeks* - A 6-week turnover time would signify a **slower-than-normal epidermal renewal**, which could be associated with conditions involving **reduced cellular activity** or metabolic slowdown. - This extended period is not characteristic of healthy epidermal homeostasis. *8 weeks* - An 8-week turnover time represents an even **more prolonged epidermal regeneration** process. - Such a long duration would imply significant impairment in cellular proliferation and differentiation, which is not found in healthy skin.

Question 288: Why do eyebrows not grow beyond a certain length?

A. Telogen phase
B. Anagen phase (Correct Answer)
C. Catagen phase
D. Exogen phase

Explanation: **Anagen phase** - The **anagen phase**, or growing phase, is significantly shorter for eyebrow hairs (typically 30-45 days) compared to scalp hair (2-7 years), which limits their maximum length. - The duration of this active growth phase **determines the ultimate length** hair can reach before it transitions to resting and shedding. *Telogen phase* - The **telogen phase** is a **resting phase** where the hair follicle is completely inactive; it does not contribute to the hair's growth or final length. - During this phase, the old hair is shed to make way for new hair growth, but it is not the phase that dictates the maximum length. *Catagen phase* - The **catagen phase** is a **transitional phase** lasting about 2-3 weeks, during which hair growth stops and the hair follicle shrinks. - This phase prepares the hair for resting and shedding but does not directly limit how long the hair grows. *Exogen phase* - The **exogen phase** is when a hair is **shed from the follicle**, often aided by activities like washing or brushing. - This phase is responsible for hair shedding, not for limiting the maximum length hair can attain.

Question 289: Which of the following is used for sex chromatin testing?

A. Testosterone receptors
B. Phenotypic features
C. Hormone levels
D. Barr body (Correct Answer)

Explanation: ***Barr body*** - The **Barr body**, or sex chromatin, is an inactivated X chromosome found in the somatic cells of females. - Its presence or absence is used in sex chromatin testing to determine the number of X chromosomes. *Testosterone receptors* - **Testosterone receptors** are involved in mediating the effects of androgens and are not directly used for sex chromatin testing. - Abnormalities in these receptors can lead to conditions like **androgen insensitivity syndrome**, but they don't assess X chromosome number. *Phenotypic features* - While **phenotypic features** (visible characteristics) can suggest a person's sex or potential chromosomal abnormalities, they do not directly provide information about sex chromatin. - Definitive diagnosis requires **cytogenetic** or genetic testing. *Hormone levels* - **Hormone levels** (e.g., testosterone, estrogen) can indicate endocrine function but are not used to directly assess sex chromatin. - They reflect the activity of the gonads rather than the presence of inactivated X chromosomes.

Question 290: What effect does insulin have on GLUT4 receptors in muscle cells?

A. Inhibits their activity
B. Decreases glucose transport
C. Activates lipolysis
D. Promotes their translocation to cell membrane (Correct Answer)

Explanation: ***Promotes their translocation to cell membrane*** - Insulin **stimulates the movement of GLUT4 vesicles** from the intracellular compartment to the plasma membrane. - This translocation increases the number of **GLUT4 transporters** on the cell surface, facilitating glucose uptake. *Inhibits their activity* - Insulin does not inhibit the activity of GLUT4 receptors; rather, it **enhances their role** in glucose transport. - Inhibition would lead to **reduced glucose uptake**, which is contrary to insulin's primary function in muscle cells. *Decreases glucose transport* - This statement is incorrect as insulin's main function in muscle cells is to **increase glucose uptake** to lower blood glucose levels. - Insulin promotes glucose transport by **increasing the availability** of GLUT4 transporters at the cell surface. *Activates lipolysis* - Insulin is a powerful **anabolic hormone** that generally inhibits lipolysis (fat breakdown) and promotes lipogenesis (fat synthesis). - Lipolysis is primarily activated by hormones like **glucagon and catecholamines**, not insulin.

Practice by Chapter

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