Cellular Physiology Practice Questions

Q: What is/are the function(s) of a microtubule?

All of the above. **Explanation:** Microtubules are the largest components of the cytoskeleton, composed of polymers of **alpha and beta-tubulin**. They are dynamic structures essential for maintaining cell architecture and facilitating intracellular transport. * **Option A (Strength):** Microtubules provide structural rigidity and shape to the cell. Along with intermediate filaments and microfilaments, they form the "scaffold" of the cell, allowing it to resist compression and maintain its 3D conformation. * **Option B (Base for Cilia):** Microtubules are the core components of cilia and flagella. The **basal body** (kinetosome), which anchors these structures to the cell membrane, is composed of a specialized arrangement of microtubule triplets (9+0 pattern). * **Option C (Cytoplasmic Movement):** Microtubules act as "railway tracks" for intracellular transport. Molecular motor proteins—**Kinesin** (anterograde) and **Dynein** (retrograde)—move organelles, vesicles, and chromosomes along these tubules, effectively facilitating the movement of contents within the cytoplasm. Since all three functions are primary roles of microtubules, **Option D** is the correct answer. **High-Yield Clinical Pearls for NEET-PG:** * **Kartagener Syndrome:** Caused by a defect in **Dynein arms**, leading to immobile cilia, bronchiectasis, and situs inversus. * **Pharmacology Link:** Several drugs target microtubules to inhibit cell division (Mitotic inhibitors): * **Vinca alkaloids (Vincristine/Vinblastine):** Inhibit microtubule polymerization. * **Taxanes (Paclitaxel):** Stabilize microtubules (prevent depolymerization). * **Colchicine:** Inhibits microtubule assembly (used in Gout). * **Griseofulvin:** Antifungal that interferes with microtubule function. * **Structure:** Cilia/Flagella have a **9+2** microtubule arrangement, while Centrioles/Basal bodies have a **9+0** arrangement.

Q: Protein synthesis occurs in which part of the cell?

Rough endoplasmic reticulum. **Explanation:** Protein synthesis is primarily the function of **ribosomes**. The **Rough Endoplasmic Reticulum (RER)** is characterized by the presence of ribosomes attached to its outer surface (giving it a "rough" appearance). These ribosomes are specifically responsible for synthesizing proteins destined for secretion, incorporation into the plasma membrane, or storage within lysosomes. Once synthesized, these proteins enter the lumen of the RER for folding and initial post-translational modifications. **Analysis of Options:** * **Smooth Endoplasmic Reticulum (SER):** Lacks ribosomes. Its primary functions include lipid and steroid synthesis, detoxification of drugs (especially in hepatocytes), and calcium storage (as sarcoplasmic reticulum in muscles). * **Golgi Body:** Does not synthesize proteins. It acts as the "post office" of the cell, responsible for modifying, sorting, and packaging proteins received from the RER into vesicles. * **All of the above:** Incorrect, as protein synthesis is localized to ribosomes (either free in the cytosol or bound to the RER). **High-Yield Facts for NEET-PG:** * **Free Ribosomes:** Synthesize proteins that remain *inside* the cell (e.g., hemoglobin, mitochondrial enzymes, cytoplasmic proteins). * **Nissl Bodies:** These are large granules of RER found in neurons; they are the site of protein synthesis for neurotransmitters. * **Clinical Correlation:** Plasma cells (which secrete antibodies) and pancreatic acinar cells (which secrete digestive enzymes) are rich in RER due to their high protein-synthetic activity.

Q: All of the following events occur during mitosis EXCEPT:

DNA replication. **Explanation:** The cell cycle is divided into two main phases: **Interphase** (preparation) and **M-phase** (mitosis/division). **Why DNA Replication is the correct answer:** DNA replication occurs during the **S-phase (Synthetic phase)** of Interphase, not during Mitosis. During this stage, the DNA content of the cell doubles (from 2n to 4n) to ensure that each daughter cell receives an identical set of chromosomes. By the time a cell enters Mitosis (Prophase), the DNA has already been replicated. **Analysis of other options:** * **Cytokinesis (Option A):** This is the final step of the M-phase, involving the physical division of the cytoplasm into two distinct daughter cells. * **Chromatids separate (Option B):** This is the hallmark of **Anaphase**. The centromeres split, and sister chromatids are pulled toward opposite poles of the cell. * **Kinetochore becomes evident (Option D):** Kinetochores are protein structures on chromatids where spindle fibers attach. They become clearly visible and functional during **Prometaphase/Metaphase**. **High-Yield Clinical Pearls for NEET-PG:** * **G0 Phase:** A quiescent stage where cells (like neurons or mature muscle cells) exit the cycle and stop dividing. * **Checkpoints:** The **G1-S checkpoint** (Rate-limiting step) is regulated by p53; mutations here are linked to most human cancers. * **Colchicine:** A drug used in Gout that inhibits mitosis by interfering with microtubule formation (arrests cells in Metaphase). * **Mnemonic for Mitosis:** **PMAT** (Prophase, Metaphase, Anaphase, Telophase).

Q: Cell drinking is also known as:

Pinocytosis. **Explanation:** The correct answer is **Pinocytosis (Option B)**. **Why Pinocytosis is correct:** Pinocytosis (derived from the Greek word *pino*, meaning "to drink") is a form of endocytosis where the cell membrane invaginates to ingest extracellular fluid and dissolved solutes. Unlike receptor-mediated processes, it is generally non-specific. The membrane forms small vesicles (pinosomes) that pinch off into the cytoplasm, allowing the cell to sample the surrounding fluid environment. This is a constitutive process occurring in almost all eukaryotic cells. **Analysis of Incorrect Options:** * **A. Phagocytosis:** Known as **"Cell Eating."** This is the ingestion of large particulate matter (e.g., bacteria, dead cells) by specialized cells like macrophages and neutrophils. It involves the formation of large vesicles called phagosomes. * **C. Endocytosis:** This is a **broad category** that encompasses both phagocytosis and pinocytosis. While pinocytosis is a type of endocytosis, the specific term for "cell drinking" is pinocytosis. * **D. None of the above:** Incorrect, as pinocytosis is the standard physiological term. **High-Yield Facts for NEET-PG:** * **ATP Dependency:** Both pinocytosis and phagocytosis are **active transport** processes requiring energy (ATP). * **Clathrin-Mediated Endocytosis:** A specific type of pinocytosis used for the uptake of specific molecules like LDL and iron (transferrin). * **Dynamin:** The GTPase enzyme responsible for "pinching off" the vesicle from the cell membrane. * **Macropinocytosis:** A larger-scale, non-specific form of fluid uptake often triggered by growth factors.

Q: Which law states that the amount of a substance crossing a given area is directly proportional to the area available for diffusion, concentration gradient, and diffusion coefficient?

Fick's law. ### Explanation **Correct Answer: C. Fick’s Law** **Why it is correct:** Fick’s First Law of Diffusion describes the rate at which a substance moves across a membrane. Mathematically, it is expressed as: **J = -DA (ΔC/ΔX)** Where: * **J** = Rate of diffusion * **D** = Diffusion coefficient (depends on the nature of the substance and temperature) * **A** = Surface area available for diffusion * **ΔC/ΔX** = Concentration gradient In medical physiology, this law explains how gases (like $O_2$ and $CO_2$) exchange across the alveolar-capillary membrane. The rate of exchange increases if the surface area or concentration gradient increases, and decreases if the membrane thickness increases. **Why the other options are incorrect:** * **A. Universal Gas Law ($PV = nRT$):** Relates pressure, volume, and temperature of an ideal gas; it does not describe the movement of substances across membranes. * **B. Dalton’s Law:** States that the total pressure exerted by a mixture of gases is equal to the sum of the partial pressures of the individual gases. It explains how partial pressures are calculated but not the rate of diffusion. **High-Yield Clinical Pearls for NEET-PG:** * **Emphysema:** Reduces the surface area (**A**) for diffusion due to alveolar wall destruction, leading to hypoxemia (Fick’s Law). * **Pulmonary Edema/Fibrosis:** Increases the diffusion distance (membrane thickness), thereby reducing the rate of gas exchange. * **Graham’s Law:** Often confused with Fick’s; it states that the diffusion rate of a gas is inversely proportional to the square root of its molecular weight. This explains why $CO_2$ (heavier) diffuses slower than $O_2$ in air, even though $CO_2$ is more soluble in liquids.

Q: Regarding brown adipose tissue, which of the following statements is false?

High ATP synthase activity. ### Explanation **Correct Option: A. High ATP synthase activity** The primary function of **Brown Adipose Tissue (BAT)** is **non-shivering thermogenesis**, not ATP production. This process is mediated by **Uncoupling Protein-1 (UCP-1)**, also known as **Thermogenin**, located in the inner mitochondrial membrane. Thermogenin acts as a proton channel that allows protons to leak back into the mitochondrial matrix, bypassing **ATP synthase (Complex V)**. Consequently, the electrochemical gradient is dissipated as **heat** rather than being used to synthesize ATP. Therefore, BAT is characterized by **low ATP synthase activity** despite having high oxidative capacity. **Analysis of Other Options:** * **B. High vascularity:** BAT is highly vascularized to ensure a steady supply of oxygen for oxidation and to efficiently distribute the generated heat to the rest of the body via the bloodstream. * **C. Reduced or absent in the obese:** Clinical studies (including PET-CT scans) show that BAT activity is inversely correlated with Body Mass Index (BMI). Obese individuals have significantly lower levels of active brown fat compared to lean individuals. * **D. High content of mitochondria:** The "brown" color of BAT is due to the high density of mitochondria (which contain iron-rich cytochromes) and extensive capillary networks. --- ### High-Yield Clinical Pearls for NEET-PG * **Location:** In adults, BAT is found in the cervical, supraclavicular, axillary, and paravertebral regions. In neonates, it is prominent (interscapular) to prevent hypothermia. * **Regulation:** BAT is activated by the **Sympathetic Nervous System** via **$\beta_3$-adrenergic receptors**. * **Imaging:** Active BAT is a common cause of "false positives" on **FDG-PET scans** because it highly consumes glucose. * **Molecular Marker:** **UCP-1 (Thermogenin)** is the definitive molecular marker for brown and "beige" adipocytes.

Q: Which organelle plays a pivotal role in apoptosis?

Mitochondria. **Explanation:** The **Mitochondrion** is the central executioner of the intrinsic (mitochondrial) pathway of apoptosis. This process is initiated in response to internal cellular stress, such as DNA damage or oxidative stress. The key event is the increase in **Mitochondrial Outer Membrane Permeability (MOMP)**, regulated by the Bcl-2 family of proteins. Pro-apoptotic proteins (Bax/Bak) create pores in the membrane, leading to the leakage of **Cytochrome c** into the cytoplasm. Once released, Cytochrome c binds with Apaf-1 to form the **apoptosome**, which activates Caspase-9, triggering the executioner caspase cascade. **Analysis of Incorrect Options:** * **A. Cytoplasm:** While the later stages of apoptosis (caspase activation) occur here, the cytoplasm serves as the medium rather than the regulatory "pivotal" organelle. * **B. Golgi Complex:** Primarily involved in protein modification, sorting, and packaging; it does not play a primary role in initiating or regulating programmed cell death. * **C. Nucleus:** Although nuclear changes (chromatin condensation and DNA fragmentation by CAD—Caspase Activated DNase) are hallmarks of apoptosis, they are downstream effects rather than the initiating trigger. **NEET-PG High-Yield Pearls:** * **Anti-apoptotic proteins:** Bcl-2, Bcl-xL (they stabilize the mitochondrial membrane). * **Pro-apoptotic proteins:** Bax, Bak, Bim, Bad, PUMA. * **Mitochondrial markers:** Cytochrome c release is the definitive sign of the intrinsic pathway. * **Extrinsic Pathway:** Initiated by Death Receptors (e.g., Fas, TNF-R) and involves **Caspase-8**.

Question 1

What is/are the function(s) of a microtubule?

Accepted Answer

All of the above

Answer

Providing strength to the cell skeleton

Answer

Serving as a base for cilia arising from the cell

Answer

Facilitating the movement of cytoplasm within the cell

Question 2

If at resting potential, the concentrations of permeable ions X and Y are represented as -50 and -30 respectively, what is the value of ion Z?

Accepted Answer

80

Answer

20

Answer

-20

Answer

-80

Question 3

Protein synthesis occurs in which part of the cell?

Accepted Answer

Rough endoplasmic reticulum

Answer

Smooth endoplasmic reticulum

Answer

Golgi body

Answer

All of the above

Question 4

All of the following events occur during mitosis EXCEPT:

Accepted Answer

DNA replication

Answer

Cytokinesis

Answer

Chromatids separate

Answer

The kinetochore becomes evident

Question 5

All of the following statements about cadherins are true, EXCEPT:

Accepted Answer

Cadherins interact with components of the basement membrane.

Answer

Adhesion is Ca++-dependent and homophilic.

Answer

When mixed together, cells expressing different cadherins sort out into homotypic cell aggregates.

Answer

Cadherins associate with the actin cytoskeleton.

Question 6

Cell drinking is also known as:

Accepted Answer

Pinocytosis

Answer

Phagocytosis

Answer

Endocytosis

Answer

None of the above

Question 7

Which law states that the amount of a substance crossing a given area is directly proportional to the area available for diffusion, concentration gradient, and diffusion coefficient?

Accepted Answer

Fick's law

Answer

Universal gas law

Answer

Dalton's law

Answer

All of the above

Question 8

Regarding brown adipose tissue, which of the following statements is false?

Accepted Answer

High ATP synthase activity

Answer

High vascularity

Answer

Reduced or absent in the obese

Answer

High content of mitochondria

Question 9

Which organelle plays a pivotal role in apoptosis?

Accepted Answer

Mitochondria

Answer

Cytoplasm

Answer

Golgi complex

Answer

Nucleus

Question 10

If a cell membrane were permeable only to K+, what would be the effect of reducing the extracellular K+ concentration from 5 mM to 2.5 mM on the membrane potential, given the following intracellular and extracellular ion concentrations: Intracellular (mM): K+ 140, Na+ 12, Cl- 5, Ca++ 0.0001; Extracellular (mM): K+ 5, Na+ 145, Cl- 125, Ca++ 5?

Accepted Answer

19 millivolts hyperpolarization

Answer

19 millivolts depolarization

Answer

38 millivolts depolarization

Answer

38 millivolts hyperpolarization

Cellular Physiology — MCQs

Cellular Physiology — MCQs

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