Cellular Physiology Practice Questions

Q: Transcytosis occurs in which of the following cells?

Epithelial cells of the intestine. **Explanation:** **Transcytosis** (also known as cytopempsis or vesicle transport) is a type of transcellular transport where various macromolecules are transported across the interior of a cell. It involves a combination of **endocytosis** on one side of the cell, movement through the cytoplasm via vesicular transport, and **exocytosis** on the opposite side. **Why Option A is Correct:** Transcytosis is a characteristic feature of polarized cells, most notably **epithelial cells of the intestine** and vascular endothelial cells. In the intestine, specialized cells called **M cells** (Microfold cells) use transcytosis to transport antigens from the intestinal lumen to the underlying lymphoid tissue (Peyer's patches). Additionally, it is the mechanism by which maternal antibodies (IgA) are transported across the intestinal epithelium in neonates to provide passive immunity. **Why Other Options are Incorrect:** * **B & C (Neuroglia and Neurons):** While neurons utilize endocytosis and exocytosis for neurotransmitter recycling and synaptic signaling, they do not typically perform transcytosis as a primary means of bulk macromolecular transport across the cell body. * **D (Axolemma):** This is the cell membrane of an axon. It is involved in the propagation of action potentials and ion exchange, not the vesicular transport of macromolecules across the cell. **High-Yield Facts for NEET-PG:** * **Key Examples:** Transcytosis is essential for the transport of **IgA** into secretions, **IgG** across the placenta, and **Insulin** across the blood-brain barrier. * **Mechanism:** It utilizes **clathrin-coated pits** or **caveolae** to form the transport vesicles. * **Clinical Relevance:** Certain pathogens, such as *Listeria monocytogenes* and *Vibrio cholerae*, hijack the transcytosis pathway to bypass epithelial barriers and enter the systemic circulation.

Q: All cells do not divide at the same rate. Events in which phase of the cell cycle determine when a cell is going to replicate?

G1 phase. **Explanation:** The cell cycle consists of Interphase (G1, S, G2) and the Mitotic (M) phase. The **G1 phase (Gap 1)** is the most variable in duration and is the primary determinant of the overall cell cycle length. During G1, the cell monitors its environment and size. The critical decision to replicate occurs at the **Restriction Point (R point)** in late G1. Once a cell passes this checkpoint, it is committed to DNA synthesis (S phase) and subsequent division, regardless of external signals. Cells that do not divide (like neurons) or enter a quiescent state (like hepatocytes) exit G1 to enter the **G0 phase**. **Analysis of Incorrect Options:** * **M phase (Mitosis):** This is the shortest phase where actual nuclear and cytoplasmic division occurs. It is a period of execution, not decision-making regarding the initiation of replication. * **S phase (Synthesis):** This is the period of DNA replication. Once the cell enters the S phase, the replication process has already been "determined" by the G1 checkpoints. * **G2 phase (Gap 2):** This phase serves as a final safety check for DNA damage and ensures all chromosomes have been replicated before mitosis. It does not determine the timing of the initial commitment to divide. **High-Yield Facts for NEET-PG:** * **G1-S Transition:** Regulated by **Cyclin D** and **CDK4/6**. These phosphorylate the Retinoblastoma (Rb) protein, releasing E2F transcription factors. * **Labile cells:** (e.g., intestinal epithelium, skin) have a very short G1 phase. * **Permanent cells:** (e.g., neurons, cardiac myocytes) remain in G0 and do not enter G1. * **Stable cells:** (e.g., liver, proximal tubules) are in G0 but can re-enter G1 upon stimulation.

Q: Transition from G2 to M phase of the cell cycle is controlled by which of the following cyclins?

Cyclin B. The cell cycle is regulated by a series of proteins called **Cyclins** and **Cyclin-Dependent Kinases (CDKs)**. These complexes act as checkpoints to ensure the cell is ready to proceed to the next phase. **Explanation of the Correct Answer:** The transition from the **G2 phase to the M phase (Mitosis)** is primarily regulated by the **Cyclin B-CDK1** complex. This complex is also known as the **Mitosis-Promoting Factor (MPF)** or Maturation-Promoting Factor. Its activation triggers essential mitotic processes such as nuclear envelope breakdown, chromosome condensation, and spindle formation. **Analysis of Incorrect Options:** * **Cyclin D (Option A):** This is the first cyclin produced in the cell cycle. It pairs with **CDK4/6** during the **G1 phase** to help the cell pass the "Restriction Point" and enter the S phase. * **Cyclin E (Option B):** This pairs with **CDK2** during the **late G1 phase** to facilitate the final transition into the S phase (DNA synthesis). * **Cyclin A (Option C):** This pairs with **CDK2** during the **S phase** (to regulate DNA replication) and with **CDK1** during the **late G2 phase** to prepare for mitosis. While it plays a role in G2, Cyclin B is the definitive regulator for the actual entry into the M phase. **NEET-PG High-Yield Pearls:** 1. **Mnemonic (DEAB):** To remember the sequence of cyclins: **D** (G1), **E** (G1/S), **A** (S/G2), **B** (G2/M). "Dog Eats A Bone." 2. **The Restriction Point:** Regulated by Cyclin D and the Retinoblastoma (Rb) protein; once passed, the cell is committed to division regardless of external growth factors. 3. **p53 Protein:** Known as the "Guardian of the Genome," it can arrest the cell cycle (usually at G1) to allow for DNA repair by inducing p21, which inhibits CDKs.

Q: Which of the following statements is true regarding transport across a cell membrane?

Sodium ions are transported with glucose via symport.. ### Explanation The correct answer is **C: Sodium ions are transported with glucose via symport.** **Underlying Concept:** Glucose transport across cell membranes occurs via two primary mechanisms: facilitated diffusion (GLUT transporters) and **Secondary Active Transport**. In the small intestine and proximal convoluted tubule (PCT) of the kidney, glucose is transported against its concentration gradient. This is achieved by the **SGLT (Sodium-Glucose Linked Transporter)**. This protein utilizes the electrochemical gradient of Sodium (created by the Na+-K+ ATPase) to pull glucose into the cell. Because both Sodium and Glucose move in the same direction across the membrane, the mechanism is classified as **Symport** (or Co-transport). **Analysis of Incorrect Options:** * **A & D:** Chloride and Potassium are not the primary ions coupled with glucose transport. While chloride is often involved in other symporters (like Na-K-2Cl in the Loop of Henle), it does not drive glucose uptake. * **B:** An **Antiporter** (Counter-transport) moves substances in opposite directions (e.g., the Na+-H+ exchanger). Since glucose and sodium enter the cell together, "antiporter" is physiologically incorrect for this process. **High-Yield NEET-PG Pearls:** * **SGLT-1:** Located in the **Small Intestine**; responsible for glucose absorption. Defect leads to Glucose-Galactose Malabsorption. * **SGLT-2:** Located in the **S1 segment of the PCT**; responsible for 90% of renal glucose reabsorption. * **Clinical Correlation:** **SGLT-2 Inhibitors** (e.g., Dapagliflozin) are a major class of drugs used in Type 2 Diabetes to induce glucosuria and lower blood sugar. * **Oral Rehydration Therapy (ORT):** The physiological basis of ORT is the SGLT-1 receptor; sodium is added to the solution specifically to facilitate glucose (and water) absorption.

Q: Which statement is true for both pinocytosis and phagocytosis?

Involves the recruitment of actin filaments. **Explanation:** Both pinocytosis ("cell drinking") and phagocytosis ("cell eating") are forms of **active transport** known as endocytosis. The fundamental mechanical requirement for both processes is the **remodeling of the cytoskeleton**. **1. Why Option A is Correct:** To internalize substances, the cell membrane must undergo structural deformation. This process is driven by the **recruitment and polymerization of actin filaments** (microfilaments) located just beneath the plasma membrane. In phagocytosis, actin drives the extension of pseudopodia; in pinocytosis, actin facilitates the invagination of the membrane to form a vesicle. **2. Why Other Options are Incorrect:** * **Option B:** While some forms of pinocytosis (fluid-phase) are nonselective, **phagocytosis is highly selective**, usually triggered by specific ligand-receptor interactions (e.g., opsonization). Neither process is "spontaneous" as both require ATP. * **Option C:** This describes the fate of the vesicle *after* endocytosis. While common in phagocytosis (forming a phagolysosome), many pinocytotic vesicles (especially in transcytosis) bypass lysosomes to release contents elsewhere or recycle them to the surface. * **Option D:** Phagocytosis is restricted to "professional phagocytes" (macrophages, neutrophils, dendritic cells). However, **pinocytosis occurs in almost all cells** of the body to take up extracellular fluid. **High-Yield NEET-PG Pearls:** * **Clathrin-dependent endocytosis:** A specific type of receptor-mediated endocytosis (e.g., LDL uptake). * **Dynamin:** The GTPase "molecular scissor" required to pinch off endocytic vesicles from the cell membrane. * **ATP Dependency:** Both processes are active and will cease if mitochondrial poisons (like cyanide) are introduced.

Q: Na+-K+ ATPase is a-

Transmembrane protein. ### Explanation **Correct Answer: C. Transmembrane protein** The **Na⁺-K⁺ ATPase** (Sodium-Potassium Pump) is a classic example of an **integral membrane protein**, specifically a **transmembrane protein**. For a protein to function as an active transporter or a pump, it must span the entire thickness of the lipid bilayer. This allows it to simultaneously access the intracellular space (to bind 3 Na⁺ ions) and the extracellular space (to bind 2 K⁺ ions), moving them against their respective concentration gradients using energy derived from ATP hydrolysis. #### Why other options are incorrect: * **A & B. Extrinsic/Peripheral proteins:** These terms are synonymous. Peripheral proteins are loosely attached to either the inner or outer surface of the membrane and do not penetrate the hydrophobic core. Since they do not span the membrane, they cannot transport ions from one side to the other. * **D. Intracellular protein:** These are proteins located entirely within the cytoplasm (e.g., metabolic enzymes like hexokinase). While the Na⁺-K⁺ ATPase has an intracellular catalytic domain, the protein itself is embedded in the plasma membrane. #### NEET-PG High-Yield Pearls: * **Stoichiometry:** It pumps **3 Na⁺ OUT** and **2 K⁺ IN** for every 1 ATP hydrolyzed. * **Electrogenic Nature:** Because it moves 3 positive charges out for every 2 in, it contributes to the negativity of the Resting Membrane Potential (RMP). * **Subunits:** It consists of an **α-subunit** (catalytic, contains binding sites for Na⁺, K⁺, and ATP) and a **β-subunit** (essential for membrane targeting). * **Inhibitors:** It is specifically inhibited by **Cardiac Glycosides** (e.g., Digoxin and Ouabain), which bind to the extracellular side of the α-subunit. * **Energy Consumption:** In a resting state, this pump accounts for approximately 30-40% of a cell's total energy expenditure.

Q: Fixed time is required for all of the following steps of the cell cycle, except?

G1 phase. ### Explanation The cell cycle duration varies significantly between different cell types, and this variation is almost entirely due to the **G1 phase**. **1. Why G1 phase is the correct answer:** The G1 phase (Gap 1) is the most variable part of the cell cycle. Its duration depends on external factors like nutrient availability, cell size, and growth factors. Cells can remain in G1 for a few hours, days, or even years (entering the G0 or quiescent phase). Because it acts as the primary "decision-making" period where the cell determines whether to commit to division at the **Restriction Point (R point)**, its timing is not fixed. **2. Why the other options are incorrect:** Once a cell passes the G1 restriction point and enters the **S phase**, the subsequent steps follow a relatively "fixed" or constant time course to ensure genomic integrity: * **S phase (DNA Synthesis):** Usually takes 8–10 hours in most human cells to ensure precise replication of the entire genome. * **G2 phase (Gap 2):** Usually lasts 2–5 hours, providing a fixed window for checking DNA errors and preparing proteins for mitosis. * **M phase (Mitosis):** The shortest and most constant phase, typically lasting only 0.5–1 hour. **3. NEET-PG High-Yield Pearls:** * **G0 Phase:** A modified G1 phase where non-dividing cells (like neurons or skeletal muscle) reside. * **Generation Time:** The total time from one mitosis to the next. In rapidly dividing human cells (like intestinal epithelium), it is about 24 hours. * **Regulation:** The transition from G1 to S is regulated by **Cyclin D-CDK4/6** complexes. * **Labile Cells:** Cells that never enter G0 and have a very short G1 (e.g., bone marrow, GI tract). * **Permanent Cells:** Cells that stay in G0 indefinitely (e.g., Neurons, Cardiac myocytes).

Q: Which of the following depicts the cell cycle sequence accurately?

G0 - G1 - S - G2 - M. **Explanation:** The cell cycle is a highly regulated, ordered sequence of events that results in cell division. The correct sequence is **G0 → G1 → S → G2 → M**. 1. **G0 (Quiescence):** A resting phase where the cell has exited the cycle and is not actively dividing (e.g., neurons). 2. **G1 (Gap 1):** The cell grows, synthesizes RNA, and prepares proteins for DNA replication. 3. **S (Synthesis):** The critical phase where **DNA replication** occurs, doubling the DNA content. 4. **G2 (Gap 2):** A period of further growth and "proofreading" of replicated DNA before division. 5. **M (Mitosis):** The phase of nuclear and cytoplasmic division. **Why other options are incorrect:** * **Options A & B:** These suggest that the M phase occurs before G1 or that G2 occurs before S. DNA must be replicated (S phase) *before* the cell prepares for division (G2) and actually divides (M). * **Option D:** This places the M phase before G2. The G2 phase is essential as a pre-mitotic checkpoint to ensure DNA integrity; division cannot occur immediately after synthesis without this quality control. **High-Yield NEET-PG Pearls:** * **Duration:** The **S phase** is typically the most constant in duration, while **G1** is the most variable. * **Checkpoints:** The **G1 to S transition** (regulated by Cyclin D/CDK4 and Rb protein) is the "Restriction Point"—the most critical point for cell cycle commitment. * **Labelling:** Radioactive thymidine is used to label cells specifically in the **S phase**. * **Permanent Cells:** Neurons, skeletal, and cardiac muscle cells remain in **G0** and do not regenerate.

Question 1

Transcytosis occurs in which of the following cells?

Accepted Answer

Epithelial cells of the intestine

Answer

Neuroglia

Answer

Neuron

Answer

Axolemma

Question 2

All cells do not divide at the same rate. Events in which phase of the cell cycle determine when a cell is going to replicate?

Accepted Answer

G1 phase

Answer

M phase

Answer

S phase

Answer

G2 phase

Question 3

Transition from G2 to M phase of the cell cycle is controlled by which of the following cyclins?

Accepted Answer

Cyclin B

Answer

Cyclin D

Answer

Cyclin A

Answer

Cyclin E

Question 4

Which ion primarily determines the resting membrane potential?

Accepted Answer

Potassium (K+)

Answer

Sodium (Na+)

Answer

Chloride (Cl-)

Answer

Magnesium (Mg++)

Question 5

Which of the following statements is true regarding transport across a cell membrane?

Accepted Answer

Sodium ions are transported with glucose via symport.

Answer

Chloride ions are transported with glucose via symport.

Answer

Sodium ions are transported with glucose via antiporter.

Answer

Potassium ions are transported with glucose via symport.

Question 6

Which statement is true for both pinocytosis and phagocytosis?

Accepted Answer

Involves the recruitment of actin filaments

Answer

Occurs spontaneously and nonselectively

Answer

Endocytotic vesicles fuse with lysosomes that release hydrolases into the vesicles

Answer

Is only observed in macrophages and neutrophils

Question 7

Na+-K+ ATPase is a-

Accepted Answer

Transmembrane protein

Answer

Extrinsic protein

Answer

Peripheral protein

Answer

Intracellular protein

Question 8

In which phase of the cell cycle is the cellular content of DNA doubled?

Accepted Answer

S phase

Answer

M phase

Answer

G1 phase

Answer

G2 phase

Question 9

Fixed time is required for all of the following steps of the cell cycle, except?

Accepted Answer

G1 phase

Answer

S phase

Answer

M phase

Answer

G2 phase

Question 10

Which of the following depicts the cell cycle sequence accurately?

Accepted Answer

G0 - G1 - S - G2 - M

Answer

G0 - M - G2 - S - G1

Answer

G0 - G1 - G2 - S - M

Answer

G0 - G1 - S - M - G2

Cellular Physiology — MCQs

Cellular Physiology — MCQs

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