Cellular Physiology Practice Questions

Q: What is the contribution of the Na+/K+ pump to the development of the resting membrane potential (RMP)?

-4 mV. ### Explanation The resting membrane potential (RMP) of a typical large nerve fiber is approximately **-90 mV**. This potential is generated by two primary mechanisms: 1. **Diffusion Potentials (Major Contributor):** The movement of ions through "leak channels" (primarily K+ leak channels) creates a potential of **-86 mV**. Because the membrane is significantly more permeable to K+ than Na+, the RMP sits close to the equilibrium potential of Potassium. 2. **Na+/K+ ATPase Pump (Electrogenic Contribution):** The pump actively transports **3 Na+ ions out** of the cell for every **2 K+ ions in**. This net loss of one positive charge from the intracellular fluid creates a small deficit of positive ions inside the membrane. This direct electrogenic contribution accounts for exactly **-4 mV**. Therefore, the total RMP is the sum of these two components: **(-86 mV) + (-4 mV) = -90 mV**. #### Analysis of Options: * **Option A (-90 mV):** This is the **total RMP** of a large myelinated nerve fiber, not the specific contribution of the pump alone. * **Option B (-89 mV):** This is a distractor value with no physiological basis in standard textbooks (like Guyton). * **Option C (-86 mV):** This represents the contribution of **passive ion diffusion** (via K+ leak channels) to the RMP. * **Option D (-4 mV):** This is the **correct** direct electrogenic contribution of the Na+/K+ pump. #### High-Yield Clinical Pearls for NEET-PG: * **Goldman-Hodgkin-Katz Equation:** Used to calculate RMP considering multiple ions and their permeabilities. * **Digitalis (Cardiac Glycosides):** Inhibits the Na+/K+ ATPase, leading to increased intracellular Na+, which subsequently slows the Na+/Ca2+ exchanger, increasing intracellular Ca2+ (positive inotropy). * **Energy Requirement:** The Na+/K+ pump consumes roughly 60-70% of the total energy requirement in a resting neuron.

Q: Glucose is reabsorbed in the proximal tubule via symport with which ion?

Na+. **Explanation:** Glucose reabsorption in the proximal convoluted tubule (PCT) occurs via **Secondary Active Transport**. This process is mediated by **Sodium-Glucose Co-transporters (SGLT)**, specifically SGLT2 (early PCT) and SGLT1 (late PCT). **Why Na+ is correct:** The process is driven by the electrochemical gradient created by the **Na+-K+ ATPase pump** on the basolateral membrane, which keeps intracellular sodium levels low. This gradient allows sodium to move down its concentration gradient from the tubular lumen into the cell. Glucose "hitchhikes" with sodium against its own concentration gradient via a **symport** mechanism. Once inside the cell, glucose exits the basolateral membrane into the blood via facilitated diffusion through **GLUT2** (or GLUT1). **Why other options are incorrect:** * **K+ (Potassium):** Potassium is primarily secreted or reabsorbed through specific channels and exchangers (like the Na-K-2Cl symporter in the Loop of Henle), but it does not drive glucose transport. * **Ca++ (Calcium):** Calcium reabsorption in the PCT is largely passive (paracellular) and follows water and sodium; it is not coupled with glucose. * **Cl- (Chloride):** Chloride is reabsorbed primarily via paracellular pathways or in exchange for other anions in the later segments of the PCT. **High-Yield Clinical Pearls for NEET-PG:** * **SGLT2 Inhibitors (e.g., Dapagliflozin):** A class of drugs used in Diabetes Mellitus that block glucose reabsorption in the PCT, leading to glucosuria. * **Renal Threshold for Glucose:** Approximately **180 mg/dL**. When blood glucose exceeds this, SGLT transporters become saturated ($T_mG$), and glucose appears in the urine. * **Fanconi Syndrome:** A generalized dysfunction of the PCT resulting in the loss of glucose, amino acids, and phosphates in the urine.

Q: Regarding transport of substances through the cell membrane, all are true except:

Facilitated diffusion requires energy.. ### Explanation The core concept tested here is the distinction between **Passive Transport** and **Active Transport**. **Why Option C is the correct answer (The "Except"):** Facilitated diffusion is a form of **passive transport**. It occurs along a concentration gradient (from high to low concentration) and, therefore, **does not require metabolic energy (ATP)**. It relies solely on the kinetic energy of the molecules and the presence of a specific carrier protein. **Analysis of other options:** * **Option A:** Glucose enters most cells (like muscle and adipose tissue) via **GLUT transporters**, which are classic examples of facilitated diffusion. (Note: Glucose absorption in the gut/kidney occurs via SGLT, which is secondary active transport). * **Option B:** Active transport (both primary and secondary) moves substances **against** a concentration gradient, which necessitates the expenditure of energy (ATP or electrochemical gradients). * **Option D:** Unlike simple diffusion, facilitated diffusion is **carrier-mediated**. It requires specific transmembrane proteins to shuttle molecules that are too large or polar to pass through the lipid bilayer alone. **NEET-PG High-Yield Pearls:** 1. **Kinetics:** Facilitated diffusion exhibits **saturation kinetics** ($V_{max}$). Once all carrier proteins are occupied, the rate of transport cannot increase further, unlike simple diffusion which is linear. 2. **GLUT vs. SGLT:** * **GLUT (1-14):** Facilitated Diffusion (Passive). * **SGLT (1-2):** Secondary Active Transport (Requires Na+ gradient). 3. **Insulin Dependency:** GLUT-4 (found in skeletal muscle and adipose tissue) is the only insulin-dependent glucose transporter.

Q: During which phase of the cell cycle is new DNA material synthesized?

Interphase. ### Explanation **Correct Answer: D. Interphase** The cell cycle is divided into two main stages: **Interphase** and the **M-phase (Mitosis)**. Interphase is the longest part of the cell cycle and is further divided into three sub-phases: $G_1$, **S (Synthesis)**, and $G_2$. The **S-phase** is specifically characterized by the replication of nuclear DNA. During this phase, the DNA content of the cell doubles (from $2C$ to $4C$), though the chromosome number remains the same. This ensures that when the cell eventually divides during mitosis, each daughter cell receives a complete and identical set of genetic material. **Why other options are incorrect:** * **A, B, and C (Prophase, Metaphase, Telophase):** These are all sub-stages of the **M-phase (Mitosis)**. Mitosis is the process of nuclear division where the *already replicated* DNA is condensed, aligned, and physically separated into two nuclei. No new DNA is synthesized during these stages; they are concerned with the distribution of genetic material rather than its production. **High-Yield Clinical Pearls for NEET-PG:** * **S-phase Marker:** The synthesis of **Histone proteins** occurs primarily during the S-phase to package the newly formed DNA. * **Checkpoints:** The transition from $G_1$ to S is the most critical checkpoint (Restriction point), regulated by **Cyclin D-CDK4/6** and the **Retinoblastoma (Rb) protein**. * **Quiescent Phase ($G_0$):** Cells that stop dividing (like mature neurons or skeletal muscle) exit the cycle at $G_1$ to enter $G_0$. * **Vinca Alkaloids/Taxanes:** These chemotherapy drugs target the M-phase (microtubules), whereas drugs like **Methotrexate** or **5-Fluorouracil** target the S-phase by inhibiting DNA synthesis.

Q: What is the primary function of the Golgi complex?

To participate in posttranslational processing of proteins.. The **Golgi complex** (or Golgi apparatus) functions as the "post office" or "shipping center" of the cell. Its primary role is the modification, sorting, and packaging of proteins and lipids received from the Endoplasmic Reticulum (ER). ### Why Option B is Correct: Proteins synthesized in the Rough ER enter the Golgi complex, where they undergo **post-translational modifications**. These include: * **Glycosylation:** Adding carbohydrate chains to form glycoproteins. * **Sulfation and Phosphorylation:** Modifying proteins to ensure they reach their correct destination. * **Proteolysis:** Cleaving precursor proteins into active forms (e.g., proinsulin to insulin). * **Sorting:** Directing proteins to lysosomes, the plasma membrane, or for secretion via secretory vesicles. ### Why Other Options are Incorrect: * **Option A:** The breakdown of proteins and lipids is the primary function of **Lysosomes** (via acid hydrolases) and **Peroxisomes** (via oxidative enzymes). * **Option C:** Energy production (ATP synthesis) occurs in the **Mitochondria** via oxidative phosphorylation. * **Option D:** Transcription occurs in the **Nucleus**, while translation occurs on **Ribosomes** (either free or attached to the Rough ER). ### High-Yield NEET-PG Pearls: * **Polarity:** The Golgi has a **Cis-face** (entry/forming face) facing the ER and a **Trans-face** (exit/maturing face) facing the plasma membrane. * **I-Cell Disease:** A clinical correlation where a deficiency in phosphorylating enzymes in the Golgi leads to failure of protein trafficking to lysosomes. * **Marker Enzyme:** **Thiamine Pyrophosphatase (TPP)** is the characteristic marker enzyme for the Golgi complex.

Q: In which phase of the cell cycle does DNA replication occur?

S phase. ### Explanation **Correct Answer: C. S phase** The cell cycle is a highly regulated sequence of events leading to cell division. The **S phase (Synthesis phase)** is the specific period during interphase when **DNA replication** occurs. During this stage, the DNA content of the cell doubles (from 2n to 4n), ensuring that each of the two daughter cells receives a complete and identical set of chromosomes. This process involves key enzymes like DNA polymerase and helicase. **Analysis of Incorrect Options:** * **A. G1 phase (Gap 1):** This is the pre-synthetic phase. It is characterized by intensive cellular growth, RNA synthesis, and protein synthesis. The cell prepares the machinery necessary for DNA replication, but the DNA content remains constant (2n). * **B. G2 phase (Gap 2):** This is the post-synthetic/pre-mitotic phase. The cell continues to grow and synthesizes proteins like **tubulin** required for spindle fiber formation. It acts as a final checkpoint to ensure DNA was replicated correctly before entering mitosis. * **C. M phase (Mitosis):** This is the shortest phase where actual nuclear (karyokinesis) and cytoplasmic (cytokinesis) division occurs. DNA is distributed, not replicated, during this phase. **High-Yield Facts for NEET-PG:** * **G0 Phase (Quiescent stage):** Cells that stop dividing (e.g., neurons, cardiac myocytes) exit the cycle at G1 and enter G0. * **Duration:** In a typical 24-hour human cell cycle, the S phase lasts about 8–10 hours. * **Regulation:** The transition from G1 to S is the most critical "restriction point," regulated by **Cyclin D and CDK4/6**. * **Clinical Correlation:** Many chemotherapy drugs (antimetabolites like Methotrexate and 5-Fluorouracil) are **S-phase specific**, as they interfere with DNA synthesis.

Q: Protein synthesis occurs in which organelle?

Ribosome. **Explanation:** **Correct Option: A. Ribosome** Ribosomes are the primary sites of **translation**, the process where genetic code from mRNA is decoded into a polypeptide chain. Known as the "protein factories" of the cell, they consist of two subunits (40S and 60S in eukaryotes) composed of ribosomal RNA (rRNA) and proteins. They can exist freely in the cytoplasm (synthesizing proteins for internal use) or attached to the Rough Endoplasmic Reticulum (synthesizing proteins for secretion or membrane insertion). **Why other options are incorrect:** * **B. Golgi apparatus:** This organelle is responsible for the **post-translational modification**, sorting, and packaging of proteins (e.g., glycosylation and phosphorylation). It does not synthesize the protein backbone itself. * **C. Lysosomes:** These are the "suicide bags" of the cell containing acid hydrolases. Their function is **intracellular digestion** and degradation of macromolecules, not synthesis. * **D. Endosomes:** These are membrane-bound vesicles involved in **endocytosis**. They sort internalized material and direct it to the appropriate destination, such as lysosomes for degradation or back to the plasma membrane. **High-Yield NEET-PG Pearls:** * **Antibiotic Target:** Many antibiotics work by inhibiting bacterial ribosomes (70S). For example, **Aminoglycosides** and **Tetracyclines** bind to the 30S subunit, while **Macrolides** and **Chloramphenicol** bind to the 50S subunit. * **Nissl Bodies:** In neurons, the Rough Endoplasmic Reticulum and free ribosomes are called Nissl bodies; they are essential for synthesizing neurotransmitters and structural proteins. * **Signal Hypothesis:** Proteins destined for secretion have a "signal peptide" that directs the ribosome to attach to the Endoplasmic Reticulum.

Question 1

What is the contribution of the Na+/K+ pump to the development of the resting membrane potential (RMP)?

Accepted Answer

-4 mV

Answer

-90 mV

Answer

-89 mV

Answer

-86 mV

Question 2

Glucose is reabsorbed in the proximal tubule via symport with which ion?

Accepted Answer

Na+

Answer

K+

Answer

Ca++

Answer

Cl-

Question 3

Which of the following is true about facilitated diffusion?

Accepted Answer

Occurs in the direction opposite to the electrical gradient.

Answer

Occurs in the direction of the concentration gradient.

Answer

Does not require energy.

Answer

Is facilitated by the charge of the molecule.

Question 4

Which organ's cells lack the deposition of mitochondria?

Accepted Answer

Kidney

Answer

Brain

Answer

Heart

Answer

Muscles

Question 5

Regarding transport of substances through the cell membrane, all are true except:

Accepted Answer

Facilitated diffusion requires energy.

Answer

Glucose is transported via facilitated diffusion.

Answer

Active transport is an energy-driven process.

Answer

Facilitated diffusion requires a carrier protein.

Question 6

During which phase of the cell cycle is new DNA material synthesized?

Accepted Answer

Interphase

Answer

Prophase

Answer

Metaphase

Answer

Telophase

Question 7

What is the primary function of the Golgi complex?

Accepted Answer

To participate in posttranslational processing of proteins.

Answer

To participate in the breakdown of proteins and lipids.

Answer

To participate in energy production.

Answer

To participate in transcription and translation.

Question 8

Which among the following is the function of cholesterol in the plasma membrane?

Accepted Answer

Decrease fluidity of the lipid bilayer.

Answer

Increase fluidity of the lipid bilayer.

Answer

Facilitate the diffusion of ions through the lipid bilayer.

Answer

Assist in the transport of hormones across the lipid bilayer.

Question 9

In which phase of the cell cycle does DNA replication occur?

Accepted Answer

S phase

Answer

G1 phase

Answer

G2 phase

Answer

M phase

Question 10

Protein synthesis occurs in which organelle?

Accepted Answer

Ribosome

Answer

Golgi apparatus

Answer

Lysosomes

Answer

Endosomes

Cellular Physiology — MCQs

Cellular Physiology — MCQs

On this page

Practice by Chapter

Want unlimited practice?