General Physiology Practice Questions

Q: Which of the following statements about facilitated diffusion is true?

It requires a carrier protein. **Explanation:** **Facilitated diffusion** is a type of carrier-mediated transport that allows large or polar molecules (like glucose and amino acids) to cross the cell membrane down their electrochemical gradient without the expenditure of energy. 1. **Why Option B is Correct:** Unlike simple diffusion, facilitated diffusion requires specific **integral membrane proteins (carriers)**. These proteins undergo conformational changes to shuttle molecules across the lipid bilayer. Because it relies on a finite number of carrier proteins, this process exhibits **saturation kinetics** ($V_{max}$). 2. **Why Other Options are Incorrect:** * **Option A:** It is a form of **passive transport**, not active. It does not move substances against a gradient. * **Option C:** This is false due to **saturation**. In simple diffusion, the rate is directly proportionate to the gradient (Fick’s Law). In facilitated diffusion, the rate increases with the gradient only until all carrier binding sites are occupied ($V_{max}$), after which the rate plateaus. * **Option D:** It requires **no metabolic energy** (ATP or Creatine Phosphate). The driving force is the concentration gradient itself. **High-Yield NEET-PG Pearls:** * **Classic Example:** Glucose transport via **GLUT transporters** (e.g., GLUT4 in muscle/adipose tissue) is the most frequently tested example of facilitated diffusion. * **Key Characteristics:** It is specific, saturable (shows a $T_m$ or Transport Maximum), and can be competitively inhibited. * **Distinction:** Unlike Primary Active Transport (e.g., Na+-K+ ATPase) or Secondary Active Transport (e.g., SGLT), facilitated diffusion **cannot** create a concentration gradient; it can only dissipate one.

Q: Natural light causes all except?

Destruction of the organ of Corti. **Explanation:** The question asks for the physiological effect that is **NOT** caused by natural light. **1. Why "Destruction of the organ of Corti" is the correct answer:** The **organ of Corti** is the sensory organ for hearing located within the inner ear (cochlea). It is stimulated by mechanical sound waves, not electromagnetic radiation (light). Destruction of the organ of Corti is typically caused by chronic exposure to loud noise (noise-induced hearing loss), ototoxic drugs (e.g., aminoglycosides), or aging—not by exposure to natural light. **2. Analysis of Incorrect Options:** * **Vitamin D synthesis:** Ultraviolet B (UVB) radiation from natural sunlight triggers the conversion of 7-dehydrocholesterol in the skin into cholecalciferol (Vitamin D3). * **Decrease in bilirubin level:** Blue-green light (wavelength 460–490 nm) helps decompose bilirubin into water-soluble isomers (lumirubin) that can be excreted without conjugation. This is the physiological basis for **phototherapy** used in neonatal jaundice. * **Melanin synthesis:** Exposure to UV light stimulates melanocytes in the basal layer of the epidermis to produce melanin (melanogenesis), which acts as a protective pigment against DNA damage. **High-Yield Clinical Pearls for NEET-PG:** * **Pineal Gland Connection:** Natural light inhibits the secretion of **Melatonin** from the pineal gland via the suprachiasmatic nucleus (SCN), regulating the circadian rhythm. * **Phototherapy:** The most effective wavelength for treating neonatal hyperbilirubinemia is approximately **450 nm**. * **Vitamin D:** The skin is the primary source of Vitamin D; deficiency leads to Rickets in children and Osteomalacia in adults. * **Retinal Damage:** While light doesn't affect the ear, excessive UV/blue light can cause **photoretinitis** or damage to the macula.

Q: Which of the following statements is true regarding intracellular receptors?

They are mainly located on the nuclear surface.. **Explanation:** **1. Why Option A is Correct:** Intracellular receptors are protein molecules located inside the target cell rather than on the cell membrane. These receptors primarily function as **ligand-activated transcription factors**. While some receptors (like glucocorticoids) are found in the cytoplasm, the majority—including those for thyroid hormones and many steroid hormones—are located **within the nucleus** or on the **nuclear surface**. Once the lipid-soluble ligand binds to the receptor, the complex binds to specific DNA sequences (Hormone Response Elements) to regulate gene transcription. **2. Why Other Options are Incorrect:** * **Option B:** Estrogen is a steroid hormone. Being lipophilic, it easily crosses the lipid bilayer and acts specifically on **intracellular (nuclear) receptors** (ER-α and ER-β). * **Option C:** Growth Hormone (GH) is a peptide hormone. Peptide hormones are water-soluble and cannot cross the cell membrane; therefore, GH acts via **cell surface receptors** (specifically the JAK-STAT signaling pathway). * **Option D:** While Vitamin A and Vitamin D act on intracellular receptors to regulate gene expression, **Vitamin E** (Tocopherol) primarily functions as a potent antioxidant within membranes and does not have a classic intracellular receptor-mediated signaling pathway like steroid hormones. **3. High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Intracellular Receptors:** "PET TV" – **P**rogesterone, **E**strogen, **T**estosterone, **T**hyroid hormone (T3/T4), and **V**itamin D/A. * **Thyroid Hormone Exception:** Unlike most others, Thyroid receptors are *always* bound to DNA in the nucleus, even in the absence of the hormone. * **Speed of Action:** Intracellular receptor signaling is **slow** (hours to days) because it requires protein synthesis, unlike ionotropic receptors which act in milliseconds.

Q: D2O (deuterium oxide) is used to measure which of the following volumes?

Total body water volume. ### Explanation The measurement of body fluid compartments is based on the **Indicator Dilution Principle** ($Volume = \frac{Amount\ of\ substance}{Concentration}$). To measure a specific compartment, the indicator must be able to distribute uniformly throughout that space and nowhere else. **Why Total Body Water (TBW) is correct:** To measure TBW, an indicator must be able to cross both the capillary wall and the cell membrane to distribute equally across all fluid compartments. **D2O (Deuterium oxide)**, also known as "heavy water," is an isotope of water. Because it is chemically identical to $H_2O$, it distributes freely throughout the entire body water volume. Other markers for TBW include Tritiated water ($HTO$) and Antipyrine. **Analysis of Incorrect Options:** * **A. Extracellular Fluid (ECF):** Markers for ECF must cross the capillary wall but **cannot** cross the cell membrane. Examples include Inulin (Gold Standard), Mannitol, and Sucrose. * **B. Intracellular Fluid (ICF):** There is no direct marker for ICF because no substance distributes exclusively inside cells. It is calculated indirectly: $ICF = TBW - ECF$. * **C. Plasma Volume:** Markers must be too large to cross the capillary wall, remaining confined to the vascular space. Examples include **Evans Blue dye (T-1824)** and Radio-iodinated Serum Albumin (RISA). **High-Yield Clinical Pearls for NEET-PG:** 1. **Interstitial Fluid (ISF):** Like ICF, it cannot be measured directly. It is calculated as $ISF = ECF - Plasma\ Volume$. 2. **Blood Volume:** Measured using Chromium-51 ($^{51}Cr$) labeled RBCs or calculated as $\frac{Plasma\ Volume}{1 - Hematocrit}$. 3. **Rule of 60-40-20:** TBW is ~60% of body weight, ICF is ~40%, and ECF is ~20%.

Q: All of the following are used to measure extracellular fluid (ECF) volume, except?

Sodium chloride. **Explanation:** The measurement of body fluid compartments is based on the **Indicator Dilution Principle** ($V = Q/C$). To measure a specific compartment, the indicator must distribute evenly within that compartment without entering others or being rapidly metabolized. **Why Sodium Chloride is the correct answer:** While sodium is the primary extracellular cation, **Sodium chloride (NaCl)** is not used to measure ECF volume because it is not restricted to the extracellular space. Sodium ions are actively transported and can enter cells via various channels and pumps. Furthermore, the body’s existing high concentration of NaCl makes it impossible to use as an exogenous tracer to calculate volume accurately. **Analysis of Incorrect Options:** * **Inulin & Sucrose:** These are large, inert saccharides. They distribute freely throughout the ECF (plasma and interstitial fluid) but cannot cross the cell membrane due to their size and lack of transporters. They are considered the "Gold Standard" for measuring ECF. * **Heavy Water ($D_2O$):** This is used to measure **Total Body Water (TBW)**, not ECF. It distributes uniformly across all fluid compartments (ECF + ICF). Since the question asks for an "except" regarding ECF measurement, and $D_2O$ measures TBW, it is often a distractor; however, in the context of this specific question, NaCl is the most physiologically incorrect choice for ECF measurement. **NEET-PG High-Yield Pearls:** * **Total Body Water:** Measured by Heavy water ($D_2O$), Tritiated water, or Aminopyrine. * **ECF Volume:** Measured by Inulin (Best), Sucrose, Mannitol, or Thiosulfate. * **Plasma Volume:** Measured by Evans Blue dye (T-1824) or Radio-iodinated Albumin ($RISA$). * **ICF Volume:** Cannot be measured directly. Calculated as $TBW - ECF$. * **Interstitial Fluid:** Calculated as $ECF - Plasma\ Volume$.

Q: Positive feedback is seen in all except?

Gastric secretion. **Explanation:** In physiology, **Positive Feedback** is a mechanism where the output of a system intensifies the original stimulus, leading to an "amplification" or "vicious cycle" until a specific endpoint is reached. Most physiological processes, however, rely on **Negative Feedback** to maintain homeostasis. **Why Gastric Secretion is the Correct Answer:** Gastric acid secretion is primarily regulated by **negative feedback**. As the pH of the stomach falls (becomes more acidic), D-cells in the antrum are stimulated to release **Somatostatin**. Somatostatin then inhibits the release of Gastrin from G-cells and Histamine from ECL cells, thereby decreasing further HCL production. This prevents the stomach from becoming excessively acidic. **Analysis of Incorrect Options (Examples of Positive Feedback):** * **LH Surge:** Increasing levels of Estrogen (above a threshold) exert positive feedback on the anterior pituitary, causing a massive release of Luteinizing Hormone (LH), which triggers ovulation. * **Entry of Calcium into Sarcoplasmic Reticulum (SR):** This refers to **Calcium-Induced Calcium Release (CICR)**. In cardiac muscle, a small amount of trigger calcium entering the cell causes a massive release of calcium from the SR, amplifying the signal for contraction. * **Thrombus Formation:** When a vessel is injured, activated platelets release chemicals that attract and activate more platelets. This cascade continues until a stable plug is formed. **High-Yield Clinical Pearls for NEET-PG:** * **Most common feedback in the body:** Negative Feedback (e.g., BP regulation, Thyroid hormone axis). * **Other Positive Feedback examples:** Parturition (Oxytocin), Nerve Action Potential (Hodgkin cycle/Sodium influx), and the Blood Clotting Cascade. * **Exception to LH:** Low levels of Estrogen exert *negative* feedback; only high, sustained levels trigger the *positive* feedback LH surge.

Q: Of the total oxygen consumed by the body per minute, which organ consumes the greatest fraction?

Liver. **Explanation:** The correct answer is **Liver (Option A)**. Oxygen consumption ($VO_2$) is determined by the metabolic activity of an organ. At rest, the liver is the most metabolically active organ in the body, accounting for approximately **20–27%** of total oxygen consumption. This high demand is due to its continuous role in protein synthesis, gluconeogenesis, urea formation, and detoxification processes. **Why other options are incorrect:** * **Brain (Option B):** The brain is highly aerobic and accounts for about **18–20%** of total $VO_2$. While it has a high metabolic rate per gram of tissue, its total consumption is slightly less than that of the liver. * **Muscle (Option C):** At rest, skeletal muscle accounts for about **15–20%** of $VO_2$. However, during heavy exercise, muscle becomes the dominant consumer, potentially accounting for over 90% of total body oxygen use. * **Kidney (Option D):** The kidneys consume about **6–7%** of total $VO_2$. Most of this energy is dedicated to the active transport of sodium ($Na^+$) in the renal tubules. **High-Yield Facts for NEET-PG:** 1. **Oxygen Consumption ($VO_2$) at Rest:** Liver (27%) > Brain (20%) > Muscle (18%) > Kidney (7%) > Heart (4%). 2. **Oxygen Extraction Ratio:** The **Heart** has the highest oxygen extraction ratio (70–80%), meaning it removes the most oxygen per unit of blood delivered. 3. **Blood Flow per 100g:** The **Carotid Body** has the highest blood flow per unit mass, while the **Kidney** receives the highest percentage of total Cardiac Output (20–25%).

Question 1

A 62-year-old woman eats a high carbohydrate meal. Her plasma glucose concentration rises, and this results in increased insulin secretion from the pancreatic islet cells. The insulin response is an example of

Accepted Answer

Negative feedback

Answer

Chemical equilibrium

Answer

End-product inhibition

Answer

Feed forward control

Question 2

Which of the following statements about facilitated diffusion is true?

Accepted Answer

It requires a carrier protein

Answer

It is a form of active transport

Answer

Rate of transport is proportionate to the concentration gradient

Answer

Requires creatine phosphate

Question 3

Which of the following is NOT an example of a feedforward control system?

Accepted Answer

Blood pressure regulation

Answer

Temperature regulation

Answer

Cephalic phase of gastric secretion

Answer

Increased heart rate before the start of exercise

Question 4

Natural light causes all except?

Accepted Answer

Destruction of the organ of Corti

Answer

Vitamin D synthesis

Answer

Decrease in bilirubin level

Answer

Melanin synthesis

Question 5

Which of the following statements is true regarding intracellular receptors?

Accepted Answer

They are mainly located on the nuclear surface.

Answer

Estrogen does not act on them.

Answer

Growth hormone (GH) acts on intracellular receptors.

Answer

Vitamin E acts on intracellular receptors.

Question 6

D2O (deuterium oxide) is used to measure which of the following volumes?

Accepted Answer

Total body water volume

Answer

Extracellular fluid volume

Answer

Intracellular fluid volume

Answer

Plasma volume

Question 7

All of the following are used to measure extracellular fluid (ECF) volume, except?

Accepted Answer

Sodium chloride

Answer

Sucrose

Answer

Inulin

Answer

Heavy water

Question 8

Common for both simple and facilitated diffusion is:

Accepted Answer

Transport along the concentration gradient

Answer

Can be blocked by specific inhibitors

Answer

Follows Fick's Law

Answer

Follows saturation kinetics

Question 9

Positive feedback is seen in all except?

Accepted Answer

Gastric secretion

Answer

LH surge

Answer

Entry of calcium into sarcoplasmic reticulum

Answer

Thrombus formation

Question 10

Of the total oxygen consumed by the body per minute, which organ consumes the greatest fraction?

Accepted Answer

Liver

Answer

Brain

Answer

Muscle

Answer

Kidney

General Physiology — MCQs

General Physiology — MCQs

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