Question 1

Which of the following blood vessels carries oxygenated blood from the lungs to the heart?

Accepted Answer

The pulmonary veins are the only veins in the human body that carry oxygenated blood. After gas exchange occurs in the lungs, oxygenated blood returns to the left atrium of the heart via four pulmonary veins (two from each lung). This is a fundamental concept in the circulatory system taught in NCERT Class 10 Biology Chapter 6 (Life Processes). Therefore, the answer is B.

Question 2

The human kidney filters approximately 180 liters of filtrate per day, but only about 1–2 liters of urine is excreted. This is because most of the filtrate is reabsorbed in which part of the nephron?

Accepted Answer

The proximal convoluted tubule (PCT) is responsible for selective reabsorption of useful substances (glucose, amino acids, ions, and water) from the filtrate back into the blood. Approximately 99% of the filtered water, glucose, and ions are reabsorbed here through active transport and osmosis. The loop of Henle and collecting duct also contribute to water reabsorption, but the PCT is the primary site of reabsorption. This is a key NCERT Class 10 excretory system concept that explains why urine volume is much less than filtrate volume.

Question 3

In the human nervous system, which of the following correctly describes the function of sensory neurons (afferent neurons)?

Accepted Answer

Sensory neurons (afferent neurons) carry nerve impulses from sensory receptors (in skin, eyes, ears, etc.) to the central nervous system (brain and spinal cord). They detect stimuli from the environment and transmit this information toward the CNS for processing. Motor neurons (efferent neurons) do the opposite—they carry impulses from the CNS to muscles and glands. This distinction is fundamental to NCERT Class 10 nervous system structure and function.

Question 4

The normal pH range of human blood is approximately 7.35–7.45. Which organ system is primarily responsible for maintaining this pH balance by regulating carbon dioxide levels?

Accepted Answer

The respiratory system maintains blood pH by controlling the elimination of carbon dioxide (CO₂). When CO₂ dissolves in blood, it forms carbonic acid (H₂CO₃), which lowers pH. By increasing or decreasing the rate of breathing, the lungs can remove more or less CO₂, thereby regulating blood pH. The kidneys also play a secondary role by regulating bicarbonate ions. However, the respiratory system is the primary and immediate pH regulator through CO₂ control, as taught in NCERT Class 10.

Question 5

Which of the following statements correctly describes the function of the diaphragm in the human respiratory system?

Accepted Answer

The diaphragm is a dome-shaped muscular partition that separates the thoracic cavity from the abdominal cavity. During inspiration, it contracts and flattens, increasing the volume of the thoracic cavity and decreasing air pressure inside the lungs, allowing air to flow in. During expiration, it relaxes and returns to its dome shape, decreasing thoracic volume and pushing air out. This is the primary mechanism of breathing in humans.

Question 6

Which of the following correctly describes the pathway of blood flow through the human heart?

Accepted Answer

The correct pathway of blood flow through the heart is: Deoxygenated blood enters the right atrium via the superior and inferior vena cava → flows into the right ventricle → pumped to the lungs via the pulmonary artery → oxygenated blood returns from the lungs via the pulmonary vein → enters the left atrium → flows into the left ventricle → pumped to the body via the aorta. This is the standard circulatory pathway taught in NCERT Class 10 Biology (Chapter 6: Life Processes). Option B correctly identifies this sequence. Option A reverses the atrial-ventricular flow. Option C confuses the pulmonary and systemic circuits. Option D incorrectly suggests blood bypasses the lungs. Therefore, answer is B.

Question 7

In the human circulatory system, which chamber of the heart receives deoxygenated blood from the superior and inferior vena cava?

Accepted Answer

The right atrium is the upper right chamber of the heart that receives deoxygenated blood from the body through two large veins: the superior vena cava (from upper body) and the inferior vena cava (from lower body). This blood then flows into the right ventricle, which pumps it to the lungs via the pulmonary artery for oxygenation. This is a fundamental concept in NCERT Class 10 circulatory system.

Question 8

During the cardiac cycle, the atria and ventricles of the heart do not contract simultaneously. The delay in ventricular contraction after atrial contraction is primarily caused by the slow conduction of electrical impulses through which structure?

Accepted Answer

The atrioventricular (AV) node is responsible for the physiological delay between atrial and ventricular contraction during the cardiac cycle. When the sinoatrial (SA) node generates an electrical impulse, it spreads rapidly through the atrial muscle, causing atrial contraction. However, the AV node deliberately slows the conduction velocity of this impulse (from ~1 m/s in atrial tissue to ~0.05 m/s in the AV node). This delay of approximately 0.1 seconds allows the atria to complete their contraction and empty blood into the ventricles before ventricular contraction begins. This ensures efficient filling of the ventricles and optimal cardiac output. The SA node initiates the heartbeat but does not cause the delay. The bundle of His and Purkinje fibers conduct impulses rapidly, not slowly. Therefore, the answer is B.

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