NCERT-Based Explanation

NCERT describes the cardiac cycle as consisting of joint diastole, atrial systole, and ventricular systole. During atrial systole, the ventricles are necessarily in diastole so that they can receive blood. However, ventricular diastole occurs not only during atrial systole but also during joint diastole, when all four chambers are relaxed. Therefore, although atrial systole always implies ventricular diastole, ventricular diastole does not always imply atrial systole. Hence, the reason correctly explains the assertion.

Pedagogical Value

This question develops logical thinking by requiring students to distinguish between a statement and its converse using the phases of the cardiac cycle. It reinforces that ventricular diastole occurs during both atrial systole and joint diastole, encouraging students to reason from the sequence of events rather than memorising isolated facts.

NCERT-Based Explanation

NCERT states that:

Cardiac output = Heart rate × Stroke volume

At rest, a trained athlete usually has a lower heart rate but a higher stroke volume, so the resting cardiac output is generally similar to that of a healthy non-athlete, not necessarily much higher. Therefore, the assertion is false.

The reason is also false because the body alters both heart rate and stroke volume to regulate cardiac output. NCERT describes neural and hormonal regulation of heart rate as well as changes in stroke volume.

Pedagogical Value

This question tests whether students understand that cardiac output is determined by two variables—heart rate and stroke volume. It also prevents the common misconception that athletes always have a much higher cardiac output simply because they have a stronger heart.

NCERT-Based Explanation

Blood vessel walls contain elastic fibres and collagen fibres. Elastic fibres enable the vessel walls to stretch and recoil in response to changes in blood pressure, whereas collagen fibres provide mechanical strength and help prevent the rupture of blood vessel walls. Therefore, the reason correctly explains the assertion.

Pedagogical Value

This question encourages students to associate the structural components of blood vessels with their functional significance rather than memorising the names of the fibres alone. It reinforces the complementary roles of elastic and collagen fibres in maintaining normal vascular function.

NCERT-Based Explanation

NCERT states that two prominent heart sounds are produced during each cardiac cycle. Therefore, irrespective of whether the individual is an athlete or not, each cardiac cycle produces only two prominent heart sounds. Hence, the assertion is false.

The reason is also false because the heart is composed of cardiac muscle, not skeletal muscle. Although an athlete’s heart may undergo physiological adaptations with training, it does not contain skeletal muscles.

Pedagogical Value

This question tests two common misconceptions simultaneously. First, it checks whether students notice the phrase “per cardiac cycle” instead of unconsciously interpreting it as “per minute”. Second, it reinforces that the heart is composed of cardiac muscle, not skeletal muscle, even in trained athletes.

NCERT-Based Explanation

NCERT states that a normal ECG consists of the P wave, QRS complex, and T wave, representing the sequence of electrical events during a cardiac cycle. Although athletes may have physiological adaptations such as a lower resting heart rate and higher stroke volume, the cardiac conduction pathway remains unchanged. Therefore, with the same lead configuration, the overall ECG morphology remains broadly similar. Hence, the reason correctly explains the assertion.

Pedagogical Value

This question encourages students to integrate concepts from Body Fluids and Circulation, Neural Control and Coordination, and Exercise Physiology. It reinforces that training adaptations alter the timing of the cardiac cycle rather than the fundamental sequence of electrical conduction. Students learn to distinguish changes in ECG intervals from changes in ECG morphology, avoiding the common misconception that an athlete’s ECG should have a completely different waveform pattern.

NCERT-Based Explanation

NCERT states that the exchange of oxygen and carbon dioxide occurs by simple diffusion. In the lungs, gases diffuse between the alveoli and blood, whereas in the tissues they diffuse between the blood and cells. Although the direction of diffusion is opposite in pulmonary and systemic circulation, the physical principle governing gas exchange is the same, namely diffusion along a partial pressure gradient. Therefore, the reason correctly explains the assertion.

Pedagogical Value

This question integrates Breathing and Exchange of Gases with Body Fluids and Circulation. It encourages students to distinguish between the mechanism of gas exchange (diffusion) and the direction of gas movement. It helps prevent the common misconception that pulmonary and systemic gas exchange occur by different mechanisms simply because the direction of oxygen and carbon dioxide movement is reversed.

Pedagogical Value

This question deliberately presents a biologically plausible generalisation that is not directly supported by NCERT. It encourages students to resist the temptation to answer solely on the basis of intuition or partial knowledge. Instead, they should recognise when the available information is insufficient to confidently establish a general principle. This reinforces an important competitive examination strategy: it is better to leave an uncertain question unanswered than to rely on an attractive but unsupported inference and risk negative marking.

It also trains students to evaluate the logical relationship between the assertion and the reason critically, rather than assuming that two physiologically related statements necessarily explain one another.

NCERT-Based Explanation

NCERT describes arteries and veins as blood vessels with three layers, including a middle smooth muscle layer. However, the statement “all arteries and veins” is an overgeneralisation. For example, capillaries do not possess a smooth muscle layer, and certain specialised vessels may show structural modifications. Thus, the assertion is false because of the absolute term “all”. Smooth muscle is of mesodermal origin, making the reason true, but this does not explain the assertion.

Pedagogical Value

This question tests whether students avoid overgeneralising anatomical descriptions. It reinforces that the embryonic origin of a tissue does not establish that every member of a structural category possesses that tissue.

NCERT-Based Explanation

NCERT states that the QRS complex represents ventricular depolarisation. The ventricles, particularly the left ventricle, possess a much greater muscle mass than the atria. Consequently, ventricular depolarisation generates a larger electrical signal, making the R wave, which is the major positive deflection of the QRS complex, the tallest wave in a normal ECG. Therefore, the reason correctly explains the assertion.

Pedagogical Value

This question encourages students to relate the amplitude of ECG waves to the amount of cardiac muscle undergoing depolarisation, rather than memorising the appearance of the ECG. It reinforces the relationship between cardiac anatomy and the electrical events recorded in an ECG.

NCERT-Based Explanation

NCERT states that the autonomic nervous system (ANS) regulates the activity of the heart by increasing or decreasing the heart rate. NCERT also shows that amphibians possess well-developed nervous and endocrine systems, reflecting an advanced level of control and coordination among vertebrates. Since tetrapods possess these regulatory systems through their common vertebrate body plan, the autonomic regulation of heart rate is possible in tetrapods. Therefore, the reason correctly explains the assertion.

Pedagogical Value

This question encourages students to integrate concepts from Structural Organisation in Animals, Neural Control and Coordination, Chemical Control and Coordination, and Body Fluids and Circulation. It reinforces that the physiological regulation of the heart is a consequence of the evolution of sophisticated control and coordination systems in vertebrates, encouraging students to connect related concepts across multiple NCERT chapters instead of studying them in isolation.

NCERT-Based Explanation

NCERT states that veins have comparatively thinner walls and a wider lumen than arteries. The tunica media, which contains smooth muscle and elastic fibres, is therefore thinner in veins because veins carry blood under lower pressure and perform a different functional role from arteries. Hence, the reason correctly explains the assertion.

Pedagogical Value

This question encourages students to relate the histological structure of blood vessels to their functional and haemodynamic differences, rather than memorising that veins simply have thinner walls. It reinforces that vascular structure reflects physiological function.

NCERT-Based Explanation

NCERT states that the characteristic sounds of the heart can be heard through a stethoscope. It also mentions that these heart sounds are clinically significant, as abnormalities in the sounds may indicate disorders of the heart. Therefore, the assertion is true, whereas the reason is false.

Pedagogical Value

This question tests whether students appreciate that heart sounds are not merely audible phenomena but also have important clinical significance. It reinforces the diagnostic value of auscultation described in NCERT.

NCERT-Based Explanation

NCERT states that an electrocardiogram (ECG) is a graphical representation of the electrical activity of the heart during a cardiac cycle. It does not measure pressure changes. Furthermore, the electrical activity generated by the nodal tissue initiates cardiac contraction, which subsequently produces pressure changes within the heart chambers. Therefore, pressure changes do not lead to the electrical activity of the heart. Hence, both the assertion and the reason are false.

Pedagogical Value

This question tests whether students correctly identify what an ECG records. It also reinforces the cause-and-effect relationship between electrical activity and mechanical events of the heart, preventing the common misconception that pressure changes generate the ECG.

The reasoning chain is:

1. NCERT: Sympathetic stimulation increases the strength of ventricular contraction and thereby increases cardiac output.
2. NCERT: Ventricles have much thicker walls than the atria.
3. NCERT: Greater muscle mass is associated with greater force generation.
4. Therefore, even if sympathetic stimulation influences both chambers, the strength of atrial contraction cannot be expected to equal that of ventricular contraction because their musculature and functions are fundamentally different.

NCERT-Based Explanation

NCERT states that the human heart is myogenic, meaning that the cardiac impulse originates within the heart itself, specifically from the SA node (nodal musculature). Therefore, the normal rhythmic activity of the heart is regulated intrinsically and does not require external nervous stimulation for initiation. The autonomic nervous system only modulates the heart rate and force of contraction. Hence, the reason correctly explains the assertion.

Pedagogical Value

This question tests whether students distinguish between intrinsic regulation and extrinsic modulation of cardiac activity. It reinforces that the heartbeat is initiated within the heart itself (myogenicity), while the autonomic nervous system merely alters its rate and force according to the body’s needs.

NCERT-Based Explanation

NCERT states that the T wave represents ventricular repolarisation and is the last wave of a normal ECG. However, the cardiac cycle includes both electrical and mechanical events, and the ECG records only the electrical activity of the heart. The end of the T wave therefore does not necessarily represent the end of the cardiac cycle. Thus, the assertion is false, whereas the reason is true.

Pedagogical Value

This question tests whether students distinguish between the completion of the electrical events recorded in an ECG and the completion of the mechanical cardiac cycle. It helps prevent the common misconception that the end of the last ECG wave automatically marks the end of the entire cardiac cycle.

NCERT-Based Explanation

NCERT states that cardiac output is the amount of blood pumped by each ventricle per minute and depends on heart rate and stroke volume. Cardiac output normally increases during exercise to meet the body’s increased metabolic demands. Therefore, a greater cardiac output is not necessarily a pathological condition, making the assertion false.

The reason is also false because an increased cardiac output does not invariably lead to high blood pressure. Arterial blood pressure depends on multiple factors, including cardiac output and peripheral resistance. An increase in cardiac output during normal physiological conditions, such as exercise, does not by itself imply hypertension.

Pedagogical Value

This question tests whether students can distinguish physiological increases in cardiac output (e.g. during exercise) from pathological conditions. It also reinforces that blood pressure cannot be inferred solely from cardiac output.

NCERT-Based Explanation

NCERT states that veins have a comparatively wider lumen than arteries. Since blood flows through veins under lower pressure, their walls are thinner and their lumens are wider than those of arteries. Therefore, the reason correctly explains the assertion.

Pedagogical Value

This question encourages students to understand that the term “comparatively wider” is a relative comparison with arteries, not an absolute description. It also reinforces the relationship between blood pressure and the structural differences between arteries and veins.

NCERT-Based Explanation

During one cardiac cycle, each atrium and each ventricle undergoes one systole and two periods of diastole. The two diastolic periods are:

1. Joint diastole, when all four chambers are relaxed.
2. The period during ventricular systole, when the atria remain in diastole (or during atrial systole, when the ventricles remain in diastole).

Thus, each chamber experiences one systole and two diastoles, not two systoles and two diastoles. NCERT also states that the SA node is the normal pacemaker and that the AV node is part of the nodal tissue capable of generating electrical impulses. Therefore, the reason is true but unrelated to the assertion.

Pedagogical Value

This question tests whether students analyse the mechanical events experienced by an individual cardiac chamber rather than memorising only the names of the phases of the cardiac cycle. It encourages students to map the sequence of joint diastole, atrial systole, and ventricular systole onto each chamber separately.

NCERT-Based Explanation

NCERT states that two prominent heart sounds are produced during each cardiac cycle. The first heart sound (lub) is produced by the closure of the atrioventricular valves (tricuspid and bicuspid/mitral valves) at the beginning of ventricular systole. The second heart sound (dub) is produced by the closure of the semilunar valves (aortic and pulmonary valves) at the beginning of ventricular diastole. Therefore, the assertion is true, whereas the reason is false.

Pedagogical Value

L2 Conceptual Trap – This question tests whether students correctly associate each heart sound with the appropriate set of valves. It helps prevent the common misconception that the two heart sounds correspond separately to the tricuspid and mitral valves.