Why Correct: An electrocardiogram (ECG) records the electrical potential differences generated by the heart's depolarization and repolarization during each cardiac cycle.
Distractor Analysis: Heart rate can be derived from ECG intervals but is not the direct recording. Ventricular concentration is not a standard physiological measurement. Volume of blood pumped per beat (stroke volume) requires echocardiography or other imaging, not ECG.
Takeaway: The P wave represents atrial depolarization, QRS complex represents ventricular depolarization, and T wave represents ventricular repolarization.

Why Correct: Human red blood cells (erythrocytes) have an average lifespan of about 120 days before being removed by macrophages in the spleen and liver.
Distractor Analysis: 60 days approximates the lifespan of platelets (thrombocytes). 180 days does not correspond to the standard lifespan of any primary human blood cell type. 240 days does not correspond to the standard lifespan of any primary human blood cell type.
Takeaway: White blood cells (leukocytes) exhibit varied lifespans from hours to years, with neutrophils surviving only 6-8 hours in circulation.

Why Correct: 100 ml of arterial blood carries approximately 20 ml of oxygen when fully saturated, with hemoglobin binding about 1.34 ml O2 per gram and blood containing around 15 g hemoglobin per 100 ml.
Distractor Analysis: 40 ml would require physiologically impossible hemoglobin levels or oxygen solubility. 10 ml represents venous blood oxygen content after tissue delivery. 30 ml exceeds normal arterial oxygen-carrying capacity.
Takeaway: Venous blood typically carries 12-15 ml O2 per 100 ml, creating an arteriovenous oxygen difference of 4-8 ml used clinically to assess tissue oxygen extraction.

Why Correct: Blood pH above 7.0 is alkaline, and the normal range of 7.35–7.45 falls within the alkaline side of the pH scale.
Distractor Analysis: Acidic pH is below 7.0, like gastric juice at pH 1.5–3.5. Neutral pH is exactly 7.0, like pure water. Variable describes fluids whose pH changes, like urine which ranges from 4.5 to 8.0.
Takeaway: The body maintains blood pH within a narrow range (7.35–7.45) through bicarbonate buffering; deviations cause acidosis (7.45).

Why Correct: Cardiac muscle cells contain abundant mitochondria that continuously produce ATP through aerobic respiration, preventing lactic acid buildup and fatigue.
Distractor Analysis: Intercalated discs enable rapid electrical conduction between cardiac cells but do not prevent fatigue. Both actin and myosin filaments are present in cardiac muscle, but their relative quantities do not determine fatigue resistance.
Takeaway: Cardiac muscle relies exclusively on aerobic respiration, unlike skeletal muscle which can use anaerobic glycolysis leading to lactic acid accumulation and fatigue.

Why Correct: An adult heart pumps approximately 5 liters per minute at rest, which equals 300 liters per hour (5 × 60).
Distractor Analysis: 150 liters per hour corresponds to 2.5 liters per minute, which is below normal resting cardiac output. 200 liters per hour equals 3.33 liters per minute, still below typical resting output. 340 liters per hour would require 5.67 liters per minute, slightly above average resting cardiac output.
Takeaway: Cardiac output is calculated as stroke volume × heart rate, with typical resting values of 70 ml stroke volume and 70 beats per minute.

Why Correct: Sphygmomanometers measure blood pressure using an inflatable cuff and pressure gauge, detecting systolic and diastolic pressures.
Distractor Analysis: Barometers measure atmospheric pressure. Tonometers measure intraocular pressure in the eye.
Takeaway: Blood pressure readings follow systolic/diastolic format (e.g., 120/80 mmHg), where systolic represents ventricular contraction and diastolic represents ventricular relaxation.

Why Correct: Blood type O negative lacks A, B, and Rh antigens, allowing safe transfusion to all blood types without triggering immune reactions.
Distractor Analysis: Type A contains A antigens, type B contains B antigens, and type AB contains both A and B antigens, all of which can cause incompatibility reactions in recipients lacking those antigens.
Takeaway: Type AB positive individuals are universal plasma donors because their plasma lacks anti-A and anti-B antibodies.

Why Correct: An average adult male has approximately 5 liters of blood, which constitutes about 7-8% of total body weight.
Distractor Analysis: One liter is the typical blood volume of a newborn infant. Two liters represents the plasma component only, not total blood volume. Ten liters would require a body weight of over 140 kg, which is far above average.
Takeaway: Blood constitutes 7-8% of body weight in adults, with females having slightly less (4-5 liters) than males.

Why Correct: Plasma cells, derived from B-lymphocytes, produce and secrete antibodies into plasma and lymph fluids.
Distractor Analysis: Bone marrow produces B-lymphocyte precursors but not mature antibody-secreting cells. Liver synthesizes plasma proteins like albumin and clotting factors, not immunoglobulins. Kidney filters blood and maintains electrolyte balance, with no role in antibody production.
Takeaway: Each antibody molecule consists of two heavy chains and two light chains, with variable regions that bind specific antigens.

Why Correct: Blood group O lacks both A and B antigens on red blood cells, allowing safe transfusion to recipients of any ABO blood type.
Distractor Analysis: Blood group A contains A antigens and anti-B antibodies. Blood group B contains B antigens and anti-A antibodies. Blood group AB contains both A and B antigens and no anti-A or anti-B antibodies, making it the universal recipient.
Takeaway: For Rh factor, Rh-negative blood (e.g., O-) serves as universal donor for Rh-negative recipients, while Rh-positive blood cannot be given to Rh-negative individuals.

Why Correct: Human red blood cells (erythrocytes) have an average lifespan of 120 days, which is approximately four months.
Distractor Analysis: One week is far too short for red blood cell lifespan. One month is the typical lifespan of platelets, not red blood cells. One year is too long; red blood cells are continuously replaced every four months.
Takeaway: White blood cells have highly variable lifespans—neutrophils live 6-8 hours, lymphocytes can live years, while red blood cells consistently last 120 days.

Why Correct: An electrocardiogram (ECG) records the electrical activity of the heart, measuring its rhythm and rate. It detects abnormalities in heartbeat, such as arrhythmias or ischemia.
Distractor Analysis: Leg function is assessed by electromyography or gait analysis, not ECG. Blood flow is measured by Doppler ultrasound or angiography. Brain cells are evaluated by EEG or imaging scans.
Takeaway: ECG is the standard test for heart rhythm; always associate 'cardio' with heart, not other organs.

Why Correct: Type O negative blood lacks A, B, and Rh antigens on red blood cells, so it does not trigger an immune reaction in recipients of any blood type, making O negative the universal donor.
Distractor Analysis: Type A blood has A antigens and would be attacked by anti-A antibodies in non-A recipients. Type B blood has B antigens and would be attacked by anti-B antibodies. Type AB blood has both A and B antigens and can receive any type but donate only to AB.
Takeaway: Universal donor = O negative (lacks all antigens). Universal recipient = AB positive (has all antigens; no antibodies).

Why Correct: Cockroach has an open circulatory system where blood (hemolymph) flows freely in the body cavity (hemocoel) rather than being confined to vessels.
Distractor Analysis: Earthworm, snake, and rat all have closed circulatory systems with blood contained in arteries, veins, and capillaries. In closed systems, blood circulates continuously through a network of vessels, unlike the open system of arthropods.
Takeaway: Open circulatory systems are characteristic of arthropods (e.g., cockroach, grasshopper) and most molluscs; closed systems are found in annelids, vertebrates, and some molluscs.

Why Correct: The sinoatrial (SA) node spontaneously generates electrical impulses that set the heart's rhythmic contraction rate, functioning as the natural pacemaker.
Distractor Analysis: The AV node delays the impulse from atria to ventricles but does not initiate the rhythm. The myocardium is the heart muscle that contracts in response to impulses. "None of the above" is incorrect as SA node is the pacemaker.
Takeaway: SA node is located in the right atrium; its intrinsic firing rate (60-100 bpm) determines heart rate.

Why Correct: William Harvey (1578–1657) discovered the closed circulatory system and demonstrated that blood circulates continuously through the heart and vessels. His 1628 work 'Exercitatio Anatomica de Motu Cordis et Sanguinis' established the modern understanding of blood circulation.
Distractor Analysis: Francis Darwin was a botanist known for plant physiology, not circulation. G. Mendel is the father of genetics, studying pea plant inheritance. Hippocrates is the father of medicine but did not discover blood circulation.
Takeaway: William Harvey's discovery is a landmark in physiology. Related high-probability fact: Harvey also accurately described the function of valves in veins.

Why Correct: Pulmonary veins are the only veins in the adult human body that carry oxygenated blood. They transport oxygen-rich blood from the lungs to the left atrium of the heart, completing the pulmonary circulation loop.
Distractor Analysis: Hepatic portal veins carry deoxygenated blood from the gastrointestinal tract and spleen to the liver for processing. Renal veins carry deoxygenated blood from the kidneys back to the inferior vena cava. Pulmonary artery is the only artery that carries deoxygenated blood, transporting it from the right ventricle to the lungs for oxygenation.
Takeaway: The pulmonary artery and pulmonary veins are the exceptions to the general rule that arteries carry oxygenated blood and veins carry deoxygenated blood; the umbilical artery and vein in fetal circulation also follow this reversed pattern.