🔬 Biology · Class 11 · NEET
Body Fluids and Circulation - Practice Questions with Answers 75 free MCQs on Body Fluids and Circulation, each with its own worked answer and explanation. Blood, lymph, the heart, the cardiac cycle, blood pressure, and ECG. High NEET weightage.
Take the timed Body Fluids and Circulation chapterwise test → 75 practice questions on Body Fluids and Circulation , sorted Easy → Hard. Try each one first, then open its answer page for the worked explanation. Want the full theory first? Read the Body Fluids and Circulation notes .
ECG: The Three Key Waves P wave (atrial depol.) QRS complex (ventricular depol.) T wave (ventricular repol.) QRS is the tallest spike - ventricles have far more muscle mass than the atria A single ECG cycle: the P wave marks atrial depolarisation (contraction signal), the large QRS complex marks ventricular depolarisation, and the T wave marks ventricular repolarisation (recovery) before the next cycle begins.
Easy - 25 questions Q1.
The white blood cells that are most abundant and act as the first line of defence by phagocytosis are the:
A NeutrophilsB LymphocytesC EosinophilsD BasophilsShow answer & explanation →
Q3.
The heart is enclosed within a protective double-walled membranous sac called the:
A PleuraB PeritoneumC EndocardiumD PericardiumShow answer & explanation →
Q4.
The valve present between the right atrium and right ventricle of the heart is the:
A Tricuspid valveB Bicuspid valveC Semilunar valveD Mitral valveShow answer & explanation →
Q5.
The percentage of blood volume that is occupied by cells, mainly red blood cells, is measured as the:
A HaematocritB Plasma indexC ESRD Buffy coatShow answer & explanation →
Q6.
The pumping chamber of the heart that sends blood to the body is:
A Right atriumB Right ventricleC Left atriumD Left ventricleShow answer & explanation →
Q7.
The main gas carried by red blood cells is:
A Carbon dioxide, dissolved directly in plasmaB Nitrogen, an inert gas with no carrier proteinC Oxygen (via haemoglobin)D Hydrogen, released during cellular respirationShow answer & explanation →
Q11.
Double circulation means blood passes through the heart:
A Only once per circuit, directly to the bodyB Twice per circuit (to lungs AND to body)C In two directions at the same simultaneous momentD As many as four separate times per single circuitShow answer & explanation →
Q13.
Which blood vessels carry blood away from the heart to the rest of the body?
A CapillariesB Lymphatic vesselsC ArteriesD VeinsShow answer & explanation →
Q14.
The fluid part of blood, in which blood cells are suspended, is called:
A CytoplasmB LymphC SerumD PlasmaShow answer & explanation →
Q15.
Red blood cells (erythrocytes) mainly function to:
A Transport oxygen to body tissuesB Initiate blood clotting at wound sitesC Engulf bacteria by phagocytosisD Produce antibodies against pathogensShow answer & explanation →
Q16.
The fluid connective tissue that transports materials around the body is:
A bloodB boneC cartilageD muscleShow answer & explanation →
Q20.
White blood cells mainly help in:
A defence against diseaseB the carrying of oxygenC the clotting of bloodD the digestion of foodShow answer & explanation →
Q21.
Blood platelets play a key role in:
A clotting of bloodB carrying oxygenC fighting infectionD digesting foodShow answer & explanation →
Medium - 25 questions Q26.
Which plasma protein is chiefly responsible for maintaining the osmotic (oncotic) pressure of blood?
A GlobulinB FibrinogenC AlbuminD ProthrombinShow answer & explanation →
Q27.
In the ABO system, a person with blood group AB has which antibodies in the plasma?
A Anti-A onlyB Anti-B onlyC Both anti-A and anti-BD Neither anti-A nor anti-BShow answer & explanation →
Q28.
The impulse from the SA node, after passing through the atria, is delayed briefly at the AV node so that:
A The ventricles contract before the atriaB The atria empty into ventricles before ventricles contractC The valves stay permanently closedD The heart rate slows to zeroShow answer & explanation →
Q29.
During ventricular systole, the semilunar valves open while the atrioventricular valves remain:
A OpenB ClosedC Partially openD AbsentShow answer & explanation →
Q30.
The final soluble protein converted into insoluble fibrin threads during blood clotting is:
A ThrombinB HeparinC ThromboplastinD FibrinogenShow answer & explanation →
Q31.
The sinoatrial (SA) node is called the pacemaker because:
A It forms the largest muscular chamber within the four chambers of the heartB It initiates electrical impulses that set heart rate (~72 bpm)C It generates the strongest contractile force of any region in the myocardiumD It regulates systemic blood pressure directly via baroreceptor reflexesShow answer & explanation →
Q32.
Erythropoietin (EPO) stimulates:
A White blood cell production within lymphoid tissueB Red blood cell production in bone marrowC Platelet production from bone marrow megakaryocytesD Insulin secretion from pancreatic beta cellsShow answer & explanation →
Q33.
The refractory period after a heartbeat prevents:
A Blood from flowing backward through the semilunar and AV valvesB Tetanic (continuous) contraction of the heart (ensures rhythmic pumping)C Autonomic nerve signals from the vagus and sympathetic trunk from reaching the SA nodeD Excessively rapid filling of the ventricles during diastoleShow answer & explanation →
Q34.
The Frank-Starling law of the heart states:
A Heart rate rises proportionally with sympathetic stimulation during physical exerciseB Greater cardiac filling → greater stretch of ventricle → greater force of contractionC The heart ejects a fixed stroke volume regardless of venous return changesD Arterial blood pressure directly sets the intrinsic rate of SA node firing each beatShow answer & explanation →
Q35.
The lub sound of the heartbeat (S1) is mainly produced by the closure of the:
A Valves present within the vena cavaB Semilunar valves at the start of diastoleC Tricuspid and bicuspid (atrioventricular) valvesD Walls of the pulmonary artery during systoleShow answer & explanation →
Q36.
A blood pressure reading of 160/100 mm Hg, when persistently elevated, is referred to as:
A Tachycardia, a faster than normal heart rateB Hypotension, a drop below the normal rangeC Bradycardia, a slower than normal heart rateD Hypertension, a rise above the normal rangeShow answer & explanation →
Q37.
Lymph differs in composition from blood plasma mainly in that lymph:
A Carries less protein and fewer red blood cells than plasmaB Carries oxygen far more efficiently than blood doesC Carries a notably higher concentration of red blood cellsD Contains no white blood cells of any kindShow answer & explanation →
Q38.
During the cardiac cycle, the period when both atria and ventricles are relaxed is called:
A Joint diastole, when both chambers rest togetherB Isovolumetric contraction, a brief tension phaseC Atrial systole, when atria are contractingD Ventricular systole, when ventricles are contractingShow answer & explanation →
Q39.
An electrocardiogram (ECG) records the:
A Volume of blood ejected with each heartbeatB Electrical activity of the heart through a cardiac cycleC Mechanical pumping force generated by the ventriclesD Rate of oxygen use by the cardiac muscleShow answer & explanation →
Q40.
Cardiac output is calculated as the product of:
A Heart rate and total blood volumeB Stroke volume and blood pressureC Heart rate and blood pressureD Stroke volume and heart rateShow answer & explanation →
Q44.
Oxygenated blood is carried from the lungs to the heart by the:
A pulmonary veinsB pulmonary arteryC aortaD vena cavaShow answer & explanation →
Q47.
The rhythmic sequence of contraction and relaxation of the heart is the:
A cardiac cycleB menstrual cycleC nitrogen cycleD water cycleShow answer & explanation →
Q48.
The valves in the heart function to prevent the ___ of blood:
A backflowB forward flowC clottingD oxygenationShow answer & explanation →
Q50.
In double circulation, blood passes through the heart ___ during one complete circuit of the body:
A twiceB onceC three timesD four timesShow answer & explanation →
Hard - 25 questions Q51.
An Rh-negative mother carrying a second Rh-positive foetus risks erythroblastosis foetalis because:
A The foetus makes anti-Rh antibodiesB Maternal anti-Rh antibodies cross the placenta and destroy foetal red cellsC The mother lacks all clotting factorsD The foetus lacks haemoglobinShow answer & explanation →
Q52.
The cardiac output of a normal adult at rest is about 5 litres per minute; this equals a stroke volume of roughly 70 mL and a heart rate of about:
A 50 beats per minuteB 72 beats per minuteC 100 beats per minuteD 120 beats per minuteShow answer & explanation →
Q53.
The QRS complex of an electrocardiogram represents the electrical event that immediately precedes:
A Ventricular contractionB Atrial contractionC Ventricular relaxationD Closure of semilunar valvesShow answer & explanation →
Q54.
Excess tissue fluid that is not reabsorbed by the blood capillaries is drained by the lymphatic system and finally returned to the blood at the:
A AortaB Hepatic portal veinC Subclavian veinsD Pulmonary arteryShow answer & explanation →
Q55.
A patient's ECG shows a greatly enlarged T wave region abnormality; the T wave normally indicates:
A Depolarisation of atriaB Depolarisation of ventriclesC Repolarisation of ventriclesD Contraction of atriaShow answer & explanation →
Q56.
The Frank-Starling mechanism operates via:
A Autonomic neural control of heart rate acting via vagal and sympathetic input to the SA node rather than any change in the intrinsic stretch-tension relationship of cardiac muscle fibresB Length-dependent activation of cardiac myofilaments: increased stretch exposes more troponin C binding sites and improves actin-myosin overlapC Hormonal modulation produced by circulating epinephrine binding beta-adrenergic receptors alone without any contribution from the length-dependent stretch of cardiac sarcomeres themselvesD Direct regulation of the rate of ATP synthesis within cardiac mitochondria during stretch independent of any sarcomere length change or troponin C binding site exposure involvedShow answer & explanation →
Q57.
Nitric oxide (NO) as a vasodilator acts by:
A Directly binding to myosin heads to physically prevent cross-bridge cycling altogether in typical laboratory settingsB Activating soluble guanylyl cyclase in VSM cells, increasing cGMP, which activates PKG, leading to smooth muscle relaxationC Directly blocking voltage-gated calcium channels on the vascular smooth muscle cell membrane under usual circumstancesD Competitively blocking angiotensin II receptors located on vascular smooth muscle cell surfaces according to most researchersShow answer & explanation →
Q58.
Pacemaker cells (SA node) depolarize spontaneously due to:
A A constitutive sodium leak through voltage-insensitive channels that never inactivate rather than the time-dependent gating actually shown by HCN-type funny current channelsB Funny current (If, HCN channels) carrying Na+/K+ inward current during diastole, plus T-type Ca<sup>2+</sup> channels near thresholdC Continuous potassium influx through inward-rectifying channels during diastole rather than the net inward cation current that actually drives diastolic depolarizationD The complete absence of any stable resting membrane potential in nodal tissue despite nodal cells reliably oscillating between a defined maximum and threshold potentialShow answer & explanation →
Q59.
Einthoven's triangle in ECG refers to:
A The anatomical triangular shape that is physically formed by the apex and base of the heart, a structural feature unrelated to limb-lead placement or electrical vector measurementB The three limb leads (I, II, III) forming an equilateral triangle around the heart for measuring cardiac electrical activity from different anglesC The isolated QRS complex waveform that is recorded from a single chest lead alone, a single waveform rather than the geometric arrangement of the three limb leadsD The combined muscular mass formed jointly by the left and right ventricles together, a description of cardiac muscle mass rather than any electrical lead configurationShow answer & explanation →
Q60.
During the cardiac cycle, the 'dub' sound of the heartbeat is produced by:
A Contraction of the ventricular myocardium during systole as generally observedB Opening of the atrioventricular valves during diastole in typical laboratory settingsC Closure of the atrioventricular valves at the start of systole under normal conditionsD Closure of the semilunar (aortic and pulmonary) valves at the start of diastoleShow answer & explanation →
Q61.
A P wave in an ECG corresponds to:
A The brief pause between atrial and ventricular contractionB Depolarization of the atria, just before atrial contractionC Repolarization of the ventricles after contractionD Depolarization of the ventricles, just before ventricular contractionShow answer & explanation →
Q62.
Lymph differs from blood plasma mainly in that lymph:
A Contains red blood cells in similar numbers to bloodB Has a higher protein concentration than blood plasmaC Contains much less protein than blood plasmaD Is transported only by active pumping from a dedicated lymph heart in mammalsShow answer & explanation →
Q63.
Cardiac output is the product of:
A Blood pressure and total peripheral resistanceB Heart rate and stroke volumeC Heart rate and total blood volumeD Stroke volume and total blood volumeShow answer & explanation →
Q64.
The dicrotic notch seen on an arterial pressure tracing is caused by:
A A brief backflow of blood against the closed aortic valve during early diastoleB Atrial contraction occurring just before ventricular systole in the majority of documented casesC The peak of ventricular systolic pressure during ejection according to most studiesD Opening of the atrioventricular valves at the start of diastole under usual circumstancesShow answer & explanation →
Q65.
Baroreceptors located in the aortic arch and carotid sinus help regulate blood pressure by:
A Directly sensing blood oxygen levels and adjusting breathing rate as widely reportedB Sensing arterial stretch and triggering reflex changes in heart rate and vessel diameterC Releasing aldosterone in response to falling blood sodium levels in standard reference materialD Producing erythropoietin in response to low oxygen delivery under most conditions studiedShow answer & explanation →
Q67.
Blood pressure is measured with an instrument called the:
A sphygmomanometerB a stethoscopeC a thermometerD a barometerShow answer & explanation →
Q69.
Deoxygenated blood returning from the body first enters the ___ of the heart:
A right atriumB left atriumC right ventricleD left ventricleShow answer & explanation →
Q70.
The lymphatic system returns ___ from the tissues back to the blood:
A tissue fluidB oxygen gasC only hormonesD waste urineShow answer & explanation →
Q72.
The first heart sound "lubb" is produced by the closure of the:
A atrioventricular valvesB the semilunar heart valvesC the main aorta wallD the vena cava veinShow answer & explanation →
Q73.
The Rh factor is a type of ___ found on the surface of red blood cells:
A antigenB enzymeC hormoneD vitaminShow answer & explanation →
Q75.
An electrocardiogram (ECG) records the ___ activity of the heart:
A electricalB chemicalC only mechanicalD thermalShow answer & explanation →