Important Questions Class 11 Biology Chapter 15: Body Fluids And Circulation With Answers

Body fluids are transport media that carry nutrients, gases, hormones, and wastes in animals.
Blood and lymph help maintain tissue function by moving useful and harmful substances through the body.

Transport keeps every living cell supplied with oxygen, nutrients, hormones, and waste-removal support. Important Questions Class 11 Biology Chapter 15 test blood composition, plasma proteins, formed elements, ABO and Rh blood groups, lymph, human heart structure, cardiac cycle, ECG, double circulation, and circulatory disorders. CBSE 2026 questions from this chapter often ask values, functions, comparisons, and labelled flow sequences. The NCERT Reprint 2026-27 also gives key numerical facts such as 72 beats per minute, 70 mL stroke volume, and 5 litres cardiac output.

Key Takeaways

• Plasma Share: Plasma forms nearly 55 per cent of blood.
• RBC Lifespan: Human RBCs survive for about 120 days.
• Pacemaker Value: SAN generates 70 to 75 action potentials per minute.
• Cardiac Output: A healthy adult pumps about 5 litres of blood per minute.

Important Questions Class 11 Biology Chapter 15 Structure 2026

Important Questions Class 11 Biology Chapter 15: Key Concepts

These class 11 biology chapter 15 important questions cover the core NCERT ideas. Students should know blood, lymph, circulatory pathways, cardiac regulation, and common disorders.

Q1. What Are Body Fluids?

Body fluids are fluids that transport nutrients, gases, hormones, and wastes in animals. Blood and lymph are the major body fluids in humans.

1. Main Fluids:
   Blood and lymph.
2. Main Function:
   Transport of useful and harmful substances.
3. Final Result:
   Body fluids maintain transport inside the body

Q2. Why Do Higher Animals Need Blood And Lymph?

Higher animals need blood and lymph because diffusion alone cannot transport materials across complex bodies. Special fluids move substances efficiently.

1. Blood Function:
   Carries gases, nutrients, hormones, and wastes.
2. Lymph Function:
   Returns tissue fluid and carries absorbed fats.
3. Final Result:
   Blood and lymph support internal transport

Q3. What Are The Main Topics In Important Questions Class 11 Biology Chapter 15?

Chapter 15 focuses on blood, lymph, circulation, cardiac cycle, ECG, double circulation, and circulatory disorders.

1. Body Fluid Topics:
   Plasma, formed elements, blood groups, lymph.
2. Circulation Topics:
   Heart, cardiac cycle, ECG, double circulation.
3. Final Result:
   Chapter 15 covers body fluids and circulation mechanisms

Body Fluids And Circulation Class 11 Important Questions MCQ With Answers

These body fluids and circulation class 11 important questions test values, definitions, blood groups, heart function, and ECG waves. Each answer follows CBSE 2026 style.

Q1. What Percentage Of Blood Is Plasma?

Plasma forms nearly 55 per cent of blood. It is straw-coloured and viscous.

1. Options:
   (A) 35 per cent
   (B) 45 per cent
   (C) 55 per cent
   (D) 90 per cent
2. Rule Used:
   Plasma constitutes nearly 55 per cent of blood.
3. Final Result:
   Answer: (C) 55 per cent

Q2. Which Plasma Protein Helps In Blood Clotting?

Fibrinogen helps in blood clotting. It converts into fibrin during coagulation.

1. Options:
   (A) Albumin
   (B) Fibrinogen
   (C) Globulin
   (D) Haemoglobin
2. Rule Used:
   Fibrinogen participates in coagulation.
3. Final Result:
   Answer: (B) Fibrinogen

Q3. Which Blood Cells Are Most Abundant?

RBCs are the most abundant blood cells. A healthy adult man has about 5 to 5.5 million RBCs per mm³ of blood.

1. Options:
   (A) RBCs
   (B) Platelets
   (C) Basophils
   (D) Lymphocytes
2. Rule Used:
   RBCs are the most abundant formed elements.
3. Final Result:
   Answer: (A) RBCs

Q4. Which Organ Is Called The Graveyard Of RBCs?

Spleen is called the graveyard of RBCs. Old RBCs are destroyed there after about 120 days.

1. Options:
   (A) Liver
   (B) Kidney
   (C) Spleen
   (D) Lung
2. Rule Used:
   RBCs are destroyed in the spleen.
3. Final Result:
   Answer: (C) Spleen

Q5. Which Blood Group Is Called Universal Donor?

O blood group is called universal donor. It has no A or B antigens on RBCs.

1. Options:
   (A) A
   (B) B
   (C) AB
   (D) O
2. Rule Used:
   O group can donate to all ABO groups.
3. Final Result:
   Answer: (D) O

Q6. Which Blood Group Is Called Universal Recipient?

AB blood group is called universal recipient. It has no anti-A or anti-B antibodies in plasma.

1. Options:
   (A) A
   (B) B
   (C) AB
   (D) O
2. Rule Used:
   AB group can receive from all ABO groups.
3. Final Result:
   Answer: (C) AB

Q7. Which Heart Node Is Called The Pacemaker?

Sino-atrial node is called the pacemaker. It initiates and maintains rhythmic heart activity.

1. Options:
   (A) AVN
   (B) SAN
   (C) Purkinje fibres
   (D) AV bundle
2. Rule Used:
   SAN generates the maximum action potentials.
3. Final Result:
   Answer: (B) SAN

Q8. What Does P-Wave Represent In ECG?

P-wave represents atrial depolarisation. It leads to contraction of both atria.

1. Options:
   (A) Ventricular repolarisation
   (B) Atrial depolarisation
   (C) Ventricular depolarisation
   (D) Atrial relaxation
2. Rule Used:
   P-wave shows electrical excitation of atria.
3. Final Result:
   Answer: (B) Atrial depolarisation

Blood Class 11 Biology Important Questions

These blood class 11 biology important questions cover plasma, formed elements, and coagulation. NCERT uses direct values and functions in this section.

Q1. What Is Blood?

Blood is a special connective tissue made of plasma and formed elements. It transports gases, nutrients, hormones, and wastes.

1. Matrix:
   Plasma.
2. Formed Elements:
   RBCs, WBCs, and platelets.
3. Final Result:
   Blood is a fluid connective tissue

Q2. What Is Plasma?

Plasma is a straw-coloured viscous fluid that forms nearly 55 per cent of blood. It contains water, proteins, minerals, and nutrients.

1. Water Content:
   90 to 92 per cent.
2. Protein Content:
   6 to 8 per cent.
3. Final Result:
   Plasma is the fluid matrix of blood

Q3. What Are The Main Plasma Proteins And Their Functions?

Fibrinogen, globulins, and albumins are the main plasma proteins. They support clotting, defence, and osmotic balance.

1. Fibrinogen:
   Helps in blood coagulation.
2. Globulins:
   Help in defence mechanisms.
3. Albumins:
   Maintain osmotic balance.
4. Final Result:
   Plasma proteins support clotting, immunity, and osmotic balance

Q4. What Are Formed Elements Of Blood Class 11?

Formed elements are RBCs, WBCs, and platelets. They form nearly 45 per cent of blood.

1. RBCs:
   Transport respiratory gases.
2. WBCs:
   Support immunity and defence.
3. Platelets:
   Help in blood clotting.
4. Final Result:
   RBCs, WBCs, and platelets are formed elements

Q5. What Are RBCs?

RBCs are red blood cells that contain haemoglobin and transport respiratory gases. They lack nuclei in most mammals.

1. Count:
   5 to 5.5 million mm⁻³ in a healthy adult man.
2. Lifespan:
   About 120 days.
3. Final Result:
   RBCs transport respiratory gases

Q6. What Are WBCs?

WBCs are colourless nucleated blood cells that defend the body. Their number averages 6000 to 8000 mm⁻³ of blood.

1. Granulocytes:
   Neutrophils, eosinophils, basophils.
2. Agranulocytes:
   Lymphocytes and monocytes.
3. Final Result:
   WBCs protect the body from foreign organisms

Q7. What Are Platelets?

Platelets are cell fragments produced from megakaryocytes in bone marrow. They release substances involved in clotting.

1. Normal Count:
   1,50,000 to 3,50,000 mm⁻³.
2. Main Role:
   Blood coagulation.
3. Final Result:
   Platelets help prevent excessive blood loss

Q8. How Does Blood Coagulation Occur?

Blood coagulation occurs when fibrin threads form a clot at the injury site. This prevents excessive blood loss.

1. Injury Response:
   Platelets release clotting factors.
2. Enzyme Action:
   Prothrombin converts into thrombin.
3. Clot Formation:
   Fibrinogen converts into fibrin.
4. Final Result:
   Fibrin threads trap blood cells to form a clot

Blood Groups Class 11 Biology Important Questions

These blood groups class 11 biology questions cover ABO grouping, Rh factor, transfusion matching, and erythroblastosis foetalis. Blood compatibility is a high-value NCERT area.

Q1. What Is ABO Blood Grouping?

ABO grouping is based on the presence or absence of A and B antigens on RBCs. Plasma contains corresponding natural antibodies.

1. A Group:
   A antigen and anti-B antibody.
2. B Group:
   B antigen and anti-A antibody.
3. AB Group:
   A and B antigens and no antibodies.
4. O Group:
   No antigens and anti-A, anti-B antibodies.
5. Final Result:
   ABO grouping depends on RBC antigens and plasma antibodies

Q2. Why Is O Group Called Universal Donor?

O group is called universal donor because its RBCs lack A and B antigens. It can donate to A, B, AB, and O groups.

1. Antigen Status:
   No A or B antigen on RBCs.
2. Donor Compatibility:
   Can donate to all ABO groups.
3. Final Result:
   O group is the universal donor

Q3. Why Is AB Group Called Universal Recipient?

AB group is called universal recipient because its plasma lacks anti-A and anti-B antibodies. It can receive all ABO groups.

1. Antibody Status:
   No anti-A or anti-B antibodies.
2. Recipient Compatibility:
   Can receive A, B, AB, and O blood.
3. Final Result:
   AB group is the universal recipient

Q4. What Is Rh Factor Class 11?

Rh factor is an antigen present on RBCs in nearly 80 per cent of humans. People with this antigen are Rh positive.

1. Rh Positive:
   Rh antigen present.
2. Rh Negative:
   Rh antigen absent.
3. Final Result:
   Rh factor must match during transfusion

Q5. What Is Erythroblastosis Foetalis?

Erythroblastosis foetalis occurs when Rh antibodies from an Rh-negative mother destroy RBCs of an Rh-positive foetus.

1. First Pregnancy:
   Foetal and maternal blood usually remain separated.
2. Later Pregnancy:
   Maternal antibodies may enter foetal blood.
3. Prevention:
   Anti-Rh antibodies after first delivery.
4. Final Result:
   Rh incompatibility can cause severe anaemia and jaundice in the baby

Lymph Class 11 Biology Questions And Answers

These lymph class 11 biology questions explain tissue fluid and lymphatic transport. Lymph supports immunity and fat absorption.

Q1. What Is Lymph?

Lymph is a colourless fluid present in the lymphatic system. It contains specialised lymphocytes and supports immune responses.

1. Origin:
   Formed from tissue fluid.
2. Main Cells:
   Lymphocytes.
3. Final Result:
   Lymph supports immunity and transport

Q2. What Is Tissue Fluid?

Tissue fluid is the fluid present between tissue cells. It forms when water and small substances move out of blood capillaries.

1. Source:
   Blood plasma.
2. Function:
   Exchange of nutrients, gases, and wastes.
3. Final Result:
   Tissue fluid connects blood and body cells

Q3. What Is The Difference Between Blood And Lymph?

Blood contains more proteins and formed elements than lymph. Lymph has fewer proteins and mainly contains lymphocytes.

1. Blood:
   Contains RBCs, WBCs, platelets, and plasma proteins.
2. Lymph:
   Contains lymphocytes and fewer proteins.
3. Final Result:
   Lymph lacks most formed elements found in blood

Q4. What Is The Function Of Lymph?

Lymph returns tissue fluid to major veins and carries immune cells. It also transports absorbed fats from intestinal lacteals.

1. Transport Role:
   Carries nutrients and hormones.
2. Fat Absorption:
   Lacteals absorb fats.
3. Final Result:
   Lymph transports fats and supports immunity

Human Circulatory System Class 11 Important Questions

These human circulatory system class 11 questions cover heart structure, valves, nodal tissue, and circulatory pathways. The human system is closed and double.

Q1. What Is The Human Circulatory System?

Human circulatory system consists of heart, blood vessels, and blood. It is also called the blood vascular system.

1. Heart:
   Muscular pumping organ.
2. Blood Vessels:
   Closed branching network.
3. Blood:
   Fluid connective tissue.
4. Final Result:
   Human circulation is closed and vascular

Q2. Where Is The Human Heart Located?

The human heart lies in the thoracic cavity between the lungs. It is slightly tilted to the left.

1. Origin:
   Mesodermally derived organ.
2. Protection:
   Enclosed by pericardium with pericardial fluid.
3. Final Result:
   Heart lies between the lungs in the thoracic cavity

Q3. What Are The Four Chambers Of The Human Heart?

The human heart has two atria and two ventricles. Atria are upper chambers, and ventricles are lower chambers.

1. Upper Chambers:
   Right atrium and left atrium.
2. Lower Chambers:
   Right ventricle and left ventricle.
3. Final Result:
   Human heart has four chambers

Q4. What Is The Function Of Heart Valves?

Heart valves allow blood flow in one direction and prevent backflow. They maintain proper circulation.

1. Tricuspid Valve:
   Between right atrium and right ventricle.
2. Bicuspid Valve:
   Between left atrium and left ventricle.
3. Semilunar Valves:
   At openings of pulmonary artery and aorta.
4. Final Result:
   Valves prevent backward flow of blood

Q5. Why Is SAN Called Pacemaker?

SAN is called pacemaker because it generates the maximum number of action potentials. It initiates rhythmic contraction.

1. Location:
   Right upper corner of right atrium.
2. Rate:
   70 to 75 action potentials per minute.
3. Final Result:
   SAN sets the pace of heartbeat

Q6. Why Is The Heart Called Myogenic?

The heart is called myogenic because its rhythmic activity starts from specialised cardiac muscles. It does not need external nerve impulses to begin beating.

1. Tissue Involved:
   Nodal tissue.
2. Main Node:
   Sino-atrial node.
3. Final Result:
   Heart rhythm starts within cardiac muscle

Cardiac Cycle Class 11 Biology Important Questions

These cardiac cycle class 11 biology questions cover systole, diastole, stroke volume, cardiac output, and heart sounds. Learn the sequence carefully.

Q1. What Is Cardiac Cycle?

Cardiac cycle is the sequence of heart events repeated during one heartbeat. It includes systole and diastole of atria and ventricles.

1. Duration:
   0.8 seconds.
2. Heart Rate:
   About 72 cycles per minute.
3. Final Result:
   One cardiac cycle equals one heartbeat

Q2. What Happens During Joint Diastole?

During joint diastole, all four chambers remain relaxed. Blood flows from atria into ventricles through open AV valves.

1. Valve Status:
   Tricuspid and bicuspid valves are open.
2. Semilunar Valves:
   Closed.
3. Final Result:
   Blood moves freely into ventricles

Q3. What Happens During Atrial Systole?

During atrial systole, both atria contract simultaneously. This increases ventricular filling by about 30 per cent.

1. Trigger:
   SAN generates action potential.
2. Effect:
   More blood enters ventricles.
3. Final Result:
   Atrial systole adds about 30 per cent blood to ventricles

Q4. What Happens During Ventricular Systole?

During ventricular systole, ventricles contract and pump blood into pulmonary artery and aorta.

1. AV Valves:
   Close due to attempted backflow.
2. Semilunar Valves:
   Open due to high ventricular pressure.
3. Final Result:
   Ventricular systole pumps blood out of the heart

Q5. What Is Stroke Volume?

Stroke volume is the amount of blood pumped by each ventricle in one cardiac cycle. It is about 70 mL.

1. Given Value:
   Stroke volume = 70 mL.
2. Unit:
   mL per beat.
3. Final Result:
   Stroke volume = 70 mL

Q6. What Is Cardiac Output?

Cardiac output is the volume of blood pumped by each ventricle per minute. It averages about 5 litres in a healthy person.

1. Formula Used:
   Cardiac output = stroke volume × heart rate.
2. Calculation:
   70 mL × 72 beats/min = 5040 mL/min.
3. Final Result:
   Cardiac output is about 5 litres per minute

Q7. What Are Heart Sounds?

Heart sounds are lub and dub sounds produced during each cardiac cycle. They occur due to valve closure.

1. Lub:
   Closure of tricuspid and bicuspid valves.
2. Dub:
   Closure of semilunar valves.
3. Final Result:
   Heart sounds have clinical diagnostic value

ECG Class 11 Biology Questions And Answers

These ECG class 11 biology questions explain electrical activity of the heart. ECG traces help detect abnormal heart function.

Q1. What Is ECG?

ECG is a graphical representation of the electrical activity of the heart during a cardiac cycle.

1. Instrument:
   Electrocardiograph.
2. Recording:
   Electrocardiogram.
3. Final Result:
   ECG records heart electrical activity

Q2. What Does P-Wave Represent In ECG?

P-wave represents depolarisation of the atria. It leads to contraction of both atria.

1. Electrical Event:
   Atrial depolarisation.
2. Mechanical Event:
   Atrial contraction.
3. Final Result:
   P-wave represents atrial excitation

Q3. What Does QRS Complex Represent In ECG?

QRS complex represents depolarisation of the ventricles. It initiates ventricular contraction.

1. Electrical Event:
   Ventricular depolarisation.
2. Mechanical Event:
   Beginning of ventricular systole.
3. Final Result:
   QRS complex represents ventricular excitation

Q4. What Does T-Wave Represent In ECG?

T-wave represents ventricular repolarisation. It marks the return of ventricles to normal state.

1. Electrical Event:
   Ventricular repolarisation.
2. Mechanical Link:
   End of systole.
3. Final Result:
   T-wave represents ventricular recovery

Q5. How Can Heart Rate Be Measured From ECG?

Heart rate can be measured by counting QRS complexes in a given time period. Each QRS complex corresponds to one ventricular contraction.

1. Count:
   Number of QRS complexes.
2. Interpretation:
   More complexes mean higher heart rate.
3. Final Result:
   QRS complex count gives heartbeat rate

Double Circulation Class 11 Important Questions

These double circulation class 11 questions explain pulmonary and systemic circulation. Mammals show complete separation of oxygenated and deoxygenated blood.

Q1. What Is Double Circulation?

Double circulation means blood passes through the heart twice in one complete circuit. It includes pulmonary and systemic circulation.

1. Pulmonary Circulation:
   Heart to lungs and back.
2. Systemic Circulation:
   Heart to body and back.
3. Final Result:
   Double circulation has two separate pathways

Q2. What Is Pulmonary Circulation?

Pulmonary circulation carries deoxygenated blood from the right ventricle to lungs and returns oxygenated blood to the left atrium.

1. Start:
   Right ventricle.
2. Path:
   Pulmonary artery, lungs, pulmonary veins.
3. End:
   Left atrium.
4. Final Result:
   Pulmonary circulation oxygenates blood

Q3. What Is Systemic Circulation?

Systemic circulation carries oxygenated blood from the left ventricle to body tissues and returns deoxygenated blood to the right atrium.

1. Start:
   Left ventricle.
2. Path:
   Aorta, arteries, capillaries, veins, vena cava.
3. End:
   Right atrium.
4. Final Result:
   Systemic circulation supplies tissues

Q4. What Is The Significance Of Double Circulation?

Double circulation prevents mixing of oxygenated and deoxygenated blood. It improves oxygen supply to tissues.

1. Separation:
   Right and left sides handle different blood types.
2. Efficiency:
   Tissues receive oxygen-rich blood.
3. Final Result:
   Double circulation supports efficient oxygen transport

Q5. What Is Hepatic Portal System?

Hepatic portal system is a vascular connection between digestive tract and liver. Hepatic portal vein carries blood from intestine to liver.

1. Source:
   Intestine.
2. Destination:
   Liver.
3. Final Result:
   Hepatic portal system carries absorbed substances to liver

Disorders Of Circulatory System Class 11 Questions

These disorders of circulatory system class 11 questions cover hypertension, CAD, angina, and heart failure. NCERT expects direct definitions and causes.

Q1. What Is Hypertension?

Hypertension is blood pressure higher than normal. Repeated readings of 140/90 mm Hg or higher indicate hypertension.

1. Normal BP:
   120/80 mm Hg.
2. Hypertension Level:
   140/90 mm Hg or higher.
3. Final Result:
   Hypertension can affect heart, brain, and kidney

Q2. What Is Coronary Artery Disease?

Coronary artery disease affects vessels that supply blood to heart muscle. It often occurs due to atherosclerosis.

1. Cause:
   Deposits of calcium, fat, cholesterol, and fibrous tissues.
2. Effect:
   Arterial lumen becomes narrower.
3. Final Result:
   CAD reduces blood supply to heart muscle

Q3. What Is Angina?

Angina is acute chest pain due to insufficient oxygen reaching the heart muscle. It is also called angina pectoris.

1. Cause:
   Reduced oxygen supply to heart muscle.
2. Common Group:
   Middle-aged and elderly people.
3. Final Result:
   Angina occurs due to affected blood flow

Q4. What Is Heart Failure?

Heart failure is a condition where the heart cannot pump blood effectively enough for body needs.

1. Main Feature:
   Ineffective pumping.
2. Common Symptom:
   Lung congestion may occur.
3. Final Result:
   Heart failure differs from cardiac arrest and heart attack

Q5. How Is Heart Failure Different From Cardiac Arrest?

Heart failure means weak pumping, while cardiac arrest means the heart stops beating. They are different conditions.

1. Heart Failure:
   Heart pumps ineffectively.
2. Cardiac Arrest:
   Heart stops beating.
3. Final Result:
   Heart failure is not the same as cardiac arrest

Body Fluids And Circulation Class 11 NCERT Questions

These body fluids and circulation class 11 important questions follow NCERT exercise patterns. They are useful for CBSE 2026 school and exam practice.

Q1. Name The Components Of Formed Elements In Blood And Mention One Function Of Each.

The formed elements are RBCs, WBCs, and platelets. Each performs transport, defence, or clotting.

1. RBCs:
   Transport respiratory gases.
2. WBCs:
   Defend the body against foreign organisms.
3. Platelets:
   Help in coagulation of blood.
4. Final Result:
   Formed elements are RBCs, WBCs, and platelets

Q2. What Is The Importance Of Plasma Proteins?

Plasma proteins support clotting, defence, and osmotic balance. The major proteins are fibrinogen, globulins, and albumins.

1. Fibrinogen:
   Helps in clotting.
2. Globulins:
   Support defence.
3. Albumins:
   Maintain osmotic balance.
4. Final Result:
   Plasma proteins maintain vital blood functions

Q3. Why Is Blood Considered A Connective Tissue?

Blood is considered a connective tissue because it has a matrix and transports materials between body tissues.

1. Matrix:
   Plasma.
2. Cells:
   RBCs, WBCs, and platelets.
3. Function:
   Connects organs through transport.
4. Final Result:
   Blood is a fluid connective tissue

Q4. What Is The Difference Between Open And Closed Circulatory Systems?

Open circulation releases blood into spaces, while closed circulation keeps blood inside vessels.

1. Open System:
   Found in arthropods and molluscs.
2. Closed System:
   Found in annelids and chordates.
3. Final Result:
   Closed circulation regulates blood flow more precisely

Q5. What Is The Difference Between Systole And Diastole?

Systole is contraction of heart chambers, while diastole is relaxation of heart chambers.

1. Systole:
   Pumps blood forward.
2. Diastole:
   Allows chambers to fill.
3. Final Result:
   Systole pumps blood, diastole fills chambers

Q6. Describe The Evolutionary Change In Vertebrate Heart Pattern.

Vertebrate hearts evolved from 2 chambers to 4 chambers. This improved separation of oxygenated and deoxygenated blood.

1. Fishes:
   2-chambered heart.
2. Amphibians And Most Reptiles:
   3-chambered heart.
3. Crocodiles, Birds, Mammals:
   4-chambered heart.
4. Final Result:
   Heart complexity increases across vertebrates

Q7. What Is The Significance Of AV Node And AV Bundle?

AV node and AV bundle conduct action potentials from atria to ventricles. They coordinate ventricular contraction.

1. AV Node:
   Receives impulse from atria.
2. AV Bundle:
   Carries impulse to ventricles.
3. Final Result:
   AVN and AV bundle coordinate heartbeat

Q8. Define Cardiac Cycle And Cardiac Output.

Cardiac cycle is one complete heartbeat sequence. Cardiac output is blood pumped by each ventricle per minute.

1. Cardiac Cycle:
   Includes systole and diastole.
2. Cardiac Output:
   Stroke volume × heart rate.
3. Value:
   About 5 litres per minute.
4. Final Result:
   Cardiac output averages 5 litres per minute