ScienceCBSE Class 10 · Life Processes

Transportation in Human Beings: Heart, Blood and Lymph

Updated 14 October 2026 · Fact-checked

In humans, the circulatory system of heart, blood and blood vessels carries oxygen, food, carbon dioxide and wastes. The four-chambered heart keeps oxygen-rich and oxygen-poor blood apart, so blood passes through it twice in each round: double circulation. Arteries carry blood away from the heart, veins bring it back, capillaries exchange materials, and lymph returns tissue fluid.

Understand Transportation in Human Beings

What needs carrying, and by what. Blood is a fluid connective tissue. Its fluid part, plasma, carries food, carbon dioxide and nitrogenous wastes in dissolved form, as well as salts. Red blood corpuscles carry oxygen (using haemoglobin). So the body needs three things: a pump (the heart), a network of tubes (blood vessels) reaching all tissues, and a way to repair leaks (platelets).

The heart. A muscular organ about as big as a fist. It has separate chambers so that oxygen-rich blood does not mix with blood carrying carbon dioxide. Follow the blood:
1. Oxygen-rich blood from the lungs enters the thin-walled left atrium, which relaxes as it fills, then contracts.
2. The left ventricle relaxes to receive it, then contracts strongly and pumps it out to the body.
3. Oxygen-poor blood from the body enters the right atrium, which then contracts.
4. The right ventricle dilates to receive it, then pumps it to the lungs for oxygenation.
Ventricles have thicker muscular walls than atria because they pump blood out to organs. Valves stop blood flowing backwards when the chambers contract.

Double circulation. In each complete round of the body, blood passes through the heart twice: once on the way to the lungs and once on the way to the body. Keeping the right (oxygen-poor) and left (oxygen-rich) sides apart gives a highly efficient oxygen supply. Birds and mammals need this because they use a lot of energy constantly to keep their body temperature steady. Amphibians and many reptiles, whose body temperature follows the surroundings, have three-chambered hearts and tolerate some mixing. Fishes have a two-chambered heart: blood is pumped to the gills, oxygenated there and goes straight to the body, passing through the heart only once per round.

The tubes.

Arteries carry blood away from the heart to organs. Blood leaves under high pressure, so arteries have thick, elastic walls.
Veins collect blood from organs and return it to the heart. The blood is no longer under high pressure, so walls are thinner, and valves keep it flowing one way.
Capillaries are the smallest vessels, with walls one cell thick. Exchange of materials between blood and cells happens across them. Capillaries join to form veins.

Platelets. If a vessel is injured, blood loss must be limited, and a leak would also lower pressure and make pumping less efficient. Platelets circulate in the blood and plug leaks by helping blood to clot at the injury.

Lymph. Some plasma, proteins and blood cells escape through pores in capillary walls into spaces between cells, forming lymph (tissue fluid). It is like plasma but colourless with less protein. It drains into lymphatic capillaries, which join into larger lymph vessels opening into larger veins. Lymph carries digested and absorbed fat from the intestine and returns excess fluid from between cells to the blood.

Transportation in Human Beings: formulas and key facts

Pulmonary path: $right atrium \to right ventricle \to lungs \to left atrium$; Oxygen-poor blood goes to the lungs and returns oxygen-rich.
Systemic path: $left atrium \to left ventricle \to body \to right atrium$; Oxygen-rich blood goes to the body and returns oxygen-poor.
Hearts compared: $fish 2 chambers; amphibians, many reptiles 3; birds, mammals 4$; Only the four-chambered heart fully separates the two kinds of blood.
What blood carries: $plasma: food, C O_{2}, nitrogenous waste, salts; RBC: O_{2}$; Platelets help clotting.

How to solve Transportation in Human Beings questions

Questions on transportation usually ask you to describe a pathway, compare vessels, or explain a design feature. Use this approach.

1For the pathway of blood, start from one point (lungs or body) and go chamber by chamber, saying which chamber relaxes and which contracts.
2For double circulation, state the two circuits and that blood passes through the heart twice per round, then give the reason (no mixing, efficient oxygen supply for high energy needs).
3For comparisons of vessels, use direction, wall thickness, valves and pressure.
4For design features, give the feature and its function: thick ventricle walls (pumping to organs), valves (no backflow), one-cell capillary walls (exchange).
5For the heart diagram, label four chambers, aorta, vena cava, pulmonary artery, pulmonary veins and show the direction of flow with arrows.

Transportation in Human Beings in real life

Each concept, met in an everyday situation. Read the situation, try the problem, then check the solution. The one-line hook is what to remember.

Double circulation and energy needs

Suppose you visit a zoo and see a garden lizard lying still in the sun, a frog by a pond, a sparrow fluttering in a cage and fish swimming in a tank. Your sibling asks why 'a bird needs a better heart than a lizard'.

Compare the hearts and circulation of these animals and explain why birds need a four-chambered heart.

Try it first, then show the solutionSolution

Fish: two-chambered heart; blood is pumped to the gills, oxygenated, and goes straight to the body, passing through the heart once per round (single circulation).
Frog (an amphibian) and lizard (a reptile): amphibians and many reptiles have three-chambered hearts that allow some mixing of oxygenated and deoxygenated blood; their body temperature depends on the surroundings, which is why the lizard basks in the sun.
Sparrow (a bird): four-chambered heart, complete separation and double circulation.
Birds constantly use energy to keep their body temperature steady, so they need a highly efficient oxygen supply; full separation of oxygen-rich and oxygen-poor blood provides this.

Answer: Fish: 2 chambers, single circulation. Frog and lizard (amphibians and many reptiles): 3 chambers, some mixing. Birds: 4 chambers and double circulation, needed for the high energy demand of keeping a steady body temperature.

Memory hook: Warm body, busy heart: four chambers keep the oxygen pure.

Tricks to remember Transportation in Human Beings

Short memory aids. Say each one aloud once, then use it on a question the same day.

Arteries Away
Arteries carry blood Away from the heart; veins bring it back in.
Use it when: Defining arteries and veins.
LORD
Left side Oxygenated, Right side Deoxygenated.
Use it when: Labelling the heart's two sides.
Atria Above
Atria are the upper chambers that receive; ventricles below pump out.
Use it when: Describing the heart's chambers.

Transportation in Human Beings: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Components of the transport system · 3 marks · Short answerBoard level

What are the components of the transport system in human beings? Give the function of each.

Try it first, then show the solutionSolution

Heart: muscular pump that pushes blood around the body (1 mark).
Blood: plasma carries food, $C O_{2}$ and nitrogenous wastes; RBCs carry oxygen; platelets help clotting (1 mark).
Blood vessels: arteries carry blood away from the heart, veins return it, capillaries allow exchange with cells; lymph returns tissue fluid and carries absorbed fat (1 mark).

Answer: Heart (pump), blood (carrier), blood vessels (tubes); lymph as an extra carrier.

Example 2: Double circulation · 5 marks · Long answerHarder board level

Describe double circulation of blood in human beings. Why is it necessary?

Try it first, then show the solutionSolution

Oxygen-poor blood from the body enters the right atrium, passes to the right ventricle and is pumped to the lungs (1 mark).
Oxygen-rich blood from the lungs enters the left atrium, passes to the left ventricle and is pumped to the body (1 mark).
So blood passes through the heart twice in one complete round: this is double circulation (1 mark).
Valves prevent backflow and the thick-walled ventricles pump blood to the organs (1 mark).
It keeps oxygenated and deoxygenated blood separate, giving a highly efficient oxygen supply, which mammals and birds need for their high energy use, including keeping body temperature constant (1 mark).

Answer: Blood goes body → right side → lungs → left side → body, passing through the heart twice; it prevents mixing and supplies oxygen efficiently for high energy needs.

Example 3: Arteries vs veins · 3 marks · Short answerHarder board level

Give three differences between arteries and veins and explain why capillaries have walls one cell thick.

Try it first, then show the solutionSolution

Direction: arteries carry blood away from the heart; veins carry it to the heart (½ mark).
Walls: arteries thick and elastic (blood under high pressure); veins thinner (blood not under high pressure) (1 mark).
Valves: veins have valves for one-way flow; arteries do not need them (½ mark).
Capillaries: one-cell-thick walls allow materials to be exchanged easily between blood and the surrounding cells (1 mark).

Answer: Away vs towards the heart; thick elastic vs thinner walls; no valves vs valves. Thin capillary walls allow exchange.

Example 4: Lymph · 3 marks · Short answerHarder board level

(a) How is lymph formed? (b) Give two differences between lymph and blood plasma. (c) State two functions of lymph.

Try it first, then show the solutionSolution

(a) Some plasma, proteins and blood cells escape through pores in capillary walls into the spaces between cells, forming tissue fluid or lymph (1 mark).
(b) Lymph is colourless and contains less protein than plasma (1 mark).
(c) It carries digested and absorbed fat from the intestine, and drains excess fluid from the spaces between cells back into the blood (1 mark).

Answer: (a) Leakage through capillary pores. (b) Colourless; less protein. (c) Carries absorbed fat; returns excess tissue fluid to blood.

Example 5: Predicting a heart defect · 3 marks · Short answerHOTS / competency

Suppose a child is born with a small opening in the wall between the left and right ventricles. Using what you know about the purpose of a four-chambered heart, predict how this would affect (a) the blood pumped to the body and (b) the child's ability to do physical activity. Give reasons.

Try it first, then show the solutionSolution

(a) Oxygen-rich and oxygen-poor blood would mix in the ventricles, so the blood pumped to the body would carry less oxygen than normal (1½ marks).
(b) Cells would get less oxygen for aerobic respiration, so less energy is released; the child would tire easily during activity (1½ marks).

Answer: (a) Mixed blood with less oxygen goes to the body. (b) Less oxygen means less energy from respiration, so lower stamina.

Where students lose marks in Transportation in Human Beings

The slips examiners see most often, and what to write instead.

Mistake: Mixing up the sides of the heart
In diagrams, the heart is drawn as seen from the front, so left and right look swapped.
Wrong working
Oxygen-rich blood enters the right atrium.
Right working
Oxygen-rich blood from the lungs enters the left atrium.
Do this: Remember LORD: left oxygenated, right deoxygenated.
Usually costs: 1-2 marks in pathway questions.
Mistake: Defining arteries as vessels with oxygenated blood
Most arteries do carry oxygen-rich blood.
Wrong working
Arteries carry oxygenated blood; veins carry deoxygenated blood.
Right working
Arteries carry blood away from the heart; veins carry it to the heart (the pulmonary artery carries oxygen-poor blood to the lungs).
Do this: Define by direction, not by oxygen.
Usually costs: 1 mark.
Mistake: Incomplete double circulation answer
Students describe only the path to the body.
Wrong working
Blood goes from the heart to the body and back.
Right working
Blood goes heart → lungs → heart → body → heart; it passes through the heart twice.
Do this: Describe both circuits and the reason.
Usually costs: 2 marks in a 5-mark answer.
Mistake: Confusing lymph with plasma
Both are fluids that carry substances.
Wrong working
Lymph is red and carries oxygen.
Right working
Lymph is colourless, has less protein, carries absorbed fat and returns tissue fluid.
Do this: Learn the two differences and two functions.
Usually costs: 1 mark.

Exam tips

In the heart diagram, show arrows for blood flow and use blue and red shading only if asked.
Use the words relax and contract for each chamber when describing the pathway.
For 'why double circulation?', mention mammals and birds and the energy used for body temperature.
Blood pressure figures are in a 'More to Know' box and are not assessed.
Write 'capillaries are one cell thick' for exchange questions; it is the key phrase.

Practice questions on Transportation in Human Beings

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
Which chamber of the human heart pumps oxygen-rich blood to all parts of the body?
(a) right atrium (b) right ventricle (c) left atrium (d) left ventricle
Hint
Oxygen-rich blood is on the left; pumping out is done by a ventricle.
Answer
(d) left ventricle.
Q2 · 1 mark · Assertion-reasonBoard level
Assertion (A): Ventricles have thicker muscular walls than atria.
Reason (R): Ventricles have to pump blood into various organs.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Hint
Which chambers push blood out of the heart?
Answer
(a).
Q3 · 2 marks · Very short answerHarder board level
What do birds and mammals gain from keeping oxygen-rich blood apart from oxygen-poor blood? Why can amphibians manage with a three-chambered heart?
Hint
Think about energy used to maintain body temperature.
Answer
Mammals and birds have high energy needs, using energy constantly to maintain body temperature; separation gives a highly efficient oxygen supply. Amphibians do not use energy for this (their body temperature depends on the surroundings), so they tolerate some mixing in a three-chambered heart.
Q4 · 4 marks · Case-basedHOTS / competency
Read the passage and answer.
Suppose a student cuts her finger while slicing vegetables. The bleeding slows and stops within a few minutes. Later, her doctor explains that blood is a fluid connective tissue made of plasma and cells, and that the loss of blood from vessels must be limited.
(a) Which blood component helped stop the bleeding? (1 mark)
(b) Give two reasons why loss of blood from the system has to be minimised. (1 mark)
(c) Plasma and red blood corpuscles have different transport jobs. State them, and predict one effect of a shortage of red blood corpuscles. (2 marks)
Hint
A leak reduces both blood volume and pressure.
Answer
(a) Platelets, which help the blood clot at the injury. (b) Blood carrying food and oxygen is lost, and a leak lowers pressure, reducing the efficiency of the pumping system. (c) Plasma carries food, $C O_{2}$ , nitrogenous wastes and salts in dissolved form; RBCs carry oxygen. With fewer RBCs, less oxygen reaches cells, so less energy is released and the person feels tired.
Q5 · 3 marks · Short answerHOTS / competency
Trace the path of a red blood corpuscle that starts in a capillary of the leg muscle and reaches a capillary in the brain, naming every chamber of the heart and the organ where it picks up oxygen. How many times does it pass through the heart?
Hint
Leg → veins → right side → lungs → left side → arteries → brain.
Answer
Leg capillary → veins → right atrium → right ventricle → lungs (picks up oxygen in alveolar capillaries) → left atrium → left ventricle → arteries → brain capillary. It passes through the heart twice.
Q6 · 3 marks · Short answerHarder board level
Explain the role of valves in the heart and in veins. What would happen if the valves between the left atrium and left ventricle did not close properly?
Hint
Valves stop backflow.
Answer
Valves make sure blood does not flow backwards when the atria or ventricles contract, and in veins they keep blood flowing towards the heart since it is no longer under high pressure. If the valve did not close, some blood would flow back into the left atrium when the left ventricle contracts, so less oxygen-rich blood would be pumped to the body and the heart would work less efficiently.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Which blood component carries oxygen?Show answer
Red blood corpuscles (haemoglobin).
2.Why do veins have valves?Show answer
Blood in veins is not under high pressure; valves keep it flowing one way.
3.How many chambers in a fish heart?Show answer
Two.
4.Function of platelets?Show answer
Help blood clot to plug leaks at injuries.
5.What does lymph carry from the intestine?Show answer
Digested and absorbed fat.
6.Which chamber receives blood from the body?Show answer
Right atrium.

Transportation in Human Beings: frequently asked questions

What is double circulation?

Blood passes through the heart twice in each complete round of the body: once to be sent to the lungs and once to be sent to the rest of the body.

Why does the left ventricle have the thickest wall?

Ventricles pump blood into organs, so they have thicker muscular walls than atria; the left ventricle pumps blood to the whole body.

What is the difference between arteries, veins and capillaries?

Arteries carry blood away from the heart and have thick elastic walls; veins bring blood back and have valves; capillaries are one-cell-thick vessels where exchange happens.

What is lymph?

A colourless fluid formed from plasma that leaks out of capillaries into spaces between cells. It has less protein than plasma, carries absorbed fat and returns excess fluid to the blood.

Is blood pressure in the board syllabus?

It appears in a 'More to Know' box in NCERT, and CBSE does not assess box content in the year-end exam.