How does the body move blood around to deliver what cells need?
Describe the heart, blood vessels and blood, and explain how the circulatory system transports oxygen and food around the body
A clear answer to the N(T) Science point on the circulatory system. The heart as a pump, the three blood vessels, what blood carries, and how oxygen and food are transported around the body.
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What this dot point is asking
This dot point wants you to describe the parts of the circulatory system - the heart, the blood vessels and the blood - and explain how this system carries oxygen and food to every cell in the body. The big idea is that the body's cells need a constant supply of oxygen and food and need their waste removed, so blood is pumped by the heart through a network of tubes to deliver these things everywhere. It is the body's delivery and collection service.
The answer
Why we need a circulatory system
Every cell in the body needs oxygen (to release energy) and food (nutrients), and every cell makes waste such as carbon dioxide that must be taken away. The circulatory system carries all of these around the body. It is made of three main parts: the heart, the blood vessels, and the blood itself.
The heart: the pump
The heart is a muscular organ that works as a pump. It squeezes (beats) over and over, pushing blood out and around the body, then receiving it back again. Because it never stops, it keeps blood flowing to every part of the body day and night. You can feel each beat as your pulse.
The blood vessels: the tubes
Blood travels through tubes called blood vessels. There are three kinds:
- Arteries: carry blood away from the heart. They have thick, strong walls to cope with the high pressure of blood leaving the heart.
- Veins: carry blood back to the heart. They have thinner walls and the blood in them is at lower pressure.
- Capillaries: tiny vessels with very thin walls that join the arteries to the veins. Their thin walls let oxygen and food pass out to the cells, and let waste pass in. This is where the actual exchange happens.
The blood: the carrier
Blood is the liquid that does the carrying. It transports:
- Oxygen from the lungs to the cells.
- Digested food (nutrients) from the gut to the cells.
- Carbon dioxide (waste) from the cells back to the lungs to be breathed out.
- Heat around the body, helping to keep it warm.
Blood also helps fight germs and helps wounds clot, but its main job here is transport.
How it all works together
The heart pumps blood through the arteries to all parts of the body. In the tissues, the blood flows through the tiny capillaries, where oxygen and food pass through the thin walls into the cells, and carbon dioxide passes from the cells into the blood. The blood, now carrying waste, returns through the veins to the heart, which pumps it to the lungs to get rid of the carbon dioxide and pick up fresh oxygen. Then the whole cycle repeats.
Examples in context
Example 1. Feeling your pulse after exercise. When you run, your muscles need more oxygen and food, so your heart beats faster to pump blood around more quickly. You can feel this as a fast pulse in your wrist or neck. The racing heart is the circulatory system delivering extra oxygen to the working muscles.
Example 2. Why a cut bleeds. When you cut your skin, you often nick a tiny capillary or vein, and blood leaks out. This shows that blood vessels run everywhere, even just under the skin, so that every part of the body can be supplied with oxygen and food. The blood then clots to seal the cut.
Try this
Cue. State the job of the heart in the circulatory system. The heart is a muscular pump that pushes blood around the body, keeping it flowing all the time.
Cue. Name the three types of blood vessel and state what each does. Arteries carry blood away from the heart, veins carry blood back to the heart, and capillaries are tiny thin-walled vessels where exchange with the cells happens.
Cue. Explain why capillaries have very thin walls. Thin walls let oxygen and food pass out to the cells easily and quickly, and let carbon dioxide pass in, because the distance is very short.
Exam-style practice questions
Practice questions written in the style of SEAB exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Original4 marksThe heart pumps blood around the body. (a) State the job of the heart. (b) Name the blood vessels that carry blood away from the heart. (c) Name the blood vessels that carry blood back to the heart. (d) State two things that blood transports around the body.Show worked answer →
(a) The job of the heart is to pump blood around the body (it acts as a muscular pump).
(b) Arteries carry blood away from the heart.
(c) Veins carry blood back to the heart.
(d) Any two things blood transports, for example: oxygen, digested food (nutrients), carbon dioxide (waste), and heat.
What markers reward: the heart as a pump, arteries away from the heart, veins back to the heart, and two correct things blood carries (oxygen, food, carbon dioxide, etc.).
Original3 marksCapillaries are very tiny blood vessels with very thin walls. (a) State where in the body oxygen and food pass from the blood into the cells. (b) Explain why thin walls are useful for this. (c) Name the gas that passes from the cells back into the blood as waste.Show worked answer →
(a) Oxygen and food pass from the blood into the cells at the capillaries.
(b) Thin walls are useful because oxygen and food can pass through them easily and quickly into the surrounding cells (the short distance makes the exchange fast).
(c) The waste gas that passes from the cells into the blood is carbon dioxide.
What markers reward: capillaries as the place of exchange, thin walls allowing easy and quick passing of oxygen and food into cells, and carbon dioxide as the waste gas collected.
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