Module 2Exchange and transport

1.2.7 The cardiac cycle

Learning Objectives Success Criteria

• Explain the meaning of the terms closed and open circulatory systems

• Describe the structures and functions of arteries, veins and capillaries

•Explain the meaning of the terms closed and open circulatory systems(Grade E - D)

• Compare the structure and functions of arteries, veins and capillaries(Grade C –B)

•Compare open and closed circulatory systems (Grade B – A)

Arteries

• Smooth layer to prevent clotting

• Thick walls as under pressure

• Muscle to rebound back into shape

Veins

• Valves to stop back flow

• Larger lumen

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Guide to blood vessels

Blood vesselsConstruct a table comparing arteries, veins and capillaries, relating structure to function.

Use page 61 – helpPeer assess table

Self assessment Peer assessment

Is the table clear and concise

Does the table include a diagram?

Does it clearly state structure?

Is structure linked to function?

•Compare the structure and functions of arteries, veins and capillaries(Grade C –B)

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Components of circulatory systems

Multi-cellular animals overcome the limitations of diffusion by having a specialized circulatory system. This comprises:

a heart

vessels through which the fluid can flow.

a fluid in which substances are transported

The two types of circulatory system are open (e.g. molluscs, arthropods) and closed (e.g. vertebrates, a few invertebrates).

Open circulatory system• Blood is not held within blood vessels, it circulates

through the body cavity, so tissues and cells are bathed directly.

• Some insects have muscular pumping organ much like a heart, blood enters through pores called ostia from the body, and the heart pumps blood towards the head by peristalsis and then it pours into the body cavity.

• Some active insects, ie locusts, have open ended tubes attached to the heart which direct blood towards active body parts.

• Why does this only work for smaller insects?• Separate systems are used to transport oxygen and

carbon dioxide• Blood doesn’t have to travel so far• Low pressure and slow flow in open circulatory

systems

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Closed circulatory systems

In a closed circulatory system, blood is fully enclosed within blood vessels at all times.

From the heart, blood is pumped through a series of progressively smaller vessels. In the smallest vessels, capillaries, substances diffuse in and out of the blood and into cells. A separate fluid called tissue fluid bathes the tissues and cells

Blood then returns to the heart via a series of progressively larger vessels. Example – Fish, mammals

heart

capillaries

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Task1) Explain why the circulatory system of a fish is described as

a)A single circulatory system

b)A closed circulatory system (2 marks)

2) Explain why the insect circulatory system is described as an open circulatory system.

(2 marks)Answers

1) a) Because blood passes through the heart once for a complete circuit of the body

b) because blood is enclosed inside blood vessels

2) Because blood isn’t enclosed in blood vessels all the time, instead it flows freely through the body cavity /4

•Explain the meaning of the terms closed and open circulatory systems(Grade E - D)