Transcript File
Module 2 Exchange and transport 1.2.7 The cardiac cycle Learning Objectives Success Criteria • •Explain the meaning of the terms closed and open circulatory systems (Grade E - D) Explain the meaning of the terms closed and open circulatory systems • Describe the structures and functions of arteries, veins and capillaries • 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 Guide to blood vessels 5 of 33 © Boardworks Ltd 2008 •Compare the structure and functions of arteries, veins and capillaries (Grade C –B) Blood vessels Construct a table comparing arteries, veins and capillaries, relating structure to function. Use page 61 – help Peer assess table Is the table clear and concise Does the table include a diagram? Does it clearly state structure? Is structure linked to function? Self assessment Peer assessment Components of circulatory systems Multi-cellular animals overcome the limitations of diffusion by having a specialized circulatory system. This comprises: a heart a fluid in which substances are transported vessels through which the fluid can flow. The two types of circulatory system are open (e.g. molluscs, arthropods) and closed (e.g. vertebrates, a few invertebrates). 7 of 33 © Boardworks Ltd 2008 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 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 heart capillaries Blood then returns to the heart via a series of progressively larger vessels. Example – Fish, mammals 9 of 33 © Boardworks Ltd 2008 Task 1) 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) •Explain the meaning of the terms closed and open circulatory systems Answers (Grade E - D) 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 10 of 33 © Boardworks Ltd 2008