Question Give two reasons why multicellular organsisms need

Question! • Give two reasons why multicellular organsisms need transport systems. • • Multicellular organisms are large Have a low sa/vol ratio Have a high metabolic rate Very active – constant, rapid supply of oxygen/glucose

Blood vessel homework

Settler Past paper question

Starter • Compile a table to compare the gas exchange systems of a human, an insects and a bony fish • What structures of the gas exchange systems allow the features below? human Large surface area Short diffusion path Steep concentration gradient fish insect

Module 3 Exchange and transport 8. 1 Transport in multicellular animals

Learning Objectives Success Criteria • Explain the need for • Describe why multicellular transport systems in organisms need transport systems (Grade E - D) multicellular animals in terms of size, activity and • Compare the different circulatory surface-area-to-volume systems ratio. (Grade C –B) • Explain the different types of circulatory systems found • Explain the advantages and disadvantages of different in multicellular organisms systems (Grade B – A) FISH DISSECTION?

Question 6 JAN 10

Starter Activity • In pairs, one person describes picture given, one person draws • Think, pair, share • What do you notice about each system? • Why are they different?

Closed circulatory systems

Why need a transport system? Single-celled organisms, such as bacteria and amoeba (below), can obtain nutrients and excrete waste simply by diffusion. nutrients waste products Multi-cellular organisms, such as insects, fish and mammals, require a more specialized transport system. Why is this? 11 of 33 © Boardworks Ltd 2008

Surface area to volume ratio In larger organisms, diffusion of substances would occur far too slowly to enable them to survive: the rate of diffusion increases with the square of the distance it has to travel. This is not just because of its size, however: more important is an organism’s surface area to volume ratio. Single-celled organisms have a very large surface area to volume ratio, because the diffusion path is so short. Describe 3 factors that would affect the need for transport systems. Discuss. • List the features of a good transport system 12 of 33 (Grade E ©-Boardworks D) Ltd 2008

Transport systems There are 3 factors that affect the need for a transport system 1)Size – If an animal has several layers of cells, any oxygen and nutrients will not reach the deeper cells within the body 2) Surface-area-to-volume-ratio – larger animals have a small surface-are-volume-ratio, this is because they are have a large volume so because they have a range of tissues, but their surface area will remain relatively small. Their surface area is not large enough to supply all the oxygen and nutrients needed by internal cells. 3)Level of activity – I f an animal is active it will require a good supply of oxygen and nutrients to supply the enegy for movement. Mammals also require more energy to keep • Explain why large, active animals need a themselves warm. transport system (Grade C –B)

Components of circulatory systems Multi-cellular animals overcome the limitations of diffusion by having a specialized circulatory system. This comprises: l a heart – pumping mechanism to move fluid around the system l a fluid in which substances are transported l vessels through which the fluid can flow. (mass flow) l An exchange surface is also needed (capillaries) The two types of circulatory system are open (e. g. mainly invertebrates inc most insects and some molluscs) and closed (e. g. vertebrates, a few invertebrates). 14 of 33 © Boardworks Ltd 2008

Open Circulatory system • Blood is not held within blood vessels, it circulates through the open body cavity (haemocoel) under low pressure, so tissues and cells are bathed directly. In insects gas exchange takes place in the tracheal system. Their blood is called haemolymph, it doesn’t carry oxygen or carbon dioxide but transports food and nitrogeneous waste products and cells involved in defence against disease. The body cavity is split by a membrane and the heart extends along the length of the thorax and abdomen. Haemolymph flow can’t be varied to meet the demands of the insect.

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 heart progressively smaller vessels. In the smallest vessels, capillaries, substances capillaries diffuse in and out of the blood and into cells. A separate fluid called tissue fluid bathes the tissues and cells. Blood flowing to a particular then returns to the heart via a tissue can be adjusted by series of progressively larger widening or narrowing of the blood vessels. Examples – vertebrates, echinoderms, cephalopod molluscs, annelid worms 16 of 33 © Boardworks Ltd 2008

Closed circulatory systems Fish have a relatively efficient single circulatory system, so they can be active, as they have a counter current gaseous exchange system in their gills, body weight is supported by the water and they don’t maintain their body temperature

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 (Grade E - D) 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 Task – Complete worksheets – Pg 99 -101 18 of 33 © Boardworks Ltd 2008

Single circulatory Systems • Eg fish • Blood pressure drops as blood passes through the gill capillaries – so low pressure = low flow rate • Exchange rate is therefore slow. • Fish, as poikilotherms, do not need as much energy – their circulatory system delivers sufficient oxygen for their needs.

Double circulation system • Blood pressure not to high – not damage capillaries in lungs • Heart increases pressure of blood after lungs – higher flow rate to body • Mammals are homeotherms – increased energy demand.

Advantages of Double over Single • Double circulatory system – blood travels through the heart twice for each complete circuit of the body • Efficient so deliver nutrients quickly • Can increase pressure of blood flow • Quicker supply oxygen • Can keep pressure to exchange surface low to avoid damage

Plenary: True or False 1. Mammals are more active that fish due to need to maintain body temperature 2. Surface area to volume ratio affects need for a transport system 3. Single circulatory system means a single chambered heart 4. Systemic circulation means the route of blood through the lungs 5. Surface area to volume ratio is affected by an animals shape

Plenary: True or False 1. Mammals are more active that fish due to need to maintain body temperature 2. Surface area to volume ratio effects need for a transport system 3. Single circulatory system means a single chambered heart 4. Systemic circulation means the route of blood through the lungs 5. Surface area to volume ratio is effected by an animals’ shape • Any answers you wrote false for now please write what the true statement would be

Plenary: Answers 1. Mammals are more active that fish due to need to maintain body temperature • True 2. Surface area to volume ratio effects need for a transport system • True 3. Single circulatory system means a single chambered heart] • False: Single circulatory system means blood does one circuit 4. Systemic circulation means the route of blood through the lungs • False: Systemic circulatory system means the route of blood through the body 5. Surface area to volume ratio is effected by an animals’ shape • True