Why is the Blue Whale bigger?

Circulation Date:

Lesson Objectives To compare and contrast single and double circulation To link pressure, diffusion and circulation to explain how double circulation works To explain how double circulation gives mammals an advantage in survival

Exam style question “Whale sharks are the largest fish, reaching a length of 19 metres. The largest animal ever to have lived is the blue whale, at 33 metres in length. Using ideas about circulation account for this difference in size” How would you go about answering the question?

Gas absorption in the blood What does high pressure mean? If blood is at high pressure what is likely to happen to any gases in the blood? What if the blood is at low pressure compared to the air in the lungs?

Single circulation Simple system Must be at low pressure otherwise oxygen will not be absorbed Cannot pump blood quickly Fish can only reach a certain size

Double circulation Separate circulation for system (body) and lungs High pressure blood flow to body Network can be longer Low pressure flow to lungs Oxygen can be easily absorbed Organism can be much larger

Exam style question “Whale sharks are the largest fish, reaching a length of 19 metres. The largest animal ever to have lived is the blue whale, at 33 metres in length. Using ideas about circulation account for this difference in size” How would you go about answering the question? Now try it for yourself!

Marking points Blue whales are mammals with double circulation Blood flows to the lungs at low pressure This means the blood can absorb more oxygen Blood returns to the heart Blood is then pumped to the body at high pressure It can move more quickly The organism can be larger All of its cells can respire effectively, generating enough energy to survive Whale sharks are fish with single circulation This means blood flows from the heart to the gills to the body and back The blood cannot be at a high pressure otherwise it will not be able to absorb oxygen (o.w.t.t.e) This means blood cannot be pumped quickly around the body This limits the size of the fish

Extra credit! SUGGEST what else may contribute to the difference in size between a whale shark and a blue whale…