8 4 Scientists can use models to explain the need for a circulation system in animals. (a) The shapes in the diagram represent two different animals that live in water. The figures represent the height, width and breadth of the animals. Determine why animal A does not need a circulation system but animal B does. (4) A 1 mm 4 mm 16 mm 4 mm 4 mm 4 mm B .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... Turn over 9 (b) During the development of the mammalian heart, there is a hole between the left ventricle and the right ventricle. This hole usually becomes sealed before the mammal is born. If it is not sealed, the mammal will become easily tired due to a lack of energy. Explain why a mammal born with a hole between the two ventricles will have these symptoms. (3) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... (c) In the lungs, oxygen moves from the alveoli into red blood cells. (i) How many times does an oxygen molecule cross a cell surface membrane to move from the centre of an alveolus to the centre of a red blood cell? (1) A 2 B 3 C 4 D 5 (ii) Oxygen enters the red blood cell by (1) A active transport B diffusion C facilitated diffusion D osmosis (Total for Question 4 = 9 marks)