Unit 2

5. Movement of water across a partially permeable membrane
7. Upper chambers of the heart that receive blood
9. Heart chamber that pumps blood out of the heart
10. Blood vessel that carries blood away from the heart
13. Network of vessels connecting arteries and veins
14. Specialised muscle found only in the heart that contracts without fatigue
16. A group of organisms that can interbreed to produce fertile offspring
17. Movement of air into and out of the lungs
19. Protein that carries oxygen in red blood cells

1. Movement of molecules from high to low concentration
2. The variety of life in a particular habitat
3. A system in fish where water flows in the opposite direction to blood
4. A community of organisms and their physical environment
6. The total area available for gas exchange
8. Iron-containing part of haemoglobin that binds oxygen
11. Tube that carries air to and from the lungs
12. Blood vessel with a large lumen and valves
15. Tiny air sacs in the lungs where gas exchange occurs
18. Number of times blood passes through the heart in a double circulatory system
20. Structures in fish gills that increase surface area for gas exchange