Aqa A-Level Biology: Mass Transport Mastery The Ultimate E

AQA A-LEVEL BIOLOGY: MASS TRANSPORT MASTERY - THE ULTIMATE EXAM-FOCUSED REVISION GUIDE AQA A-Level Biology - Mass Transport, Mass Transport A level Biology Single Circulatory System A system where blood is not confined to blood vessels and only passes through the heart once, smaller animals have this system Mass Transport System This system exists when organisms have: - A large surface area to volume ratio (simple diffusion cannot accommodate for the organisms) - A large activity of the organism (require more substances at one time than smaller organisms) Arteries Vessels that carry blood away from the heart and to arterioles at a high pressure. Most layers are thick so that they can function correctly and efficiently ArteriolesVessels that control blood flow from arteries to capillaries. Layers are thinner than arteries due to lower blood pressure Capillaries Tiny vessels that link arterioles to veins. These have branched networks to allow for a larger total surface area across the body, as they are so thin but have a vast network, no cell is too far away from one Veins Vessels that carry blood towards the heart from capillaries. Layers are very thin with a large lumen to ensure pressure is very low