A-Level Biology Revision Exchange and Transport in Animals Surface Area to Volume Ratio Breathing in Humans Gas Exchange in Insects Single and Double Circulatory Systems Gas Exchange in Bony Fish The Human Circulatory System Gas Exchange in Mammals Arteries and Arterioles Structure and Function of Capillaries Haemoglobin and the Bohr Effect Structure and Function of Veins Fetal Haemoglobin (OCR / Edexcel) Tissue Fluid and Lymph Fluid Transport of Carbon Dioxide (OCR) Haemoglobin and the Oxygen Dissociation Curve Structure of the Human Heart Initiation and Coordination of the Action of the Heart The Cardiac Cycle Pressure Changes during the Cardiac Cycle Interpreting an Electrocardiogram (OCR / Edexcel) Cardiac Output A-Level Biology Videos