WJEC Biology for AS: Study and Rev Guide

Unit 2 Summary Classification and biodiversity ◾ ◾ Classification is hierarchical and organises similar organisms into domains, kingdoms, phyla, classes, orders, families, genera and species ◾ ◾ Relatedness of organisms can be investigated using physical features, DNA and amino acid sequences and immunology ◾ ◾ Biodiversity can vary over time and spatially ◾ ◾ Adaptation to different environments by natural selection Adaptations for gas exchange ◾ ◾ Problems associated with increase in size – an organism’s requirements increases by the X 3 , availability via the X 2 therefore larger organisms need a specialised gas exchange surface e.g. gills or lungs, a ventilation mechanism, and a transport system. Unicellular organisms use simple diffusion ◾ ◾ Gas exchange in fish via gills, using parallel flow of water and blood in sharks and counter-current flow in bony fish. Gills are ventilated by movements of operculum ◾ ◾ Humans exchange gases via alveoli in lungs. Lungs are ventilated by negative pressure breathing ◾ ◾ Insects have a tracheal system of chitin lined tubes that end in tracheoles that come into direct contact with the tissues. Spiracles can close to reduce water loss ◾ ◾ Plants exchange gases via stomata which close at night or during times of water shortage Adaptations for transport in animals ◾ ◾ Circulatory systems are either open or closed and use a pump. In animals, the main vessels are arteries, arterioles, capillaries, venules and veins ◾ ◾ Heart is myogenic and is controlled by specialised regions of cardiac fibres. The cardiac cycle involves atrial systole, ventricular systole and total diastole ◾ ◾ Blood consists of plasma, red blood cells containing haemoglobin (transport of oxygen), and white blood cells (body defence). Oxygen is transported as oxyhaemoglobin. Carbon dioxide is transported largely as hydrogen carbonate ions ◾ ◾ Formation and role of tissue fluid in supplying nutrients to cells and removing waste 116 AS Biology: Study and Revision Guide