Aqa A Level Biology - Paper 3 (Synoptic) Study Guide Graded A+

Evidence for cohesion tension theory {Ans: Tension has been measured in xylem as plants transpire. If a column of water in xylem is broken air bubbles can form and stop any further upward movement of water. Respiratory inhibitors , cyanide or lack of oxygen, do not inhibit this process. Diameter of trees decrease during transpiration as tension pulls xylem walls in and can be measured by a dendrometer}Polymer {Ans: A molecule ( carbohydrate, nucleotide or protein) made up of many monomers ( small repeating units) joined together by condensation reactions and broken down my hydrolysis}Gas exchange in a single called organism {Ans: No special gas exchange surface as they rely on simple diffusion of gases across their outer surface membrane. They have a large surface area to volume ratio, a very thin cell membrane so a short diffusion pathway to ensure fast rates of diffusion maintained by respiration.}Define the concept of herd immunity {Ans: Vaccines protect individuals as the pathogen will be killed quickly so reduce the occurrence of the disease, therefore reducing the risk of non vaccinated people developing the disease as they have a low chance of becoming in contact with another unvaccinated person.}Name