A level biology讲义7 Transportmulticellular plants.doc

G1 Transport-multicellular plants Ⅰ Syllabus Contents 1 The need for, and functioning of, a transport system in multicellular plants Multicellular plants need oxygen and carbon dioxide, which travel to and from cells and their environment by diffusion alone. Organic nutrients needed are transported by phloem sieve tube elements. Inorganic ions and water are transported by xylem vessels. Ⅱ Samples of A-LEVEL biology examination for analyzing 1 explain the need for transport systems in multicellular plants and animals in terms of size and surface area to volume ratios; Very small organisms can meet their requirements for the supply of nutrients and oxygen, and the removal of waste products, by means of diffusion. These tiny organisms have a large surface area compared to their total volume, so there is a relativity large area of membrane across which gases ,nutrients and waste products can diffuse in and out of their bodies. Larger, more active, organisms cannot rely on diffusion alone. They need more nutrients, oxygen and the removal of waste products, but they just have small surface area to volume ratios which cannot meet their needs. In the other hand, cells are often deep within their bodies and cannot directly communicate with nutrients and oxygen in environment. As a result, transport systems are evolved to meet their needs. Sample: 1.(9700_w09_qp_11,33) A disease damages alveoli. Which effect does this have on the gas exchange surface area and volume of the lungs? Key: B Interpretion: alveoli are adapted for gaseous exchange for expanding the surface area available for oxygen and carbon dioxide diffusion between air and blood. When a disease damages alveoli, the gas exchange surface area will decrease. But the volume of lung has no change, because it has no relationship with alveoli. It depends on the volume of air breathed in and out. 2 define the term transpiration and explain that it is an inevitable consequence of gas exchange in plants; If there is a wat