Biology Slide 1 of 30 Copyright Pearson Prentice Hall 23-5 Transport in Plants Slide 2 of 30 Copyright Pearson Prentice Hall 23-5 Transport in Plants Water Transport Water Transport Xylem tissue forms a continuous set of tubes that runs from the roots through stems and out into the spongy mesophyll of leaves. Active transport and root pressure cause water to move from soil into plant roots. Capillary action and transpiration also are needed to transport water and minerals. Slide 3 of 30 Copyright Pearson Prentice Hall 23-5 Transport in Plants Water Transport How is water transported throughout a plant? Slide 4 of 30 Copyright Pearson Prentice Hall 23-5 Transport in Plants Water Transport The combination of root pressure, capillary action, and transpiration provides enough force to move water through the xylem tissue of even the tallest plant. Slide 5 of 30 Copyright Pearson Prentice Hall 23-5 Transport in Plants Water Transport Cohesion is the attraction of molecules of the same substance to each other. Adhesion is the attraction between unlike molecules. Slide 6 of 30 Copyright Pearson Prentice Hall 23-5 Transport in Plants Water Transport The tendency of water to rise in a thin tube is called capillary action. Water is attracted to the walls of the tube, and water molecules are attracted to one another. Slide 7 of 30 Copyright Pearson Prentice Hall 23-5 Transport in Plants Water Transport Capillary action causes water to move much higher in a narrow tube than in a wide tube. Slide 8 of 30 Copyright Pearson Prentice Hall 23-5 Transport in Plants Water Transport Tracheids and vessel elements form hollow connected tubes in a plant. Capillary action in these structures causes water to rise well above the level of the ground. Slide 9 of 30 Copyright Pearson Prentice Hall 23-5 Transport in Plants Water Transport Transpiration In tall plants, the major force in water transport comes from the evaporation of water from leaves during transpiration. Slide 10 of 30 Copyright Pearson Prentice Hall 23-5 Transport in Plants Water Transport When water is lost through transpiration, osmotic pressure moves water out of the vascular tissue of the leaf. Slide 11 of 30 Copyright Pearson Prentice Hall 23-5 Transport in Plants Water Transport The movement of water out of the leaf “pulls” water upward through the vascular system all the way from the roots. This process is known as transpirational pull. Slide 12 of 30 Copyright Pearson Prentice Hall 23-5 Transport in Plants Water Transport Controlling Transpiration The water content of the leaf is kept relatively constant. When there is a lot of water, water pressure in the guard cells is increased and the stomata open. Excess water is then lost through the open stomata by transpiration. Slide 13 of 30 Copyright Pearson Prentice Hall 23-5 Transport in Plants Water Transport When water is scarce, the opposite occurs. Water pressure in the leaf decreases. The guard cells respond by closing the stomata. This reduces further water loss by limiting transpiration. When too much water is lost, wilting occurs. When a leaf wilts, its stomata close and transpiration slows down. This helps a plant conserve water. Slide 14 of 30 Copyright Pearson Prentice Hall 23-5 Transport in Plants Nutrient Transport How are the products of photosynthesis transported throughout a plant? Slide 15 of 30 Copyright Pearson Prentice Hall 23-5 Transport in Plants Nutrient Transport Nutrient Transport Many plants pump sugars into their fruits. In cold climates, plants pump food into their roots for winter storage. This stored food must be moved back into the trunk and branches of the plant before growth begins again in the spring. Slide 16 of 30 Copyright Pearson Prentice Hall 23-5 Transport in Plants Nutrient Transport Movement from Source to Sink A process of phloem transport moves sugars through a plant from a source to a sink. A source is any cell in which sugars are produced by photosynthesis. A sink is any cell where the sugars are used or stored. Slide 17 of 30 Copyright Pearson Prentice Hall 23-5 Transport in Plants Nutrient Transport When nutrients are pumped into or removed from the phloem system, the change in concentration causes a movement of fluid in that same direction. As a result, phloem is able to move nutrients in either direction to meet the nutritional needs of the plant. Slide 18 of 30 Copyright Pearson Prentice Hall 23-5 Transport in Plants Nutrient Transport One idea that explains how phloem transport takes place is called the pressure-flow hypothesis. Slide 19 of 30 Copyright Pearson Prentice Hall 23-5 Transport in Plants Nutrient Transport Phloem Xylem Sugars produced during photosynthesis are pumped into the phloem (source). Sugar molecules Source cell Movement of water Movement of sugar Slide 20 of 30 Copyright Pearson Prentice Hall 23-5 Transport in Plants Nutrient Transport Phloem Xylem As sugar concentrations increase in the phloem, water from the xylem moves in by osmosis. Sugar molecules Source cell Movement of water Movement of sugar Slide 21 of 30 Copyright Pearson Prentice Hall 23-5 Transport in Plants Nutrient Transport Phloem Xylem This movement causes an increase in pressure at that point, forcing nutrient-rich fluid to move through the phloem from nutrient-producing regions …. Sugar molecules Source cell Movement of water Movement of sugar Slide 22 of 30 Copyright Pearson Prentice Hall 23-5 Transport in Plants Nutrient Transport …. toward a region that uses these nutrients (sink). Movement of water Movement of sugar Sink cell Copyright Pearson Prentice Hall Phloem Xylem Slide 23 of 30 23-5 Transport in Plants Nutrient Transport If part of a plant actively absorbs nutrients from the phloem, osmosis causes water to follow. Movement of water Movement of sugar This decreases pressure and causes a movement of fluid in the phloem toward the sink. Sink cell Copyright Pearson Prentice Hall Phloem Xylem Slide 24 of 30 23–5 Click to Launch: Continue to: - or - Slide 25 of 30 Copyright Pearson Prentice Hall 23–5 In a plant stem, water moves from a. leaves to roots through xylem. b. roots to leaves through xylem. c. leaves to roots through phloem. d. roots to leaves through phloem. Slide 26 of 30 Copyright Pearson Prentice Hall 23–5 Which of the following is NOT involved in the movement of water in xylem tissue? a. cohesion b. osmosis c. capillary action d. adhesion Slide 27 of 30 Copyright Pearson Prentice Hall 23–5 When nutrients are pumped into the phloem system of a plant, the increased concentration a. causes fluid to move into the system. b. causes fluid to move out of the system. c. has no effect on the movement of fluid. d. causes fluid to move into the xylem vessels. Slide 28 of 30 Copyright Pearson Prentice Hall 23–5 In a plant, sugar is moved from source cells to sink cells by a process of a. phloem transport. b. xylem transport. c. osmosis. d. diffusion. Slide 29 of 30 Copyright Pearson Prentice Hall 23–5 In very tall trees, which of the following is primarily involved in moving water to the top of the tree? a. transpirational pull b. capillary action c. root pressure d. osmosis Slide 30 of 30 Copyright Pearson Prentice Hall END OF SECTION