1. Plants have developed transport systems to efficiently move water, minerals, and food throughout their bodies since diffusion and osmosis alone are too slow for multicellular organisms. 2. The xylem transports water and minerals from the roots to the leaves, while the phloem transports food from the leaves to all parts. They are arranged together in vascular bundles with the cambium. 3. Transpiration pull is the force that drives the movement of water through the xylem. Water evaporates from the leaves and is replaced via cohesion between water molecules.

1. Plant Transport Reason for transport system Transport system in plants Adaptations of xylem tissues Adaptations of phloem tissues Absorption of root hair cells Water movement processes Transpiration pull Rate of transpiration

2. 1. Reason for transport system Unicellular organisms They can transport materials like oxygen and urea in and out of their bodies by diffusion or osmosis easily. Multicellular organisms Most of the cells inside the organisms are too far from the surface of their bodies and diffusion and osmosis are too slow to be relied on. A transportation system is required for food and oxygen to be brought efficiently from one place to another. Diffusion and osmosis would take place between the transport system and the cells.

3. 2. Transport system in plants Xylem and Phloem tissues Xylems transport water and minerals salts (nitrates) from roots to leaves in a unidirectional motion Phloems transport organic products (sucrose) from the leaves to all parts of the plant in a bidirectional motion Vascular bundles Xylem and Phloem tissues are arranged in vascular bundles. A cambium separates the xylems and phloems. The cambium undergoes division to produce new xylems and phloems.

4. 2. Diagrams of the system Sites of xylem and phloem tissues

5. 3. Functions of Xylem tissues Support Consists of lignin to provide the plant with support Transport of water and nitrates Conducts water and dissolved mineral salts from the roots to all other parts of the plant

6. 3. Formation of Xylem tubes The xylem cells die when they mature. The cross walls and cell contents will break down. A hollow lumen will be left. There is no obstruction to the flow of water. The walls of the cells are thickened with lignin. It causes the walls to be rigid, supporting the plant.

7. 3. Adaptations of Xylem tissues Absence cross walls Maintains a continuous lumen Protoplasm disintegrate Allows water to move efficiently Dead empty tube Maintains a continuous lumen Lignified walls Walls are rigid Xylem will not collapse Supports the plant

8. 4. Adaptations of Phloem tissues Bi-directional sucrose flow Food can be transported to all parts of the plant Cross walls perforated by sieve tubes Single row of thin elongated walls with minute pores Living cells to conduct the food in the tube Companion cell present Consists of protoplasm and mitochondria Assists sieve tubes in transport of food Provides energy required for active transport When dead, sieve elements will die off

9. 5. Root hair cells Plants absorb water and minerals from the soil through the root hairs. Root hair cells absorb water and nitrates from the soil efficiently. They help to hold the plant more firmly to the ground.

10. 5. Adaptations of root hairs Finger-like extensions Increases surface area to volume ratio To absorb water and mineral salts at a faster rate Lower water potential Allow osmosis and diffusion of nitrates to take place Large vacuole To absorb as much water as it can hold Is a living cell Carries out respiration This provides energy for active transport to take place when water potential is lower in the soil

11. 5. Osmosis in the Root cells The soil particles have a higher water potential than the vacuole of the root hair cell. Water and nitrates diffuse from the soil particles to the root hair cell. The root hair cell becomes more dilute than the surrounding cortex cells. Water and nitrates diffuse from the root hair cell to the cortex cells by osmosis. Water diffuses from one cell to another until water eventually enters the xylem tubes Intake of water in the roots, the root hair cells become turgid. A pressure is thus generated. This pressure is called root pressure. This forces water up the xylem tissues.

12. 6. Forces causing water movement Root pressure Produced by the continuous movement of water through the root hair cells Pushes water up the xylem Transpiration pull Produced by the evaporation of water from the leaves Pulls water up the xylem Capillary action Produced by the conduction of water by the xylem through its continuous lumen Pushes water up narrow xylem vessels

13. 7. Transpiration in the stomata In the stem xylem, water is pulled up the stem by transpiration pull. Osmosis continues through the leaf cells and water is eventually drawn in from the xylem vessels in the stem. As the water evaporates, the water potential of cell sap decreases. It draws water from the lower cells by osmosis. Water evaporates from the surfaces of leaf cells into air spaces. Water vapour from the air spaces diffuses through the stoma and into the atmosphere.

14. 7. Transpiration pull of plants Plants absorb a large amount of water, but make use of only a small portion of the water. A large portion of water is lost by evaporation of water through the stomata of the leaves. This process is called transpiration. Transpiration is the loss of water vapour mainly from the stomata of the leaves. As water evaporates from the leaves, more is drawn up through the plant to replace it due to cohesion forces between water molecules in the xylem tissues. A pulling force called the transpiration pull is formed.

15. 7. Importance of Transpiration pull Transpiration pull is the transport of water and mineral salts or nitrate ions from the soil to the leaves. Ensures a constant flow of water to be taken from the soil to the leaves. Enables photosynthesis to occur.

16. 8. Rate of transpiration increase Humidity of air Low Dryness of air High Temperature of air High Speed of wind High Light intensity High

17. 8. Light intensity Presence of light Photosynthesis occurs. Cell sap in guard cells has higher concentration of glucose. Water enters the guard cells by osmosis causing guard cells to become turgid. Stomata opens and transpiration increases. Absence of light No photosynthesis occurs. Plant loses water, guard cells flaccid. Stomata closes and transpiration decreases.