TRANSPORT IN PLANTS

Transport System The vascular tissues found in plants are the xylem and the phloem The function of the xylem is to transport water and mineral salts The function of the phloem is to transport food materials: mainly sugars and amino acids

Where Are The Xylem And Pholem? In the Leaf mid-rib vein phloem xylem

Where Are The Xylem And Pholem? In the Stem Phloem Xylem (note thickened cross walls) Cross-section of stem High magnification of a single vascular bundle

Transport Of Water And Mineral Salts and is lost to the surroundings by the process called transpiration is used in respiration and other cellular activities transported up the stem by xylem vessels Water is absorbed from surrounding soil by root hairs

Transport Of Water And Mineral Salts The Uptake of Water Up xylem vessels to plant Water from soil absorbed into root hair cell across cortex cells across phloem into xylem vessels

Transport Of Water And Mineral Salts The Uptake of Mineral Salts Plants absorb mineral salts in the form of ions dissolved in soil water through the root hairs. This may take place via diffusion. When there is a lower concentration of ions in the soil than the root hairs, ions do not diffuse into the root hairs. It involves the movement of ions against a concentration gradient, and to do this root hairs need energy. This process is called active transport.

Transport Of Water And Mineral Salts Adaptations of the Root Hair Cell The root hair extends from the root cell. It is long and narrow. This provides a larger surface area to volume ratio for water and nutrients to be absorbed. Soil particles Water and mineral salts The root hair cell is living. It carries out respiration to replace energy that is required for active transport. The cell sap in the root hair cell is of lower water potential than the soil solution. This allows water to enter the root hair by osmosis.

Transport Of Water And Mineral Salts Transport in the Xylem There are 3 forces that move the water upwards in the xylem: Root pressure - a force that pushes water up the xylem (produced by the continuous movement of water through the root cells. Capillary action - a force that pushes water up the narrow xylem vessels. Transpirational pull - a force that pulls water up the xylem (produced by evaporation of water from the leaves).

Transpiration Pull In Plants Transpiration is the loss of water in the form of water vapour from the leaves, especially through the stomata, as a consequence of gaseous exchange The importance of transpiration: Transpiration pull which is a main factor in ‘lifting’ and sustaining the flow of water and mineral salts from roots up to the rest of the plant

Factors Affecting The Rate Of Transpiration Transpiration is dependent on the opening of the stomata and the evaporation of water in the intracellular spaces of the leaf This is affected by environmental conditions: Humidity of the air – the more water vapour present in the surrounding air, the lower the rate of evaporation from the plant Temperature – which also affects the rate of evaporation Light – which stimulates the stomata to open Wind speed – which transports water vapour away from the transpiring surface

Factors Affecting The Rate Of Transpiration Wilting cell surface membrane cytoplasm What happens during wilting? Water escapes from the vacuole. Turgor pressure decreases. The cytoplasm shrinks and the cell membrane pulls away from the cell wall. The cell loses its firmness and becomes soft. The plant becomes flaccid and limp. At this stage, cell is plasmolysed.

Translocation The movement of sugars and amino acids via the phloem is called translocation Glucose produced by photosynthesis in leaf is converted to sugars (mainly sucrose) and translocated to different parts of the plant To growing regions to be used as energy for growth If the plant requires more energy than can be produced, food stores are mobilised, converted back to sugars, and transported to wherever it is needed Transport in the phloem occurs in both directions up and down the plant (bidirectional movement) To storage organ (fruit) to be stored mainly as sugars To storage organ (tubers in roots) To be stored mainly as starch