Presentation on theme: "Transport in Plants Explain the need for transport systems in multicellular plants in terms of size and surface- area-to-volume ratio. Describe the distribution."— Presentation transcript:
1 Transport in PlantsExplain the need for transport systems in multicellular plants in terms of size and surface- area-to-volume ratio.Describe the distribution of xylem and phloem tissues in roots, stems and leaves of dicotyledonous plants.
2 Transport systems and surface area to volume ratio Single celled organisms have large surface area: vol ratio and can obtain all their requirements (oxygen, CO2, water and minerals) by diffusion. The sugar they make is available throughout the cell.Large plants need to transport water and minerals up from the roots. Sugars need to be moved from the leaves where they are made to other areas of the plant. In order to do this they need transport systems
4 Distribution of vascular tissue in plant roots Xylem forms a cross shape in the centre with areas of phloem between the armsThe vascular (transport) tissue is surrounded by a layer of endodermisThe Pericycle is a layer of meristem (dividing) cells inside the endodermis
5 Distribution of vascular bundles in stem In the stem the vascular bundles of Xylem, Cambium and Phloem are arranged around the edge of the stemXylem is always on the inside of the bundle,Cambium is a layer of meristem cells in the middle of the bundlePhloem is always on the outside of the bundle
6 Distribution of vascular tissue in leaves In leaves the vascular tissue is seen as the midrib and veins in the leafThe xylem is always closer to the top surface of the leafThe phloem is below the xylem
7 Describe the structure and function of xylem vessels, sieve tube elements and companion cells.
10 Pure water has a water potential of zero Explain, in terms of water potential, the movement of water between plant cells, and between plant cells and their environment.Pure water has a water potential of zeroAny solute dissolved in water lowers the water potential and makes it more negativeWater always moves from an area of higher water potential to an area of lower water potential
11 Movement of water into plant cells This cell has a water potential of kPaIt is bathed in pure water with a water potential of 0kPaSo water enters the cell down the water potential gradient (from higher to lower) by osmosisEventually the pressure exerted by the water entering the cell equals the pressure exerted by the cell wall on the contents, water stops going into the cellThe cell becomes turgidA pair of adjacent cells, A and B, have water potentials of -1000kPa and 1200kPa respectively. Which cell will gain water from the other
12 Movement of water out of plant cells If a plant cell is put into a solution with a much lower water potential than the cell then water will leave the cell by osmosis.The vacuole shrinks and then the cytoplasm shrinks and becomes smaller in volumeEventually the cell membrane pulls away from the cell wallThe cell becomes plasmolysed.What is in the space between the cell wall and the plasma membrane of the plasmolysed cell?
15 Movement of water through plants A, the Apoplast pathway. Water and dissolved ions move through the cell walls between the cellulose moleculesB, the Symplast pathway. Water goes into the cell through the plasma membrane into the cytoplasm. It moves from cell to cell through the plasmodesmataC, the Vacuolar pathway. Water goes into the cell through the plasma membrane into the cytoplasm and then into the vacuole.
17 Describe, with the aid of diagrams, the pathway by which water is transported from the root cortex to the air surrounding the leaves, with reference to:the Casparian strip,apoplast pathwaysymplast pathway,xylem and stomata.
18 Water movement into the plant Water goes into the root cells and moves across the cortex by osmosis, water can move by any of the pathwaysAt the Casparian strip in the Endodermis water is forced out of the Apoplast pathway and into symplast or vacuolar pathwayWater and ions pass through proteins in the plasma membrane into the cytoplasmNitrate ions are actively pumped from the endodermis cells into the xylemThis lowers the water potential in the xylem so water follows by osmosis
19 Movement up the stem and out of the leaves Pumping ions into the xylem forces water to follow by osmosisWater can rise up stems about 3 metres by this processWater evaporates from leaves through the stomata, water moves through the leaf by osmosis down the water potential gradientWater leaves the xylem creating tension in the xylem, this is why the xylem needs to be strengthened with lignin, to prevent collapse.Cohesion between water molecules means that the whole column of water is pushed upwards from below and pulled upwards from above
20 Loss of water from leaf by Transpiration Osmosis moves water from xylem to palisade and spongey mesophyllWater evaporates from the mesophyll cells into the intercellular spacesWater diffuses from intercellular spaces out through stomata
21 Factors that increase transpiration rates Number of leavesNumber of stomataCuticleLightTemperatureRelative humidityAir movement/ windWater availableMore leaves = larger surface areaMore stomata = more spaces for evaporationMore cuticle= slower evaporationStomata open in sunlightHigher temp = faster evaporation, faster diffusion through stomataLower gradient slows water lossMaintains water potential gradientLittle water in plant closes stomata and reduces water loss