Packet #55 Chapter #36 6/2/2016 1:53:02 AM1

Reasons for Transport Within Plants Absorption of water and minerals by roots Transport of xylem sap Control of transpiration Transport of organic nutrients within phloem 6/2/20162

Review of Important Terms Water Potential Solution Solvent Solute Hypotonic Hypertonic Isotonic Diffusion Osmosis Dialysis Movement of a solute from an area of high concentration to an area of low concentration across a semi-permeable membrane Cohesion Adhesion Osmotic Pressure Plasmolysis Turgidity 6/2/20163

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Introduction Plants take up water through the roots and release “excess” through the stomata. The release of water through the stomata is called transpiration. *About 90% of all water entering the roots leaves the leaves via the stomatas without ever taking part in plant’s metabolic reactions. 6/2/20165

Water Movement Through Xylem I Water movement, through the xylem, is due to the differences in water potential between the soil, root, stem, leaf and atmosphere. The water potential becomes higher (more negative) as water flows from the soil up and out into the atmosphere through the stomata of the leaf. Shoot tension 6/2/20166

Water Movement Through the Xylem II As water enters the root, from the soil, it may travel different routes in order to reach the xylem. Two of those routes are the: - Apoplastic Route Symplastic Route 6/2/20167

Apoplastic Pathway An apoplast consists of interconnected pourous cell walls of a plant, along which water and nutrient mineral ions move freely. Water and minerals diffuse freely without ever entering a living cell. 6/2/2016 1:53:02 AM8

Symplastic Pathway A symplast is a continuum of living cytoplasm, which is connected from one cell to the next by cytoplasmic bridges called plasmodesmata. 6/2/2016 1:53:02 AM9

Transpiration Pull 6/2/2016 1:53:02 AM10

Introduction I There are three ways to describe the movement of solutes, or fluids, from one end of the plant to another. Bulk Flow Hydrostatic Pressure Transpiration Pull 6/2/201611

Bulk Flow Movement of fluid that is driven by pressure Osmotic Pressure** Roots to leaves Overall movement of water in response to differences in the potential energy of water. 6/2/201612

Hydrostatic Pressure The pressure at a point in a fluid at rest due to the weight of the fluid above it. Also known as gravitational pressure. 6/2/201613

Transpiration Pull Tension, or negative pressure, due to the evaporation of water from a leaf Based on cohesion, adhesion and differences in pressure. 6/2/201614

Transpiration Pull II In the leaf, water diffuses from the xylem into the spaces inside the spongy layer, out through the stomata and into the atmosphere.

Transpiration Pull III Tension is generated as water is pulled from between the cells. The tension formed is negative pressure. This pressure “pulls” water from areas of greater hydrostatic pressure into areas of lower hydrostatic pressure. Fluid filled areas such as xylem vessels are areas of higher hydrostatic pressure.

Root Pressure 6/2/2016 1:53:02 AM17

Root Pressure Caused by the movement of water into roots from the soil as a result of the active absorption of nutrient mineral ions from the soil 6/2/2016 1:53:02 AM18

Root Pressure II At night, depending on the species of plant, stomata close and transpiration ceases. Water potential decreases However, root cells still pump nutrients into the xylem Minerals accumulate in the steele As minerals aggregate, the water potential in the roots becomes higher in comparison to that in the leaf. Water is “pushed” up into the stem and into the leaves because of the differences in water potential that has been produced as a result of the minerals accumulating in the steele Root Pressure. 6/2/2016 1:53:02 AM19

Introduction Unlike the movement of xylem sap, phloem sap requires the use of energy.

Movement Within Phloem Sugars are moved through the phloem and to their final location via the use of proton pumps, transport protein (Sucrose-H + co- transporter) and co- transport.

Important Definitions Source Any location in a plant where sugar is either produced or stored. Sink Location in a plant where sugar is used.

Review I Movement of Water Through Xylem Transpiration

Review II Movement of Water into the Xylem from Roots Apoplastic Pathway Cell Walls Symplastic Pathway Plasmdesmata

Review III Reasoning Behind Movement of Water Through Xylem Transpiration PullBulk Flow Hydrostatic Pressure Root PressureOccurs at Night

Review IV Movement of Materials Through Phloem Active TransportUse of energy Movement of Sugar(s) Source Location where sugar is produced or stored Sink Location where sugar is used