Transportation in Plants Section 4.2

Learning Goal To enhance our knowledge of plant systems by looking at now water and minerals are transported within them

Introduction Plants have a system to transport fluids and nutrients from 1 part of the plant to another Basically – a plant is a tube with its base embedded in the ground, where the base of the tube is the root system, and the leaves are at the top of the tube

Introduction A plant needs 2 kinds of transportation Job One – move sugars Sugars made in the leaves by photosynthesis must be carried to all other living cells in the plant So WATER that carries these dissolved sugars must move up and down the tube Cells in the Phloem do this Job Two – move water up Water and dissolved nutrients must be taken up by the roots and sent to cells, so water moves up the tube Cells in the Xylem do this

How things move in / out Particles move based on concentration gradients – the amount of a substance on one side versus the other This happens because of DIFFUSION Where substances move from a HIGH concentration to a LOW concentration

How things move in / out Similarly, water also moves from a HIGH [ ] to a LOW [ ] This more specific type of diffusion is called OSMOSIS Diffusion and Osmosis occur naturally and allow water, sugars, and nutrients to be transported throughout the plant

Transport in the Xylem The root cells have a higher [ ] of dissolved nutrients than the surrounding soil So water moves INTO the roots by Osmosis, where: Water moves through the root cells or intercellular spaces within the root and enters the Xylem The water is then transported in the Xylem up through the root into the stem Inside the stem, water moves by Osmosis into other tissues

Transport in the Xylem As the xylem tissue carrying water and minerals enters the leaf, the conducting vessels branch into the many veins From the end of each vein, water and minerals can diffuse into the cells of the leaf Unfortunately, more than 90% of the water that reaches the leaf evaporates out through the stomata through a process called transpiration

Transport in the Xylem

Transport in the Xylem But how does water from the ground reach the tops of a 30 foot tree? Well there are 2 processes that let this happen: Root Pressure –positive pressure (pushing mechanism)that pushes water up through the xylem Transitional Pull – negative pressure (pulling mechanism) help move water move up through the xylem https://www.youtube.com/watch?v=uzXrwNyNldk

Transport in the Xylem

Transport in the Xylem Root Pressure Is created under certain conditions, like at night time when there isn’t so much transpiration and the soil is moist As root cells bring minerals into the xylem, the mineral [ ] in the xylem increases This high [ ] of minerals increases the tendency of water to diffuse into the root xylem by OSMOSIS As water flows in, the pressure in the roots builds up in the xylem and push water upwards in the plant However, this root pressure is not enough to force to move water alone – so plants also use Transpiration Pull Water entering the roots create a POSITIVE Pressure that pushes water UP Minerals move from the soil into the xylem against their [ ] gradients by Active Transport The now added minerals in the xylem makes MORE water move up by OSMOSIS This process is added by the adhesion (sticking) of water molecules to the cell walls of the xylem tissue

Transport in the Xylem Transpirational Pull Looks at pulling water up AGAINST Gravity Negative pressure (Pulling) from above is the Strongest force for long-distance heights The COHESION-TENSION MODEL accounts for the majority of water and minerals moving from the roots all the way up in the leaves of the tallest trees Since more than 90% of water that is absorbed from the roots is lost via Transpiration, water from the leaves creates a negative pressure that PULLS water up to replace its loss in evaporation

Transport in the Xylem Transpirational Pull There are 3 Main Factors that make this process work: Transpiration – the evaporation of water molecules from the shoot system, is responsible for the movement of water and dissolved minerals upward in a plant stem. Dry air, heat, and wind cause this to take place, as water exits through the stomata

Transport in the Xylem Transpirational Pull Cohesion – the columns of water in the xylem have a property called cohesion, where the force of attraction between water molecules keeps them together in the xylem

Transport in the Xylem Transpirational Pull Adhesion – causes the water molecules to stick to the xylem walls. Adhesion works with cohesion to keep water from separating and keeps on being pulled up in the plant

Transport in the Xylem

Nutrient Transport in Phloem How does the sugar made in the leaves through photosynthesis get to the other plant cells for food? Phloem, carries sugars from the leaves to other parts of the plant that need the nutrients.   http://www.biology4kids.com/files/plants_xylemphloem.html

Nutrient Transport in Phloem Within the phloem, sugars travel from areas of high sugar concentration and high water pressure, called sources (like a leaf cell) To regions of low sugar concentration and low water pressure, called sinks (like a root cell) (Osmotic concentration refers the concentration of solutes, or sugars in this case; where the concentration of solutes is highest, so is the osmotic concentration). *High [ ] to Low [ ] = Diffusion!*

Nutrient Transport in Phloem This movement of sugar molecules from high [ ] to low [ ] is called Translocation Translocation allows other cells in the plants to receive the nutrition it needs (sugars) to survive

Nutrient Transport in Phloem A perfect example of this movement is seen when you collect sap from a tree! During the spring, lots of new leaves begin to grow, for this to happen they need nutrition (sugar)! Sap contains lots of sugar that is converted into starch, and moves throughout the tree to where its needed Once the new leaves have grown, they make their own sugar via photosynthesis and provide nutrition to other cells in the plant

Review (6) https://www.youtube.com/watch?v=xGCnuXxbZGk Pg. 69 # 3, 5