Ch. 35 Plant Structure, Growth, and Development & Ch Ch. 35 Plant Structure, Growth, and Development & Ch. 36 Resource Acquisition and Transport in Vascular Plants Objectives: LO 4.17 The student is able to analyze data to identify how molecular interactions affect structure and function. LO 4.18 The student is able to use representations and models to analyze how cooperative interactions within organisms promote efficiency in the use of energy and matter.

Plant Structure Roots – anchors plants, absorbs minerals/water, and stores carbohydrates Stems – raises/separates leaves Leaves – main photosynthetic organ

Plant Structure Leaf anatomy: Stomata: pores for gas exchange Guard cells: flank stomata to open/close it Mesophyll: photosynthesizing area Epidermis: protective layer

Nonvascular vs Vascular Plants Nonvascular plants have no way to transport food or water (Ex: mosses, algae) Vascular plants have a transportation system xylem (moves water and dissolved minerals upward from roots into the shoots) phloem (transports organic nutrients from where they are made to where they are needed) http://thomson.fosterscience.com/Biology/Unit-ProtistsFungiPlants/XylemPhloem.jpg

36.2 Different Mechanisms for Transport over short/long distances Transport in vascular plants occurs on three scales: Transport of water and solutes by individual cells, such as root hairs Short-distance transport of substances from cell to cell at the levels of tissues and organs Long-distance transport within xylem and phloem at the level of the whole plant

Transport at Cellular Level Relies on selective permeability of membranes Transport proteins Facilitated diffusion Selective channels (K+ channels) Aquaporins—water-specific protein channels that facilitate water diffusion across plasma membrane

Transport at Cellular Level Proton pumps create a hydrogen ion gradient that is a form of potential energy contribute to a voltage known as a membrane potential

Transport at Cellular Level Plant cells use energy stored in the proton gradient and membrane potential to drive the transport of many different solutes

Transport at Cellular Level In the mechanism called cotransport, a transport protein couples the passage of one solute to the passage of another

Water Potential - Review (Ψ) Direction water will move due to differing factors. (Ψ = Ψs + Ψp) Movement from high Ψ → low Ψ Measured in megapascal (Mpa) Ψs = solute potential. Adding solutes decreases potential; always negative. Ψp = pressure potential. Can be positive or negative Solutes have a negative effect on  by binding water molecules. Pure water at equilibrium H2O Adding solutes to the right arm makes  lower there, resulting in net movement of water to the right arm: Pure water Membrane Solutes Positive pressure has a positive effect on  by pushing water. Positive pressure Applying positive pressure to the right arm makes  higher there, resulting in net movement of water to the left arm: Solutes and positive pressure have opposing effects on water movement. In this example, the effect of adding solutes is offset by positive pressure, resulting in no net movement of water: Negative pressure (tension) has a negative effect on  by pulling water. Negative pressure Applying negative pressure to the right arm makes  lower there, resulting in net movement of water to the right arm:

Differences in Water Potential Drive Water Transport in Plant Cells  = P + S

36.3 Transpiration Root tips absorb water and minerals via diffusion and active transport. These diffuse into the xylem. This creates pressure potential in the roots, but this is not greater than gravity. The rest gets pulled up due to transpiration; loss of water vapor from leaves.

Transportation of Xylem Sap (Water): Transpiration-Cohesion Theory Water evaporates from leaves through stomata—creates a low pressure at top of water column Water replaced by water from xylem—water in areas of high pressure move to areas of low pressure Strong cohesion of water with the pressure difference helps to pull the entire water column up from roots to rest of plant

Transpiration Water evaporates from leaves through stomata, leaving a pocket of air in cells. Due to cohesive and adhesive properties, nearby water molecules in xylem move in and take up the air space. Entire xylem column of water moves up due to hydrogen bonding of water molecules.

Animation: Transport in Roots Right-click slide / select “Play” © 2011 Pearson Education, Inc.

Animation: Water Transport Right-click slide / select “Play” © 2011 Pearson Education, Inc.

Animation: Transpiration Right-click slide / select “Play” © 2011 Pearson Education, Inc.

36.4 The Rate of Transpiration is Regulated by Stomata Stomata allow the transport of CO2 in and O2 out for photosynthesis. However, water is also lost due to transpiration Stomata are flanked with guard cells which can open/close the pore.

Guard cells turgid/ Stoma open Guard cells flaccid/ Stoma closed Radially oriented cellulose microfibrils Guard cells turgid/ Stoma open Guard cells flaccid/ Stoma closed Cell wall Vacuole Guard cell (a) Changes in guard cell shape and stomatal opening and closing (surface view) (b) Role of potassium in stomatal opening and closing K H2O During the day, K+ moves into guard cells causing water to move in by osmosis. This builds turgor and opens the stomata. At night, K+ moves out causing water to move out. This makes the cells flaccid and opens stomata.

Stimuli for Stomatal Opening and Closing Generally, stomata open during the day and close at night to minimize water loss Stomatal opening at dawn is triggered by Light CO2 depletion An internal “clock” in guard cells All eukaryotic organisms have internal clocks; circadian rhythms are 24-hour cycles Drought, high temperature, and wind can cause stomata to close during the daytime The hormone abscisic acid is produced in response to water deficiency and causes the closure of stomata

Adaptations That Reduce Evaporative Water Loss

36.5 Sugars Are Transported From Sources to Sinks Via Phloem (Translocation) Phloem sap is an aqueous solution that is high in sucrose A sugar source is an organ that is a net producer of sugar, such as mature leaves A sugar sink is an organ that is a net consumer or storer of sugar, such as a tuber or bulb

Sugars are actively pumped via an H+ co-transporter into a sieve-tube

Difference in pressure causes sugars to move from source to sink Sugars are made in photosynthetic cells and pumped by active transport into sieve tubes. Concentration of dissolved substances increases in the sieve tube and water flows in by osmosis Pressure builds up at the source end of the sieve tube Sink Sugars are pumped out Water leaves the sieve tube by osmosis Pressure drops at the sink end of the sieve tube Difference in pressure causes sugars to move from source to sink Loading of sugar Uptake of water Unloading of sugar Water recycled Source cell (leaf) Vessel (xylem) Sieve tube (phloem) Sucrose H2O Sink cell (storage root) Bulk flow by negative pressure Bulk flow by positive pressure 2 1 3 4