Presentation on theme: "LG 3 – Plant Transport Plant Material Transport Material Transport – Passive and Active Transport – Water Movement in Plants – Transport in Roots Water."— Presentation transcript:
LG 3 – Plant Transport Plant Material Transport Material Transport – Passive and Active Transport – Water Movement in Plants – Transport in Roots Water in Roots – Mineral Active Transport – Transport of Water and Minerals in Xylem – Mechanical Properties of Water Transpiration – Cohesion-tension Mechanisms of Water Transport – Cohesion-Tension in Tallest Trees - Leaf Anatomy Stomata – Physiology of Stomata- Arid Adaptations – Transport of Organic Substances in Phloem Organic Compounds – Sources and Sinks -
Unit II Plants Learning Goal 3 Examine how materials are transported throughout the body of a plant.
Plant Material Transport Material transport –Short distances between cells –Long distances between roots and leaves (xylem and phloem)
Fig. 32.2, p. 739 Stepped Art Sugar from photosynthesis Mineral ions a. Short distance transport across cell membranes into roots Minerals Water and solutes from soil enter plant roots by passive or active transport through the plasma membrane of root hairs. Water and mineral ions travel from root hairs into xylem vessels by passing through or between cells (black arrow into/out of xylem). Xylem: transport of H 2 O and O 2 b. Transport in vascular tissues Phloem: transport of sugars Vascular tissue distributes substances throughout the plant, sometimes over great distances. c. Long distance transport throughout the plant Sugar from photosynthesis Cells load and unload organic molecules (including CO2) into and out of phloem (purple arrows to/from phloem).
Passive and Active Transport Passive transport requires no metabolic energy –Substance moves down concentration or electrochemical gradient or by membrane potential Active transport requires metabolic energy (ATP) –Substance moves against gradient
Water Movement in Plants Bulk flow of water due to pressure differences Xylem sap –Dilute water movement from roots to leaves Osmosis –Passive movement of water across cell membrane Water potential (Ψ) –Driving force (pressure and/or solutes)
Transport in Roots Water in Roots Apoplastic pathway: Water does not cross cell membrane, includes dead xylem transport Symplastic pathway: Water moves through plasmodesmata (openings between plant cells). Transmembrane pathway: Water moves between living cells through cell membranes. Casparian strip in root endodermis forces apoplastic water to symplast
Fig. 32.6, p. 743 In the transmembrane pathway (black), water that enters the cytoplasm moves between living cells by diffusing across cell membranes, including the plasma membrane and perhaps the tonoplast. In the apoplastic pathway (red), water moves through nonliving regions–the continuous network of adjoining cell walls and tissue air spaces. However, when it reaches the endodermis, it passes through one layer of living cells. In the symplastic pathway (green), water passes into and through living cells. After being taken up into root hairs water diffuses through the cytoplasm and passes from one living cell to the next through plasmo- desmata. Epidermis Root hair Cell wall Tonoplast Plasmodesma Air space Endodermis with Casparian strips Xylem vessel in stele Root cortex
Casparian Strips in Roots
Fig. 32.7, p. 744 a. Rootb. Stele in cross section (stained) Exodermis Root cortex Stele Abutting walls of endodermal cells Primary xylem Primary phloem In root cortex, water molecules move through the apoplast, around cell walls and through them (arrows). Endodermal cells with Casparian strip Stele Endodermis c. Casparian strip (from above)
Fig. 32.7, p. 744 Sieve tubes in phloem d. Movement of water into the stele Endodermis (one cell thick) Pericycle (one or more cells thick) Stele Tracheids and vessels in xylem Route water takes into the stele Waxy, water-impervious Casparian strip (gold) in abutting walls of endodermal cells that control water and nutrient uptake Radial wall region impregnated with suberin Wall of endodermal cell facing root cortex Transverse wall regions impregnated with suberin
Mineral Active Transport Most minerals for growth are more concentrated in root than in soil –Active transport into symplast –Active transport at Casparian strip across membrane Minerals loaded into apoplast of dead xylem in root stele –Transported long distance to other tissues
Transport of Water and Minerals in the Xylem Mechanical properties of water have key roles in its transport Leaf anatomy contributes to cohesion- tension forces In the tallest trees, the cohesion-tension mechanism may reach its physical limit
Root pressure contributes to upward water movement in some plants Stomata regulate the loss of water by transpiration In dry climates, plants exhibit various adaptations for conserving water
Mechanical Properties of Water Transpiration –Evaporation of water out of plants –Greater than water used in growth and metabolism Cohesion-tension mechanism of water transport –Evaporation from mesophyll walls –Replacment by cohesion (H-bonded) water in xylem –Tension, negative pressure gradient, maintained by narrow xylem walls, wilting is excess tension
Fig. 32.8, p. 746 The driving force of evaporation into dry air Upper epidermisVein Mesophyll Growing cells also remove small amounts of water from xylem. Cohesion in the xylem of roots, stems, and leaves Xylem Vascular cambium Phloem Water uptake in growth regions Water uptake from soil by roots Stoma Stele cylinder EndodermisCortex Water molecule Root hair 1 Transpiration is the evaporation of water molecules from above ground plant parts, especially at stomata. The process puts the water in the xylem sap in a state of tension that extends from roots to leaves. 2 The collective strength of hydrogen bonds among water molecules, which are confined within the tracheids and vessels in xylem, imparts cohesion to the water. 3 As long as water molecules continue to escape by transpiration, that tension will drive the uptake of replacement water molecules from soil water.
Cohesion-Tension in Tallest Trees Transpiration follows atmospheric evaporation –Driving forces: Dryness and radiation –Tallest trees (>110m) near physical limit of cohesion Root pressure occurs in moist to wet soils –Moves water up short distances Guttation –Water movement under pressure out leaves
Leaf Anatomy Stomata Transpiration losses of water must be regulated to prevent rapid dessication –Cuticle limits H 2 O loss but also prevents CO 2 uptake –Water is always lost when stomata open for photosynthesis
Fig , p. 748 Guard cell a. Open stomab. Closed stoma Chloroplast (guard cells are the only epidermal cells that have these organelles) Stoma Guard cell
Physiology of Stomata Stomata must balance H 2 O loss and CO 2 uptake by responding to many signals, biological clock Stomata open to increase photosynthesis –Increasing light (blue) –Decreasing CO 2 concentration in leaf Stomata close under water stress –Abscisic acid is hormonal signal for closure, synthesized by roots and leaves
Arid Adaptations Xenophytes have adaptations to aridity Thickened cuticle, sunken stomata, water storage in stems
Transport of Organic Substances in the Phloem Organic compounds are stored and transported in different forms Organic solutes move by translocation Phloem sap moves from source to sink under pressure
Organic Compounds Translocation –Long-distance transport of substances via phloem –Phloem flow under pressure, moves any direction Macromolecules broken down into constituents for transport across cell membranes Phloem sap composed of water and organic compounds that move through sieve tubes Transport of Organic Substances in the Phloem
Sources and Sinks Source: Any region of plant where organic substance is loaded into phloem –Companion and transfer cells, use free energy Sink: Any region of plant where organic substance is unloaded from phloem Pressure flow mechanism moves substance by bulk flow under pressure from sources to sinks –Based on water potential gradients
Fig , p. 752 Sieve tube of the phloem Source (for example, mature leaf cells) Sink (for example, developing root cells) bulk flow Solute Water 3 The pressure then pushes solutes by bulk flow between a source and a sink, with water moving into and out of the system all along the way. 5 Solutes are unloaded into sink cells, and the water potential in those cells is lowered. Water moves out of the seive tube and into sink cells. 1 Active transport mechanisms move solutes into the companion cells and then into the sieve tube, against concentration gradients. 2 As a result of the increased solute con-centration, the water potential is decreased in the sieve tube, and water moves in by osmosis, increasing turgor pressure. 4 Pressure and solute con- centrations gradually decrease between the source and the sink as substances move into the sink from phloem.
LG 3 Vocab Terms 1.Passive Transport - 2.Active Transport - 3.Osmosis - 4.Water Potential - 5.Apoplastic vs Symplastic Pathway - 6.Casparian Strip - 7.Cohesion-Tension Mechanism - 8.Source - 9.Sink - 10.Pressure Flow Mechanism -