9.2 - Transport in Angiospermophytes

Transport in Angiospermophytes

Minerals in the Soil Minerals must be able to move through the soil to the roots of plants to be absorbed - how do they do this? Diffusion - Fungal hyphae - Dissolved in soil water - 9.2.2

Mineral Uptake Minerals are absorbed by the plant via active transport Minerals include potassium, phosphate, nitrates and other ions The concentration of ions is higher inside the root cell than in the surrounding soil Move against the concentration gradient Allows for selective absorption of minerals by plants Cortex cells absorb mineral ions that are dissolved in water From cortex, minerals dissolved in water travel through the endodermis and into the vascular cylinder. 9.2.3

Mineral Uptake 9.2.3

Mineral Uptake 9.2.3

Vascular Tissue - Xylem Xylem – water and mineral conducting tissue At maturity, cells are dead and lack plasma membranes – so water flows through freely End walls break down forming long tubes Pores in side walls allow water movement between adjacent cells 9.2.6

Vascular Tissue - Xylem Composed of tracheids and/or vessel elements Tracheids: Narrow cells arranged in columns Overlapping ends help with support and water movement Vessel Elements: Cell wall arranged in a helical pattern that enable walls to withstand pressure and stretch as other living cells grow Wide diameter allows for efficient water transport Only found in angiosperms 9.2.6

Vascular Tissue - Xylem 9.2.6

Vascular Tissue - Xylem 9.2.6

Transpiration Transpiration - the loss of water vapor from the leaves and stems through evaporation Plants are adapted to limit water loss – how? 9.2.5 9.2.6

Transpiration

Transpiration Stream Transpiration stream - transpiration creates a flow of water from the roots, through the stems, to the leaves Movement of water through plants depends on the cohesion and adhesion of water molecules - what are these properties? Water forms a column due to hydrogen bonding 9.2.6

Transpiration Stream Steps in water movement: Water evaporates from spongy mesophyll in leaf tissue (transpiration) Water is replaced with water from xylem tissue in leaf veins Water moves into leaf tissue via capillary action When water is pulled out of xylem, suction develops, and more water is pulled up from roots and stem – transpiration pull Like using a straw to suck up liquid 9.2.6

Transpiration Stream 9.2.6

Regulation of Transpiration Water evaporates out of the leaf tissue through the stomata (transpiration) Guard cells control transpiration by opening and closing the stomata Generally, guard cells open stomata during the day and close them at night - why? 9.2.7

Regulation of Transpiration Changes in turgor pressure in the guard cells open and close the stomata: Guard cells actively uptake potassium ions (K+) and increase solute concentration Water enters the guard cells by osmosis to balance solute concentration and cells become turgid. Turgid guard cell = open stomata Reverse process makes guard cells flaccid and closes stomata Flaccid guard cell = closed stomata 9.2.7

Regulation of Transpiration 9.2.7

Regulation of Transpiration 9.2.7

Regulation of Transpiration Environmental factors and stressors can also affect transpiration and opening and closing of the stomata: When plants are water deficient, cells may lose turgor and stomata close - why important? Abscisic acid, a plant hormone, signals stomata to close during water deficiencies. 9.2.8

Factors Affecting Transpiration Light – guard cells close in darkness, open in light – why? Increased transpiration during day Temperature – higher temperatures increase transpiration Also decrease outside humidity – thus increase diffusion out water out of leaf 9.2.9

Factors Affecting Transpiration Humidity – lower humidity increases transpiration – why? Wind – air movement moves air saturated with water vapor away from stomata – thereby increasing transpiration 9.2.9

Xerophytes Plants adapted to grow in very dry environments Have evolved different adaptations to help reduce transpiration - why? 9.2.10

Xerophytes Adaptations of Xerophytes: Spines instead of leaves – why? Thick stems with water storage tissue Thick, waxy cuticle Vertical stems instead of lateral reaching branches – why? Wide-spreading network of shallow roots – why? 9.2.10

Vascular Tissue - Phloem Phloem – sugar and amino acid conducting tissue Formed from long chains of sieve-tube members Alive a maturity (however they lack nuclei and ribosomes) End walls (sieve plates) have pores that allow for flow of sugar between cells Each sieve tube cell has an adjacent companion cell that helps serve sieve tube member 9.2.11

Vascular Tissue - Phloem 9.2.11

Translocation Translocation – movement of substances from one area in a plant to another Moves sugars and amino acids from source areas (photosynthetic tissue and storage organs) to sinks (fruits, seeds, and roots) Active process that occurs in phloem 9.2.11

Translocation How Translocation Works: Plasma membranes in sieve tube members pump organic compounds into cell via active transport Creates high solute concentration inside sieve tube member Therefore, water diffuses into sieve tube via osmosis - forms sap (sugars dissolved in water) Creates pressure inside sieve tube and pushes sap throughout plant 9.2.11

Translocation 9.2.11

Translocation Sugar loading in sieve tube raises solute concentration and draws in water Water influx increases pressure forcing flow of sap Sugar unloading lowers solute concentration, water effluxes and pressure decreases Water pulled back up via transpiration stream 9.2.11

Translocation 9.2.11