The need for transport systems

The need for transport systems Why large organisms have specialised transport systems while smaller ones not? With large size comes a small SA:vol ratio The consequence of this is specialised organs of exchange and with these come a need to transport materials between the cells and these sites of exchange which is met with a transport system Achievements of plant transport Water transport From roots to leaves Achievements of plant transport Water transport From roots to leaves Nutrient (sucrose / amino acid) transport From leaves throughout the plant Achievements of plant transport Water transport From roots to leaves Nutrient (sucrose / amino acid) transport From leaves throughout the plant Ion transport From roots to growing points Xylem • The term ‘xylem’ refers to a tissue made up from the following cell types: vessels, fibres, tracheids and xylem parenchyma • Xylem vessels transport water (the ‘transpiration stream’) and mineral ions absorbed by the roots • Flow is unidirectional (upward) ‘pulled’ by evaporation from the leaves Specialisations of xylem vessels Lignified To provide waterproofing and to increase mechanical strength Dead A result of the lignification, this means that cytoplasmic contents are absent thus reducing resistance to water flow Pitted To allow lateral movement of water from the xylem Made from fused cells which have lost their internal walls To reduce resistance to water flow and to allow the cohesive and adhesive forces between water molecules to aid transpiration Distributed around the periphery of the stem To increase resistance of the stem to bending (lateral) forces Held in the middle of the root To increase resistance to pulling forces Held in the midrib of leaves To provide support and help present a flat surface for photosynthesis Specialisations of xylem vessels Lignified To provide waterproofing and to increase mechanical strength Dead A result of the lignification, this means that cytoplasmic contents are absent thus reducing resistance to water flow Pitted To allow lateral movement of water from the xylem Made from fused cells which have lost their internal walls To reduce resistance to water flow and to allow the cohesive and adhesive forces between water molecules to aid transpiration Distributed around the periphery of the stem To increase resistance of the stem to bending (lateral) forces Held in the middle of the root To increase resistance to pulling forces Held in the midrib of leaves To provide support and help present a flat surface for photosynthesis Specialisations of xylem vessels Lignified To provide waterproofing and to increase mechanical strength Dead A result of the lignification, this means that cytoplasmic contents are absent thus reducing resistance to water flow Pitted To allow lateral movement of water from the xylem Made from fused cells which have lost their internal walls To reduce resistance to water flow and to allow the cohesive and adhesive forces between water molecules to aid transpiration Distributed around the periphery of the stem To increase resistance of the stem to bending (lateral) forces Held in the middle of the root To increase resistance to pulling forces Held in the midrib of leaves To provide support and help present a flat surface for photosynthesis Specialisations of xylem vessels Lignified To provide waterproofing and to increase mechanical strength Dead A result of the lignification, this means that cytoplasmic contents are absent thus reducing resistance to water flow Pitted To allow lateral movement of water from the xylem Made from fused cells which have lost their internal walls To reduce resistance to water flow and to allow the cohesive and adhesive forces between water molecules to aid transpiration Distributed around the periphery of the stem To increase resistance of the stem to bending (lateral) forces Held in the middle of the root To increase resistance to pulling forces Held in the midrib of leaves To provide support and help present a flat surface for photosynthesis Translocation • Movement of organic solutes (sucrose, amino acids etc) • Occurs in phloem sieve tubes (not ‘phloem’) • Bi-directional movement • Selective and active process Phloem • A tissue made from several cell types – Sieve tubes – Companion cells – Transfer cells – Phloem parenchyma Phloem – transverse section Phloem within the vascular bundle Sieve tube Phloem parenchyma Companion cell Phloem – longitudinal section Most of the cytoplasmic contents of the sieve tube are removed and its metabolic demands are met by the companion cells associated with it Phloem – longitudinal section The sieve plates are responsible for pumping materials from cell to cell This process is active and selective and controlled by threads of protein which pass through the sieves’ pores Phloem loading The transfer cell is a key cell in loading sieve tubes with sucrose It has a highly folded membrane and many mitochondria to aid active transport into the sieve tube Mineral uptake and transport Uptake • Most minerals are taken up from the soil by active transport by root hair cells • These cells have a large surface area for uptake • In certain soils some ions are taken up passively (e.g Ca2+ in lime soils) Mineral uptake and transport Transport • The ions move in solution via the apoplast route to the endodermis • Here they are pumped into the stele – this accounts for root pressure Mineral uptake and transport Transport • The ions move in solution via the apoplast route to the endodermis • Here they are pumped into the stele – this accounts for root pressure Mineral uptake and transport Transport • The ions move in solution via the apoplast route to the endodermis • Here they are pumped into the stele – this accounts for root pressure • They then are taken into the xylem vessels and are transported in the transpiration stream Mineral uptake and transport Transport • The ions move in solution via the apoplast route to the endodermis • Here they are pumped into the stele – this accounts for root pressure • They then are taken into the xylem vessels and are transported in the transpiration stream • Transfer cells can pass specific ions into phloem (lateral movement) for more selective transport Analysing data - absorption of mineral ions • Root tissue from trees can be extracted and cultured in an ion-rich medium • Its mineral absorbing activity can be measured by analysing the contents of the cytoplasm over time • Two such groups of such tissue were cultured and their potassium (K+) content recorded over a 150 minute period Analysing data - absorption of mineral ions Sealed chamber with controlled atmosphere Root tissue blocks in culture solution • One group was cultured as above in air, a second with an atmosphere of pure nitrogen Results Intra-cellular potassium concentration / arbitrary units 160 140 120 100 Air Nitrogen 80 60 40 20 0 50 100 Time / minutes 150 Questions 1) Compare the results of the two groups [3] 2) What is the K+ concentration of the culture solution? Explain your answer [3] 3) List three factors, other than K+ concentration, which must be controlled in this experiment [3] 4) Explain the differences in K+ absorption between the two groups [4] [...]... pectates) The transpiration stream Evaporation of water from the spongy mesophyll tissue… …draws water across the leaf by apoplast, symplast and vacuolar routes… …and out of the xylem in the leaves This pulls water up the continuous column of water in the xylem (cohesive forces stop the column from breaking) In the roots water is withdrawn from the cells which surround the xylem… …this draws water across the. .. to water flow and to allow the cohesive and adhesive forces between water molecules to aid transpiration Distributed around the periphery of the stem To increase resistance of the stem to bending (lateral) forces Held in the middle of the root To increase resistance to pulling forces Held in the midrib of leaves To provide support and help present a flat surface for photosynthesis Cell A Cell B Cell... water from the xylem Made from fused cells which have lost their internal walls To reduce resistance to water flow and to allow the cohesive and adhesive forces between water molecules to aid transpiration Distributed around the periphery of the stem To increase resistance of the stem to bending (lateral) forces Held in the middle of the root To increase resistance to pulling forces Held in the midrib... across the root tissue… …and into the root hair cells from the soil The endodermis Root cortex Endodermis Xylem vessel The stele The endodermis • Endodermal cells have a waterproof layer (made of suberin) impregnated into their cell wall called the Casparian strip Band of suberin The endodermis • The Casparian strip blocks the apoplast route and so any water passing though the endodermis must pass through... of the stem To increase resistance of the stem to bending (lateral) forces Held in the middle of the root To increase resistance to pulling forces Held in the midrib of leaves To provide support and help present a flat surface for photosynthesis Specialisations of xylem vessels Lignified To provide waterproofing and to increase mechanical strength Dead A result of the lignification, this means that cytoplasmic... communication further Three modes of water transfer between cells… Apoplast route Three modes of water transfer between cells… Apoplast route Water flows within the cell walls Cellulose if freely permeable to water Relies on the cohesive forces of water (H-bonds) cell has no control over water movement since the water never enters the living contents of the cell (protoplasm) By far the most significant... result of the lignification, this means that cytoplasmic contents are absent thus reducing resistance to water flow Pitted To allow lateral movement of water from the xylem Made from fused cells which have lost their internal walls To reduce resistance to water flow and to allow the cohesive and adhesive forces between water molecules to aid transpiration Distributed around the periphery of the stem... symplast route • This gives the plant control of water and mineral uptake since both must pass across a membrane Stomata • Stomata exist to allow CO2 into leaves for photosynthesis • Opening and closure is controlled by the plant • Water is lost by evaporation and then diffusion Major water loss is an unavoidable consequence of leaf function • Gas exchange is critical for photosynthesis • Gas exchange requires... function • Gas exchange is critical for photosynthesis • Gas exchange requires a huge, moist surface area (provided by the spongy mesophyll) • The gas exchange surface must be ventilated (achieved by diffusion though air spaces and open stomata) Measuring transpiration – the potometer • Measures uptake of water into a plant • Makes the assumption that uptake is the same as evaporative loss • Some have... huge, moist surface area (provided by the spongy mesophyll) • The gas exchange surface must be ventilated (achieved by diffusion though air spaces and open stomata) Major water loss is an unavoidable consequence of leaf function • Gas exchange is critical for photosynthesis • Gas exchange requires a huge, moist surface area (provided by the spongy mesophyll) • The gas exchange surface must be ventilated ... and transport Transport • The ions move in solution via the apoplast route to the endodermis • Here they are pumped into the stele – this accounts for root pressure • They then are taken into the. .. solution via the apoplast route to the endodermis • Here they are pumped into the stele – this accounts for root pressure • They then are taken into the xylem vessels and are transported in the transpiration... transport Transport • The ions move in solution via the apoplast route to the endodermis • Here they are pumped into the stele – this accounts for root pressure Mineral uptake and transport Transport