9.2 transport in angiospermophytes

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9.2 transport in angiospermophytes

  1. 1. 9.2 Transport in Angiospermophytes Topic 9 Plant Science
  2. 2. Transport in Angiospermophytes  9.2.1 Outline how the root system provides a large surface area for mineral ion and water uptake by means of branching and root hairs.  9.2.2 List ways in which mineral ions in the soil move to the root. (There are three processes: diffusion of mineral ions, fungal hyphae (mutualism), and mass flow of water in the soil carrying ions).  9.2.3 Explain the process of mineral ion absorption from the soil into roots by active transport.  9.2.4 State that terrestrial plants support themselves by means of thickened cellulose, cell turgor and lignified xylem.
  3. 3. Transport in Angiospermophytes  9.2.5 Define transpiration. Transpiration is the loss of water vapour from the leaves and stems of plants.  Aim 7: Data logging with pressure sensors, humidity, light or temperature probes to measure rates of transpiration can be performed.  9.2.6 Explain how water is carried by the transpiration stream, including the structure of xylem vessels, transpiration pull, cohesion, adhesion and evaporation. (Limit the structure of xylem vessels to one type of primary xylem).
  4. 4. Transport in Angiospermophytes  9.2.7 State that guard cells can regulate transpiration by opening and closing stomata.  9.2.8 State that the plant hormone abscisic acid causes the closing of stomata.  9.2.9 Explain how the abiotic factors light, temperature, wind and humidity, affect the rate of transpiration in a typical terrestrial plant.
  5. 5. Transport in Angiospermophytes 9.2.10 Outline four adaptations of xerophytes that help to reduce transpiration. These could include: reduced leaves, rolled leaves, spines, deep roots, thickened waxy cuticle, reduced number of stomata, stomata in pits surrounded by hairs, water storage tissue, low growth form, CAM (crassulacean acid metabolism) and C4 physiology.
  6. 6. Transport in Angiospermophytes  9.2.11 Outline the role of phloem in active translocation of sugars (sucrose) and amino acids from source (photosynthetic tissue and storage organs) to sink (fruits, seeds, roots).  No detail of the mechanism of translocation or the structure of phloem is required.
  7. 7. Water Uptake in Roots  As well as anchoring the plant, the roots provide the surface area through which water is taken up.  The surface area is greatly increased by the presence of thousands of tiny root hairs, just behind the tip of each root.  A branching root system also creates a large surface
  8. 8. Water Uptake in Roots  The plant’s roots provide an enormous surface area for the absorption of water and mineral ions.  The root hairs are a slender extension of a single epidermal cell up to 4mm long.  Root hairs penetrate between soil particles and are in close contact with the soil water. Ref: Advanced Biology, Roberts Etal p248.
  9. 9. Mineral Ion Uptake by Active Transport  Mineral ion concentration inside the root is usually higher that in the surrounding soil.  Thus mineral ions are taken up by Active Transport (requiring energy to move ions against the concentration gradient).  This is supported by the fact that mineral uptake requires energy (in the form of ATP).  In experiments, mineral uptake has been brought to a halt by depriving the roots of oxygen or adding a substance that blocks cellular respiration.
  10. 10. Additional mechanisms of mineral ion uptake  Facilitated diffusion (if suitable concentration gradient)  Mass flow (minerals move in with water)  Mutualistic fungi growing on the root: their fine threadlike hyphae provide a large surface area for mineral uptake and most of these are passed on to the plant
  11. 11. Water Uptake  The epidermal cells absorb mineral ions by active transport.  Thus the solute concentration is higher in the epidermal cell that in the soil water.  Thus water moves into the cells by Osmosis (down the concentration gradient).  Solute concentration in the epidermal cells less than in the cortex, so water moves into the cortex.  This repeats across the cortex into the Xylem vessels, in the center of the root
  12. 12. Movement of Water Across the Root (not in current course)  To get water from the root hairs to the xylem, 3 routes are possible:  The apoplastic pathway  Water does not enter the cell.  Water travels along the cell walls until it reaches the endodermis  The symplastic pathway  Water enters the cells3  It passes from cell to cell via plasmodesmata (tiny holes in the cell walls
  13. 13. Movement of Water Across the Root Ref: IB Biology, OSC
  14. 14. Movement of Water Across the Root Ref: Advanced Biology, Roberts Etal p250.
  15. 15. Support in Terrestrial Plants  Plants do not have a skeleton to keep them upright.  Trees and shrubs have woody stems that support them.  However herbaceous plants depend mainly on turgor for their support:  The vacuole swells with water pushing the cell walls out.  This gives the cells a rigid structure.  Other methods terrestrial plants use to support themselves are:  Thickened cellulose cell walls  Xylem with thickened walls.
  16. 16. Transpiration  Transpiration is: “the loss of water vapour from the leaves and stems of the plant”  Transpiration causes a flow of water from the roots, through the stem to the leaves of plants.  This is called the Transpiration Stream.
  17. 17. Transpiration  The process starts with evaporation of water from the leaves.  This water is replaced with water from the xylem vessels in the leaf.  Low pressure or suction is created inside xylem vessels when water is pulled out. This is called transpiration pull.  Xylem vessels are long continuous columns of water and this transpiration pull is transmitted down to the roots.  The transmission of the transpiration pull through the xylem vessels depends on the cohesion of water molecules, due to hydrogen bonding.  Adhesion of water to the wall of vessels is also important when water starts to rise up the vessel again in spring.
  18. 18. Water Transport through the Plant Ref: IB Biology, OSC
  19. 19. Xylem  Xylem vessels are system of long pipes through which water can travel.  They are dead cells in which their cell walls have been impregnated with lignin.  With the lignification of the cell walls, the cell dies and lose their contents except for the water and mineral salts they transport. Ref: IB Biology, OSC
  20. 20. Xylem Ref: IB Biology, Allott
  21. 21. Xylem Ref: Advanced Biology, Roberts Etal p253
  22. 22. Guard Cells and Transpiration  Stomata (singular: stoma) are pores in the epidermis of the leaves and stems which can open and close.  The stoma itself is bordered by a pair of specialised epidermal cells called guard cells.  These guard cells can fill with water and become turgid, causing the stoma to open.  Conversely, they can lose water and thus the stoma closes.  In this way, stomata can regulate the exchange of gases.  Stomata can also regulate transpiration by opening and closing to allow the movement of water vapour out of the plant.  When water stressed the plant hormone abscisic acid causes the guard cells to rapidly close the stomata, preventing further water loss.
  23. 23. Factors Affecting Transpiration  There are 4 main abiotic factors that can affect the rate of transpiration in a typical terrestrial mesophytic plant:  Temperature  Increase in temp  increase in transpiration  Light  Increase in light  increase in transpiration  Wind  Increase in wind  increase in transpiration  Humidity  Increase in humidity  decrease in transpiration
  24. 24. Explanation of external factors  Light: guard cells close in darkness so transpiration greater in the light.  Temperature: higher temperatures increase evaporation, rate of diffusion of water vapour through the air spaces and reduce relative humidity of the external air (increasing conc. gradient).  Humidity: a lower humidity outside the leaf increases the concentration gradient for water vapour.  Wind: blows air saturated with water vapour away,
  25. 25. Translocation  Translocation is the movement of substances from one part of the plant to another in the phloem.  Translocation occurs through the phloem.  Phloem is made up of two elements:  Sieve tubes  Companion cells  Sieve tubes are long specialised cells which have pores in the ends of them, forming a sieve plate.  This allows the contents of the sieve tubes to pass from one cell to another.
  26. 26. Translocation  Associated with sieve tubes are companion cells.  These assist the sieve tubes with those metabolic processes it cannot do itself.  eg: to generate energy  Sieve tubes carry materials in either direction.  Eg: in summer Maple trees will transport sugars from leaves to roots for storage.  In spring, the sieve tubes will transport sugars from the roots to the branches to allow for new growth.  Phloem also transports some spray chemicals if they have been absorbed into the leaves.
  27. 27. Translocation
  28. 28. Food Storage in Plants  Many plants develop a food storage organ in which food is stored.  Examples include:  potatoes, carrots, corms, bulbs  The steps in food storage are:  Photosynthesis in the leaves produce glucose.  The sugars are translocated in the phloem from the leaves to the storage organ.  The sugars are converted into starch, proteins and other organic compounds for storage.
  29. 29. Food Storage in Plants Ref: IB Biology, OSC
  30. 30. Transport in Angiospermophytes  9.2.1 Outline how the root system provides a large surface area for mineral ion and water uptake by means of branching and root hairs.  9.2.2 List ways in which mineral ions in the soil move to the root. (There are three processes: diffusion of mineral ions, fungal hyphae (mutualism), and mass flow of water in the soil carrying ions).  9.2.3 Explain the process of mineral ion absorption from the soil into roots by active transport.  9.2.4 State that terrestrial plants support themselves by means of thickened cellulose, cell turgor and lignified xylem.
  31. 31. Transport in Angiospermophytes  9.2.5 Define transpiration. Transpiration is the loss of water vapour from the leaves and stems of plants.  Aim 7: Data logging with pressure sensors, humidity, light or temperature probes to measure rates of transpiration can be performed.  9.2.6 Explain how water is carried by the transpiration stream, including the structure of xylem vessels, transpiration pull, cohesion, adhesion and evaporation. (Limit the structure of xylem vessels to one type of primary xylem).
  32. 32. Transport in Angiospermophytes  9.2.7 State that guard cells can regulate transpiration by opening and closing stomata.  9.2.8 State that the plant hormone abscisic acid causes the closing of stomata.  9.2.9 Explain how the abiotic factors light, temperature, wind and humidity, affect the rate of transpiration in a typical terrestrial plant.
  33. 33. Transport in Angiospermophytes 9.2.10 Outline four adaptations of xerophytes that help to reduce transpiration. These could include: reduced leaves, rolled leaves, spines, deep roots, thickened waxy cuticle, reduced number of stomata, stomata in pits surrounded by hairs, water storage tissue, low growth form, CAM (crassulacean acid metabolism) and C4 physiology.
  34. 34. Transport in Angiospermophytes  9.2.11 Outline the role of phloem in active translocation of sugars (sucrose) and amino acids from source (photosynthetic tissue and storage organs) to sink (fruits, seeds, roots).  No detail of the mechanism of translocation or the structure of phloem is required.

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