Chapter 9 transport in plants lecture

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Chapter 9 transport in plants lecture

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Chapter 9 transport in plants lecture

  1. 1. Chapter 9 Transport in Plants
  2. 2. How is water transported against gravity from the roots, up the xylem and to the leaves?
  3. 3. I wonder where trees get water from? Well, obviously from the ground. What are the processes involved?
  4. 4. How does water move through the transport system of a plant IF it does not have a heart to act as a pump? PAUSE to PONDER •How is water lifted against gravity from the ground to the leaves through this transport system? • Are the products of photosynthesis also carried in a set of vessels from the leaves to the roots? 4
  5. 5. Diagram of Xylem Vessel
  6. 6. Transport Structures of Flowering Plants 1) Xylem • Consists of mainly xylem vessels that are made up of dead cells. • Inner walls of xylem vessels are strengthened by lignin. • Lignin deposited in the form of rings or spirals.
  7. 7. 1) Xylem (cont) • Function: – Conduct water and mineral salts from roots to stems and leaves. – Provide mechanical support for plant. Transport Structures of Flowering Plants
  8. 8. Adaptations of the xylem vessel for its function 1) Empty lumen, no protoplasm or cross-walls. – Reduces resistance to water flowing through 2) Walls thickened with lignin. – Lignin is a hard and rigid substance. – Prevents collapse of the vessel (Mechanical support)
  9. 9. 2) Phloem • Consists mainly of sieve tubes and companion cells. • Sieve tube consists of columns of sieve tube cells, that are elongated and thin-walled. • Companion cells provide the nutrients and help the sieve tube cells transport manufactured food. (Sucrose) Transport Structures of Flowering Plants
  10. 10. Diagram of Phloem
  11. 11. 2) Phloem (cont) • Function: – Conducts manufactured food (sucrose and amino acids) from the leaves to the other parts of the plant. Transport Structures of Flowering Plants
  12. 12. Monocotyledon VS Dicotyledon
  13. 13. 1 Vascular bundles 14 How Are the Vascular Tissues Organised in Stems? In a dicotyledonous stem, the xylem and phloem are grouped together to form vascular bundles. xylem cambium phloem vascular bundle The phloem lies outside the xylem with a tissue called the cambium between them. •Cambium cells can divide and differentiate to form new xylem and phloem tissues, •Giving rise to a thickening of the stem. 2 Cambium
  14. 14. How Are the Vascular Tissues Organised in Stems? Pith The vascular bundles are arranged in a ring around a central region called the pith. 3 Cortex4 The region between the vascular bundles and the epidermis is the cortex. •Both the cortex and the pith serve to store up food substances, such as starch.
  15. 15. How Are the Vascular Tissues Organised in Stems? Epidermis The stem is covered by a layer of cells called the epidermis. •The epidermal cells are protected by a waxy, waterproof cuticle •Which greatly reduces evaporation of water from the stem. 5
  16. 16. 2 Pith 1 Vascular Bundles 3 4 Cortex 5 Epidermis Xylem Cambium Phloem Vascular bundle 17 How Are the Vascular Tissues Organised in Stems?
  17. 17. How Are the Vascular Tissues Organised in Roots? xylem phloem In a dicotyledonous root, the xylem and phloem are not bundled together. Instead, they alternate with each other. 1 Vascular bundles 2 Cortex The cortex of the root is also a storage tissue. The innermost layer of root cortex is called the endodermis.
  18. 18. How Are the Vascular Tissues Organised in Roots? Piliferous layer The epidermis of the root is the outermost layer of cells. It bears root hairs. It is also called the piliferous layer. Root hair Each root hair is a tubular outgrowth of an epidermal cell. •This outgrowth increases the surface area to volume ratio of the root hair cell. •The absorption of water and mineral salts is increased through this adaptation. 4 3
  19. 19. 1 Xylem and phloem alternate with each other. 2 Cortex Endodermis 3 Piliferous layer 4 Root hair 20 How Are the Vascular Tissues Organised in Roots?
  20. 20. How Are the Vascular Tissues Organised in Leaves?
  21. 21. Distribution of vascular bundles in leaves. xylem phloem
  22. 22. xylem phloem Diagram showing a section through a leaf.
  23. 23. How you ever noticed such dots on tree trunks? WH AT IS IT?
  24. 24. Formation of Lenticles • In woody stems the stomata are blocked by the presence of cork cells • The epidermis of woody stems breaks up to form tiny pores called lenticles which allow gaseous exchange.
  25. 25. Test yourself! (pg.179) • Qn 1
  26. 26. The Journey so far… • Xylem – Structure: Arrangement of lignin – 2 functions – 2 adaptations • Phloem – Structure: Made of ? & ? – Function – Adaptation • Arrangements of X & P (VB) in roots, stems, leaves
  27. 27. Lesson Objectives • Movement of substances and the processes involved in the roots and leaves
  28. 28. 29 cytoplasm vacuole nucleus cell wall cell surface membrane of root hair cell film of liquid (dilute solution of mineral salts) soil particles Entry of Water into a Plant
  29. 29. Entry of Water into a Plant 30 ABC xylem phloem cortex root hair piliferous layer A section of root showing the path of water through it
  30. 30. 31 cytoplasm vacuole nucleus cell wall cell surface membrane of root hair cell film of liquid (dilute solution of mineral salts) soil particles Each root hair is a fine tubular outgrowth of an epidermal cell. •It grows between the soil particles, •Coming into close contact with the water surrounding them. 1 Entry of Water into a Plant 1
  31. 31. 32 cytoplasm vacuole nucleus cell wall cell surface membrane of root hair cell film of liquid (dilute solution of mineral salts) soil particles 1 Entry of Water into a Plant 2 The thin film of liquid surrounding each soil particle is a dilute solution of mineral salts. 2
  32. 32. Entry of Water into a Plant 33 The sap in the root hair cell is a relatively concentrated solution of sugars and various salts. •Thus the sap has a lower water potential than the soil solution. • These two solutions are separated by the partially permeable cell surface membrane of the root hair cell. • Water enters the root hair by osmosis. 3 ABC xylem phloem cortex root hair piliferous layer water entering the root hair A section of root showing the path of water through it 3
  33. 33. Entry of Water into a Plant 34 The entry of water dilutes the sap. • The sap of the root hair cell now has a higher water potential than that of the next cell (cell B) • Hence, water passes by osmosis from the root hair cell into the inner cell. 4 ABC xylem phloem cortex root hair piliferous layer water entering the root hair A section of root showing the path of water through it 34
  34. 34. Entry of Water into a Plant 35 Similarly, water passes from cell B into the next cell (cell C) of the cortex. •This continues until the water enters the xylem vessels and moves up the plant. 5 ABC xylem phloem cortex root hair piliferous layer water entering the root hair A section of root showing the path of water through it 3 4 5
  35. 35. How do nitrate ions get into plants? Are they directly absorbed from the air? No. Even though the air has 79% of nitrogen, it is highly unreactive.PAUSE to PONDER •How are ions transported around in plants?
  36. 36. How do root hairs absorb ions and mineral salts? 1) Active Transport • When the concentration of ions in the salt solution is lower than that in the root hair cell sap • Root hairs absorb the salts against a concentration gradient • Energy for this process comes from cellular respiration in the root hair cell.
  37. 37. 2) Diffusion • When concentration of certain ions in the soil solution are higher than that in the root hair cell. How do root hairs absorb ions and mineral salts?
  38. 38. How the root hair cell is adapted to its function of absorption 1) Root hair is long and narrow • Increases surface area to volume ratio • Which in turn increases the rate of absorption of minerals and water. 2) Cell surface membrane prevents cell sap from leaking out • Cell sap contains sugars, amino acids and salts • Has lower water potential than soil solution • Results in water entering the root hair by osmosis
  39. 39. 3) Living root hair cell • Able to provide energy for active transport of ions (mineral salts) into the cell. • Energy produced by the mitochondria during cellular respiration. How the root hair cell is adapted to its function of absorption
  40. 40. Movement of Water inside a Leaf 41 Cuticle Film of water Xylem Phloem Intercellular air space Upper epidermis Palisade mesophyll Spongy mesophyll Lower epidermis Guard cell Stomatal pore
  41. 41. Movement of Water inside a Leaf 42 Cuticle chloroplast s Nucleus Film of water Xylem of vein Phloem Intercellular air space Sub-stomatal air space Upper epidermis Palisade mesophyll Spongy mesophyll Lower epidermis 1 arrows show path of water vapour and water Guard cell Stomatal pore Cell sap Water continuously moves out of the mesophyll cells to form a thin film of moisture over their surfaces. 1
  42. 42. 43 cuticle chloroplast s nucleus film of water xylem of vein phloem intercellular air space sub-stomatal air space upper epidermis palisade mesophyll spongy mesophyll lower epidermis 1 guard cell Water evaporates from this thin film of moisture • moves into the intercellular air spaces. • Water vapour accumulates in the large air spaces near the stomata (sub-stomatal air spaces). 2 2 stomatal pore Movement of Water inside a Leaf
  43. 43. Movement of Water inside a Leaf 44 cuticle chloroplasts nucleus film of water xylem of vein phloem intercellular air space sub-stomatal air space upper epidermis palisade mesophyll spongy mesophyll lower epidermis 1 guard cell cell sap 2 Water vapour then diffuses throughout the stomata to the drier air outside the leaf. This is transpiration. 3 3 stomatal pore
  44. 44. 45 cuticle chloroplasts nucleus film of water xylem of vein phloem intercellular air space sub-stomatal air space upper epidermis palisade mesophyll spongy mesophyll lower epidermis 1 guard cell 2 stomatal pore Movement of Water inside a Leaf 3 4 cell sap As water evaporates from the mesophyll cells, • the water potential of the cell sap decreases. • The mesophyll cells begin to absorb water by osmosis from the cells deeper inside the leaf. • These cells, in turn, remove water from the vein, that is, from the xylem vessels. 4
  45. 45. 46 cuticle chloroplasts nucleus film of water xylem of vein phloem intercellular air space sub-stomatal air space upper epidermis palisade mesophyll spongy mesophyll lower epidermis 1 guard cell 2 stomatal pore Movement of Water inside a Leaf 3 4 cell sap This results in a suction force which pulls the whole column of water up the xylem vessel. 5
  46. 46. Transpiration Definition: It is the loss of water vapour through the stomata of the leaves.
  47. 47. Importance of Transpiration 1) Transpiration pull • helps to draw water and mineral salts from the roots to the leaves 1) Evaporation of water removes latent heat from the plant. • prevent the plant from overheating 3) Water transported to the leaves can: • be used for photosynthesis • keep cells turgid • replace water lost by the cells.
  48. 48. Factors affecting the rate of Transpiration 1) Humidity of the air • Humidity refers to the amount of water vapor in the air. • Increasing humidity decreases the concentration gradient between air and leaf. • Therefore, deceasing the rate of transpiration 2) Wind or Air movement • The stronger the wind, the faster the rate of transpiration.
  49. 49. 3) Temperature of air • Increasing temperatures increases the rate of evaporation. • Thus increasing the rate of transpiration 4) Light • Light affects the stomata. • With increasing light intensity, stomata open and become wider. • Therefore, this increases the rate of transpiration Factors affecting the rate of Transpiration
  50. 50. Wilting
  51. 51. Wilting • Occurs when excess transpiration occurs • In strong sunlight, rate of transpiration exceed rate of water absorption by the roots • cells lose more water than they absorb water, resulting in plasmolysis  water leaves the cells, causing the cell membrane to shrink from the cellulose cell wall • cells lose their turgor pressure and become flaccid • This results in the plant wilting.
  52. 52. Advantages of Wilting • The folding up of the leaves – Surface area exposed to sunlight is reduced • Leads to the guard cells becoming flaccid and close up – Therefore reducing the rate of transpiration
  53. 53. Disadvantages of Wilting • Water is the limiting factor for photosynthesis • Stomata is closed, – Amount of CO2 entering the leaf is also reduced. – CO2 becomes a limiting factor, • Therefore decreasing the rate of photosynthesis.
  54. 54. Experiments
  55. 55. Investigation 9.1
  56. 56. • What is transverse? • Which tissue has been stained red? • What conclusion can you draw from your investigation?
  57. 57. Investigation 9.2 • Make drawings of your observations • What does this experiment tell you about the phloem? • Suggest an explanation of your observations.
  58. 58. Investigation 9.2 • The phloem tissues have been removed. • Manufactured food substances (e.g sugar and amino acid) accumulate above the cut region and cause swelling in twigs A and C. However in twig B, manufactured food can pass through the phloem without any barrier. • This suggests that food is made in the leaves and are transported through the phloem. twig A twig B twig C

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