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Transportation in Plants | Xylem Transport in Plants

Transportation in Plants

Transportation in Plants | Xylem Transport in Plants

Botany Chapter “Transport in Plants” contains 2% weightage in NEET Exam (2000-2021).Here is the List of Some Important Topics of this Chapter:-

1. Transpiration

2. Plant-water relations

3. Long distance transport of water

4. Means of Transport


Noteworthy Points of the Chapter :

  1. Transport over long distance proceeds through the vascular system which is called translocation.
  2. Transport in xylem is essentially unidirectional, however in phloem it is multidirectional.
  3. In diffusion, substances move from regions of higher concentration to regions of lower concentration.
  4. Diffusion is very important in plants since it is the only means for gaseous movements within the plant body.
  5. The diffusion of any substance across a membrane also depends on its solubility in lipids, the major constituent of the membrane.
  6. In facilitated diffusion special proteins help to move substances across membranes without expenditure of ATP/energy.
  7. The porins are proteins that form huge pores in the outer membranes of the plastids, mitochondria and some bacteria allowing molecules upto the size of small proteins to pass through.
  8. Water channels are made of eight different types of aquaporins .
  9. In a symport, both molecules move across the membrane in the same direction; and in an antiport they move in opposite direction.
  10. Pumps are proteins that use energy to carry substance across the cell membrane during active transport.
  11. A watermelon has over 92% water, most of the herbaceous plants have only about 10-15% of its fresh weight as dry matter.
  12. Terrestrial plants take up huge amount of water but most of it is lost through evaporation from the leaves due to transpiration.
  13. Water potential is potential energy of water that helps in movement of water.
  14. Water potential of pure water at standard temperature and without any pressure is zero.
  15. Solute potential and pressure potential are the two main components that determine water potential.
  16. Water potential is denoted by the Greek symbol Psi or \(\Psi\) and is expressed in pressure units such as pascals(Pa).
  17. For a solution at atmospheric pressure, water potential (\({\Psi}_{w}\)) = solute potential (\({\Psi}_{s}\)) .
  18. Osmosis is the term used to refer specifically to the diffusion of water across a differentially or semi-permeable membrane.
  19. The net direction and rate of osmosis depends on both the pressure and concentration gradient.
  20. More the solute concentration, greater will be the osmotic pressure required to prevent water from diffusing in.
  21. Numerically osmotic pressure is equivalent to the osmotic potential, but the sign is opposite.
  22. Osmotic pressure is the positive pressure applied, while osmotic potential is negative.
  23. If the external solution balances the osmotic pressure of the cytoplasm, it is said to be isotonic.
  24. Cells swell in hypotonic solution and shrinks in hypertonic solution.
  25. Plamolysis occurs when water moves out of the cell and the protoplast shrinks away from the walls.
  26. When the cell is placed in an isotonic solution, there is no net flow of water inside or outside the cell.
  27. Water diffuses into the cell causing the cytoplasm to build up a pressure against the wall, which is called turgor pressure.
  28. The turgor pressure is ultimately responsible for enlargement and extension of growth of cells.
  29. Imbibition is a special type of diffusion when water is absorbed by solids-colloids-causing them to enormously increase in volume.
  30. Absorption of water by seeds and dry wood are examples of imbibition.
  31. The movement of a molecule across a typical plant cell takes approximately 2.5 seconds.
  32. The movement of water exclusively through the intercellular spaces and the walls of cells occur through apoplastic pathway.
  33. During symplastic movement, the water travels through the cells- their cytoplasm; intercellular movement of water is through the plasmodesmata.
  34. Symplastic movement may be aided by cytoplasmic streaming.
  35. Most of the water flow in the roots occurs via the apoplast.
  36. The endodermis is impervious to water because of a band of suberised matrix called the casparian strip.
  37. Mycorrhiza is a symbiotic association of fungi with root system of higher plants.
  38. Pinus seeds cannot germinate and establish without the presence of mycorrhiza.
  39. Various ions from the soil are actively transported into the vascular tissue of the roots, water follows and increases the pressure inside the xylem, this positive pressure is called root pressure.
  40. Water loss in its liquid phase from plants in known as guttation.
  41. Root pressure does not account for the majority of water transport; most plants meet their need by transpiration pull.
  42. Water is mainly pulled through the plant, and that the driving force for this process is transpiration from the leaves, this is referred to as cohesion-tension-transpiration pull model for water transport.
  43. The evaporative losses of water by plants occur mainly through the stomata in the leaves.
  44. The opening of the stomata is also aided due to the orientation of the microfibrils in the cell walls of the guard cells.
  45. Cellulose microfibrils are oriented radially rather than longitudinally making it easier for the stoma to open.
  46. The inner cell wall of each guard cell, towards the stomatal aperture is thick and elastic.
  47. Usually the lower surface of a dorsiventral leaf has greater number of stomata while in an isobilateral leaf they are about equal on both surfaces.
  48. Attraction of water molecules to polar surface such as the surface of tracheary elements is called adhesion. Whereas mutual attraction between water molecules is called cohesion.
  49. Measurements reveals that the forces generated by transpiration can create pressure sufficient to lift a xylem sized column of water over 130 meters high.
  50. Most minerals enter the root by active absorption into the cytoplasm of epidermal cells
  51. Transport proteins of endodermal cells are control points, where a plant adjusts the quantity and types of solutes that reach the xylem.
  52. The root of endodermis, because of the layer of suberin, has the ability to actively transport ions in one direction only.
  53. Food, primarily sucrose, is transported by the vascular tissue phloem from source to sink. Usually the source is understood to be that part of the plant which synthesizes the food, i.e., the leaf, and sink, the part that needs or stores the food.
  54. The accepted mechanism used for the translocation of sugars in the form of sucrose from source to sink is called the pressure flow hypothesis.
  55. The sugar enter in the form of sucrose into the companion cell and then into the living phloem sieve tube cells by active transport.
  56. Phloem sap is mainly water and sucrose but other sugars, hormones and amino acids are also transported through phloem.
  57. Elements most readily mobilized are P, N , K etc. while some elements like Ca are not remobilised.
  58. C4 plants are twice as efficient as C3 plants in terms of fixing carbon because they loses only half as much water as a C3 plant for the same amount of CO2 fixed.