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Leaf Tissue and Gas Exchange

Leaf Tissue and Gas Exchange. Dermal Tissue or Epidermis. Stomata are tiny openings on the underside of the leaf Stomata are formed in the dermal tissue or epidermis Stomata regulate the movement of gases in and out of the cell.

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Leaf Tissue and Gas Exchange

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  1. Leaf Tissue and Gas Exchange

  2. Dermal Tissue or Epidermis • Stomata are tiny openings on the underside of the leaf • Stomata are formed in the dermal tissue or epidermis • Stomata regulate the movement of gases in and out of the cell

  3. Carbon dioxide can therefore enter or leave the leaf by diffusion at any time • The direction of the movement of these gases depends on their concentration gradients • The guard cells that surround the stomata control whether they are open or closed

  4. Light striking the leaf stimulates the guard cells to accumulate potassium ions by active transport (requires ENERGY to move from [low] to [high] ) • As a result the number of particles present in the guard cells increases, water enters by osmosis, and the guard cells swell up • Swelling up causes the guard cells to bulge outwards and open the stomata • Look at it: http://www.youtube.com/watch?v=IlmgFYmbAUg

  5. Guard cells also function to protect the leaves from losing too much water • Because all gases must dissolve in water before they pass across the cell membranes, when they pass through, water is lost • This water loss out the stomata is known as transpiration

  6. If the stomata were open continuously water would be continuously being lost, therefore the guard cells are very important. • The number of stomata in the epidermis is sensitive to environmental conditions • In hot dry climates with low humidity, plants have adapted to having fewer stomata, so they lose less water through transpiration

  7. In places of high humidity water loss is not a problem and plants may have many stomata

  8. Ground tissue • Between the upper epidermis and the lower epidermis of the leaf there are specialized ground tissues called mesophyll.

  9. Mesophyll types • Palisade tissue cells- are just below the upper epidermis which are responsible for holding chloroplasts and therefore photosynthesis, they are tightly packed together

  10. Spongy tissue cells- loosely spaced mesophyll cells in the leaf; the increased distance between cells allows for the primary function of these cells; gas exchange by diffusion

  11. Vascular tissue • The xylem and phloem tissues are bunched together like a handful of straws in a structure called a vascular bundle

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