16. Opening and closing stomata

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4 Terms

1
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Why do guard cells change shape?

Turgor -> when water enters guard cell by osmosis it swells

2
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What happens when water leaves guard cell?

Becomes flaccid, closing stomatal pore

3
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Describe the stomatal opening

  1. In light, chloroplasts in guard cell make ATP by photosynthesis

  2. Potassium ions (K+) pumped by AT into guard cell

  3. Stored starch converts into malate ions

  4. Malate ions and potassium ions lower WP

  5. Water enters by osmosis

  6. Guard cells become turgid and curve apart -> Outer walls thinner than inner walls

  7. Opens stomatal pore, allowing gas exchange

4
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Describe stomatal closing

  1. When light intensity too low for photosynthesis, potssium ions diffuse down conc. gradient out of guard cell

  2. Malate ions converted back into starch (condensation reaction)

  3. WP of guard cells increase

  4. Water leaves guard cells by osmosis

  5. Guard cells become flaccid, closing stomatal pore preventing gas exchange -> reduces water loss