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Chapter 30.4

Chapter 30.4. How Do Stems and Leaves Conserve Water?. AP Biology Spring 2011. Water Loss. Most of water (>90%) absorbed by plant is lost due to evaporation out at the leaves Only a small amount of water is available to maintain the plants metabolism . Water-Conserving Cuticle.

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Chapter 30.4

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  1. Chapter 30.4 How Do Stems and Leaves Conserve Water? AP Biology Spring 2011

  2. Water Loss • Most of water (>90%) absorbed by plant is lost due to evaporation out at the leaves • Only a small amount of water is available to maintain the plants metabolism

  3. Water-Conserving Cuticle • Cuticle: translucent, water-impermeable layer of waxes, pectin, and cellulose fibers embedded in cutin • Secreted from epidermal cells which cover the outer surfaces of the plant

  4. Water-Conserving Cuticle • Cuticle does not prevent sunlight from entering the leaf • Cuticle does restricts water loss, the inward diffusion of CO2, and outward diffusion of O2

  5. Controlled Water Loss of Stomata • Stomata: tiny, collapsible openings at the plant epidermis that regulate the passage of water, carbon dioxide, and oxygen • Guard Cells: a pair of these controls the opening and closing of the stomata

  6. Controlled Water Loss of Stomata • Stomata open and close in response to environmental cues • Open stomata allow carbon dioxide to enter • BENEFIT • Open stomata allow water to be lost • DETRIMENT

  7. Controlled Water Loss of Stomata • When plants are exposed to sunlight: • Potassium and water move into the guard cells • Causes guard cells to swell: Turgor Pressure • Stomata of most plants are open during the day and closed during the night

  8. Controlled Water Loss of Stomata • CAM Plants • Cacti • Adaptations allow stomata to open at night when cells of these plants fix carbon dioxide • Stomata close during the day to conserve water in arid habitats

  9. Controlled Water Loss of Stomata • Water-stessed plants close their stomata in response to abscisic acid • Absicsic acid: controls calcium ion entry into guard cells • Pollution: • Can clog stomata and damage them so that they remain permanently closed

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