Plant Gaseous Exchange and Stomata

Plant Gaseous Exchange

• Plants require oxygen for cellular respiration, like other organisms.
• Unlike animals, plants make their own food (photosynthesis).
• Efficient photosynthesis requires gas exchange.
• Plants exchange oxygen and carbon dioxide through stomata, pores located on the lower epidermis of leaves.

Stomata

• Stomata are pores on the lower leaf epidermis.
• Each stoma has guard cells that control opening/closing by changing shape.
• Guard cells have chloroplasts for photosynthesis.
• Stomatal opening/closing depends on turgor pressure.
• Turgor pressure is controlled by potassium ion (K+) uptake and sucrose concentration.
• Potassium ion (K+) uptake changes water potential, causing water to move by osmosis between guard cells and the environment.
• Sucrose concentration in guard cells affects water balance; photosynthesis increases sucrose during the day, converting it to starch overnight.

Stomatal Opening

• Potassium ions (K+) move into guard cells.
• Increased solute potential draws water in by osmosis.
• Turgid guard cells bow outwards, opening the stoma.

Stomatal Closing

• Potassium ions (K+) move out of guard cells.
• Decreased solute potential causes water loss by osmosis.
• Guard cells become flaccid, causing stoma to close

Water Deficiency in Plants

• Adequate water supplies maintain guard cell turgor for stoma opening.
• Lack of water causes guard cells to lose turgor, closing stomata to prevent water loss.
• Stomata close to conserve water during periods of water deficiency.