Water Movement in Plants

Forces that move water in plants Osmosis - allows water to enter cells

Forces that move water in plants Capillary Action - forces that allow water to be drawn up through xylem tubules (cohesion, surface tension, adhesion)

Forces that move water in plants Transpiration - process by which plants lose water vapor through the leaves

Transpiration a) water enters leaf through veins b) water leaves xylem & enters mesophyll c) water evaporates = vapor d) water vapor diffuses into airspaces of mesophyll e) water vapor passes out into air through stomata *more water moves in to replace lost water = continuous process that helps pull water through the plant and cool the leaves **over 90% of water taken in by plants is lost through the process of transpiration

Rate of Transpiration Controlled by guard cells & stomata -guard cells take in water through osmosis = increased turgor pressure (guard cells swell & open) -guard cells lose water through osmosis/evaporation (guard cells shrink & close)

Rate of Transpiration Stomata are open during the day - take in carbon dioxide for photosynthesis; stomata close at night but on a hot, dry day, they may close to prevent excessive water loss

Environmental Factors Affecting Water Loss Humidity - rate of water loss decreases when humidity levels are high

Environmental Factors Affecting Water Loss Wind - rate of water loss increases during windy conditions (evaporation rate increases)

Environmental Factors Affecting Water Loss Temperature - rate of water loss increases as temperature goes up due to the increased rate of photosynthesis

Environmental Factors Affecting Water Loss Light - rate of water loss increases as light levels increase; due to increased rate of photosynthesis

Leaf Modifications to Prevent Water Loss Smaller leaves - reduced surface area limits water loss (curled leaves, needles, or spines)

Leaf Modifications to Prevent Water Loss Succulents - thick fleshy leaves that store water (aloe vera, jade, etc.)

Leaf Modifications to Prevent Water Loss Stomata only on bottom of leaf - protects it from exposure to direct light = reduced evaporation rates

Leaf Modifications to Prevent Water Loss Hairs - trap moisture, help prevent water loss

End