Water Movement In Plants

Forces that move water in plants

• Osmosis - allows water to enter root cells

• 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

a) Water enters leaf through veinsb) Water leaves xylem & enters mesophyllc) Water evaporates from wet cell surface = vapord) Water vapor diffuses into airspaces of mesophylle) Water vapor passes out into air through stomata

Forces that move water in plants

Transpiration (continued)

*more water moves in to replace lost water = a continuous process that helps pull water through the plant & cools the leaves

**Over 90% of water taken in by plants is lost through the process of transpiration

Rate of Tranpiration• 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 (cont.)

• 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

• Wind - rate of water loss increases during windy conditions (evaporation rate increased)

Environmental Factors Affecting Water Loss:

• Temperature - rate of water loss increases as temperature goes up due to increased rate of photosynthesis

• Light - rate of water loss increases as light levels increase; due to increased photosynthsis

Leaf Modifications to Prevent Water Loss

• Smaller leaves - reduced surface area limits water loss (curled leaves, needles, or spines)

• Succulents - thick, fleshy leaves that store water (aloe vera, jade)

Leaf Modifications to Prevent Water Loss

• Stomata only on leaf bottom - not exposed to direct light = reduced evaporation rates

• Hairs - trap moisture, help prevent water loss

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