WaterFrom roots to leaves

Transpiration

Transpiration is the process of water movement through a plant and its evaporation as water vapor from aerial parts, such as from leaves but also from stems and flowers.

Guard cells control the opening and closing if the stomata through which the water vapor leaves and carbon dioxide can enter.

As the water evaporates it must be replaced by other water molecules that move by capillary action from the roots through the stem to the leaves

Factors that Affect Transpiration Rate

Light - heats up leaf, opens stomata increase rate

Humidity - water vapor in the air so when high there is decreased rate

Wind -removes humid air from the outside of stoma and the rate increases

Temperature - increases evaporation and also transpiration rate

Soil water - keeps the turgor pressure in the cells so if less water, less turgor and therefore the guard cells close and the rate is decreased

Carbon dioxide - a high presence around the stomata cause closure of the stomata and less transpiration

Discuss xerophyte adaptations which

allow the plant to live in dry arid climates.

8 points

Guard cells Allowing water vapor out and carbon dioxide in - must be

controlled

StomataSince carbon dioxide must get in for photosynthesis, the guard cells can only close

Guard cell walls are not the same as there is a thicker wall around the stoma and a thinner wall on the opposite side of the cell

With the increase of water and turgor pressure in the cell it swells and bends toward the thinner wall, opening the stoma. Less water in the soil can cause less turgor pressure and the cell shrinks closing the stoma. No transpiration when closed.

Potassium ions control the gain or loss of water by the guard cells. Proton pumps in the plasma membrane are triggered by light from the blue part of the spectrum.

The proton pumps trigger an uptake of potassium ions by the guard cell. Now there is an imbalance of solute sand water will diffuse into the cell

Abscisic acid is a hormone that will cause the departure of these ions and thus the reduction of water and turgor pressure

Explain how water is carried by the transpiration stream, including the structure of xylem vessels, transpirational pull, cohesion, adhesion, and evaporation

Outline the role of phloem in active translocation of sugar (sucrose) and amino acids from source (photosynthetic tissue and storage organs) to sink (fruit, seeds, roots)

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