Transpiration, Respiration and Water Uptake

Floral Careers Plant Propagation

Transpiration Defined

• The loss of water vapor through open leaf stomata.

Transpiration

• How does transpiration work?• On sunny, warm days the sun warms up the leaf

surfaces.• The water in the cells of a leaf begins to

evaporate.

Transpiration• Water vapor collects in the spongy mesophyll

tissue of the leaf.• The water vapor moves out of spongy mesophyll,

through the open stomata, and into the drier air surrounding the leaf.

• As water evaporates from the spongy mesophyll, new water molecules are delivered to the leaf through the xylem in leaf veins.

Rate of Transpiration

• The rate of transpiration is affected by the following 3 things:

• Humidity; during dry, less humid days the rate of transpiration increases.

• Temperature; the rate of transpiration is greater on hot days than on cooler, cloudy days.

• Wind; the rate of transpiration is greater on windy days than calmer days.

Water Movement

• There are 3 main factors that affect the movement of water through plants. They are:

• Osmosis• Transpiration• The properties of water molecules

Root Hairs Osmosis• Water enters root hairs by

osmosis.• Water quickly moves

through the root hairs and into the xylem.

• Transpiration “pulls” or “sucks” water up stems in much the same way that you pull liquid up through a straw.

• Water molecules (H2O) are electrically charged.

• Because of this water molecules stick to one another like little magnets.

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Respiration• Compliments photosynthesis.• Inputs:

– sugar– oxygen

• Outputs:– water– carbon dioxide– heat– chemical energy (used in plant growth)

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