Transpiration and translocation

Phloem:

• Are tubes that act like the plant's food delivery system. 

• They're made of living cells with tiny pores that allow food substances to flow through. 

• These tubes transport food, mainly dissolved sugars made in the leaves, to the rest of the plant. 

• This food is used for immediate growth or stored for later.

Xylem 

• Are tubes that act like the plant's water and mineral highway. 

• They're made of dead cells joined end to end with a hollow center. 

• These tubes carry water and minerals from the roots up to the leaves. 

• This movement of water is called the transpiration stream.

Transpiration

Transpiration is the loss of water from the plant, mainly through the leaves. 

It happens when water evaporates and diffuses out of the plant's surface. 

This evaporation creates a water shortage in the leaf, so more water is drawn up from the roots through the xylem tubes to replace it. 

A plant does not want transpiration to happen but is actually a side effect of the way leaves are adapted for photosynthesis. 

The stomata, tiny pores in the leaves, allow gases to exchange, but they also allow water to escape.

Rate of transpiration

Transpiration, is affected by several factors:

• Light Intensity: More light means more photosynthesis, which requires open stomata for gas exchange. This leads to increased transpiration.

• Temperature: Warmer temperatures increase the energy of water molecules, making them more likely to evaporate.

• Air Flow: Stronger winds carry away water vapor, increasing the diffusion gradient and promoting transpiration.

• Humidity: Higher humidity means more water vapor in the air, reducing the diffusion gradient and slowing transpiration.

You can estimate transpiration rate by measuring the uptake of water by the plant. 

This is because water uptake is closely related to water loss through the leaves. 

To measure water uptake, set up a potometer, a device that measures the movement of an air bubble in a capillary tubes.

Guard cells