Importance of Water and Its Properties-Transpiration too PT2

Transpiration

from the leaves produces a negative water potential gradient that causes water to move upwards from the roots through the xylem vessels to the leaves, facilitating nutrient transport.

Transpiration

From the leaves produces a negative water potential gradient that causes water to move upwards from the roots through the xylem vessels to the leaves, facilitating nutrient transport.

-Passive process, no ATP needed

-Energy driving is the difference in water potential between the soil and the plant/atmosphere.

Excessive Transpiration

water loss more than water uptake → slow growth or kill the plant (dehydration)

Diagram of a stomata

Stomata 90% of transpiration

Cuticle and lenticel

Stomatal transpiration

• Evaporation of water from the cell wall surfaces bordering the intercellular (air) spaces of the leaf

• Diffusion of this water vapor from the intercellular spaces into the atmosphere through the stomata

Stomata

All aboveground parts of the plant body, more in leaves

Density depends on the specie and surface of the leaf.

Closing Stomata prevents:

Loss of water

Entry of CO2

Stomata movement → changes in turgor pressure in the guard cell

What is the main signal in controlling stomatal movement?

• In well watered plants light is main signal in controlling stomatal movement

chloroplasts capture blue light→ cascade → ATP pumps → H moves out of the cell → from inside to outside of the cell → negative gradient → K+ moves → uptake in the morning

Stomata movement → changes in turgor pressure in the guard cell
What type of movement is turgor pressure?

passive osmotic movement of water in or out of the guard cells (created by active solute transport)

Stomata movement → changes in turgor pressure in the guard cell
Stomatal opening is associated with what element in the morning?

Stomatal opening associated with K+ uptake in the morning: sucrose content determines changes in the afternoon.

Why is structure of the guard cells important for stomatal movement?

There is a radial orientation of cellulose microfibrils in the:

guard cell

Environmental factors affecting the rate of transpiration

Temperature: water evaporation doubles every 10 C

Humidity: vapor pressure difference between the intercellular spaces and the surface of the leaf.

Air currents: wind blows away the water vapor from the leaf surfaces affecting the vapor pressure differences.