Transpiration Virtual Lab

Stomatal opening

1. Potassium ions move into the vacuoles. 2. Water moves into the vacuoles, following potassium ions. 3. The guard cells expand. 4. The stoma opens.

Stomatal closing

1. Potassium ions move out of the vacuole and out of the cells. 2. Water moves out of the vacuoles, following potassium ions. 3. The guard cells shrink in size. 4. The stoma closes.

Which label line identifies the tissue that functions in water transport?

2

Which line indicates a guard cell?

4

By now you should have the basic equation for photosynthesis fixed in your memory! Just to be sure, type it in here:

6CO2 + 6H2O → C6H12O6 + 6O2 or 6CO2 + 12H2O → C6H12O6 + 6O2 + 6H2O

What property of water accounts for the fact that molecules of water "grab" the walls of the thin xylem vessels?

Adhesion. In adhesion, polar water molecules adhere (hold on) to the surface of a material that is polar; an example is water droplets clinging to the inside of a glass. If water is contained inside a thin capillary tube, this tendency to adhere will allow the water to move a short distance up the tube. This is the property of water that is demonstrated in the formation of a meniscus in a burette or pipette. Because xylem vessels are so thin, water moves up inside them a short distance simply by adhesion.

Which condition would result in the higher rate of transpiration: breezy conditions or still air?

Breezy conditions. Breezy conditions would increase the rate of evaporation of water from the surface of the leaves, lowering the water potential, and resulting in more rapid evaporation. However, if the plant is subjected to very high wind movement, the stomata may actually close, which prevents water loss.

Water molecules pull each other like beads on a string; as one molecule is evaporated through a stoma, another is pulled up. What property of water is demonstrated here?

Cohesion. In cohesion, water molecules stick to other water molecules. This is made possible by hydrogen bonding.

Which condition would result in the higher rate of transpiration: humid environment or dry environment?

Dry environment. A dry environment would result in the higher rate of transpiration because the water potential in the surrounding air would be lowest, resulting in more rapid evaporation.

Several factors account for the movement of water up xylem vessels. Which single factor is most important in pulling water toward the top of a tall tree?

Evaporation of water through stomata

All of the following enhance water transport in terrestrial plants EXCEPT:

K+ being transported out of the guard cells

Which condition would result in the higher rate of transpiration: light or dark?

Light. Light conditions would generally result in the higher rate of transpiration. Stomata are generally open in the light, and solar energy increases evaporation.

If guard cells in a plant were deficient in K+, which of the following would be most likely to occur?

Photosynthesis would decrease.

Under conditions of bright light, in which part of a transpiring plant would water potential be lowest?

Spongy mesophyll of the leaves

Which condition would result in the higher rate of transpiration: hot environment or warm environment?

The answer to this question depends somewhat on the type of plant and the situation for which it is adapted. In general, however, unless a plant is specially adapted for hot conditions, the rate of transpiration will drop in a hot environment because heat stress may cause the stomata to close, which conserves water. This is why you do not want to shine a 100-watt light bulb directly on your experimental plant!

Place the following in order (list the letters), from highest water potential to lowest water potential, under normal conditions. a. Mesophyll of leaves b. Outside air around leaf c. Spaces around roots d. Inside the xylem vessels

The correct sequence is c,d,a,b. Recall that water moves from regions of higher water potential to regions of lower water potential. Therefore, the region of lowest water potential is at the farthest end of the transpiration pathway.

Name tissue type A and describe its function.

The correct tissue type: epidermis. The correct function: protection.

Name tissue type D and describe its function.

The correct tissue type: parenchyma. The correct function: store food.

Name tissue type B and describe its function.

The correct tissue type: phloem. The correct function: transport food.

Name tissue type C and describe its function.

The correct tissue type: xylem. The correct function: transport water.

What type of environment would result in the greatest rate of transpiration?

Warm, light-breezy conditions

What tissue is indicated by label line 1?

epidermis

Which of the following pairs is correctly matched?

epidermis: protective outer covering of plant body

Which type of cells are indicated by label line 4?

parenchyma

What tissue is indicated by label line 2?

xylem

Which type of cells are indicated by label line 2?

xylem