<
L earning Objective 11 
 
 
11. Describe briefly the water pathway in plants, where water enters, travels and exits. Explain water stress. Define TRANSPIRATION and its impact on the environment.

I. PATHWAY OF WATER in Plants. (See Fig. 11-A).

A. Water travels from soil into the vascular system of the roots.

B. It continues into the stem and into the leaf's vascular system.

C. Water continues to move into the leaf, with most of the water "escaping" through stomates.

 
 
II. TRANSPIRATION.
A. The escape of water from stomates is called TRANSPIRATION.

It is the normal loss of water from the plant through the stomates of the leaves.

B. About 1% of the entering water is used in photosynthesis, and 99% is lost by transpiration.

During the growing season, a medium-sized tree can lose 1 to 2 thousand gallons of water a day by transpiration!

C. Water molecules are linked to each other inside the plant and transpiration provides an important force in "pulling" water molecules up through the plant.

D. Transpiration by many plants, as in a forest, contributes massively to generation of rainfall. (In order to demonstrate that you fully understand this idea, answer the questions below.)

1. Hawaiians had a phrase for it, roughly translated: The rainfall that follows or is, where there is forest .

2. Conversely, what is the effect of removing plants (deforestation) from an area?  What happens to rainfall?

3. By transpiration, not only rainfall is assisted, but there is a significant cooling effect as water leaves the plant by evaporation. What is happening to both the world's temperature and rainfall as massive deforestation is taking place?

4. What is the effect of planting trees around your house, as compared to having large areas of gravel, blacktop or concrete surrounding your house?

5. Do plants around your house cool just by shading or is there an additional cooling effect happening?

III. WATER STRESS OCCURS any time when more water is being lost from the leaves than is being taken in from the soil. Plants wilt under high water stress.
A. Some factors causing water stress are drought, high temperatures and strong winds.

B. What happens to the plant under water stress? Stomates may close if too much water escapes. As a result, little carbon dioxide enters the leaf and photosynthesis stops.

C. As a further result, less sugar is formed by the plant and it has less growth. Water stress results in less growth, less reproduction of a plant.

Have you noticed that a plant not watered regularly will grow more slowly than one that is?

 
Click here to leave your comments and suggestions.
 
Learning Objectives
[1 ] [2 ] [3 ] [4 ] [5 ] [6 ] [7 ] [8 ] [9 ] [10 ]
[11 ] [12 ] [13 ] [14 ] [15 ] [16 ] [17 ] [18 ] [19 ] [20 ]
[21 ] [22 ] [23 ] [24 ] [25 ] [26 ] [27 ] [28 ] [29 ] [30 ]
[Learning Objectives Numerical Index]
[Learning Objectives Descriptive Index]
[Main Menu]