Transpiration Lab Outline

Transpiration Lab

Introduction:

Paragraph 1: Restate in your own words the objectives of the lab and Problem
To understand how water moves from roots to leaves in terms of the physical and
chemical properties of water and the forces provided by differences in water potential.
-- To understand the role of transpiration in the transport of water within a plant.
-- To understand the structures used by plants to transport water and regulate water movement.
-- To test the effects of environmental variables on rates of transpiration using a
controlled experiment
-- To understand how leaf anatomy and photosynthesis relate to the process of transpiration in vascular plants.
PROBLEM: How do some environmental factors influence the rate of transpiration in mums?



Paragraph 2: Discuss Background Information – Summarize the following in your own words:

The amount of water needed daily by plants for the growth and maintenance of tissues is small in comparison to the amount that is lost through the process of transpiration and guttation. If this water is not replaced, the plant will wilt and may die. The transport up from the roots in the xylem is governed by differences in water potential (the potential energy of water molecules). These differences account for water movement from cell to cell and over long distances in the plant. Gravity, pressure, and solute concentration all contribute to water potential and water always moves from an area of high water potential to an area of low water potential. The movement itself is facilitated by osmosis, root pressure, and adhesion and cohesion of water molecules.

The overall process: Minerals actively transported into the root accumulate in the xylem, increase solute concentration and decrease water potential. Water moves in by osmosis. As water enters the xylem, it forces fluid up the xylem due to hydrostatic root pressure. But this pressure can only move fluid a short distance. The most significant force moving the water and dissolved minerals in the xylem is upward pull as a result of transpiration, which creates a negative tension. The "pull" on the water from transpiration is increased as a result of cohesion and adhesion of water molecules.

The details: Transpiration begins with evaporation of water through the stomata, small openings in the leaf surface which open into air spaces that surround the mesophyll cells of the leaf. The moist air in these spaces has a higher water potential than the outside air, and water tends to evaporate from the leaf surface. The moisture in the air spaces is replaced by water from the adjacent mesophyll cells, lowering their water potential. Water will then move into the mesophyll cells by osmosis from surrounding cells with the higher water potentials including the xylem. As each water molecule moves into a mesophyll cell, it exerts a pull on the column of water molecules existing in the xylem all the way from the leaves to the roots. This transpiration pull is caused by (1) the cohesion of water molecules to one another due to hydrogen bond formation, (2) by adhesion of water molecules to the walls of the xylem cells which aids in offsetting the downward pull of gravity. The upward transpiration pull on the fluid in the xylem causes a tension (negative pressure) to form in the xylem, pulling the xylem walls inward. The
tension also contributes to the lowering of the water potential in the xylem. This decrease in water potential, transmitted all the way from the leaf to the roots, causes water to move inward from the soil, across the cortex of the root, and into the xylem. Evaporation through the open stomata is a major route of water loss in the plant. However, the stomata must open allow the entry of CO2 used in photosynthesis. Therefore, a balance must be maintained between the gain of CO2 and the loss of water by regulating the opening and closing of stomata on the leaf surface. Many environmental conditions influence the opening and closing of the stomata and also affect the rate of transpiration. Temperature, light intensity, air currents, and humidity are some of these factors. Different plants also vary in the rate of transpiration and in the regulation of stomata openings.

Paragraph 3: Briefly Summarize Procedure and Predictions. Bag roots of plants, mass plants for Day 1 reading, put plants in control, fan, light, moist, and dark conditions, record mass every day for five consecutive days. Discuss predictions

Paragraph 4: Discuss how this lab relates to one of the major themes of AP Biology.
* 1. Science as a Process of Inquiry
* 2. Evolution
* 3. Energy Transfer
* 4. Continuity & Change
* 5. Relationship of Structure to Function
* 6. Regulation
* 7. Interdependence in Nature
* 8. Science, Technology & Society

PROCEDURE: Write procedure paragraph form.

1. Water the plants well (saturate) the day before beginning the lab
2. Wrap the root ball of plant in a plastic bag
3. Tie bag around the base of the plant with string so that only the leaves are exposed
4. Remove flowers and buds from the plant before massing.
drop off plant during the lab
5. Write the initial mass of the plant and bag on the plastic bag.
6. Weigh the mass of the plant and the bag each day for the next three days. Write the mass
on the plastic bag for each day so data will not get lost
7. If your plant blooms, be sure any leaves or blooms that fall off are put back in the |
center of the plant to be weighed each day so as not to represent water loss.
8. Write a hypothesis about what you think what will happen based on your knowledge
of transpiration and plants.


Set-up the following treatments:

!"Control = normal light conditions in your room.
!"Fan = place plants about 1-2 meters away from a fan on low. Leaves should not be
rustling as this can cause some plants to close their stomata.
!"Light = put one setup in a classroom window getting more light than the window in
our classroom
!"Moist = place inside a closed garbage bag which contained some initial moisture to simulate
humid conditions
!"Dark = Inside a cabinet

DATA

Include Individual Data Table and Class Table Here – see link

Graph – Show % Change in Mass of Plants for Five Conditions over Five Days (Use a Key – you should have five lines on your graph)

CONCLUSION

First Paragraph: Restate Problem, Objective, Procedure, and Hypothesis Briefly

2nd Paragraph: Compare results to hypothesis. Use Data Tables and Graphs as references. Does it agree with what you know about principles of transpiration? Discuss this here

3rd Paragraph: Errors with lab or inconsistent data. Also discuss ways to Improve Lab

4th Paragraph: Relate Lab to theme of biology and importance in Society!