Ap Lab 9 Transpiration 133c62

AP BIO LAB REPORT: Transpiration Elioth Gomez March.29.2012 Pd.02

Transpiration: Intro/Purpose: The transport of water is controlled by water potential. Water will always move from an area of high water potential to an area with low water potential. This water potential is affected by pressure, and solute concentration. Water moves into the plant through osmosis and creates a hydrostatic root pressure that forces the water upward however; the main force in moving water is the upward pull due to transpiration. Root pressure and transpiration pull together can offset the pull of gravity. This pull is increased by water’s natural properties such as adhesion and cohesion. Transpiration decreases the water potential in the stele causing water to move in and pull upward into the leaves and other areas of low water potential. When stomates are open, water transpires from higher water potential in the mesophyll spaces to lower potential in the air. Loss of water through transpiration can be facilitated by the opening and closing of the stomata depending on environmental conditions. There are three types of cells in plants: parenchyma, sclerenchyma, and collenchyma. Parenchyma cells are the most abundant and are not specialized. They are found in the mesophyll of leaves, the flesh of fruits, the pith of stems, and the root and stem cortex. Sclerenchyma are elongated cells that make up fibers. They have thick secondary walls and the protoplasts often die as they grow older. They are used for and are found in vascular tissue. Collenchyma cells are living at maturity and have a thickened secondary wall. Hypothesis: If environmental conditions are related to the rate of transpiration, then an increase in light will result in an increase of the rate of transpiration. Materials: In this lab you will need bean seeding, potometer setup, syringe, plastic bag, petroleum jelly, spray bottle, ring stand, ring stand clamps, flood light, electric fan, and a balance. Method (Procedure): 9A: Transpiration Placed the tip of the pipette in the plastic tubing and they were submerged in a tray of water. Water was drawn into the pipette and tubing until no bubbles were left. Cut the plant stem underwater and inserted into the plastic tubing. Use petroleum jelly immediately around the tube edging to form an airtight seal around the stem. The tubing was bent into a "U" shape and two clamps were used on the ring stand to hold the potometer in place. The potometer was allowed to equilibrate for ten minutes. The plant was exposed to a fan, which was placed one meter away and set on low speed. The time zero reading was recorded and then it was continually recorded every 10 minutes for 30 minutes. Then repeat exposing it to heat, light, humid and again without

any extreme environmental condition this will act as the control. After the experiment, all the leaves were cut off the plant and massed and the surface area was estimated by laying the leaves to be measured on a 1-cm grid and trace their outlines. Then count the number of square centimeters. Estimate the area of the partial squares Data:

Class Potometer Readings Table 1 Reading Setup

Initial

10 min.

20 min.

30 min.

1 control

0

.06

.12

.19

2 light

0

.14

.22

.33

3 wind

0

.01

.02

.034

4 humid 5 heat

0 0

.02 .08

.03 .16

.05 .24

* The table above shows the amount of water lost in ml over a 30 minute period for four environmental conditions light, wind, humidity, and heat the fifth is the control .

Class leaf surface area Table 2 Setup 1 control 2 light 3 wind 4 humid 5 heat

Leaf surface area 44cm2 29cm2 39cm2 25cm2 23cm2

* This table shows the surface area of the leaves experimented on for each condition.

Enviormental conditions VS Time 0.35 Control

0.3

Light

Water loss

0.25

wind

0.2

Humid Heat

0.15

Linear (Control )

0.1

Linear (Light)

0.05

Linear (wind) Linear (Humid)

0 -0.05

0

10

20

30

40

Linear (Heat)

Time (min)

* This graph illustrates the water loss for each condition over a 30 minute period.

Analysis: 1. Determine the plants rate of transpiration per minute for each of the enviromental conditions. Condition Control Light Windy humid Heat

Total water loss after 30 min .19 .33 .034 .05 .24

Leaf surface area in cm2 44 29 39 25 23

Leaf surface area in m2 .0044 .0029 .0039 .0025 .0023

Rate of transpiration 1.43 3.79 2.9 .67 3.47

Control 44/10000=.0044/.19=42.9/30 min = 1.43 = the rate of transpiration for the control 2. Name three functions of transpiration. - Transpiration cools plants and enables the flow of mineral nutrients and water from roots to shoots. 3. How is the molecular structure of water significant to the transport of water in plants? - Water is a polar molecule, with the region around the oxygen atom having a negative charge and the regions around the hydrogen atoms having a positive

charge, the negative regions on one molecule are attracted to the positive regions on another, and the molecules form hydrogen bonds. When water travel up the plant through xylem, the hydrogen bonds lets them to have a cohesive reaction, wich is when a water molecule is pulled up the xylem, the the water molecule is also pulled up and adhesion allows the water molecules to stick to the sides of the xylem tubs. 4. Explain the purpose of each of the followinf with regard to transpiration: Cuticle- allows the cell to retain water on the upper side of the leaf when expossed to the sun. Guard cells- allow the exchange of CO2 and O2 to happen Leaf hairs- protect the tissue when it is hot and decrease the transpiration rate. 5. place the folloing in the proper colum Collenchyma

Parenchyma

Found in stems Photosynthetic cells Thick cell walled, irregularly Thin walled, many sided shaped cells Leaf ground tissue

Sclerenchyma Dead at maturity Contain lignin Found near vascular bundles

6. You came in to the class one morning and one of the classroom plants was looking wilted and unhealthy. You watered the plant ans a couple hours later, the plants appeared rigid and healthy. What happened. - Water is absorbed by the roots, cause the roots pressure. Water from the roots enters the xylem where it is pulled up by root pressure and transpirational pull to the leaves, this causes the plant to become turgid. 7. Creat a Venn diagram comparing bryophytes and tracheophytes.

Bryophytes

Similarities

Tracheophytes

• No vacular tissue • Spores • small • sperm need to swim to the egg • lack true root , stems and leaves • moist areas

• Alternation of generations • chlorophyl • photosynthis • waxy cuticel • cell walls • store food as amylose

• vascular tissue • xylem and ploem • big • pollen • heterospores • Wider rang of envierments

8. Do you think the number of stomata on the underside of a leaf is more, less, or the same as on the upper surface of a leaf? Design an experiment to determine the answer. - Obtain a leaf and look at the upper side under a micscope and compare the number to the number on the under side. 9. One of the following statement is not true. Decide which one is false and explain your answer. - The guard cells of desert plants often close during the daytime and open at night to conserve water. Because during the day the heat would increase the rate of transpiration and would cause the cells of the plants to wither, thus if CO2 and O2 is exchanged at night water can be retained. 10. When you receive a bouquet of flowers , it is recommended that you cut ta couple of inches off of the stems before placing them in a vase. Why do you think this is. - To cut the stem will allow the xylem and phloem to be exposed to water and minerals esier. 11. Create a concept map about transpiration:

Transpiration

Roots absorb water

water up xylem

Xylem

Water reaches leaves

Root pressure

Transpirational pull

Guard cells open

Stomata exchang O2 and CO2

Water is rleased and evaporates.

Discussion and Conclusion: If environmental conditions are related to the rate of transpiration, then an increase in light will result in an increase of the rate of transpiration. The hypothesis was ed by the data collected. After 30 minutes the leaves subjected to the intense light loss .33 ml of water. Transpiration in plants is controlled by water potential. This change in water potential in leaves causes a gradient by which water can be moved upward. When the water potential of the air increased by the mist and plastic bag creating a humid condition, less water evaporated from the leaves, decreasing the water potential between the root and stem, this decreased the transpiration pull. From the data .05 ml were lost the lowest when compared to the rest of the conditions. From the data we can conclude that in humid environments the stomata of plants don’t close and can do photosynthesis most of the time during the day. Wind, heat, and intense light increase the amount of water transpired by plants. Heat caused the air to have lower water potential, which in return caused water to move from the leaves out and evaporate. Heat over 30 minutes lost .24 ml of water. Wind causes an increase in evaporation causing more water to leave the plant. Wind over 30 minutes had .34 ml loss of water. Finally light caused more photosynthesis to occur, thus more CO2 was needed so the stomata had to remain open and thus more water left the leaves. Over a 30-minute period the leaves under the light conditions loss .33ml of water. The control plant should have had normal rates of transpiration.