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Lab 9: Transpiration

Pedro De La Rosa AP Biology A2

Dennis Dagounis

on 18 April 2013

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Transcript of Lab 9: Transpiration

Lab 9: Transpiration By Pedro De La Rosa Background Transpiration- the major mechanism that drives water movement in a plant
Transpiration is made possible by adhesion and cohesion caused by hydrogen bonds Hydrogen Bonds •Hydrogen bond- weak bonds between water molecules that give water its special properties
•Formed by the attraction between the slightly negative oxygen atom and the slightly positive hydrogen bonds
•A water molecule can form up to four hydrogen bonds The Process • The water from transpiration is absorbed by the roots and passes through the root tissues into the xylem
• It is pulled up through the xylem by the tug of transpiration
Water molecules cling together through cohesion and to the walls of the xylem through adhesion
• As more water transpires from the leaves, the same amount of water is also pulled up to fill the lost water
• The pull of the water continues to the leaves where the water evaporates through the stomata • Stomata-the pores in the epidermis of leaves,
• Water vapor leaves and carbon dioxide for photosynthesis enters
• Most of the hundreds of stomata are located in the lower epidermis to reduce water loss because of the increased protection from solar radiation
• Guard cells-surround each stomata and help in regulating transpiration rates by opening and closing
• As the guard cells become turgid they open, while the opposite occurs when they become flaccid Experiment 4 plants of the same type
4 ring stands with 2 clamps each
4 calibrated pipettes to measure water loss
4 clear plastic tubing
air tight sealing agent
1 bag
1 water spray bottle
1 fan
1 lamp
1-4 small tubs Construct 4 potometers, each will represent a plant in a different environment
Control: no changes to the already established setup
Windy environment: potometer with an activated fan directed towards it
Humid environment: the plastic bag will cover the potometer and a spray of water will be applied inside the bags enclosed environment
Bright environment: the lamp will be directed towards the potometer Procedure • As soon as an environment is established be sure to check the level of water in the pipette and set a timer for 30 minutes
• After every 3 minutes measure the drop in water level and record Stomata to identify the effects of environmental conditions on rates of transpiration Purpose: Materials: Setup Potometer Construction 1. Fill pipette and tubing with water and attach them to each other, make sure there are no leaks
2. Insert cut stem into tubing underwater, keep leaves dry and make sure the fir is air tight
3. Bring tubing and pipette above water and stabilize as shown
This experiment requires you to do this procedure three times Comparing Data To adequately compare data, data must be in mL/m
First measure the total mass (grams) of the leaves from which the data came from
Then divide the value by the mass of 1 cm of leaf
Next divide the value by 10,000 cm /m
Do this for each data set separately 2 2 2 2 Expected Results Need more help? Mr. Anderson knows all. Light Wind Humidity The humid environment will have the slowest transpiration rate out of all of the tests
In an humid environment, there is a higher water potential in the atmosphere
It is the low water potential environment that drives transpiration The windy environment will have a higher transpiration rate compared to the control
In a windy environment water molecules are more likely to blown off of the leaf and into the atmosphere The environment affected by light will have the highest rate of transpiration out of all of the tested conditions
When light is directed towards water, it heats up and evaporates more quickly What are some other experiments we could test using the same idea? example: test different types of plants, CAM, C4 or C3 plants. Homework: using the same idea and principles, create another experiment w could test. Include, materials, lab set up, and expected outcomes!
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