1. The Effect of plants on the concentration of Oxygen in water A student wanted to conduct an experiment. She gathered 2 sprigs of Elodea and 3 test tubes. She filled each of the test tubes 2/3 full of water and Placed a sprig of elodea in test tube 1 and test tube 2. She did not place a spring of Elodea in test tube 3. Next, she placed each test tube in a container and placed the containers in the sunlight. She came back 2 hours later and used an oxygen sensor to measure the amount of Oxygen gas present in the container. On a separate piece of paper, answer the following in complete sentences: 1. What is the independent variable? 2. What is the dependent variable? 3. What is the control? 4. By measuring the concentration of oxygen, what process was she testing?

2. Stomata Activity, page 63 lm Read through pages 595 and 596 in your textbook to answer questions 1-6 on page 63 of your lab manual.

3. Stomata Activity A stoma is like a pore that is found in the leaf and stem epidermis. The stoma is used for gas exchange. The pore is formed by a pair of specialized cells that are known as guard cells which regulate the size of the opening. Air containing CO2 and O2 enters the plant through these pores where it is used in photosynthesis and respiration. Water vapor is also released into the atmosphere through the process of transpiration. The word stoma is derived for the Greeks meaning mouth Stoma –singular; Stomata- plural

4. Draw the pictures of the closed and open stomata provided at the bottom of page 597 in the locations provided on page 63 lm. Consider carefully – Which stomata should you draw in the “light” conditions? Which stomata should you draw in the “dark” conditions?

5. Stomata This is a picture of a closed and open stomata. The left picture is a closed stomata, and the right picture is an open stomata.

6. Stomata Activity, page 63 lm Plants can regulate the movements of water vapor, O2 and CO2 through the leaf surface. This is accomplished by opening and closing pores, called stomata (sing., stoma), usually found on the bottom side of the leaf. Opening and closing of stomata is controlled by specialized cells called guard cells. The figure below shows a section of the bottom of a typical leaf as seen through a microscope. The stomata exists as the small opening between the pairs of guard cells. Guard cells can respond to a variety of environmental and physiological stimuli by opening and closing the stoma. For example, under hot, dry conditions stomata of many plants close to help conserve water. Stomata of most plants also close in the dark.

7. CAM plants, like cactus CO2 is stored in the form of an acid before use in photosynthesis. Stomata open at night (when evaporation rates are usually lower) and are usually closed during the day. The CO2 is converted to an acid and stored during the night. During the day, the acid is broken down and the CO2 is released for photosynthesis Adaptive Value: Better Water Use Efficiency under arid conditions due to opening stomata at night when transpiration rates are lower (no sunlight, lower temperatures, lower wind speeds, etc.).