Bio 181 Lab Photosynthesis 2024

BE AWARE THAT UPLOADING empty or completed LAB FILES to sharing websites, or using AI-generated responses (e.g. ChatGPT) constitutes academic dishonesty, and will be penalized. If you are repeating this course, you need to complete the assignments again, you may not resubmit the same assignment (they change!!) Bio 181: Photosynthesis Lab Introduction Today we are going to talk about photosynthesis! watch these videos: Amoeba Sisters Ricochet Science HHMI (Howard Hughes Medical Institute) The structure of leaves The leaf is a plant organ that functions in photosynthesis and gas exchange. Photosynthesis occurs in the palisade cells, and gas exchange occurs through the stomata (single = stoma). Label the palisade cells GREEN and the guard cells on the stoma ORANGE (click edit on the image) (image by Zephyris – Richard Wheeler, Wikipedia) Bio 181: Online 1

Within the palisade cells there are cellular organelles called chloroplasts. The main role of the chloroplast is to conduct photosynthesis . The thylakoids are made of membranes where the Light reactions of photosynthesis occur. Embedded in the thylakoids are protein complexes that contain the light sensitive plant pigments such as chlorophyll and carotenoids that absorb light energy and use it to energize electrons. These electrons are used to create a hydrogen ion gradient. ATP synthase molecules on the thylakoid membranes use the hydrogen ion concentration gradient to generate ATP . Label the thylakoids GREEN and the stroma BLUE (click edit on the image) Photosynthesis “Photosynthesis is the most important chemical process on Earth.” This statement has become something of a cliché, but like all clichés there is a lot of truth to it. Life can only be maintained with a constant supply of energy in the right form (chemical bond energy). Almost all of the energy utilized by living organisms on this planet arrives here from the sun in the form of light. Photosynthetic organisms such as cyanobacteria, algae (protists), and plants have the ability to convert light energy into chemical bond energy. Life might exist on earth if photosynthesis had never evolved, but it would likely be simple, rare, and lacking in diversity. Stated in its simplest form, photosynthesis is a process that synthesizes high-energy organic compounds from low-energy inorganic compounds by using sunlight. The most common form of photosynthesis converts carbon dioxide and water into carbohydrates and Bio 181: Online 2

VIRTUAL EXPERIMENTS There are 2 experiments on photosynthesis in this lab. You will not be able to run the experiment at home, but you will be given some websites to look at, and you will be given data that was collected by previous Bio 181 students. Using this data, you will be able to fill in all the tables and graphs. Light Gradient Experiment In this experiment we exposed sprigs of the aquatic plant, Elodea, to different amounts of light and measured the amount of oxygen produced in each tube. Since molecular oxygen is produced in photosynthesis (see photosynthesis equation above), it is a reliable measure of the rate of photosynthesis. The Elodea was placed in large test tubes and positioned at varying distances from a light source (see figure below). After a period of time the amount of oxygen in the bottles was measured with a dissolved oxygen (DO) meter and compared with the starting oxygen level. A control Elodea tube (wrapped in aluminum foil) will be used to determine how much oxygen is consumed by the Elodea (in cellular respiration) during the same time period. Look at this photo of an aquatic Elodea plant generating bubbles .: What do you think the bubbles are? (Carbon dioxide/Oxygen) Explain! Below is the experimental set up for this first experiment. Aquatic plants are put in a dozen test tubes with baking soda and exposed to different light intensity. Light level was measured as photosynthetically active radiation (PAR), the number of light particles (photons) that are driving photosynthesis. The unit of measure is µmol m-2 s-1 , the number of photons (µmol) striking a unit area (m-2) in a given time period (s-1). A light meter was used to measure this. The suggested levels were 400, 200, 100, 50, 25, 0 (wrapped in aluminum foil). Bio 181: Online 4

In the Table below are results obtained for this experiment. Column 2 represents the Dissolved Oxygen (DO) measured after 30 minutes of light exposure. Column 1 Column 2 Column 3 Column 4 Light level (µmol m -2 s -1 ) DO with Elodea (mg O 2 liter -1 solution) DO no Elodea average (mg O 2 liter -1 solution) DO change (Column 2 minus Column 3) (mg O 2 liter -1 solution) ----- ------ 7.0 ----- 350 13.9 7.0 350 12.6 7.0 160 15.0 7.0 160 14.8 7.0 80 12.1 7.0 80 11.2 7.0 40 9.6 7.0 40 10.1 7.0 20 7.6 7.0 20 8.1 7.0 0 6.2 7.0 0 5.2 7.0 1. Calculate column 4 by subtraction (Column 2-Column 3). Column 3 represents DO when no Elodea is added (i.e., the DO of the original solution). 2. Make a line chart (start by making an x-y-scatter and then ADD trendines) and insert it below. Plot the X-axis with Light Level (column 1) and the Y-axis with DO change (column 4). For the Y-axis, there are some negative values . Bio 181: Online 5

SUMMARY QUESTIONS: 1. How does measuring photons of light (PAR) differ from measuring light as waves? 2. Give the light level at which the compensation point was reached. ________ µmol m-2 s-1. Explain what the compensation point represents. 3. Give the light level at which the saturation point was reached. ________ µmol m-2 s-1. Explain what the saturation point represents. 4. Explain why the change in oxygen was negative when Elodea was placed in the dark (i.e., why was oxygen consumed?) Hint: Do plant cells have mitochondria? 5. Explain why some molecules travel faster on chromatography paper than others. 6. . What is a pigment? Bio 181: Online 7