Kevin Meng - Algae beads lab

Photosynthesis and Cellular Respiration Are Interdependent Pathways That Are Central to Life In one way or another, all life on Earth depends on photosynthesis and cellular respiration. Photosynthesis is the only biological process that can capture energy from sunlight and convert it into chemical compounds that all organisms — from bacteria to humans — use to power metabolism, growth, and reproduction. Cellular respiration, in turn, is the process all organisms require to derive energy from the products of photosynthesis (for example, sugars) they consume. The carbohydrates produced by photosynthesis can be used to drive multiple different metabolic processes, including cellular respiration. Cellular respiration uses the free energy from sugar, for example, to produce a variety of metabolites and to phosphorylate ADP into ATP to fuel other processes. Although photosynthesis and cellular respiration evolved as independent processes in early prokaryotes, a look at the summary reactions (see figure below) highlights their interdependence today: The products of photosynthesis — oxygen and carbohydrates — are the reactants for cellular respiration, and vice versa. Photosynthesis and Cellular Respiration Occur within the Same Cell It is important to understand that, although only autotrophs perform photosynthesis, ALL organisms (you, your teacher, the neighbor’s cat, and the tree at the end of the street) perform glycolysis and cellular respiration . In fact, the reactions that break down glucose in the presence of oxygen are universal. Even autotrophs, who produce their own food, use glycolysis and cellular respiration to break down the sugars they synthesize in order to extract energy and metabolites along the way. Where photosynthesis is the capture and transformation of light energy to chemical energy ( photosynthates ), respiration is the burning of those photosynthates for energy to grow and to do the work of living. Both plants and animals (including microorganisms) need oxygen for aerobic respiration. This is why overly wet or saturated soils are detrimental to root growth and function, as well as to the decomposition processes carried out by microorganisms in the soil. In autotrophs such as algae, these pathways occur within the same cells! In fact, if you could look inside one of the algal cells you will be using in the lab investigations, you’d see a large central chloroplast as well as smaller mitochondria — all within the same cell. Though photosynthesis and cellular respiration are connected through common intermediate metabolites in the cytosol, elegant regulatory pathways and differences in resource availability ensure the algal cells balance the rates of photosynthesis and cellular respiration as needed to survive environmental changes. The algae beads used in the following investigations allow you to observe both pathways at the same time, or simultaneously. You will incubate the algae beads in a CO2 indicator solution that is sensitive to changes in pH caused by gaseous CO 2 dissolving in water to form carbonic acid: CO2 + H2O H2CO3 HCO3 + H+ When the CO2 levels are high, the CO2 indicator will turn yellow, and when CO2 levels decrease, it turns purple.

Pre-Lab Questions: Use a different font color when you write your answers 1. Scientists measure the rates of biochemical processes by monitoring either substrate depletion or product generation. Considering this, what substrates or products might you monitor to determine the rate of photosynthesis? Of cellular respiration? To determine the rate of photosynthesis, we could measure the change in concentration of CO2 or change in concentration of O2. The same applies to measuring the rate of cellular respiration. 2. What type of organism would you need to use to be able to monitor both photosynthesis and cellular respiration? Why are the eukaryotic algal cells in the Photosynthesis and Cellular Respiration lab a good choice? We would need a photoautotroph, such a algae, to monitor both photosynthesis and cellular respiration. Eukaryotic algal cells are a good choice because they are small, and do both photosynthesis and cellular respiration. 3. Which process (photosynthesis, cellular respiration, or both) do the algae perform when incubated in the light? In the dark? In the light, algae performs both photosynthesis and cellular respiration. In the dark, the algae only performs cellular respiration. 4. Photosynthesis uses CO 2 and cellular respiration produces CO 2 . We call the point when the two processes are in balance — when there is no net production of CO 2 — the compensation point. How might you limit one of the processes in order to achieve a compensation point? We would prevent one of the algae bead incubators to do photosynthesis by preventing light from reaching it. When light is very little, the plant should be producing CO2 from photosynthesis at a similar rate that the plant uses CO2 for cellular respiration. 5. Examining the data below, how do you expect the rate of cellular respiration to impact the rate of photosynthesis that you can measure in the light and the dark? When the rate of cellular respiration rises and falls, the photosynthesis occurs at a more extreme rate. As light intensity increases photosynthesis has more drastic results. 6. What would happen to life on Earth if the rates of photosynthesis and cellular respiration in all phototrophs were equal? If the rates of photosynthesis and cellular respiration in all phototrophs were equal, the organisms would not be able to compensate for a lack of CO2 because photosynthesis uses CO2 to form glucose and oxygen. When the rates of the 2 processes are equal, phototrophs wouldn't be able to produce

Record your data in the chart below LIGHT DARK Time (min) Indicator Color pH Abs at 550 nm Indicator Color pH Abs at 550 nm 0 Dark Red 8.3 .155 Dark Red 8.3 .150 10 Dark Red 8.4 .270 Dark red 8.35 .233 20 Maroon 8.5 .404 Dark Red 8.3 .201 30 Maroon 8.55 .458 Dark Red 8.3 .173 40 Magenta 8.7 .647 Dark Red 8.3 .184 50 Purple 8.9 .882 Dark Red 8.3 .180 60 Dark Purple 9.1 .972 Dark Red 8.3 .194 70 Dark Purple 9.1 1.102 Dark Red 8.3 .216 80 Dark Purple 9.1 1.106 Dark Red 8.3 .207 90 Dark Purple 9.1 1.133 Dark Red 8.3 .178 1. Create a graph on Excel or Google sheets comparing the light & dark cuvettes over time using the pH data. Copy and paste. https://docs.google.com/spreadsheets/d/1XxqwEoLyX0irL72D7DTxoOb_z9jBYj-AR1TenVqkgUA/edit ?usp=sharing

2. Create a second graph on Excel or Google sheets comparing the light & dark cuvettes over time using the absorbance (A 550 ) data. Copy and paste. 3. Calculate the slope. Mark two points along your light best fit line. The slope of the graph indicates the change in CO2 over time. Calculate the slope from your light and dark best fit lines. (Try to choose points that are far apart but are still in the linear range of the graph. Label the point on the left L i and the point on the right L f . Do the same with the dark best fit line but label the points D i and D f .) L i =_ (0, 8.3) ___ D i =_ (10, 8.35) ___ Slope = Δy or ΔpH L f =_ (78, 9.1) ___ D f =_ (90, 8.3) ___ Δx Δtime Slope of Light: __ 0.010256 ___ Slope of Dark: __ -0.000625 ___ 3. Are your slopes positive or negative for light and dark conditions? What does this mean about the change in CO2? Our slopes are positive for the light conditions and negative for the dark conditions. We believe that the CO2 concentrations increased in light conditions over time and CO2 concentrations increased then decreased over time. Algae beads do photosynthesis at a faster rate when exposed to light whereas in dark conditions the algae beads won’t do photosynthesis but rather cellular respiration. The CO2 concentration for the dark conditions should go down due to no light to do the photosynthesis process.