November 14, 2018 Introduction Purpose and Importance of topic Cellular respiration and photosynthesis are necessary modes of life for creating and expending energy in plants. Photosynthesis produces oxygen while cellular respiration creates ATP, the energy currency of the cell. These processes are necessary for plant and animal life because plants produce oxygen through photosynthesis, which provides animals and mammalian populations with necessary oxygen. It is important to explore the different ways photosynthesis and cellular respiration can occur and what factors affect them in order to make connections to larger scientific studies. Background The locations of photosynthesis and cellular respiration differ because photosynthesis takes place only in plants, while cellular respiration takes place in plants and many other organisms. Photosynthesis occurs in a chloroplast, and cellular respiration occurs in mitochondria.
Mitochondria can be found both in plants and animals while chloroplasts can only be found in plants. Locations of cellular cycles specific to photosynthesis and cellular respiration are also important. Photosynthesis uses light and dark reactions to prepare energy from the sun into consumable energy for the plant and oxygen. Light reactions, also known as light-dependent reactions, use energy to take electrons from water, which then create nicotinamide adenine phosphate (NADPH) to push protons into a membrane. The protons go back across the gradient in adenosine triphosphate (ATP) synthase to help make ATP that is coupled with NADPH, then yielding oxygen and water (Johnson, 2016). This reaction takes place in the thylakoid membrane of the chloroplast. Types of photosynthesis vary depending on the environment the plant is in. The types include C3, C4 and CAMs. C3 Photosynthesis C3 plants make up around 85% of the plant species, including wheat, barley and most trees. C3 plants have a disadvantage when the climate is arid, because useless photorespiration intervenes during the normal process of light capturing and transfer to ATP. Photorespiration fixes oxygen instead of CO2 to bind with rubisco when the concentration of CO2 drops too low inside of the cell (Georgia State University, 2016).
C4 photosynthesis takes place in the mesophyll cell walls. CO2 is still fixed in the process, and is then pushed across the membrane to become a molecule of CO2 and a carbon-3 compound. Next, the CO2 goes through the Calvin cycle and produces 2 molecules of G3P. G3P is then converted into sugar (Georgia State University, 2016). Photorespiration Photorespiration is a useless process to plant life, and in fact, wastes molecules of nutrients that are important to plant growth and photosynthesis. In the process of photosynthesis, Rubisco is used to help turn the Calvin cycle, and make the fixing of CO2 possible. Rubisco, otherwise known as RuBP, is a flirtatious enzyme that sometimes binds with O2 instead of CO2, it is supposed to. This causes the plant to use precious molecules and waste them (Georgia State University, 2016). Seed germination To begin, germinating seeds are seeds that have not yet formed leaves or began to photosynthesize. Germinated peas and corn were used in this experiment, and each only had small sprouts. Seeds can be germinated in a few different ways, which can include the paper towel method, the submersion method, and the Rockwool method. Each produces the same form of germinated seeds, while the methods are slightly different. The paper towel method was used to germinate the seeds used in this experiment.
Paper Towel germination method Begin with a damp paper towel, and then arrange seeds in a spread-out fashion. Fold the paper towel back over the seeds, and place a cover over the seeds. There does not have to be a heat source, but the seeds will germinate faster if there is. If a heat source is available, place it under the container at 70-80°F (Full Bloom Hydroponics, 2018). Cellular Respiration The basic way of explaining cellular respiration is to note that carbon dioxide (CO2) and water (H2O) are taken from sugar (C6H12O6) and during that process, ATP is created. ATP is then used to do all of the metabolic work in the cell (IUPUI Department of Biology, 2004). Cellular respiration takes place in mitochondria, and consists of processes called glycolysis, citric acid cycle, the electron transport chain, and oxidative phosphorylation. Glycolysis, which takes glucose and creates two molecules of pyruvic acid, results in two ATP molecules. Pyruvate then becomes Acetyl CoA, which is an enzyme that delivers the acetyl group to the next step, known as the citric acid cycle.
The citric acid cycle takes place in the mitochondrial matrix, and results in the overall production of four ATP and NADH. NADH (reduced form of NADPH) carries electrons to the next step, known as the electron transport chain. The electron transport chain is a chain of several Hydrogen gradients that result in the reduction of charge of electrons, which can be compared to a staircase. If an electron dropped a step lower on the stairs every time it moved, energy would be removed and eventually the electron would stop once its energy was too low. This is what happens when electrons enter the ETC, and at the end of the chain, oxygen accepts the electrons and then the molecules are converted into ATP through chemiosmosis (changing ADP and inorganic phosphate groups to ATP). The electron transport chain takes place in the cristae of the mitochondria. Hypothesis It was hypothesized that C3 seeds would respire more than C4 seeds in the preferred environment of 10°C, and that C4 plants would respire more than C3 plants in their preferred environments of 40°C. I predicted that C3 seeds would consume more oxygen (O2) in the 10°C environment than C4 seeds, and that C4 seeds would consume more O2 than C3 seeds in the 40°C environment.
The importance of this topic is heavily researched in science today because of climate change and the deterioration of the environment. It is relevant to connect this to climate change because if its growing epidemic. Configuring data in this experiment consisted of observing and measuring the amount of oxygen respired in the pipets and then determining exactly what that data meant in relevance to the group hypothesis. The data was skewed to the right when depicted as a histogram. The data were continuous, did not depend on each other, and were two different subjects, which meant that it is appropriate to use a non-paired t-test in order to correctly represent the values. Methods Description of procedure This experiment was to determine how the independent variables of C3 and C4 photosynthesis affect the dependent variable, the amount of respiration in the corresponding plants, peas (C3) and corn (C4). The amount of oxygen being respired is the dependent variable, and measured in mL, as it is the amount of water that enters the pipet of the respirometer. The seeds of peas and corn were the experimental groups.
In this experiment, the temperature of the water bath the seeds were placed in (°C), the amount of the seeds and beads in the respirometers (ten corn seeds, equal volume of pea seeds), the length of time the respirometers are left in the water (10 minutes), and the amount of time between trials were controlled by the group. Materials To prepare the ten respirometers for the experiment, the group tore an absorbent cotton ball in half and placed one half in the bottom of the ten respirometers, then added two milliliters (mL) of potassium hydroxide at 15% concentration by pipet on top of the cotton absorbent ball. A full non-absorbent cotton ball was placed on top of the contents. The cotton was completely covering the bottom half of the respirometer so no potassium hydroxide could leak farther into the respirometer. We then placed 10 corn seeds in four respirometers, an equal volume of pea seeds in four other respirometers, and an equal volume of beads in two respirometers, which served as the control group. After, the respirometers were sealed with rubber stoppers that held the pipets. Four liters (L) of water was heated in a boiling water bath to around 60°C, but ice was placed in the water bath to cool it to 40° C.
The group poured two L of the water into a tray. In a separate beaker, one person measured two L of 10° C water and poured it into a separate tray. The trays were halfway filled with water. Experimental setup Experimental setup consisted of two respirometers that held C3 seeds (peas) in 10° C water bath, two respirometers that held the C4 seeds (corn) in the 10° C water bath, and a single respirometer that held red beads, which was the control group for both water baths. The same set up applied to the other water bath, which was set at 40°C. A model similar to the respirometer used in the experiment is pictured to the right of this paragraph as Figure 1 (StudyLib, 2018). The respirometers were placed in the water baths, not completely submerged for three minutes to equilibrate. Calculating results The group recorded the data by observing how much oxygen was respired in the pipet which is represented by how much water is sucked into the pipet. This appeared to be a large number, but after double-checking our measurements, the group found that the respirometer pipet needed to be read in tenths of a millimeter. The same steps were repeated for five more respirometers in the 40° C water bath. The data was recorded in mL, and entered into the corresponding row in the data table. Two trials were completed to ensure the data was not spontaneous.
Overall, the group discovered that the hypothesis was incorrect and not supported after further exploration of what photosynthesis is. It is important to realize that seeds were tested in different temperatures, however, that does not mean only tested temperatures were able to yield the same or similar results. Although the difference between seed types respiration was very small, seeds and plants do respire more in warmer temperatures.
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