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Metabolic Processes - Photosynthesis.

Extracts from this document...

Introduction

Unit 1 Test - Metabolic Processes: Photosynthesis Modified True/False Indicate whether the sentence or statement is true or false. If false, change the identified word or phrase to make the sentence or statement true. ____ 1. The organelle that is unique to eukaryotic photoautotrophs is the chromoplast. _________________________ ____ 2. Light energy is principally transferred by chlorophyll b. _________________________ ____ 3. When exposed to bright white light chlorophyll fluoresces green. _________________________ ____ 4. In general, photosynthesis rates are lower at lower oxygen concentrations. ________________________________________ ____ 5. The location of the H+ reservoir in the chloroplast is the intermembrane space. ___________________________________ Multiple Choice Identify the letter of the choice that best completes the statement or answers the question. ____ 1. Of the following biological compounds, which one contains the element, nitrogen? a. fatty acids d. starch b. sugar e. protein c. glycerol ____ 2. An oxidation/reduction is best shown by which of the following? a. an amino and carboxyl group form a peptide bond b. two small molecules chemically combine to form a large one c. a base reacts with an acid to form water and a salt d. electrons are transferred from one substance to another e. a large molecule is broken into two smaller molecules ____ 3. The activity of an enzyme can be altered by changing the pH of its surroundings slightly. This change in pH works by a. causing the enzyme to precipitate b. masking its active site c. increasing the activation energy of the reaction d. breaking its peptide bonds e. altering its three dimensional shape ____ 4. Which of the following is not a cofactor or coenzyme? a. Zn2+ d. Fe2+ b. Mn2+ e. NADP+ c. NAD+ ____ 5. Which of the following statements concerning allosteric regulation is not true? a. Allosteric sites are usually located next to, but separate from, the active site. b. Alosterically controlled enzymes usually have quaternary structure. ...read more.

Middle

As with all other reactions, enzyme-catalyzed reactions _________________________ in speed with an increase in temperature. However, as the temperature increases beyond a critical point, the protein structure begins to get disrupted , resulting in _________________________ and loss of enzyme function. Every enzyme has a(n) _________________________ temperature at which it works best and activity tends to decrease on either side of this temperature. Most human enzymes work best at around _________________________. Some enzymes require nonprotein _________________________, such as zinc and manganese ions. Other enzymes may require organic _________________________ such as NAD+ and NADP+. A variety of substances inhibit enzyme activity. ___________________________________ are so similar to the enzyme's substrate that they are able to enter he enzyme's active site and block the normal substrate from binding. This process is reversible and can be overcome be increasing the concentration of the enzyme's substrate. Another class of inhibitors does not affect an enzyme at its' active site, they are called ___________________________________ and their effect cannot be overcome by adding more substrate. 2. In a general, overall comparison of the reactions that occur during cellular respiration and photosynthesis, it can be said that the main reactant in respiration is ____________________, while in photosynthesis it is ______________________________ and _________________________. In contrast to this, the main products of cellular respiration are _________________________ and _________________________, while in photosynthesis the main product is ____________________ with an interesting waste product ____________________ that is very useful to many creatures on Earth. Cellular respiration is a process that ____________________ energy , while photosynthesis ____________________ energy. Matching Match each item with the correct statement below. a. ground state g. photosystem I b. excitation h. photosystem II c. fluorescence i. noncyclic electron flow d. primary electron acceptor j. Z protein e. antenna complex k. photophosphorylation f. reaction centre l. cyclic electron flow ____ 1. The release of energy as light as an electron returns to ground state. ____ 2. ...read more.

Conclusion

This is a process that typically occurs in C3 plants such as many deciduous trees. Two mechanisms have evolved in higher plants to counteract the process of respiration, they are C4 and CAM photosynthesis. C4 photosynthesis is one response some plants have evolved to the problem of photorespiration. Plants such a corn and sugar cane are examples of such plants. The enzyme that fixes carbon dioxide in these plants is PEP carboxylase in the mesophyll cells of the vascular bundles, and the first product formed is oxaloacetate, a four carbon compound. PEP carboxylase has no oxygenase function as rubisco has so there is no initial problem with photorespiration. The oxaloacetate is converted to malate and shuttled into the bundle sheath cells where it is decarboxylated to pyruvate with the release of carbon dioxide which can now be fixed by rubisco which is present in these cells. However, the oxygen concentration in these cells is very low so photorespiration has been effectively eliminated but at the expense of some ATP. C4 represents a spatial separation of photosynthesis. CAM stands for crassulacean acid metabolism and is so named because it was first discovered in members of the plant family known as a the Crassulacea (e.g., cacti, pineapples, aloe). CAM is a way that some plants have evolved to avoid the problem of photorespiration. In this process the stomata of the plants are open during the night when it is cooler and less water can be lost. Carbon dioxide can enter, but the usual method of fixing the carbon, by using the energy produced in the light-dependent reactions obviously is not available. PEP carboxylase is used to fix carbon dioxide into organic acids which are stored in the vacuoles of the mesophyll cells. During the day, when the stomata are closed, the organic acids are decarboxylated and the carbon dioxide that is released is fixed by rubisco in the Calvin cycle which is located in the bundle sheath cells. There is a cost of some ATP in the process. CAM represents a temporal separation of photosynthesis. REF: K/U OBJ: 3.4 LOC: MP1.05 ...read more.

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