Reaction against hydrogen peroxide Essay Example for Free

Reaction against hydrogen peroxide Essay The action of catalase on hydrogen peroxide Aim The aim of this experiment is to discover the relationship between the concentration of the substrate and the rate of the reaction catalysed by an enzyme, by looking at the decomposition of hydrogen peroxide under the action of catalase, and to determine a value for Vmax and the Michaelis constant for catalase. Background Theory An enzyme is a protein biological catalyst. Catalysts speed up or slow down the rate at which chemical reactions occur. They are not used up in the reactions and can be retrieved unchanged afterwards. Biological catalysts control the rate of reactions in living things. Each enzyme is substrate specific it can control only one reaction. For example, the digestion of starch is begun in the mouth by the enzyme amylase. An equation for this reaction can be shown like this: Amylase Starch Simple sugars The enzyme only facilitates the reaction, it is not used up. Each molecule of enzyme can be reused indefinitely, unless it is damaged, or denatured. Enzymes are proteins, so they are denatured if the polypeptide chains, which are precisely coiled and folded to form the active site, become unfolded by the kinetic energy from heat, or the covalent bonds are disrupted. Whilst some heat will increase the rate of reaction because of the increased number of collisions between enzyme and substrate, too much heat will denature the enzyme and render it completely ineffective. Enzymes are also affected by the pH at which they have to work. Charged hydrogen or hydroxide ions in acids or alkalis can cancel out the charges on the active sites of the enzymes, and render them ineffective. Hydrogen peroxide is a toxin produced in every cell of living organisms as a by-product of respiration. It is the same chemical that is used to bleach hair, and so must be broken down before it can damage the cells. It decomposes to give water and oxygen. This reaction will occur naturally, but at a very slow rate. To speed it up an enzyme is used. The enzyme which catalyses the decomposition of hydrogen peroxide is called catalase. Catalase is found in all living cells to decompose the hydrogen peroxide. In this experiment it is being obtained from live yeast in a suspension. The method by which catalase works is called the lock and key method. Catalase works because it has an active site. At this point the enzyme attaches to the hydrogen peroxide molecule, because the opposite charges of enzyme and substrate attract each other, forming an enzyme substrate complex. The enzyme catalyses the reaction, and then the new charges on the product repel the enzyme away to act on a new substrate molecule. (see fig 1) The decomposition of hydrogen peroxide has the following formula: catalase 2H2O2 2H2O + O2 The rate of a reaction is a measure of the change in the amount of reactant or product with time. The rate of decomposition H2O2 can be measured using the volume of oxygen produced, from the formula: Rate of reaction = change in amount of product time The rate of reaction is determined by collision theory:- For a reaction between two substances to occur, the enzyme and substrate particles must collide with each other. If more collisions occur in a reaction, rate will increase. If the reactant particles gain energy and collide faster, then each collision will have more energy, there will be more successful collisions, and rate will also increase. In this case, the more collisions between hydrogen peroxide and catalase molecules, the more hydrogen peroxide will decompose. Anything which increases collisions will increase rate. Increasing the concentration of the substrate (hydrogen peroxide) solution means that there are more substrate molecules in the same volume, causing more collisions, and thus increasing rate. The rate of reaction changes with concentration, but the overall yield of oxygen is independent of factors affecting the rate, so measuring the amount of oxygen produced over the whole reaction is meaningless. Instead, the initial rate of reaction can be estimated by measuring the volume of oxygen produced in the early stages of the reaction. This value can then be compared between the different concentrations of hydrogen peroxide, and used to plot a graph of substrate concentration against rate, from which values for Vmax and the Michaelis constant (Km) can be obtained. The relationship between substrate concentration and rate of reaction is described by the Michaelis-Menton equation: v = Vmax [S] Km + [S]. Vmax is a measure of the maximum rate at which an enzyme can act, and it is the horizontal asymptote of the graph of substrate against time that is when the amount of enzyme is the limiting factor. The Km is defined as the substrate concentration at which the rate of enzyme action is half Vmax. It is measure of the affinity of an enzyme for its substrate molecule the higher Km, the weaker the binding force between the enzyme and substrate. Both Km and Vmax are constants at a specific enzyme concentration and temperature. Pilot Experiment A pilot experiment was carried out in order to see whether the method was practical and could produce good, reliable results, and to choose the concentrations of hydrogen peroxide and the length of time over which the oxygen would be collected so that no more than 50cm3 of gas was given off. Pilot Method 1. 10cm3 of hydrogen peroxide solution was measured into boiling tubes using a syringe, and the apparatus set up as shown below. 2. Using a 1cm3 syringe the yeast suspension was added to the boiling tube and the stopwatch started. 3. Thirty seconds was timed, and then the burette was taken off the end of the delivery tube, but not out of the water, and the volume of gas collected was measured. 4. This was recorded and repeated for each concentration of hydrogen peroxide, made up as shown in the dilution tables below. Pilot Results Concentration of hydrogen peroxide Initial reading on burette (cm3) Final reading on burette (cm3) Volume of gas collected (cm3) Rate of reaction (cm3/s) to 2dOff scale. Analysis of and Modifications to the Pilot These results show a clear increase in the volume of gas collected as the concentration increases, suggesting that with modifications this method will enable clear conclusions to be drawn. Carrying the experiment out over 30s resulted in too much gas being produced at the highest concentration to be recorded with the apparatus available, so for the main experiment the oxygen will be collected over 15s. More readings will be taken to enable a more reliable graph to be drawn at9 and 20%. The experiment will be repeated three times and any anomalous results will be identified and excluded from the average in order to enable more reliable results. Prediction I predict that initially the rate of reaction will increase with the concentration. As the concentration of hydrogen peroxide increases so will the number of collisions between enzyme and substrate molecules, so the hydrogen peroxide will decompose faster into water and oxygen. I predict that this reaction will obey Michaelis-Menton kinetics, and that the graph of rate of reaction against hydrogen peroxide concentration will give a rectangular hyperbola as shown below: The increase in rate of reaction will not continue indefinitely there will be an asymptote when Rate = Vmax, when all the catalase molecules are catalysing the reaction as fast as possible, and so the rate cannot increase without supplying more enzyme. Main Experiment Plan Fair Test A fair test is one from which a reliable conclusion can be drawn. For a fair test only one variable must be changed at a time. In this experiment the concentration of hydrogen peroxide is being changed, and so all others must be controlled. Variables. Independent Variable:- concentration of hydrogen peroxide Dependent Variable:- volume of oxygen gas collected in 15s Controlled Variables:- temperature, volume of hydrogen peroxide, amount of yeast, apparatus, time.   The reaction will be carried out in a water bath at 20? C. Since water is a good thermal buffer it should be fairly easy to keep the temperature constant.   Volume of hydrogen peroxide solution will be controlled quite easily by using two syringes to measure the water and hydrogen peroxide volumes as dictated by the dilution table below.

Writing and Reading for a New Generation Essay -- Internet Cyberspace

â€Å"Writing and Reading for a New Generation† In the past decade, the Internet has taken over. Everyone from young children to senior citizens can communicate, send e-mail, or look up any bit of information in seconds. Because of the overwhelming shift to Internet technology and communication, many aspects of writing have been forever changed. Writers often write differently for the Internet than they do for a physical publication. Readers often read differently on the Internet than physically written text. Within the forms of Internet writing exists one unlike the others and that is personal publishing web sites, such as blogger, live journal, diary land—the list goes on. By allowing any individual to publish anything onto the web, the traditional ideas of writing and reading are automatically forfeited to a new generation of writers. The first thing to understand about personal publishing sites is their uses. What the site will be used for can also dictate which site a person will utilize. For instance, something like diary land (diaryland.com) is typically used strictly as an online journal. People record their thoughts, what they’ve been doing, and what events are coming up in their lives. Like a personal web site, users will personalize the layout of the â€Å"diary† including pictures, borders, etc. Other sites, like blogger (blogger.com), can be used for personal means or professional ones. In the case of my English 328 class, blogs can even be used as a place to respond to writing prompts for homework. In looking at these sites, I noticed that blogger more than the others also had blogs specific to certain interests. For instance, one blog was dedicated solely to lovers of palm pilots. The wa... ...sible to imagine a world in which books were an outdated, archaic technology but as we push further into the future and the future of writing, the possibility looms as a larger and larger force to be reckoned with. Works Cited Bradbury, Grace. â€Å"Diary of a Call Girl.† The Times(London). 10 Mar. 2004, n.68019. T2, p.4. Tribble, Evelyn B. and Anne Trubek, eds. Writing Material: Readings for Plato to the Digital Age. New York: Longman, 2003. Landow, George. â€Å"Twenty Minutes into the Future, or How Are We Moving Beyond the Book?† Tribble & Trubek 214-226. Sosnoski, James. â€Å"Hyper-readers and their Reading Engines.† Tribble & Trubek 400-417. Wagner, Erica. â€Å"A High Price to Pay for Sex Without Love.† The Times (London). 10 Mar. 2004, n. 68019. T2, p.5.

Influence of Parents on Academic Performance Essay

Authorities parenting, psychosocial maturity and academic success among adolescents, study of Steinberg et al. (1989) describes that when a parents treat their child warmly, democratically, and firmly, they will develop positive attitudes, they will achieve more and do better in school. Multidimensional conceptualization of parent involvement in children’s schooling according to Grolmck’s (1994), it describes that parents must support their child specially to their experiences. Parental Involvement and academic achievement of peer accepted and peer rejected children, a study by Chowdhary and Jayasmita (1997), describes that parental involvement may have influence to the academic performance of a child as a accepted or rejected. Comparative study of parent-child relationships of high and low achievers, study by Kang et al. (1997); the Tiwari (1997) was used to develop this study, it used eight dimensions at parent and child relations such as acceptance, rejection, domina nce-submission, encouragement-discouragement, love-hate, authoritarian-democratic, reward-punishment, trust-disburst, tolerance-hostility. In this study it reveals that children who had warm relationships with their parents achieved higher in classroom. Parent-child relationship and academic motivation, study of Suman et al. (2003), it revealed that the achievement motivation was higher when adolescents perceived their parents as loving and demanding. Sibling rivalry and relation to achievement motivation, study of Vasuki et. al (2004), data were from Neerakatwal’s (1988) and Deo Mohan’s Achievement Motivation Scale (1985), it showed that rivalry towards siblings, tended to have low levels of achievement motivation. Effect of Peer Academic Reputation on Achievement Gest et. al (2005) argued that peer academic reputation (PAR) may influence children’s academic motivation and achievement even if it is not veridical. This argument is consistent with research on the effect of teacher expectations on achievement, which demonstrates that teacher perception of children’s academic ability, whether accurate or not, affect student’s grades and scores on standardized achievement tests (for reviews see Brophy, 1983, Jussim Eccles, and Mardon 1996, and Jussim and Harber, 2005) Developmental Issues Researchers speculate that growth in social cognitive skills, including the capacity and motivation to use social comparison information to shape self-evaluations, account for the trend toward more negative and more differentiated self-perception in grades K-3 (Kuklinsks and Weinstein 2001: Markus and Wurf, 1987). Also make children the transition from kindergarten to the more formal academic setting of grades 1-3, more social comparison cues, may be available, and feedback on one’s academic performance may be based more on comparison to others versus improvement over one’s prior performance (Eccles et. al, 1993: Ruble and Frey, 1987: Ruble, Grosovsky, Frey, and Cohen, 1992) Influence of siblings on adjustment of adolescents Conger et al. (1997) carried a study on parents, siblings, psychological control and adolescents. Data were obtained by using Rosenberg measure of self esteem (Rosenberg, 1965) Pearten measure of control and mastery developed by (Pearlin, 1981), SCR-90-R (Symptom checklist revised; Derogatis, 1983) was administered. Results of the study indicated that psychological control both by parents and by siblings contributes to increase adolescents adjustment problems and to diminished self-confidence. Vasuki et al. (2004) carried a study on â€Å"sibling rivalry and its relation to frustration, mental health and self conflict of adolescents† on a sample of 60 girls and 60 boys from three city schools of in the age group of 15-18 years. Data were obtained using Neerakatual’s (1998) sibling relationship questionnaire, Chauhan and Govind Tiwari’s (1969) Frustration test, Smt Rama Tiwari’s (1986) self conflict questionnaire, Jagdish and Srivastava’s Mental health questionnaire. Results of the study revealed that both males and females of dyads and multiples showed rivalry towards their siblings in a homogeneous way. Greater extent of sibling rivalry also lead the adolescents to become more frustrated. Oliva et al. (2005) carriedout a study on â€Å"sibling relationship during adolescence† on a sample of 513 adolescents aged between 13 and 19 years. Data were obtained by using an instrument created by Steinberg et al. (1991) to assess the parenting style, questionnaire on sibling relationships (QSR; Arranz et al., 1994), inventory of peer attachment (IPA) developed by Armsdeu and Greenberg (1987) and Rosenberg self-esteem scale (RSES; Rosenberg, 1965). Results of this study indicated that having siblings was related to adolescent’s social and personal adjustment, although only among girls and only in cases of good sibling relationships. In cases of poor sibling adjustment, it was the negative effects of every day situations of rivalry and conflict outweighed the benefits of any support that was provided.

Analysis Dogville - 30953 Words

Resumà © I denne projektrapport foretages en analyse af filmen Dogville, 2003, instrueret af Lars von Trier. Ved premieren og i den debat, filmen vakte, blev den karakteriseret som anti-amerikansk, moralsk, religià ¸s m.m. Projektet er udarbejdet ud fra den tese, at Dogville er en film med en meget kompleks form, hvilket gà ¸r det svà ¦rt at tage den til indtà ¦gt for bestemte holdninger. I analysen undersà ¸ges denne tese, og i diskussionen holdes filmens form op imod dens indhold. Rapporten konkluderer, at filmen er udprà ¦get formbevidst, og at de temaer, den prà ¦senterer, er underlagt dette. Filmen er en à ¦stetisk provokation. Analysen er eksemplificeret, men ikke gennemfà ¸rt dokumenteret, hvorfor rapportens forfattere tillader sig at anbefale†¦show more content†¦De gà ¸r sammen med den lidt gammeldags voice-over-fortà ¦ller og dens mindelser om teater Dogville usà ¦dvanlig. Det gà ¸r ogsà ¥, at filmen stritter i mange retninger, og det er derfor svà ¦rt at tag e den til indtà ¦gt for à ©n bestemt holdning. Alligevel er den blevet anmeldt, anskuet og diskuteret som om, den udtrykker en sà ¥dan. Det er den diskrepans, der er emnet i denne rapport. 1.1 Motivation Film er levende billeder. Narrative film er historier fortalt via levende billeder – altsà ¥ en visuel gestaltning af fiktioner, som vi kender dem fra bl.a. romaner. Vores interesse var ved projektarbejdets start, hvordan disse levende billeder bliver fortalt tilskueren, og hvilken indflydelse fortà ¦lleformen har pà ¥ den mà ¥de, vi afkoder de levende billeder pà ¥ là ¦rredet. Pà ¥ et helt overordnet plan handler det om, hvordan der fortà ¦lles i film. En filmfortà ¦lling bestà ¥r af en rà ¦kke sammenklippede billedsekvenser, der kan và ¦re struktureret pà ¥ forskellig vis, og som suppleres af lyd. Den kan benytte mere eller mindre tydelige narrative greb, men der vil altid và ¦re tale om en formidlende instans: en fortà ¦ller. I litteraturen kendes denne instans i et utal af afskygninger: fà ¸rstepersons-fortà ¦ller, tredjepersons-fortà ¦ller, scenisk og olympisk fortà ¦ller etc. Og der findes igen massevis af variationer indenfor de enkelteShow MoreRelate dAnalysis Of Why Not Just Call It Dogville?1365 Words   |  6 PagesMark Shasha Friday, February 27, 2015 DogVille – Film Analysis Why not just call it DogVille? DogVille, a film adaptation of the book DogVille written and directed by Lars von Trier, takes place in a small town of the same name in the Rocky Mountains in Colorado during the period of the Great Depression. DogVille has a population of about 13 adults and a few children, most of which have never left the town in their entire lives. One night, one of the residents, Tom Edison Jr., hears a gunshots coming