Safety. Although the hazards in the following experiments are negligible, you are advised to consult the latest edition of 'Safeguards in the School Laboratory' published by The Association for Science Education (ase.org.uk) before embarking on any experiment.
Outline. Catalase is an enzyme which occurs in the cells of many living organisms. Certain of the energy-releasing reactions in the cell produce hydrogen peroxide as an end-product. This compound, which is toxic to the cell, is split to water and oxygen by the action of catalase. 2H2O2 = 2H2O + O2
Compound Saw
Samples of liver and yeast are dropped into hydrogen peroxide. Oxygen is evolved and the student is asked to extend the experiment to try and decide if an enzyme in the tissues is responsible. The experiments and the questions take about one hour.
Prior knowledge. The existence of inorganic catalysts; enzymes denatured on boiling; oxygen relights a glowing splint.
Advance preparation and materials - per group
20 volume hydrogen peroxide 50 cm3
splint
liver, about 1 cm cube
distilled water 20 cm3
dried yeast about 1 g
clean sand about 1 g
activated charcoal granules, about 1 g
Apparatus - per group
test-tube rack and 4 test-tubes
forceps or seeker for pushing liver into test-tube
4 labels or spirit marker
filter funnel
Bunsen burner
filter paper
test-tube holder
mortar and pestle
Experiment
The investigation below is a fairly critical examination of plant and animal tissues to see if
they contain catalase.
(a) Label three test-tubes 1-3.
(b) Pour about 20 mm (depth) hydrogen peroxide into each tube.
(c) Cut the liver into 3 pieces.
(d) To tube 1 add a small piece of liver, and to tube 2 add a pinch of dried yeast.
(e) Insert a glowing splint into tubes 1 and 2, bringing it close to the liquid surface or into the upper part of the froth.
1 Describe what you saw happening and the effect on the glowing splint.
2 How do you interpret these observations?
3 Is there any evidence from this experiment so far, to indicate whether the gas is coming from the hydrogen peroxide or from the solid?
4 Is there any evidence at this stage that an enzyme is involved in the production of gas in this reaction?
(f) In tube 3 place a few granules of charcoal and observe the reaction.
5 Could charcoal be an enzyme? Explain your answer.
6 Assuming (i) that the gas in (f) is the same as before and (ii) that the charcoal is almost pure carbon, does the result with charcoal help you to decide on the source of the gas in this and the previous experiments?
(g) Suppose the hypothesis is advanced that there is an enzyme in the liver and yeast, which decomposes hydrogen peroxide to oxygen and water; design and carry out a control experiment to test this hypothesis.
7 Record (i) the experiment, (ii) the reasons which led you to conduct it, (iii) the observed
results and (iv) your conclusions.
(h) Wash out the test-tubes. Design and carry out an experiment to see if the supposed enzyme in the plant and animal material can be extracted and still retain its properties. The experiment should include a control.
8 Describe briefly your procedure, your results and your conclusions.
9 Assuming that liver and yeast each contain an enzyme which splits hydrogen peroxide, is there any evidence to show that it is the same enzyme? What would have to be done to find this out for certain?
Discussion - answers
1 Effervescence should be observed in each case but it is more vigorous with yeast than with liver. The glowing splint should relight.
2 Oxygen is being produced.
3 There is no evidence to indicate whether the liquid or solid is giving the gas. If the students think that a solid is unlikely to give off a gas they could be reminded of marble and hydrochloric acid in which it is the solid producing the carbon dioxide. It seems less likely, however, that yeast and liver would both give off oxygen when treated with hydrogen peroxide, than that hydrogen peroxide should give oxygen when treated with diverse substances.
4 So far, there is no evidence of an enzyme being involved.
5 A gas will come off but not sufficiently rapidly to relight a glowing splint. Charcoal could not
be an enzyme because (a) it is an element and (b) it has been produced by very high temperatures that would destroy enzymes.
6 Charcoal, as an element, could not be giving off oxygen. The gas must be coming from the
hydrogen peroxide.
7 (i) The experiment should involve boiling the tissues and then putting them into hydrogen peroxide.
(ii) If an enzyme is involved,
(iii) no gas will be produced.
8 The student should grind the samples with a little sand and distilled water, filter and test the filtrate with hydrogen peroxide. Oxygen will be evolved with a vigour proportional to that witnessed when the original substances were tested.
The student should boil half of each extract and show that it loses its activity.
9 There seems no fundamental reason why yeast and liver should not have different enzymes which catalyse the decomposition of hydrogen peroxide. To be certain on this point, the enzymes would have to be extracted and their chemical composition determined.
Christmas Sales Makita LS1216LX 12-Inch Dual Slide Compound Miter Saw with Laser and Stand 201
Dec 26, 2011 00:58:47
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Christmas Sales Makita LS1216LX 12-Inch Dual Slide Compound Miter Saw with Laser and Stand Feature
- 4-steel rail sliding system and 6 linear ball bearings deliver adjustment-free dead-on cuts
- Exclusive 5-1/2-inch tall dual sliding fence system features upper and lower fence adjustment
- Independent micro fine laser with on/off switch indicates line of cut left or right of blade
- Includes 5-position jobsite miter stand with 9-foot material extensions for easy jobsite portability
- Cuts 8-inch crown molding (vertically nested), 6-1/2-inch baseboard (vertical), 15-inch crosscuts at 90 degrees
Christmas Sales Makita LS1216LX 12-Inch Dual Slide Compound Miter Saw with Laser and Stand Overview
The Makita LS1216LX combines the LS1216L 12-inch dual slide miter saw and the largest crosscutting and crown cutting capacity in its class with the convenience and mobility of Makita's jobsite miter saw stand. The LS1216L miter saw has a patented 4-steel rail sliding system that further increases rigidity to produce superior cuts, and an exclusive 6 linear ball bearing design for smooth, adjustment-free, "dead-on" accurate cuts. The LS1216LX miter saw and stand is ideal for jobsite use, as well as high-production/manufacturing settings.Christmas Sales Makita LS1216LX 12-Inch Dual Slide Compound Miter Saw with Laser and Stand Specifications
The Makita LS1216LX combines the LS1216L 12" dual slide miter saw and the largest crosscutting and crown cutting capacity in its class with the convenience and mobility of Makita's jobsite miter saw stand. The LS1216L miter saw has a patented 4-Steel Rail Sliding System that further increases rigidity to produce superior cuts, and an exclusive 6 linear ball bearing design for smooth, adjustment-free, "dead-on" accurate cuts. The LS1216LX miter saw and stand is ideal for jobsite use, as well as high-production/manufacturing settings. View larger | ||||
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The LS1216L will crosscut boards up to 15" wide at 90°, right out of the box with no special setup required. It has an innovative direct drive gearbox and patented retractable guard system engineered for increased vertical cutting capacity and the largest crown molding cutting capacity (8" vertically nested) in its class. The patented retractable rear guard also provides 6-1/2" baseboard cutting capacity (vertical). In addition, the exclusive 6 linear ball bearings deliver smooth, solid and adjustment-free "dead-on" accurate cuts. The saw also has a patented 4-Steel Rail Sliding System that further increases rigidity to produce superior cuts, as the four steel rails provide less deflection. The result is a larger cutting capacity and more accuracy.
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In addition to the large cutting capacity, power, and accuracy, the LS1216L offers a range of conveniences and ease-of-use features. The LS1216L has a patented 4-Steel Rail Sliding System that requires less rear space than competitor dual sliding miter saws. The see-through blade guard system provides greater visibility of blade and line of cut, and has a one-step blade change process for increased efficiency. The ergonomic rubberized horizontal D-handle design has a better fit and added comfort, and the large trigger switch is designed for easier operation.
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The LS1216L has a 15 AMP direct gear box motor that never slips, bogs down, or requires maintenance like belt-driven saws. The soft start feature delivers smoother startups, and the Electronic Speed Control maintains constant speed under load for smoother, higher-quality cutting. The LS1216LX includes the Makita Jobsite Miter Saw Stand. The stand adjusts to five positions with a spring-loaded mechanism for quick and easy setups in seconds. It also includes a large platform base and 9' material support extensions with feed roller to support long crown molding. The stand is equipped with a large rubberized handle and solid rubber 12" wheels for easy jobsite portability.
Best in Class for a Range of Applications
The LS1216LX is engineered for precision tasks in woodworking shops, as well as for cutting large materials like 4" x 16" beams and wide boards up to 15". It is ideal for a broad range of tradespeople, including finish carpenters, professional woodworkers, case and base installers, cabinet installers, cabinet manufacturers, closet installers, decking and flooring professionals, siding installers, stair installers, and general contractors seeking a best-in-class 12" dual slide compound miter saw and stand for the jobsite or high-production/manufacturing setting.
About Makita's Miter Saws with DXT
Makita's new miter saws with DXT (Deep and eXact Cutting Technology) are designed with an innovative direct drive gearbox and patented retractable guard system that are engineered for large vertical cutting. In addition, the exclusive 6 linear ball bearings deliver smooth, solid and adjustment-free "dead-on" accurate cuts. The saws also have a patented 4-Steel Rail Sliding System that further increases rigidity to produce superior cuts, as the four steel rails provide less deflection. The four steel rails also enable a more compact rear design than standard two-rail systems. Makita's new miter saws deliver a larger cutting capacity and more accuracy combined with a more compact rear design.
About Makita
Makita is a worldwide manufacturer of industrial-quality power tools, and it offers a wide range of industrial accessories. Makita applies leading-edge innovation to engineer power tools that are more compact and energy efficient, yet deliver industrial-strength power and results. Makita U.S.A., Inc. is located in La Mirada, California, and operates an extensive distribution network located throughout the U.S. For more information, please call 800-4-MAKITA (800-462-5482) or visit makitatools.com. Makita is Best in Class Engineering.
What's in the Box
Makita LS1216L 12-inch Dual Slide Compound Miter Saw, 60T TCT Saw Blade, Vertical Vise, Dust Bag, Triangular Rule, Wrench and Stand.
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