• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

AS Biology Practical - Planning Exercise

Extracts from this document...

Introduction

Biology Practical Examination 1 (Part A - Planning Exercise) Aim: To investigate the effect of the concentration of calcium ions on the coagulation of milk. Scientific Knowledge and Prediction[1][2][3][4][5] The major proteins in milk are the caseins; ?-caseins, �-caseins and ?-caseins which a group of small phosphoproteins that are able to easily form aggregates (called sub-micelles (see Fig 1.1)). In the presence of calcium ions, these sub-micelles can together form a larger aggregate called the casein micelles (see Figs 1.2 and 1.3). The enzyme rennin binds with ?-casein, forming an enzyme-substrate complex [3], hydrolysing a peptide bond and thus splitting it into two fragments (see Fig 2). The fragment that does not remain part of the sub-micelle (the macropeptide) carries the carbohydrate units[1]; the loss of the carbohydrate 'coats' means that strong cross-links between micelles can be formed which is essentially the process of coagulation [1][4] (see Fig 3). Notice how all bonds between sub-micelles in a micelle contain calcium (Fig 1.2). Therefore without calcium ions, no bonds can be made between sub-micelles meaning that micelles can not be formed. Even if rennin did act on the ?-casein, no effect would take place due to the lack of micelles in the first place. Fig 1: Fig 2: Fig 3: Hypothesis: As long as there is plenty of substrate available, if the calcium chloride solution concentration increases then the rate of coagulation also increases because there will be an increased number of micelles formed. ...read more.

Middle

3. Add to each beaker: Beaker Volume of Calcium Chloride solution (cm3) Volume of Water (cm3) Concentration of Calcium Chloride added altogether (mol dm-3) 1 3.0 0 1.0 2 2.7 0.3 0.9 3 2.4 0.6 0.8 4 2.1 0.9 0.7 5 1.8 1.2 0.6 6 1.5 1.5 0.5 7 1.2 1.8 0.4 By this method, a fixed final volume is maintained. Separate 5cm3 syringes are used for calcium chloride solution and water to prevent contamination. Mix each solution thoroughly with a glass rod, remembering to wash the rod with distilled water before use with each beaker so as to prevent cross-contamination. 4. Using a fresh 10cm3 syringe, add 10cm3 of solution 1 to a clean 50cm3 beaker. Using a 1cm3 syringe, add 1cm3 of the rennin solution, starting a stopwatch. Stir with a fresh microscope slide for roughly five seconds and take it out. A thin layer of milk should be now on the surface. Stop the stopwatch as soon as signs of coagulation first appear i.e. for 'flecks' of curd to appear on the slide. Record the time taken. The appearance of the coagulum is distinguishable by its whiter appearance to the liquid milk. Wash out the beaker tested in with distilled water, and repeat this step with the remaining 20cm3 of milk solution in beaker 1 a further two times. ...read more.

Conclusion

Also wash off any solution in contact with skin. Sodium Citrate solution Contains sodium hydroxide solution which is an irritant in such small concentrations. As above. General care to be taken with the apparatus; if glass is broken then immediate disposal required to prevent broken shards which can cause cuts. Calculations: The time taken for the test will be recorded in a table as following: Beaker Concentration of Calcium Chloride solution added (mol dm-3) Time taken for the first signs of coagulation (s) Mean time taken (s) Rate of Reaction (1/s) 1 1.0 2 0.9 3 0.8 4 0.7 5 0.6 6 0.5 7 0.4 A mean time of the three readings will be taken for further reliability. The rate of reaction is usually taken to be the initial rate of reaction, and is usually measured by taking the product produced per unit time. Unfortunately, there is no way in this experiment that one can measure accurately how much coagulation has occurred. As a result, the only distinguishably common moment, between tests of different concentrations of calcium ions, is the starting point of coagulation i.e. when 'flecks' of curd first begin to appear. The reciprocal of the time taken will then be proportional to the true rate; however this also means that the actual values and units are arbitrary. i.e. Rate of Coagulation= A graph would then be plotted of the rate against concentration of calcium chloride solution added, labelled as below, from which inferences could be made. ...read more.

The above preview is unformatted text

This student written piece of work is one of many that can be found in our AS and A Level Energy, Respiration & the Environment section.

Found what you're looking for?

  • Start learning 29% faster today
  • 150,000+ documents available
  • Just £6.99 a month

Not the one? Search for your essay title...
  • Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

See related essaysSee related essays

Related AS and A Level Energy, Respiration & the Environment essays

  1. Marked by a teacher

    Effect of nitrate concentration on the growth of Duckweeds

    5 star(s)

    So these two solutions had the most favourable uptake of water. Water is a very important component for plant, especially in photosynthesis and in nutrients uptake. The more water taken inside by the cells means that the photolysis part of water during photosynthesis takes place more, and therefore H+ from water is used for reducing the co- enzyme NADP.

  2. Investigate the effect of bile salt concentration on the digestion of milk by the ...

    Chemical digestion occurs in the mouth, stomach and small intestine. Temperature: In a reaction, increasing the temperature of the reactants usually increases the rate of reaction. This can be explained using the molecular kinetic theory. Temperature is proportional to the kinetic energy in a closed system; therefore increasing the temperature

  1. the effect of bile concentration on the activity of the enzyme lipase during the ...

    pH - pH is a measure of the acidity or hydrogen ion concentration of a solution. It is measured on a scale of 0-14 with pH values below 7 being acidic, values above 7 being basic and a value around 7 is neutral.

  2. Investigating the effects of Sodium Hydroxide concentration on Catalase

    H2O2= Na2O2 The chemical in which I will need for my experiment are Sodium hydroxide at different concentration and 10% hydroxide peroxide, in which the precaution that I will have to take will these two chemical is that sodium hydroxide is corrosive meaning that if I was to get any on my hands I should wash it right away.

  1. Effect of Concentration of Enzyme on the Rate of Reaction

    As the temperature increases, the activity of catalase increases and reaches maximum at optimum temperature of 37oC, which is about the temperature of human body. Any further increase in temperature will not increase the activity of enzyme, instead the activity of enzyme will decrease due to the fact that more and more enzymes are denatured by heat at increasing temperature.

  2. out how different concentrations of the enzyme pectinase affect the degradation of the substrate ...

    Hence pectinases break down the cell wall of plants (with no wood) this way, they are widely used in the fruit juice industry, where they are widely used to help extract, clarify and modify fruit juices. The optimal activity of these enzymes is at a pH of 5.5 and generally below 50�C, around 35�C.

  1. Investigating the effects of different lead chloride concentrations on the growth of cress seedlings

    By changing or removing one of the factors that plant growth is dependant on plants will not grow. For example, a plant that has little access to light will grow slower than a plant that is completely exposed to light.

  2. Effects of exercise on tidal volume and breathing rate

    These neurones automatically maintain the rhythmic cycle of inspiration and expiration. These neurones can be controlled by higher brain functions and afferent information from the body. Afferent Supply 1. Central chemoreceptor ? these are a group of cells that respond to changes in pH.

  • Over 160,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work