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Plan an investigation to find out what effect changing the concentration of calcium ions has on the rate of coagulation of milk.

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Introduction

Biology Practical Write-up Aim: Plan an investigation to find out what effect changing the concentration of calcium ions has on the rate of coagulation of milk. Prediction: I predict that as the concentrations of calcium ions is increased; the rate of milk coagulation will also increase, but at a certain point the calcium ions will stop affecting the rate of coagulation, as the amount of Rennin the calcium can bind to will be kept constant. Explanation: Rennin is an enzyme; enzymes help lower the activation energy required for a reaction, but remain unchanged at the end. They work by forming an Enzyme Substrate complex, in which the substrate binds with the active site of the enzyme and the substrate will be broken down. The rate at which an enzyme works depends mainly on 4 factors: * Enzyme Concentration - The more of the enzyme, the more molecules that can be broken down (up to a certain point). ...read more.

Middle

Diagram: Method: * Setup apparatus as shown in the diagram. * Add 25cm3 of milk to a beaker, with 2.5cm3 of Sodium Citrate. * Add 25cm3 of milk to a beaker, with 2.5cm3 of Sodium Citrate, and to this add 3cm3 of the rennin, and add 3cm3 of distilled water; this will be used as a control. * Heat the milk solution and rennin, separately to 37oC. * Simultaneously start the stop clock, and add 3cm3 of the rennin solution and 3cm3 of Calcium Chloride at the selected concentration, maintaining the temperature throughout 37oC. * Dip the slide in the milk at 5 second intervals until flecks are observed, record the time taken. * Repeat the experiment with same concentration of calcium ions 3 times and calculate the average time taken, record the results in a table like the one shown below. Calcium Chloride Concentration Coagulation time - 1 Coagulation time - 2 Coagulation time - 3 Coagulation time - Average 0 - Water 0.2 moldm-3 0.4 moldm-3 0.6 moldm-3 0.8 ...read more.

Conclusion

* Care must be taken with all chemicals used; Calcium Chloride and Sodium Citrate can cause irritation to eyes and skin [5] [6]. * The experiment will be done in a well ventilated area to prevent inhalation of any chemicals. * Care must be taken when using glass equipment such as graduated pipettes and microscope slides, if any glass is broken it must be cleaned away immediately. Preliminary Work In the preliminary work, I first test the coagulation rate using: * 50cm3 of milk. * 3cm3 of 0.1 moldm-3 Rennin solution. * 3cm3 of 0.2 moldm-3 Calcium Chloride solution. The mixture did not coagulate after 3 minutes and so we halved the amount of milk to 25 cm3 and used 1moldm3 Calcium Chloride solution, this coagulated after 64 seconds, because of this I will now be using cm3 of milk, and to speed up the rate at which Rennin works, we will heat the solution to 37oC in a water bath, as well as this I found the flecks are easily noticeable with the eye, and so a microscope is not necessary. ...read more.

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    Example is a haemoglobin molecule. For this plan, I will use rennin (chymosin) as an enzyme to coagulate milk. As with most enzymes, rennin works best at optimum temperature of 37� C. Rennin will act as a constant in this experiment, whilst the variable will be the concentration of calcium ions in the form of calcium chloride.

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