[填空题]
Students were investigating metabolic reactions k.:h3wp 1mkin/h at e7in the classroom 7t19 m a4ikgxyand were given an experiment which demonstrated the effect of temperature on xia7kym 4 9t1ga catabolic reaction.
A sample of fat was added to a beaker, which contained 150ml of a 1% sodium chloride solution.
The beaker and its contents were then added to a water bath, which was set at 15
o
C. The beaker was given 5 minutes to equalise with the temperature of the water bath. After 5 minutes,5 ml of a 2% lipase solution, at the same temperature as the water bath, was added to the beaker.
5 ml of 2 % sodium hydroxide (NaOH), pH 8.4, was added to a test tube and phenolphthalein, a colourless solution which turns pink in basic environments, was then added. The intensity of the pink colour is proportionate to the strength of the basic solution.
At exactly 20 minutes, a 5ml sample was taken from the beaker incubated in the water bath and added to the test tube.
The contents of the test tube were then immediately transferred into a cuvette and placed in a spectrophotometer set at 420 nm. The percentage transmission of light able to pass through the sample was measured and recorded.
The procedure was then repeated using water baths set at a range of different temperatures. The measurements were recorded in a table and presented in a graph.
1. 1.State the independent variable in this experiment.
2.Identify two factors, not already mentioned, that would need to be controlled in this experiment.
2. 1.Explain how the spectrophotometer is able to measure the breakdown of fat.
2.Explain the effect of increasing the temperature from 15
o
C to 35
o
C on the rate of the catabolic reaction.
3.Predict the percentage transmission for a sample incubated at 20
o
C. %
4.Evaluate the claim that based on the data, the optimum temperature for lipase activity is 35
o
C.
