Scottish Highers Human Biology Experimental Design: 3. An investigation was carried

Question

3. An investigation was carried out into the effect of a competitive inhibitor on the activity of phosphatase at different substrate concentrations.

Phosphatase is an enzyme which catalyses the reaction shown.

phenolphthalein phosphate  ↔  phosphatase  ↔  phenolphthalein + phosphate

Substrate

Six test tubes each containing a different concentration of substrate were set up. The inhibitor and then the enzyme were added to each tube.

Figure 1 shows the contents of each tube.

After 30 minutes, 1 cm³ of alkali was added to each tube.

Phenolphthalein turns pink in the presence of alkali. The more phenolphthalein produced, the more intense the pink colour and the higher the absorbance reading measured by a colorimeter.

Table 1 shows the results of the investigation.

Figure 1

Table 1

| Concentration of substrate (M) | Absorbance (units) |
| ------------------------------- | ------------------ |
| 0.05                            | 0.20               |
| 0.10                            | 0.30               |
| 0.20                            | 0.48               |
| 0.40                            | 0.64               |
| 0.60                            | 0.78               |
| 0.80                            | 0.90               |

(a) Suggest why alkali was not added to each tube at the start of the investigation.

(b) State two variables, other than those shown above, which should be kept constant to make this investigation valid.

1 ______________________________________
2 ______________________________________

(c) Construct a line graph to show the data in Table 1.

(Additional graph paper, if required, can be found on Page 28)

(d) It was concluded that increasing substrate concentration reduces the effect of the competitive inhibitor.

Explain how the results of this investigation support this conclusion.

(e) Suggest how the results of this investigation would be different if a non-competitive inhibitor had been used.

3. An investigation was carried out into the effect of a competitive inhibitor on the activity of phosphatase at different substrate concentrations - Scottish Highers Human Biology - Question 3 - 2017

Worked Solution & Example Answer:3. An investigation was carried out into the effect of a competitive inhibitor on the activity of phosphatase at different substrate concentrations - Scottish Highers Human Biology - Question 3 - 2017

Suggest why alkali was not added to each tube at the start of the investigation.

State two variables, other than those shown above, which should be kept constant to make this investigation valid.

Construct a line graph to show the data in Table 1.

It was concluded that increasing substrate concentration reduces the effect of the competitive inhibitor. Explain how the results of this investigation support this conclusion.

Suggest how the results of this investigation would be different if a non-competitive inhibitor had been used.

Join the Scottish Highers students using SimpleStudy...