Effects of Temperature & pH (Cambridge O Level Biology)

Fig. 1 illustrates the results of two enzyme-controlled reactions involving two different types of enzyme.

Fig. 1

Catalase is an enzyme found in many different tissues in plants and animals. It speeds up the rate of the following reaction.

Fig. 2

A scientist investigated the effect of pH on the activity of the enzyme catalase in a geranium plant.

Table 1 shows the scientist's results. 

Table 1

Calculate a mean result for pH 3.5

Use the grid below to draw a graph of the scientist's results. 

Fig. 3

Use Table 1 and the graph to answer the following:

Describe the results shown in the graph.

[3]

Predict the catalase activity at pH 7.

[1]

Explain why the catalase activity is zero at pH 2.

[1]

• 1. Place a drop of biuret solution into every well in a spotting tile.
  2. Put 4 cm³ of 1 % protein solution into a boiling tube.
  3. Put 4 cm³ of pepsin solution into a second boiling tube.
  4. Put both boiling tubes into a water bath at 20 °C.
  5. After 4 minutes add the pepsin solution to the protein solution together in one boiling tube, mixing together with a stirring rod.
  6. After 20 seconds add a drop of the protein/pepsin mixture to a drop of biuret solution in one well of the spotting tile.
  7. Repeat step 6 until the biuret solution no longer changes colour.
  8. Repeat steps 1–7 at 10 °C (using an ice water bath), 30 °C, 40 °C and 50 °C.

The concentration of protein present in the solution can also be measured using a colorimeter.

In a colorimeter, the amount of light that cannot pass through a solution is measured; giving the ‘absorbance’ of a solution. The darker the colour, the higher the absorbance.

Suggest advantages of using the colorimeter method rather than the method used by the students.

The graph below shows a calibration curve of concentration of protein versus absorbance.

An experiment was carried out to investigate the effect of a protease enzyme on a 1 % protein solution.

The absorbance at 30 °C was 0.8 arbitrary units after 20 seconds.Using the calibration curve, estimate the final concentration of protein in this solution after 20 seconds.

Explain why the concentration of protein in the solution at 10 °C after 1 minute is different from the concentration at 30 °C after 1 minute in the graph in part (b).

The student repeated the experiment but incubated the protease and 1% protein solution at 80 °C.

The absorbance was measured at approximately 1.14 arbitrary units.

Suggest a reason for this result.

Catalase is an enzyme that catalyses the breakdown of hydrogen peroxide into water and oxygen. 

The effect of temperature on catalase activity was investigated. 

The results are shown in Fig. 1

Fig. 1

State the temperature at which catalase is most active in Fig. 1. Give your answer in °C.

[1]

[1]

State one factor other than temperature that affects enzyme activity.

Fig. 1 shows an enzyme in its optimum pH and in a pH that is much lower.

Fig. 1

Describe what has happened to the enzyme. 

Sketch an appropriate substrate for the enzyme shown in Fig. 1

A farmer tested a range of pHs on the soil in a section of a field and recorded the percentage of germination of carrot seedlings at each pH. 

Fig. 2 shows the results. 

Fig. 2

Describe and explain which pH is the optimum pH for the carrot seedlings. 

Another farmer suggested they plant radish seedlings at the carrot seedling's optimum pH shown in Fig. 2. 

Explain why this farmer's suggestion may be incorrect. 

During the fermentation of yeast, enzymes that break down sugar release carbon dioxide gas. The volume of carbon dioxide released can be used to measure how fast these enzymes are working.

A student investigates if fermentation works faster at two different temperatures: 25°C or 30°C.
They measured the volume of carbon dioxide released in 15 minutes.
Fig. 1 shows the apparatus she uses.

Fig. 1

The student used a gas syringe, as shown in Fig. 1 to collect and measure the volume of carbon dioxide released. They could have measured the volume of carbon dioxide by collecting the gas over water in a measuring cylinder.

Use the information provided in Fig. 1 to suggest why it is better to use a gas syringe.

 [3]

[3]

[1]

Enzymes can be inhibited by chemicals called phenols during fermentation.

Phenols bind to amino acids on enzyme molecules.

Suggest how phenols inhibit enzymes.

Salivary amylase is an enzyme that is produced and secreted by salivary gland cells in the mouth.

Carbohydrate digestion, by amylase, begins in the mouth.

Starch, a polysaccharide, is hydrolysed into the disaccharide maltose by the enzyme salivary amylase.

The effect of changing pH and temperature on the digestion of starch by salivary amylase was investigated by a group of students. The results are shown in Table 1 and Table 2 below.

Table 1 - Effect of pH

Table 2 - Effect of temperature

A student reads the following statement on the Internet: ‘The main site for carbohydrate digestion is the small intestine.’

One of the students states that salivary amylase must be responsible for digesting starch in the small intestine. The student is incorrect.

Use the results in Table 1 to explain why.

Using the results shown in Table 2, explain how temperature affects digestion.