Food tests

State one other method for immobilising enzymes.

One advantage of using immobilised enzymes is that the enzyme can be reused many times. However, the process of immobilisation can reduce the activity of enzymes.

With reference to Fig. 18.1, explain why the activity of immobilised enzymes might be lower than that of enzymes that are free in solution.

Invertase is an enzyme that catalyses the following reaction:

Invertase is present in cells of baker’s yeast, a type of fungus.

It is possible to immobilise invertase and it is also possible to immobilise yeast cells.

Suggest one reason why using immobilised yeast might be more expensive than using immobilised invertase.

Microorganisms can be used to produce a variety of food products.

Microorganisms have simple nutrient requirements, which helps to reduce production costs.

List two other advantages of using microorganisms in food production.

Yoghurt is a food produced from milk using microorganisms.

Yoghurt production involves two bacteria: Lactobacillus delbrueckii and Streptococcus thermophilus.

The bacteria convert the lactose present in milk into lactic acid.

Lactic acid is an important contributor to the flavour of yoghurt. Lactic acid also helps to give yoghurt a longer shelf life than milk.

Suggest how lactic acid helps to extend the shelf life of yoghurt.

Both bacteria also break down some of the protein casein, which is present in milk.

Name the product of protein breakdown and describe the type of reaction that takes place.

The microorganism that is used to produce mycoprotein is a fungus.

The diagram is of a fermenter used for mycoprotein production.

Use the diagram to name the type of fermentation process used for mycoprotein production.

Justify your answer.

Suggest and explain why a cooling system is necessary.

The air inlet provides the fungus with oxygen for respiration, and ammonia.

Suggest and explain why the fungus is provided with ammonia.

Mycoprotein foods contain protein.

The presence of protein in a solution can be detected using biuret reagent.

In the presence of protein, biuret reagent turns from blue to violet.

A colorimeter can be used, along with biuret reagent, to determine the concentration of protein in a solution.

Outline how to use a colorimeter to determine the concentration of protein in a solution.

State one alternative method for determining the concentration of protein in a solution.

Fig. 16.1 shows the structure of ATP.

Name the circled component in Fig. 16.1.

Name the type of reaction that occurs when ATP is converted to ADP.

A teacher told his students that the human body makes the equivalent of its own mass in ATP every day.

Explain why, at the end of the day, only a small proportion of the students’ mass was ATP.

A student investigated the uptake of two different substances in cultured cells.

The rate of uptake was measured at different concentrations of each substance in the medium surrounding the cells.

The results are shown in Fig. 16.2.

The student concluded that one substance entered the cells by simple diffusion and the other by active transport.

Evaluate the student’s conclusion.

The student then added 2,4-dinitrophenol (DNP) to the cells. DNP inhibits respiration.

Predict the effect of DNP on the uptake of each substance and explain your prediction.

Substance A

Substance B

The student used a colorimeter to measure the concentration of each substance in the liquid surrounding the cells.

The colorimeter had an analogue display. The reading was indicated by a needle moving across a scale. The smallest divisions on the scale corresponded to 0.1 absorbance unit.

After the investigation the student suggested some improvements.

Draw a line between each of the improvements to the corresponding justification.

to 3 decimal places.

before use.

For each concentration, repeat the measurement of the rate of reaction

Ask students in several schools to

Gibberellin causes stem elongation in plants.

Fig. 17.1 shows the effect of gibberellin on cabbage plants.

Gibberellin causes an increase in the distance between the leaves on the stem, which is known as the internodal length.

Explain why gibberellin is classed as a plant hormone.

A scientist carried out an investigation into the effect of gibberellin on cabbage plants.

The scientist applied a range of volumes of gibberellin and measured the rate of increase of internodal length over 30 days.

Table 17 shows the scientist’s results.

Plot the results from Table 17 as a suitable graph.

Gibberellin causes an increase in internodal length.

State one other role of gibberellin in plants.

A student carried out chemical tests on cabbage leaves to investigate which molecules were present.

The student’s method was as follows:

Name a type of food molecule that the student will not be able to detect using these chemical tests.

The table below is a summary of some of the student’s findings.

Complete the table by writing in the missing observations and conclusions.

The student then used a colorimeter to measure the absorbance of the contents of Tube 2.

Explain how the use of a colorimeter could improve the student’s conclusion.

ATP can be produced in various ways. Each stage of respiration contributes to the production of ATP.

Describe the production of ATP by substrate-level phosphorylation in different stages of respiration with reference to the number of ATP molecules produced.

Glucose and other carbohydrates are present in respiring cells. The concentrations of carbohydrate molecules vary between tissues.

A student conducted tests on three tissues, A, B and C. Table 2 shows the results of these

Two of the tissues were known to be phloem tissue and liver tissue.

Use the evidence in Table 2 to identify which tissue, A, B or C, is phloem and which tissue is liver. Explain your answer.

Tissue........ must be phloem because........

Tissue........ must be liver because........

Using the information in Fig. 2, calculate the percentage of carbon atoms in the fatty acid that are able to enter the Krebs cycle.

The percentage of carbon atoms that a reaction makes available for use in the Krebs cycle can be described as the efficiency of the reaction.

Calculate the efficiency of the link reaction. Using your answer to part (i), state whether the link reaction is more, less or equally efficient when compared to the reactions described in Fig. 2.

Show your working.

Link reaction is........ efficient

Fig. 2 shows the role of coenzyme A in beta oxidation.

Suggest a role for coenzymes other than coenzyme A in beta oxidation.

Fig. 20 shows the disaccharide lactose, which is found in milk.

Another disaccharide is maltose. Maltose and lactose both contain the same number of atoms of each element, C, H and O.

State two other structural similarities between lactose and maltose.

Complete the table below to identify differences between the structures of lactose and maltose. The first one has been completed for you.

One of the monomers of lactose is galactose.

The bacterium E. coli usually uses glucose as a respiratory substrate.

Under certain circumstances, E. coli is able to use galactose as a respiratory substrate by breaking down lactose into glucose and galactose and then using both glucose and galactose as respiratory substrates.

Explain how the structure of galactose allows it to be used as a respiratory substrate.

E. coli usually grows in conditions where the extracellular concentration of lactose is low. In such conditions lactose does not easily cross the bacterial cell surface membrane.

Suggest and explain why lactose is unable to cross membranes.

In order for lactose to enter the cytoplasm of E. coli a protein is required.

The E. coli living in the digestive system of young mammals are more likely to contain this protein than E. coli living in the digestive system of old mammals.

Suggest an explanation for this observation.

Lactose is a reducing sugar.

Benedict’s reagent can be used to detect the presence of lactose in a solution.

A colorimeter can be used to measure the concentration of lactose.

The colorimeter first needs to be calibrated.

Describe how a method that uses Benedict’s reagent and a colorimeter could be calibrated to measure the concentration of lactose in an unknown sample.