Which statement about the function of enzymes is not correct?
A Enzymes affect the structure of whole organisms.
B Enzymes build larger molecules from smaller molecules.
C Enzymes carry signals from one part of the body to another.
D Enzymes catalyse reactions that affect cellular metabolism.
Your answer
The image below shows an enzyme and its substrate.
Enzyme Substrate
Which option represents a coenzyme for this enzyme?
Vitamins are molecules that are consumed in the diet of animals and have essential roles in the body.
Thin layer chromatography (TLC) was used to separate a mixture of vitamins from a vitamin supplement tablet.
Most vitamins are colourless.
Suggest one method for visualising the vitamins in TLC.
The results of the TLC are shown in the chromatogram in Fig. 2.1.
Use Fig. 2.1 to calculate the Rf value of vitamin B2.
Vitamin B9 is needed for the synthesis of molecule D, shown in Fig. 2.2.
Fig. 2.2
Molecule D is a component in the structure of DNA.
A deficiency of vitamin B9 in the diet can cause interphase to stop in some cells.
Use Fig. 2.2 to explain why a deficiency of vitamin B9 can cause interphase to stop.
Vitamin B2 is used by the body to make FAD. Vitamin B3 is used by the body to make NAD.
A mitochondrion is shown in Fig. 2.3.
Label Fig. 2.3 to show the locations where FAD gains H atoms and where FAD releases H atoms during respiration.
• Use the letter E to show where FAD gains H atoms.
• Use the letter F to show where FAD releases H atoms.
The table lists features that are correct for FAD, NAD, both or neither.
Complete the table by adding a tick (✓) to a box where the feature is correct and a cross (✗) where the feature is incorrect. You should add either a tick or a cross to every box in the table.
ATP is produced in respiration. Some of these molecules of ATP are used to release energy for processes in respiration. For example, ATP is used in the early stages of glycolysis.
Suggest one other way in which ATP contributes to the process of respiration.
Vitamin C affects the activity of enzymes in different ways.
Vitamin C acts as a coenzyme for several enzymes in the synthesis of collagen.
Outline the role of coenzymes in biological reactions.
A scientist investigates the effect of vitamin C on the activity of the enzyme adenylyl cyclase.
Adenylyl cyclase catalyses the conversion of ATP to cAMP.
The scientist measures the activity of adenylyl cyclase without vitamin C and with 1 mmol dm–3 of vitamin C.
The scientist’s results are shown in Fig. 2.4.
Explain what can be concluded from the results in Fig. 2.4 about the effect of vitamin C on the activity of adenylyl cyclase.
Many processes in the body are controlled by enzymes.
Which of the options is an extracellular process controlled by enzymes?
A Conversion of fibrinogen to fibrin during blood clotting
B Digestion of a pathogen inside a lysosome
C DNA replication
D Movement of vesicles from the Golgi apparatus to the cell membrane
Your answer
The liver is an organ with a wide variety of functions.
Fig. 18.1, in the insert, shows a light micrograph of a section of normal human liver.
Identify the structures labelled N and O in Fig. 18.1.
The walls of the structure labelled M in Fig. 18.1 are lined with cells.
Suggest and explain how these cells are adapted to carry out their function.
Liver is a rich source of the enzyme catalase.
The table below describes examples of three terms from the list below.
coenzyme competitive inhibition enzyme-product complex
induced-fit lock and key non-competitive inhibition
prosthetic group secondary structure tertiary structure
Complete the table by choosing a term from the list that matches each example.
Fig. 18.2 shows the effect of concentration of hydrogen peroxide on the rate of reaction of catalase.
Cyanide ions inhibit catalase, even at high concentrations of hydrogen peroxide.
Sketch a line on Fig. 18.2 to show the effect of repeating the experiment in the presence of cyanide ions.
[Answer on Fig. 18.2]
Icefish live in very cold water.
Icefish contain biological molecules that allow them to tolerate cold temperatures.
Adaptations can be grouped into three general categories.
Which category of adaptation is represented by cold-tolerant molecules?
Suggest and explain two improvements that would increase the validity of the students’ investigation.
Suggest appropriate units to use to represent the rate of enzyme activity in this investigation.
The students recorded the temperature that produced the fastest reaction rate in each of the five replicates. These results are shown in Table 3.
One of the students made the following statement:
I think the mean is a more accurate measure than the median or mode for these results.
Evaluate the student’s statement.
The students wanted to know whether there was a difference between the reaction rates of the two forms of trypsin at 30 °C.
They performed a statistical test on the mean of the five replicates for human trypsin and the five replicates for icefish trypsin.
Suggest the most appropriate statistical test for the students to use and explain why this test is appropriate.
* Plants lose water by transpiration.
The rate of transpiration varies between different species of plant.
The rate of transpiration can be measured using a potometer.
Plan an investigation into the rate of transpiration in two species of plant that would allow valid data to be collected.
Details of how to set up a potometer are not required.
Plant cell walls are made of cellulose. Cellulose is a polymer of 
-glucose.
Give three properties of cellulose that make it suitable as the basis of plant cell walls.
Cellulose cannot be digested by animals. Some mammals have bacteria in their stomachs that produce enzymes that can digest cellulose.
Explain whether the action of these enzymes is intracellular or extracellular.
Nitrogen cycling within ecosystems is controlled by various bacterial species. The table below lists four groups of bacterium that are involved in the nitrogen cycle.
Complete the table to show the locations of each type of bacterium in the cycle and the reactions they perform.
| Type of bacteria | Location | Reactant(s) | Product | Oxidation or reduction of nitrogen? |
| Rhizobium | N2 and H+ ions | NH3 | reduction | |
| Nitrosomonas | soil | oxidation | ||
| Nitrobacter | soil | NO3– | ||
| Denitrifiying bacteria | NO3– |
Nitrogen fixation is an important part of the nitrogen cycle.
The rate of nitrogen fixation is reduced by the presence of oxygen.
Rhizobium uses the enzyme nitrogenase to fix atmospheric nitrogen.
Fig. 4 shows a simplified representation of the structure of nitrogenase and the reaction that it
Overall reaction: N2 + 8H+ + 8e– + 16ATP 
2NH3 + H2 + 16ADP + 16Pi
Fig. 4
What can you conclude from Fig. 4 about the molecules or ions that affect the functioning of the nitrogenase enzyme?
Leghaemoglobin is a molecule that improves the performance of nitrogenase. It has very similar properties to mammalian haemoglobin.
Suggest two ways in which leghaemoglobin improves the performance of the nitrogenase enzyme.
Many species of bacteria act as decomposers within ecosystems by breaking down organic material.
Scientists analysed the energy flow within a grassland ecosystem.
They estimated that the energy in the decomposers’ trophic level was 950 000 J m–2 yr–1.
The energy within the producers’ trophic level was 800% greater than that of the decomposers.
Calculate the energy in the producers’ trophic level in kJ m–2 yr–1.
Answer:........ kJ m–2 yr–1
Calculate the percentage efficiency of the energy transfer from producers to decomposers.
Give your answer to two significant figures.
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