Explain why the cell surface membrane is important to cells.
Explain how enzymes work.
Suggest what changes occur in the enzyme’s molecular structure during 'cold denaturation'.
Cryoprotectants, such as trehalose, are especially important in preserving cells, tissues or organisms for later use. An investigation was done to determine the protective effect of different concentrations of two cryoprotectants, trehalose and glycerol, on a respiratory enzyme. The enzyme was exposed to a freezing temperature and then returned to its optimum temperature. The enzyme activity was measured at its optimum temperature. Fig. 4.2 is a graph showing the results of the investigation. Using Fig. 4.2, describe the results of the investigation.
Complete the table by giving three differences between DNA replication and DNA transcription.
Replication errors may cause gene mutations. Define the term gene mutation.
Some disease-causing organisms mutate frequently, altering their antigens and making the disease much harder to control through a vaccination programme. Explain why existing vaccines may no longer be effective when the surface antigens of a disease-causing organism change.
State exactly the type of immunity acquired by a vaccinated person.
The virus that causes measles is described as antigenically stable because it rarely mutates. Measles vaccination programmes have been successful at preventing epidemics in many regions. Outline two reasons why measles is still common in many parts of the world, even though the vaccine is available.