Module 2

Question 1

Vaccines protect people against disease. Explain how. (5)

Answer 1

• vaccines contain weakened pathogen
• produces memory cells
• on second exposure, memory cells produce antibodies and become active (recognise pathogen)
• rapidly produce more antibodies
• antibodies destroy pathogens

Question 2

Contrast how an optical microscope and a TEM work and contrast the limitations of their use when studying cells (6)

Answer 2

• TEM uses electrons and optical use light
• TEM allows a greater resolution
• TEM allows you to view smaller organelles in greater detail
• TEM allows you to view dead samples but optical can view live samples
• TEM doesn’t show colour but optical can
• TEM needs thinner samples
• TEM is more complex and time consuming preparation
• TEM focuses using magnets and optical uses glass lenses