Communicable Diseases

Question 1

What are the steps involved with phagocytosis?

Answer 1

1. A pathogen releases chemicals that attract a phagocyte
2. The phagocyte recognises the pathogens antigens as being non-self and binds to the pathogen
3. The phagocyte engulfs the pathogen
4. The pathogen is contained within a phagosome
5. A lysosome fuses with a phagosome to form a phagolysosome
6. Lysozymes digest and destroy the pathogen and the phagocyte presents the pathogen’s antigens on its cell surface membrane

Question 2

Describe the steps involved in the cellular response to pathogens?

Answer 2

1. Macrophages engulf pathogens and display their antigens on their cell-surface membrane
2. T helper cells with complementary receptors bind to these antigens
3. This activates the T cells to divide by mitosis to form genetically identical cells
4. These clones can carry out specific functions

Question 3

What is the role of B cells in the humoral response?

Answer 3

1. B cells with complementary antibodies bind to a pathogen’s antigens, engulf them, and present them on their cell surface membrane
2. B cells are then activated by a T helper cell binding to these antigens
3. On activation, B cells divide by mitosis to form plasma cells and memory cells