Last Minute Bio Revision

Question 1

What is the role of phytoalexins?

Answer 1

-disrupt pathogen metabolism
-delay pathogen reproduction
-disrupt bacterial CSMs
-stimulate release of chitinases (breakdown of chitin walls of fungi)

Question 2

Active plant defences?

Answer 2

-reinforce cell walls using Callose and Lignin in between CSM and cell wall (reduce pathogen spread)
-narrow plasmodesmata (channels between neighbouring cells) using callose
-callose ingrowths in xylem vessels
-blocking of phloem (seive pores are blocked w callose)

Question 3

Passive chemical defences? (Plant)

Answer 3

-toxic substances e.g catchenol
-competitive growths e.g yeast
-enzyme inhibitors e.g tannins
-receptor molecules

Question 4

Describe humoral immunity

Answer 4

-Helper T Cell binds to antigen on an APC macrophage
-Activated Helper T Cell releases interleukins which stimulate mitosis and increase phagocytosis in other macrophages
-B lymphocytes engulf pathogens and become APCs
-Activated Helper T cell binds to B lymphocyte (clonal selection), activating B lymphocyte and releasing more interleukins
-interleukins trigger B lymphocyte mitosis into plasma cells and B memory cells (clonal expansion)
-plasma cells release antibodies….
-memory cells remain in blood….