Immunity: plant defences and the lymphatic system
Answers are for parents and teachers.
1
A fungus spore lands on a leaf with a waxy surface and on a leaf where water stays in drops. On which is it more likely to grow, and why?
On the leaf where water stays, because fungi need water to grow and water does not settle on cutin.
2
Compare tyloses and gums: one way they are alike and one way they differ.
Both are induced defences formed after an injury or invasion. Tyloses block the xylem vessels from inside, while gum is deposited at the injury to trap microbes.
3
A leaf has a small dead spot surrounded by healthy leaf, and the infection has not spread. Explain how this could be a defence, and name it.
The plant may have killed the infected tissue itself so that the pathogen could not reach healthy tissue. This is the hypersensitive response.
4
Explain why the bone marrow is a primary lymphoid organ but the spleen is a secondary one.
In the bone marrow lymphocytes are produced, mature and differentiate, while the spleen holds large numbers of lymphocytes that are already formed.
5
Why is the thymus gland counted both as a gland and as part of the immune system?
It makes the hormone thymosin, which matures T cells, so it belongs to both.