30 points

rhizobium is a bacteria that invades the root nodules of certain plants. these bacteria obtain nutrients from the plant cells and also fix atmospheric nitrogen so it can be used by the plants. which statement describes the relationship between the two organisms?

a. the bacteria don’t harm the plants but benefit only themselves.
b. the plants harm the bacteria but benefit themselves.
c. the relationship benefits both the plants and the bacteria.
d. the association harms both the bacteria and the plants.

The breakdown of food is accomplished by enzymes. a. physical b. chemical c. mechanical d. none of the above

Astudy by solloch and et. al., in 2017, gives the map above which shows the frequency of alleles with a ccr5-delta32 mutations over 87 different countries. this mutation deletes the presence of a co-receptor (ccr5) on the outside of human t-cells (lymphocytes). some viruses, such as the one responsible for the black death and human immunodeficiency virus (hiv), require this receptor for attachment to host cells during the infection process. the black death was an epidemic that passed over northern europe during the 14th century killing nearly 60% of europeans. according to this information, which explanation best explains why northern europeans show a greater immunity for hiv than some other parts of the world?

Pulmonary arteries carry highly oxygenated blood. true or false?