Question

(19) a tick lands on a dog. it feeds on the dogs blood. large infestations may weaken the dog and make it susceptible to other illnesses. a commensalism b mutualism c parasitism (20) lichens are a combination of an alga and a fungus. the alga produces food for the fungus; the fungus provides protection for the alga and supplies needed nutrients. a mutualism b commensalism c parasitism

Explanation:

• For question (19): Parasitism is a relationship where one organism (the parasite, here the tick) benefits at the expense of another (the host, the dog). The tick feeds on the dog's blood and harms it, which fits parasitism. Commensalism is when one benefits and the other is neither helped nor harmed. Mutualism is when both benefit.
• For question (20): Mutualism is a relationship where both organisms benefit. The alga produces food for the fungus (benefiting the fungus) and the fungus provides protection and nutrients for the alga (benefiting the alga). Commensalism and parasitism do not fit as both are benefited here.

Answer:

1. C. Parasitism
2. A. Mutualism