Question

the oak mistletoe is a green, leafy plant that grows on trees and has white berries. mistletoe seeds are spread to other trees through the waste of birds that feed on the berries. the mistletoe seedlings grow into the tree to obtain water and nutrients
which answer choice correctly identifies a relationship between two of these organisms?
a the relationship between the tree and the mistletoe is commensalism.
b the relationship between the birds and the trees is predator - prey.
c the relationship between the birds and the trees is mutualism.
d the relationship between the tree and the mistletoe is parasitism.

spores of the fungus ustilago maydis land and grow on sweet corn. the fungus then infects the plant tissue, extracting nutrients from the plant’s cells.
the relationship between sweet corn and ustilago maydis can best be described as —
a competition
b commensalism
c predation
d parasitism

leaf - cutter ants harvest leaves and carry them to fungi that convert plant material into a usable form for the ants to digest. the fungi depend on the leaves for nutrients. the ants also produce an antibiotic on their bodies that helps protect the fungi from harmful bacteria.
which of these explains the relationship between the leaf - cutter ants and the fungi?
a predation, because the ants feed on the fungi
b mutualism, because both the ants and the fungi benefit from each other
c competition, because both organisms consume the same resource for energy
d commensalism, because the ants receive energy from the fungi and the fungi are unaffected

the edwards aquifer in south central texas is home to several unique species, some of which are found nowhere else in the world. a food web with some aquifer species is shown.
image of a food web with organisms: texas blind salamanders, texas cave shrimp, fernweeds, snails, bacteria, fungi
an environmental change that harms which organism would cause the most instability in the aquifer ecosystem?
a texas cave shrimp
b snails
c texas blind salamanders
d bacteria

Explanation:

First Question (Oak Mistletoe)

• Option A: Commensalism is when one benefits, the other is unaffected. Mistletoe takes water/nutrients from the tree, so the tree is harmed, not unaffected. Eliminate A.
• Option B: Predator - prey is when one organism hunts and eats another. Birds eat berries (not the tree itself), so this is not predator - prey. Eliminate B.
• Option C: Mutualism is when both benefit. Birds get food from berries, but the tree doesn't get a clear benefit from the birds (the birds spread mistletoe seeds which harm the tree). So not mutualism. Eliminate C.
• Option D: Parasitism is when one (parasite) benefits at the expense of the other (host). Mistletoe gets water/nutrients from the tree, harming it. This fits.

• Option A: Competition is when organisms compete for the same resource. The fungus is extracting nutrients from the corn, not competing. Eliminate A.
• Option B: Commensalism is when one benefits, the other is unaffected. The corn is harmed as the fungus takes its nutrients. Eliminate B.
• Option C: Predation is when one organism kills and eats another. The fungus is not eating the corn in the predation sense (it's extracting nutrients from cells). Eliminate C.
• Option D: Parasitism is when one (fungus) benefits by taking nutrients from the corn (host), harming it. This fits.

• Option A: Predation is when one eats the other. The ants use the fungi - converted material, not eat the fungi. Eliminate A.
• Option B: Mutualism is when both benefit. Ants get usable food from fungi, fungi get leaves (nutrients) and protection from ants' antibiotic. Both benefit. This fits.
• Option C: Competition is when they compete for the same resource. They are helping each other, not competing. Eliminate C.
• Option D: Commensalism is when one benefits, the other is unaffected. The fungi depend on the ants for protection, so they are affected (benefit), not unaffected. Eliminate D.

Answer:

D. The relationship between the tree and the mistletoe is parasitism.

Second Question (Ustilago maydis and Sweet Corn)