Epistasis describes the interaction of genes, where the epistatic gene masks the effects of another gene, called the hypostatic gene.

Epistasis describes the interaction of genes, where the gene at the epistatic locus masks the effects of another gene at the hypostatic locus.

As this is recessive epistasis, only the genotype aa will mask gene B (Aa will not mask B). BB or Bb will give the dominant phenotype as B is dominant to b. Thus, AaBb will yield the dominant phenotype.

Epistasis describes the interaction of genes, where the epistatic locus masks the effects of a gene at another locus. In this example, locus E is epistatic. As this is stated to be dominant epistasis, when the E locus is either Ee or EE this locus will mask the effect of the B locus (color). Thus, any combination of B/b with Ee or EE will result in white squash. When the E locus is homozygous recessive (ee), the effect of the B locus will not be masked. Thus, BbEe will result in yellow squash as ee will not mask the color, and B (yellow) is dominant.

Epistasis describes the interaction of genes, where the epistatic locus masks the effects of a gene at another locus. In this example, locus A is epistatic. As this is stated to be recessive epistasis, when the A locus is aa this locus will mask the effect of the B locus (color). Thus, any combination of B/b with aa will result in white snapdragon. Thus, bbaa will result in white snapdragon, as the epistatic locus will mask the effect of the B locus.

Symbiosis describes a relationship in which both parties benefit. It has been theorized that eukaryotic cells evolved from a symbiotic relationship in which one prokaryote engulfed another. The engulfed cell gained protection from the environment, while the engulfing cell gained an energy source from the engulfed cell.

Commensalism describes a relationship in which one party benefits and the other is neither helped, nor harmed. Parasitism describes a relationship in which one party benefits, while the other is harmed. Amensalism describes a relationship in which one party is unaffected, while the other party is obliterated. Synnecrosis is a relationship that is deadly to both parties involved.

Mutualistic relationships exist when both organisms benefit from a shared relationship. In the correct answer choice, plants provide energy to the fungi through carbohydrates and the fungi provides nitrogenous compounds to the plant.

Human blood vessel and S. mansoni is a parasitic relationship, as the worm is actually damaging to the host. Cat and mouse is a predatory relationship. The barnacle and mollusk shell is commensalism, with the barnacle benefitting and no effect occurring on the mollusk shell.

Symbiosis is when two organisms live in close proximity and usually benefit each other, such as in mutualism. However, this is not always the case. Commensalism is a type of symbiosis and only benefits one of the organisms or has neutral effects. Parasitism is another form of symbiosis, where one organism benefits at the expense of its host. 

The biosphere consists of all parts of Earth that supports life. An ecosystem consists of communities of organisms interacting with their environment. A community consists of populations of various species living in close proximity and interacting. A population consists of organisms of the same species living in close proximity and interacting. An organism is a living being that can reproduce, react to stimuli, grow, and maintain homeostasis. An organ system consists of a group of organs working together to achieve a specific function. An organ is a group of tissues that performs a specific function. A tissue is a group of cells with similar structure working together to perform a specific function. A cell is the fundamental unit of life, and composes all living things.

An ecosystem consists of communities of organisms interacting with their environment. A community consists of populations of various species living in close proximity and interacting. A population consists of organisms of the same species living in close proximity and interacting.