Penicillium (the source of the antibiotic penicillin) is a mold that secretes a toxin that kills bacteria and other organisms. Penicillium, however, is not harmed by this toxin. This is an example of: a. predator-prey.
b. commensalism.
c. mutualism.
d. amensalism.

This is an example of amensalism (Option d).

Explanation:

The interaction between penicillium and bacteria is a typical example of amensalism.

Amensalism refers to a biological relationship established between two organisms, in which one of them avoids the growth, development, or survival of the other one. In this interaction, one of them is strongly affected by the other one, which does not seem to be affected at all. Antibiosis is referred to as amensalism interaction.

Antibiosis is the interaction in which one of the species secretes a chemical that kills the other species organism or inhibits its actions by causing severe damage. The organism that releases the toxic substance is called the inhibitor. For the inhibitor species, this relationship is neutral because it does not seem to be beneficiated or affected.    

Another classic example of amensalism is those plants that secrete chemicals to damage or kill other plants that live near them. In this way, the secretory plants may live and grow with no competition.  

interphase

the period of cell growth when the cell synthesizes new molecules and organelles. the cell is not dividing and it constitutes the majority of the time spent in the cell cycle

prophase

changes occur in the nucleus and cytoplasm. the chromatin condenses to form structures (sister chromatids) visible with a light microscope and the mitotic spindle begins to form, but the nucleus is still in tact

prometaphase

the nuclear envelope fragments and the spindle microtubules attach to the kinetochores of the sister chromatids

metaphase

all the cell's duplicated chromosomes are lined up at an imaginary plane equidistant between the poles of the mitotic spindle

anaphase

begins when sister chromatids separate from each other and ending when a complete set of daughter chromosomes arrives at each of the two poles of the cell

telophase

the daughter nuclei form at the two poles of a cell

cytokinesis

the division of a cytoplasm to form two separate daughter cells. usually occurs during telophase during mitosis. this and mitosis make up to mitotic (m) phase of the cell cycle