Organism: the Definition is online “ A living thing, whether made of one cell (like bacteria) or many cells (like a human), is called an organism
The answer is Paramecium.
The paramecium is a unicellular ciliated protozoan. They are
often found in fresh water and brackish water areas. They have the elongated
shaped that looks like a rod and has the color violet under the stain because it signifies that it is positive.
The mechanisms of reproductive isolation prevent the reproduction of two individuals from different species. The prezygotic mechanisms disrupt the stages of reproduction before the forming of the zygote or prevent the mating at the start, and the postzygotic mechanisms affect the stages of reproduction after the forming of the zygote.
So, the first and the third example (the urchins and the grasshoppers) show the prezygotic mechanism, as the two individuals are not able to mate or form a zygote.
The second and the fourth example ( zonkey and the death of a zygote) show the working of the postzygotic mechanisms, as the zygote is formed, but it seems to be inviable, and the zonkeys are sterile, preventing the individual to reproduce.
The earthworm has a closed circulatory system. An earthwormcirculates blood exclusively through vessels. There are three main vessels that supply the blood to organs within the earthworm. These vessels are the aortic arches, dorsal blood vessels, and ventral blood vessel
