The first electron micrograph of a virus (tobacco mosaic virus) was produced in 1939. before that time, how did scientists know that viruses existed if they could not see them? (hint: early scientists called viruses "filterable agents.")

As a bee feeds upon the nectar produced by a flower, the bee may become coated with the flower's pollen. as the bee flies from flower to flower, some of this pollen may contact a flower's pistil, resulting in pollination. this relationship between the bee and the flower is an example of a. parasitism b. commensalism c. mutualism d. competition