A seed was discovered and, when planted, grew to be a large flowering plant. This organism is a single cell that was isolated from the human body, has no nucleus, and was causing the patient to be ill.

- A seed that when planted produces a flowering plant is an angiosperms.

- The single and non-nucleated cell that can make humans sick is a bacteria.

Explanation:

1. Seed is a germinal structure consisting of the embryo of plants called spermatophytes, a division of the embryophyte clade, capable of reproduction by the production of seeds.

Within the plants spermatophytes are found:

The seeds that spermatophytes produce are embryonic structures of the plants, which have a rigid external cover, that in suitable conditions can hatch to develop as adult plants.

2. Bacteria are unicellular prokaryotic organisms, whose cellular characteristics include being devoid of nuclei, not possessing most organelles, and possessing free circular DNA in their cytoplasm.

These prokaryotic organisms are considered pathogenic, because of their potential ability to produce disease by entering other living organisms.  A cell removed from the human body, unique, without a nucleus, and which can make a patient ill is certainly a bacteria.