Definitions:
the unit of reproduction of a flowering plant, capable of developing into another such plant

a man's semen.

any of a number of stronger competitors in a sports tournament who have been assigned a specified position in an ordered list with the aim of ensuring that they do not play each other in the early rounds

a small crystal introduced into a liquid to act as a nucleus for crystallization.

a small container for radioactive material placed in body tissue during radiotherapy.

sow (land) with seeds

(of a plant) produce or drop seeds

remove the seeds from (vegetables or fruit)

give (a competitor) the status of seed in a tournament