Answer: Option D
Step-by-step explanation:
The pollen grains can be defined as the male reproductive cell which helps in reproduction. The pollen grains are produced from the anther which is the male reproductive organ of the plant.
The pollen grains fuse with the ovum in order to produce is a seed. Seed is the part of the system. The level of organization states that the the pollen grains are cells, anther from where it is produced is organ.
The seed formed is a part of system.