A portion of the electromagnetic spectrum is visible to the human eye, but I'm not sure what your options are.
Its b. Ecosystem
Population is the number of a species in an area, it has nothing to do with physical characteristics.
Abiotic is just an adjective meaning not alive
Competition is just the interactions between organisms in the struggle for food, water, space, mates, and many other things again not physical characteristics
To ensure there safety and comfort of subjects and to make sure the subjects are taken advantage of.
The main difference between vascular and nonvascular plants is that a vascular plant has vascular vessels to carry water and food to all the different parts of the plant.
