The membrane bound organelle you refer to is the lysosome. The lysosome fuses with a vacuole where it digest the contents.
The Natural Selections do act on the population of living things,more on a specific trait. The best statement among the options then would be a. the trait is being pass on to the next generation through genetics.Hope this would be of help.
Because their carbon and energy must be obtained by eating or absorbing organic compounds originating from other living organisms
epipelagic or photic zone