What type of herbicide is effective when absorbed through the leaves or roots, killing the entire plant?

A systemic herbicide is designed to be absorbed by the plant, either through the leaves or roots, and is then transported throughout the plant's system. This type of herbicide works on the principle that once absorbed, the chemical disrupts vital processes within the plant, such as photosynthesis or growth regulation, ultimately leading to the death of the entire plant.

This absorption capability distinguishes systemic herbicides from other types. For instance, contact herbicides typically only affect the parts of the plant that they physically touch and do not penetrate or move through the plant's vascular system. Cultural herbicides refer more generally to practices in agriculture that enhance plant health and manage weeds rather than specific chemical actions. Chemical herbicide is a broad term but does not specify the mechanism of action, making it less precise than referring to a systemic herbicide specifically.

Therefore, the effectiveness of systemic herbicides in killing the entire plant is a key characteristic that separates them from other types mentioned in the options.