Rhizopus (commonly known as bread mould) is a saprophytic fungus. Saprophytes are organisms that obtain their nutrition by secreting digestive enzymes onto dead or decaying organic matter and then absorbing the resulting soluble products. Rhizopus grows on stale bread, decaying fruits, and other dead organic substrates, breaking them down extracellularly and absorbing the nutrients.
The other organisms listed obtain nutrition by different means. Bladderwort (Utricularia) and sundew (Drosera) are both carnivorous (insectivorous) plants that trap and digest small insects to supplement the mineral nutrients they cannot obtain from their nutrient-poor habitats. Mistletoe (Viscum) is a parasitic plant that grows on host trees and extracts water and nutrients from the host's vascular tissue using specialised structures called haustoria.
To distinguish modes of nutrition in exams, remember: saprophytes feed on dead matter, parasites feed on living hosts, and carnivorous plants trap living prey.
