Plant Differentiation From Other Kingdoms
Plants are multicellular eukaryotes —that is, their cells contain membrane-bound structures called organelles. Plants differ from other eukaryotes because their cells are enclosed by more or less rigid cell walls composed primarily of cellulose . The most important characteristic of plants is their ability to photosynthesize. During photosynthesis, plants make their own food by converting light energy into chemical energy—a process carried out in the green cellular organelles called chloroplasts (see Chlorophyll ; Chloroplast ). A few plants have lost their chlorophyll and have become saprophytes or parasites —that is, they absorb their food from dead organic matter or living organic matter, respectively—but details of their structure show that they are evolved plant forms. Fungi , also eukaryotic and long considered members of the plant kingdom, have now been placed in a separate kingdom because they lack chlorophyll and plastids and because their rigid cell walls contain chitin rat...