Green plants are a large and diverse group of organisms. Called Plantae or sometimes, Viridiplantae, the group includes the land plants as well as green algae and seaweeds and stoneworts. This group contains hundreds of thousands of species and is one of the five kingdoms of organisms.
All green plants contain chlorophyll. Chlorophyll is a mixture of two pigments called chlorophyll A and chlorophyll B. These pigments have a very similar structure to human hemoglobin, the molecule that transports oxygen in red blood cells. In land plants, chlorophyll is "suspended in the cell fluids of the leaves and other parts of the plant," according to Newton Ask a Scientist. In more primitive plants, such as algae, it is simply dissolved inside of cells.
All plants use their chlorophyll to manufacture food. Plants take in carbon dioxide, water, nitrogen, magnesium and trace molecules from their environment. They use energy from the sunlight to turn these raw materials to food in the form of starch. This starch feeds the plant. Plants are a crucial first stage in the food chain. Not only do they produce their own food, but they produce the food that animals and other organisms eat.
Lack Sensory Organs
Animals posses nervous systems, and animals and some bacteria also posses specialized sensory organs. These organs are have evolved specifically to detect stimuli such as sound, heat, scent, direction and light. Plants have neither a central nervous system nor sensory organs. They can respond to their environments to some degree, tilting to follow the sun is an example, but cannot respond quickly as can animals.