Taxis response is to move towards or away from the stimulus. If the organism moves towards the stimulus the taxis is positive, while if it moves away the taxis is negative. For example, flagellate protozoans of the genus "Euglena" move towards a light source. This reaction or behaviour is called "positive phototaxis", since phototaxis refers to a response to light and the organism is moving towards the stimulus. Many types of taxis have been identified, including: Depending on the type of sensory organs present, a taxis can be classified as a "klinotaxis", where an organism continuously samples the environment to determine
Largest organisms Largest organisms The largest organisms now found on Earth can be determined according to various aspects of an organism's size, such as: mass, volume, area, length, height, or even genome size. Some organisms group together to form a superorganism (such as ants or bees), but such are not classed as single large organisms. The Great Barrier Reef is the world's largest structure composed of living entities, stretching , but contains many organisms of many types of species. This article lists the largest species for various types of organisms, and mostly considers extant species. The organism sizes listed are frequently considered