This is a photo of a yellow lily. A yellow lily is an example of tropism. Tropism is directional growth towards an external stimulus such as light or gravity in an organism. There are two ways of movement in tropism, positive and negative. Positive tropism is growth towards the stimulus and negative tropism is growth away from the stimulus. The yellow lily in the photo is demonstrating positive tropism because it is facing towards the external stimulus in this case being the sun. There are different types of tropism in organisms. The three main types of tropism are phototropism, heliotropsim, and chemotropism. Phototropism is used by organisms who produce their food from sunlight and move towards the light. This type is used by organisms such as algae, plankton, and small invertebrates. The next type of tropism is heliotropism; this type is used by land plants. Plants are restricted in their movements; therefore, they position themselves towards the sun. The yellow lily is experiencing heliotropism because its flowers are positioned towards the sun in order to receive maximum sunlight. The last type of tropism is chemotropism; this involves an organisms tendency to turn towards or away from specific chemicals. For example, an organism may use a chemical signal in order to mate or as a warning signal. In response, other organisms react to the chemical signal demonstrating chemotropism.
Editors. “Tropism - Definition, Types and Examples.” Biology Dictionary, Biology Dictionary, 29 Apr. 2017,
biologydictionary.net/tropism/.
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