What are stomata in animals

am Puls Biologie 7 RG, textbook

77 Movement In addition to the nastia, there are also plant movements that are based on the direction of stimulus. These movements are called tropisms 3. A distinction is made here whether the movement is towards the stimulus source (positive tropism, eg growth towards the light source) or away from the stimulus source (negative tropism, eg growth against gravity) (k Fig. 8). Furthermore, tropisms such as nastia can be classified according to the type of stimulus: If light is the triggering stimulus, one speaks of photo-tropism, for a heat stimulus a thermo-tropism, etc. Tropisms usually take place relatively slowly and often have a lasting effect Changes for the plant. So tropisms are mostly growth movements. Tropisms are movements in which the organs of plants orient themselves to the direction of the stimulus. Fig.8: Tropisms: The sprout of the plant grows towards the light (positive photo tropism), the roots in the direction of gravity (positive gravitropism). The direction of movement is often independent of the direction of the stimulus. In most cases, movements are triggered by stimuli from the environment. The direction of movement can - but does not have to - have to do with the direction of the stimulus. If the movement is independent of the direction of the stimulus, it is called a nastie 1. Nastias are triggered by an external stimulus, but take place in a given direction. A typical example is the opening or closing of the stomata (stomata 2) in the epidermis of the leaves: The stomata open to let CO 2 into the tissue of the leaf so that it can be processed in photosynthesis. Since water vapor is also lost when the stomata is open, these openings close at night, but also when there is a lack of water. The opening or closing of the stomata is triggered by various stimuli (light, water, temperature). Other nastias are only triggered by one type of stimulus, these are then named according to the type of stimulus. For example, the movement of mimosa described on the previous page is triggered by vibrations and described as seismo nastie. If light is the trigger, one speaks of photo nastia, the movement occurs as a reaction to a temperature stimulus, one calls it thermo nastia, etc. You surely also know the Venus flytrap Dionaea, which quickly catches its leaves when touched closes (k Fig. 7). The sequence of movements has not been fully clarified. In addition to the shape of the leaves, turgor and growth movements play a role. The stimulus causes them to jump into a concave shape - and snap shut. This movement is also a nastia - more precisely a thigmo-nastia. Fig.7: Catch leaves of the Venus flytrap Dionaea. Inside the catch leaves of the Venus flytrap are fine bristles which, when touched, cause the leaves to close in order to catch insects. In nastia, organs of plants move independently of the direction of stimulation. Glossary 1 Nastie: from the Greek nastos for firmly pressed. 2 stomata, singular stoma: from the Greek stoma for mouth or opening. 3 tropism: from the Greek trope for phrase. Exercise E 1 Nastias and tropisms: In the following three plant movements are listed. Match them to the following types: hydro-tropism, photo-tropism, thermo-nasty: a. Plant shoot grows into a light source b. Tulips close flowers when the temperature drops c. Rhizoids of mosses grow towards water (hydro-tropism). Certain movements follow the direction of the stimuli. For testing purposes only - property of the publisher Öbv

Made with FlippingBook