What is meant by bilaterally symmetrical animals

am Puls Biologie 5, textbook

95 Animal Physiology 4.1 Metabolism in the Animal Kingdom Animals are agile and have compact bodies If you ask a young child what distinguishes animals from plants, they will probably name the most obvious animal characteristic: animals move. Strictly speaking, this does not only apply to animals: Plants can also move, albeit mostly very slowly. In spite of this, the child recognized an essential characteristic with this statement: animals generally have a high degree of mobility. On the one hand, this means the ability to move parts of the body against each other. On the other hand, this also means the ability to change location. Mobility is vital for animals: they have to move in order to get to food. This even applies to simple animals such as corals, which are stuck to their subsoil and catch or filter food from the surrounding water. The rapid movements are made possible by muscle cells, a type of cell that is only found in animals. The compact, symmetrical build of the animals goes hand in hand with the mobility. A compact body is essential for animals. The development of a slim, bilaterally 1, bilaterally symmetrical body has proven to be an evolutionary advantage: unlike, for example, jellyfish, most animals have a “front” and “back”. At the front end there are control and eating organs, the remaining organs are "stowed" in the body behind. Mobility and a compact body structure are necessary in order to get to food. Variability, relationship, history and evolution Glossary 1 bilateral: “two-sided”, from Latin to = twice and latus = side Basic concepts variability, relationship, history and Evolution: Bilateral symmetry has great advantages in terms of freedom of movement when searching for food. Therefore, a change from radial symmetry (i.e. from a round body shape) to bilateral symmetry can be observed in many animal groups in the course of evolution. Information and communication: In order to be able to react quickly to the environment, environmental stimuli must be filtered and decoded in such a way that a suitable reaction is possible. The perception of the environment occurs through the processing of the stimuli by sensory cells and the nervous system. Nervous systems and sensory organs: efficient control and stimulus reception Every cell, every living being has a highly complex control system in order to be able to absorb and process stimuli from the environment. The control systems of animals are, however, much more efficient than those of all other living beings. Of course, a tree must also react to stimuli from the environment. But anyone who has ever tried to catch a fly with their bare hands knows how quickly and effectively the controls work on animals. In addition to control systems within individual cells and, in the case of multicellulars, control with chemical messenger substances (hormones) between cells, animals have a particularly powerful system: the nervous system. The concentration and interconnection of many nerve cells gave rise to brains, the most complex biological systems of all. Like a computer, a brain is only useful if it has data to work with. Accordingly, the development of nerves and brains went hand in hand with the development of sense organs. The quick and effective absorption of stimuli from the environment is necessary in order to give the nervous system information about which reaction should take place. Animals have powerful systems for absorbing stimuli and for controlling the body. Information and communication Turning food into usable energy It seems simple that food contains nutrients. How complex it is, however, to break down an apple into its molecules, to sort them, to distribute them in the body and ultimately to convert them into a usable form of energy, is less easy. In order to cope with this task, complex digestive systems for breaking down and processing food have emerged in the course of evolution. Transport systems (eg our blood circulation) distribute the substances in the body. Respiratory systems are used to absorb O 2, which is required for processing the nutrients (see p. 104 ff.). Ultimately, animals need excretion systems to remove harmful or unusable waste from the body. Digestive, transport, respiratory and excretory systems enable metabolism. For testing purposes only - property of the publisher öbv

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