Despite the variety of unicellular, more complex organisms are much better known to humans. They represent the largest group, which includes more than one and a half million species. All multicellular organisms have certain common characteristics, but at the same time vary greatly. Therefore, it is worth considering individual kingdoms, and in the case of animals, classes.
General properties
The main feature separating unicellular and multicellular organisms is the functional difference. It arose in the course of evolution. As a result, the cells of the complex body began to specialize, uniting into tissues. The simplest ones use only one for all the necessary functions. Moreover, traditionally plants and fungi are counted separately, since animal and plant cells also have significant differences. But they should also be taken into account in the study of this topic. Unlike protozoa, they always consist of many cells, many of which have their own functions.
Mammals class
Of course, the most famous multicellular organisms are animals. Of these, in turn, mammals stand out. This is a highly organized class of chordates, which includes four and a half thousand species. Its representatives are found in any environment - on land, in soil, in fresh and salt bodies of water, in the air. The advantages of multicellular organisms of this type over others in the complex structure of the body. It is divided into the head, neck and torso, pairs of front and hind limbs, as well as the tail. Due to the special arrangement of the legs, the body is raised above the ground, which ensures speed of movement. All of them are distinguished by rather thick and elastic skin with sweat, sebaceous, odorous and mammary glands located in it. Animals have a large skull and complex muscles. There is a special abdominal septum called the diaphragm. Animal modes of movement include various activities, from walking to climbing. The heart consists of four chambers and supplies arterial blood to all organs and tissues. The lungs are used for breathing, the kidneys are used for excretion. The brain consists of five sections with several large hemispheres and cerebellum.
Bird class
Answering which organisms are multicellular, one cannot but mention birds. These are highly organized warm-blooded creatures that can fly. There are more than nine thousand modern species. The importance of a multicellular organism of this class is incredibly large, since they are as widespread as possible, which means they take part in the economic activities of people and play an important role in nature. From other creatures, birds are distinguished by several basic properties. They have streamlined torsos with forelimbs transformed into wings and hind limbs, which are used as a support. Birds are distinguished by dry skin without glands, with horn formations known as feathers. The skeleton is thin and durable, with air cavities ensuring its lightness. The muscular system provides the ability to walk, run, jump, swim, climb and two types of flight - hovering and waving. Most species can travel long distances. The birds have no teeth and there is goiter, as well as the muscular part, grinding food. The structure of the tongue and beak depends on the specialization of food.
Reptile class
It is worth mentioning this type of creature representing multicellular organisms. Animals of this class were the first to become terrestrial vertebrates. At the moment, about six thousand species are known. The skin of reptiles is dry and devoid of glands, it is covered by the stratum corneum, periodically descending during the molting process. The strong ossified skeleton is distinguished by a strengthened shoulder and pelvic girdles, as well as developed ribs and chest. The digestive tract is quite long and clearly differentiated, food is captured using jaws with sharp teeth. Respiratory organs are represented by lungs with a large surface, bronchi and trachea. The heart consists of three chambers. Body temperature is determined by the habitat. The excretory organs are the kidneys and the bladder. Fertilization is internal; eggs are laid on land and protected by a leathery or shell shell.
Amphibian class
Listing multicellular organisms, it is worth mentioning amphibians. This group of animals is ubiquitous, and is especially common in warm and humid climates. They have mastered the terrestrial environment, but have a direct connection with water. Amphibians came from brushfish. The amphibian body is distinguished by a flat shape and division into a head, trunk and two pairs of limbs with five fingers. Some also have a tail. Thin skin is characterized by many mucous glands. The skeleton consists of many cartilages. Muscles allow you to make a variety of movements. Amphibians are predators, food is digested by the stomach. The respiratory organs are the skin and lungs. Larvae use gills. The heart is three-chambered, with two circles of blood circulation - multicellular organisms often differ in such a system. The kidneys are used for excretion. Fertilization is external, occurs in water, development takes place with metamorphoses.
Insect class
Unicellular and multicellular organisms are not least distinguished by an amazing variety. Insects also belong to this type. This is the largest class - it includes more than a million species. Insects are distinguished by the ability to fly and greater mobility, which is provided by developed muscles with jointed limbs. The body is covered with a chitinous cuticle, the outer layer of which contains fatty substances that protect the body from drying out, ultraviolet radiation and damage. Different oral devices reduce the competition of species, which allows you to constantly maintain a high number of individuals. Small sizes become an additional advantage for survival, as does a wide range of breeding methods - parthenogenetic, bisexual, larval. Some also differ in polyembryony. The respiratory organs provide intensive gas exchange, and the nervous system with perfect sensory organs creates complex forms of behavior due to instincts.
Kingdom of plants
Of course, animals are the most common. But it is worth mentioning other multicellular organisms - plants. There are about three hundred and fifty thousand species. Their difference from other organisms is the ability to carry out photosynthesis. Plants act as food for many other organisms. Their cells have solid cellulose walls, and inside contains chlorophyll. Most are unable to carry out active movements. Lower plants do not have a separation into leaves, stem and root. Green algae live in the water and can be with different structures and methods of reproduction. Brown carry out photosynthesis using fucoxanthin. Red algae are found even at a depth of 200 meters. Lichens are the next kingdom. They are most significant in soil formation, and are also used in medicine, perfumery and the chemical industry. Higher plants are distinguished by the presence of leaves, root system and stems. The most primitive are mosses. The most developed are trees that can be flowering, dicotyledonous, monocotyledonous, or coniferous.
The kingdom of mushrooms
It is necessary to pass to the latter type, which can be multicellular organisms. Mushrooms combine traits of both plants and animals. More than one hundred thousand species are known. The variety of cells of multicellular organisms manifests itself most clearly in fungi - they are able to multiply by spores, synthesize vitamins and remain motionless, but at the same time, like animals, they can eat heterotrophically, do not carry out photosynthesis and have chitin, which is also found in arthropods.