Animals are multicellular eukaryotic organisms in the biological kingdom Animalia. Animals are bipedal, have a symmetric body plan, and reproduce sexually. They can live independently from humans and other species, but have certain characteristics in common. Read on to learn more about animals. Here are some things you should know:
Animals are eukaryotic
The cells in animals are made up of microscopic structures called organelles. These cells perform specific functions for the body. Animal cells are highly diverse, with different shapes, sizes, and functions. For example, they may carry oxygen, contract muscles, secrete mucus, or protect organs. These cells are also advanced and eukaryotic, containing a nucleus and organelles. Read on to learn more about organelles and their function in animals.
In addition to their multicellular structure, all animals are eukaryotic, which means they do not have a rigid cell wall. They are motile, oxygen-dependent, and heterotrophic. Animals also have an internal chamber to digest their food, which distinguishes them from plants and algae. Moreover, all animals are heterotrophic, meaning they depend on other organisms to grow and survive.
They have a bilaterally symmetric body plan
Many animals are symmetric, but what are the advantages of symmetry? Bilateral symmetry means that the body has two sides. It gives the animal a more efficient nervous system. These creatures also have better eyesight and hearing, as their waste is excreted in another part of the body from the food they consume. Bilateral symmetry is a feature found in animals that live in the ocean, including echinoderm larvae.
Most multicellular organisms have a symmetrical body plan, with structures on one side of the axis of symmetry mirroring those on the other. Asymmetrical bodies are relatively rare in the animal kingdom, with sponges being notable exceptions. Nevertheless, most animals exhibit bilateral or radial symmetry. If you’re wondering how symmetry affects animal life, consider this:
They reproduce by sexual means
Most animal species reproduce by sexual means, although they are more closely related to plants than fungi. The reason for this is that sexual reproduction allows a species to combine their genome and stay ahead of parasites, which tend to evolve quickly and often overwhelm the host’s immune system. This process is known as the “Red Queen Hypothesis”, named for a character in Lewis Carol’s novel, “Through the Looking Glass”.
They have a backbone
Did you know that mammals and birds have backbones? The reason is simple: backbones help protect their spinal cords. Vertebrates include mammals, reptiles, birds, and fish. These animals all have internal skeletons that support their organs and help them move. The most well-known vertebrates are elephants, whales, dolphins, and sharks. The rest of the animal kingdom is composed of invertebrates.
Vertebrates, or animals with a backbone, are classified into five classes. Most vertebrates have a spinal column made of tiny, rigid bones, but sharks have a spine made of cartilage instead of bone. Vertebrates are bilaterally symmetrical, which means they all have a head and a trunk. There are forty thousand vertebrate species, or classified as such.
They have a nervous system
There are three types of nerve cells in the nervous system of animals. Elephants and jellyfish both have a nervous system. Despite being brainless, jellyfish are extremely sensitive and have a complex nervous system. The tentacles are sensitive to touch and the nerves help them interpret contact as an impending predator. The brain determines what to do and the nerves tell the muscles, skin, and trunk to act accordingly.
Jellyfish and earthworms are the simplest forms of animals with nervous systems. Jellyfish and echinoderms do not have true brains, but they do have nerve nets that bundle neurons into fibers, which are called “nerves”. The ragworm is the smallest animal known to have a nervous system, and its neurons are similar to those found in humans. For further explanation, see the article titled “What Is the Nervous System of an Animal?”
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