What comes to people’s mind when they hear the word “animal’? Most people will picture a furry creature with four legs such as a dog or a cat in their mind, but none will picture a sand dollar even though it’s an animal. Most people would find it’s difficult to label a sand dollar as an animal. To begin with, it doesn’t even look like a living thing; it looks like a flat piece of rock. Secondly, sand dollar looks nothing like a typical animal that people see daily; it doesn’t seem to have animal-like characteristics. How can sand dollar be considered an “animal”? Sand dollar is categorized as an animal because it has animal characteristics. Well, what are the characteristics of an animal? What make a creature an “animal”? To be categorized as an animal, the creature must be eukaryotic and multicellular.
On the macroscopic level a sand dollar looks nothing like other animals, but on the microscope level they are shares similarities. Animals are made up of eukaryotic cells which contain a nucleus enclosed in a membrane. This set them apart from bacteria and archaea which are made up of prokaryotic cells. Bacteria
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To be a eukaryote organism, animals’ cells must have membrane bound nucleus and organelles. To separate animal from other eukaryotic organisms, their cells not possess cell wall, vacuole and chloroplast like plant and fungi. Animal must be a heterotroph/holotroph. To be a multicellular organism, an animal must have more than one type of cells. Their cells must be able to differentiate and become specialized. These specialized must work together to allow an animal to have an advanced body system. These systems allow an animal to have advanced trait such as locomotion. Plant and fungi are also multicellular organism, but they are not advanced as animal. They do not possess locomotion; they cannot move freely on their