Living Things Essay

659 Words3 Pages
Characteristics of Living Organisms Every living thing is made of smaller parts. The smaller parts have different functions, but all of the parts work together to enable the organism to live and survive in its environment. The smaller parts are made of even smaller parts, until you reach the smallest part of all: the cell. The cell is the basic building block of all living things. These cells, too small to be seen with the unaided eye, are organized into tissues. A tissue is a series of cells that accomplish a shared function. Tissues, in turn, form organs, such as the stomach and kidney. A number of organs working together compose an organ system. An organism is a complex series of various organ systems. All living organisms, from microbes to mammals, are composed of chemical substances from both the inorganic and organic world, that appear in roughly the same proportions, and perform the same general tasks. Hydrogen, oxygen, nitrogen, carbon, phosphorus, and sulfur normally make up more than 99% of the mass of living cells, and when combined in various ways, form virtually all known organic biomolecules. There are four general classes of macromolecules within living cells: nucleic acids, proteins, polysaccharides, and lipids. There are some very general rules to follow when trying to decide if something is living, or non-living. 1. Living things are composed of cells: * Single-cell organisms have everything they need to be self-sufficient. * In multicellular organisms, specialization increases until some cells do only certain things. 2. Living things use energy: * Generally living things function by homeostasis (balance) between all systems working together to make it work. They are a series of chemical reactions, exchanges, removals, wastes degradations and a constant exchange of energy * Living things take in energy
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