From atoms to living organisms



All living organisms, from microbes to mammals, are composed of chemical substances from both the inorganic and organic world. That is, all living organisms are comprised of the same chemical elements that make up nonliving things.


Atoms make up molecules,

Molecules form organelles,

Organelles form cells,

Cells form tissues and organs,

And organ systems combine to form the living organisms.


Molecule is a group of atoms that are bound tightly together by strong chemical bonds called covalent bonds. When two or more atoms combine, they form a molecule, nonliving structure. For example, two atoms of the element hydrogen (abbreviated H) combine with one atom of the element oxygen (O) to form a molecule of water (H20). Small molecules serve as building blocks for larger molecules. Proteins, nucleic acids, carbonhydrates, and lipids, which include fats and oils, are the four major molecules that underlie cell structure and also participate in cell funcctions. For example, a tightly organized arrangement of lipids, proteins, and protein-sugar compounds forms the plasma membrane, or outer boundary, of certain cells. The organelles, membrane-bound compartments in cells, are built largely from proteins. Biochemical reactions in cells are guided by enzymes, specialized proteins that speed up chemical reactions. The nucleic acid deoxyribonucleic acid (DNA) contains the hereditary information for cells, and another nucleic acid, ribonucleic acid (RNA), works with DNA to build the thousands of proteins the cell needs.


Many substances on Earth are made of molecules. Millions of molecules join together to make up the cells in humans or in any other plant or animal. The food we eat, the air we breathe, the clothes we wear, and the wood, paint, and carpeting that we use in homes are all made of molecules. The nature of each molecule depends on the atoms that it contains and how they link to each other. For example, the oxygen that animals require is made of molecules that have two oxygen atoms bound together. If one oxygen atom binds to a carbon atom, the molecule is instead the poisonous gas carbon monoxide.


Molecules form organelles as endoplasmic reticum, ribosome, golgi apparatus, lysososme, mitochondria, and organelles form cells. Cells are the smallest structures capable of basic life processes, such as taking in nutrients, expelling waste, and reproducing. All living things are composed of cells. Some microscopic organisms, such as bacteria and protozoa, are unicellular, meaning they consist of a single cell. Plants, animals, and fungi are multicellular; that is, they are composed of a great many cells working in concert. But whether it makes up an entire bacterium or is just one of trillions in a human being, the cell is a marvel of design and efficiency. Cells carry out thousands of biochemical reactions each minute and reproduce new cells that perpetuate life.


Cells display a remarkable ability to join, communicate, and coordinate with other cells. The human body, for example, consists of an estimated 75 trillion cells. Dozens of different kinds of cells are organized into specialized groups called tissues such as tendon, bone, skin, mucosa. Different tissue types are assembled into organs such as stomach, heart, brain and liver, which are structures specialized to perform particular funcctions. Organs, in turn, are organized into systems such as the circulatory, digestive, or nervous systems. All together, these assembled organ systems form the human body or the other living organisms. Can an alive be created from dead or nonliving things? or Can living things be created from dead and nonliving things?

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