Living Organisms Are All Around

Living organisms are all around us and all have some basic, common characteristics that. This does not make any living organism any less complex or any less unique. This essay will consider those characteristics which identify a living organism from a non-living organism and take a look at the complexity of cells in living organisms. How the atoms within a cell work, the complexity of a cell's organization compared to that of a city, the help a cell gets from enzymes, respiration vs. photosynthesis, and the formation of peptide and disaccharide molecules will all be considered.

Living organisms have a number of common characteristics that could help one determine if there were living organisms when on a star planet. First of all, organization; even the simplest living organisms have a high level of organization. Next there is homeostasis. Living organisms are able to keep a constant, stable internal environment. Then there is adaptation to consider. Living organisms are made in a way that allows them to live in their specific environment. Reproduction must also be looked at. Living organisms all have some way of reproducing either asexually or sexually. Next to consider is that all living organisms must grow and develop. Living organisms must also have some way to get energy through sunlight, inorganic chemicals, or another organism; and then be able to release it. It must also be considered that living organisms must be able to detect and respond to stimuli internally and externally. Last to consider is interactions. Living organisms are able to interact with their environment, along with each other. (Farabee, 2010a)

An atom is a chemical unit within the structure of a cell and consists of a nucleus in the center with protons, neutrons and electrons. The protons have a +1 positive charge while the neutrons have a -1 negative charge. Electrons also have a -1 negative charge. If an atom gains neutrons, its atomic weight increases. If it loses neutrons, then its atomic weight decreases. When an atom gains protons it becomes an atom of the element with the next highest atomic number and if it loses protons, then it becomes an atom of the element with the next lowest atomic number. The gain of an electron gives an atom an extra -1 charge, while the loss of an electron gives it an extra +1 charge. ("Chemical Composition of the Body," 2005)

From looking at atoms, one can tell that cells can be pretty complex. They could be compared to a city. Take the nucleus, which contains the cells genetic material, or DNA; it can be thought of as city hall, while the DNA within the nucleus is the laws and regulations of the city. The cell membrane has gates, channels and pumps that either let in or force out certain molecules in order to protect the cell's internal environment and could be thought of as the police force of the city. The Endoplasmic Reticulum (ER) assembles the cell's proteins and could be considered the factory or manufacturing plant of the city. The Golgi receives new proteins and lipids from the ER, finishes them up, addresses them and sends them to their final destination. In this way, the Golgi could be the postal service of the city. Lysosomes get rid of unusable waste within the cell and recycles those materials that can be reused, making it the recycling and garbage center of the city. Mitochondria are where ATP, the main energy molecule, is made. It could be considered the city's power plant. Then we have the cell's cytoskeleton, which gives the cell its shape, strength and its ability to move. It can be looked at as the roadways and bridges of the city. ("Chemical Composition of the Body," 2005)

Cells do not act alone and have help from things like enzymes to complete their job. Enzymes are proteins make chemical reactions within cells occur faster ("Chemical Composition of the Body," 2005). Without enzymes, most reactions would not occur under the conditions of the temperatures and pressures compatible with life ("Chemical Composition of the Body," 2005). Respiration and photosynthesis both occur within living organisms and are different reactions, but they complement one another. Respiration occurs when there is an inhalation and an exhalation ("Chemical Composition of the Body," 2005). Photosynthesis is the process where plants, algae and photosynthetic bacteria use energy from light to synthesize organic compounds and results in the release of molecular oxygen (Whitmarsh and Govindjee, 1995). Both respiration and photosynthesis take something from the external environment, bring it into the living organism and then release it back out into the external environment.