Basic Features of Life

Biology is the science of living things or organisms.  Scientific evidence suggests that life began on Earth approximately 3.5 billion years ago by variously proposed mechanisms.

Basic Features

Life is considered a characteristic of organisms that exhibit all or most of the certain phenomena such as Homeostasis, organization, growth, adaptation, response to stimuli and reproduction.

• Homeostasis is the regulation of the internal environment to maintain a constant state. For example: electrolyte concentration or sweating to reduce temperature.
• Organization means that any living organism is made of one or more cells and cells serve as basic unit of life.
• Metabolism refers to life-sustaining chemical transformations within the cells of living organisms. Metabolic reactions are of two types viz. anabolism and catabolism. Anabolism refers to transformation of energy by converting chemicals and energy into cellular components. Catabolism refers to decomposing organic matter. Living things require energy to maintain internal organization (homeostasis) and to produce the other phenomena associated with life.
• Growth refers to increase in size in all of parts of an organism. To grow, the organisms need to maintain a higher rate of metabolism than catabolism.
• Adaptation is the ability to change over time in response to the environment. This ability is fundamental to the process of evolution and is determined by the organism’s heredity, diet, and external factors.
• Response to stimuli can take many forms, from the contraction of a unicellular organism to external chemicals, to complex reactions involving all the senses of multicellular organisms.  A response is often expressed by motion; for example, the leaves of a plant turning toward the sun (phototropism), and chemotaxis.
• Reproduction is the ability to produce new individual organisms, either asexually from a single parent organism, or sexually from two parent organisms.

Are Viruses Living Organisms?

Viruses are most often considered replicators rather than forms of life. They have been described as “organisms at the edge of life, because

• They possess genes
• They evolve by natural selection
• They replicate by creating multiple copies of themselves through self-assembly.

However, viruses do not metabolize and they require a host cell to make new products. Virus self-assembly within host cells has implications for the study of the origin of life, as it may support the hypothesis that life could have started as self-assembling organic molecules.
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Carbon Bonds – The Basic Feature of Life on Earth

Life on earth is carbon based because carbon makes up 18 percent of the weight of the human body. Due to its unique electron configuration, carbon needs to share electrons. It can form four covalent bonds with other carbon atoms or a variety of other elements.

Comparison of Carbon and Silicon

We note here that technically, life on Earth could be based on silicon also because this element has the same bonding properties as carbon. However, there is much less silicon than there is carbon on Earth. Further, Carbon wins the competition on many accounts as follows:

• The bonding versatility of Carbon allows it take on many forms: long side chains that make up fatty acids and cell membranes, ring structures that compose hormones and sugars, and even simple gaseous molecules like methane (CH4) or carbon dioxide (CO2). Silicon has not those capabilities.
• While carbon is perfectly comfortable in a variety of different structures (rings, long chains, multi-ring chains, and double-bonded carbon catenations), silicon’s analogous structures are comparatively unstable and sometimes highly reactive. Additionally, such analogous silicon compounds may never occur in nature; the largest silicon molecule ever observed had only six silicon atoms. In contrast, some carbon-based molecules can have tens of thousands!