There are traits that human beings share with all other living things. All living organisms share several key characteristics or functions including: order, sensitivity or response to the environment, reproduction, adaptation, growth and development, regulation, homeostasis, energy processing, and evolution. When viewed together, these characteristics help serve to define life.
ORDER
Organisms are highly organized, coordinated structures that consist of one or more cells. Even very simple, single-celled organisms are remarkably complex: inside each cell, atoms make up molecules; these in turn make up cell organelles and other cellular inclusions. In multicellular organisms, similar cells form tissues. Tissues, in turn, collaborate to create organs (body structures with a distinct function). Organs work together to form organ systems.
SENSITIVITY OR RESPONSE TO STIMULI
Organisms respond to diverse stimuli. For example, plants can bend toward a source of light, climb on fences and walls, or respond to touch. Even tiny bacteria can move toward or away from chemicals (a process called chemotaxis) or light (phototaxis). Movement toward a stimulus is considered a positive response, while movement away from a stimulus is considered a negative response.
REPRODUCTION
Single-celled organisms reproduce by first duplicating their DNA, and then dividing it equally as the cell prepares to divide to form two new cells. Multicellular organisms often produce specialized reproductive germline cells that will form new individuals. When reproduction occurs, genes containing DNA are passed along to an organism’s offspring. These genes ensure that the offspring will belong to the same species and will have similar characteristics, such as size and shape.
GROWTH AND DEVELOPMENT
Organisms grow and develop following specific instructions coded for by their genes. These genes provide instructions that will direct cellular growth and development, ensuring that a species’ young will grow up to exhibit many of the same characteristics as its parents.
REGULATION
Even the smallest organisms are complex and require multiple regulatory mechanisms to coordinate internal functions, respond to stimuli, and cope with environmental stresses. Two examples of internal functions regulated in an organism are nutrient transport and blood flow. Organs (groups of tissues working together) perform specific functions, such as carrying oxygen throughout the body, removing wastes, delivering nutrients to every cell, and cooling the body.
HOMEOSTASIS
Living Things Must Maintain Homeostasis. Homeostasis means “steady state”. Homeostasis is the tendency of an organism or cell to maintain a constant internal environment. Living things constantly adjust to internal and external changes. Homeostasis means to maintain dynamic equilibrium in the body. It is dynamic because it is constantly adjusting to the changes that the body’s systems encounter. It is equilibrium because body functions are kept within specific ranges or normal limits.
Thermoregulation
Thermoregulation is a process that allows your body to maintain its core internal temperature. The set point for normal human body temperature is approximately 37°C (98.6°F). Body temperature affects body activities. Body proteins, including enzymes, begin to denature and lose their function with high heat (around 50ºC for mammals). Enzyme activity will decrease by half for every ten-degree centigrade drop in temperature, to the point of freezing, with a few exceptions.
During body temperature regulation, temperature receptors in the skin (sensory receptor) communicate information to the brain (the control center) which signals the blood vessels and sweat glands in the skin (effectors). As the internal and external environment of the body are constantly changing, adjustments must be made continuously to stay at or near a specific value: the set point. (approximately 37°C / 98.6°F)
ENERGY PROCESSING
All organisms use a source of energy for their metabolic activities. Some organisms capture energy from the sun and convert it into chemical energy in food; others use chemical energy in molecules they take in as food.
THE DIVERSITY OF LIFE
There is a tremendous diversity of life on earth. The source of this diversity is evolution, the process of gradual change during which new species arise from older species. Evolutionary biologists study the evolution of living things in everything from the microscopic world to ecosystems.
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