molecule: The smallest particle of a specific compound that retains the chemical properties of that compound two or more atoms held together by chemical bonds.The biological levels of organization of living things arranged from the simplest to most complex are: organelle, cells, tissues, organs, organ systems, organisms, populations, communities, ecosystem, and biosphere.The highest level of organization for living things is the biosphere it encompasses all other levels.The simplest level of organization for living things is a single organelle, which is composed of aggregates of macromolecules.The bonding of at least two atoms or more form molecules.

The atom is the smallest and most fundamental unit of matter.In hot climates, organisms have methods (such as perspiration in humans or panting in dogs) that help them to shed excess body heat. Structures that aid in this type of insulation include fur, feathers, blubber, and fat. Organisms that live in cold climates, such as the polar bear, have body structures that help them withstand low temperatures and conserve body heat. For example, an organism needs to regulate body temperature through a process known as thermoregulation. Organisms are able to maintain internal conditions within a narrow range almost constantly, despite environmental changes, through homeostasis (literally, вЂњsteady stateвЂќ)-the ability of an organism to maintain constant internal conditions. These conditions may, however, change from one moment to the next. In order to function properly, cells need to have appropriate conditions such as proper temperature, pH, and appropriate concentration of diverse chemicals. Homeostasis: Polar bears (Ursus maritimus) and other mammals living in ice-covered regions maintain their body temperature by generating heat and reducing heat loss through thick fur and a dense layer of fat under their skin. These genes ensure that the offspring will belong to the same species and will have similar characteristics, such as size and shape. When reproduction occurs, genes containing DNA are passed along to an organismвЂ™s offspring. Multicellular organisms often produce specialized reproductive germline cells that will form new individuals.

They then divide it equally as the cell prepares to divide to form two new cells. Single-celled organisms reproduce by first duplicating their DNA. Movement toward a stimulus is considered a positive response, while movement away from a stimulus is considered a negative response. Even tiny bacteria can move toward or away from chemicals (a process called chemotaxis) or light (phototaxis). For example, plants can grow toward a source of light, climb on fences and walls, or respond to touch. Organisms can respond to diverse stimuli. After a few minutes, the plant returns to normal. Response to Stimuli: The leaves of this sensitive plant (Mimosa pudica) will instantly droop and fold when touched.

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