Growth and Life Cycle

An organism is any living thing. Organisms may vary in size and shape, but all organisms are similar in that they can function independently and carry out life processes. A life process is a function that is essential for an organism to remain alive and produce new members of the species. When the life processes stop, the organism dies.

All organisms are unique, though they share many similarities. All organisms are alike in that they share the following characteristics:

All organisms are made of cells. A cell is a unit or building block with a definite structure and function. The number of cells in an organism varies from one to millions, depending on the size of the organism. Cells have membranes and substances that carry out chemical activities needed for life processes. Protoplasm is a liquid-like substance inside a cell that contains various suspended solid materials that carry out chemical processes needed for living.

All organisms need energy to carry out life processes. Energy for plants and animals comes from food.

All organisms grow, reproduce, and have life spans. Growth is increasing in size by adding cells. Reproduction is the process by which organisms produce new individuals of

the same kind. Lifespan is the length of time an organism lives.

Organisms respond and adapt to their environment. The environment may promote growth and life processes, or it may prevent growth or cause death.

As previously mentioned, a life process is a function that is essential for an organism to remain alive and produce new members of the species. All living organisms carry out life processes in different ways. Living organisms carry out the following eight life processes:

Acquisition and use of food -- Food is the material that provides nourishment for a living organism. The nutrients found in food provide organisms with energy. Some organ-

isms require food in a ready-to-use form. Other organisms, such as plants, can convert solar energy into chemical energy. The original source of energy for most living organisms

in the sun.

Movement -- Movement refers to internal processes as well as locomotion. Locomotion is the ability of an organism to move itself from one place to another. Locomotion is obviously very important to animals, as it helps them find food.

Circulation -- Circulation is the movement of necessary materials throughout an organism. Circulatory systems move blood, nutrients, oxygen, and wastes throughout animals, whereas vascular systems move water and nutrients throughout plants.

Respiration -- Respiration is the process by which the cells of an organism receive oxygen so that the energy in nutrients can be released. Respiratory structures vary among organisms and species.

Growth and repair -- Growth processes occur from the beginning to the end of life. During growth, an organism increases in size. Growth occurs when cells become larger,

multiply,or specialize into tissues and organs. Repair is the replacement of worn-out or damaged cells by new cells.

Secretion -- Secretion is an organism's production of substances that it needs for the living condition to occur. Secretions are often important in how an organism carries out

other life processes. For example, saliva is important to the digestive process in animals.

Sensation -- Sensation is an organism's awareness of its environment and the responses it makes to it. Organisms respond to stimuli received through their senses. Animals have highly developed systems for sensation in five areas: vision, hearing, touch, smell, and taste. Plants are responsive to light and to deficiencies or conditions in their

environment.

Reproduction -- Reproductive processes vary, but all sexual reproduction involves the union of a male sex cell and a female sex cell, regardless of the species involved.