Characteristics of Life *What are the criteria for assigning something to the living world or nonliving world? *Biologists have established that living things share Eight characteristics of life. *These characteristics are: Presence of cells, Response to Stimuli, Homeostasis, Metabolism, Growth and Development, Reproduction, Change Over Time, and Organization

1) You must be made up of at least one cell. *The cell is a membrane-bound structure that is the basic unit of life. *The MINIMUM required to be living is one cell. No matter how many cells you have, you are an organism (any living thing). Unicellular = describes any organism made up of only ONE cell (ex: bacteria). Multicellular = describes any organism made up of two or more cells (ex: plants and animals).

2) You must be able to react to your environment. Any living thing can respond to a stimulus in the environment; a stimulus is a change in the environment that causes an organism to react (response). Ex: Stimulus = Heat Response = Sweating Stimulus = Pinch Response = Pain Stimulus = Smell of Freshly Baked Cookies Response = ?????

3) You must be able to maintain homeostasis Homeostasis – the ability of a living organism to maintain internal stability. *All living things must have mechanisms that allow them to maintain a stable internal environment or the organisms will die. Ex: Body Temperature Cell Water Content Glucose Levels *The above three examples are conditions that need to remain stable; the mechanisms that control these abilities: Body Temperature = Sweating Cell Water Content = Cellular Pumps Glucose Levels = Hormones in Pancreas

4) You must be able to reproduce and pass on hereditary information (DNA) Reproduction – the process of transferring hereditary information (DNA) to offspring; two types of reproduction: Sexual Reproduction – two parents pass on combined hereditary information to one offspring; offspring is genetically unique. Asexual Reproduction – one cell gives rise to two cells, passing on the same hereditary information. *Reproduction is NOT essential for the survival of an individual organism, but is essential for the survival of the species as a whole. *DNA contains the genetic information that will determine the type of organism produced: DNA is made up of thousands of small segments called “genes”.....each single gene coding for a particular trait.

5) You must be able to grow and develop Growth – process of getting larger by cell division. Development – process of changing from one phase to another. Growth is not essential at all points in an organisms life (each organism is unique regarding where, when, and how often growth occurs); however, development in organisms takes place during all points of life from birth to death.

6) You must be able to obtain and use energy *All living organisms require energy to build new cells and to maintain life processes. Metabolism – sum of all energy processes (input and output). Anabolism + Catabolism = METABOLISM Anabolism = building of complex substances from smaller substances. A + B = AB (ex: building of blood from water, proteins, ions, etc.) Catabolism = breakdown of complex substance to form simple substances (ex: breakdown of glucose during respiration to extract energy; breakdown of dead tissue) AB = A + B

Plants and certain species of bacteria metabolize their energy by using the sun’s energy in a chemical process called photosynthesis. Animals depend on other living things to metabolize their energy; the chemical reaction required for metabolism is called cellular respiration.

7) You must be able to change over time “Change” refers to a change in the genetic material that can affect the physical and chemical properties of organisms (all called “mutations”). This change is usually due to some change in the environment. Changes in DNA usually do not occur within an individual organism, but rather the species as a whole over a longer period of time. These mutations are referred to as adaptations and are required by the species to survive a changing world. This factor of acquiring adaptations from DNA mutations explains why there is much diversity of life-forms we see on Earth today.

8) You must show organization. *Organization is the high degree of order within an organism; all living things, whether made up of one cell or many cells, have some degree of organization.

Most cells are structured according to their function: Red Blood Cells Muscle Cells

Unicellular or Multicellular? Unicellular Multicellular No cells

Osteocytes (bone cells) Neurons (nerve cells)

Adipose Cells (fat!) Plant Cells

Sexual vs. Asexual?