How do we know that something is alive?

The answer generally comes down to a series of conditions:

(1) Movement - Living things have an ability to detect and respond to stimuli (both internal and external) and are capable of moving as a response to a stimulus.

(2) Reproduction and heredity - All cells come from existing cells and must have some way of reproducing. Living things use a molecule called DNA (deoxyribonucleic acid) that we will study in more detail in future lectures as the physical carrier of inheritance and genetic information. This information is passed from one generation to the next and controls a large number of different characteristics. These instructions must be unchanging most of the time, but provide for the rare change in instructions. Changes in the hereditary instructions that can lead to evolution are called mutations

(3) Growth and development - Even single-celled organisms which reproduce by dividing themselves in half, grow. DNA contains the instructions for growth and development. When first formed by cell division, cells are small, and must grow and develop into mature cells. Animals and plants that are composed of large numbers of cells pass through a more complicated process of growth and development. Cells increase in number and also change themselves into different kinds of cells to form the various tissues and organs that make up the individual.

(4) Organization - Living things exhibit a high level of organization. Organisms are made up of cells. Cells contain organelles. Organelles are made up of molecules.

(5) Metabolism - Living things acquire energy (from sunlight, inorganic chemicals, or another organism), and by chemical processes use it to keep themselves alive. The chemical processes in the living cell are collectively called metabolism. A molecule called ATP (adenosine triphosphate) that we will study in more detail in a future lecture is an energy source for reproduction, growth, and maintenance.

(6) Homeostasis - essentially means remaining the same. Our bodies strive to maintain a constant yet dynamic internal environment. This includes such things as temperature, pH, and water concentrations.

We will be discussing each of the above topics in greater detail as we proceed through the course.

REVIEW: Hereditary instructions must
a. be unchanging most of the time.
b. pass from one generation to the next.
c. control a large number of different characteristics.
d. provide for the rare change in instructions.
e. all of these
Answer e