| A | B |
|---|
| cell | The basic unit of structure and function in living things |
| cell membrane | The outside boundary of a cell; controls which substances can enter and leave the cell |
| nucleus | The control center of a cell that directs the cell's activities; contains the chemical instructions that direct all the cell's activities and determine the cell's characteristics |
| cytoplasm | The region of a cell located inside the cell membrane or between the cell membrane and nucleus; contains a gel-like material and cell organelles |
| tissue | A group of similar cells that perform a specific function in an organism |
| muscle tissue | A body tissue that contracts or shortens, making body parts move |
| nerve tissue | A body tissue that carries messages back and forth between the brain and every other part of the body |
| connective tissue | A body tissue that provides support for the body and connects all of its parts. |
| epithelial tissue | A body tissue that covers the surfaces of the body, inside and out |
| organ | A structure in the body that is composed of different kinds of tissues |
| organ system | A group of organs that work together to perform a major function in the body |
| homeostasis | The process by which an organism’s internal environment is kept stable in spite of changes in the external environment |
| stress | The reaction of a person’s body and mind to threatening, challenging, or disturbing events |
| vertebrae | The bones that make up the backbone of an animal |
| marrow | The soft tissue that fills the internal spaces in bone |
| cartilage | A connective tissue that is more flexible than bone and that gives support to some parts of the body |
| joint | A place where two bones come together |
| ligament | Strong connective tissue that holds together the bones in a movable joint |
| osteoporosis | A condition in which the body’s bones become weak and break easily |
| involuntary muscle | A muscle that is not under conscious control |
| voluntary muscle | A muscle that is under conscious control. |
| skeletal muscle | A muscle that is attached to the bones of the skeleton. |
| tendon | Strong connective tissue that attaches a muscle to a bone |
| smooth muscle | Involuntary muscle found inside many internal organs of the body |
| cardiac muscle | Muscle tissue found only in the heart |
| epidermis | The outermost layer of the skin |
| melanin | A pigment that gives the skin its color |
| dermis | The lower layer of the skin. |
| pore | An opening through which sweat reaches the surface of the skin |
| follicle | A structure in the dermis of the skin from which a strand of hair grows |
| cancer | A disease in which some body cells grow and divide uncontrollably, damaging the parts of the body around them |
| acne | A bacterial infection of the skin in which the oil glands become blocked and swollen |
