| A | B |
|---|
| Organ system | group of organs that work together and perform a specific task. |
| Homeostasis | steady internal conditions when external conditions change. |
| Nutrient | part of food that is used by the body to grow and survive. |
| Calorie | unit of measurement of the amount of energy in food. |
| Lymphocyte | type of white blood cell that is made in the thymus, the spleen, and bone marrow. |
| Immunity | protection from infection or toxins. |
| Compact bone | hard outer layer of bone. |
| Hormone | chemical signal that is released by the organs of the endocrine system. |
| Neuron | basic unit of the nervous system; nerve cell. |
| Reflex | automatic movement in response to a signal. |
| Spongy bone | interior region of bone that contains many tiny holes. |
| Fertilization | joining of an egg and a sperm. |
| Gamete | human reproductive cell. |
| Ovum | female gamete. |
| Reproduction | process by which new organisms are produced. |
| Sperm | male gamete. |
| Zygote | cell that forms when an egg and a sperm join together. |
