Do you mean electron? If so they are molecules that transport electrons during cellular respiration.
Serous membrane is a thin membrane with two layers that lines and covers the wall and organs of the thoracic and abdominopelvic cavities, these organs includes the heart, lungs and the body cavity. Its role is to prevent friction between the organ and the body cavity wall. The membrane is formed by simple squamous epithelium which are filled with connective tissues.
The embryonic endoderm<span> develops into the interior linings of two tubes in the body, the digestive and respiratory tube. the </span>lining<span> of the follicles of the thyroid gland and the</span>epithelial<span> component of the thymus (i.e. thymic </span>epithelial<span> cells). Liver and pancreas cells are believed to </span>derive<span> from a common precursor.</span>
Scientist study index fossils so they will get an understanding of what life was like back then.
Answer:
Organisms respond to a signal called a stimulus.
Explanation: