It is the amount of the substance required (usually per body weight) to kill 50% of the test population.

However, it is by design an imperfect barrier since it must transport substances required for growth and development.

A biological resource is a substance or object required by an organism for normal growth, maintenance, and reproduction.

For example, biological activity can be expressed quantitatively as the concentration of a substance required to give a certain biological response.

The substances thus required, if the wants of the body are to be satisfied correctly, are called the food-stuffs; and they are the same during pregnancy as at other times.

That Haoma is the capable provider of all substance required to accommodate a comfortable, healthy, productive, full-bearing life.

They found the substance required.

Coenzyme Q-10 is an important vitamin-like substance required for the proper function of many organs and chemical reactions in the body.

You thus take out of the air the metal-substance contained therein; you can even taste the iron which you convert into substance required for making the blood.

In biology and ecology a resource is defined as a substance or object required by a living organism for normal growth, maintenance, and reproduction (see biological resource).