A scientist is searching for chemical compounds involved in embryonic limb development. He discovers a new compound that is transiently expressed in the limbs and only seems to affect cells in its immediate vicinity (up to a few cell lengths away). How should the scientist classify this chemical compound

What was dr. willem johan kolff’s first step in using the scientific process to invent the hemodialysis machine? he built the machine and tried it with various patients, collecting data about its effectiveness. when a patient’s kidneys failed, he wondered if it would be possible to perform kidney functions with an external machine. he researched and collected data about numerous patients who exhibited symptoms of kidney failure. he drew conclusions from studies of various symptoms of kidney failure, and drew a design for the ideal external blood-processing machine.

An easy way to calculate the amount of energy available at each level is to what?

Sea stars, sea urchins, sand dollars, and brittle stars are all memeber of a group, what is the common name of the group they are all in