In human development, which of these must be present before tissue if formed?
1. organ
2. organ system
3. vein
4. fertilized egg

Control of the body is accomplished by which of the following body systems? nervous system and circulatory system endocrine and repertory system circulatory and respiratory systems nervous system and endocrine systems

Which part of the neuron below is indicated by the arrow, and what is its function? hormones send chemical signals throughout the body to regulate other body processes. hormones are chemical signals that are sent throughout the body to regulate other body processes. hormones send electrical signals throughout the body to regulate other body processes. hormones are electrical signals that are sent throughout the body to regulate other body processes.

There are fewer than 100 naturally occurring elements in the universe, but there are millions of different unified substances. explain how this can be true.