What is the dietary iron of food sources not associated with hemoglobin called?

What feature of cell theory is best demonstrated in the image

The nervous system interacts with the endocrine system by a. using hormones as connections b. sending nerve impulses directly to glands c. using neuroendocrine cells as connections d. sending neurotransmitters directly to neurons

Substances that can pass through cell membranes by diffusion include a. na ions. b. proteins c. glucose. d. oxygen.