Hormones because if you think about it. Vertebrates must have backbones and mammals have them. And, humans are basically mammals. And the glands secrete hormones.
Answer: classification key ! :))
Explanation:
Answer:
it Changes according to the receptor.
Explanation:
Every cell has different receptors in the membrane, these receptors are specific, but different receptors can read one signal molecule, according to the receptor, this molecule can activate or inactivate different path ways.
Let me put it this way, if I give the same message to a botanist and a gardener they both are going to read it in different way even knowing it is the same.
They are the same because if u simplify both fractions they are both 1/4
