Cambridge O Level Biology · Syllabus 5090 · Coordination and Control
Hormone
What is Hormone?
A chemical substance, produced by a gland and carried by the blood, which alters the activity of one or more specific target organs. Hormones travel in the blood plasma and reach the whole body, but only cells carrying complementary receptors respond to them. Hormonal responses are generally slower to begin and longer-lasting than nervous ones.
This definition is part of the Coordination and Control chapter in Cambridge O Level Biology.
Common mistakes with Hormone
- Three things a hormone is not. It is not an enzyme — it is not a catalyst and it is not used to speed up a specific reaction. It is not an electrical impulse — it is a chemical, and it travels in blood, not along a neurone. And it is not a neurotransmitter — that acts across a single synapse, not around the whole body.
- Glycogen, glucagon, glucose. Three words, and in an exam under pressure they blur. Glucose is the sugar dissolved in the blood. Glycogen is the storage carbohydrate made of many glucose molecules, held in the liver. Glucagon is the hormone. Write each one out slowly the first time you use it in an answer.
Questions students ask about Hormone
What is a hormone?
A hormone is a chemical substance, produced by a gland and carried by the blood, which alters the activity of one or more specific target organs. Although a hormone reaches every organ in the body, only cells carrying receptors complementary to that hormone respond to it.
What is the difference between nervous and hormonal control?
Nervous control uses electrical impulses travelling along neurones, is rapid, is usually short-lived, and acts on the effectors that those neurones connect to. Hormonal control uses chemical hormones carried in the blood, is generally slower to begin, is often longer-lasting, and acts on any cells carrying complementary receptors.
What is Type 1 diabetes and how is it treated?
In Type 1 diabetes the pancreas does not produce enough insulin. The blood glucose concentration therefore becomes abnormally high, and glucose appears in the urine. It is treated by the administration of insulin, under professional medical guidance. Insulin replaces the missing hormone so that blood glucose can be controlled; it does not cure the condition, and the condition is not caused by eating sugar.