Learning focus
Use precise biological vocabulary, trace control pathways, explain cause-and-effect mechanisms, interpret diagrams and apply ideas to unfamiliar contexts.
Definition of a hormone
A hormone is a chemical substance produced by a gland, carried in the blood and able to alter the activity of one or more specific target organs. Only target cells with suitable receptor proteins respond. Hormones may circulate throughout the body but do not affect every cell.
Required glands and hormones
The adrenal glands produce adrenaline. The pancreas produces insulin and glucagon. The pituitary gland produces FSH and LH. The testes produce testosterone, and the ovaries produce oestrogen and progesterone. These reproductive hormones are developed further in the reproduction lessons.
Transport and target response
Endocrine glands release hormones directly into blood rather than through ducts. Plasma transports them. On reaching a target organ, the hormone binds to receptors and changes cell activity. The response can involve enzymes, membrane transport, growth or secretion.
Coordination with nerves
Hormonal and nervous control frequently work together. During stress, nervous signals rapidly activate organs and stimulate adrenaline release, while hormonal effects help sustain the response. Homeostasis often depends on both communication systems.
Practical or data skill
Construct a table with columns for gland, hormone, transport medium and principal target effect. Use arrow diagrams to trace each hormone from source to target.
Examination tip
A hormone is produced by a gland and carried by blood; it is not an electrical impulse.
Review questions and suggested answers
Question 1
Which gland produces FSH and LH?
Suggested answer
The pituitary gland.
Question 2
Which hormones are produced by the pancreas?
Suggested answer
Insulin and glucagon.
Question 3
Why do only certain cells respond to a hormone?
Suggested answer
They possess the complementary receptor protein.
