Question

Define.

(a) Reflex action

(b) Hormones

Answer 1

(a) Reflex action - The automatic action or response provoked by a stimulus is known as a reflex action. However, the reflex actions show sudden responses and do not involve any thinking.

When we accidentally touch a hot object, we withdraw our hands immediately without thinking. If we do not do this, our hands will burn. The sensory nerves detect the heat. They are connected to the nerves, which move the muscles of the hand. Such a connection of detecting the signal from the nerves (input), and responding to it immediately (output) is called a reflex arc.

A reflex arc makes instant and automatic responses possible. It connects the input nerve and the output nerve, and meets in a bundle in the spinal cord. In fact, nerves from all over the body meet in a bundle in the spinal cord, on their way to the brain. Therefore, the information input reaches the brain.

(b) Hormones - A hormone is a chemical messenger which is a small soluble organic molecule that travels in the blood and has its effect at a site different from the site from where it is released. Examples of hormones are adrenalin, estrogen, thyroid hormone and growth hormones.