Maintaining a constant environment

What is homeostasis?

Maintenance of a constant internal environment

What can changes to external conditions do to enzymes?

Enzyme denaturation

What is a stimulus?

A change in environment

Examples of a stimulus and the response caused

Cold = shiver

Hot = sweat

UV = melanin produced

How is the composition of tissue fluid maintained?

By the blood

Why are communication systems needed in multicellular organisms?

Cells that detect the stimulus and cells that bring about a response may be in different parts of the body

What is negative feedback?

Stimulus is detected and a response is issued to bring the value back to normal

What is positive feedback?

Detects a stimulus and brings about a response that moves the factor away from the normal level

What is an example of positive feedback?

Oxytocin

• triggers contractions during labour

• when it is detected, more is secreted

• hence increasingly strong contractions