Structures and Functions in Living Organisms · 4 question types
Past paper frequency (2018 to 2024)
This topic accounts for approximately 16% of your exam marks.
Blood glucose regulation and temperature control are increasing in frequency; insulin/glucagon tested every series.
Homeostasis is the maintenance of a constant internal environment in the body, despite changes in the outside environment
Body cells only work properly within a narrow range of conditions. Enzymes have a fixed optimum temperature and pH; cell membranes only function inside a narrow range of solute concentrations. If conditions drift outside this safe range, the body's chemistry breaks down. A drop in body temperature of more than a few degrees can be fatal, as can a drop in blood glucose to zero or a 30% loss of body water.
Homeostasis is the collection of mechanisms that keep these conditions stable. The major variables that the body keeps constant include:
The mechanisms covered in detail in this topic are blood glucose regulation and osmoregulation (water balance). Temperature regulation by the skin was covered in topic 10 (Coordination and Response), and water reabsorption by the kidneys was covered in topic 9 (Excretion). All of them are examples of the same general principle: negative feedback.