IP Biology Notes: Homeostasis, Coordination, and Response (Upper Sec 08)

For Integrated Programme students: Your current school materials, teacher instructions, and assessment scope take precedence because IP topic sequence and depth vary by school. This is an Eclat IP guide, not the O-Level / SEC G3 exam-track guide.

How this chapter applies

• Eclat core: negative feedback, thermoregulation, hormones, endocrine glands, blood-glucose regulation, type 2 diabetes, ADH, nervous coordination, reflexes, and the eye form the main route.
• School-sensitive extension: action potentials, synaptic chemistry, wider endocrine axes, detailed kidney osmoregulation, and quantitative eye optics should be used only where the current school teaches them.
• 2027 national comparison: K325 Topic B8 covers the full common route, including the islets of Langerhans, insulin and glucagon, type 2 diabetes, ADH, reflex arcs, accommodation, and the pupil reflex.
• Check your school: terminology for co-ordination, neurone diagrams, eye-ray conventions, and the expected molecular depth of hormonal control can differ.
• Exam-track route: use the separate O-Level and SEC G3 Biology notes for K325 topic ownership.

The core idea is simple: Homeostasis keeps internal conditions close to a set point.

Use it as a working check: Use the same chain each time: receptor detects change, control centre coordinates, effector responds, and negative feedback reverses the change.

Then go one layer deeper: Example: when body temperature rises, the skin increases sweating and vasodilation so more heat is lost and temperature moves back down.

What you must know

• Homeostasis keeps internal environment constant; change detected by receptors → effectors act → negative feedback reverses change.
• Thermoregulation: hypothalamus as controller; responses include vasodilation/vasoconstriction of skin arterioles, sweating vs shivering, hairs lie flat vs stand, behavioural changes.
• A hormone is a chemical substance made by a gland, carried in the blood, and able to change the activity of specific target organs. An endocrine gland releases hormones directly into the blood. The islets of Langerhans in the pancreas contain cells that secrete insulin and glucagon.
• Blood glucose: insulin lowers blood glucose through uptake and glycogen storage; glucagon raises it through glycogen breakdown. Type 2 diabetes involves insulin resistance or insufficient insulin production. ADH increases water reabsorption in the collecting duct.
• Nervous system: CNS (brain, spinal cord) + peripheral nerves; reflex arc = receptor → sensory neurone → relay neurone → motor neurone → effector (fast, involuntary).