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

Study guide26 Nov 2025, 00:00 Z

Free IP Biology notes on thermoregulation, hormonal control, and nervous coordination for Sec 3 to Sec 4.

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Use this as a free IP Biology notes chapter on homeostasis, coordination, and response for Year 3 to Year 4. It keeps the IP pacing while reinforcing the 6093 biology foundations most schools test through DBQs, diagrams, and practical explanations.

Status: SEAB O-Level Biology 6093 syllabus (exams from 2026) checked 2025-11-30 - scope unchanged; remains the reference for this note.

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.
Hormones: insulin from pancreas beta cells lowers blood glucose (uptake, glycogen storage); glucagon from alpha cells raises it (glycogen breakdown). Type 2 diabetes risk factors: diet, inactivity, obesity. ADH from pituitary increases water reabsorption in collecting duct.
Nervous system: CNS (brain, spinal cord) + peripheral nerves; reflex arc = receptor → sensory neurone → relay neurone → motor neurone → effector (fast, involuntary).
Eye: parts (cornea, lens, iris, retina, optic nerve), focusing (ciliary muscle, suspensory ligaments), pupil reflex (bright light constricts, dim dilates).

Before writing any homeostasis answer, fill this feedback-loop skeleton:

Step	What to identify	Example wording
Change	Which condition moved away from the set point?	Blood glucose concentration rises after a meal.
Receptor	What detects the change?

Reviewed by

Ezekiel Tan·Academic Advisor (Biology)

Sources

SEAB GCE O-Level Biology (6093) syllabus (examinations from 2026)

Feature	Nervous control	Hormonal control	Common trap
Signal pathway	Electrical impulses travel along neurones and cross synapses by chemicals.	Hormones are carried in the blood.	Saying hormones travel along nerves.
Speed	Very fast because impulses follow a direct pathway.	Slower because hormones must circulate in the blood.	Saying all body responses are instant.
Duration	Usually short-lived because impulses stop quickly.	Often longer-lasting because hormones remain in blood for longer.	Treating hormone effects like a one-second reflex.
Target	Usually specific muscles or glands.	Only cells with the correct receptors respond, even though the hormone travels widely.	Saying every cell responds to every hormone.

Starting change	Skin blood vessels	Sweat glands	Muscles and hairs	Correction
Body temperature rises	Vasodilation sends more blood near the skin surface	More sweat is produced and evaporates	Hairs lie flat; shivering stops	More heat is lost, so temperature falls towards the set point.
Body temperature falls	Vasoconstriction keeps more blood away from the skin surface	Less sweat is produced	Shivering may start; hairs stand more upright	Less heat is lost and more heat is generated, so temperature rises towards the set point.

Starting change	Hormone released	Main effector response	Correction
Blood glucose rises after a meal	More insulin	Liver and muscle cells take up more glucose; liver converts glucose to glycogen	Blood glucose falls back towards the set point.
Blood glucose falls between meals or during exercise	More glucagon	Liver converts glycogen back to glucose and releases glucose into the blood	Blood glucose rises back towards the set point.
Insulin is present but body cells respond poorly	Insulin response is less effective	Less glucose is removed from the blood for the same signal	Blood glucose remains higher for longer.

Body state	ADH level	Collecting duct permeability	Water reabsorbed	Urine produced
Too little water in blood	Higher ADH	More permeable to water	More water returns to the blood	Smaller volume, more concentrated urine
Too much water in blood	Lower ADH	Less permeable to water	Less water returns to the blood	Larger volume, more dilute urine

Question cue	Main response	What changes	Purpose	Common trap
Looking at a nearby object	Accommodation for near vision	Ciliary muscles contract, suspensory ligaments slacken, lens becomes thicker	Refract light more strongly so the image forms on the retina	Do not describe the pupil first; the lens shape is the key change.
Looking at a distant object	Accommodation for far vision	Ciliary muscles relax, suspensory ligaments become taut, lens becomes thinner	Refract light less strongly so the image forms on the retina	Do not say the lens moves forward or backward; its shape changes.
Bright light enters the eye	Pupil reflex in bright light	Circular iris muscles contract, radial iris muscles relax, pupil constricts	Reduce the amount of light entering the eye	This protects the retina by changing pupil size, not lens shape.
Dim light enters the eye	Pupil reflex in dim light	Radial iris muscles contract, circular iris muscles relax, pupil dilates	Allow more light to enter the eye	A larger pupil does not focus the image; the lens still does focusing.

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

What you must know

Sources

Nervous versus hormonal control checkpoint

Thermoregulation response checkpoint

Blood glucose feedback checkpoint

ADH water-balance checkpoint

Eye response checkpoint

Reflex arc sequence checkpoint

Detailed notes

Worked walkthroughs

Pitfalls and fixes

Practice drills

Quick applications

Exam cues

Next steps

Related Posts

Step	What to name	What happens
1. Stimulus	The change that starts the response	A sharp object pricks the skin.
2. Receptor	The cell or organ that detects the stimulus	Pain receptors in the skin detect the prick.
3. Sensory neurone	Carries impulse towards the CNS	The impulse travels to the spinal cord.
4. Relay neurone	Connects neurones inside the CNS	The impulse is passed across synapses in the spinal cord.
5. Motor neurone	Carries impulse away from the CNS	The impulse travels to the arm muscle.
6. Effector	Muscle or gland that responds	The muscle contracts and pulls the hand away.