IP Biology Notes: Excretion in Humans (Upper Sec 07)

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: excretion, the urinary system, nephron function, ultrafiltration, selective reabsorption, urine formation, kidney failure, and dialysis form the main route.
• School-sensitive extension: detailed Loop of Henle mechanisms, counter-current language, hormonal water-balance detail, and calculations should be used only where the current school teaches them.
• 2027 national comparison: K325 Topic B7 requires the kidneys, ureters, bladder, and urethra, plus nephron function and dialysis at outline level.
• Check your school: nephron labels, the depth of pressure explanation, and the treatment of ADH or water balance can differ. Keep the urinary-system route distinct from nephron detail.
• Exam-track route: use the separate O-Level and SEC G3 Biology notes for K325 topic ownership.

The core idea is simple: Excretion removes metabolic waste from the body.

Use it as a working check: Do not confuse excretion with egestion. Kidneys remove urea, excess salts, and excess water by ultrafiltration and selective reabsorption.

Then go one layer deeper: Example: glucose is small enough to enter the filtrate, but a healthy nephron reabsorbs it in the proximal convoluted tubule so it does not appear in urine.

What you must know

• Urinary route: kidneys form urine, ureters carry it to the bladder, the bladder stores it, and the urethra carries it out of the body.
• Excretion = removal of metabolic waste ($\ce{CO2}$

Reviewed by

Ezekiel Tan·Academic Advisor (Biology)