ZIMSEC O-Level Biology (4025)

Excretion, Homeostasis and Coordination: notes

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Excretion: removal of waste from metabolism. Lungs remove carbon dioxide; kidneys remove urea; skin removes sweat.
Kidney: filters blood, reabsorbs useful substances and passes out urine.
Homeostasis: keeping the internal environment steady. Sweating and vasodilation cool the body; shivering warms it.
Blood sugar: insulin lowers it. Lack of insulin causes diabetes.
Reflex arc: stimulus, receptor, sensory neurone, relay neurone, motor neurone, effector.
Eye: the iris controls the pupil size; the lens focuses light on the retina.
Hormones: chemical messengers carried in blood. Adrenaline prepares the body for action.
Tropism: plant growth response; shoots grow towards light, roots grow towards gravity and water.