Coordination and Response covers how organisms detect and respond to changes in their environment using the nervous system and hormones, and how they maintain a stable internal environment (homeostasis).
Stimulus → receptor → coordinator (CNS) → effector → response. CNS: brain and spinal cord. Neurones: sensory (receptor → CNS), relay (within CNS), motor (CNS → effector). Reflex arc: rapid, automatic, protective. Example: touching hot object → pain receptor → sensory neurone → relay neurone → motor neurone → muscle contracts (hand pulled away). Synapse: gap between neurones. Chemical (neurotransmitter) diffuses across to trigger impulse in next neurone.
Hormones: chemical messengers carried in blood, slower but longer-lasting than nerves. Adrenaline: prepares body for fight-or-flight (increases heart rate, blood glucose). Insulin: lowers blood glucose (liver converts glucose → glycogen). Glucagon (Supplement): raises blood glucose (glycogen → glucose). Diabetes: Type 1 (no insulin produced — inject insulin) and Type 2 (cells respond less to insulin — diet/exercise). Homeostasis: maintaining constant internal environment (temperature ≈37°C, blood glucose, water balance).
Eye: cornea (refracts light), iris (controls pupil size), lens (focuses, accommodation), retina (receptors — rods for dim light, cones for colour). Near object: ciliary muscles contract, lens becomes thicker. Far object: ciliary muscles relax, lens thinner. Plant hormones: auxin causes cell elongation. Phototropism: shoot grows towards light (auxin moves to shaded side → more growth on shaded side → bends towards light). Gravitropism: root grows downwards, shoot grows upwards.
Type 1 diabetes: the immune system destroys insulin-producing beta cells in the pancreas — no insulin is produced. It usually develops in childhood. Treatment: regular insulin injections and monitoring blood glucose. Type 2 diabetes: the body still produces insulin but cells become resistant to it (they respond less). Often linked to obesity, poor diet, and lack of exercise. Treatment: controlled diet, exercise, medication. Type 2 is more common (~90% of diabetes cases) and can often be managed through lifestyle changes.
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