Ch 7 covers how organisms detect changes in the environment and respond — through the nervous system (fast, electrical) and hormonal/endocrine system (slow, chemical). It also covers plant hormones.
Neuron structure: dendrites (receive) → cell body → axon (transmit). Impulse travels as electrical signal along neuron, chemical signal across synapse. Reflex arc: receptor → sensory neuron → spinal cord (relay) → motor neuron → effector (muscle/gland). Brain: cerebrum (thinking, memory, voluntary actions), cerebellum (balance, posture), medulla (involuntary — breathing, heartbeat).
Hormones: chemical messengers secreted by endocrine glands into blood. Pituitary (master gland): growth hormone. Thyroid: thyroxine (metabolism, needs iodine). Pancreas: insulin (lowers blood sugar), glucagon (raises blood sugar). Adrenals: adrenaline (fight-or-flight). Feedback mechanisms regulate hormone levels.
Plants respond to stimuli by growth (tropisms): phototropism (light), geotropism (gravity), hydrotropism (water), chemotropism (chemicals), thigmotropism (touch). Plant hormones: auxin (growth, phototropism), gibberellin (stem elongation), cytokinin (cell division), abscisic acid (inhibits growth, wilting).
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Diabetes occurs when the pancreas doesn't produce enough insulin (Type 1) or the body doesn't respond to it properly (Type 2). Insulin is needed to allow sugar (glucose) from blood into cells. Without proper insulin function, blood sugar remains high, causing damage to eyes, kidneys, nerves, and heart over time.
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