Control and Coordination — Karnataka (SSLC) Class 10 Science Solutions (Free)

Nervous system = network of neurons and ganglia; controls body responses to environment. Two divisions: 1) Central nervous system (CNS): brain + spinal cord; processes information and coordinates responses. 2) Peripheral nervous system (PNS): nerves connected to CNS; carries signals to/from body. Reflex arc (spinal cord): stimulus → sensory neuron → spinal cord → motor neuron → response (fastest, no brain involvement). Enables rapid response to danger.

Reflex action = involuntary, rapid response to stimulus without conscious control. Reflex arc pathway: 1) Receptor detects stimulus (pain, heat). 2) Sensory neuron carries signal to spinal cord. 3) Synapse in spinal cord (neurotransmitter bridged). 4) Motor neuron carries signal from spinal cord. 5) Effector (muscle) responds (withdrawal). Example: touching hot object = instant hand withdrawal. Reflex is faster than voluntary action (conscious path through brain takes time). Protects from injury.

Synapse = junction between two neurons where electrical signal converts to chemical signal. Synaptic transmission: 1) Action potential reaches axon terminal of presynaptic neuron. 2) Neurotransmitter (acetylcholine, dopamine) released into synaptic cleft. 3) Neurotransmitter binds to receptors on postsynaptic neuron membrane. 4) Postsynaptic neuron depolarizes, generating new action potential. Transmission is one-way (from axon of one neuron to dendrite of next). Allows signal processing and regulation.

Hormones = chemical messengers secreted by endocrine glands; regulate body processes. Four examples: 1) Insulin (from pancreas): lowers blood glucose by promoting uptake. 2) Thyroxine (from thyroid): increases metabolic rate, growth, development. 3) Testosterone (from testes): male sexual characteristics, sperm production. 4) Estrogen (from ovaries): female sexual characteristics, egg maturation. Hormones travel through blood, act on specific target cells, slower than nervous system but longer-lasting effects.

Nervous system: electrical signals via neurons, rapid response (milliseconds), short duration, affects specific organs. Endocrine system: chemical signals (hormones) via blood, slower response (seconds/minutes), prolonged effects, affects multiple target organs. Nervous system: immediate reactions (reflex, muscle contraction). Endocrine: long-term regulation (growth, metabolism, reproduction). Both coordinate and integrate body functions; often work together (sympathetic nervous system triggers adrenaline release).

Tropism = directional growth response of plants to external stimulus. Phototropism: growth toward light (positive) due to uneven auxin distribution; shaded side has more auxin, grows more (bends toward light). Geotropism: growth response to gravity; root grows downward (positive geotropism), shoot upward (negative geotropism). Auxin (plant hormone) accumulates on shaded/lower side, promotes cell elongation there. Enables plants to maximize light absorption and anchor firmly in soil.

Plant hormones (auxins) = chemicals that regulate plant growth and development; primary auxin is indole-3-acetic acid (IAA). Sources: produced in shoot tips, transported downward. Two functions: 1) Promote cell elongation (enables growth). 2) Control tropisms (phototropism, geotropism) by uneven distribution. Auxins inhibit lateral bud growth (apical dominance), promote fruit development, enable root formation in cuttings. Synthetic auxins used in agriculture for rooting powder, weedkillers. Other hormones: gibberellins (growth), cytokinins (cell division), ethylene (ripening).