Control and coordination are processes that allow organisms to respond to internal and external stimuli, maintaining order and homeostasis. They are achieved mainly via the nervous and endocrine systems.
Nervous System
Endocrine System
Plant Hormones
Reflex Actions
NCERT Class 10 — Control & Coordination
A stimulus is any change detected by an organism (e.g., heat). A receptor senses it (e.g., skin thermoreceptors). An effector brings response (e.g., sweat glands, skeletal muscles).
Two main divisions: Central Nervous System (CNS) — brain and spinal cord; Peripheral Nervous System (PNS) — nerves connecting CNS to organs. PNS includes somatic and autonomic systems.
A neuron has a cell body (nucleus), dendrites (receive signals), and an axon (conducts impulses away). Some axons have a myelin sheath (insulation) and end in synaptic terminals for communication.
A synapse is a small gap between neuron terminals and the next cell. When an impulse arrives, neurotransmitters (chemical messengers, e.g., acetylcholine) are released, cross the gap, and trigger a response in the next cell.
Impulse conduction is an electrical change (action potential) moving along the membrane. In myelinated axons, propagation is faster via saltatory conduction — impulse jumps between Nodes of Ranvier.
A reflex action is an automatic, rapid response to a stimulus (no conscious control). The reflex arc includes receptor → sensory neuron → interneuron (in spinal cord) → motor neuron → effector (muscle/gland). Example: knee-jerk reflex.
Voluntary: under conscious control (e.g., walking). Involuntary: not consciously controlled (e.g., heartbeat, reflexes).
Spinal cord conducts impulses between brain and body and serves as a center for many reflexes. It has grey matter (cell bodies) and white matter (nerve fibers) and is protected by meninges and vertebral column.
- Cerebrum: higher functions — thinking, memory, voluntary actions.
- Cerebellum: balance and coordination.
- Medulla oblongata: involuntary actions — breathing, heart rate, digestion control.
The endocrine system uses hormones (chemical messengers) secreted by glands into the blood. Its effects are generally slower but longer-lasting compared to the fast and short-lived nervous impulses.
Pituitary secretes hormones like growth hormone (GH), FSH, LH, TSH and ACTH. It's often called the "master gland" because it regulates other endocrine glands.
Thyroid secretes thyroxine which regulates metabolic rate and growth. Iodine is essential for thyroxine synthesis; deficiency can cause goitre and developmental problems (cretinism).
Adrenal glands secrete adrenaline in emergencies — increases heart rate, breathing rate, blood flow to muscles, and mobilizes glucose (fight-or-flight response).
Insulin (from pancreas) lowers blood sugar by promoting glucose uptake and glycogen formation. Glucagon raises blood sugar by promoting glycogen breakdown. Malfunction can lead to diabetes.
In males, testosterone (from testes) controls secondary sexual features; in females, estrogen and progesterone (from ovaries) regulate secondary characteristics and reproductive cycles.
- Nervous: fast, short-lived, specific target via nerves.
- Endocrine: slower, long-lasting, widespread targets via bloodstream.
- Auxins: cell elongation, apical dominance.
- Gibberellins: stem elongation, seed germination.
- Cytokinins: cell division.
- Ethylene: fruit ripening.
- Abscisic acid (ABA): induces dormancy, closes stomata.
Phototropism is growth toward/away from light. Auxin redistributes to the shaded side causing cell elongation there, bending the shoot toward light (Darwin's coleoptile experiments demonstrated this).
Apical dominance is suppression of lateral bud growth by the apical bud via auxin. Removing the apical bud reduces auxin influence and lateral buds grow, making the plant bushier.
Geotropism is growth in response to gravity. Roots show positive geotropism (grow downward); shoots show negative geotropism (grow upward). Auxin inhibits elongation in roots but promotes it in shoots.
Tropism is directional growth response to stimulus. Types: phototropism (light), geotropism (gravity), hydrotropism (water), thigmotropism (touch).
Plants use chemical coordination via hormones. Hormones are produced in one part and transported (via phloem/xylem or cell-to-cell) to effectors; responses are usually slower and longer-lasting.
Tropic: directional growth depending on stimulus direction (phototropism). Nastic: non-directional response dependent on intensity (e.g., touch response of Mimosa pudica — seismonasty).
Homeostasis is maintaining stable internal conditions. Examples: body temperature regulation (sweating/shivering) and blood glucose regulation (insulin/glucagon).
- Sight: photoreceptors (retina)
- Hearing: mechanoreceptors (cochlea)
- Taste: taste buds on tongue
- Smell: olfactory receptors in nose
Taste receptors (taste buds) detect chemicals dissolved in saliva; olfactory receptors detect volatile chemicals (airborne) in the nasal cavity. Both are chemoreceptors.
Myelin insulates axons and speeds impulse conduction (saltatory conduction). Demyelinating disease like multiple sclerosis slows/blocks nerve signals causing neurological symptoms.
Resting potential: neuron is polarized (inside negatively charged) maintained by Na⁺/K⁺ pumps. Action potential: stimulus causes depolarization (Na⁺ influx) then repolarization (K⁺ efflux) producing an electrical impulse.
Accommodation is adjustment of lens shape by ciliary muscles to focus on near or distant objects (lens becomes thicker for near vision, thinner for distant vision).
In bright light, the pupil constricts (circular muscles contract) reducing light entering to protect the retina; in low light, the pupil dilates (radial muscles contract).
Sound waves enter outer ear → vibrate tympanic membrane → ossicles amplify vibration → cochlea fluid vibrates → hair cells convert to electrical impulses sent to brain via auditory nerve.
Taste buds on the tongue detect chemicals and send signals via cranial nerves (VII, IX) to the gustatory cortex in the brain for perception of taste.
Spinal reflexes provide immediate protective responses (withdrawal from pain) without waiting for brain processing, minimising damage.
Hormones travel in blood to target cells which have specific receptors. Binding triggers intracellular responses (through direct gene action or second messenger systems) producing physiological effects.
Type I: insulin deficiency (autoimmune) → requires insulin. Type II: insulin resistance often linked to lifestyle; managed by diet, exercise, medication.
Negative feedback reduces deviation from setpoint. Example: high blood glucose stimulates insulin release, lowering glucose; reduced glucose then decreases insulin secretion.
Positive feedback amplifies a response. Example: oxytocin during childbirth increases uterine contractions, which causes more oxytocin release until delivery.
Reflexes use a short neural pathway (reflex arc) passing through spinal cord without routing to brain, making responses rapid and protective.
Cerebrum controls conscious activities, thinking, learning, memory, language and perception. Different lobes have specialised roles (e.g., occipital — vision; frontal — planning, speech).
Medulla controls breathing, heart rate, blood pressure and reflexes like coughing and vomiting.
Hypothyroidism (low thyroxine) leads to fatigue, slow metabolism and weight gain. Hormone replacement can treat it.
Goitre is thyroid enlargement often due to iodine deficiency. Prevention: iodized salt and dietary iodine sources.
- Auxins: used to promote rooting in cuttings, and as weed killers (synthetic auxins).
- Gibberellins: used to stimulate seed germination and increase fruit size.
Darwin's coleoptile experiments showed that the tip senses light and sends a chemical signal (auxin) causing bending — evidence for chemical coordination in plants.
Plant growth regulators are natural or synthetic hormones used to control growth, delay/accelerate ripening, promote rooting or prevent fruit drop in agriculture.
Signal transduction is how a receptor's activation is converted into a cellular response — often involving a cascade of events and second messengers (e.g., cAMP) that amplify the signal.
- Parkinson's: loss of dopaminergic neurons causing tremors and stiffness.
- Alzheimer's: progressive memory loss associated with brain cell degeneration.
- Pituitary: GH, FSH, LH, TSH
- Thyroid: Thyroxine
- Adrenal: Adrenaline
- Pancreas: Insulin, Glucagon
- Gonads: Estrogen, Testosterone
- Nervous system — fast electrical signals via neurons; reflex arc for quick action.
- Endocrine system — chemical hormones in blood; slower but long-lasting.
- Plant coordination via hormones (auxin, gibberellin, cytokinin, ethylene, ABA).
- Homeostasis maintained by feedback mechanisms.