NCERT Science: Control and Coordination (Nervous and Hormonal)

The one-line takeaway

Living things sense and respond to their environment through two coordinating systems. In animals the nervous system gives fast, electrical, short-lived control, and the endocrine system gives slower, chemical, longer-lasting control through hormones. Plants coordinate through plant hormones and directional growth movements (tropisms). Reproduction continues the species.

The nervous system

• The basic unit is the neuron (nerve cell), which carries electrical impulses. A stimulus is detected by receptors, the impulse travels along neurons, and a response follows. The tiny gap where one neuron passes a signal to the next is the synapse, crossed by chemical neurotransmitters.
• The system has two parts: the central nervous system (the brain and spinal cord) and the peripheral nervous system (the nerves branching to the body).
• The brain has three main parts: the cerebrum (thinking, memory, voluntary action, intelligence), the cerebellum (balance and coordination of movement) and the medulla / brain stem (involuntary actions such as heartbeat, breathing, blood pressure, vomiting).
• A reflex action is an immediate, involuntary response to a stimulus (jerking the hand off a hot surface). It travels by a short pathway, the reflex arc, through the spinal cord without waiting for the brain, which saves time and protects the body.

The endocrine system (hormones)

• Hormones are chemical messengers secreted by ductless endocrine glands directly into the blood, which carries them to target organs. They act slowly but their effects last.
• The key human glands and hormones to recognise:
  • Pituitary (the "master gland"): growth hormone (its excess or deficiency causes gigantism or dwarfism); it also controls other glands.
  • Thyroid: thyroxine, which regulates metabolism; it needs iodine, and its deficiency causes goitre (the basis of iodised salt).
  • Pancreas: insulin, which lowers blood sugar; its deficiency causes diabetes.
  • Adrenal glands: adrenaline, the "fight or flight" hormone, released in fear, anger or stress, raising heart rate, blood pressure and breathing.
  • Testes and ovaries: the sex hormones (testosterone, oestrogen and progesterone) that bring about the changes of puberty and control reproduction.

Coordination in plants

• Plants have no nervous system; they coordinate through plant hormones (phytohormones) and slow growth movements.
• The main plant hormones: auxin (promotes cell elongation, controls bending toward light), gibberellin (stem growth), cytokinin (cell division), abscisic acid (inhibits growth, closes stomata, the "stress hormone"), and ethylene (ripens fruit).
• Tropisms are directional growth responses: phototropism (toward light, as a shoot bends to a window), geotropism / gravitropism (roots grow down, shoots grow up), hydrotropism (toward water) and chemotropism (toward chemicals, as pollen tubes grow toward the ovule). Nastic movements (the rapid folding of the touch-me-not, Mimosa) are non-directional.

Reproduction

• Asexual reproduction involves a single parent and produces genetically identical offspring: binary fission (Amoeba, bacteria), budding (yeast, Hydra), spore formation (fungi), fragmentation (Spirogyra), regeneration (Planaria), and vegetative propagation in plants (by roots, stems, leaves, or grafting and cutting).
• Sexual reproduction involves two parents and the fusion of male and female gametes, giving variation. In flowering plants the flower is the reproductive organ; pollination (transfer of pollen) is followed by fertilisation, then seed and fruit formation.
• The human reproductive system, in outline: the male system (testes producing sperm) and the female system (ovaries producing eggs, the uterus where the embryo develops). Fertilisation forms a zygote, which develops into an embryo. Reproductive health, contraception and the prevention of sexually transmitted infections are public-health themes.

Key terms to fix

• Neuron and the reflex arc: the fast, spinal-cord pathway of involuntary response.
• Cerebrum (thinking), cerebellum (balance), medulla (involuntary functions).
• Insulin (pancreas, blood sugar), thyroxine (thyroid, iodine, goitre), adrenaline (adrenal, fight or flight).
• Auxin and the tropisms: phototropism, geotropism, hydrotropism.
• Asexual versus sexual reproduction: one parent, identical offspring versus two parents, variation.

CAPF angle

The fight-or-flight response (adrenaline) and the stress physiology of the body are directly relevant to performance under fire and to stress management in the forces, an interview and welfare theme. Reflex action explains rapid combat and self-protective responses. Knowledge of hormonal disorders (diabetes, thyroid) is relevant to the medical-standards assessment. Iodised-salt and goitre awareness is a public-health topic that the forces support in remote postings.

Authored practice