Control and Coordination — RBSE Class 10 (Science)
Touch something hot and your hand jerks back before you even decide to move it. Feel afraid and your heart races without any command. Living bodies constantly sense their surroundings and respond — instantly through nerves, and more slowly and lastingly through hormones. This chapter is about those two great control systems, in animals and in plants.
1. The nervous system — the neuron
The neuron (nerve cell) is the unit of the nervous system. Information travels as an electrical impulse: dendrites receive it → cell body → axon carries it → nerve endings pass it on. At the gap between two neurons — the synapse — the electrical signal triggers chemicals (neurotransmitters) that carry the message across.
2. Reflex action and the reflex arc
A reflex action is a rapid, automatic response to a stimulus, not involving conscious thought. The pathway — the reflex arc — runs: receptor → sensory neuron → spinal cord → motor neuron → effector (muscle). Because the signal is processed in the spinal cord (not the brain), the response is faster — vital for danger (hot object, pinprick).
3. The human brain and its parts
The brain and spinal cord form the central nervous system (CNS); nerves form the peripheral nervous system. Main parts of the brain:
- Fore-brain (cerebrum) — thinking, memory, voluntary actions, and the centres for sensations.
- Mid-brain + Hind-brain:
- Cerebellum — precision of voluntary movement, posture and balance.
- Medulla (part of hind-brain) — involuntary actions: heartbeat, breathing, blood pressure, vomiting.
- Pons — regulation of breathing.
The delicate brain is protected by the skull and a fluid cushion; the spinal cord by the vertebral column.
4. How the response happens
Nervous messages reach muscle cells, which contract by changing shape (special proteins). But nervous control has limits — cells cannot conduct impulses continually, and some effects must be slow, widespread and sustained. For those, the body uses chemical coordination.
5. Chemical coordination — hormones
Endocrine glands release hormones directly into the blood, which carries them to target organs. Hormones act in tiny amounts and their secretion is finely regulated by feedback.
| Gland | Hormone | Main role |
|---|---|---|
| Pituitary | Growth hormone | growth of the body |
| Thyroid | Thyroxine (needs iodine) | regulates metabolism; deficiency → goitre |
| Pancreas | Insulin | lowers blood sugar; deficiency → diabetes |
| Adrenal | Adrenaline | "fight or flight" response |
| Testis / Ovary | Testosterone / Oestrogen | male / female sexual development |
Feedback example: if blood sugar rises, the pancreas releases more insulin; as sugar falls, insulin release drops.
6. Coordination in plants
Plants have no nerves or muscles; they respond by growth movements and chemical messengers (plant hormones / phytohormones).
- Tropisms (directional growth responses): phototropism (towards light — shoots), geotropism (roots grow down, shoots up), hydrotropism (roots towards water), chemotropism (e.g. pollen tube to ovule).
- Nastic movement (non-directional): the touch-me-not (Mimosa) folding its leaves — a quick response without growth, by change in water/turgor.
- Plant hormones: auxin (cell elongation, bends shoot to light), gibberellin (stem growth), cytokinin (cell division), abscisic acid (inhibits growth, closes stomata; the "stress" hormone).
7. Closing thought
Two systems, two speeds: nerves give fast, short-lived, targeted responses; hormones give slow, lasting, widespread control — and plants manage with hormones and growth alone. Learn the reflex arc, the brain parts with their functions, the gland-hormone-disease table, and the tropisms. In the RBSE board this chapter reliably yields diagram-based and short-answer questions worth 5–6 marks.
