Short Summary

Chapter 7, Control and Coordination, explains how living organisms respond to internal and external stimuli through nervous and endocrine regulation in animals and through growth and chemical movements in plants. In animals, specialised cells called neurons transmit information through electrical impulses and communicate across microscopic gaps called synapses using chemical signals. The central nervous system, consisting of the brain and spinal cord, processes these signals, with the forebrain responsible for thinking, sensory reception, and voluntary actions, while the hindbrain controls involuntary functions through the medulla and maintains posture and balance through the cerebellum. Quick and involuntary emergency responses to stimuli are carried out through reflex arcs, in which signals are routed through the spinal cord without requiring lengthy processing by the brain, allowing the body to respond rapidly. Plants coordinate their responses through movements that may be independent of growth, involving changes in the amount of water in cells, and growth-dependent directional movements known as tropic movements, including phototropism in response to light, geotropism in response to gravity, chemotropism in response to chemicals, and hydrotropism in response to water. Plant responses are regulated by hormones such as auxins, which promote cell elongation; gibberellins, which facilitate stem growth; cytokinins, which stimulate cell division in rapidly growing tissues; and abscisic acid, which inhibits growth and can cause leaves to wilt. In animals, the endocrine system consists of glands that secrete chemical messengers called hormones directly into the bloodstream to regulate metabolism, growth, development, and other physiological changes. Important hormones include thyroxin, which requires iodine for normal metabolic function; growth hormone, secreted by the pituitary gland; insulin, produced by the pancreas to regulate blood sugar levels; adrenaline, released by the adrenal glands during fight-or-flight responses; and sex hormones such as testosterone and oestrogen, which regulate reproductive development and related physiological changes.