Self-regulation in living organisms: evolution of the humoral and nervous systems
Self-regulation is the automatic keeping of an organism’s parameters (sugar, temperature, hormone level) at set levels. Bacteria and unicellular organisms respond to external factors by taxis (for example movement toward light); plants and fungi are regulated humorally – by phytohormones and other biologically active substances. In animals the nervous system evolved through four stages: diffuse (net-like) in cnidarians, trunk (ladder-like) in flatworms and roundworms, chain type in annelids, molluscs and arthropods, and a tubular nervous system in chordates. Vertebrates have a five-part brain (forebrain, diencephalon, midbrain, medulla and cerebellum); from fish to mammals the cerebral cortex of the forebrain enlarged, giving complex behaviour and higher nervous activity. In humoral regulation hormones are carried by blood and lymph; nervous and humoral regulation work together as one neurohumoral system. Immune regulation protects the organism from foreign substances: barriers, leukocytes and antibodies; plant defence relies on the cell wall and phytoncides.
Measure reaction speed: a classmate drops a ruler and you catch it; measure the distance it fell. Repeat 5 times and find the average. Safety: use a soft flat ruler and do not throw it at each other.