Moisture as an ecological factor
About two thirds of an organism’s body is water: it is a universal solvent, takes part in hydrolysis and photosynthesis, regulates heat and transports substances. On land moisture depends on annual precipitation, and both its shortage and its excess can be limiting. By moisture needs land plants fall into three groups: xerophytes (desert and steppe), mesophytes (meadow, forest and most crops in moderate moisture) and hygrophytes (wet places; rice, reed – weak root system, thin leaves, stomata always open). Xerophytes divide into succulents, which store water in internal tissues (cactus, agave, aloe), and sclerophytes (saxaul, camel-thorn, wormwood), which do not store water but economise it with deep roots, a cell sap of high osmotic pressure and ways of reducing leaf surface. Animal adaptations: physiological (excreting uric acid, using water in food and metabolic water from fat oxidation – the camel’s hump stores fat, not water), morphological (horny scales, chitin, shells, feathers) and ethological (migrating to find water, nocturnal life, summer dormancy, hiding in burrows).
Observe the leaves of three plants (a houseplant, a cactus, a water plant) and estimate their water use. If you experiment with more or less watering, agree it with an adult; do not touch cactus spines.