Lessons 9–10 · 2 lessons · A. G‘afurov, A. Abdukarimov, J. Tolipova, O. Ishankulov, M. Umaraliyeva, I. Abdurahmonova. Biology Grade 11, 1st edition. Sharq Publishing and Printing Joint-Stock Company, Tashkent, 2018
9
Temperature as an abiotic factor
Textbook: pp. 53–57
GoalExplain the effect of temperature as an ecological factor, poikilothermic and homeothermic organisms, and the adaptations of plants and animals to temperature.
Temperature sets the rate of metabolism and enzyme activity: at very high temperatures proteins and enzymes are denatured, and below 0 °C ice crystals in cells damage membranes. Most organisms live between roughly 0 and +50 °C, but in hot springs some bacteria and archaea multiply even above 80 °C. Poikilotherms (invertebrates, fish, amphibians, reptiles) have a body temperature that depends on the surroundings: in the warmth metabolism and development speed up, in the cold they slow or the animal becomes torpid. Homeotherms (birds, mammals) keep body temperature constant: a four-chambered heart, feathers or fur, subcutaneous fat, sweating, dilation and constriction of skin vessels and shivering in the cold all help; some hibernate in winter (marmot, hedgehog). Plant adaptations: against heat – transpiration, a wax layer, hairs, smaller leaf area (saxaul, the cactus spine); against cold – more sugar in cell sap, a low or cushion form; in deserts ephemerals (surviving as seeds) and ephemeroids (as bulbs or tubers) spend the summer heat dormant. Animal behaviour is also an adaptation: migration, hiding in burrows, basking in the sun.
Worked examples
Compare a frog and a hedgehog: at 5 °C the frog is almost immobile (a poikilotherm), while the hedgehog in hibernation lowers its body temperature to save energy but, once awake, quickly restores it to about 35–37 °C (a homeotherm).
Spring annual desert herbs – ephemerals – grow quickly in February–March, set seed and wither before the desert heats in May–June: they pass the unfavourable summer as seeds. The tulip is an ephemeroid: after flowering in spring it spends the summer dormant in an underground bulb.
Class activity
In pairs make a «hot – cold» table: write three adaptations of animals and plants in each column. If a thermometer is used, take care not to break a mercury one; handle hot water only with an adult’s help.
Practice
1
Give two examples each of poikilothermic and homeothermic animals.