A-Level生物-在极端温度中适应并求生Survival in Extreme Climate.

Revision: Adaptations for survival - Methods of avoiding extremes of climate

Coping with Cold Conditions

Dormancy in Plants

Annuals survive cold as seeds while perennials use organs of perennation e.g. bulbs, tubers and rhizomes.

Deciduous trees lose leaves, reducing transpiration rate.

Hibernation in Animals

Certain animals can't function at low temperatures due either to a lack of food availability or, in the case of reptiles for example, due to the fact that they rely entirely on external temperature to stay warm. These animals may over come this problem by hibernation. They sleep through the cold period relying on their fat stores to stay alive, slowing their metabolism down and making use of the lower energy requirements during sleep. This method requires the animal to build up its fat stores while food is plentiful

Migration

This behavior is particularly prevalent amongst birds many species of which travel vast distances to find improved food sources and warmer temperatures.

Depression of freezing point in cells

Plants and animals in cold climates have substances within cells that lower the freezing point of the cell cytoplasm e.g. glycerol.

Air Spaces

Air spaces, for example in the gut of animals or the leaves of plants provide a certain amount of insulation.

Body size and shape

Animals with large surface areas to volume ration (smaller animals) lose heat more quickly than those with a smaller surface area to volume ratio. (Heat is lost by conduction, convection and radiation.) This means animals in cold climates tend to be larger with smaller extremities than those in warm climates.

Coping with Dry Climates

Xerophytes

Xerophytes are plants adapted to withstand dry conditions for example marram grass and cacti, they have various adaptations to allow them to survive, these will vary from species to species but may include

Rolled up leaves to reduce evaporation from the stomata

Hairs on the underside of their leaves in order to trap in evaporating water.

Surface area of leaves reduced –needles

Increased thickness of cuticle

Succulence – Leaves and stems with the ability to store large quantities of water. (Often combined with spines as being a good store of water makes them a tempting food source in dry conditions.

Extensive root networks (to better allow them to make the most of what little water is around.)

Improved Water Conservation in Animals

In the kidneys of desert dwellers in the nephrons which regulate the reabsorbing of useful molecules from urine the loop of Henle which is responsible for reabsorbing water is far longer meaning that there is far less water wasted in urine. 

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