● While considering the various alternatives available to `color{violet}("organisms for coping with extremes")` in their `color{violet}("environment")`, we have seen that some are able to respond through certain `color{violet}("physiological adjustments")` while others do so behaviourally (migrating temporarily to a less stressful habitat).

● These responses are also actually, their `color{violet}("adaptations")`.

● So, an `color{violet}("adaptation")` is any attribute of the `color{violet}("organism (morphological, physiological, behavioural)")` that enables the `color{violet}("organism")` to `color{violet}("survive")` and reproduce in its `color{violet}("habitat.")`

● `color{violet}("Many adaptations")` have evolved over a `color{violet}("long evolutionary time")` and are genetically fixed.

● In the absence of an `color{violet}("external source of water,")` the `color{violet}("kangaroo rat in North American deserts")` is capable of meeting all its `color{violet}("water requirements")` through its `color{violet}("internal fat oxidation (in which water is a by product).")`

● It also has the ability to concentrate its urine so that `color{violet}("minimal volume of water")` is used to remove `color{violet}("excretory products.")`

● `color{violet}("Many desert plants")` have a thick cuticle on their `color{violet}("leaf surfaces")` and have their `color{violet}("stomata")` arranged in `color{violet}("deep pits")` to minimise water loss through `color{violet}("transpiration.")`

● They also have a special `color{violet}("photosynthetic pathway (CAM)")` that enables their `color{violet}("stomata")` to remain closed during day time.

● Some `color{violet}("desert plants like Opuntia,")` have no leaves – they are reduced to spines–and the `color{violet}("photosynthetic function")` is taken over by the `color{violet}("flattened stems.")`

● `color{violet}("Mammals")` from `color{violet}("colder climates")` generally have `color{violet}("shorter ears")` and `color{violet}("limbs")` to `color{violet}("minimise heat loss")`. (This is called the `color{Brown}("Allen’s Rule")`.)

● In the `color{violet}("polar seas aquatic mammals")` like seals have a thick layer of fat (blubber) below their skin that acts as an `color{violet}("insulator")` and `color{violet}("reduces")` loss of `color{violet}("body heat.")`



`color{brown}("Altitude Sickness:")`

● Some organisms possess `color{violet}("adaptations")` that are `color{violet}("physiological")` which allow them to respond quickly to a `color{violet}("stressful situation.")`

● When travelling to `color{violet}("any high altitude place")` (> 3,500m Rohtang Pass near Manali and Mansarovar, in China occupied Tibet) you must have experienced what is called `color{violet}("altitude sickness.")`

● Its `color{violet}("symptoms")` include `color{violet}("nausea, fatigue")` and `color{violet}("heart palpitations.")`

● This is because in the low atmospheric pressure of `color{violet}("high altitudes,")` the body does not get `color{violet}("enough oxygen.")`

● But, gradually you get acclimatised and stop experiencing `color{violet}("altitude sickness.")`

● The body compensates `color{violet}("low oxygen availability")` by `color{violet}("increasing red blood cell production, decreasing the binding capacity of hemoglobin")` and by `color{violet}("increasing breathing rate")`.

● In most animals, the `color{violet}("metabolic reactions")` and hence all the `color{violet}("physiological functions")` proceed optimally in a narrow temperature range (in humans, it is `– 37^0C`).

● But there are `color{violet}("microbes (archaebacteria)")` that flourish in `color{violet}("hot springs")` and `color{violet}("deep sea hydrothermal vents ")`where temperatures far exceed `100^0C.`

● `color{violet}("Many fish")` thrive in `color{violet}("Antarctic waters")` where the `color{violet}("temperature")` is always below `color{violet}("zero")`.

● A large variety of `color{violet}("marine invertebrates and fish")` live at great depths in the `color{violet}("ocean")` where the pressure could be >100 times the `color{violet}("normal atmospheric pressure")` that we experience.

● `color{violet}("Organisms living")` in such `color{violet}("extreme environments")` show a fascinating array of `color{violet}("biochemical adaptations.")`

● `color{violet}("Some organisms")` show behavioural responses to cope with `color{violet}("variations")` in their environment.

● `color{violet}("Desert lizards lack")` the `color{violet}("physiological")` ability that `color{violet}("mammals")` have to deal with the `color{violet}("high temperatures")` of their habitat, but manage to keep their body temperature fairly constant by behavioural means.

● They bask in the sun and `color{violet}("absorb heat")` when their `color{violet}("body temperature drops below the comfort zone")`, but move into shade when the `color{violet}("ambient temperature starts increasing.")`

● Some species are capable of burrowing into the `color{violet}("soil")` to `color{violet}("hide")` and `color{violet}("escape")` from the `color{violet}("above-ground heat.")`