Unit 9. Undersea world

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SEA HORSE
STAR FISH
TURTLE
CRAB
SQUID
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WARM-BLOODED AND COLD BLOODED ANIMALS
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DEFINITION
Warm-bloodedness generally refers to three separate aspects of thermoregulation.
Endothermic is the ability of some creatures to control their body temperatures through internal means such as muscle shivering, fat burning, drawing and panting.
Homoeothermic is thermoregulation that maintains a stable internal body temperature regardless of external influence. This temperature is often higher than the immediate environment. The opposite is poikilothermy.
Tachymetabolism is the kind of thermoregulation used by creatures that maintain a high resting metabolism. Tachymetabolic creatures are, essentially, "on" all the time. Though their resting metabolism is still many times slower than their active metabolism, the difference is often not as large as that seen in Brady metabolic creatures. Tachymetabolic creatures have greater difficulty dealing with a scarcity of food.

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MECHANISMS
Generating and conserving heat
The creatures traditionally regarded as warm-blooded have a larger number of mitochondria per cell, which enables them to generate heat by increasing the rate at which they "burn" fats and sugars. This requires a much greater quantity of food than is needed by cold-blooded animals in order to replace the fat and sugar reserves.
Avoiding over-heating
In equatorial climates and during temperate summers over-heating is as great a threat as cold. In hot conditions many warm-blooded animals increase heat loss by panting and or flushing (increasing the blood flow to the skin). Hairless and short-haired mammals also sweat, since the evaporation of sweat uses a lot of heat.
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Advantages of a fast metabolism
The overall speed of an animal`s metabolism increases by a factor of about 2 for every 10 C° rise in temperature (limited by the need to avoid hyperthermia). Warm-bloodedness does not provide greater speed than cold-bloodedness - cold-blooded animals can move as fast as warm-blooded animals of the same size and build. But warm-blooded animals have much greater stamina than cold-blooded creatures of the same size and build
Advantages of homeothermy
Enzymes have strong temperature preferences and their efficiency is much reduced outside their preferred ranges. A creature with a fairly constant body temperature can therefore use enzymes which are efficient at that temperature. Another advantage of a homeothermic animal would be its ability to maintain its constant body temperature even in freezing cold weather
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Disadvantages of warm-bloodedness
Because warm-blooded animals use enzymes which are specialised for a narrow range of body temperatures over-cooling rapidly leads to torpor and then death. Also, the energy required to maintain the homeothermic temperature comes from food - this results in homeothermic animals needing to eat much more food than poikilothermic animals.
Shivering and fat-burning to maintain temperature are very energy-intensive, for example:
in winter many small birds lose one third of their body weight overnight.
in general a warm-blooded animal requires 5 to 10 times as much food as a cold-blooded animal of the same size and build, so cold-blooded animals are better at surviving famines and barren environments.

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Thermographic image: a coldblooded snake is eating a warmblooded mouse
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DEFINITION
Cold-bloodedness generally refers to three separate areas of thermoregulation.
Ectothermy - This refers to creatures that control body temperature through external means , such as the sun, or flowing air/water.
Poikilothermy - This refers to creatures whose internal temperatures vary, often matching the ambient temperature of the immediate environment
Bradymetabolism - This term refers to creatures with a high active metabolism and a considerably slower resting metabolism Bradymetabolic animals can often undergo dramatic changes in metabolic speed, according to food availability and temperature. Many bradymetabolic creatures in deserts and in areas that experience extreme winters are capable of "shutting down" their metabolisms to approach near-death states, until favourable conditions return
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Types of temperature control
Examples of temperature control include:
Snakes and lizards sunning themselves on rocks.
Fish changing depths in the water column to find a suitable temperature.
Desert animals burrowing beneath the sand during the day.
Insects that warm their flight muscles by vibrating them in place.
Dilating or constricting peripheral blood vessels to adapt more or less quickly to the ambient temperature.

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Ecological niches
It is comparatively easy for a poikilotherm to accumulate enough energy to reproduce. Poikilotherms in the same ecological niche often have much shorter lifetimes than homeotherms: weeks rather than years.
This energy difference also means that a given niche of a given ecology can support three to ten times the number of poikilothermic animals as homeothermic animals. However, in a given niche, homeotherms often drive poikilothermic competitors to extinction because homeotherms can gather food for a greater fraction of each day.
Poikilotherms succeed in some niches, such as islands, or distinct bioregions (such as the small bioregions of the Amazon basin). These often do not have enough food to support a viable breeding population of homeothermic animals. In these niches, poikilotherms such as large lizards, crabs and frogs supplant homeotherms such as birds and mammals.
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WARM-BLOODED AND COLD BLOODED ANIMALS
Thermal image of a cold-blooded tarantula on a human hand
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Many "cold-blooded" animals use behavioral means to adjust their internal temperatures:
lizards and snakes bask in the sun in the early morning and late evening, and seek shelter around noon.
bees in large hives will cool the hive in hot periods by going to its entrances and using their wings as fans to draw cooling air through the hive.
Some other "cold-blooded" creatures use internal mechanisms to maintain body temperatures significantly above the ambient level:
Tuna and swordfish fish have long been thought to be cold blooded. Tuna and swordfish dive deep into the ocean where the water is very cold. Swordfish are able to raise the temperature of their brains and eyes, which allows faster eye movements when hunting. Tuna are able to warm their entire bodies through a heat exchange mechanism called the rete mirabile, which helps keep heat inside the body, and minimizes the loss of heat through the gills. They also have their swimming muscles near the center of their bodies instead of near the surface, which minimises heat loss.

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Many species of bees and moths flap their wings vigorously to raise the temperature of their flight muscles before taking off.
Warm-blooded" sharks (e.g. mako and white sharks), to minimize heat loss through their gills, pass their blood through rete mirabile heat exchangers before it enters into the gills and after it exits from them: Veins are right next to arteries and thus extract heat from the arteries and carry it back into the body.
Large sea turtles exhibit inertial homeothermy (Gigantothermy) - their low ratio of surface area to volume minimises heat loss.



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Oasis of the Pacific
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