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Polar bear

Formed less skin walking to give environment freezing relatively swimming spending prey blood breeds tissue remains insulation coat reaches den circulates relatives to transmit features insulating reduces supplying enable absorbing

The polar bearlives in the Arctic, …………… much of its time on snow and ice. Several physical …………… contribute to its adaptation to this cold …………… . It is a very large bear, which means that the ratio of its surface area to its volume is …………… small. The relatively small surface area means that the polar bear loses proportionately …………… heat than its more southerly…………… . Also its ears are small, another feature which …………… heat loss.

It has a thick …………… with long loosely packed сoarse hairs (guard hairs) and a denser layer of shorter wooly hairs forming an ………….. layer. The long hairs are oily and water-repellant and ………… the bear to shake off water when it emerges from a spell of ………….. .

The principal thermal …………… comes from a 19 cm layer of fat (blubber) beneath the …………. . The thermal conductivity of fat is little different from any other …………… but it has a limited blood supply. This means that very little warm blood …………… close to the skin surface.

The hollow hairs of the white fur are thought …………… the sun's heat to the black skin below. Black is an efficient colour for …………… heat. The white colour is also probably an effective camouflage when hunting its …………… , mainly seals.

A specific adaptation to …………… on snow and ice is the heat-exchange arrangement in the limbs. The arteries …………… the feet run very close to the veins returning ………… to the heart. Heat from the arteries is transferred to the veins before the blood …………… the feet. So, little heat is lost from the feet but their temperature is maintained above …………. point,preventing frost-bite.

The polar bear …………… in winter when temperatures fall well below zero. However, the pregnant female excavates a …………… in the snow in which …………… birth and rear her two cubs. In this way the cubs are protected from the extreme cold. The female …………… in the den for about 140 days, suckling her young on the rich milk which is …………… from her fat reserves.

1. Plants and trees.

2. Process in which the plant produces chemical energy (in the form of sugars) from water, minerals, and carbon dioxide with the aid of pigments and the radiant energy of the Sun,

3. The process of the transfer of pollen from the anthers to the stigma.

4. The system that anchors the plant and absorbs water and minerals from the soil.

5. A specialized conducting system for the transport of water, minerals, and food materials.

6. The nutrient element that is necessary to make amino acids, nucleic acids and proteins.

7. An enzyme co-factor important in making plant cell walls.

8. The light-sensitive membrane that lines the back wall of the eyeball and is composed of several layers, including one containing the rods and cones.

9. Animals without backbones.

10. Numerous pigment-filled bags with the help of which cephalopods change color.

11. One of the oldest living creatures in the world existed on the face of this planet since before the dinosaurs.

12. Any member of a group of vertebrate animals in which the young are nourished with milk from special secreting glands of the mother.

13. Any of the most numerous of existing mammals, characterized by upper and lower pairs of ever-growing rootless incisor teeth.

14. A baby of dolphins.


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    The use of the hierarchical classification system Order defined classify features are sorted living reproduce share capable of classifying kingdom to identify Classification to sort offspring species scientists to breed breeding CLASSIFICATION helps us to impose order and a general plan on the diversity of …………… things. Scientists have always tried to organize and …………… the objects, including living organisms, around them. …………… can be defined as... [читать подробенее]