Why high-altitude mountain climbers use oxygen bottles

The air becomes thinner at the top. So, higher the elevation, the thinner the air becomes and breathing becomes very difficult at above 4,500m or 15,000 feet.

Any type of physical activity becomes a tiring effort and mountain climbers need to carry their own supply of oxygen to keep them going.

Aircraft also fly at high altitudes. However, aircraft passengers are able to breathe normally and function without feeling tired because the cabins in such aircraft are always pressurised.

What the main sources of energy are

Whenever something moves or changes in any way, some form of energy is used to do so. Energy occurs in many different forms. Thousands of years ago, humans knew no sources of energy (like in the modern world) except their muscular force.

They used their muscular energy to hunt, lift and carry objects. So, muscles are the first source of energy. With time, man learned to domesticate animals and use their muscle strength as sources of energy.

Then natural forces were used as sources of energy. By about 100 BC the energy of flowing water was used to turn millstones that crushed the grain.

Today this form of energy is used to produce another kind of energy – electricity (dams and hydroelectric plants). Electrical energy is in great demand and is sent through wires very quickly to operate various kinds of equipment and also provide lighting.

The various forms of natural energy used in the world today includes ocean-thermal energy, fuel energy, solar energy, geothermal energy and nuclear energy. Mechanical energy too is used to some extent.

Aeolian energy or wind energy is used to turn windmills and sail boats while oil and gas obtained from the seabed are used for various activities such as to operate machines and vehicles. In the past wood and above all coal was used to operate the first engines.

Even today coal power plants are operated to supply electricity.

The energy produced during the combustion of certain gases propels rockets. Nuclear energy is used in many countries like Japan and Canada. India too is setting up a nuclear plantto generate electricity and it will be quite close to Sri Lanka.

The first nuclear reactor was completed at the University of Chicago in 1942 and hundreds have been built since.

Solar energy another source of energy is becoming popular in Sri Lanka too with many using solar panels to obtain hot water and electricity.

What the world’s only sea lizard is

The marine iguana. It can be grey, green, brown or pink and may grow up to 1.5m in length.

It uses its powerful tail to propel itself through the water. Its legs are used to steer. The marine iguana has powerful jaws and sharp claws.

It can gnaw at the nutritious seaweed with its powerful jaws, clinging on to the rocks with its claws.

Where the home of the Galapagos tortoise is

The world’s largest tortoise lives in the Galapagos islands which are a group of volcanic islands in the Pacific Ocean, about 1,000 km west of South America. Isabela and Santa Cruz are the largest islands. Santiago, Fernandina and San Cristobal are also fairly large but the other islands such as Pinta, Santa Maria, Santa Fe, Espanola, Marchena, Genovesa are rather small. The islands of Gulpepper and Weinman are further north to the island of Isabella.

Scientists believe that the rich wildlife found in the islands arrived there initially by flying, floating or swimming from the mainland.There are 11 subspecies of the famous Galapagos giant tortoises in these islands which are rich in biodiversity.

What coniferous and deciduous trees are

They are the two main groups of trees. Coniferous trees are also known as resinous trees. They have narrow leaves which are actually needles or scales which are not shed in winter (with the exception of the larch). Their fruits are cones which is why they are called ‘conifers.’ Their sap is called resin.

Some coniferous trees are fir trees, spruce, juniper, cypress, larch, cluster pine, yew, stone pine and scots pine.

Deciduous trees shed leaves in the autumn and grow new leaves in the spring. Leaves may be simple or compound. Compound leaves are divided into a number of leaflets.

Trees that keep their leaves in winter are called evergreen trees. Some of the deciduous trees are elm, birch, beech, chestnut, oak, poplar and ash trees.