When you exercise, your muscles have to work much harder than normal, so need much more oxygen and glucose (a kind of sugar) from the blood.
To boost oxygen, your heart beats twice as fast and pumps twice as much blood, and your lungs take in ten times more air with each breath.
To boost glucose, adrenalin triggers your liver to release its store of glucose.
If oxygen delivery to muscles lags, the muscles fill up with lactic acid, affecting your body for hours and sometimes causing cramp.
The fitter you are, the quicker your body returns to normal after exercise.
Aerobic exercise is exercise that is long and hard enough for the oxygen supply to the muscles to rise enough to match the rapid burning of glucose
Regular aerobic exercise strengthens your heart and builds up your body’s ability to supply extra oxygen through your lungs to your muscles.
Regular exercise multiplies muscle fibers and strengthens tendons.
Regular exercise helps to reduce weight when it is combined with a controlled diet.
Global warming is the increase in average temperatures around the world. This increase has been between 0.3°C and 0.8°C over the 20th century.
Most scientists now think that global warming is caused by human activities, which have resulted in an increase in the Earth’s natural greenhouse effect.
The greenhouse effect is the way that certain gases in the air – notably carbon dioxide – trap some of the Sun’s warmth, like the panes of glass in the walls and roof of a greenhouse.
The greenhouse effect keeps the Earth pleasantly warm – but if it increases, the Earth may become very hot.
Many experts expect a 4°C rise in average temperatures over the next 100 years.
Humans boost the greenhouse effect by burning fossil fuels, such as coal, oil and natural gas that produce carbon dioxide.
Emission of the greenhouse gas methane from the world’s cattle has added to the increase in global warming.
Global warming is bringing stormier weather by trapping more energy inside the atmosphere.
Global warming may melt much of the polar ice caps, flooding low-lying countries such as Bangladesh.
Recent observations show global warming 14 could be much worse than we thought.
There are three species of kiwi, found only in New Zealand. All are flightless birds that live in burrows. The female dwarf cassowary, or moruk, is an extremely dangerous bird and will attack anything that comes near its nest with its 10-cm long claws. The three species of cassowary live in rainforests in New Zealand and northeastern Australia. Largest of its family is the brown kiwi, which is about 55 cm long and weighs up to 3.5 kg.
Only the kiwi has nostrils at the end of its beak.
The kiwi is the national symbol of New Zealand, appearing on stamps, coins and banknotes.
Cassowaries in Australia are known to eat the fruits of at least 75 different types of tree.
The female cassowary mates with several males, laying 6-8 eggs each time. The males care for the young.
About 1200 years ago there were probably 12 million kiwis in New Zealand. Today there are only 70,000.
The nocturnal kiwi’s good sense of smell helps it to find worms, insects and spiders in the ground at night.
A kiwi lays the largest eggs for its size of any bird – each egg weighs 25% of its body weight. Females lay up to 100 in a lifetime.
Although air is light, there is so much of it that air can exert huge pressure at ground level. Air pressure is the constant bombardment of billions of air molecules as they zoom about.
Air pushes in all directions at ground level with a force of over 1 kg per sq cm – that is the equivalent of an elephant standing on a coffee table.
Air pressure varies constantly from place to place and from time to time as the Sun’s heat varies.
Air pressure is measured with a device called a barometer in millibars.
Normal air pressure at sea level is 1013 mb, but it can vary from between 800 mb and 1050 mb.
Barometers are used to detect changes in air pressure. The first barometer was invented by Evangelista Toricelli in 1644.
In this satellite picture, a spiral of clouds indicates that stormy weather in a depression is heading for California, USA.
Air pressure is shown on weather maps with lines called isobars, which join together places of equal pressure.
High-pressure zones are called anticyclones; low-pressure zones are called cyclones, or depressions.
Barometers help us to forecast weather because changes in air pressure are linked to changes in weather.
A fall in air pressure warns that stormy weather is on its way, because depressions are linked to storms.
Steady high pressure indicates clear weather, because sinking air in a high means that clouds cannot form.
Saturn is the second biggest planet in the Solar System – 815 times as big in volume as the Earth, and measuring 120,000 km around its equator.
Saturn takes 29 and a half years to travel round the Sun, so Saturn’s year is 29.46 Earth years. The planet’s complete orbit is a journey of more than 4.5 billion km.
Winds ten times stronger than a hurricane on Earth swirl around Saturn’s equator, reaching up to 1,100 km/h – and they never let up, even for a moment.
Saturn is named after Saturnus, the Ancient Roman god of seed-time and harvest. He was celebrated in the Roman’s wild, Christmas-time festival of Saturnalia.
Saturn is not solid, but is made almost entirely of gas – mostly liquid hydrogen and helium. Only in the planet’s very small core is there any solid rock.
Because Saturn is so massive, the pressure at its heart is enough to turn hydrogen solid. That is why there is a layer of metallic hydrogen around the planet’s inner core of rock.
Saturn is one of the fastest spinning of all the planets. Despite its size, it rotates in just 11.5 hours – which means it turns round at over 10,000 km/h.
Saturn’s surface appears to be almost completely smooth, though Voyager 1 and 2 did photograph a few small, swirling storms when they flew past.
Saturn has a very powerful magnetic field (see magnetism) and sends out strong radio signals. Saturn’s rings are made of many millions of tiny, ice-coated rock fragments Saturn is almost as big as Jupiter.
Saturn’s rings are sets of thin rings of ice, dust and tiny rocks, which orbit the planet around its equator.
The rings shimmer as their ice is caught by sunlight.
The rings may be fragments of a moon that was torn apart by Saturn’s gravity before it formed properly.
Galileo was first to see Saturn’s rings, in 1610. But it was Dutch scientist Christian Huygens (1629-95) who first realized they were rings, in 1659.
There are two main sets of rings – the A and the B rings.
The A and B rings are separated by a gap called the Cassini division, after Italian astronomer Jean Cassini (1625-1712), who spotted it in 1675.
A third large ring called the C or crepe ring was spotted closer to the planet in 1850.
In the 1980s, space probes revealed many other rings and 10,000 or more ringlets, some just 10 m wide.
The rings are (in order out from the planet) D, C, B, Cassini division, A, F, G and E. The A ring has its own gap called the Encke division.
Migration is when animals move from one place to another to avoid the cold or to find food and water.
Some migrations are daily, some are seasonal, and some are permanent.
Starlings migrate every day from the country to their roosts in towns and cities.
Many birds, whales seals and bats migrate closer to the tropics in the autumn to escape the winter cold.
One knot (a kind of small bird) took just 8 days to fly 5,600 km, from Britain to West Africa.
Barheaded geese migrate right over the top of the Himalayan mountains, flying as high as 8,000 m.
Migrating birds are often brilliant navigators. Bristle-thighed curlews find their way from Alaska to tiny islands in the Pacific 9,000 km away.
Shearwaters, sparrows and homing pigeons are able to fly home when released by scientists in strange places, thousands of kilometres away.
The Arctic tern is the greatest migrator, flying 30,000 km from the Arctic to the Antarctic and back again each year.
Monarch butterflies migrate 4,000 km every year, from North America to small clumps of trees in Mexico. Remarkably, the migrating butterflies have never made the journey before.
No other creature migrates so far every year as the Arctic tern. It breeds in the short Arctic summer, then flies halfway around the world to spend another summer in Antarctica.
In summer, moose spend most of the time alone. lin winter they gather and trample areas of snow (called yai to help each other get at the grass bole,
Migration is the journey made twice a year between a summer breeding area, where food is plentiful, and a wintering area with a good climate.
Many migrating birds have to build up fat stores to allow them to fly non-stop for many days without food.
A migrating bird can fly across the Sahara Desert in 50-60 hours without stopping to ‘refuel’.
Birds find their way by observing landmarks, the patterns of stars and the position of the setting sun. They also use their sense of smell and monitor the Earth’s magnetic field.
Most birds that migrate long distances fly at night.
The snow goose migrates nearly 5000 km south from Arctic Canada at an altitude of 9000 m.
Before migration was studied, some people thought swallows simply spent the winter asleep in mud.
Even flightless birds migrate. Emus make journeys on foot of 500 km or more, and penguins migrate in water.
Every year at least 5 billion birds migrate from North to Central and South America.
The Arctic tern spends the northern summer in the Arctic and migrates to the Antarctic for the southern summer, enjoying 24 hours of daylight in both places.
Florida manatees usually migrate south in winter, but recently they have moved instead into the warm water outlets of hydroelectric generating plants.
Hooded seals usually migrate south from Greenland in the Atlantic Ocean, but in 1990 one seal ended up off California in the Pacific, having taken a wrong turn.
Migrating noctule bats established themselves in Hawaii, after being blown 3000 km off course.
Migrating whales travel immense distances with the aid of their internal magnetic navigation.
Oil pipe-lines are serious obstacles to caribou, which follow traditional migratory routes every year.
Migrating European noctule bats fly at high altitude, emitting loud, low frequency sounds at one second intervals to keep in ground contact.
American grey squirrels sometimes travel in their thousands, crossing roads, rivers and towns in their search for food.
Beluga whales return to the estuaries where they were born to give birth.
Over 1 million wildebeest take part in a circular seasonal migration in east Africa’s Serengeti region. Each year, grey whales migrate 20,000 km in all, going to and from their breeding grounds.
Antelopes and deer are four-legged, hooved animals. Along with cows, hippos and pigs, they belong to the huge group called artiodactyls – animals with an even number of toes on each foot.
Antelopes and deer chew the cud like cows – they chew food again, after first partially digesting it in a special stomach.
Most antelope species live in herds in Africa. Many are very graceful, including the impala and Thompson’s gazelle. Most are also fast runners.
The horns on an antelope’s head last its lifetime.
Deer have branching antlers of bone (not horn) on their heads, which drop off and grow back again each year.
Most deer species live in woods and grasslands in mild regions such as northern Europe and North America.
The moose or elk grows antlers that are more than 2 m wide.
Male deer are called stags, young males are bucks, females are does and babies are fawns.
Usually only stags have antlers. The only female deer to have them are caribou or reindeer, which are the same species of deer but with different names.
Caribou can survive in the icy cold of Spitsbergen Island in the Arctic circle.
Chameleons are 85 species of lizard, most of which live on the island of Madagascar and in mainland Africa.
The smallest chameleon, the dwarf Brookesia, could balance on your little finger. The biggest, Oustalet’s chameleon, is the size of a small cat.
A chameleon can look forwards and backwards at the same time, as each of its amazing eyes can swivel in all directions independently of the other.
Chameleons feed on insects and spiders, hunting them in trees by day.
A chameleon’s tongue is almost as long as its body, but is normally squashed up inside its mouth.
The chameleon’s tongue is fired out from a special launching bone that is located on its lower jaw.
The chameleon can shoot out its tongue to a great length.
Most of a chameleon’s bulging eyes are protected by skin.
A chameleon shoots out its tongue in a fraction of a second to trap its victim on a sticky pad at the tip.
Most lizards can change color, but chameleons are experts, changing quickly to all sorts of colors.
Chameleons change color when they are angry or frightened, too cold or too hot, or sick — but they change color less often to match their surroundings.
The color of the skin is controlled by pigment cells called melanophores, which change color as they change size.
Recent evidence from microfossils suggests that the Mediterranean was never completely dry.
Warm seas such as the Mediterranean lose much more water by evaporation than they gain from rivers. So a current of water flows in steadily from the ocean.
Seas are small oceans, completely enclosed or partly enclosed by land.
Seas are shallower than oceans and have do not have any major currents flowing through them.
In the Mediterranean and other seas, tides can set up a seiche — a standing wave that sloshes back and forth like a ripple running up and down a bath.
If the wave cycle of a seiche is different from the ocean tides, the tides are canceled.
If the natural wave cycle of a seiche is similar to ocean tides, the tides are magnified.
Scientists thought that the Mediterranean was a dry desert 6 million years ago. They believed it was 3000 m lower than it is today, and covered in salts.
Warm seas lose so much water by evaporation that they are usually much saltier than the open ocean.
Waves in enclosed seas tend to be much smaller than those in the open ocean, because there is less space for them to develop.
The Dead Sea is the lowest sea on Earth, 400 m below sea level.
The warm waters of the Mediterranean attract tourists to the coast of Spain.
The Southern Ocean is the world’s fourth largest ocean. It stretches all the way round Antarctica, and has an area of 35,000,000 sq km.
It is the only ocean that stretches all around the world.
In winter over half the Southern Ocean is covered with ice and icebergs that break off the Antarctic ice sheet.
The East Wind Drift is a current that flows anticlockwise around Antarctica close to the coast.
Further out from the coast of Antarctica, the Antarctic circumpolar current flows in the opposite direction – clockwise from west to east.
The circumpolar current carries more water than any other current in the world.
Many penguins such as the Emperor, the world’s largest penguin, live on the ice floes of the Southern Ocean.
Beneath the surface of the Antarctic ice, the sea temperature reaches just -2°C. The freezing water is also a rich source of krill tiny shrimp-like creatures.
The ‘Roaring Forties’ is the band between 40° and 50° South latitude. Within this band strong westerly winds blow unobstructed around the world.
The waves in the ‘Roaring Forties’ are the biggest in the world, sometimes higher than a ten-storey building.
Sea ice forms in round pieces called pancake ice.
The circumpolar current could fill the Great Lakes in North America in just 48 hours.