TEST 37

In organic farming, crops, meat and other food are produced without chemicals. Fertilizers, pesticides, growth hormones and antibiotics are forbidden. During thousands of years of civilization the raising of animals and growing of plants have always been organic.

Chemicals for farming first came up at the turn of the 20th century. Widespread use of chemicals began after World War II.

In the 1950s and 60s farmers started using chemical fertilizers and pesticides. Recently, however, more and more farmers have been returning to more natural ways of producing farm products.

Organic farming methods

Instead of chemicals, organic farming uses a lot of organic matter to give crops the nutrients that they need to grow. Clover, for example, has a lot of nitrogen in it and farmers use it to make the soil better. Manure from animals and compost are also used to enrich the soil. These fertilizers also help conserve the soil, not destroy it after a few years.

Organic farmers also use crop rotation to preserve the good qualities of soils and avoid monoculture.

Chemical pesticides destroy or weaken many of the natural enemies of pests, like birds or frogs. They also can kill those insects that control a great number of pests.

Organic farming creates new living areas for wasps, bugs, beetles and flies by giving them water and food.

Weeds are controlled by using special machines. Hay, straw and wood chips are put between the rows of plants to stop weeding.

Many agricultural products can be produced in an organic way. Meat, dairy products and eggs come from animals that are fed organically and can graze outdoors. They live in conditions that are natural to them. Cows, for example, are kept in pastures and fields. Vegetables and fruit are also produced with organic methods.

Conventional vs. organic farming

Conventional farmers

apply chemical fertilizers to soil to grow crops

spray crops with insecticides and pesticides to prevent them from being damaged by pests and disease use herbicides to stop the growth of weeds

Organic farmers

build soil with natural fertilizers in order to grow crops

rely on the natural enemies of pests

use crop rotation to conserve soil

pull out weeds by hand

Advantages of organic farming

Farmers can reduce their production costs because they do not need to buy expensive chemicals and fertilizers.

Healthier farm workers.

In the long term , organic farms save energy and protect the environment.

It can slow down global warming.

Fewer residues in food.

More animals and plants can live in the same place in a natural way. This is called biodiversity.

Pollution of ground water is stopped.

Disadvantages of organic farming

Organic food is more expensive because farmers do not get as much out of their land as conventional farmers do. Organic products may cost up to 40% more.

Production costs are higher because farmers need more workers .

Marketing and distribution is not efficient because organic food is produced in smaller amounts.

Food illnesses may happen more often.

Organic farming cannot produce enough food that the world’s population needs to survive. This could lead to starvation in countries that produce enough food today.

About 1-2% of the world’s food is produced with organic methods. The market however is growing very quickly - by about 20% a year. In Europe, Austria (11%), Italy (9%) and the Czech Republic (7%) are the countries in which organic food production as it its highest.

TEST 38

When the sun rises on a warm and sunny day you can see the trumpet-shaped flowers of the morning glory open up. When they close late in the afternoon primrose flowers open and before daylight arrives the next morning they close again.

Biological rhythms, like the opening and closing of flowers happen all over nature. But not all of them are daily rhythms. Some, like the beating of our heart, occur every second. Other rhythms are based on months, seasons or years.

Scientists use the term biological clock to describe the timing that controls biological rhythms. But what is this clock and where can you find it? In animals it is probably controlled by the brain, but in plants and other living things that have no brain it must be something else.

The biological rhythms of seashore organisms are connected to the rise and fall of the water. When the tide comes in they open their shells and get food, when the water goes back the shells close to protect the animals from the dry air.

The migration of animals is also an event that happens when a signal is sent out. When days become shorter birds leave the northern parts of the world and fly south where it is warm and they have enough food. In the summer they fly back to have babies .

Humans also have biological clocks that control their daily rhythms. Body temperature, blood pressure , sleeping and waking up have a 24-hour rhythm. Many illnesses have a yearly rhythm. Colds and flus often happen in winter. Measles occur mostly during the spring and summer.

When people travel by plane from one continent to another they often cross many time zones. Their internal clocks don’t seem to work correctly. We call this jet lag. It makes you feel tired and it takes many days for your body’s biological clock to get used to the new place.

People who work night shifts also have problems with their biological clocks. In general, they may not be as alert or active as people who work during the daytime . They also have more accidents during work. Sometimes they have more health and sleeping problems than other people.

By using the right medicine you can fight off problems that are connected with different times of day. Heart attacks and strokes often happen in the morning hours—between the time you get up and noon. Asthma often occurs between midnight and the morning hours. So when people with weak hearts take their medicine right after waking up it might prevent a heart attack.

Biological clocks control many rhythms of life. We are learning more and more about these rhythms. Doctors are looking for new ways to make travelling more comfortable and medical treatment more effective.

TEST 39

Rice is one of the world’s most important food crops . It is a grain, like wheat and corn. Almost all the people who depend on rice for their food live in Asia.

Young rice plants are bright green. After planting, the grain is ripe about 120 to 180 days later. It turns golden yellow during the time of harvest . In some tropical countries rice can be harvested up to three times a year.

Each rice plant carries hundreds or thousands of kernels . A typical rice kernel is 6—10 mm long and has four parts:

The hull is the hard outer part which is not good to eat. The bran layers protect the inner parts of the kernel They have vitamins and minerals in them. The endosperm makes up most of the kernel. It has a lot of starch in it. The embryo is a small part from which a new rice plant can grow.

Rice grows best in tropical regions. It needs a lot of water and high temperatures. It grows on heavy, muddy soils that can hold water. In many cases farmers grow rice in paddies. These are fields that have dirt walls around them to keep the water inside. The fields are flooded with water and seeds or small rice plants are placed into the muddy soil .

In southeast Asia and other developing countries farmers do most of the work by hand. They use oxen or water buffaloes to pull the ploughs . In industrialized countries work is done mostly by machines.

Two or three weeks before the harvest begins water is pumped out of the fields. The rice is cut and the kernels are separated from the rest of the plant. The wet kernels are laid on mats to dry in the sun.

After harvest, rice is processed in mills . First the hull and the bran layers are removed carefully so that the inner part of the kernel doesn’t break. The endosperm is the white rice that most people eat because it is easier to cook. It is enriched with vitamins and minerals to make it better. Sometimes brown rice , in which the bran layers remain, is produced . Then it is packaged and sold.

Rice gives your body energy in the form of carbohydrates . It also has vitamin B and other minerals in it. Rice has little fat and is easy to digest .

Rice is in many other foods as well. It is in breakfast cereals , frozen and baby foods and soup. Breweries use rice to make beer. In Japan , rice kernels are used to make an alcoholic drink.

Most rice is grown in lowland regions but about one fifth of the world’s rice is upland rice , which grows on terraces in the mountains. The world’s farmers grow more than 700 million tons a year. 90 % of the rice production comes from Asia. China and India are the world’s biggest producers. In these countries rice is planted in the big river plains of the Ganges and Yangtze.

Almost all of Asia’s rice is eaten by the population there. Sometimes they don’t even have enough to feed their own people. Other counties , like the USA, produce rice for export.

TEST 40

Teeth are hard, bony structures that grow from the jawbone. Humans and other animals use their teeth to bite and chew food.

Unlike your brain, your teeth were not ready to work from the day you were born. Although babies start growing their first teeth before they are born, you can’t see them until they are about 6 to 12 months old.

Humans grow two sets of teeth during their lives. The first set has 20 teeth baby teeth. When a child is about 6 years old, these teeth become loose and fall out. Over the next few years 28 permanent teeth replace the baby teeth. When a person is around 20, four more back teeth, called wisdom teeth grow in. Many people have their wisdom teeth removed, so that the others have more space to grow straight.

We have different types of teeth in our mouth. Each one has a different function. The four front teeth are called incisors. They are very sharp and are used for cutting and chopping food. You use your incisors, for example, to crunch the skin of an apple.

The pointy teeth beside them are canine teeth or cuspids. There are four of them, two on top and two on bottom. They help tear and grind food. Teeth with two points are called bicuspids; you have eight of them in all, four on the top and four on the bottom. You need to open your mouth a bit wider to see them. They are bigger and stronger and have ridges that make them perfect for crushing and grinding food.

We have eight back teeth, called molars. They are even wider and stronger than bicuspids and have more ridges. The tongue brings the food to your molars where it is crunched and then swallowed. Wisdom teeth are the last teeth way back in the corner of the mouth. They aren’t used for anything and are often removed because they can cause problems in a person’s mouth. They are called wisdom teeth because they come later on in life when a young person is older and “ wiser”.

Parts of a Tooth

The part of the tooth that you can see is called the crown. The outer part of it is covered with a hard white material called enamel which protects the tooth. It is often hard and shiny and acts as a tooth's bodyguard. It protects the inside parts of the tooth. Below it is dentin, a yellow bonelike material that is softer than the outer part. Dentin makes up the largest part of the tooth.

The centre of the tooth is called pulp. It is soft and contains blood and nerves. When you eat hot soup, bite into cold ice cream, fall or hurt a tooth it’s your pulp that hurts. Nerves in your teeth send signals to the brain about heat, cold or pain. The pulp also keeps the tooth alive.

The soft tissue around the base of each tooth is called gum. The roots of the teeth are below the gums. A tooth can have between one and three roots. A glue- like substance called cementum keeps the teeth connected to the jawbone.

One of the biggest problems with teeth is tooth decay. Bacteria forms in the teeth and eats away tooth enamel. This leads to a cavity or hole in your teeth. It may cause pain and infection. Dentists fill holes with metal or plastic to prevent any damage. Plaque can also make gums red and weak. As time goes on gums can become so soft and weak that teeth can fall out. That’s why we should brush our teeth regularly and go to the dentist at least twice a year to prevent these problems.

How to treat your teeth

Try to brush your teeth with fluoride toothpaste at least twice a day. It’s especially important to brush before you go to bed.

The best way to brush is to move in little circles, go around until you have covered every surface of every tooth. You should clean the space between your teeth with a string called dental floss at least once a day. It removes food and plaque that get stuck between them.

You can also prevent problems by eating fewer sugary snacks and drinks that contain sugar. Sugar can hurt your teeth and cause tooth decay or cavities.

TEST 41

Tea is one of the most popular drinks in the world. You make it by pouring hot water over the dried leaves of a tea plant. For centuries people believed that teas could cure illnesses, they used it as medicine. Today scientists know that tea contains chemicals that prevent cells from dying. Most teas have caffeine in them, a substance that makes you feel more active. Some people have problems drinking tea because it can cause sleeplessness.

Tea plant

The tea plant grows best in tropical and temperate places where rain falls throughout the year. Tea can be grown from sea level to about 2,000 metres, but the best quality grows in higher regions.

Tea comes from the leaves and buds of tea plants. Wild plants can be up to 9 metres high but on tea plantations they are cut back to a bush of about a metre in height so that workers can pluck the leaves easily. The plant produces pointed, leathery dark leaves, small white flowers and seeds that look like hazelnuts. It takes a plant three to five years before is ready for plucking.

A plucker can harvest about 20 kg of tea a day. On large tea plantations the leaves are harvested by machines, but the quality of tea is higher when the leaves are hand-plucked.

Types of tea

The most common types of tea are black and green tea. They come from the same plant but are processed differently.

Workers take the leaves and spread them out on shelves where they can dry. Next, they are rolled and broken into pieces and put into a room where they absorb oxygen. Chemical reactions change the taste and character of the tea. Finally , the leaves are dried with hot air until they turn brownish-black. Most black tea comes from Sri Lanka, Indonesia and eastern Africa.

To make green tea, workers put the freshly picked leaves into a steamer, which keeps them green. Then they are crushed and dried in ovens. Japan is the biggest producers of green tea

Tea can be bought in many forms – leaves, powder or tea bags. Some of them are added with flavours, like vanilla, orange or lemon. Although most people drink their tea hot, many enjoy iced tea, especially during the summer months.

Black tea is brewed by pouring water over a teaspoon of tea. The tea should soak for three to five minutes before you drink it. Green tea should be left in water longer. Instead of putting tea leaves into a pot people often put tea bags into a cup.

History

 People first drank tea in China about 5000 years ago. Originally it was used as a medicine, then as a daily drink. It spread to Japan in the 3rd century A.D. Dutch and Portuguese traders brought tea from eastern Asia to Europe in the 1600s.

In 1657 the beverage was sold for the first time in coffee houses in Great Britain. When the English started a tradition of tea drinking in the afternoon it became England’s national drink. In the 17th and 18th centuries tea spread to British colonies overseas.

In 1767 Great Britain placed a tax on tea imported by American colonists. During the Boston Tea Party of 1773 they were so angry that they threw a ship full of British tea into the harbour to protest British rule. Two years later the American Revolutionary War started.

Today about 3.3 million tons of tea are produced. India, with its famous tea growing regions like Darjeeling and Assam, and China produce about half of the world’s tea. It also grows in many other parts of Asia, especially in Sri Lanka and Indonesia. In the course of time growing tea has spread to countries in Eastern Europe, Africa and South America.

TEST 42

Mushrooms are small living organisms that look like umbrellas. They are not plants because they do not have chlorophyll, the green material that plants use to make food. Mushrooms get their food from the living or dead plants around them. The 3,000 types of mushrooms around the world belong to the group of fungi.

Parts of a mushroom

A mushroom has two parts. The part underground is called the mycelium. It gets food for the mushroom. Sometimes it dies quickly, but if it gets enough food it may live for hundreds of years.

The umbrella-shaped body of a mushroom that we can see is called the fruit or sporophore. It only lives for a few days. The fruit starts out as a small button which grows into a stalk and a cap. The stalk or stem grows quickly because it can absorb a lot of water. As the cap becomes larger it unfolds like an umbrella. Soon small plates, called gills, appear under the mushroom’s cap. They have small seeds or spores on them. When these spores fall off the mushroom the wind blows them away. If they fall on a warm, wet area a new mycelium develops.

Mushrooms can have a diameter of up to 40 cm. Although some may be very colourful, most mushrooms are white, brown or yellow.

Edible and poisonous mushrooms

Some mushrooms are eaten as tasty food. We use them to flavour meat or soup or mix them into salads. They have a lot of vitamin B in them, as well as minerals like iron and phosphorus.

The common field mushroom is normally white with brown or pink gills. They are often grown in dark wet rooms where the temperature is always the same. Then they are brought to stores and markets where they are sold at high prices.

The best known and most widely eaten mushroom is the button mushroom. It has a short thick stalk and a white cap. Button mushrooms are found in all kinds of food, from pizzas to salads and stews.

Truffles are mushrooms that grow completely underground. Dogs and pigs can smell them and find the places where they grow. These mushrooms are very expensive and can be eaten in very luxurious restaurants around the world.

Other types of mushrooms are poisonous. They produce chemicals called toxins. Some toxins lead to diarrhoea or other illnesses, a few mushrooms are even deadly. They can cause liver damage or attack kidneys. Unless you get quick treatment death may come very fast.

Two very deadly mushrooms are the death cap and the destroying angel. The death cap appears in many colours, which is why it is difficult to identify. It has over twenty different kinds of poison it. The destroying angel is a beautiful white mushroom which grows in summer and autumn.

It is often very hard for people to tell between edible and poisonous mushrooms. So, never eat a mushroom you find unless you know what it is.

Importance of mushrooms

Mushrooms help plants grow. Together with bacteria they help dead material and minerals get back into the soil so that it can be used again. Some are useful in controlling pests of crops.

The Chinese have used mushrooms in medicine for hundreds of years. Certain types are turned into a tonic and used for treatment of illnesses. Scientists have found out that some mushrooms prevent high blood pressure.

TEST 43

A reptile has a dry and scaly skin and it breathes through its lungs. There are about 6,000 different types of reptiles. The most common ones are alligators, crocodiles, lizards, snakes and turtles.

Reptiles are cold-blooded. Their body temperature stays the same as the outside temperature around them. In hot places most reptiles look for shady areas during the day. Many species are active at night. In cold regions reptiles hibernate during the winter months.

Reptiles can be small or large, heavy or lightweight. Pythons are snakes that can grow more than 9 metres long. Turtles can weigh more than 1000 kg. On the other hand, some lizards are not more than 5 cm long.

Reptiles live all over the world, except in Antarctica. Most reptile species can be found in tropic and subtopic regions. Many types of lizards like the hot , dry desert areas. Some turtles and snakes spend most of their life in oceans.

Although many people are afraid of reptiles, most of them are harmless and don’t attack human beings. Some, however, are dangerous, like crocodiles or snakes with poisonous bites.

People hunt reptiles for their skin. It is used to make leather products like belts, shoes or handbags. 

A reptile’s body

The skin of a reptile has scales. Some animals lose their old scales and grow new ones two or three times a year .

Turtles have very hard scales called plates. They use them as a kind of protection from enemies in the outside world.

The digestive system of a reptile depends on what kind of food it eats.

Meat eaters have a very simple stomach and a short intestine. Plant eaters, like turtles, have a more complicated stomach and long intestines. Crocodiles have large stomach muscles because they have to chew the flesh they eat into small pieces.

Some reptiles produce poison. They bite their attackers and inject poison into them. The victim may be paralyzed or even killed.

Most reptiles have a good sense of vision. Not all of them can hear well. Some of them hear by feeling vibrations on the ground.

Reptiles breathe through their lungs. They normally have two lungs , but some snakes only have one.

How reptiles live

Male reptiles release their sperm inside a female. The sperm gets to the female’s egg inside her body. This is called fertilization. These new eggs later become new reptiles.

Turtles, crocodiles, as well as some lizards and snakes lay eggs that have hard shells. When they are laid in warm places they hatch more easily. Some reptiles keep their eggs in their babies until they hatch.

Only a few species of reptiles care for their eggs or their babies. Some of them wrap their body around the eggs to protect them.

Most reptiles eat other animals, however some lizards and turtles eat mainly plants. They usually grab their food and chew it or swallow it whole. Some crocodiles drown other animals before eating them.

Snakes and some other reptiles bite their victims and poison them before they eat them. Pythons and many kinds of snakes wrap their bodies tightly around their prey, so that they can’t breathe anymore and die.

Reptiles can live for a long time without food—sometimes even for weeks.

Reptiles can defend themselves from other animals in many ways. Lizards can change the colour of their skin to avoid attacks. Some snakes lie on the ground and play dead until an attacker goes away. Crocodiles use their powerful tail as a whip , that can hurt or even kill other animals.

Reptiles hibernate in winter by burrowing themselves deep into the ground or sliding between rocks. They stay there until it gets warmer. Before they go to sleep for the winter, they eat lots of food and grow some fat.

TEST 44

Birds are animal with feathers. Because they can fly, they are the fastest animals on Earth . Some birds can reach speeds of up to 160 km an hour. However, not all birds can fly. Some birds, like ostriches can run and penguins can swim.

There are about 10,000 kinds of birds. The smallest bird is the hummingbird which gets only about 5 cm big and the largest one is the ostrich which may grow up to 2.5 metres tall. Birds live everywhere in the world—from the cold polar regions to the rain forests of Africa.

There are birds, like ducks or seagulls that always live near water. Many birds from colder areas migrate to warmer regions to avoid harsh winters, but others stay in their living area all through the year.

All birds hatch from eggs. Female birds lay their eggs in nests that they build. Baby birds remain in the nest for several weeks or months after hatching. Their parents feed them and care for them until they are old enough to leave them.

The body

Birds belong to the group of animals that have backbones, like we do. These animals are called vertebrates. Like mammals, birds are warm-blooded – their temperature always stays the same , even if it is cold outside. Bird don't have teeth, they have a hard beak that they use to get food or defend themselves.

A bird has a light but strong skeleton and bones that are hollow. Many of them are joined together. The strongest muscles are in the wings. These powerful wings help birds stay in the air. Some birds, which are fast runners or have a lot of weight to carry, have the strongest muscles in their legs.

Feathers cover most of a bird's body. Some birds have up to 25,000 feathers. In many types of birds the feathers are brightly coloured in order to attract other birds. Birds lose their feathers at least once a year. They grow new ones – mostly during the breeding season.

The bills or beaks of birds are built differently, depending on what they eat. Woodpeckers have a chisel-like bill, so they can bore into trees and look for insects. Ducks have flat bills because they eat plants that float in the water.

All birds have two legs, however, they don't always look the same. Birds that fly most of the time have very short legs and wading birds or fast runners have long ones. The majority of birds have 4 toes on each foot – one of them points backwards. Climbing birds have two toes pointed to the back to give it more grip.

Birds that mostly live in the water have skin between their toes. This lets them swim better than others.

In order to fly, birds need a lot of oxygen, so they need a powerful heart to get it into their lungs. A bird's heart beats much faster than ours does – up to 1000 times a minute.

Senses of Birds

Birds have a good sense of sight. In proportion to other animals, they have the biggest eyes. They are on the sides of their heads , so each eye can see in a different direction. This is called monocular vision.

Birds have ears, but they are not visible. In most cases, they are covered with feathers. They hear as well as we do, some of them even better. Some birds use their sense of hearing to navigate in dark caves where they can't see anything.

Birds' sense of smell is not very well developed, but there are some birds that are almost blind and rely on their smell to get food.

Why birds fly

A bird's wing is curved on the top and flat on the bottom. The air can flow faster over the top than under the bottom part. Fast moving air has less pressure than slow-moving air, so the air under the wing pushes it upwards. This is called lift . To climb very high, birds start flapping their wings and push more and more air down.

Some birds can fly really fast. Falcons are considered to be the fastest birds. Experts think they can travel at speeds of up to 250 km/h.

Feathers

Birds are the only animals with feathers. They weigh very little , but birds could not live without them. They help them fly, keep them warm and keep rain and snow away from their skin.

A feather is made up of a central shaft that is very stiff. The vanes on both sides are made up of thousands of tiny barbs.

 Why birds are important

We need birds for many reasons. In nature, birds eat fruit and carry the seeds from flower to flower. Some birds, like chickens and ducks provide us with meat or eggs. Others help farmers eat insects that attack their fields.

But some birds are thought to be more dangerous than helpful. Starlings and pigeons have become numerous in cities and make lots of dirt.

People have always hunted birds for food. Turkeys or ducks are hunted because of their valuable meet. Farmers today produce hundreds of millions of chickens every year for meat.

Birds can also be kept as pets. Parrots and canaries are very common pets because they can be trained to talk or to whistle.

Bird Migration

Birds migrate to certain places in order to get food and water all year round. They also travel to other places to escape from extreme weather and temperatures. Seabirds are the greatest travellers. Some of them travel over a distance of 30,000 km or more every year.

Migrating birds have many ways of finding out the right direction. They help themselves by using the position of the sun or moon during the daytime and watch the stars at night. Some of them get help from familiar things they see or hear.

Sometimes, birds get lost and fly in wrong directions. They are observed thousands of km away from their normal living areas.

TEST 45

The human heart is a muscle that lies left of the chest . It has about the size of a fist . The heart is like a pump that sends blood around your body. The blood gives you the oxygen you need . An average heart pumps about 70 millilitres of blood into your body with every beat . That’s about 5 litres every minute or about 7200 litres every day.

Parts of the heart

The heart is made up of 4 chambers . There are two chambers on each side of the heart. The top two chambers are called the atria. They fill with blood. The two chambers at the bottom of the heart are called ventricles. Their job is to squirt out the blood. In the middle of the heart there is a thick muscle called the septum that separates the left and the right side.

The atria and ventricles work together. The atria fill with blood and when they are full they let the blood into the ventricles. When these ventricles pump the blood out of the heart, the atria fill up again and the whole process starts again.

There are valves in the heart that make sure that the blood is pumped in the right direction. When the heart contracts , it pumps blood from its chambers into the body. Then the heart muscle relaxes and lets the chambers fill up.

Blood circulation

Every cell in your body needs oxygen to live. The role of the heart is to send blood that is full of oxygen to all the cells in your body.

The passageways that carry this blood are called blood vessels. Arteries carry oxygen-rich blood to the cells that need it. The largest artery is the aorta. Veins carry blood back to the heart again. It is pumped into your lungs where it picks up oxygen and then goes back to your heart, from where it is pumped back again into your body.

It only takes about 20 seconds to pump blood to every cell of your body.

Your heartbeat

Even though your heart is inside you, you can see it work by feeling your pulse. You can find your pulse in many parts of your body. It’s best to press your finger on the inside of your hand, just below the thumb. You can feel a small beat under your skin. This is caused by the contraction of your heart.

When you rest or sleep your heart does not beat that fast—about 60 to 80 beats a minute. When you run around a lot your heart pumps more blood into your body—maybe up to 200 times a minute.

 Changing heart rates

As people grow older their heart rates change. A newborn baby has a heart rate of about 130, a three-year old has about 100 and an eight-year old’s heart beats about 90 times a minute. An adult has a heart rate of about 70 to 80. The older you get the slower your heart beats.

 Heart attack

Your heart is probably the most important part of your body. If it stops pumping blood you cannot survive .

The greatest danger for your heart is a heart attack. It happens suddenly and is like an explosion. When the heart stops pumping blood, muscles must die because they cannot get any oxygen.

In some cases blood is not able to flow through the blood vessels because they are clogged up. So the heart does not get enough blood to work. Chest pain may be a possible warning sign of an upcoming heart attack.

How to keep your heart healthy

Most people are born with a healthy heart, but it’s important to keep it healthy.

Your heart is a muscle. It needs exercise . About twenty minutes of exercise a day will keep it strong and healthy.

Eat different kinds of food and don’t eat too much fat.

Smoking is bad for your heart.

TEST 46

Why do human beings look a bit like monkey or apes ? Why are dolphins good swimmers? Why do giraffes have long necks ? The answer to all these questions is evolution. Evolution is the way life changes through time.

All living things are connected together like branches in a tree. Plants and animals are related to one another through their ancestors. For example, we share a common ancestor with gorillas, dogs or even mushrooms.

Evolution shows us how and why all living things change over a certain period of time.

Evidence of Evolution

We cannot watch changes in life directly. They take place over thousands or millions of years. However, scientists cannot find proof that these changes have taken place. Important evidence for evolution comes from fossils, the leftovers of ancient life. When animals or plants die they are pressed into sand or clay. Over millions of years rocks are formed.

Scientists have found out that different fossils are found in rocks of different ages. For example, the oldest rocks of our earth are about 3.8 billion years old. They contain no fossils because there was probably no life at that time. Fossils of bacteria appear in rocks that are about 3.5 billion years old. Fish , reptile and mammal fossils appear in younger rocks. Human fossils are found only in the youngest and highest rock layers.

Fossils also show that certain groups of animals have evolved from other groups. Amphibians evolved from fish that could breathe air and move on land. They had legs but also scales and a fin.

Birds probably evolved from dinosaurs. The archaeopteryx was an animal that had feathers like a bird and could fly. It also had teeth, claws on its wings and a skeleton that looked like a meat-eating dinosaur.

But even without fossils there is other proof which shows that evolution has taken place. Different species often have similar features which they probably got from a common ancestor. For example the front limbs of lizards, birds, bats and humans are very much alike. They have one bone in the upper arm, two in the forearm, wrist bones and five fingers.

Living creatures might also have structures that they have inherited from an ancestor but have become useless. They don't need them any more. Pythons, for example, have the remains of back leg bones, but snakes do not have such legs. The appendix was used by animals that ate only plants but in our bodies these organs have become useless.

The way in which different species occur all over the world also gives us evidence for evolution. Similar species, for example, are found together in certain areas. All types of kangaroos are found in Australia. This is because the kangaroos' ancestors also lived there.

Plants and animals do not always live in ideal places. Tropical ocean islands, for example, are ideal places for frogs to live, but no frogs are found there. This is because the frogs' ancestors lived on the mainland and could not get to ocean islands far away.

How evolution happens

Natural selection

Although we are all human beings, each one of us is different. We all belong to the same species but there are never two people on earth who are exactly the same. We are like our parents because we inherit certain features from them.

Because there is not always enough food for animals and plants to eat they compete against each other in order to survive. Some individuals are better than others because they have certain advantages. On average , those that are better or stronger will survive. The advantages that they have are then passed on to their children and as time goes on these characteristics will be passed on to the whole species. We call this natural selection.

Example : In 1977 no rain fell on the Galapagos Islands. Food became very scarce and many of the island's finches died. They normally ate small seeds that were lying on the ground. Biologists observed that finches with larger beaks were able to survive because they could eat larger and harder seeds that finches with smaller beaks couldn't open. In the fight for food large-beaked birds had a great advantage. After the drought ended biologists found out that the next generations of finches were larger than the ones before.

Genetics and Inheritance

Today, scientists know that a molecule called DNA has all the information which controls the way life will develop. This information is stored in genes and the structure of genes is called the genetic code.

When a male and female have children the male sperm and the female egg join together to a single cell with two genetic codes, one set from the mother and one set from the father. A baby then develops from this cell. This is how we get certain features from our parents.

Sometimes parts of the genetic code change by accident. We call this mutation. Some mutations in genes are dangerous , others may be an advantage. In the example of the birds, the larger beaks were a mutation that was good for the whole species.

Adaptation

Sometimes animals and plants fit beautifully into the world around them. The Arctic fox, for example, is adapted to the polar ice in the far north. It has a thick fur that helps it stay warm and the white colour makes it harder for enemies to see . With its hairy feet it can walk more easily in the snow.

Giraffes also got used to the world they live in. Ancient giraffes normally did not have long necks, but those that did were able to find more food because they could reach the leaves of the trees . Longer-necked giraffes had more babies than others and as a result they developed into the tallest land animals in the world.

Adaptations can cause plants or animals to look alike even if they are not closely related. The bodies of sharks and dolphins are similar, but the shark is a fish and the dolphin a mammal.

Speciation

Speciation happens when one species divides itself into two or more new species. This happens, for example, when the same group of animals or plants live in different places. Sometimes species migrate to new habitats. In other cases a population may be divided by natural disasters like floods or volcanic eruptions.

When species are separated they don't have contact with each other any more and they develop in separate ways. As time goes on the two groups become more and more different, simply because they live in different habitats maybe with more or less food or a hotter or cooler climate. If they get together again they cannot have babies any more because they are completely different.

Speed of evolution

How fast does evolution happen ? Sometimes it occurs very quickly. In only a few decades insects evolved that were able to survive insecticides. Viruses also develop quickly. The AIDS virus was unknown before the 1980s.

Some animals evolve very slowly for millions of years and then change occurs very quickly.

Human Evolution

Fossils show that many species which are now extinct belong to the same family as we humans do— Homo Sapiens. The oldest members of this family are primates that lived in Africa a few million years ago. They were able to walk upright and had a brain that was a bit bigger than that of an ape.

Charles Darwin

Charles Darwin was an English scientist who studied nature. In his famous book "On the Origin of Species " he claimed that all living plants and animals developed from earlier forms of life.

Darwin was born in England in 1809 . His father was a doctor and his mother died when he was 8 years old. Although Darwin was interested in nature, he was sent to a university to study medicine, but he didn't do well there.

In 1831 Charles Darwin was invited to sail on the HMS Beagle to study natural history. The voyage lasted for five years and took Darwin to the Galapagos Islands and other places on the western coast of South America. There he studied fossils in old rocks and noticed that there was a connection between them and plant and animal life. As time went on he developed his theory of natural selection. Those plants and animals that fit better into their environment can survive better and produce more offspring.

When his book was published it caused a lot of discussion but in a short time it was accepted by scientists around the world.

TEST 47

Blood is an important fluid that keeps us alive. We cannot live without it. The heart pumps blood to all parts of the body and brings them oxygen and food. At the same time blood carries all the substances we don’t need away from us. Blood fights infections, keeps our body temperature the same and carries chemicals that control body functions. Finally, blood has substances that repair broken blood vessels so that we don’t bleed to death.

What blood is made of

Blood is a mixture of fluid and solid matter.

Plasma is the liquid part of our blood. It makes up about 50 – 60 % of it. Plasma consists mostly of water but many other substances are in it. It contains dissolved food, chemicals that control our growth and do other jobs, proteins, minerals and waste products.

Red blood cells look like flat round discs. They contain haemoglobin, a protein that carries oxygen to the body and gives blood its red colour. Each drop of blood has about 300 million of these red cells.

            White blood cells, also called leukocytes, fight infections and harmful substances that invade the body. Most of these cells are round and colourless. They have different sizes and shapes. White blood cells are not as numerous as red ones. For every 700 red blood cells there is only one white blood cell.

Platelets are tiny bodies that are much smaller than red blood cells. They stick to the edges of a cut and form blood clots to stop bleeding. The blood of a normal adult has about 2 trillion platelets.

How blood works in the body

The circulatory system carries blood to all parts of your body. The heart pumps blood through big blood vessels called arteries and veins. In our body there are also millions of small blood vessels called capillaries. Oxygen, food and other substances pass through the thin walls of these capillaries into the tissue.

When you inhale air oxygen passes through your lungs and and is picked up by haemoglobin which transports it to your whole body. It is released into cells which produce energy. In return cells produce carbon dioxide which enters your blood stream and is transported back to your lungs where it is exhaled.

Food also reaches your body by means of blood. It is digested in your stomach and important substances like fat, sugar, proteins, vitamins and minerals are separated. These nutrients enter your blood stream and are moved to the cells and muscles where they are needed in order to give you energy or fuel. The work of the muscles and other tissue creates heat. Blood is the transporting system which carries heat throughout your body and warms you. The things that you don’t need are transported to your intestines and kidneys and leave your body again.

White blood cells play an important role in your immune system. When harmful substances invade your body an alarm goes off and white blood cells are activated. Then they work to destroy the invaders. They fight off viruses, harmful bacteria and begin anti-body production.

Blood also carries hormones to places where they are needed. When a hormone reaches a part of the body it controls growth, how the body uses food and other things.

You would bleed to death from a small cut if your blood didn’t clot. When a blood vessel breaks platelets rush to the damaged area and stick to one another , forming a plug.

The blood supply

Blood cells come from bone marrow. They begin as stem cells and then develop into red or white blood cells, or platelets. They don’t live forever and must be replaced by new ones. Red blood cells live an average of 120 days before wearing out. Then they are captured and destroyed in the liver and spleen. Platelets live only for about 10 days.

The amount of blood in your body depends on your size, weight and the altitude at which you live. An adult who weighs 80 kg has about 5 litres of blood, a 40 kg child about half the amount. People who live in high areas where the air is thinner need more blood to deliver more oxygen to the body.

Blood groups

Blood groups are very important in order to find out if a person can donate blood or receive blood in case of an accident or another disease. Almost everyone’s plasma has antibodies that that may not work together with another person’s blood.

There are four main blood groups :

Type 0 is the most common blood group. In an emergency type 0 blood can be transfused to anybody.

Type AB is the most seldom group. People with this blood group can receive any other blood in case of an emergency.

Type A can only be received by donors with A or 0.

Type B can only be received by donors with B or 0.

Blood transfusion

If an adult suddenly loses a litre or more of blood he may die unless the blood in his body can be replaced. Over the years blood transfusions have saved countless lives. Transfusions can also help patients who cannot produce enough blood cells to survive. They also help during operations when patients lose some blood.

Blood banks collect blood from donors and put it in sterile bags. It is cooled down and can be stored for up to 50 days. Laboratory workers screen blood for infectious diseases like AIDS and hepatitis. Only clean and safe blood can be given to patients.

Blood diseases

When a person suffers from anaemia there are not enough red blood cells to supply the body with the oxygen he needs. Leukaemia is a kind of cancer of the bone marrow, in which not enough or abnormal white blood cells are produced. Without white blood cells diseases can enter your body without being controlled.

When your body does not have enough platelets blood cannot clot well. Even small injuries can lead to a loss of blood because bleeding doesn’t stop.

TEST 48

The bones in our body form our skeleton. They help to support our body and protect important organs. Bones also store nutrients and minerals, and they are places where blood cells are made. Humans have more than 200 bones in their bodies – all of different shapes and sizes. Like other parts of our body bones keep changing all the time. They are alive and grow, especially when you are young.

Parts of a bone

The outer surface of a bone is called the periosteum. It is a very thin membrane that has nerves and blood vessels in it. They carry nutrients to the bones.

The compact bone is the smooth and very hard part of the bone. It is the part you see when you look at a skeleton.

Spongy bone is lighter than compact bone but it is still very strong. It looks like a sponge or honeycomb with a lot of spaces in between.

The inside parts of a bone are hollow. They are filled with a jelly called bone marrow. In adults the long bones of the legs and arms are filled with yellow marrow. The ends have red marrow. It is the place where billions of new blood cells are produced every day.

When a child is born it has about 300 “soft” bones . As it grows up some of these bones grow together to form the 206 bones that a normal grown-up has. During childhood bones grow with the help of calcium. By the time you are about 20, bones stop growing.

The Spine and Chest

The spine is a special part of our skeleton. It has 26 small bones that look like rings and are linked together. These rings are called vertebrae. The spine lets you twist and bend your body and it holds your body upright. It also supports your head so that it can’t fall down. The spine protects the spinal cords which are the nerves that send information to the rest of your body.

Between each ring there are small soft discs. They keep the vertebrae from rubbing against each other and act as a pillow, so when you jump into the air and come to the ground again it doesn’t hurt.

Ribs are a cage of bones that protect the most important organs: your heart, lungs, liver and others. You can feel your ribs by touching your chest.

Most people have twelve pairs of ribs that look the same on the right and left side. They are attached to the spine in the back. In the centre of your chest there is a strong bone called the sternum. It keeps your ribs in place, so that they don’t fall apart.

Skull

The bones in your head make up your skull. They protect your brain. Some bones in your skull are fixed, so that you can’t move them. Others, like your jawbone can be moved. It opens and closes your mouth when you eat, talk or chew food.

Babies are born with spaces between the bones in their skull. As a baby grows the spaces disappear and the bones grow together.

Arms and hands

Your arms and hands make up a total of about 54 bones. They let you write, pick up things or throw a ball. Each arm is attached to a shoulder blade. There are two long bones in your arm which are connected through your elbow. These bones are wider at the ends and thinner in the middle.

The wrist connects the lower part of your arm with your hand. It is very flexible so you can twist it and turn it around in many directions. The hand is made up of small separate bones. Each finger has three bones, only your thumb has two.

Legs

A leg is made up of three bones. They are very large and strong and help support the weight of your body. They are connected to a group of bones called the pelvis, which supports the upper part of your body.

The longest bone of our body is the femur. It runs from the pelvis to the knee. The knee itself is protected by the kneecap. The ankle connects the lower part of your leg with your foot. The bones in your feet help you stand and balance your body.

Joints

A joint is a place that holds two bones together. Fixed joints don’t move at all. Some of them are in your skull and in other parts of your body.

Moving joints allow you to twist, bend and move different parts of your body. Some of them let you move in only one direction, others allow you to move freely in many directions. Joints have fluids in them, so they can work more easily and don’t hurt.

Diseases and injuries

Like all parts of the body our bones can also suffer from certain diseases. Bones need calcium to make them hard. If your body does not get enough vitamin D bones don’t have enough calcium, they become soft and curved. People suffer from osteoporosis when they have weak bones.

Bones can also break. In babies and young children broken bones grow together quickly, but when people get older it takes longer for bones to be repaired. In elderly people bones heal very slowly – sometimes not at all.

Joints also attract diseases when a person gets older. Arthritis is an inflammation of the joint that hurts and sometimes makes it impossible for you to move.

Taking care of bones

Protect your skull bones by wearing a helmet when you ride your bike or do other sports.

Wear elbow and knee pads when you go skating.

Strengthen your bones by drinking milk and eating dairy products like cheese and yoghurt. They all have calcium in them, which makes bones harder.

TEST 49

Butterflies and moths are flying insects that have brightly coloured wings. There are about 100 000 different types of butterflies and moths in our world today. They live in all regions, except Antarctica.

Physical features

Like all insects, butterflies and moths have three pairs of legs. Their bodies are divided into three parts: the head, thorax and abdomen. Butterflies have a large eye on both sides of their head and two pairs of wings on the middle part of the body. When you touch them you can feel dust-like scales. They grow in rows and give the wings their special colours. These insects have a good sense of taste, especially for sweet things .

Butterflies and moths can be big or small. The smallest moths have wings that are only a few mm wide. Some have wingspans of up to 30 cm.

Differences

Although butterflies and moths may look alike they are different in some ways. The best way to tell them apart is by looking at their feelers or antennae . Butterfly feelers are thinner and the ends have small round knobs on them. Moth feelers don’t have these knobs, they look like more like feathers.

Butterfly wings are usually more colourful and brighter than those of moths . Moths have a thicker body and smaller wings than butterflies.

Most butterflies fly during the daytime while moths are more active at night.

 Behaviour

Butterflies and moths eat the nectar of flowers. Some species also eat mosses and ferns. Others may eat seeds and dead plants that lie on the ground.

Some insects travel over large distances. Several species in Europe and North America migrate to warmer regions during the winter and come back to their normal habitat in summer.

Life cycle

Butterflies and moths pass through four stages in life:

EGG
The first stage is the egg. Females lay their eggs on plants.

LARVA
Eggs hatch into small worms that are known as caterpillars. Such caterpillars are busy and hungry. They eat a lot, sometimes twice as much as their own weight every day. After a few days their bodies become too big and their skins crack open. This is called moulting . A caterpillar can shed its skin many times during this phase.

PUPA
After moulting, caterpillars rest. Sometimes they bury their bodies into the ground. Other caterpillars hide in logs or rest in cocoons that they make. This resting stage can last for a few weeks, sometimes even for a whole winter. During this period a caterpillar changes into an adult butterfly.

ADULT
When caterpillars come out of their rest the wings are soft and wet. They fan the wings to pump blood into them and to dry and harden them. After a few hours the adult butterfly is ready to fly. Most adults live between four and six weeks. Some live only a few days while others may live up to ten months.

Butterflies and moths have many enemies, especially birds. In order to survive they protect themselves in different ways. Some butterflies have a bad smell . Other species have strange marks on them that frighten away birds. In addition, many butterflies and moths that are in rest look like dead animals or the twigs of leaves.

TEST 50

Chocolate is a food that is popular all over the world. It is made from the seeds of the cacao tree. It can be eaten and also used as a flavour in ice cream, candy and other foods. Many people like the taste of chocolate and those who work hard eat it to give them energy.

History of chocolate

Chocolate originally came from Mexico and Central America. Historians think that the Maya took the wild cacao trees from the rainforest and planted them in their own gardens. They crushed the seeds and mixed them with water and spices to make a hot drink.

Chocolate and cacao were very important for the Mayan culture. Families drank a hot chocolate drink at special occasions and at parties.

The Aztecs, a people who lived centuries later, used cacao beans as a form of money. They traded other valuable goods to get them because they didn’t grow there. Only the rich people had the money to buy cacao and drink hot chocolate.

In the 16th century Spanish explorers brought cacao back to Europe, where the drink became popular quickly, especially among kings, queens and noblemen. Other European powers began to plant cacao trees in their own colonies.

During the Industrial Revolution new technologies were able to make the production of cacao cheaper, so that poorer people could also afford it. In the 19th century the beans were pressed together with butter and mixed with sugar into a new form, chocolate.

Today the biggest chocolate producing countries are the United States, Great Britain, Germany, Switzerland, the Netherlands and France.

How cacao grows

Cacao trees grow in the tropical regions of South America, Africa and Asia. The biggest cacao bean producers are the Ivory Coast, Ghana, Indonesia and Brazil. The cacao tree can grow to a height of 7 metres. After about 5 years the cacao trees produce large fruits. When the fruit is ripe it can contain 20 to 40 seeds.

How chocolate is made

After the cacao seeds are harvested they are transported to factories, where they are cleaned and dried. The outer parts of the seeds are removed.

Workers then roast the beans to give them a certain flavour. The seeds of the cacao beans have a lot of fat in them. They are grinded and mixed together with butter to form cocoa butter.

A dry powder can be made by pressing fat and water out of the cocoa butter. This powder is used for baking and also mixed with hot milk to drink.

Chocolate bars are made by putting sugar and milk into the cocoa butter. This paste is then put into different kinds of moulds.

Chocolate making is a big business. More than five billion dollars worth of cacao beans are sold every year. Americans, for example, eat five kilograms of chocolate every year.

Value of Chocolate

Chocolate has a lot of calories but it also has carbohydrates, fats, and other vitamins and minerals. It can give you a lot of energy that you need to do sports or hard work.

Scientists have found out that eating chocolate reduces blood pressure and the risk of heart disease and cancer.

There are also negative effects of chocolate. It can make you addicted and lead to obesity. Chocolate in large amounts lead to tooth decay.