A mammal is an animal that feeds its babies with milk when it is young. There are over 4,500 types of mammals. Many of the most popular animals we know are mammals, for example, dogs, cats, horses, cows, but exotic animals like kangaroos, giraffes, elephants and anteaters belong to this group, too. Humans are also mammals.

Mammals live in all regions and climates. They live on the ground, in trees and even underground. Polar bears, reindeer and seals are mammals that live in the Arctic regions. Others, for example camels or kangaroos, prefer the world’s dry areas. Seals and whales are mammals that swim in the oceans; bats are the only mammals that can fly.

Colony of seals
Image: M. Boylan [Public domain]

Mammals have five features that make them different from other animals:

• Female mammals produce milk and feed their babies with it.
• Only mammals have hair or hair-like skin. All mammals have hair at least some time in their lives.
• Mammals are warm-blooded. Their body temperature always stays the same and does not change with the outside temperature.
• Most mammals have a larger and well-developed brain. They are more intelligent than other animals.
• Mammals protect their babies more than other animals. They prepare them for future life.

People have hunted mammals for ages.They ate their food and made clothes out of their skins. Thousands of years ago wild mammals were domesticated and gave human beings milk, wool and other products. Some mammals, like elephants and camels, are still used to transport goods. In poorer countries farmers use cows or oxen, to plough fields.

Animals ploughing fields in India
Image: © Yann Forget / Wikimedia Commons / CC-BY-SA

Today some mammals are hunted illegally. Whales are killed because people want their meat and oil, elephants are killed for their ivory and tusks.

Mammals are often kept as pets. Among them are cats, dogs, rabbits or guinea pigs.

Mammals are useful to people in many other ways. Some help plants grow and eat harmful insects. Others eat weeds and prevent them from spreading too far. The waste of mammals is used as fertilizers that improve the quality of soil.

Tusk of an African elephant
Image: Taken by Schuyler Shepherd, CC BY 2.5, via Wikimedia Commons

History of Mammals

The first mammals probably evolved from reptiles about 200 million years ago during the Mesozoic period. They were rather small in a time when dinosaurs ruled the lands. When the dinosaurs died out about 65 million years ago mammals became the dominant land animals. Many mammals became extinct during the Ice Age , which ended thousands of years ago.

Today, some species are in constant danger of becoming extinct because they are hunted by humans. Hunters and poachers earn money by selling fur, tusks and other parts of mammals. Larger wild animals are often brought to zoos where they are protected.

Artist’s image of wooly mammoths during the Ice Age
Image : Charles R. Knight, Public domain, via Wikimedia Commons

Types of Mammals

Mammals are divided into three groups:

• Monotremes are mammals that lay eggs, like a bird. They live in Australia and New Zealand. The platypus belongs to this group.
• Marsupials are mammals that raise their young ones in a pouch in their bodies.
• Placentals are the largest group of mammals. The babies grow inside their mothers until they are ready to be born. Humans are placentals.

Platypus
Image:Stefan Kraft, CC BY-SA 3.0, via Wikimedia Commons

Bodies of Mammals

Skin and hair cover a mammal’s body. Some mammals have horns, claws and hoofs. The hair or fur of a mammal has many functions. The colour often blends in with the world around them and allows them to hide from their enemies. Some mammals produce needles or sharp hair that protects them from attack. But the main function is to keep the body warm.

Mammals have glands that produce substances that the body needs like hormones, sweat and milk.

A mammal’s skeleton is made up of three parts:

• The skull contains the brain, teeth and other organs.
• The spine or backbone enables mammals to stand or walk.
• Limbs are legs and arms of a mammal, often with strong bones.

Mammals have a four-chambered heart system that pumps blood into all parts of their body. The blood brings oxygen to muscles and tissue. The red blood cells of mammals can carry more oxygen than many other animals. Because mammals have a high body temperature they must burn a lot of food.

Mammals digest food through their digestive system. After food is eaten through the mouth it goes down the throat into the stomach and passes through the intestines. Mammals that eat plants have a complicated system with long intestines that help break down food. Flesh is easier to digest so meat-eating mammals have a simpler stomach.

Mammals breathe air through their lungs. Most of them have noses or snouts with which they take in air. Dolphins and whales breathe through a hole in the top of their back.

The needles of a hedgehog
Gibe [CC BY-SA 3.0], via Wikimedia Commons

A deer is a plant-eating mammal
Alastair Rae from London, United Kingdom [CC BY-SA 2.0], via Wikimedia Commons

Whales breathe through holes on top of their heads
AWeith [CC BY-SA 4.0], via Wikimedia Commons

Mammals and Their Senses

Mammals have five senses that tell them what is happening in their surroundings. Not all senses are developed equally among mammals.

Mammals rely on a sense of smell to find food and warn them of their enemies. Many species use smell to communicate with each other. Humans, apes and monkeys have a relatively bad sense of smell. Taste helps mammals identify the food that they eat.

Most mammals have a good sense of hearing. Some mammals use their hearing to detect objects in the dark. Bats, for example, use sounds to navigate and detect tiny insects. Dolphins also use such a system to find their way around.

While higher primates, like humans, apes and monkeys have a highly developed sense of sight other mammals are nearly blind. Most of these mammals, like bats, are active at night.

Mammals have a good sense of touch. They have nerves in all parts of their body that let them feel things. Cats and mice have whiskers with which that they can feel themselves around in the dark.

The whiskers of a cat help them feel things
Image:  Wolf Reynolds, CC BY 3.0, via Wikimedia Commons

What Mammals Eat

Herbivores are mammals that eat plants. They have special teeth that allow them to chew food better. Examples of herbivores are deer, cows and elephants. The giant panda is a plant eater that only eats bamboo.

Carnivores are mammals that eat other animals. Cats, dogs, tigers, lions, wolves belong to this group. They are hunters that tear their prey apart with sharp teeth. They do not chew their food very much.

Omnivores are mammals that eat plants and meat. Bears, , apes, pigs and humans are examples of omnivores.

Giant Panda eating bamboo
Image: Chi King, CC BY 2.0, via Wikimedia Commons

How Mammals Move

Most mammals live and move on the ground. They have four legs and walk by lifting one foot at a time or by trotting. Kangaroos hop and use their tail for balancing.

Mammals that live in forests spend a lot of their time in trees. Monkeys can grasp tree branches with claws and can hang on to them with their curved tail. Mammals often spend time hanging upside down in trees.

Dolphins and whales are mammals that live and move around in water. Instead of limbs they have flippers which they use to move forward. Other animals, like the hippopotamus, only spend some time in the water.

Bats are the only flying mammals. Their wings are made of skin stretched over their bones. They can fly by beating their wings up and down.

Gophers and moles are mammals that spend most of their life underground.

Monkeys hang around in trees most of the time.
Image:  Dmitry Makeev, CC BY-SA 4.0, via Wikimedia Commons

Gophers live underground most of the time
Image: LeonardoWeiss, CC BY 3.0, via Wikimedia Commons

How Mammals Reproduce

Mammals reproduce when a male’s sperm gets into contact with a female egg and fertilizes it. A young mammal grows inside the female’s body. Before this can happen mammals mate. Males and females stay together for a certain time.

Unborn mammals live in their mother’s body for different periods of time. While hamsters are born after only 16 days, it takes elephants 650 days to give birth. Human pregnancies last about 9 months. Many new-born mammals, like horses and camels, can walk and run shortly after they are born.

Marsupials give birth to babies that attach themselves to their mothers. They stay in pouches because they are too weak to live alone. Almost all marsupials, including kangaroos, koala bears or wombats live in Australia .

After birth, the glands of female mammals produce milk. Some mammals nurse their babies for only a few weeks. Others, for example elephants, give milk to their babies for a few years.

The duck-billed platypus and echidnas are the only mammals that lay eggs. After the young hatch they drink milk from their mother, just like other mammals do.

Lions mating in Africa
Image: Christopher Michel, CC BY 2.0, via Wikimedia Commons

Mother nursing a young horse
Image: Adamantios, CC BY-SA 4.0, via Wikimedia Commons

Life Habits of Mammals

Many mammals live in families or groups. Wolves and lions help each other in their search for food and protect each other from attackers. Leopards, cats, tigers and other mammals prefer living alone . They do not share their living space and food that they have, however males and females get together to mate. Mammals can mark the areas that they live in. They defend these areas by fighting off attackers. Some mammals claim territories only during the breeding season.

Many mammals migrate during special times of the year in order to get food and survive. North American bats travel to the south because insects become scarce during the cold winter months. Zebras and other wild animals follow the rainy seasons in Africa to find green grass. Whales migrate to warmer southern waters off the coast of Mexico to give birth to babies because they can not survive in the cold waters of the Arctic Ocean.

Some mammals hibernate because they cannot find enough food to survive. Their body temperature falls, heartbeat and breathing become slower. During this period hibernating mammals do not eat. They live from the fat of their bodies. Bats, squirrels and other rodents hibernate.

Mammals defend themselves from attackers in many ways. Hoofed mammals can run quickly in order to get food or escape. Squirrels rush into trees to hide. Some animals have special features that protect them from enemies. Skunks spray a bad smelling liquid to keep off attackers. The fur of mammals sometimes changes with its surroundings. Arctic foxes, for example, are brown in summer and in the winter their coats turn white.

Herds of zebras migrating in eastern Africa
Richard Mortel from Riyadh, Saudi Arabia [CC BY 2.0], via Wikimedia Commons

Arctic fox
Erik F. Brandsborg from Oslo, Norway [CC BY-SA 2.0], via Wikimedia Commons

Videos

Amazing Mammals
The Blue Whale
Eastern Grey Kangaroo
Cheetah
Hippo

Exercises

Multiple Choice Test
TRUE or FALSE?
Facts About Mammals 1
Facts About Mammals 2
Words and Definitions 1
Words and Definitions 2
Missing Word Cloze
Why Mammals Stopped Growing – Multiple Choice Cloze
Crossword 1
Crossword 2

Word Search

Jigsaw Puzzle

Mammals Memory

Some animals and plants in our world are very common, like houseflies, cats or daisies. They are not in danger of dying out. Other species are very rare. Sometimes only a few of them are left. Such species may disappear forever.

Ever since life on earth began, animals and plants have died out and new ones have appeared. Dinosaurs, for example, roamed the planet during the earth’s middle ages. 65 million years ago, they disappeared forever.

Animals and plants need each other to survive. They keep the world of nature in balance. If a certain plant dies out, some animals may become extinct too, because they depend on the plant for food.

Image:  Clker-Free-Vector-Images
via Pixabay

Why Species Become Extinct

Long ago, most animals and plants became extinct because of natural events, like earthquakes or volcano eruptions. Climatic changes, like the beginning of the Ice Age, also led to the disappearance of certain species. Today, plants and animals are in danger mostly because of human beings

Some plants and animals can survive in many areas. When they move to other places, they adapt to their new environment very quickly. Others can only live in certain areas. We call such a living place a habitat. If a habitat is destroyed, the species cannot find any more food or a place to live, sleep or have babies. So it dies out.

Habitats can be destroyed in many ways. More and more people live in our world. They need more space to live in. Rainforests, grasslands and other parts of nature are cleared and people start to settle there. They take away the natural home of plants and animals.

Deforestation in the Amazon rainforest
Image: Daniele Gidsicki, CC BY 2.0, via Wikimedia Commons

Pollution can also kill off certain species. Acid rain from factories goes down in rivers and lakes and can poison fish there.

The most endangered areas are the tropical rainforests. More than 50 % of all animals and plants live there. Every day, thousands of acres of rainforest are destroyed and many species become extinct every day.

Ever since man appeared on earth he has killed animals and gathered plants. They have been used for food, medicine, clothes and to make homes. Cheetahs, tigers and other wild cats have been killed for their skins. Whales have been hunted for centuries because of their oil and blubber.

Most animals today are protected by international law, but many, like the black rhinoceros and the African elephant are hunted illegally. Some species, like wolves, have been killed by humans because they were seen as a danger to farm animals.

The African elephant is in danger of becoming extinct
Image:  Bernard DUPONT from FRANCE, CC BY-SA 2.0,
via Wikimedia Commons

Sometimes native animals become endangered when a new species comes to live in a place. Foxes were brought to Australia to kill off rabbits, which were seen as a pest. But instead of killing rabbits, the foxes killed kangaroos and other marsupials of Australia.

Parasites belong to the greatest threats to plants and animals. Tiny organisms, bacteria and fungi can destroy trees, kill birds and fish.

How Can Endangered Species Be Protected

People have hurt plants and animals, but they are also willing to help them survive. All over the world organizations like the World Wildlife Fund, the Rainforest Action Network or Friends of the Earth are helping to protect habitats. They raise money for their projects and make governments and the public listen to them. New laws have also been made to protect endangered plants and animals all over the world.

Endangered Animals

African and Indian Elephants

Pandas

Reptiles

Sea Turtles

Tigers

Bald Eagles

The African elephant
Image: Andreas from Pixabay

African and Indian elephants are killed for their tusks, which are used for ivory earrings and other art objects

The giant panda
Image:  Dim Hou from Pixabay

The giant panda lives in zoos and in some parts of China. There are only about 1,500 left in the world today

Alligator in Louisiana
Image:  RENE RAUSCHENBERGER from Pixabay

Reptiles (lizards, crocodiles and alligators) are killed for their skins. People make leather handbags and shoes.

Sea Turtle
Image: Brocken Inaglory, CC BY-SA 3.0,
via Wikimedia Commons

Sea turtles are in danger because people often collect their eggs. They often die in the sea because of water pollution.

Siberian Tiger
Image: Appaloosa, CC BY-SA 3.0,
via Wikimedia Commons

There are only about five thousand tigers left in the world today. They live in southern Asia, mostly in national reserves.

Bald Eagle
Image:  Brigitte Werner from Pixabay

The bald eagle is the national symbol of the USA. The bird almost died out at the beginning of the century, but today the population is stable.

Endangered Plants

Some cactus types are in danger of becoming extinct because they grow slowly and are hurt by animals.

One out of three cacti are in danger of becoming extinct
Image by David Mark from Pixabay

The World Wildlife Fund

In 1960, biologist Sir Julian Huxley returned from a research trip to Africa. He was very much shocked by what he had seen there: the hunting of rare animals and the destruction of their habitat. Other scientists shared his opinion that something had to be done about this. The following year, Huxley, some fellow scientists and a few politicians founded the World Wildlife Fund. It became the largest conservation group in the world.

Today, the WWF has 5 million supporters around the world. It has national organisations in more than 50 countries and raises more than 100 million dollars a year.

The most important task of the WWF is to protect endangered species around the world. Among them are the tiger, whale, elephant and many others. The giant panda, one of the most endangered animals, has become the WWF logo.

The WWF also tries to protect habitats like the tropical rainforest. In the past decade alone, it has been able to conserve over 1 billion acres of forest in Asia, South America and Africa.

The organisation fights against the pollution of natural resources, and it is worried about the destruction of fish in the world’s oceans.

Over the past years, the WWF has been working on projects in over one hundred countries. It also gives money to research work and spends a lot to teach children and parents about our world in danger.

The giant panda has become the symbol of the World Wildlife Fund
Image: J. Patrick Fischer

Videos

Endangered Animal Species
Endangered Animals
60 Years of the World Wildlife Fund

Exercises

Words and Definitions
World Wildlife Fund – Multiple Choice Cloze
Match the Sentence Parts
TRUE or FALSE ?
African Elephants in Danger – Word Formation
Crossword

Wordsearch

Jigsaw Puzzle

Printable Downloads (PDF)

Word List
End of Unit Test
Key

Coffee is one of the most popular hot drinks in the world. Almost a third of the world’s population drinks coffee. People often meet at cafés or coffee shops for a coffee break during the middle of the morning or stop work in the afternoon to drink coffee.

About 10 million tons of coffee are produced every year. Brazil is, by far, the world’s largest coffee producer. About a third of the world’s production comes from this South American country. Other coffee producing countries include Vietnam, Indonesia and Columbia.

Europeans are the biggest coffee consumers in the world. In Finland, the average person drinks about 4 cups a day, that’s over 12 kg of coffee per year. Norway, Iceland and Denmark are other northern European countries, where drinking coffee is extremely popular. Canada is the only non-European country in the top ten list.

World Coffee Production

The Coffee Plant

Coffee grows as a green-leaved tree or bush with blossoming white flowers. The coffee shrub originally comes from Ethiopia but, in the course of time, spread to Southeast Asia and South America.

There are two basic types of coffee:

• Arabica accounts for about 70% of the world’s coffee production. It is grown in the higher regions of Central and South America and is popular for its flavor and fragrance.
• Robusta has spread throughout central and eastern Africa. Although it makes up only thirty per cent of the total coffee production, it has become more important because it can resist diseases better. It also has smaller beans and can grow at lower altitudes than Arabica.

Map of Coffee Production
r = coffee robusta
a = coffee arabica
m = cultivation of both

Image: “Coffee Cultivation by type” by Pixeltoo
is licensed under CC BY 1.0/Public Domain

Coffee plants grow in the warm and moist climate of the tropics and subtropics. Most coffee trees grow best between 1000 and 2500 meters above sea level.

Coffee trees produce fruits called berries. At first they are yellow, and then become red as they mature. An average coffee tree can produce enough berries to make about a pound (half a kilo) of roasted coffee.

Coffee seeds are grown in nursery beds. After a year they are planted in specially prepared fields. It takes a coffee tree about six years to produce a full harvest of coffee berries. The largest ones can get up to six meters tall, but they are normally trimmed to a height of 1.5 to 4 meters.

Berries of a coffee tree
Image: Cornellier, CC BY-SA 4.0,
via Wikimedia Commons

Harvesting and Processing

Most coffee berries are picked by hand, which makes sure that only the good berries are used. After separating berries from leaves and other waste materials, the beans are then taken out, cleaned and dried. Only the best beans make it to the market. Then they are put into bags and shipped to countries where they are roasted.

At their destination, the beans are combined to make different blends of coffee. Roasting for about 15 minutes brings out the true flavor of the coffee. The roasted coffee beans are packaged; some of them are crushed to ground coffee.

Effects of Coffee

Coffee contains caffeine, a substance that stimulates parts of the body, especially heart and muscles. People often drink coffee to help them stay awake or keep them alert. Although coffee has some negative effects, it is not thought to be a harmful drink. Children and people who have heart problems should not drink coffee in great quantities. In decaffeinated coffee, the caffeine is extracted in a chemical process.

How Coffee is Brewed

Coffee must be ground before it is brewed. Grounding usually takes place inside a coffee machine, but you can also buy ground coffee in shops. The simplest brewing process is pouring boiling water over a filter of ground coffee and letting it flow into a pot. Coffee is often made by using simple machines that force hot water through a pad of pressed coffee. Espresso machines press hot water through ground coffee.

Instant coffee is made by pouring hot water over powdery coffee. It dissolves at once, and you do not need a special machine.

Coffee brewed in an espresso machine
Image: The original uploader was Coffeegeek at English Wikipedia.,
Public domain, via Wikimedia Commons

History of Coffee

Coffee originated in the east African highlands in the 6th century. It was then brought to Arabia, where people used it as food and medicine. During the 11th century, the first coffee drinks came up. In the 16th and 17th centuries coffee became widely popular in Europe when the Turks brought it to Central Europe. In the 17th and 18th century, coffee conquered North and South America.

Coffee houses soon became popular all over the world. In the 1900s, chains of coffee shops emerged in Europe and America. Today, Starbucks is the largest coffee house chain in the world, with over 20,000 stores in 60 countries.

Types of Coffee

Coffee can be brewed in different ways.

Espresso

Americano

Café Latte

Cappuccino

Café Mocha

Frappe

Turkish Coffee

Espresso is probably the most popular coffee drink in the world. It is made by forcing hot water through a pad filled with dark ground coffee. Although there is not much coffee in the cup an espresso is very strong. It is usually drunk black, with no milk added.

Espresso

Image : Nonami2 at German Wikipedia, Public domain,
via Wikimedia Commons

Americano is an espresso with hot water added to make it weaker.

Café Latte is an espresso with a lot of hot milk and foam added on the top.

Café Latte
Image: Maksym Kozlenko, CC BY-SA 4.0,
via Wikimedia Commons

Cappuccino is a cup of espresso, together with warm milk and a lot of milk foam at the top. In some coffee shops it is decorated with flaked chocolate or cocoa.

Cappuccino

Image : Chris Brown, CC BY 2.0,
via Wikimedia Commons

Cafe Mocha is a cappuccino with chocolate or cocoa added.

Frappe is a cold espresso that you can get at some coffee shops during the hot summer months.

Turkish coffee is usually thicker than normal coffee. It is made by combining ground coffee and water to a muddy mixture.

Turkish Coffee

Image : Eaeeae, CC BY-SA 3.0,
via Wikimedia Commons

Videos

World Coffee Production
Coffee Types Explained

Exercises

Multiple Choice Test
From Plant to Cup – Ordering Exercise
Coffee Facts – Fill in the missing words
Coffee- Multiple Choice Cloze
Crossword

Word Search

PDF Downloads

Coffee – Word List
Coffee – End of Unit Test
Coffee – Key

Mountain Stream Tree Frog
Image:en:user:Froggydarb, CC BY-SA 3.0, via Wikimedia Commons

Salamander
Image:Hisanori Okamiya, Hirotaka Sugawara, Masahiro Nagano, Nikolay A. Poyarkov, CC BY-SA 4.0, via Wikimedia Commons

Caecilian
Image:José Gabriel Julio Guzmán, CC BY 4.0, via Wikimedia Commons

Physical Features

Amphibians can grow to different sizes, smaller ones are only 1 cm in length and larger ones can reach up to one and a half metres. Those that live mostly on land breathe through their lungs, others, which live mainly in water have gills. An amphibian’s skin is wet and often covered with a sticky fluid that prevents it from becoming dry. Some species lose their outer skin layer several times a year. Others produce poison that protects them from enemies.Many amphibians are colourful animals that blend in with their surroundings.

Some amphibians, for example frogs have thick bodies and four powerful legs that they use to leap and swim. Toads have shorter legs than frogs and a drier skin. They have no tail. Salamanders are amphibians with a short body and a long tail, which they can grow if they lose them. These creatures , which are found mostly in temperate climate zones , live near rivers and under rocks.Caecilians look a lot like worms. They have long thin bodies without legs. These tropical amphibians are nearly blind because their eyes are covered with skin or bone. Only few of them live in water.

How Amphibians Live

Amphibians are cold-blooded animals. Their body temperature is about the same as their surroundings. Most animals move to other places to adjust their body temperature if it gets too hot or too cold. Depending on the climate, amphibians hibernate or are inactive during the year when it gets too hot or cold. They eat many different kinds of food including insects and worms.

Life Cycle

Most amphibians lay their eggs in the water. Young animals have fish-like features. After living as a larva they grow gills which allow them to breathe under water. During a phase called metamorphosis a young amphibian develops from a larva into an adult. This stage can take from a few weeks to several years. Some amphibians then lose their gills and develop lungs for breathing. They often change their appearance.

Toad carrying eggs
Image:Laurent Lebois, CC BY 2.0, via Wikimedia Commons

Exercises

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.

Image: von Clker-Free-Vector-Images via Pixabay

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.

Blood components

Image (altered) : Alan Sved, CC BY-SA 4.0,
via Wikimedia Commons

How blood works in our 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 body’s circulatory system
Image (modified) : Termininja, CC BY-SA 3.0, via Wikimedia Commons

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.

High-altitude training in the Swiss Alps
Professional athletes often carry out training in mountain regions. Such training produces more red blood cells, which can then carry more oxygen to other parts of the body.
Image: Christof Sonderegger von Photoplus.ch, CC BY-SA 3.0,
via Wikimedia Commons

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 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 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 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 they may die unless the blood in their 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.

Image:BruceBlaus. When using this image in external sources it can be cited as:Blausen.com staff (2014). “Medical gallery of Blausen Medical 2014”. WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436., CC BY 3.0,
via Wikimedia Commons

Blood diseases

When a person suffers from anaemia there are not enough red blood cells to supply the body with the oxygen it needs. Leukemia 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.

Image: (modified) Mikael Häggström,
Public domain, via Wikimedia Commons

fatigue = to become very tired
shortness of breath = to have problems breathing in a normal way
joint = part of your body that can bend because two bones meet there
swelling = part of your body that becomes larger than normal
lymph node = a small rounded swelling in your body through which a liquid passes before entering your blood system
enlargement = when something gets bigger
spleen = an organ near your stomach that controls the quality of your blood

Videos

Blood Components and Blood Cells
The Circulatory System
Blood Groups
Blood Transfusions

Exercises

Multiple Choice Test
Words and Definitions 1
Words and Definitions 2
Unscramble the words
True or False
Match the sentence parts
Blood and the circulatory system – Missing word cloze
New blood test to detect cancer – Word formation
Crossword 1
Crossword 2

Wordsearch