How do plants breathe without a lungs

The oxygen cycle

The air we breathe contains about a fifth of oxygen. This gas is invisible, has no smell and no taste - but it is vital to us. Because we need oxygen to gain energy from our metabolism. Without this gas, neither humans nor most animals can survive.

Almost all of the oxygen in the air is made by plants through photosynthesis. During this process, the plant uses sunlight to create important nutrients from carbon dioxide and water. Photosynthesis also produces oxygen as a by-product.

The oxygen that the plant does not need is released into its environment. For example, a large beech tree produces about as much oxygen in one hour as 50 people need to breathe in the same time. Humans and animals breathe in this oxygen, use it up and breathe out carbon dioxide. Plants absorb this carbon dioxide during photosynthesis while at the same time generating new oxygen. A cycle is created between plants, people and animals.

In the course of the earth's history, much more oxygen has been released than living things have used to breathe. In this way, more and more oxygen was released into the atmosphere. The ozone layer, which protects us from dangerous UV radiation, could form from the increasing proportion of oxygen high up in the stratosphere.

Since people have been burning more and more oil, natural gas and coal, this natural oxygen cycle has been severely disrupted: burning consumes oxygen and at the same time carbon dioxide is also emitted. For this reason, the amount of carbon dioxide in the air has risen sharply over the past 250 years. The rise in this trace gas is the main cause of the man-made greenhouse effect and thus also of the warming of the atmosphere.


No sensible person would have thought that possible: Reinhold Messner and Peter Habeler climbed the highest mountain on earth without an oxygen device. The two extreme mountaineers arrived at the base camp yesterday, completely exhausted but happy.

Your climb to the summit of Everest begins on May 8, in the morning at half past five, after an icy night in a tent. They have been on their way up from base camp since May 6th. They are not frightened by the warnings of many doctors: They want to climb the roof of the world without artificial oxygen. A failed attempt is already behind them. Another attempt now follows from a height of almost 8,000 meters. The ascent in the thin mountain air is an ordeal, every step is torture. But both of them are in top shape and they have experience.

At noon they reach an altitude of 8,800 meters. The legs are heavy as lead, the tiredness can hardly be described. But they overcome their pain and trudge on, as if in a trance. Finally they achieve the seemingly impossible: You are standing on the summit of Everest. World record! From exhaustion, they let themselves fall into the snow. After a long break, Messner takes his camera out of his backpack and films. Back in the tent, they radio the base camp: They made it!

During the night Messner is tormented by terrible pain in his eyes: he is snow-blind. Habeler's ankle is injured. Nevertheless, the two manage to descend to base camp on May 10th. Only now do they understand their success, a feeling of triumph fills them. The sensation is perfect: Peter Habeler and Reinhold Messner have proven that Mount Everest can also be climbed without an oxygen device.

In the death zone

Doctors had warned Reinhold Messner and Peter Habeler: Moving around 8,000 meters above sea level without artificial oxygen is extremely dangerous to health. Brain cells could die and suspend controlled thinking, including the threat of unconsciousness. "You will come back as a fool," it was said briefly and drastically.

In fact, altitude sickness is not to be trifled with. From around 2,000 meters, the thinning air can make itself felt through shortness of breath, dizziness, headache or vomiting. The lungs take in less and less oxygen with increasing altitude, and the body is undersupplied. Above 7,000 meters - in the death zone - most people will pass out if they do not get extra oxygen. In the worst case, the extreme altitude leads to death. This fact has already cost many climbers their lives. The fact that Habeler and Messner climbed the summit without breathing apparatus actually borders on a miracle. It can only be explained with meticulous planning, incredible physical fitness and an iron will.


Global carbon dioxide emissions have never been as high as they are today. In 2010, it actually rose more sharply than ever before. This has now been announced by the US Department of Energy. The numbers exceed even worst fears.

For years, experts have warned of the speed of global warming. Apparently without success: The proportion of the climate-damaging gas carbon dioxide in the air is increasing rapidly. In the industrialized countries in particular, it gushes continuously from chimneys and exhaust pipes. The new numbers are frightening: In total, the world emitted over 33,500 million tons of carbon dioxide in 2010. That is 1,900 million tons more than in the previous year, an increase of six percent!

According to the US study, China and India are primarily responsible for the increase in horror. The two countries are on a growth path economically. They get their energy primarily from coal-fired power plants - and thus produce a lot of CO2. Overall, China is the record holder for greenhouse gas emissions, followed by the USA, Russia and India.

The policy for global climate protection has so far failed completely. China and the US refuse to sell their CO2- Reduce emissions. Russia, Canada and Japan also no longer want to comply with guidelines if the main polluters are reluctant to comply with international limit values. Bad for the climate, as the new study clearly confirms on the basis of the figures.

The Keeling curve

The first CO2-Measuring station in the world was opened far away from car exhaust fumes and factories: In 1958, the American climate researcher David Keeling began to regularly measure the carbon dioxide content of the air on the Mauna Loa volcano on the island of Hawaii. This place was chosen deliberately. Because neither chimneys nor forests influenced the result, an average value of the trace gas in the air could be measured here. A second station in Antarctica also met these conditions. After two years, Keeling presented his results to the world: The level of carbon dioxide in the air increased! In the following years, Keeling continued to fight for regular CO2-Measurements of the atmosphere. With success: The result is the so-called Keeling curve, a collection of data that to this day records the carbon dioxide content of the air and the significant increase in CO2 documented.

A shell made of gas

Seen from space, it appears like a fine bluish veil that surrounds the earth: the atmosphere. It is the envelope of air that surrounds our planet. Compared to the diameter of the earth, this shell is quite thin: if the earth were the size of an apple, the atmosphere would be about the thickness of its shell.

Without the atmosphere there would be no life on this planet, because plants, animals and humans need air to breathe. It protects us from the cold and from harmful radiation from space. It also lets meteorites burn up before they can hit the surface of the earth. This atmosphere is vital for us - but what is it actually made of?

The atmosphere is a mix of different gases. A large part of this gas mixture is nitrogen: At 78 percent, that's almost four fifths of the entire atmosphere. Only 21 percent consists of oxygen, which we need to breathe. The remaining one percent is made up of various trace gases - gases that only occur in traces in the atmosphere. These trace gases include methane, nitrogen oxides and, above all, carbon dioxide, or CO for short2 called. Although the CO2-Proportion is quite low, this trace gas has a huge impact on our earth's climate. This can be seen in the greenhouse effect, which is heating up our planet.

The fact that the earth has an atmosphere at all is due to gravity. It holds the gas molecules on earth and prevents them from simply flying out into space. In fact, the air becomes thinner and thinner with increasing altitude and thus decreasing gravity. Even at 2000 meters above sea level, this can become uncomfortable for people: He suffers from altitude sickness with shortness of breath, headaches and nausea. Extreme mountaineers who want to climb high peaks such as the 8000m high in the Himalayas therefore usually take artificial oxygen with them on their tour.

How was our air we breathe created?

What do people and animals need to live? Food and water, of course, but above all oxygen! We get it from the air we breathe. But that was not always the case: the primordial atmosphere consisted of water vapor and poisonous gases such as carbon dioxide and foul-smelling hydrogen sulfide. We would immediately suffocate in this “air”. But what has changed since then? Why is there oxygen in the atmosphere today? And since when?

If you look back in the history of the earth, you will find traces of living things that must have needed oxygen more than two billion years ago. So there must have been oxygen in the air back then.

Petrified traces of microscopic bacteria, called blue-green algae, are much older. And they have it all: These organisms were the first to use the energy of sunlight for their metabolism. They absorbed water and carbon dioxide from their environment and, with the help of solar energy, converted them into sugar, which they used to store energy. In addition, this chemical reaction produced oxygen - as a waste product, so to speak. However, the bacteria could not do anything with the oxygen and simply released it into the environment.

At that time there was plenty of sunlight and carbon dioxide, and the world's oceans were comparatively warm. These were the best conditions for the blue-green algae to multiply and spread. In doing so, they produced more and more oxygen, which accumulated over millions of years, first in the oceans and later in the atmosphere.

The waste product of these bacteria created the conditions for higher forms of life in water and on land. From the bacteria later emerged the chloroplasts, which to this day capture the solar energy in every plant. The principle of so-called photosynthesis has also remained the same: with the help of sunlight, water and carbon dioxide are converted into sugar and oxygen. The sugar serves as a nutrient for the plant, the oxygen is released into the air and inhaled by humans and animals.

What pollutes the air?

A thick cloud of haze hangs close to the floor. Such a gray veil of fog can often be seen, especially in large cities and metropolitan areas. Here the air quality suffers from the fact that a lot of dust particles are floating around. Because they are too small to be seen with the naked eye, these suspended particles are also called fine dust. In addition to fine dust, there are also toxic gases such as carbon monoxide or sulfur dioxide, which float in the lower atmosphere and pollute the air.

A large part of these exhaust gases are produced when crude oil, coal and other substances are burned. Cars, power plants, waste incinerators and residential heating systems blow loads of dirt into the air. In addition, there is the blown up dust - from streets, but also from factory farming, for example. The “exhaust gases” from the livestock also contribute to the fact that the air is getting worse and worse. But it is not always humans who pollute the air: volcanic eruptions can also contribute to higher levels of fine dust in the atmosphere.

The more pollutants there are in the air, the worse it is for our health: the respiratory tract can become ill, and the circulation and brain are damaged. Not only humans and animals suffer from the polluted air, plants are also damaged: If too much carbon dioxide and sulfur oxide are suspended in the air, acid (carbonic and sulfuric acid) forms in connection with water. The result is what is known as “acid rain”, which makes the soil acidic. Plants growing on such soil become withered and die. We are talking about "forest dieback". This can also happen far away from where the exhaust gases get into the air, because the wind carries the acid rain clouds away for hundreds of kilometers.

Air pollution is particularly bad in megacities in India, Pakistan and Iran, or in Mexico City. In Germany there are regulations on how heavily the air can be polluted. But here, too, the values ​​are not always adhered to and car traffic continues to increase.

In order to keep pollutants in the air low, it is therefore particularly important that enough forests and parks clean the air. Because trees, like all green plants, absorb carbon dioxide from the air and produce the oxygen that is essential for us. “Green lungs” in large cities, ie green spaces and forests close to cities, are therefore particularly important for our health. And those who often get on their bikes instead of driving the car also help to keep the air clean.

The greenhouse effect

In a greenhouse, vegetables or flowers can thrive even when it's cold outside. That's because greenhouses are built out of glass. The glass - or a transparent film - allows the short-wave rays of the sun to enter the interior unhindered: the air warms up. On the other hand, the glass is impermeable to long-wave heat radiation, so the heat can no longer get out. That’s why it’s cozy and warm in a greenhouse.

Something similar is happening on a large scale on Earth. The greenhouse gases carbon dioxide (CO2) and water vapor are naturally present in the atmosphere. Water vapor enters the air through evaporation, carbon dioxide through the exhalation. Volcanic eruptions also contribute to the natural carbon dioxide content of the air. Both gases have the same effect as the glass in a greenhouse: They allow the short-wave rays of the sun to penetrate to the earth. At the same time, like an invisible barrier, they hinder the long-wave thermal radiation on its way back into space. The heat builds up and the atmosphere heats up.

Without this natural greenhouse effect, life on earth would hardly be possible, because it would be far too cold for most living things. Instead of the current average temperature of plus 15 degrees, it would be an icy minus 18 degrees Celsius. The surface of the earth would be frozen!

The problem starts when we increase the amount of greenhouse gases in the atmosphere. This is mainly done by burning oil, natural gas and coal. Heating the apartment, driving a car, burning rubbish: all of these processes emit carbon dioxide. This CO2 has the largest share in the man-made greenhouse effect. But the cultivation of rice or cattle farming also increase the effect: Large amounts of methane (CH4) - also a greenhouse gas. In addition, nitrous oxide, ozone and fluorocarbons are among the greenhouse gases. Because all these gases slow down the earth's heat radiation, the temperatures on our globe continue to rise.