What a Wonderful World Read Online Free PDF

energy for the cell. Crucially, haemoglobin changes its behaviour depending on the acidity of its surroundings. The acidity at its cellular destination changes the protein in a subtle way so that it
repels
rather than attracts its passenger. The protein therefore drops off its precious oxygen molecule. But the change in the haemoglobin means that it now
attracts
a molecule of carbon dioxide. As soon as one latches on, it is promptly ferried back to the lungs, where it passes from blood vessels to alveoli and is exhaled.
    The oxygen we breathe and that powers all the biological processes in our bodies is essential to keep us alive. Whereas we can survive without food for a month, and without water for a week, we can survive with our air supply cut off for only about three minutes. 9 Every instant of our lives we are a mere three minutes from death. This fact becomes shockingly apparent to a heart-attack victim whose heart stutters to a halt and stops pumping oxygen around the arteries and blood vessels of his or her body. 10
Photosynthesis
    But where does the oxygen we breathe come from? The answer, of course, is plants. Rather than breathing in oxygen and breathing out carbon dioxide, they take in carbon dioxide and pump out oxygen.
    Pretty much all the energy used by life on Earth is therefore ultimately the energy of sunlight, which plants capture directly from the Sun. 11 The trick is mind-bogglingly clever – otherwise we would long ago have found a way of mimicking it and powering human civilisation directly from sunlight. The energy of a particle of light – a photon – is transferred to an electron in a giant protein called chlorophyll. This is the molecule responsible for the green pigment of plants, although life also uses a second, non-green version. Bursting with energy, the electron can then energise chemical processes. Photosynthesis is a bewilderingly complex process but, in essence, it achieves the exact opposite of respiration.
    Whereas respiration splits hydrogen from foods such as sugars and passes its electron to oxygen, ejecting as waste carbon dioxide, photosynthesis splits hydrogen from water and uses it with carbon from carbon dioxide to build sugars, ejecting as waste the leftover oxygen. Pause for a moment to think what an amazing trick this is. Using nothing more than water, carbon dioxide from the air and sunlight, plants are able to synthesise energy-rich food.
    The sugars made by plants are in essence captured sunlight. And, whenever we eat plants, we in effect unleash the energy of this captured sunlight. But the miracle does not end there. Some plants such as trees, when they die, can become buried and transformed by heat and pressure deep down in the ground into fossil fuels such as coal. When we burn coal, we unleash yesterday’s sunlight. Ultimately, everything on Earth is powered by a beam of captured sunlight.
    Photosynthesis is actually quite inefficient. The percentage of incoming light energy that is converted into sugar in most plantsis only about 1 per cent. The race is on, therefore, not only to create artificial photosynthesis but to make it
significantly better
than in nature – converting say 20 per cent of incident sunlight into hydrogen.
    Hydrogen when combined with oxygen – think rocket fuel, think respiration – liberates large amounts of energy. It could therefore be used, in fuel cells, to power all manner of machines from cars to computers. There are three main steps in the creation of artificial photosynthesis. First, light must be captured and its energy transferred to an electron, boosting its energy. Next, the electron must be freed from its parent atom. Finally, the super-energetic electron must be used to smash apart water to liberate the all-important hydrogen. Artificial photosynthesis, able to make hydrogen fuel from sunlight, would wean the human race from its dependence on fast-dwindling reserves of fossil fuels such as oil. It would be a game-changing