Cell theory II – cellular processes and the environment

Wentworth shire in rural Victoria may become the site of one of Australia’s most ambitious engineering projects. A private company plans to build a 1 km high solar tower surrounded by a 5 km wide greenhouse to generate electricity to power up to 200 000 homes. If it proceeds, the large-scale venture will be a commercial version of a 200 m tall, 50 kW prototype built near Manzanares, south-eastern Spain, in 1982. It ran with minimal maintenance for 7 years, delivering power night and day to the local grid. The principles of solar tower technology are simple. Hot air is generated from solar energy in a glass or polycarbonate greenhouse surrounding the tower. Within the tower, temperatures fall by 1°C per 100 m of altitude, so the air at the top of a 1 km-tall tower will be about 10°C cooler than at the base. Heated air entering the tower from the surrounding greenhouse increases the temperature differential, so the hot air rises by convection, just like the updraught in a chimney. The rising air spins wind turbines mounted in the tower to generate electricity. At night, heat stored in solar cells during the day is released to continue heating air and powering the turbines. Although the capital cost of building a solar tower is high, the final product is non-polluting and very cheap to run and maintain. Solar towers show how human ingenuity can transform solar energy into forms suitable for our use. But using solar energy is hardly original. Green plants and some prokaryotic organisms have done that for millennia, converting solar energy into organic compounds in the process of photosynthesis. In turn, the energy stored in those organic compounds can be released in cellular respiration to power cellular functions. Chapter aims: In this chapter the important processes of photosynthesis and respiration which make solar energy available to all organisms, are described. This requires an appreciation Of how energy can be trapped, stored and released from chemical bonds so a knowledge of the key molecules and metabolic pathways is important