It’s always fascinating to see that something familiar to us at a large level can also be found in a corresponding form at the microscopic level. Cell membranes, for instance which delineates the cell from the external environment or from neighbouring cells, are like city limits. So it’s not surprising that there are cellular “power stations“ and “energy transmitters“, too. Plant cells possess „solar panels“, the so-called chloroplasts. With the help of these, they are able to capture light energy and convert it into chemical energy, without which biomass could not be created.
Natural solar panels
Chloroplasts are extremely complex units and there are several scientific theories about their origin. Within the chloroplasts are rolled up membrane systems, the thylakoids. It is here that the light-absorbing agents are stored, particularly the green pigment chlorophyll. And it’s here that the wonder of energy-capture and conversion occurs – photosynthesis.
The process of photosynthesis can be divided into three stages:
• First, light – a form of electromagnetic energy – is absorbed;
• It is converted directly into chemical energy;
• Finally, the chemical energy is used in the production of organic matter.
With the help of ATP (adenosine triphosphate), the plant cell is able to synthesize the energy-rich substance glucose within its chloroplasts, using energy-poor carbon dioxide (CO2) and water as building blocks.
Energy production in the mitochondria
When the cell needs energy – as it always does – then the glucose energy safe must be “cracked”. The cell does this with the help of mitochondria. These are found in the cells of all complex organisms, in plants as well as in animals and fungi. In the mitochondria, the chemical energy stored in glucose or other organic substances is made available through oxidative degradation. With the release of energy, the cell’s „batteries“ – the ADP/ATP-System – is “recharged”. The efficiency of oxidative glycolysis lies at almost 40 percent – making it a pretty effective system, on a par with the energy yield of modern steam turbines. Thus the mitochondria really do earn their reputation as the cell’s powerhouse. You could consider this process – cell respiration, as it is called – as being the opposite of photosynthesis.
Consequences for the farmer
The growth and yield of crop plants will increase as the factors that are important for photosynthesis approach their optimum levels. Drought has a negative effect on photosynthetic productivity. Factors such as sunlight and temperature are of course beyond the farmer’s control.
With the expected increase in the atmosphere’s CO2 concentration, climate change over the next couple of decades should, in theory, boost the growth of plants. Indeed, laboratory studies have shown that considerable yield increases (of 20-30 percent) might be anticipated as the result of this so-called CO2-fertilising effect. But results obtained from a field experiment are sobering. Biomass production in wheat and sugar beet increased rather modestly by 6-14 percent. At the same time however, protein content decreased. Thus, the yield may increase, but the quality of the harvest also changes.
This demonstrates once again how highly complex the metabolism of plant cells is. Accordingly, one cannot easily intervene or indeed steer it. And that’s just another way in which a microscopically small cell is similar to a large municipality.
Download: (1273 KB pdf)
