In the Beginning Was Information (32 page)

In 1993, the total amount of energy generated in Germany was 536.6 TWh [F2, p 1007]. About 5% of this total was water energy, 29.6% was obtained from nuclear reactions, and the rest was generated by the combustion of fossil and other fuels (coal and lignite 55.4%, plus natural gas, oil, and diverse other sources). With the exception of the limited hydro-electrical sources, all these processes involve heat conversion with its low efficiency.

Great technological efforts are exerted to achieve direct conversion of energy without any intermediate forms. Examples include fuel cells, magnetohydrodynamic generators, and photo-voltaic elements. The efficiency of the latter is only about 10%, and the others are not yet technologically viable.

Even in the sunny southern regions of Europe, solar power installations, employing concave mirrors to generate steam (which then drives turbines for the production of electricity), require a total mirror surface of 26,000 m
²
(2.5 football fields) to generate 1 GWh per annum [X1]. This amounts to one million kilowatt-hours per year — enough to supply 350 homes. It would require an enormous area of 42 square miles (68 square km) to generate the same quantity of electricity as that which can be produced by one 1,300 megawatt nuclear power plant. This area could accommodate 150,000 urban inhabitants.

Wind-driven power plants also require a lot of space. It would require 800 to 900 windmill towers of 492 feet (150 m) to equal the energy production of one 1,300 megawatt nuclear plant. Four chains of such windmills separated by a distance of 1,312 feet (400 m) would extend over a distance of 50 miles (80 km).

A3.2.2 Utilization of Energy in Biological Systems (Photosynthesis)

Photosynthesis is the only natural process by means of which large quantities of solar energy can be stored. Requiring only carbon dioxide (CO
₂
), water (H
₂
O), and small quantities of certain minerals, it is the fundamental process for supplying the energy which plants need for growth and reproduction. The organic substances produced by plants are the primary source of nutrition and energy for all heterotrophic
^[25]
organisms which cannot utilize photosynthesis directly. It can truthfully be stated that photosynthesis is the primary source of energy for all life processes and it also provides most of the usable energy on earth. All fossil fuels and raw materials like coal, lignite, crude oil, and natural gas have been derived from the biomass of earlier times which was formed by photosynthesis.

This process synthesizes complex, energy-rich substances. What usually happens in oxidation/reduction reactions is that a strong oxidizing agent oxidizes a reducing substance, but photosynthesis is exceptional in this respect. It employs a weak oxidizing substance (CO
₂
) to oxidize a weak reducing agent (H
₂
O) to produce a strong oxidizing substance (O
₂
) and a strong reducing compound (carbohydrate). This process requires the input of external energy, namely sunlight. Such a process can only occur in the presence of a substance which can absorb light quanta, transfer the energy to other molecules, and then revert to its initial state where it can again absorb quanta of light. Chlorophyll performs this complex function. There are five types of chlorophyll (a, b, c, d, and f), which differ only slightly in chemical structure. Occurring in "higher" plants and in green algae, types a and b are the most important. The chemical equation for photosynthesis is:

(1)  6 CO
₂
+ 6 H
₂
O + light energy ® C
₆
H
₁₂
O
₆
+ 6 O
₂

In this process, glucose is synthesized from CO
₂
and H
₂
O by employing the energy of sunlight. The capture of light energy and its conversion to chemical energy is only one part of the process. These initial reactions are called photochemical reactions, and all subsequent reactions where chemical energy is utilized for the synthesis of glucose do not require light energy; they are thus known as dark or umbral reactions.

The ability to absorb light varies very strongly from one substance to another. Water absorbs very little light and thus appears to be colorless. The color of a substance depends on the absorption (and reflection) of certain wavelengths of light. When the degree of absorption is plotted against wavelength, we obtain an absorption spectrum. Chlorophyll only absorbs blue light (wavelength 400 to 450 nm) and red light (640–660 nm), so that the reflected light is green. The active spectrum of a process refers to its efficiency in relation to its wavelength. It is therefore noteworthy that the absorption spectrum of chlorophyll closely corresponds to the active spectrum of photosynthesis. This indicates that a finely tuned concept underlies this vital process and an efficiency calculation supports the view that a brilliant mind is involved.

The efficiency of photosynthesis:
According to equation (1), exactly 1 mol
^[26]
of glucose is generated from 6 mol CO
₂
[1] requiring an energy input of 2,872.1 kJ. For 1 mol of CO
₂
, this amounts to 478.7 kJ. As a loss of energy is inherent in each and every energy conversion, the actual quantity of light energy required is greater. Although red light quanta possess less energy (about 2 eV/light quantum) than blue light quanta (approximately 3 eV/quantum), due to different efficiency both types produce approximately the same amount of photochemical work. It has been determined experimentally that 8 to 10 light quanta are required for every molecule of CO
₂
. The energy content of 1 mol of red light quanta (= 6.022 x 10
²³
quanta [2]
^[27]
) amounts to 171.7 kJ. Therefore, 9 mol of red light quanta (the average of 8 and 10) is found by multiplying 171.7 kJ x 9. The result is 1,545.3 kJ. The efficiency Ë can be calculated as the ratio between the theoretical amount of energy required to assimilate 1 mol CO
₂
 (478.7 kJ) and the actual energy content of the incident red light (1545.3 kJ):

η
_red
= 478.7/1,545.3 x 100% = 31%

The energy content of blue light quanta is 272.1 kJ/mol, so it follows that
η
_blue
= 20%.

Volume of photosynthesis:
The productivity of plants is not only qualitatively but also quantitatively highly impressive. A single beech tree which is 115 years old has 200,000 leaves which contain 180 grams of chlorophyll and have a total area of 1,200 m
²
, and can synthesize 12 kg of carbohydrates on a sunny day, consuming 9,400 liters of CO
₂
 from a total volume of 36,000 m
³
of air [S4]. Through the simultaneous production of 9,400 liters of oxygen, 45,000 liters of air are "regenerated"! On a worldwide scale, 2 x 10
¹¹
tons of biomass is produced annually by means of photosynthesis [F6]. The heat value of this mass is about 10
¹⁴
watt-years (= 3.15 x 10
²¹
Ws). The entire human population annually consumes about 0.4 TWa = 1.26 x 10
¹⁹
Ws (1 TWa = 1 Terawatt-year = 3.1536 x 10
¹⁹
Ws), and all the animals require 0.6 TWa. Together, these add up to only one percent of the total annual biomass production.

Respiration:
The result of breathing, namely the release of energy, is the opposite of photosynthesis. These two processes are in ecological equilibrium, so that the composition of the atmosphere stays constant, unless it is disturbed by human intervention like heavy industries. It should also be noted that the mechanisms for photosynthesis and respiration are astoundingly similar. The substances involved belong to the same chemical classes. For example, a chlorophyll molecule consists of four pyrrole rings arranged round a central atom, which is magnesium in the case of chlorophyll, and iron in the case of hemoglobin, the active substance on which respiration is based. Both processes occur at the interface of permeable lipid membranes. The inevitable conclusion is that a single brilliant concept underlies both processes and that both are finely tuned to each other. We can thus reject an evolutionary origin, since two such astonishingly perfect and similar processes could not possibly have originated by chance in such diverse organisms.

Conclusion: It has not yet been possible to explain the incredible complexity of the molecular mechanisms on which photosynthesis is based. The same situation holds for respiration. The fact that the chemical equations and some of the intermediate enzyme driven steps are known should not create the impression that these processes are really understood; on the contrary, what we don’t yet know is incomparably more than what we do know. The American biophysicist Albert L. Lehniger [L1] regards these unresolved questions as some of the most fascinating biological problems. All solar energy engineers dream of devising a process which can convert sunlight directly into fuel. Although photosynthesis takes place in every single green leaf of all plants, having been conceived in an astoundingly brilliant way,
even the most inventive engineer is unable to imitate the process.
Every phototropic cell is supplied with the information required to undertake such an optimal energy conversion process.

A3.3 The Consumption of Energy in Biological Systems: Strategies for Minimization

Every cell requires energy continuously for its vital functions like the synthesis of new molecules, or the production of a daughter cell. In multicellular organisms there are further purposeful reactions (e.g., locomotion, and the control of body temperature). The conversion of energy in every cell, whether animal, vegetable, or microbial, is based on the same principles and mechanisms. In contrast to technological practices, living organisms avoid the inefficient use of heat as an intermediate energy form. Cellular processes are isothermic; this means that the temperature does not change.

The concept of energy:
It should be emphasized that the energy-carrying nutrient molecules do not generate heat when they are oxidized. The molecular concept of biological oxidation involves numerous precisely tuned individual catalytic enzyme reactions which follow one another in exactly the required sequence, and employ just as many intermediate compounds. Adenosin triphosphate (ATP) has some special chemical properties which enable it to perform important functions. It belongs to the group of nucleotides, comprising adenine, C5-sugar, D-ribose, and phosphate groups. When nutrients are oxidized to generate energy, the more energy-rich ATP is formed from adenosin diphosphate (ADP). The energy stored in ATP can then subsequently be utilized by conversion into chemical work (e.g., biosynthesis), mechanical actions (e.g., muscular effort), or osmotic transportation. When this happens, the ATP loses one phosphate group, and reverts to ADP. In this energy transfer system, ATP is thus the charged substance, and the ADP is neutral. The numerous very complex intermediate chemical steps in this ATP/ADP energy cycle are catalyzed by a specific set of enzymes. In addition to this general flow of biological energy, there are some very clever special mechanisms for energy conversion.

Certain fishes like the electric eel can generate electrical pulses of several hundred volts directly from chemical energy. Similarly, light flashes emitted by some animals and organisms represent converted chemical energy. The bombardier beetle converts the chemical energy contained in hydrogen peroxide into explosive pressure and volume changes.

Machines constructed for the purpose of energy utilization essentially involve the generation of easily transportable electrical energy in a round-about way by first producing heat. Heat
Q
can only perform useful work
W
when there is a temperature difference
T
₂
-
T
₁
. The theoretical maximum amount of work that can be performed by a heat engine, is given by the Carnot formula:

W
=
Q
x (
T
₂
-
T
₁
)/
T
₂

T
₂
can be the initial temperature of the steam entering a turbine, for example, and
T
₁
can be the exhaust temperature. It follows that large temperature differences are required to produce a reasonable amount of useful work. In living cells, the processes for generating energy must be fundamentally different, since all reactions have to take place at the temperature of the cell; in other words, the processes must be isothermic. The refined energy concepts realized in cells utilize substances which are unstable to heating, but still achieve exceptionally high degrees of efficiency.

The cells:
A living cell can be compared with a factory comprising several departments, each of which has a certain number of machines.

The work of all the cell’s departments and machines involves optimally geared interrelationships exhibiting planning down to the last detail. The end products are produced through a coordinated sequence of numerous individual processes. We can rightly state that we are dealing with the smallest fully automated production line in the world; it even has its own computer center and its own power generating plants (the mitochondria). With their diameter of 100 nm, the prokaryotes are the smallest cells, while birds’ eggs are the largest. Ostrich eggs measure about 0.1 m = 10
⁸
nm, and the average radius of the cells of multicellular organisms lies between 2,000 nm and 20,000 nm (= 2 to 20 µm). Large living beings consist of tremendously large numbers of cells (about 10
¹⁴
for humans), while the smallest organisms like bacteria are unicellular. Two large classes of cells are distinguished according to their structural organization, namely prokaryotic cells (Greek karyon = nucleus) and eukaryotic cells (Greek
eu
= good). Many unicellular organisms like yeast cells, protozoa, and some algae, are eukaryotic, as well as nearly all multicellular forms. Their cells contain a nucleus, mitochondria, and an endoplasmic reticulum. The prokaryotes comprise the bacteria and the blue algae. Compared to the eukaryotes, they are considerably smaller (only 1/5,000th in volume), less differentiated and less specialized, and they lack many of the structures like a nucleus or mitochondria.