Page 25 - Biofuels Refining and Performance

8 Chapter One

It is easy to observe that extremely cold or hot regions are not favor-
able for the growth of living things. Likewise, the absence of light limits
the propagation and proliferation of photosynthetic biotic species.
The sun, of course, radiates energy into space of which only an insignif-
icant part is shared by this planet of ours called Earth. Because of its spin
and its orbital rotation, a seasonal variation occurs in the total insolation
2
on the earth’s surface, which averages approximately 20 kcal/(m
yr).
The incident radiation comprises 2000–8000 Å, 50% of which is in the
visible range (3700–7700 Å); only a small part of the incident energy is
utilized by living systems.
33
2
Solar constants are given as 1.968 cal/(cm
min) 3.86 10 erg/s
2
1.373 kW/m . There are variations in the figures, depending on the
source of information. However, the energy received on the earth’s sur-
face is mostly thermal and wasted. Biological fixation is restricted to pho-
tophosphorylation.
Let us look at the components of ecosystems that are capable of uti-
lizing incident energy and some interrelationships between them.

Autotrophs (meaning self-surviving), also known as producers,
mainly the photosynthetic systems, are the largest users of sunlight.
Theoretically, anywhere there is light they should grow, provided
other inputs are favorable. In arid land, the lack of nutrients; in deserts,
the lack of water; and at higher-altitude, low temperatures, low CO 2
tension and other adverse conditions will prevent the proliferation
of autotrophs, leaving otherwise sufficient insolation unutilized
(energy fixation by photosynthetic pathway is treated elsewhere).
Producers growing on detritus (dead organic materials) are not well
described in the literature, but these could be autotrophs.
Heterotrophs (mixed surviving or unlike surviving), on the other
hand, survive partly depending on the nutrient sources made avail-
able by other living systems. Most animals are heterotrophic.
Therefore, animals are also called consumers.
If animals survive mainly on autotrophic materials, they are called
primary consumers, commonly known as herbivores. If animals
largely survive on other animals as their source of food, they are
called secondary consumers, popularly known as carnivores. Predators
are animals that hunt their animate food, known as prey. The
prey–predator relationship plays an important role in nature and con-
tributes to the ecologic balance.

1.3.1 Photosynthetic factors
Assuming that the wavelength of light remains constant, the intensity
influences the rate of photosynthesis, which is why the earlier part of the