Energy can be derived from living systems in restricted forms only. Lignocelluloses are burned to get heat, and vegetable oils are often used for illumination. These may also serve as nutrients for different biotic species in various forms, i. e., cellulose, starch, and sugars. In other words, chemically stored energy may be reused in the form of fuel (fire­wood) or nutrients (food, feed, fodder, etc.). Animals can be employed to do different mechanical work. Animals directly (fish, meat) or indirectly (egg, milk) may provide nutrients for others. Use of dried cow dung as

cooking fuel in rural areas is also a well-known example of animal prod­ucts indirectly contributing to this field. But examples of direct energy flow from living systems are still in the conceptual state. Scientists dream that, one day, light emitted by fireflies or high voltage generated by electric eels may be of great use in the near future.

The production of alcohol or methane by microbial fermentation of common plant wastes are well-known phenomena. Recently however, scientists have started looking into these phenomena with greater inter­est, so that, in either gas or liquid form, their production and use can be optimized and made efficient. Plant bodies have been used as anten­nas, and plant leaves have been demonstrated to work as batteries. The survival of all biotic species depends directly or indirectly on solar energy. Studying the energy-based ecosystem raises awareness of this fact. Obviously, the most common question becomes: If the sun happens to be the source of all energy, why then is the solar energy not har­nessed by different devices? There are inherent limitations of most of the physical devices by (a) way of efficiency, (b) critical cost, (c) mainte­nance, (d) reliability, and (e) other factors.

In photosynthetic systems operating in green vegetations of the above points, (b), (c), and (d) are enormously better. Its characteristic limita­tions are [for point (a)] the incident insolation, the ability to use only a narrow spectrum [for point (e)], and requiring the proportionate amount of soil surface area for insolation, optimal nutrients, temperature, and moisture in the microenvironment. Here nature provides several mutants from which we can take, pick, screen, or select the most toler­ant variety. We may resort to genetic engineering for tissue cultures or selective hybridization.

What is our objective? Along with the effort to harness the solar energy by different physical methods, parallel efforts of optimal use of solar energy through biotic fixation should be attempted. This involves under­standing the following:

1. The living world in its entirety, i. e., ecology.

2. The photosynthetic systems in different species: terrestrial, aquatic, or mixed.

3. Application of the above to develop science and technology for:

a. Better management of the biotic systems useful for our purpose

b. Conversion of biological raw materials into energy rich products

4. Coordination for quality of life, pollution abatement, and sparing of nonrenewable resources for future generations.

A few examples that may not be out of place include potato, tomato, eucalyptus, and so forth. Though of wild origin, they have been appreci­ated and have been cultivated for this use after studying and admiring

their productivity and receptivity. Later by scientific manipulation, new strains have been developed for cultivation.

It is justified to discuss certain established facts for making suffi­cient conceptual clarity for special topics. Some aspects of energy rela­tions in living systems will be discussed in detail. Some other aspects will not be discussed in detail because existing “know-how” is rather limited.