Home Random Page



The Transformation of Energy

The energy flow of an ecosystem occurs as an open system; the sun constantly gives the planet energy in the form of light while it is eventually used and lost in the form of heat throughout the trophic levels of a food web. Transformation of energy in ecosystems occurs in accordance with the universal laws of thermodynamics:

The first law of thermodynamics states that energy can be transformed from one form (ie light energy) into another (chemical energy), but it cannot be created or destroyed. The total amount of energy and matter in the Universe remains constant, merely changing from one form to another. The First Law of Thermodynamics (Conservation) states that energy is always conserved, it cannot be created or destroyed. In essence, energy can be converted from one form into another.

12. The second law of thermodynamics states that "in all energy exchanges, if no energy enters or leaves the system, the potential energy of the state will always be less than that of the initial state." The transformation of energy results in its lost to the system as heat. There is no transformation of energy that goes with 100% efficiency.

This is also commonly referred to as entropy. Entropy is the degree of disorder in a system. Cells are not disordered and so have low entropy. The flow of energy maintains order and life. As energy is transferred from one form to another, some is lost as heat; as the energy decreases, the disorder in the system increases. Entropy wins when organisms cease to take in energy and die.



The transformations of energy in an ecosystem begin first with the input of energy from the sun which is captured by the process of photosynthesis. Photosynthesis is the process by which plants and photosynthetic microorganisms use the energy from the sunlight to produce glucose (a simple sugar) and release the oxygen.


6H2O + 6CO2 ----------> C6H12O6+ 6O2


Organisms that use inorganic sources of both carbon and energy are called autotrophs (“self-feeders”). Photosynthetic autotrophs use carbon dioxide and light as a source of energy to synthesize organic compounds, such as sugars (glucose), amino acids and fats. The conversion of unusable sunlight energy into usable chemical energy, is associated with the actions of the green pigment chlorophyll.

Cellular respiration is the process by which organisms (like mammals) break the glucose back down into its constituents, water and carbon dioxide, thus regaining the stored energy the sun originally taken by the plants. The energy is stored in the high energy bonds of adenosine triphosphate, or ATP, the "fuel" used by all living things. The proportion of photosynthetic activity of plants and other photosynthesizes to the respiration of other organisms determines the specific composition of the atmosphere, particularly its oxygen level.

Then chemical energy in organic molecules ultimately is converted to heat energy. This energy is dissipated, meaning it is lost to the system as heat; once it is lost it cannot be recycled. In ecosystems, the biggest losses occur as respiration. Without the continued input of solar energy, biological systems would quickly shut down.Thus the Earth is an open system with respect to energy.In contrast, all the nutrients - such as carbon, nitrogen, oxygen, phosphorus, and sulfur - used in ecosystems by living organisms operate in a closed system; therefore, these chemicals are recycled instead of being lost and replenished constantly like in an open system.

14 Food chains and food webs are methods of describing how energy flows from one species to another in an ecosystem. Food chains and food webs describe the successive transfer of energy from plants to the animals that eat them, and so on. Food webs can be thought of as interconnected or intersecting food chains.

A food chain is a series of steps by which energy is obtained, used, and transformed by living organisms. For example; sunlight helps plants to grow, the plants are eaten by cattle, and lions eat the cattle. In a food network, there will be fewer organisms at each level as one follows the links of the network up the chain, forming a pyramid.

The components of food chains and food webs - producers, consumers, and decomposers - exist at different stages in the transfer of energy through an ecosystem. The position of every group of organisms obtaining their food in the same manner is known as a trophic level. The term comes from a Greek word meaning "nursing," and the implication is that each stage nourishes the next. The first tropic level consists of autotrophs (producers), the second - herbivores (primary consumers), the third - primary carnivores (or secondary consumers), etc. The trophic level is determined by how many steps it is above the primary producer level.

Food chain always begins with the producers, i.e., green plants. Next in the chain is always the plant eater or the herbivore which is called the primary consumer. The primary consumers are eaten by the secondary (carnivores-organisms that mainly eat animals) and tertiary (omnivores) consumers.

Producers - autotrophic organisms (mainly green plants) capable of synthesizing organic food during photosynthesis by converting solar energy into chemical energy.

Consumers-heterotrophic organisms (mainly animals). They feed on other organisms (plants or animals) to meet their food requirement:

Predators - animals that stalk their prey and

Parasites - line and grow on other organisms and adapt them as their habitat

Decomposers- saprophytic organisms (mainly bacteria and fungi) that live on dead animals and plants. This group of organisms plays a vital role in releasing back the biotic components into the environment.

15.Trophic Pyramidis a graphic model describing the distribution of energy, biomass, or some other measurable quantity between the different trophic levels found in an ecosystem.

An ecological pyramid


16. Lindemann’s law of 10 % of energy

Raymond Lindeman revolutionized ecological thinking by describing ecosystems in the terminology of energy transformationin his paper entitled "The Tropic-Dynamic Aspect of Ecology" (1942). He used data from his studies of Cedar Bog Lake in Minnesota to construct the first energy budget for an entire ecosystem. He measured harvestable net production at three trophic levels: primary producer, herbivore, and carnivore. He did this by measuring gross production minus growth, reproduction, respiration, and excretion. He was able to calculate the assimilation efficiency at each tropic level, and the efficiency of energy transfers between each level.

17. Gross primary productivity(GPP) is the measure of the total amount of dry matter produced by plant in photosynthesis. All organisms respire. During respiration some of the matter is converted back into water and carbon dioxide, thus dry weight lost


Net primary productivity(NPP) is the overall gain of dry weight by plant after respiration. It is the amount of energy left after the primary producer has met its own energy needs, or more specifically, the rate of photosynthesis – the rate of cell respiration.


Net primary productivity = Gross primary productivity - Respiration


Secondary productivityis the rate at which consumers in the ecosystem convert the energy and materials they consume into their own biomass. We measure productivity most often by looking at biomass (dry weight) or by measuring the amount of energy per unit per time.

Productivityisthe rate of new biomass, not the total standing biomass in the ecosystem.

Date: 2015-12-24; view: 2791

<== previous page | next page ==>
The law of ecological succession | Pyramids of productivity
doclecture.net - lectures - 2014-2024 year. Copyright infringement or personal data (0.007 sec.)