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October, 2006
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Metabolic Labeling

JoVE 5687

Metabolic labeling is used to probe the biochemical transformations and modifications that occur in a cell. This is accomplished by using chemical analogs that mimic the structure of natural biomolecules. Cells utilize analogs in their endogenous biochemical processes, producing compounds that are labeled. The label allows for the incorporation of detection and affinity tags, which can then be …


Production Efficiency

JoVE 10929

Net production efficiency (NPE) is the efficiency at which organisms assimilate energy into biomass for the next trophic level. Due to low metabolic rates and less energy spent on thermoregulatory processes, the NPE of ectotherms (cold-blooded animals) is 10 times higher than endotherms (warm-blooded animals).

Energy flows through ecosystems, from one organism to the next. However, only the energy stored in an organism as biomass is available as food for the next trophic level. The rest of the energy is lost over time as heat as a byproduct of metabolic processes and excreted wastes. The efficiency with which organisms assimilate this usable energy into biomass is called net production efficiency (NPE), or the percentage of energy stored in biomass that is not used for respiration. For example, in a study of a desert scrub ecosystem, it was found that only 0.016% of the energy produced by primary producers was then assimilated into small herbivore mammal tissue and available for carnivores in this system. Endotherms like birds and mammals typically have low production efficiencies due to the larger quantities of energy spent maintaining constant high body temperatures, and high metabolic rates. On the other hand, the NPE for ectotherms is an order of magnitude higher due to their lower metabolic rates and thermoregulatory behaviors. Therefore, a mammal

 Core: Biology

Cell Structure- Concept

JoVE 10587


Cells represent the most basic biological units of all organisms, whether it be simple, single-celled organisms like bacteria, or large, multicellular organisms like elephants and giant redwood trees. In the mid 19th century, the Cell Theory was proposed to define a cell, which states:

Every living organism is made up of one or more cells.
The cells…

 Lab Bio

A Human 3D Extracellular Matrix-Adipocyte Culture Model for Studying Matrix-Cell Metabolic Crosstalk

1Department of Surgery, University of Michigan Medical School, 2Department of Pediatrics and Communicable Diseases, University of Michigan Medical School, 3Graduate Program in Immunology, University of Michigan Medical School, 4Graduate Program in Cellular and Molecular Biology, University of Michigan Medical School, 5Undergraduate Research Opportunity Program, University of Michigan, 6Department of Surgery, Ann Arbor Veterans Affairs Healthcare System

JoVE 60486


Hyperpolarized 13C Metabolic Magnetic Resonance Spectroscopy and Imaging

1Department of Nuclear Medicine, Klinikum rechts der Isar, Technische Universität München, 2Department of Chemistry, Technische Universität München, 3GE Global Research, 4Zentralinstitut für Medizintechnik der Technischen Universität München (IMETUM), Technische Universität München, 5Institute for Biological and Medical Imaging (IBMI), Helmholtz Zentrum München, 6IDG Institute of Developmental Genetics, Helmholtz Zentrum München

JoVE 54751

 Cancer Research

Second Law of Thermodynamics

JoVE 10727

The Second Law of Thermodynamics states that entropy, or the amount of disorder in a system, increases each time energy is transferred or transformed. Each energy transfer results in a certain amount of energy that is lost—usually in the form of heat—that increases the disorder of the surroundings. This can also be demonstrated in a classic food web. Herbivores harvest chemical energy from plants and release heat and carbon dioxide into the environment. Carnivores harvest the chemical energy produced by herbivores—with only a fraction of it representing the original radiant energy from the sun—and also release heat energy with carbon dioxide into their surroundings. As a result, the heat energy and other metabolic by-products released at each stage of the food web have increased its entropy. The Second Law of Thermodynamics states that entropy, or the amount of disorder in a system, increases each time energy is transferred or transformed. In every energy transfer, a certain amount of energy is lost in a form that is unusable—usually in the form of heat. This heat energy can temporarily increase the speed of molecules it encounters. As such, the more energy that a system loses to its surroundings, the less ordered and the more random it becomes. Similar to the First Law of Thermodynamics, the Second Law of Thermodynamics c

 Core: Biology

Trophic Efficiency

JoVE 10930

Trophic level transfer efficiency (TLTE) is a measure of the total energy transfer from one trophic level to the next. Due to extensive energy loss as metabolic heat, an average of only 10% of the original energy obtained is passed on to the next level. This pattern of energy loss severely limits the possible number of trophic levels in a food chain.

Following the second law of thermodynamics, large amounts of energy are lost from the ecosystem and from one trophic level to the next as it is transferred and transformed. In biological systems, this energy is lost as metabolic heat during respiration as one organism consumes the next. The measurement of energy transfer from one trophic level to the next is known as trophic level transfer efficiency (TLTE) and is a function of energy production of the present trophic level and that at the previous level. This measurement has broad implications concerning the total length of food chains. In general, only about 10% of energy is transferred from one trophic level to the next, and this number can vary from 5-20% depending on the ecosystem. This means that 90% of obtained energy is lost at each trophic level, greatly affecting the maximum number of possible levels in the ecosystem. For example, if an ecosystem received 600,000 Kcal of solar energy from the sun, primary producers would pass on only 60,000 K

 Core: Biology
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