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Carbon Dioxide: A colorless, odorless gas that can be formed by the body and is necessary for the respiration cycle of plants and animals.

The Carbon Cycle

JoVE 10933

Carbon is the basis of all organic matter on Earth, and is recycled through the ecosystem in two primary processes: one in which carbon is exchanged among living organisms, and one in which carbon is cycled over long periods of time through fossilized organic remains, weathering of rocks, and volcanic activity. Human activities, including increased agricultural practices and the burning of fossil fuels, has greatly affected the balance of the natural carbon cycle. All living things are composed of organic molecules that contain atoms of the element carbon. Carbon exists in the atmosphere as carbon dioxide gas, which reacts with water to form bicarbonate. During photosynthesis, primary producers (or autotrophs) convert carbon dioxide and bicarbonate into organic carbon-containing compounds, such as glucose, to provide energy for growth, maintenance and other processes. Heterotrophs receive organic carbon for growth and maintenance by consuming autotrophs. Through the process of cellular respiration, these organic molecules are broken down to release the energy stored within them. The byproducts of this process are water and carbon dioxide, which is released into the atmosphere through respiration, continuing the cycle. Carbon can also return to the environment as animal waste or as decaying material from dead organisms. Decomposers, such as bact

 Core: Biology


JoVE 10700

Diffusion is the passive movement of substances down their concentration gradients—requiring no expenditure of cellular energy. Substances, such as molecules or ions, diffuse from an area of high concentration to an area of low concentration in the cytosol or across membranes. Eventually, the concentration will even out, with the substance moving randomly but causing no net change in concentration. Such a state is called dynamic equilibrium, which is essential for maintaining overall homeostasis in living organisms. Diffusion plays an integral role in biological processes such as respiration, the process by which organisms exchange gases with their environment. After breathing in air, the concentration of oxygen in the alveoli, air sacs of the human lung, is higher than the oxygen concentration in the blood. Consequently, oxygen diffuses down its concentration gradient into the blood. In order to get into body tissue, oxygen and other nutrients carried in the blood must diffuse into tissues down their concentration gradients. Metabolic waste such as carbon dioxide diffuses from tissues into capillaries where the carbon dioxide concentration is less than that inside body tissues. Blood carrying carbon dioxide is then pumped to the lungs where carbon dioxide readily diffuses into alveoli that have a lower concentration of the gas than blood. Carbon dioxide

 Core: Biology

Cellular Respiration- Concept

JoVE 10567

Autotrophs and Heterotrophs

Living organisms require a continuous input of energy to maintain cellular and organismal functions such as growth, repair, movement, defense, and reproduction. Cells can only use chemical energy to fuel their functions, therefore they need to harvest energy from chemical bonds of biomolecules, such as sugars and lipids. Autotrophic organisms, namely…

 Lab Bio

Carbon and Nitrogen Analysis of Environmental Samples

JoVE 10012

Source: Laboratories of Margaret Workman and Kimberly Frye - Depaul University

Elemental Analysis is a method used to determine elemental composition of a material. In environmental samples such as soils, scientists are particularly interested in the amounts of two ecologically important elements, nitrogen and carbon. Elemental analysis by …

 Environmental Science

Redox Reactions- Concept

JoVE 11144

Oxidation and Reduction

Some chemical reactions can be classified as reduction-oxidation reactions, or redox reactions. Oxidation is the process of an atom losing one or more electrons, and reduction is the process of an atom gaining one or more electrons.

Oxidation States

Each atom in a molecule has its own oxidation state or oxidation number. The oxidation state…

 Lab: Chemistry

Free Energy

JoVE 10730

Free energy—abbreviated as G for the scientist Gibbs who discovered it—is a measurement of useful energy that can be extracted from a reaction to do work. It is the energy in a chemical reaction that is available after entropy is accounted for. Reactions that take in energy are considered endergonic and reactions that release energy are exergonic. Plants carry out endergonic reactions by taking in sunlight and carbon dioxide to produce glucose and oxygen. Animals, in turn, break down the glucose from plants using oxygen and make carbon dioxide and water. When a system is at equilibrium, there is no net change in free energy. In order for cells to keep metabolism running and stay alive, they must stay out of equilibrium by constantly changing concentrations of reactants and products The direction of energy flow through the system determines if the reaction is endergonic or exergonic. Systems with no net change in free energy are considered to be at equilibrium. Most chemical reactions are reversible—they can proceed in both directions. To stay alive, cells must stay out of equilibrium by constantly changing the concentrations of reactants and products so that metabolism continues to run. If a reaction requires an input of energy to move forward, then the change in free energy, or the ΔG of the reaction is positive and the re

 Core: Biology


JoVE 10745

Most eukaryotic organisms require oxygen to survive and function adequately. Such organisms produce large amounts of energy during aerobic respiration by metabolizing glucose and oxygen into carbon dioxide and water. However, most eukaryotes can generate some energy in the absence of oxygen by anaerobic metabolism.

Aerobic respiration proceeds through a series of oxidation-reduction reactions that end when oxygen–the final electron acceptor–is reduced to water. In the absence of oxygen, this reaction cannot proceed. Instead, cells regenerate NADH produced during glycolysis by using an organic molecule, such as pyruvate, as the final electron acceptor. The process of using an organic molecule to regenerate NAD+ from NADH is called fermentation. There are two types of fermentation based on the end products of the reaction: 1) lactic acid fermentation and 2) alcohol fermentation. In mammals, lactic acid fermentation takes place in red blood cells that cannot respire aerobically due to lack of mitochondria, as well as in skeletal muscles during strenuous exercise. It also occurs in certain bacteria, like those found in yogurt. In this reaction, pyruvate and NADH are converted to lactic acid and NAD+. Alcohol fermentation is a two-step process. In the first step, pyruvate is converted to carbon dioxide and acetaldehyde

 Core: Biology

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

Redox Reactions

JoVE 10671

Oxidation-reduction, or redox, reactions change the oxidation states of atoms via the transfer of electrons from one atom, the reducing agent, to another atom that receives the electron, the oxidizing agent. Here, the atom that donates electrons is oxidized—it loses electrons—and the atom that accepts electrons is reduced—it has a less positive charge because it gains electrons. The movement of energy in redox reactions is dependent on the potential of the atoms to attract bonding electrons—their electronegativity. If the oxidizing agent is more electronegative than the reducing agent, then energy is released. However, if the oxidizing agent is less electronegative than the reducing agent, the input of energy is required. Is oxidation a loss or gain of electrons? The terminology can be confusing. The acronym OIL RIG is commonly used to remember. It stands for oxidation is loss; reduction is gain. So, if an atom is oxidized, then it loses electrons. As a reducing agent, the oxidized atom transfers electrons to another atom, causing it to be reduced. With OIL RIG in mind, most questions about the members of a redox reaction can be answered. Redox reactions either produce or require energy. If an atom loses an electron to a more electronegative atom, then it is an energetically favorable reaction, and energy is released. This

 Core: Biology
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