Show Advanced Search

REFINE YOUR SEARCH:

Containing Text
- - -
+
Filter by author or institution
GO
Filter by publication date
From:
October, 2006
Until:
Today
Filter by journal section

Filter by science education

 
 
Methane: The simplest saturated hydrocarbon. It is a colorless, flammable gas, slightly soluble in water. It is one of the chief constituents of natural gas and is formed in the decomposition of organic matter. (Grant & Hackh's Chemical Dictionary, 5th ed)

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

Melting Points- Concept

JoVE 11189

Melting Points in Organic Chemistry

The melting point of a compound is the temperature at which the solid phase transitions into the liquid phase at a standard pressure of 1 atmosphere. The melting point of a compound is a physical property, like solubility, density, color, and electronegativity that can be used to identify a compound. Determining the exact temperature…

 Lab: Chemistry

Conditions on Early Earth

JoVE 11015

Around 4 billion years ago, oceans began to condense on earth while volcanic eruptions released nitrogen, carbon dioxide, methane, ammonia, and hydrogen into the primordial atmosphere. However, organisms with the characteristics of life were not initially present on earth. Scientists have used experimentation to determine how organisms evolved that could grow, reproduce, and maintain an internal environment. In the 1920s, the scientists Oparin and Haldane proposed the idea that simple biological compounds could have formed on the early earth. More than 30 years later, Stanley Miller and Harold Urey at the University of Chicago tested this hypothesis by simulating the conditions of the early earth's atmosphere and oceans in a laboratory apparatus. Using electricity as an energy source, the Miller-Urey experiment generated amino acids and other organic molecules, showing that the environment of early earth was conducive to the formation of biological molecules. More recent experiments have yielded comparable results and suggest that amino acids may have formed near areas of volcanic activity or hydrothermal vents in the ocean. Amino acids and small organic molecules may then have self-assembled to form more complex macromolecules. For instance, dripping amino acids or nucleotides into hot sand can result in the formation of the corresponding polymer

 Core: Biology

Climate Change- Concept

JoVE 10609

The certainty of climate change remains a public controversy despite the consensus among approximately 97% of active climate researchers, who not only agree that the Earth’s climate is changing but also state that this change is intensified by human activity, predominantly carbon emissions 1. The disconnect between the public and the experts is partly due to poor understanding of the…

 Lab Bio

Responses to Drought and Flooding

JoVE 11118

Water plays a significant role in the life cycle of plants. However, insufficient or excess of water can be detrimental and pose a serious threat to plants.

Under normal conditions, water taken up by the plant evaporates from leaves and other parts in a process called transpiration. In times of drought stress, water that evaporates by transpiration far exceeds the water absorbed from the soil, causing plants to wilt. The general plant response to drought stress is the synthesis of hormone abscisic acid that keeps stomata closed and reduces transpiration. Additionally, plants may respond to extreme water insufficiency by shedding leaves. This method, however, reduces photosynthesis and consequently hampers plant growth. Mitigation of drought stress in plants by microbes Drought stress limits the growth and productivity of plants in arid and semi-arid regions. However, certain microbes present in the vicinity of plants may release physical and chemical signals that induce changes related to plant defense under drought conditions. For example, the soil bacterium Paenibacillus polymyx is reported to induce drought tolerance in Arabidopsis. The most significant effect of this bacteria was observed in the growth of legumes under water stress. Leguminous plants depend on soil rhizobium for nitrogen fixation - but rhizobia are ext

 Core: Biology

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

Covalent Bonds

JoVE 10664

When two atoms share electrons to complete their valence shells they create a covalent bond. An atom’s electronegativity—the force with which shared electrons are pulled towards an atom—determines how the electrons are shared. Molecules formed with covalent bonds can be either polar or nonpolar. Atoms with similar electronegativities form nonpolar covalent bonds; the electrons are shared equally. Atoms with different electronegativities share electrons unequally, creating polar bonds. The number of covalent bonds that an atom can form is dictated by how many valence electrons it has. Oxygen, for example, has six out of eight possible valence electrons, meaning that each oxygen atom needs two more electrons to become stable. Oxygen can form single bonds with two other atoms, as it does when it forms water with two hydrogen atoms (chemical formula H2O). Oxygen can also form a double bond with just one other atom that also needs two more electrons to complete its octet (e.g., another oxygen atom). Carbon has four valence electrons and therefore can form four covalent bonds, as it does in methane (CH4). When a covalent bond is made, both atoms share a pair of electrons in a hybrid orbital that differs in shape from a normal orbital. The electrons participating in the bond thus orbit in a modified path around the

 Core: Biology

Proton Exchange Membrane Fuel Cells

JoVE 10022

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


The United States consumes a large amount of energy – the current rate is around 97.5 quadrillion BTUs annually. The vast majority (90%) of this energy comes from non-renewable fuel sources. This energy is used for electricity (39%), transportation (28%),…

 Environmental Science
12345678913
More Results...