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October, 2006
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Steam Distillation - Student Protocol

JoVE 11205

Source: Lara Al Hariri and Ahmed Basabrain at the University of Massachusetts Amherst, MA, USA

Steam Distillation

In this experiment, you will perform a steam distillation to extract an essential oil from an orange peel.

Before you start the lab, put on the appropriate personal protective equipment,…

 Lab: Chemistry

Key Elements for Plant Nutrition

JoVE 11103

Like all living organisms, plants require organic and inorganic nutrients to survive, reproduce, grow and maintain homeostasis. To identify nutrients that are essential for plant functioning, researchers have leveraged a technique called hydroponics. In hydroponic culture systems, plants are grown—without soil—in water-based solutions containing nutrients. At least 17 nutrients have been identified as essential elements required by plants. Plants acquire these elements from the atmosphere, the soil in which they are rooted, and water. Nine of these essential nutrients—collectively called macronutrients—are needed by plants in more significant amounts. The macronutrients include carbon, oxygen, hydrogen, nitrogen, phosphorus, sulfur, calcium, magnesium, and potassium. Critical plant compounds, such as water, proteins, nucleic acids, and carbohydrates, contain macronutrients. Macronutrients also regulate cellular processes. For example, potassium regulates the opening and closing of stomata for gas exchange. Plants need micronutrients in smaller amounts. These include chlorine, iron, manganese, boron, zinc, copper, nickel, and molybdenum. Many micronutrients function as cofactors, which enable the activity of enzymes. Therefore, without micronutrients, plants are unable to perform critical functions. A plant experiencing an

 Core: Biology

Responses to Salt Stress

JoVE 11120

Salt stress—which can be triggered by high salt concentrations in a plant’s environment—can significantly affect plant growth and crop production by influencing photosynthesis and the absorption of water and nutrients.

Plant cell cytoplasm has a high solute concentration, which causes water to flow from the soil into the plant due to osmosis. However, excess salt in the surrounding soil increases the soil solute concentration, reducing the plant’s ability to take up water. High levels of sodium are toxic to plants, so increasing their sodium content to compensate is not a viable option. However, many plants can respond to moderate salt stress by increasing internal levels of solutes that are well-tolerated at high concentrations—like proline and glycine. The resulting increased solute concentration within the cell cytoplasm allows the roots to increase water uptake from the soil without taking in toxic levels of sodium. Sodium is not essential for most plants, and excess sodium affects the absorption of essential nutrients. For example, the uptake of potassium—which regulates photosynthesis, protein synthesis, and other essential plant functions—is impeded by sodium in highly saline conditions. Calcium can ameliorate some effects of salt stress by facilitating potassium uptake through the regulation of ion

 Core: Biology

Epiphytes, Parasites, and Carnivores

JoVE 11105

Plants often form mutualistic relationships with soil-dwelling fungi or bacteria to enhance their roots’ nutrient uptake ability. Root-colonizing fungi (e.g., mycorrhizae) increase a plant’s root surface area, which promotes nutrient absorption. While root-colonizing, nitrogen-fixing bacteria (e.g., rhizobia) convert atmospheric nitrogen (N2) into ammonia (NH3), making nitrogen available to plants for various biological functions. For example, nitrogen is essential for the biosynthesis of the chlorophyll molecules that capture light energy during photosynthesis. Bacteria and fungi, in return, gain access to the sugars and amino acids secreted by the plant’s roots. A variety of plant species evolved root-bacteria and root-fungi nutritional adaptation to thrive. Other plant species, such as epiphytes, parasites, and carnivores, evolved nutritional adaptations that allowed them to use different organisms for survival. Rather than compete for bioavailable soil nutrients and light, epiphytes grow on other living plants (especially trees) for better nutritional opportunities. Epiphyte-plant relationships are commensal, as only the epiphyte benefits (i.e., better nutrient and light access for photosynthesis) while its host remains unaffected. Epiphytes absorb nearby nutrients through either leaf structures called tric

 Core: Biology

The Periodic Table and Organismal Elements

JoVE 10655

Elements are the smallest units of matter that cannot be broken down further by chemical processes. There are 118 known elements, but not all of these are naturally-occurring, and fewer still are essential for life. Living matter is composed primarily of carbon, nitrogen, hydrogen, and oxygen, with smaller amounts of other elements like calcium, phosphorus, potassium, and sulfur. Other elements are also necessary for life but only in trace amounts. The periodic table organizes elements based on their physical and chemical properties. The atomic number of an element corresponds to the number of protons found in its nucleus, and each square in the periodic table also provides the full name, chemical symbol, and atomic weight of an element. The number of protons provides information about the size of an element, but it is not the only organizational principle underlying the structure of the periodic table. Elements are organized into columns (groups) and rows (periods) based on other physical and chemical properties, such as reactivity, the location of their outermost electrons, and the ability to make certain types of bonds. Elements in the same group (i.e., column) vary in size but have many chemical properties in common with one another. By contrast, elements in the same period (i.e., row) are more similar in size and have their electrons located in a simi

 Core: Biology

Lab Techniques- Concept

JoVE 11135

Measurement Accuracy

The ability to repeat an experiment and get the same results, or reproducibility, is essential in scientific research. However, it’s impossible to repeat an experiment if you don’t know how you did it. Thus, scientists keep detailed records of their experiments in lab notebooks. These records include important information like the amount of each…

 Lab: Chemistry

Threats to Biodiversity

JoVE 10951

There have been five major extinction events throughout geological history, resulting in the elimination of biodiversity, followed by a rebound of species that adapted to the new conditions. In the current geological epoch, the Holocene, there is a sixth extinction event in progress. This mass extinction has been attributed to human activities and is thus provisionally called the Anthropocene. In 2019 the human population reached 7.7 billion people and is projected to comprise 10 billion by 2060. Indicative of our impact, by biomass (the actual mass of a particular species), humans make up 36% of Earth’s mammals, livestock 60%, and wild mammals only 4%. Approximately 70% of all birds are poultry, so only 30% are wild. To minimize human impact on biodiversity and climate, we have to understand which of our activities are problematic and balance the needs of human civilization and progress with a sustainable plan for future generations. Some of the major threats to biodiversity include habitat loss due to human development, over-farming, and increased carbon dioxide emissions from factories and vehicles. A case study in human impact on the weather can be found in the 1930s event known as the Dust Bowl. In the 1920s and 30s, a large number of farmers moved to the Great Plains and clear cut the land, removing the native ground covering plants in order to

 Core: Biology

What is Biodiversity?

JoVE 10950

Biodiversity describes the variety of living things at multiple organizational levels: genetic, species and ecosystem diversity. Species diversity includes all branches of the evolutionary tree from single-celled prokaryotic organisms, bacteria, and archaea, to the eukaryotic kingdoms: plants; animals; fungi; and protists. To date, there have been about 1.75 million species identified, and new species are discovered every week. Biodiversity also includes the interactions that connect organisms to each other and to the environment in which they live. Organisms have evolved together to create the intricate webs of life that involve both cooperative (symbiotic) relationships and predator-prey relationships. Biodiversity is, therefore, a much broader concept than the simple collection of species to which it is often reduced. All living things depend on the existence and activities of other living things. Groups of populations of different species interacting with one another and with their physical environment constitute an ecosystem. Ecosystems themselves are very diverse: for example forests, ponds, deserts, coral reefs, and even the human intestinal flora. Scientists who study biodiversity are not only interested in the number of different species in an ecosystem, but also in how many individuals of each species is present. Studying biodiversity indicates in w

 Core: Biology


JoVE 10873

Nociception—the ability to feel pain—is essential for an organism’s survival and overall well-being. Noxious stimuli such as piercing pain from a sharp object, heat from an open flame, or contact with corrosive chemicals are first detected by sensory receptors, called nociceptors, located on nerve endings. Nociceptors express ion channels that convert noxious stimuli into electrical signals. When these signals reach the brain via sensory neurons, they are perceived as pain. Thus, pain helps the organism avoid noxious stimuli. The immune system plays an essential role in pain pathology. Upon encountering noxious stimuli, immune cells such as mast cells and macrophages present at the site of injury release inflammatory chemicals such as cytokines, chemokines, histamines, and prostaglandins. These chemicals attract other immune cells such as monocytes and T cells to the injury site. They also stimulate nociceptors, resulting in hyperalgesia—a more intense response to a previously painful stimulus, or allodynia—a painful response to a normally innocuous stimulus such as light touch. Such pain sensitization helps protect the injured site during healing. In some cases, pain outlives its role as an acute warning system if sensitization fails to resolve over time. Chronic pain—persistent or recurrent pain lasting longer than t

 Core: Biology
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