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Death: Irreversible cessation of all bodily functions, manifested by absence of spontaneous breathing and total loss of cardiovascular and cerebral functions.

Diagnostic Necropsy and Tissue Harvest

JoVE 10294

Source: Kay Stewart, RVT, RLATG, CMAR; Valerie A. Schroeder, RVT, RLATG. University of Notre Dame, IN


Many animal experiments rely on final data collection time points that are gathered from the harvesting and testing of organs and tissues. The use of appropriate methods for the collection of organs and tissues can impact the quality of…

 Lab Animal Research

Blood Withdrawal I

JoVE 10246

Source: Kay Stewart, RVT, RLATG, CMAR; Valerie A. Schroeder, RVT, RLATG. University of Notre Dame, IN


Blood collection is a common requirement for research studies that involve mice and rats. The method of blood withdrawal in mice and rats is dependent upon the volume of blood needed, the frequency of the sampling, the health status of the …

 Lab Animal Research

Rodent Handling and Restraint Techniques

JoVE 10221

Source: Kay Stewart, RVT, RLATG, CMAR; Valerie A. Schroeder, RVT, RLATG. University of Notre Dame, IN 


It has been demonstrated that even minimal handling of mice and rats is stressful to the animals. Handling for cage changing and other noninvasive procedures causes an increase in heart rate, blood pressure, and other physiological…

 Lab Animal Research

Detecting Reactive Oxygen Species

JoVE 5654

Reactive oxygen species are chemically active, oxygen-derived molecules capable of oxidizing other molecules. Because of their reactive nature, there are many deleterious effects associated with unchecked ROS production, including structural damage to DNA and other biological molecules. However, ROS can also be mediators of physiological signaling. There is accumulating…

 Cell Biology

Buffers- Concept

JoVE 11153

Buffers

When an Arrhenius acid (HA) is added to water, it dissociates into its conjugate base (A-) and a hydrogen cation (H+).


HA + H2O → H+(aq) + A-(aq)


The amount of hydrogen ions present in the solution determines the acidity of the solution, where more hydrogen ions indicate a lower or more acidic pH. Similarly, when a…

 Lab: Chemistry

The Fossil Record

JoVE 11132

The fossil record documents only a small fraction of all organisms that have ever inhabited Earth. Fossilization is a rare process, and most organisms never become fossils. Moreover, the fossil record only exhibits fossils that have been discovered. Nevertheless, sedimentary rock fossils of long-lived, abundant, hard-bodied organisms dominate the fossil record. These fossils offer valuable information, such as an organism's physical form, behavior, and age. Studying the fossil record helps scientists to place fossils into geological (e.g., Paleozoic era; 250-570 million years ago) and evolutionary (e.g., first tetrapod organism) contexts. Whale evolution, for example, is one of the most well-studied examples of evolutionary change in the fossil record. Modern whales descended from a terrestrial, tetrapod ancestor that transitioned from land, back to water. Ancestral whales' forelimbs later evolved into flippers to aid swimming, while their hindlimbs disappeared. The fossil record reveals whales' terrestrial (e.g., Indohyus), semi-aquatic (e.g., Ambulocetus), and aquatic (e.g., Dorudon) ancestors throughout the early Cenozoic era—nearly 50 million years ago. Both modern and extinct organisms can inform scientists' understanding of life on Earth. In addition to showing evolutionary changes in organisms thems

 Core: Biology

Defenses Against Pathogens and Herbivores

JoVE 11121

Plants present a rich source of nutrients for many organisms, making it a target for herbivores and infectious agents. Plants, though lacking a proper immune system, have developed an array of constitutive and inducible defenses to fend off these attacks.

Mechanical defenses form the first line of defense in plants. The thick barrier formed by the bark protects plants from herbivores. Hard shells, modified branches like thorns, and modified leaves like spines can also discourage herbivores from preying on plants. Other physical barriers like the waxy cuticle, epidermis, cell-wall, and trichomes can help resist invasion by several pathogens. Plants also resort to the production of chemicals or organic compounds in the form of secondary metabolites like terpenes, phenolics, glycosides, and alkaloids, for defense against both herbivores and pathogens. Many secondary metabolites are toxic and lethal to other organisms. Some specific metabolites can repel predators with noxious odors, repellant tastes, or allergenic characteristics. Plants also produce proteins and enzymes that specifically inhibit pathogen-proteins or pathogen-enzymes by blocking active sites or altering enzyme conformations. Proteins like defensins, lectins, amylase inhibitors, and proteinase inhibitors are produced in significant quantities during pathogen attack and are activated to

 Core: Biology

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

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 Cochlea

JoVE 10855

The cochlea is a coiled structure in the inner ear that contains hair cells—the sensory receptors of the auditory system. Sound waves are transmitted to the cochlea by small bones attached to the eardrum called the ossicles, which vibrate the oval window that leads to the inner ear. This causes fluid in the chambers of the cochlea to move, vibrating the basilar membrane.

The basilar membrane extends from the basal end of the cochlea near the oval window to the apical end at its tip. Although the cochlea itself narrows towards the apical end, the basilar membrane has the opposite geometry—becoming wider and more flexible towards the apical end. Primarily because of these physical characteristics, the apical end of the basilar membrane maximally vibrates when exposed to low-frequency sounds, while the narrower, stiffer basal end maximally vibrates when exposed to high frequencies. This gradient of frequency response creates tonotopy—a topographic map of pitch—in the cochlea. The hair cells are stimulated by the shearing force created by the vibration of the basilar membrane below them, relative to the stiffer tectorial membrane above them. Because of the tonotopy of the basilar membrane, hair cells are maximally stimulated by different frequencies depending on where they are in the cochlea. Those at the basal end respond be

 Core: Biology
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