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Heart-Rate Monitor

This project uses a sensitive light-detecting resistor to detect small changes in the light beaming through your finger as your blood pumps through tiny arteries in the finger. This device is not the same as the heart-rate monitors typically used in…

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from article Swim bladder

Young trout (Salmo trutta), showing the swim bladder. The trout is one of the primitive teleosts which have the swim bladder connected to the gut.

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from article Swim bladder

Diagram showing the blood supply to the gas gland. Blood traveling away from the gland is stippled. There are far more capillaries in the rete than are shown in this diagram.

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from article Clypeasteroida

Major features of a clypeasteroid sand dollar, Leodia sexiesperforata (a species typical of the Caribbean), from the family Mellitidae. Aboral view is on the left; oral view is on the right.

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from article Batrachoidiformes

Atlantic midshipman (Porichthys plectrodon, order Batrachoidiformes). (Photo courtesy of the SEFSC Pascagoula Laboratory, Collection of Brandi Noble, Southeast Fisheries Science Center, National Marine Fisheries Service, National Oceanic and…

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from article Vacuole

Vacuoles are important membrane-bound intracellular compartments. (Left) Protozoan vacuoles serve a variety of functions. For example, contractile vacuoles are involved in osmoregulation, controlling the excretion of water from the cell. The food…

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from article Vacuole

A large lipid vacuole surrounded by a mantle of multinucleated giant cells. This type of vacuole occurs in exogenous lipid (lipoid) pneumonia, which is caused by inhalation or aspiration of a fatty substance. (Credit: Yale Rosen)

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from article Mycoplasmas

Mycoplasmas. (a) Mycoplasma hominis, phase contrast micrograph (courtesy of W. Bredt). (b) Spiroplasma citri, electron micrograph of negatively stained specimen (courtesy of R. M. Cole). (c) Mycoplasma colony on solid nutrient medium. (d) Ureaplasma…

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from article Fibrinogen

Fibrinogen models. (a) Computer image of the symmetrical molecule. (b) Model for end-to-end aggregation. (c) Half-staggered molecular overlap between side-to-side aggregated filaments in a clot network. (Parts a and b from C. Cohen et al., The…

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from article Fibrinogen

Physiological pathway for the clotting of fibrinogen in normal plasma. Clotting time is measured by forming the (fibrin)n network; this, however, is not the end product. Unless this clot undergoes ligation by γ-glutamyl-ε-lysine cross-links,…

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from article Fibrinogen

Formation of γ-glutamyl-ε-lysine peptide bridges between fibrin molecules is the last enzyme-catalyzed reaction in blood clotting.

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from article Plant hormone

Plant hormones, such as gibberellins, are chemical messengers synthesized within plants, where they help to regulate a variety of physiological processes, including growth, differentiation, and development. The stunted plant on the left lacks…

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from article Plant hormone

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from article Plant hormone

A simplified view of the interaction of three branching hormones. (Left) Auxin promotes production of strigolactones (SL), while limiting that of cytokinins (CK) at bud nodes. This blocks bud outgrowth in intact plants. (Right) After decapitation,…

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from article Plant hormone

The plant hormone ethylene initiates a signal transduction cascade that activates the transcription of a suite of genes needed for fully developed, ripe fruits and vegetables. The top illustration shows a normal path of ethylene synthesis leading to…

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from article Plant hormone

Auxin transport within a plant takes place in a cell-to-cell fashion, mainly in the vascular cambium and the procambial strands, but probably also in epidermal cells. Transport to the root probably involves the phloem. The transport mechanism…

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from article Endocrinology

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from article Paracrinoidea

Reconstructions of two paracrinoids showing different proposed living positions. (a) Amygdalocystites from the Late Ordovician of Ontario, Canada, held up some distance in the water column by a curved attached stem (after T. E. Guensburg, J.…

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from article Sporozoa

Fine structure of a coccidian merozoite (Eimeria miyairii from the rat). (a) Longitudinal section. Cross sections at levels of (b) nucleus, (c) Golgi complex, (d) large dense granules, (e) cytostome, (f) paired organelle, and (g) conoid. (After…

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from article Sporozoa

Mature (sporulated) oocyst of a coccidium (Eimeria). (After N.D.Levine, Protozoan Parasites of Domestic Animals and of Man, Burgess, 1961)

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from article Sporozoa

Life cycle of the chicken coccidium Eimeria tenella. The numbered steps are explained in the text. (After N.D.Levine, Protozoan Parasites of Domestic Animals and of Man, Burgess, 1961)

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from article DNA microarray

An example of microarray data presentation is shown. In this experiment, five to seven different samples of a series of tissues are organized by column. Each column is one tissue. Tissue names are indicated across the top. The level of expression of…

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from article Nitrogen fixation

A mechanism for the functioning of the two components of nitrogenase. The box signifies that a complex of Fe and Mo-Fe proteins forms the active enzyme.

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from article Temperature adaptation in animals

Body temperature (°C) versus ambient temperature (°C) for (left) endotherm and (right) ectotherm animals. Temperature adaptation is one of the key characteristics necessary to ensure that an animal can live and exist in its environment over a…

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from article Temperature adaptation in animals

A collared lizard basking on a dried lava rock. The body temperature of this ectotherm is determined by sources of heat external to the body. (Credit: David Parsons/iStockphoto/Getty Images)

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from article Temperature adaptation in animals

The Arctic wolf is an endotherm with a thick pelage that reduces the cost of thermoregulation in cold environments. (Credit: Cultura Creative/Alamy Stock Photo)

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from article Hippo pathway (developmental biology)

Illustration depicting Hippo pathway components in (a) Drosophila and (b) mammals, with arrows and blunt lines indicating activation and inhibition, respectively. Expression of the pro-proliferative genes occurs when the Hippo pathway is “OFF.”…

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from article Synbranchiformes

Synbranchus madeirae, a swamp eel belonging to the family Synbranchidae. [Photo from T. P. Carvalho et al., Fishes from the upper Yuruá river, Amazon basin, Peru, Check List, 5(3):673–691, 2009]

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from article Synbranchiformes

Macrognathus siamensis, commonly called the spotfin spiny eel, belonging to the family Mastacembelidae. (Photo courtesy of the U.S. Geological Survey)

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from article Teleostei

An Atlantic blue marlin (Makaira nigricans) jumping out of the ocean. This popular sport fish is one of the members of the Teleostei. (Photo by Ken Neill, National Marine Fisheries Service, National Oceanic and Atmospheric Administration)

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from article Teleostei

Phylogeny of the Teleostei.

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from article Spinal cord

Spinal cord and brain (ventral aspect). Nerve roots and chief autonomic ganglia are shown. (Credit: Based on an original illustration by H. V. Neal and H. W. Rand)

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from article Spinal cord

Human spinal cord sectioned to show the white matter and gray matter. (Credit: Based on an original illustration by G. M. Wyburn)

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from article Oligosaccharide

Blood group antigens. Five antigens are formed from a single glycolipid or glycoprotein precursor by adding various monosaccharide residues to different places in the oligosaccharide chain (where R can be protein or lipid). The monosaccharide…

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from article Death

Structural changes of cells undergoing the two processes of cell death—necrosis and apoptosis. Necrosis refers to the death of a cell or group of cells as a result of injury, disease, or some other pathologic state. Apoptosis (programmed cell death)…

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from article Death

Changes that can occur in living systems following an injury. In the case of a lethal or fatal injury, the system can be assumed to pass a point, shown as the zero level of homeostatic ability, beyond which the system is unable to restore a normal…

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from article Death

Coagulative necrosis of the myocardium (the muscular tissue of the heart wall). In the right upper half of the image (arrow), the cells are necrotic. The cytoplasm has lost protein, and lysis of the nuclei has occurred, with few nuclei of cardiac…

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from article Detection of respiratory viruses

Electron microscopic image of SARS coronavirus. The arrow indicates the presence of the "corona" or crown formed by a single surface protein. (Credit: James B. Mahony)

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from article Detection of respiratory viruses

Direct fluorescent antibody (DFA) staining of an influenza-positive specimen (left) showing the presence of virus-infected cells (green) stained with a fluorescent monoclonal antibody, and a negative specimen (right) showing uninfected cells stained…

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from article Ascidiacea

Left side of a zooid of the colonial ascidian Perophora. The tunic, mantle, and anterior wall of the pharynx have been removed from the left. The two arrows indicate direction of water intake and expulsion.

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from article Extinction (paleontology)

Diversity of marine families and genera in the fossil record. Sharp drops (designated by the numbers 1–5) indicate times of mass extinctions: 1 = Late Ordovician (−12%); 2 = Late Devonian (−14%); 3 = Late Permian (−52%); 4 = Late Triassic (−12%); 5…

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from article Extinction (paleontology)

Times and places of extinctions of large mammals during the Late Pleistocene. (Credit: Adapted from P. S. Martin and R. G. Klein, eds., Quaternary Extinctions: A Prehistoric Revolution, University of Arizona Press, 1984)

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from article Crinoidea

Stemmed crinoid in feeding posture.

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from article Crinoidea

Calyx and proximal stem and arm morphology, vertical section.

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from article Crinoidea

Arm morphology, back (aboral) view.

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from article Crinoidea

Arm morphology, side view.

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from article Coelacanthiformes

Latimeria chalumnae (West Indian Ocean coelacanth), one of the two extant species of the order Coelacanthiformes. (Photo courtesy of the Muséum de Toulouse, France)

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from article Coelacanthiformes