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Eukaryotic Organisms

Eukaryotes include fungi, animals, and plants as well as some unicellular organisms. Eukaryotic cells are about 10 times the size of a prokaryote and can be as much as 1000 times greater in volume. The major and extremely significant difference between prokaryotes and eukaryotes is that eukaryotic cells contain membrane-bound compartments in which ...

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EukaryoticOrganisms
Astronomy

Ancient Planet

Long before our Sun and Earth ever existed, a Jupiter-sized planet formed around a sun-like star. Now, almost 13 billion years later, NASA's Hubble Space Telescope has precisely measured the mass of ... Continue reading

AncientPlanet
Chemistry

Hydrogen Reaction Experiment Reaps a Surprise

Scientists got a surprise recently when a team of physical chemists at Stanford University studied a common hydrogen reaction. Scientists got a surprise recently when a team of physical chemists at ... Continue reading

HydrogenReactionExperiment
Astronomy

Reading The Colors of the Spectrum

Did you ever wonder how scientists can tell us so much about distant stars, for example, the surface temperature or chemical makeup of a star, light years away from Earth? Scientists can only use what ... Continue reading

SpectrumColors
Medicine

Eating Disorders

Eating is controlled by many factors, including appetite, food availability, family, peer, and cultural practices, and attempts at voluntary control. Dieting to a body weight leaner than needed for ... Continue reading

EatingDisorders

Nematodes Are Everywhere

NematodesAreEverywhereNematodes are simple worms consisting of an elongate stomach and reproduction system inside a resistant outer cuticle (outer skin). Most nematodes are so small, between 400 micrometers to 5 mm long, that a microscope is needed to see them. Their small size, resistant cuticle, and ability to adapt to severe and changing environments have made nematodes one of the most abundant types of animals on earth. The cuticle is the flexible coating around the nematode [its skin], which protects the nematode from physical and chemical dangers. The most noticeable feature of the cuticle is the system of grooves across the body from head to tail. As nematodes grow they usually shed their cuticle four times.

Most nematodes feed on bacteria, fungi, and other soil organisms. Others are parasitic, obtaining their food from animals (such as the dog heartworm), humans (such as the pinworm), and plants. Agricultural cultivation encourages an increase in parasitic nematodes that feed on the crops being grown. Occasionally, new kinds of plant parasitic nematodes may be introduced into a field by contaminated plant parts, soil on farm equipment and irrigation water. Nematodes which parasitize plants may cause yield losses by themselves or they may join with other soilborne organisms such as viruses, fungi, and bacteria, to promote disease development in plants. Most often, nematode feeding reduces the flow of water and nutrients into the plant, increasing the plant's susceptibility to other stress factors such as heat, water, and nutritional deficiencies.

After hatching, plant-parasitic nematodes move through the soil to find areas on plant roots to feed. Some nematodes stay outside the root and use long stylets to puncture cells inside the root (ring, stubby root, and sting nematodes). Nematodes which enter the root may move throughout the root (lesion nematode) and feed at many sites (causing root lesions), or stay in one feeding site (cyst and root-knot nematodes). Nematodes which stay at one feeding site swell from eel-shaped to pear-shaped and stay at the same site until they die.