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Science in Focus: Shedding Light: Glossary


Decomposers are organisms which gain their food (and therefore their energy) from the excretions and dead bodies of animals and plants.. Included in this group are bacteria and fungi. Many fungi and all bacteria can only be seen with the aid of a microscope, and are known as microbes. Decomposers return nutrients to the ecosystem for use by producers.

The mass of an object is the density multiplied by the volume. It is mass per unit volume of a substance expressed as kilograms per cubic meter. The weight of an object is its mass multiplied by the acceleration of gravity.

For two objects of exactly the same volume, the one that is heavier is more dense. For example, a wooden dowel rod found in a clothes closet has less mass than a steel bar of exactly the same volume used for weight lifting.

depth of field
The range of distance which is in focus. A greater depth of field results from a small camera aperture or a small pupil size in the eye.

dew point
The temperature to which air must be cooled such that it cannot hold any more water (saturated). When air at ground level reaches its dew point, dew forms on any exposed surface. Under certain conditions, air at its dew point forms a fog.

In a camera, a diaphragm adjusts the size of the opening for light, the aperture. A diaphragm is analogous to the iris of the human eye.


An ecosystem is an interconnected web of living (biotic) things and non-living (abiotic) things (such as sunlight, water, air soil). Thus, any place may be considered to be an ecosystem if it contains a variety of different types of organisms whose behaviors influence one another, and whose lives are also affected by abiotic things. Our Earth is one enormous ecosystem, but an ecosystem could also be a rotting log, or an ocean, a tree or a city park. When there is no interference from humans, ecosystems maintain a natural, balanced system.

electromagnetic spectrum
The entire array of photon energy levels, which includes radio waves, microwaves, infrared radiation, ultraviolet light, x-rays, gamma rays, and visible light.

Existing in many states (potential, kinetic, mechanical, nuclear, heat, light, etc.), energy is anything that is capable of changing the motion, physical composition or temperature of an object.

In a given system, energy is never lost, but rather changes from one form to another. With a carbon filament light bulb, for example, electrical energy that comes from a battery is converted into light energy and heat energy

1. The imaginary great circle around the Earth's surface, equidistant from the poles and lying in a plane perpendicular to the Earth's axis of rotation. It divides the Earth into the Northern Hemisphere and the Southern Hemisphere. The equator has 0 * latitude.
2. A similar great circle drawn on the surface of a celestial body at right angles to the axis of rotation.

See tropic of Cancer and tropic of Capricorn.

Describes the appearance of a plant grown in very low levels or absence of light. The plant is pale yellow in color because of a lack of chlorophyll; the stem is often elongated and the leaves are small.

The process of water as a liquid changing to gas (water vapor). The most energetic water molecules at the surface of liquid water fly off and mix with air molecules.


This type of defective vision usually results from an eyeball which is too short or is a result of the loss of lens elasticity with age. A farsighted individual will see far objects well but needs corrective lenses (thicker in the middle) to see objects that are close.

focal point
The path of light through a convex lens is refracted (bent) such that parallel rays of light that enter the lens are brought to a common point or focus.

A nutrient which is a source of energy for living organisms. Carbohydrates (such as starch and sugar) and fats are the primary sources of energy for living things.

The region of the eye which is most sensitive to light. The fovea contains a concentration of light detectors (cones).

A front is the area of contact between air masses.


heat conduction
The transfer of energy due to temperature differences between adjacent parts of a body.

If you are cooking with a pan on a stove or over a campfire, and the pan has a metal handle, the handle will get hot even if it is not in the fire because heat is conducted to the handle from the part of the pan that was in the fire.

heat energy
The energy that flows from part of an object to another because of a difference in temperature. Heat energy can be transferred by conduction convection or radiation.

A term that refers to water vapor in the air.

1. A severe tropical cyclone originating in the equatorial regions of the Atlantic Ocean or Caribbean Sea, and usually involving heavy rains.
2. A wind with a speed greater than 74 miles (119 kilometers) per hour, according to the Beaufort scale.

See cyclone and typhoon.

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