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I

iris
The colored portion of the eye. The iris controls the size of the pupil (the hole through which light enters the eye).

invertebrate
An invertebrate is an animal that does not possess a backbone (vertebral column). There are many groups of invertebrates including: worms (earthworms and leeches), mollusks (snails and oysters), and arthropods (insects, spiders and crabs).

K

kinetic energy
The form of energy that an object has because of its motion. The amount of kinetic energy an object has depends on its mass as well as its velocity. The more massive an object is and the faster it is going, the more kinetic energy it has. Specifically, kinetic energy is defined as equal to one half the mass of the object times the square of its velocity (1/2 mv²). The total kinetic energy of a system is the sum of the kinetic energy of each of the objects or particles in the system.

L

latent heat energy
When a material changes from one state to another (for example a solid changes to a liquid or a gas changes to a liquid), energy changes also occur. Energy is required when a solid melts, a liquid evaporates, or when a solid vaporizes. When these processes take place, the amount of energy transferred as heat is called the latent heat (or the heat of transformation).

For example, water vapor contains latent heat. When a material goes from a vapor to a liquid or from a liquid to a solid, energy is released. So when water vapor condenses to water, the latent heat originally required to evaporate the water is released.

See also heat energy.

light
A stream of very small packets of energy, called photons, traveling very fast (3 times 10⁵ km/sec, in vacuum).

M

matter
Matter is the term used to describe the substance of which all living and non-living things are made. It has mass and can be experienced with our senses. Matter is made up of atoms which group together to form molecules. Matter can be in the form of a solid, a liquid, or a gas. At exceedingly high temperatures, the atoms of matter are shaken apart creating a state of matter called plasma. Our Sun and other stars are in the plasma state.

mineral
A nutrient required by a living organism, but one that does not supply energy.

Nitrates in the soil are a source of nitrogen needed by the plant to make protein. Magnesium is a mineral needed by plants to make chlorophyll. Calcium is a mineral needed by humans for bone growth.

mirror
A very smooth surface that can reflect photons all in the same direction.

molecules
Atoms consist of a single nucleus surrounded by a cloud of electrons. Atoms are the fundamental building blocks of molecules. A molecule is any group of atoms that are bonded together and act as a unit. For example a water molecule contains two atoms of hydrogen and one of oxygen (H₂O). Hydrogen and oxygen do not always bond to form water. Two atoms of hydrogen and two atoms of oxygen can bond to form hydrogen peroxide. While the periodic table has about 100 different chemical elements, these can combine in different ways to form tens of millions of different molecules.

N

nearsightedness
This type of defective vision usually results from an eyeball which is too long. A nearsighted individual will see near objects well but needs corrective lenses (thinner in the middle) to see objects at a distance.

normal
a line that is perpendicular to a surface.

See reflection.

North Pole
1. The northern end of Earth's axis of rotation at 90° latitude, a point in the Arctic Ocean. The North Pole has six months of sunlight followed by six months of darkness each year.
2. The northern end of the axis of rotation of a planet or other celestial body.

The terms "north" and "south" are conventions for naming the poles of a magnet and have nothing to do with "up" and "down" related to gravity.

See South Pole.

Northern Hemisphere
The half of the Earth north of the equator.

See equator and Southern Hemisphere.

nutrient
Any substance which is required by a living organism which is required for its normal growth and development.

Food and minerals are both nutrients.

O

occluded front
A front that occurs when a cold front occludes or obstructs a warm front. A front is the area of contact between air masses.

opaque
Describes the property of a material that does not allow visible light to pass through.

A piece of thick wood is considered opaque.

optic nerve
The nerve that carries messages from the retina to the brain. On the retina, the region where the nerve fibers collect to form the optic nerve has no detectors, so it is known as 'the blind spot'.

P

photon
A discrete packet of light energy that travels extremely fast (3 times 10⁵ km/sec, in vacuum).

phytoplankton
These are microscopic one-celled organisms, found free-floating in the upper layer of the oceans. Next to bacteria, these are the most numerous organisms on earth. Phytoplankton photosynthesize, and together with seaweed, are responsible for about 85% of the world's photosynthesis. Phytoplankton are eaten by microscopic consumers known as zooplankton.

photosynthesis
1) The process in which photons of light energy are absorbed by chlorophyll. The energy is used to join carbon dioxide to the hydrogen from water forming sugar and oxygen.

2) The process by which plants make their food and release oxygen as a by-product.

pixels (from picture elements)
The individual phosphors that form the image on a television screen. A color television screen or computer monitor screen consists of red, green and blue pixels (RGB) in a black background.

plane mirror
a flat mirror.

primary colors of light
Primary colors are the minimum number that can be mixed to produce all other colors. The primary colors of light (red, green, blue) can be mixed to form lighter, brighter colors; mixing all three produces white light.

primary colors of pigment
The primary colors of pigment or paint (cyan, magenta, yellow) can be mixed to form darker colors; mixing all three produces black.

prism
A prism is a transparent column of glass with equilateral triangles at the ends; the three sides are quadrilaterals.

A glass prism can be used to spread out white light into the colors of the rainbow, or into the colors of the visible spectrum.

producer
A producer is an organism that makes its food by photosynthesis. Thus, green plants, phytoplankton, seaweed and some bacteria are producers. Producers absorb some of the Sun's energy and use it to manufacture sugar. The rest of the living world depends on producers as the ultimate source of food. There are some bacteria which photosynthesize in a similar way to green plants. Deep in the oceans, however, there are bacteria which make their own food, not by using energy from the Sun, but by using energy contained in sulfur-rich chemicals which come from the molten rock of the Earth itself.

pupil
The hole in the center of the iris is the pupil. Light enters the eye through the pupil.

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