1. 5,800 kelvins
   3,600 kelvins
2. 1,200 kelvins
   98 kelvins

The sun's surface measures approximately 5,800 kelvins. The sun is a star and the dominate force of the solar system around which the Earth and other planets orbit.

1. Mercury
   Benzene
2. Water
   Petroleum

Water is often known as the universal solvent because of its ability to dissolve many substances. Water is the main constituent of most living organisms.

1. Helium
   Magnesium
2. Hydrogen
   Neon

Hydrogen is the first element of the periodic table and is placed in group 1, but it is not considered an alkali metal. Of all the elements, hydrogen is the most abundant chemical element.

1. 212 degrees fahrenheit
   32 degrees Fahrenheit
2. 0 degrees Fahrenheit
   100 degrees Fahrenheit

The boiling point of a liquid substance is the temperature at which the pressure applied by the surroundings upon the liquid is matched by the pressure of the liquid vapor. When this pressure equalization occurs, liquid transforms to gas without a temperature increase.

1. Olfactory bulb
   Cerebellum
2. Hippocampus
   Basal ganglia

The three main parts of the brain are the cerebrum, cerebellum and the brain stem. The cerebrum is the largest part of the brain that contains the hippocampus, basal ganglia and olfactory bulb. The cerebellum is based just below and behind the cerebral hemispheres.

1. Arm
   Stage clips
2. Illuminator
   Nosepiece

Scientists use microscopes to examine small specimens that are difficult to analyze without the aid of an enlarged image, which microscopes provide. Two common types are the electron microscope and the light microscope.

1. Lithosphere
   Atmosphere
2. Heliosphere
   Rhizosphere

The term "lithosphere" is derived from the Greek word "lithos" meaning "rock." The lithosphere is the solid outer layer of the Earth which includes the Earth's crust.

1. Positive
   Neutral
2. Negative
   Ionic

Valence electrons are negatively charged particles that dwell in the outermost region of atoms. They are essential in the creation of chemical bonds.

1. Cilia
   Ribosomes
2. Mitochondrion
   Golgi apparatus

A mitochondrion is a specialized cell structure found in the cytoplasm of practically all cells with delineated nuclei. The energy that mitochondrion generate come in the form of adenosine triphosphate (ATP) molecules, which capture energy from food and distribute it as fuel for other cellular activities.

1. Nose
   Esophagus
2. Larynx
   Pharynx

The larynx is located in the neck of mammals, amphibians and reptiles. This vital structure protects from breathing in food particles. It's also used for creating sounds and breathing.

1. Ruska and Knoll
   Marie Curie
2. Ernst Mayr
   Louis Pasteur

Electron microscopes are powerful magnifying devices that achieve high resolution using an electron beam as opposed to a light ray. Many research laboratories use light microscopes to support electron microscopy.

1. Quantum theory
   Continental drift
2. Relativity
   Evolution

Continental drift recognizes complementary shapes of continents that appear as if they could fit together like pieces of a jigsaw puzzle. The concept of earth plate shifting, or tectonics, incorporates this theory.

1. Heart
   Wrist
2. Stomach
   Lung

The system of eight bones in the wrist is referred to as the carpal bones or the carpus. The wrist joint is also called the radiocarpal joint.

1. 5 million km
   225 million km
2. 967 million km
   12 million km

The distance between Earth and Mars varies depending on the position of these two planets which orbit the sun. Mars is the fourth planet from the sun, and Earth is the third planet from the sun. On average, Mars is 225 million km from Earth.

1. Magnesium
   Calcium
2. Hydrogen
   Barium

Hydrogen is a flammable, gaseous substance. It has a single positively charged proton in its nucleus and one negatively charged electron. Hydrogen is the lightest chemical element of the periodic table.

1. Thermometer
   Hydrometer
2. Altimeter
   Ammeter

Aside from measuring the altitude of the land surface, altimeters can determine the elevation of any object in relation to ground level or sea level. Radio altimeters measure the distance above water or land by recording the time it takes for sound waves to travel from an elevated object to the Earth and back. Pressure altimeters measure atmospheric pressure above sea level to determine altitude.

1. 0 degrees Fahrenheit
   100 degrees Fahrenheit
2. 32 degrees Fahrenheit
   212 degrees Fahrenheit

The freezing point is the temperature at which a liquid becomes a solid through increased pressure. The composition of the solid changes from that of its liquid state in a way that tends to lower the substance's freezing point.

1. Macula
   Choroid
2. Retina
   Iris

For most mammals, the iris controls the size and diameter of the pupil which also regulates the amount of light that reaches the retina. A person's eye color is determined by the iris color.

1. Ventricle
   Left atrium
2. Right atrium
   Esophagus

A heart ventricle is a muscular chamber that pumps blood out of the heart and into the circulatory system of an organism. Humans have two ventricles called the left ventricle and the right ventricle, which are the two lower chambers of the heart. The right ventricle supplies blood to the lungs, and the left ventricle pumps blood to the aorta, which then supplies blood to the body's tissues.

1. Photosynthesis
   Cytokinesis
2. Tropism
   Metamorphosis

Cytokinesis occurs when single-cell organisms reproduce to form two organisms and with embryos during development. Plant and animal matter also undergo cytokinesis during growth and repair processes.

1. Electroscope
   Galvanometer
2. Barometer
   Cyclotron

Barometers also measure altitude since atmospheric pressure changes depending on the distance below or above sea level. Aneroid and mercury are the two main types of barometers.

1. Arc
   Constellation
2. Configuration
   Ephemeris

Constellation patterns assist astronomers in locating certain stars or other celestial objects. Asterisms are the smaller groups of stars that comprise the larger constellation.

1. Calcium
   Kryptonite
2. Potassium
   Phosphorus

Potassium has an atomic number of 19 and is of the alkali metal group from the periodic table. Potassium chloride, potassium carbonate and potassium chlorate are common potassium salt compounds.

1. Group 5
   Group 7
2. Group 17
   Group 13

Halogens are six nonmetallic elements of Group 17 from the periodic table. The halogen elements are fluorine, chlorine, bromine, iodine, astatine and tennessine.

1. Flower
   Roots
2. Leaf
   Stem

The plant stem is primarily a structure of support that conducts and stores food for the plant. Some plants have underground stems which help the plant to survive adverse growing conditions.

1. Centrosome
   Vesicle
2. Nucleolus
   Lysosome

A lysosome is an organelle, or specialized cell structure, found in most eukaryotic cells. In addition to macromolecules, lysosomes digest microorganisms and damaged cell parts.

1. Accretion
   Acceleration
2. Momentum
   Oscillation

Acceleration describes bodies in motion that speed up and slow down. Both acceleration and velocity are vector quantities. Acceleration's quantity is expressed as the change in velocity divided by a time interval.

1. Asia
   North America
2. Antarctica
   Europe

North America is the third largest of the world's continents and it's where most of the dinosaur fossils have been found. Only solid and durable skeletons from past geological periods were preserved in the Earth's crust.

1. Reproduce
   Taste
2. Hear
   Smell

Antennae are sensory appendages that insects, crustaceans and certain arthropods use to taste, hear and smell. These animals feel along surfaces and filter air currents with these highly sensitive structures.

1. Neuron
   Photon
2. Platelet
   Electron

Neurons are the basic cells of the nervous system. A nerve cell has one nucleus and carries impulses along fibers called dendrites.

1. 45
   10
2. 4
   5

Beryllium is a member of the alkaline-earth metal group from the periodic table. This rare element is used in the production of nuclear and aerospace constituents.

1. Liver
   Heart
2. Brain
   Small intestine

The pituitary gland is a gland of the endocrine system located on the underside of the brain. This "master gland" discharges hormones directly into the bloodstream.

1. Ethmoid
   Femur
2. Palatine
   Patella

The femur bone is also called the upper bone and it forms joints at the knee and the hip. Gluteus medius and maximus muscles are attached to the upper thigh.

1. Chitin
   Melanin
2. Flouride
   Collagen

Chitin is a polysaccharide that contains glucosamine, which is a monosaccharide and amino sugar. Chitin is abundant in the exoskeletons of animals and is useful for protecting soft tissues.

1. Cretaceous
   Quaternary
2. Triassic
   Cambrian

Many lines of dinosaurs began to die off during the Cretaceous period. The Cretaceous, Jurassic and Triassic periods are part of the Mesozoic era.