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7th Grade Science Benchmark Study Guide (cont.)
End of 4th Quarter
Evolution and its Evidence (cont.)
 Methods used to divide geologic time into units include mass extinctions, major changes in life-forms, and index
fossils.
 Common explanations for mass extinctions include asteroid impacts, volcanic activity and climate changes.
Volcanic activity can include explosive eruptions, basalt flows, and volcanic haze. Climate changes include
global warming and global cooling.
 Mass extinctions occur at the end of a geologic era.
Physical Principles in Living Systems
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Relaxation is the lengthening of inactive muscles or muscle fibers. During relaxation, the muscle filaments
move away from each other.
The types of joints in the human body include: saddle joints, immovable joints, hinge joints, ball-and-socket
joints, gliding joints, and pivot joints.
The ball-and-socket joints allow for the greatest range in motion.
A lever is a simple machine made of anything rigid that pivots around a fixed point. There are first-class,
second-class, and third-class levers.
A first-class lever common object is a pair of scissors and in the human body the neck holding the weight of
your head. A second-class lever common object is a rolling suitcase and in the human body your calf holding
up the weight of your body. A third-class lever common object is a rake/shovel and in the human body lifting an
object in your hand.
A heart attack is the result of insufficient blood flow to the heart, often resulting in tissue damage or the heart
stopping beating. A heart attack occurs when coronary arteries cannot supply enough blood to the heart.
Valves prevent the backflow of blood.
The electromagnetic spectrum is the entire range of electromagnetic waves of different wavelengths and
frequencies. Visible light is a narrow band of wavelengths in the electromagnetic spectrum. Radio waves,
microwaves, infrared, visible light, ultraviolet light, x rays, and gamma rays all make up the spectrum.
Refraction occurs when a light ray changes direction as it passes from one material to another. An example of
this would be when you look at an object at the bottom of a pool of water.
The law of reflection states that when a light ray is reflected from a surface, the angle of incidence equals the
angle of reflection.
Prisms separate white light into the various colors of the visible spectrum by refracting light waves into different
wavelengths.
A hand lens produces an enlarged image of an object when the lens is less than one focal length from the
object.
Light rays travel in straight lines unless the change from one medium into another, such as from air to water.
Light waves change direction, or refract, whenever they change speed in moving from one medium into
another. When the speed of the light wave doesn’t change, light rays continue to travel in straight lines.
The pupil is the dark opening into the interior of the eye through which light enters.
The tympanic membrane is a thin layer of skin that separates the outer and middle ear. It is commonly called
the eardrum. This thin layer of skin vibrates when sound waves hit it.