Sections 1 and 4
Levels of Organization
Human body consists of
 Cells- smallest unit
 Tissues
 Organs
 Organ systems- largest unit
Cells
 The cell is the basic unit of structure and
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function
Complex organisms are made of many
cells
Human body contains about 100 trillion
cells
Nucleus directs the cell’s activities
Cytoplasm is made of clear, jellylike
substance containing many cell
structures called organelles (the
material within a cell apart from the
nucleus)
Cheek Cells
Tissue
 Tissue- a group of specialized cells that
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perform the same function
4 basic types of tissues in the human
body: muscle tissue, nervous tissue,
connective tissue, and epithelial tissue
Muscle tissue- contract or shorten to
make part of your body move
Nervous tissue- carries electrical
messages back and forth between the
brain and other parts of the body
Connective tissue- provides support for
your body and connects all its parts
Epithelial tissue- covers the surfaces of
your body, inside and out (skin and lining
of the digestive system)
Your skin is
epithelial tissue
Organs and Organ Systems
 An organ is a structure that is composed of different
kinds of tissue and does a specific job (like a stomach,
heart, brain, lungs)
 Organ System- is a group of organs that work together
to perform a major function
 Human body has 11 organ systems
Organs and Organ Systems
 Each organ in your body is part of an organ system, which is a
group of organs that work together to perform a major
function.
Reproductive System- male and female systems
that produce sex cells
Integumentary System- hair,
nails, skin- the body’s
covering
Immune System- protects your body
from disease
•Pathogens- bacteria or viruses
•Antibodies- proteins that destroy
pathogens
•Immunity- the ability to destroy
pathogens before they can cause
disease
Homeostasis
 The different systems work together and depend on
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each other
Homeostasis is the process by which an organism’s
internal environment is kept stable in spite of changes
in the external environment. (Key concept)
No matter what the temperature around you your
temperature stays the same (except when you are sick
but it goes back to normal eventually)
Our body maintains homeostasis by sweating when we
are hot or shivering when we are cold
Stress- the reaction of your body to potentially
threatening, challenging, or disturbing events
Homeostasis is restored after the stress is gone
Machines and the Body
 Force-is a push or a pull on an object as described by
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its strength (or magnitude) and direction in which it
acts
Standard unit for magnitude of force is newton (N)
Arrow represents the direction and strength of the
force
Work- when you exert a force on an object that causes
the object to move some distance in the same direction
as the force
Work= Force x Distance
Machine- a device that allows you to do work in a way
that is easier or more effective
Lever
 Lever- a rigid rod that is free to rotate around a fixed pivot
point
 Fulcrum- a fixed point that a lever rotates around (the pivot
point of a lever)
A lever makes work easier
by changing the amount
of force exerted, the
distance over which the
force is exerted, or the
direction of the force.
(key concept)
Effort Force
Resistance Force
Fulcrum
Force and Work
 A lever is a simple machine that makes
lifting heavy objects easier.
 Effort force- the force that is exerted on the lever (the
force applied to a machine)
 Effort distance- the distance pushed down
 Resistance force- the force that a lever exerts on an
object
 Resistance distance- the distance the lever pushes up
on an object
Resistance force
Effort force
Mechanical Advantage
 The number of times a lever increases a force exerted
on it
 Comparing the effort force to the resistance force you
can find the advantage
 Mechanical Advantage= Resistance Force
Effort Force
The Law of the Lever
 Lever may be balanced when the effort force and
resistance force are different
 Effort arm- the distance from the fulcrum to the effort
force
 Resistance arm- the distance from the fulcrum to the
resistance force
Levers
 Levers are classified according to the location of the
fulcrum relative to the input and output forces.
*hint- you might want to draw a stick figure similar to the third-class
lever in figure 25 for the test
Simple Machines in the Body
 Most of the machines in your body are levers that
consist of bones and muscles.
 Example of a fulcrum for a first-class lever in your body
is the joint at the top of your neck
 Example of a fulcrum for a second-class lever is the
ball of your foot
 Examples of fulcrums for third-class levers are the
thigh joint, wrist joint, shoulder joint, knee joint,
elbow joint
 Most common type of lever in your body is the thirdclass lever
How does a lever make
work easier?