Chapter 13 ReviewSections 1 and 4

Levels of OrganizationHuman body consists of Cells- smallest unitTissuesOrgansOrgan systems- largest unit

CellsThe cell is the basic unit of

structure and functionComplex organisms are made of

many cellsHuman body contains about 100

trillion cellsNucleus directs the cell’s activitiesCytoplasm is made of clear,

jellylike substance containing many cell structures called organelles (the material within a cell apart from the nucleus)

Cheek Cells

TissueTissue- a group of specialized cells that

perform the same function4 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 SystemsAn 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 SystemsEach organ in your body is part of an organ system, which is

a group of organs that work together to perform a major function.

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

Reproductive System- male and female systems that produce sex cells

HomeostasisThe different systems work together and depend on

each otherHomeostasis 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 BodyForce-is a push or a pull on an object as

described by 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 DistanceMachine- a device that allows you to do work in

a way that is easier or more effective

LeverLever- a rigid rod that is free to rotate around a fixed

pivot pointFulcrum- a fixed point that a lever rotates around

(the pivot point of a lever)

Effort Force

Resistance Force

Fulcrum

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)

Force and WorkA 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 downResistance force- the force that a lever exerts

on an objectResistance distance- the distance the lever

pushes up on an objectEffort force

Resistance force

Mechanical AdvantageThe number of times a lever increases a force

exerted on itComparing the effort force to the resistance

force you can find the advantageMechanical Advantage= Resistance Force

Effort Force

The Law of the LeverLever may be balanced when the effort force

and resistance force are differentEffort arm- the distance from the fulcrum to

the effort forceResistance arm- the distance from the

fulcrum to the resistance force

LeversLevers 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 BodyMost 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 third-class lever

How does a lever make work easier?