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 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 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.

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

Homeostasis The different systems work together and depend on 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 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) 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 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 Effort force Resistance 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 third- class lever

How does a lever make work easier?