S

Requirements for Life&

Homeostasis

What do you think?

In the space provided on your paper: Make a list of the requirements for something to be

considered living.

Share your list with a partner. Add what they have that you didn’t to your list. Star the new additions to your list.

Create a new life form

Before we review the requirements for life, create a new life form with a group What will it need to be considered living? What will it need to stay alive?

Draw a picture of your life form and its requirements for life on a white board

Necessary Life Functions

Maintain boundaries

Movement Locomotion Movement of substances

Responsiveness Ability to sense changes and react

Digestion Breakdown and absorption of nutrients

Necessary Life Functions

Metabolism—chemical reactions within the body Break down complex molecules into smaller ones Build larger molecules from smaller ones Produces energy Regulated by hormones

Excretion Eliminates waste from metabolic reactions Wastes may be removed in urine or feces

Necessary Life Functions

Reproduction Occurs on cellular level or organismal level Produces future generation

Growth Increases cell size and number of cells

Survival Needs

Nutrients Chemicals for energy and cell building Includes carbohydrates, proteins, lipids, vitamins, and

minerals

Oxygen Required for chemical reactions

Survival Needs

Water 60 to 80 percent of body weight Most abundant chemical in the human body Provides for metabolic reaction

Stable body temperature 37°C (98°F)

Atmospheric pressure Must be appropriate for gas exchange

NutrientsHeart

Interstitial fluid

Blood

Food

Digestive systemTakes in nutrients, breaks them down, and eliminates unabsorbed matter (feces)

Respiratory systemTakes in oxygen and eliminates carbon dioxide

Cardiovascular systemVia the blood, distributes oxygen and nutrients to all body cells and delivers wastes and carbondioxide to disposal organs

Urinary system Eliminates nitrogen-containing wastes and excess ions

Feces Urine

Nutrients and wastes pass between blood and cells via the interstitial fluid

O2

CO2

Integumentary systemProtects the body as a whole from the external environment

CO2O2

Figure 1.3

Homeostasis

Homeostasis—maintenance of a stable internal environment A dynamic state of equilibrium Necessary for normal body functioning and to sustain life

Homeostatic imbalance A disturbance in homeostasis resulting in disease

Figure 1.4

Input: Information sent along afferent pathway to control center.

Receptor

ControlCenter

Effector Receptor detects change.

Afferentpathway

Efferentpathway

IMBALANCE

VARIABLE (in homeostasis)

Stimulusproduceschange invariable.

Output: Information sent along efferent pathway to effector.

Responseof effector feedsback to reducethe effect ofstimulus andreturns variableto homeostatic level.

1

2

3 4

5

IMBALANCE

Figure 1.4, step 1

IMBALANCE

VARIABLE (in homeostasis)

Stimulusproduceschange invariable.

1

IMBALANCE

Figure 1.4, step 2

Receptor Receptor detects change.

IMBALANCE Stimulusproduceschange invariable.

1

IMBALANCE

2

VARIABLE (in homeostasis)

Figure 1.4, step 3

Input: Information sent along afferent pathway to control center.

Receptor

ControlCenter

Receptor detects change.

Afferentpathway

IMBALANCE

VARIABLE (in homeostasis)

Stimulusproduceschange invariable.

1

3

IMBALANCE

2

Figure 1.4, step 4

Input: Information sent along afferent pathway to control center.

Receptor

ControlCenter

Effector Receptor detects change.

Afferentpathway

Efferentpathway

IMBALANCE

VARIABLE (in homeostasis)

Stimulusproduceschange invariable.

Output: Information sent along efferent pathway to effector.

1

3 4

IMBALANCE

2

Figure 1.4, step 5

Input: Information sent along afferent pathway to control center.

Receptor

ControlCenter

Effector Receptor detects change.

Afferentpathway

Efferentpathway

IMBALANCE

VARIABLE (in homeostasis)

Stimulusproduceschange invariable.

Output: Information sent along efferent pathway to effector.

Responseof effector feedsback to reducethe effect ofstimulus andreturns variableto homeostatic level.

1

3 4

5

IMBALANCE

2

Maintaining Homeostasis

The body communicates through neural and hormonal control systems Receptor

Responds to changes in the environment (stimuli) Sends information to control center

Maintaining Homeostasis

Control center Determines set point Analyzes information Determines appropriate response

Effector Provides a means for response to the stimulus

Feedback Mechanisms

Negative feedback Includes most homeostatic control mechanisms Shuts off the original stimulus, or reduces its intensity Works like a household thermostat

Feedback Mechanisms

Positive feedback Increases the original stimulus to push the variable

farther In the body this only occurs in blood clotting and during

the birth of a baby