Homeostasis and Feedback Mechanisms in Biology: Key Concepts and Examples

Homeostasis

stability of the internal environment and the mechanisms that maintain the stability

Is the external environment always changing?

yes

dynamic equilibrium

is maintained where the rate of loss balances out with the rate of gain

Organisms not ony detect but _______

respond to stimuli

How is homeostasis maintained?

through regulation at the organ system level all the way down to the cellular level

feedback mechanisms

evolved to help maintain homeostasis in organisms

feedback mechanisms are _____

loops

these loops us the output of a system to signal a change in ___________

input so that a system response can be stabilized or amplified

+ Feedback Mechanisms _______

Amplification

In a _______ feedback loop, the output of a system ________ the response

Positive; intensifies

What are examples of positive feedback mechanisms

Human Child birth; fruit ripeing

negative feedback mechanisms

stablization

In a ________ feedback loop the output of a system causes a counter response to return to a set point

negative

Examples of negative feedback mechanisms

Human Body temperature; Water concentration

All feedback loops have what?

receptors, stimulus, effector, and response

receptor

sensory organ that receives the stimulus

Stimulus

an action that evokes a response

effector

an organ that does the response

response

the effect, caused by the stimulus

When a mistake happens the feedback loop______

homeostasis

Living systems depend on reactions that occur spontaneously but___________

at a very slow rates

Catalyst

substances that speed up the reactions without being permanently altered

Most biological catalysts are proteins or _______

enzymes

what suffix does enzymes end in

-ase

Every step in a metabolic pathway is ______________

catalyzed by a specific enzyme

Cells can regulate metabolism by controllling the ________ of an enzyme

amount

Cells can turn synthesis of enzymes _______ or _______

on : off

feedback inhibition

The output of a process is used as an input to control the behavior of the overall process itself, usually leading to inhibition of the process.

The _______ of an enzyme can also be regulated.

activity

Chemical inhibitors

can bind to enzymes and slow down reaction rates

enviromental conditions

play a role in enzyme function too.

pH and temperature changes can lead to _________

denaturation

Cells also maintain homeostasis with highly__________

regulated signaling and transport mechanisms

Remember, the cell membrane consist of a _______________ phospholipid bilayer to control what goes in and out

selectively permeable

Transport can be ______--, requiring _______ no extra energy as molecules move down the concentration gradient, or ______ requiring ________- energy to move molecules _________- the gradient

passive: no : active : extra : against

Simple diffusion

the spreading out of molecules across a membrane until equilibrium is reached

a net movement from regions ______________

of greater concentration to regions of lesser concentration

faciliated diffusion

A transport protein acts to help the diffusion of molecules that normally couldn't pass through the cell membrane (large and polar molecules)

transport protein can act as a ___________ to allow specific molecules through.

channel

Transport proteins can also act as _______that bind to substances to carry them across the membrane

carriers

Osmosis

the simple diffusion of water across the cell membrane

Water moves from areas of high-water concentration to _________ until equilibrium.

areas of low water concentration

hypertonic solution

water is lower than the cells cytoplasm. (high solute and low H20)

Net movement of water _______ of cell

The cell ______

out: shrivels

hypotonic solution

water is higher than the cells cytoplasm (low solute high H20)

net movement of water ________

cell ___

into a cell: Swells

Isotonic Solutions

water to cells cytoplasm

cell______

stays the same

Active transport

up

Molecular Pumps

When a cell uses energy to pump molecules across the membrane, against the gradient, through a protein channel

Examples of vesicles

endocytosis : exocytosis

endocytosis

uses vesicles to move large particles into the cell

exocytosis

uses vesicles to export materials out of the cell

cell signaling

allows cells to process information from their environment (stimuli) and communicate to other cells.

Signals can be ________

physical stimuli and chemical stimuli

Ligands

molecules that bind to other molecules (receptor proteins) for signaling purposes

signal transduction pathway

a sequence of events initiated by a signal that leads to a cellular response

What are the chemical signals

Autocrine, paracrine, juxtracrine, hormones

Autocrine

signals "self" affects the same cell that releases them

Paracrine

signals diffuse to nearby cells

Juxtacrine

signals: require direct contact between the signaling cell and the receiving cell

Hormones

signal travels to distant cells

hormones known as

endocrine signaling

Receptors

protein where the signal is received on the target cell

intracellular receptors

(located inside a cell) Ligands for these signals are small and/or nonpolar so they cam easily diffuse across the membrane to reach these receptors

Membrane receptors

(located on surface of the cell) Ligands for these signals are large and/or polar that cannot diffuse through the cell membrane

Receptors are ________ and 3-D

highly specific

When a ligand binds to receptor protein, the bond is _______ (not strong) and is ________

noncovalent: reversible

inhibitors

can block the normal ligand to prevent communication