Hierarchy and Characteristics of Life

Organism

a single complete individual

Organ system

group of organs with a unique collective function like circulation, respiration, digestion

Organ

structure composed of two or more tissue types that work together to carry out a function

Tissue

similar cells and cell products forming a discrete region of an organ and performs a specific function

Cell

smallest unit to carry out all basic functions of life

Organelle

structure within a cell that carry out a function

Molecule

particle composed of two or more atoms

macromolecules

largest molecules (proteins, fats, DNA)

Atom

smallest particle with unique chemical identity

Reductionism

theory that large, complex systems can be understood by studying their simpler components

Holism

“emergent properties” occur as we ascend the levels of organization; these cannot be predicted from the properties of individual parts alone

Organization

living things exhibit a higher level of organization than nonliving things

Cellular composition

living matter is always compartmentalized into one or more cells

Metabolism

the sum of internal chemical change

Responsiveness

ability to sense and react to changes in environment

Movement

movement of entire organism or of substances within the organism

Homeostasis

maintaining relatively stable internal conditions

Development

change in form or function over time

Differentiation

transformation of unspecialized cells into cells with a committed task

Growth

increase in size; occurs through chemical change

Reproduction

organisms produce copies of themselves; pass genes to offsprings

Evolution

genetic change from generation to generation; occurs due to mutations

Homeostasis

the ability to detect change, activate mechanisms that oppose it, and thereby maintain relatively stable internal conditions

Walter Cannon

(1871-1925)
created the term homeostasis to describe the body’s ability to stay balanced
explained fight or flight response
ex: the body reacts to stress (like danger) by speeding up the heart, raising blood pressure, and preparing for action.

Claude Bernard

(1813-1878)
Father of Modern Physiology
discovered that the body keeps its internal environment stable, which is necessary for survival — even when the outside world changes ==> Homeostasis

Negative feedback

the body senses a change and negates it

dynamic equilibrium within a limited range around a set point 

Positive feedback

leads to greater change in the same direction

ex: childbirth, blood clotting, protein digestion, and generation of nerve signals 

Loss of homeostatic control =>

death or illness

Receptor

structure that senses change in the body

Integrating (control) center

control center that processes the sensory information, “makes a decision,” and directs the response

Effector

cell or organ that carries out the final corrective action to restore homeostasis

Gradient

difference in chemical concentration, charge, temperature, or pressure between two points 

Pressure Gradient

Concentration Gradient

Electrical Gradient

Thermal Gradient