Classifying LifeHow do we identify something as living?

Biology, defined

Biology is defined as “the study of the living world”.

One of the most important base concepts of biology is deciding what is living, and what is not.

So, what is “alive”?

Biologists agree that something is alive if it shows several common traits. Anything that is alive is called an organism.

All living organisms have all of these traits. There may be things that show some of these traits, but they are NOT alive, because they do not show all those traits.

Made up of cells

If something is alive, it is made up of cells.

Cells are considered the smallest living units of matter.

Mad

e u

p o

f cells

Unice

llula

rM

ultice

llula

r

Unicellular organisms are made up of only ONE cell.

“Uni-” means one

Multicellular organisms are made up of MORE than one cell.

“Multi-” means many or several

Reproduction

All living organisms can reproduce.

This means that living organisms can create new organisms.

Rep

rod

uctio

n

Ase

xual R

epro

ductio

nSexual R

epro

ductio

n

Asexual reproduction only requires ONE parent.

Includes fission and budding.

Sexual reproduction requires TWO parents.

Two different cells combine to form a new organism.

Uses a genetic code

All living organisms use a genetic code.

This code is the reason why many traits can be inherited, or passed on.

Growth and development

All living organisms grow. Many multicellular organisms

develop special tissues. However, unicellular organisms do NOT

exhibit development.

Use materials and energy

All living organisms require materials and energy.

This is because both materials and energy are required for growth and development!

Metabolism: the building or breaking of materials to support life.

Respond to the environment

All living organisms can sense and respond to changes in the environment.

These changes are called stimuli.

Stimuli can be external or internal.

Maintain internal balance

Living organisms have to maintain internal conditions to live.

We call these conditions homeostasis.

What is homeostasis?

Homeostasis is the state of balance that an organism can exist at.

For instance, we must maintain our water content to live.› Too much or too little water and we die!

We also have to maintain our internal temperature, or we will die!