Biology…What is it?
Biology is the study of life.
SO….What does it
mean to be living?
Characteristics of Life
To be considered living, an
organism must…..
1. Be based on a universal
genetic code.
– DNA
2.
Grow and develop
Characteristics of Life
3.
Be able to Reproduce
-Asexually
-Sexually
4.
Use materials and energy
-Metabolism
Characteristics of Life
5.
Be able to respond to
their environment
-stimulus
response
Humans:
Plants:
Characteristics of Life
6.
Maintain stable internal
environment
-Homeostasis
Characteristics of Life
7.
Change over time, as a group.
-Evolution
8. Made of units called Cells
-Unicellular
-Multicellular
Cell Theory
Matthias
Schleiden
concluded that all
plants are made of
cells (1838)
Theodore
Schwann
concluded that all
animals are made
of cells (1839)
Rudolf Virchow
concluded that all
cells came from
pre-existing cells
(1855)
Cell Theory
• all living things are made up of cells
• cells are the basic units of structure and function in
an organism
• new cells are produced from existing cells
Levels of Organization
Level
Function
Organism
Single living thing
Organ System
Different organs function
together
Nervous
System
Organ
Different tissues function
together
Brain
Tissues
Similar cells function
together
Cells
Smallest unit of life
Molecules
Smallest unit of a substance
with the same properties
Atom
Smallest unit of matter
Example
Human
Nervous
Tissue
Nerve
Cell
Protein
Carbon
Viruses…Living or not?
Viruses
comewe
in many
shapes and
 Now that
knowdifferent
what makes
they
cause many
different
something
living,
let’sdiseases
look atbut,
a they
allvirus.
have something in common….
Viruses and Living Cells
Characteristic
Virus
Cell
Structure
Genetic material
surrounded by a
protein capsid
Cell membrane,
cytoplasm; genetic
material, ribosomes
Reproduction
Only within a host cell
Yes, sexually and
asexually
Genetic Code
DNA or RNA
DNA
Growth and
Development
No
Yes
Obtain and Use
Energy
No
Yes
Response to
Environment
No
Yes
Evolve
Yes
Yes
Homeostasis
No
Yes
Verdict?

No, Viruses are not considered a
living thing because they do not
meet all of the living
characteristics.