Chapter 2 – Part 2
Cell Theory
Cell Types
The Cell Theory
1. All living things
are made of one
or more cells
2. Cells are the
basic units of
structure and
function in all
organisms
3. All cells arise
from preexisting
cells
Cell Size
There are many types of cells in our
body, each with a different shape
and function
 Some cells, like human egg cells,
can be seen with the naked eye
 Other cells are very small, like sperm
cells, and need a microscope to be
seen

Cell Size
Cell Size

Humans have trillions of cells in the
body

Size of cells range from 5µm to 20µm
in size

http://learn.genetics.utah.edu/cont
ent/begin/cells/scale/
Cell Size Continued…
Small cells function more efficiently
than large cells
 If surface area to volume ratio is too
low, substances cannot enter and
leave the cell well enough to meet
the cell’s needs
 Small cells have high surface area to
volume ratio

Surface Area-to-Volume
Types of Cells

Prokaryote – “Before nuclei”

Eukaryote – “True nuclei”
Prokaryotes

Consists of unicellular organisms
Ex: Bacteria and archea

Can live in many environments
Ex: extreme temperatures, pH,
and radiation
Prokaryotes

Some can make their
own food

Grow and divide
rapidly using asexual
reproduction
Prokaryote Cells
-Lacks a nucleus and most organelles
-Much smaller than a eukaryote cell
-One single circular strand of DNA
found in the cytoplasm
Prokaryote Cells Continued…
Plasmid: Circular
strand of DNA
Flagella: Aids in
movement
Pili: Helps bacteria
attach to surfaces
Capsule: a
polysaccharide
barrier used for
protection
Eukaryotes
Consists of unicellular and
multicellular organisms
Ex: Plants, animals, fungi, protists…
 Organisms can asexually and
sexually reproduce

Eukaryote Cells

Contains a nucleus with DNA and
membrane-bound organelles

Larger, more complex cells

May have evolved from a
prokaryotic cell
Types of Eukaryote Cells
Plant Cells and Animal Cells