Cells are the basic unit of life.

What are Cells?

History of Cells & Cell Theory

The cell theory grew from the work and

research of many scientists.

Who Was Involved?

Hooke's Microscope

First to View Cells • In 1665, Robert

Hooke was the first

to use a light

microscope to

examine a thin slice

of cork (dead plant

tissue)

• What he saw looked

like small boxes Hooke's drawing of Cork Cells

First to View Cells

• Hooke is responsible

for naming cells.

• Hooke called them

“CELLS” because

they looked like the

small rooms that

monks lived in

(called cells).

• Dutch microscope maker.

• One of the first people to

use a microscope to study

living things in nature &

was the first to view

microorganisms .

• Leeuwenhoek used a

simple, handheld

microscope to view pond

water & scrapings from

his teeth.

• Observed living cells, which

he called “animalcules.”

Anton van Leeuwenhoek (LAY-vuhn-hook)

Beginning of the Cell Theory

• In 1838, a German botanist named Matthias Schleiden concluded that all plants were made of cells

• Schleiden is a cofounder of the cell theory

Beginning of the Cell Theory

• In 1839, a German zoologist named Theodore Schwann concluded that all animals were made of cells.

• Schwann also cofounded the cell theory.

Beginning of the Cell Theory

• In 1855, a German

medical doctor named

Rudolph Virchow

observed, under the

microscope, cells dividing.

• He reasoned that all

cells come from other

preexisting cells by cell

division.

Three Principles of Cell Theory

1. All living things are made

of one or more cells.

2. Cells are the basic unit of

structure and function in

an organism (they are the

smallest unit that can

perform life functions).

3. Cells come from the

reproduction of existing

cells (cell division).

Why is the Cell Theory called a Theory and not a Fact?

Cell Theory

All organisms are made of one or more cells.

• Some organisms are made up of one cell or

unicellular

• Others are multicellular or made up of many cells

Principle #1

The cell is the most basic unit of life.

Principle #2

All existing cells are produced by other living cells.

Principle #3

1. They are flexible in function

• Become different types of tissues and material

• Ex: fetal development

2. They can let things in and out

• Communication

• Getting nutrients, energy

3. They have their own command center

• DNA tells cells what to do

4. They have the ability to divide and make more

• Ex: growth & reproduction

Characteristics of Cells

Cells are small so they

can exchange materials

with their surroundings.

Surface area relative to the volume decreases as

size of cell increases.

- limits the size of cells

Cells need a large surface area to absorb enough

nutrients.

Cell Size

Surface area = 96 (only 4 times greater)

Volume = 8

Factors Affecting Cell Size

• Volume of a cell is

determined by

multiplying length

times width times

height (L x W x H).

• Surface area (cell

membrane) is the total

area (L x W) of all sides

(the entire surface of

the object).

• Therefore, Volume

increases FASTER

than the surface area.

4

4

4

2 2

2

Surface area = 24

Volume = 64 (8 times greater)

• When the surface area is no longer

great enough to get rid of all the

wastes and to get in enough food

and water, then the cell must divide.

• Therefore, all of the cells in an

organism are close in size.

Cell Size

Cell Size

Question: Are the cells in

an elephant

bigger,

smaller, or

about the same

size as those in

a mouse?

Cell Size Answer:

The elephant’s

cells are about

the same size

as those of the

mouse, but the

elephant has

MANY MORE

cells than the

mouse.

Sizes of living things

The Cellular Level of Organization

Living things are constructed of cells.

Living things may be unicellular or multicellular.

Cell structure is diverse but all cells share

common characteristics.

Types of Cells

Prokaryote: Lacking a true

nucleus Bacteria

Eukaryote: With a nucleus

bounded by a membrane

Plant

Animal

Fungi

Protists

Types of Cells

Cell Size and Types

• Cells, the basic units of organisms, can only

be observed under microscope

• Three Basic types of cells include:

Animal Cell Plant Cell Bacterial Cell

_________ > _____________ > ___________

Which Cell Type is Larger?

Plant cell Animal cell bacteria

Number of Cells Although ALL living things are made of

cells, organisms may be:

• Unicellular – composed of one cell

• Multicellular- composed of many cells that may

organize into tissues, etc.

How Big is a Micron ( µ ) ?

1 cm = 10,000 microns 1” = 25,000 microns

Cell Features ALL cells have these parts:

• Ribosomes – make protein for use by the organism

• Cytoplasm – fluid material within cell

• DNA – genetic material

• Cytoskeleton – internal framework of cell

• Cell Membrane – outer boundary, some things can cross the cell membrane

Prokaryotes – The first Cells

• Cells that lack a nucleus or membrane-

bound organelles

• Includes bacteria

• Simplest type of cell

• Single, circular chromosome

Eukaryotes

• Cells that have a nucleus and membrane-bound intracellular organelles

• Includes protists, fungi, plants, and animals

• More complex type of cells

Organelles With DNA • Mitochondria and chloroplasts have their own DNA (separate

from the nucleus)

• This supports the ENDOSYMBIOSIS THEORY which states that eukaryotic cells evolved when prokaryote cells engulfed or absorbed other cells.