THE CELL THEORY

SOME RANDOM CELL FACTS

• The average human being is composed of around 37 Trillion individual

cells!!!

• If a red blood cell is 0.006mm wide, how many would it take to fill the

1mm space on a ruler?

• About 167!

WOW!!!

DISCOVERY OF CELLS

• 1665- English Scientist, Robert Hooke, discovered cells

while looking at a thin slice of cork.

• He described the cells as tiny boxes or a honeycomb

• He thought that cells only existed in plants and fungi

Robert Hooke’s microscope

and image of the plant cells he

saw.

ANTON VAN LEUWENHOEK

• 1673- Used a handmade microscope to observe pond scum &

discovered single-celled organisms

• He called them “animalcules” which

meant “little animals.”

• Was the first person to see bacteria

• Discovered that baker’s yeast is a

Single-celled organism.

• He also observed blood cells from fish, birds, frogs, dogs, and humans

and discovered they are not all the same shape.

• Therefore, it was known that cells are found in animals as well as

plants

150-200 YEAR GAP???

• Between the Hooke/Leuwenhoek discoveries and the mid 19th century, very little cell advancements were made.

• “Spontaneous Generation” was a widely accepted theory.

• Examples:

-fleas from dust

-maggots from rotting meat

19TH CENTURY ADVANCEMENT

Much doubt existed around Spontaneous Generation

Conclusively disproved by Fransico Redi and Louis Pasteur

?

DEVELOPMENT OF CELL THEORY

• 1838- German Botanist, Matthias Schleiden, concluded that all plant parts are made of cells

• 1839- German physiologist, Theodor Schwann, who was a close friend of Schleiden, stated that all animal tissues are composed of cells.

• Schwann wrote the first two parts of the CELL THEORY: 1) All organisms are made of

one or more cells. 2) The cell is the basic

unit of all living things.

DEVELOPMENT OF CELL THEORY

• 1858- Rudolf Virchow, German physician, after

extensive study of cellular pathology, concluded

that all cells must arise from preexisting cells. This

became the 3rd part of the CELL THEORY.

THE CELL THEORY COMPLETE

• The 3 Basic Components of the Cell Theory were

now complete:

• 1. All organisms are composed of one or more cells.

(Schleiden & Schwann)(1838-39)

• 2. The cell is the basic unit of life in all living things.

(Schleiden & Schwann)(1838-39)

• 3. All cells are produced by the division of preexisting

cells. (Virchow)(1858)

HOW HAS THE CELL THEORY BEEN USED?

• The basic discovered truths about cells, listed in

the Cell Theory, are the basis for things such as:

– Disease/Health/Medical Research and Cures(AIDS, Cancer,

Vaccines, Cloning, Stem Cell Research, etc.)

CELL SIZE

• Most cells are too small to see

• Some cells you can see with

the naked eye: egg yolk,

• Caulerpa is a type of algae that

is single-celled but has many

nuclei.

WHY ARE CELLS SO SMALL?

• Cells take in food and get rid of wastes through the cell membrane.

• As a cell gets larger, it needs more nutrients and produces more

waste (just like we do).

• A cell’s volume grows faster than its surface area. Therefore as a cell

gets larger, its surface membrane can not take in enough nutrients or

let out enough wastes.

• The formula for calculating the cells’ surface area to volume ratio is:

surface area-to-volume ratio= surface area

volume

Math hint: surface are of a cube = number of sides x area of one side

Volume of a cube = LWH

PRACTICE • What is the surface area – to – volume ratio of a cube whose sides

measure 3cm?

Step 1: Surface area of the cube = 6 x (3cm x 3cm)

= 6 x 9cm ²

= 54 cm ²

Step 2: Volume = 3cm x 3cm x 3cm = 9cm ² x 3cm

= 27cm³

Step 3: Surface Area – to – volume ratio = 54/27 = 2 or 2:1

PRACTICE

• What is the surface area – to – volume ratio of a cube whose sides

measure 10cm?

Step 1: Surface area of the cube = 6 x (10cm x 10cm)

= 6 x 100cm ²

= 600 cm ²

Step 2: Volume = 10cm x 10cm x 10cm = 100cm ² x 10cm

= 1000cm³

Step 3: Surface Area – to – volume ratio = 600/1000 = .6

Was this cube bigger or smaller than the first cube?

BIGGER

What the ratio greater or less than the 1st ratio of 2?

LESS THAN

THEREFORE,

• As the cell gets BIGGER– The ratio gets SMALLER

The cell membrane can’t keep up.

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