The History of the Cell TheoryThe History of the Cell Theory• Before microscopes were invented, people believed that diseases were caused by curses and supernatural spirits.

• Microscopes enabled scientists to view and study cells, the basic units of living organisms.

• As scientists began using microscopes, they quickly realized they were entering a new world–one of microorganisms.

• The first person to record looking at water under a microscope was Anton van Leeuwenhoek.

• The microscope van Leeuwenhoek used is considered a simple light microscope because it contained one lens and used natural light to view objects.

Development of Light MicroscopesDevelopment of Light Microscopes

Compound light microscopes use a series of lenses to magnify objects in steps.

These microscopes can magnify objects up to 1,500 times.

Development of Light MicroscopesDevelopment of Light Microscopes

• Robert Hooke was an English scientist who lived at the same time as van Leeuwenhock.

The Cell TheoryThe Cell Theory

• Hooke used a compound light microscope to study cork, the dead cells of oak bark.

•He saw empty boxes that he called cells.

• Cells are the basic building blocks of all living things.

• In 1830, two German scientist, Matthias Schleiden and Theodor Schwann viewed different organisms with microscopes.– Schleiden studied plants– Schwann studied animals

• The observations of these two men made summarized into the cell theory.

Rudolf Virchow

• in 1855 proposed that "All living cells arise from pre-existing cells". ("Omnis cellula e cellula")

The cell theory is made up of three main ideas:

All cells come from preexisting cells.

The cell is the basic unit of organization of organisms.

All organisms are composed of one or more cells.

• The electron microscope was invented in the 1940s.

• This microscope uses a beam of electrons to magnify structures up to 500 000 times their actual size.

Development of Electron MicroscopesDevelopment of Electron Microscopes

There are two basic types of electron microscopes.

• The scanning electron microscope scans the surface of cells to learn their three dimensional shape.

Development of Electron MicroscopesDevelopment of Electron Microscopes

2. The transmission electron microscope allows scientists to study the structures contained within a cell.

Electron Microscopes

1. Prokaryotes – small, simple cells

2. Eukaryotes – larger, more complex cells

Two Basic Cell TypesTwo Basic Cell Types

• Cells that do not contain internal membrane-bound structures are called prokaryotic cells.

• Cells containing membrane-bound structures are called eukaryotic cells.

• Most of the multi-cellular plants and animals we know are made up of cells containing membrane-bound structures and are therefore called eukaryotes.

• Each organelle has a specific function that contributes to cell survival.

• The membrane-bound structures within eukaryotic cells are called organelles.

• Separation of organelles into distinct compartments benefits the eukaryotic cells.

•This separation allows many chemical reactions to take place inside the same cell at the same time without interfering with each other.

•Remember, prokaryotic cells do not have internal organelles surrounded by a membrane. Most of a prokaryote’s metabolism takes place in the cytoplasm.

• The cells of most unicellular organisms such as bacteria do not have membrane bound structures and are therefore called

prokaryotes.

Prokaryotes = Bacteria

•A prokaryotic cell does not have internal organelles surrounded by a membrane. Most of a prokaryote’s metabolism takes place in the cytoplasm.

DNA

Prokaryotic cells do not have true nuclei; their DNA is not separated from the rest of the cell by a membrane. They have ribosomes and a cell membrane.

Prokaryote vs. Eukaryote

The fluid mosaic model describes the plasma membrane as a flexible boundary of a cell. It is made of may tiny parts that move within the membrane.

Cellular Organization• Unicellular

– Single-celled organisms– Perform all of an organisms metabolism

within one cell• Multicellular

– Many celled organisms– Cells specialized to perform distinct

metabolic functions– Each individual cell no longer carries out

all life functions, but rather depends on each other

• Tissues– A group of cells that functions together to

perform an activity– Ex. Muscle tissue, nerve tissue– Cells in tissues are linked to each other at

sites called cell “gap” junctions• Allows cells to communicate, anchor cells

together, and maintain differences in the internal environments between adjacent cells

– Plasmodesmata in plant cells

• Organs– Groups of 2 or more tissues that function

together– Ex. Your stomach, a leaf

• Organ systems– A group of organs that work together to

carry out major life functions– Ex. Nervous system

• cells form tissue, tissues form organs, organs form systems, and systems form organisms

Plant Cell vs. Animal Cell• There are 3 main difference between plant

and animal cells.1. Plant cells have cell walls, animal cells

do not.2. Plant cells have chloroplasts, animal

cells do not.3. Plant cells have large vacuoles, animal

cells have several small vacuoles.