The History of the Cell Theory Before microscopes were invented, people believed that diseases were caused by curses and supernatural spirits. As scientists began using microscopes, they quickly realized they were entering a new world–one of microorganisms. Microscopes enabled scientists to view and study cells, the basic units of living organisms.

Development of Light Microscopes 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 Microscopes Compound light microscopes use a series of lenses to magnify objects in steps. These microscopes can magnify objects up to 1,500 times.

The Cell Theory Cells are the basic building blocks of all living things. Robert Hooke was an English scientist who lived at the same time as van Leeuwenhock. Hooke used a compound light microscope to study cork, the dead cells of oak bark. He saw empty boxes that he called cells.

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 organisms are composed of one or more cells. The cell is the basic unit of organization of organisms. All cells come from preexisting cells.

Development of Electron Microscopes 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 Microscopes There are two basic types of electron microscopes. The scanning electron microscope scans the surface of cells to learn their three dimensional shape.

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

Two Basic Cell Types Prokaryotes – small, simple cells 2. Eukaryotes – larger, more complex cells 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. The membrane-bound structures within eukaryotic cells are called organelles. Each organelle has a specific function that contributes to cell survival.

Separation of organelles into distinct 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. Plant cells have cell walls, animal cells do not. Plant cells have chloroplasts, animal cells do not. Plant cells have large vacuoles, animal cells have several small vacuoles.