3.1 Cell Theory

KEY CONCEPT Cells are the Basic unit of life.

Macrophages (large tan cells) take in and digest foreign material, such as invading bacteria (small red cells). They play an important role in your immune system. Many macrophages travel the body, recognize foreign material, engulf it, and break it down using chemicals. They have an adaptable internal skeleton that helps them move and stretch out their “arm” to capture invading particles.

3.1 Cell Theory

! The cell theory grew out of the work of many scientists and improvements in the microscope. •  Many scientists contributed to the cell theory.

v In 1665, the English scientist Robert Hooke used the three-lens compound microscope to examine thin slices of cork.

§ Cork is the tough outer bark of a species of oak tree.

v He observed that cork is made of tiny, hollow compartments.

§ The compartments reminded Hooke of small rooms found in a monastery, so he gave them the same name: cells.

3.1 Cell Theory

! The cell theory grew out of the work of many scientists and improvements in the microscope. •  Many scientists contributed to the cell theory.

3.1 Cell Theory

! The cell theory grew out of the work of many scientists and improvements in the microscope. •  Many scientists contributed to the cell theory.

v  Anton van Leeuwenhoek, a Dutch tradesman, was studying new methods for making lenses to examine cloth. v As a result of his research, his single-lens microscopes were much more powerful than Hooke’s crude compound microscope. v In 1674, Leeuwenhoek became one of the first people to describe living cells when he observed numerous single-celled organisms swimming in a drop of pond water.

3.1 Cell Theory ! The cell theory grew out of the work of many scientists

and improvements in the microscope.

•  Leeuwenhoek à “animalcules” from pond water.

3.1 Cell Theory ! The cell theory grew out of the work of many scientists

and improvements in the microscope. •  Born the son of a basket-maker, Leeuwenhoek was trained as

a draper, a fabric merchant. o  He was accustomed to using magnifying Lenses to examine

threads. •  At the age of 28, this successful merchant was appointed to a

government position that ensured his financial security. o  Free to train his microscope on the invisible world of living

matter, Leeuwenhoek’s work earned him the title of the Father of Microbiology.

•  Such was his celebrity that he was visited by several reigning monarchs, including Queen Elizabeth I of England and Czar Peter the Great of Russia.

3.1 Cell Theory

! The cell theory grew out of the work of many scientists and improvements in the microscope. •  Many scientists contributed to the cell theory.

v  The German scientist Matthias Schleiden also used compound microscopes to study plant tissue. v  In 1838, he proposed that plants are made of cells. v  Schleiden originally studied law.

3.1 Cell Theory

! The cell theory grew out of the work of many scientists and improvements in the microscope. •  Many scientists contributed to the cell theory.

v  In 1839 Theodor Schwann concluded that all animals are made of cells. v  Shortly thereafter, he published the first statement of the cell theory, concluding that all living things are made of cells and cell products. v  Schwann was originally a medical doctor.

3.1 Cell Theory

! The cell theory grew out of the work of many scientists and improvements in the microscope. •  Many scientists contributed to the cell theory.

v  In 1855, Rudolf Virchow, another German scientist, reported that all cells come from preexisting cells. v  Virchow was originally a medical doctor.

3.1 Cell Theory

! The cell theory grew out of the work of many scientists and improvements in the microscope. •  Many scientists contributed to the cell theory. •  More was learned about cells

as microscopes improved.

3.1 Cell Theory

! The cell theory grew out of the work of many scientists and improvements in the microscope. •  Many scientists contributed to the cell theory. •  More was learned about cells

as microscopes improved. •  The cell theory is a unifying

concept of biology.

3.1 Cell Theory

! Early studies led to the development of the cell theory. •  The Cell theory has three principles.

– All organisms are made of cells.

3.1 Cell Theory

! Early studies led to the development of the cell theory. •  The Cell theory has three principles.

– All organisms are made of cells. – All existing cells are produced by other living cells.

3.1 Cell Theory

! Early studies led to the development of the cell theory. •  The Cell theory has three principles.

– All organisms are made of cells. – All existing cells are produced by other living cells. – The cell is the most basic unit of life.

3.1 Cell Theory

! Prokaryotic cells lack a nucleus and most internal structures of eukaryotic cells. •  All cells share certain characteristics.

3.1 Cell Theory

! Prokaryotic cells lack a nucleus and most internal structures of eukaryotic cells. •  All cells share certain characteristics.

– Cells tend to be microscopic.

Bacterium (colored SEM; magnification 8800x)

3.1 Cell Theory

! Prokaryotic cells lack a nucleus and most internal structures of eukaryotic cells. •  All cells share certain characteristics.

– Cells tend to be microscopic. – All cells are enclosed

by a membrane.

Bacterium (colored SEM; magnification 8800x)

cell membrane

3.1 Cell Theory

! Prokaryotic cells lack a nucleus and most internal structures of eukaryotic cells. •  All cells share certain characteristics.

– Cells tend to be microscopic. – All cells are enclosed

by a membrane. – All cells are filled with

cytoplasm.

Bacterium (colored SEM; magnification 8800x)

cell membrane

cytoplasm

3.1 Cell Theory

! Prokaryotic cells lack a nucleus and most internal structures of eukaryotic cells.

v  In prokaryotic cells, such as this bacterium (top), DNA is suspended in the cytoplasm.

v  In eukaryotic cells, such as this protozoan (bottom), the nuclear envelope separates DNA from the cytoplasm.

3.1 Cell Theory

! There are two cell types: eukaryotic cells and prokaryotic cells.

3.1 Cell Theory

! There are two cell types: eukaryotic cells and prokaryotic cells. •  Eukaryotic cells have a

nucleus. nucleus

cell membrane

3.1 Cell Theory

! There are two cell types: eukaryotic cells and prokaryotic cells. •  Eukaryotic cells have a

nucleus. •  Prokaryotic cells do

not have membrane- bound organelles.

nucleus

cell membrane

organelles

3.1 Cell Theory

! There are two cell types: eukaryotic cells and prokaryotic cells. •  Prokaryotic cells do not

have a nucleus. nucleus

cell membrane

organelles

3.1 Cell Theory

! There are two cell types: eukaryotic cells and prokaryotic cells. •  Prokaryotic cells do not

have a nucleus. •  Prokaryotic cells do not

have membrane-bound organelles.

nucleus

cell membrane

organelles

cytoplasm