The History of Cell Biology

Chapter 4 – Section 1

The Discovery of Cells

• All living things are made up of one or more cells

• A cell is the smallest unit that can carry on all of the processes of life

Robert Hooke

• In 1665, Robert Hooke used a light microscope to look at a thin slice of cork

• Where does cork come from?

Robert Hooke

• Hooke looked at cork as well as tree stems, roots, and ferns

• He found that each had similar little boxes

• He named the little boxes cells, because they reminded him of the cubicles that monks lived in

Anton van Leeuwenhoek

• First person to observe living cells

• In 1673, he was able to observe microorganisms in pond water

• He called them “animalcules,” we now call them protists

The Cell Theory

• The importance of cells was not recognized until about 150 years later

• Biologists began to organize information about cells into a unified understanding

The Cell Theory

• In 1838, Matthias Schleiden concluded that all plants were composed of cells

• In 1839, Theodor Schwann concluded that all animals were composed of cells

• Finally, in 1855, Rudolph Virchow noted that all cells come from other cells

• These three observations were combined to form the cell theory

The Cell Theory

• The cell theory states that…

– All living organisms are composed of one or more cells

– Cells are the basic units of structure and function in an organism

– Cells come from existing cells

Developments in Cell Biology

The Cellular Basis of Life

• All living things share several basic characteristics

– Consist of organized parts, obtain energy from their surroundings, perform chemical reactions, change with time, respond to their environment, reproduce, and maintain homeostasis

Introduction to Cells

Section 4-2

Cell Diversity

• Cells are very diverse in terms of shape, size, and internal organization

• A cell’s function influences its physical features

Cell Shape

• The diversity in cell shape reflects the different functions of cells

• A cell’s shape can be simple or complexdepending on the function of the cell

• Each cell has a shape that has evolved to allow the cell to perform its function effectively

Cell Shape

Cell Size

• Cells differ greatly in their sizes– Nerve cells in a giraffe’s spinal cord can be 2 m

long

– A human egg cell is about the size of a period at the end of a sentence

– Most cells are only about 1/500 the size of a period at the end of a sentence

– http://learn.genetics.utah.edu/content/begin/cells/scale/

Cell Size

• The size of a cell is limited by the cell’s surface area to volume ratio

• As a cell grows, its volume increases much faster than its surface area

• This is important because material needed by a cell (such as nutrients and oxygen) and wastes produced by a cell (such as carbon dioxide) must pass into and out of the cell through its surface

Cell Size

• If a cell became very large, there would not be enough surface area to allow materials to enter or leave the cell quickly enough to meet the cell’s needs

• Therefore, most cells are microscopic in size

Cell Size

Example

Cube 1

Surface Area of Cube 1= Length x Width x ______________

Surface Area of Cube 1= 2 cm x 2 cm x 6 = ________

Volume of Cube 1= ______ x width x __________

Volume of Cube 1 = 2 cm x 2 cm x 2 cm

Volume of Cube 1 = ____________

Surface area to Volume ratio= Surface area/volume

Surface Area to Volume ratio of Cube 1=

24 cm2/8 cm3 = __________

Cube 2Surface Area of Cube 2= Length x Width x 6 Sides

Surface Area of Cube 2= 4 cm x 4 cm x 6 = ______________

Volume of Cube 2= length x width x height

Volume of Cube 2 = 4 cm x 4 cm x 4 cm

Volume of Cube 2 = 64 cm3

Surface area to Volume ratio= Surface area/volume

Surface Area to Volume ratio of Cube 2= 96 cm2/64 cm3 = ____________

2 cm

Cube 1

4 cm

Cube 2

Basic Part of a Cell

• Three basic features are common to all cell types – an outer boundary, an interior substance, and a control region

Plasma Membrane (Cell Membrane)

• Cell Membrane – the cell’s outer boundary which covers a cell’s surface and acts as a barrier between the inside and the outside of a cell

• All materials enter or exit through the cell membrane

Cytoplasm

• Cytoplasm – the region of the cell inside the plasma membrane that includes the fluid, the cytoskeleton, and all of the organelles except for the nucleus

– Cytosol – part of the cytoplasm that includes molecules and small particles but not membrane-bound organelles

Control Center

• Cells carry DNA for regulating their functions and reproducing themselves

– Floats freely in some cells, other cells keep the DNA in a nucleus

• Most of the functions of a eukaryotic cell are controlled by the nucleus

Control Center

• Most prominent structure in eukaryotic cells

• Maintains its shape with a protein skeleton called a nuclear matrix

Two Basic Types of Cells

Eukaryotes Prokaryotes

Prokaryotes

• Organisms that lack a membrane-bound nucleus and membrane bound organelles

• Genetic information (DNA) is often located in a part of the cell called the nucleoid

• Usually smaller and less complex than eukaryotes

Eukaryotes

• Organisms that are made up of one or more cells and have a nucleus and membrane-bound organelles

• Have a variety of organelles, which are well-defined, intracellular bodies that perform specific functions for the cell

• Generally larger and more complex than prokaryotic cells

Cellular Organization

• Over time, cells began to form groups that functioned together

• Some cells retained the ability to live outside a group

• Others became dependent on each other for survival

Colonies

• A colonial organism is a collection of genetically identical cells that live together in a connected group

• Not truly multicellular because few cell activities are coordinated

True Multicellularity

• Tissue – a group of similar cells and their products that carry out a specific function

• Organs – groups of tissues that perform a particular job in an organism

• Organ System – group of organs that accomplish related tasks

• Organism – several organ systems combined

Cellular Organization