All living things are composed of cells, the basic unit of structure and function. Robert Hooke first observed cells in 1665 using a microscope to look at cork, naming the structures "cells". The cell theory developed in the 1800s states that all organisms are made of cells, cells are the basic unit of life, and new cells are produced from existing cells.

1. The History of Cell Biology
Chapter 4 – Section 1

2. 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

3. Robert Hooke
• In 1665, Robert Hooke
used a light microscope
to look at a thin slice of
cork
• Where does cork come
from?

4. 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

5. 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

6. 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

7. 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

8. 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

9. Developments in Cell Biology

10. 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

11. Introduction to Cells
Section 4-2

12. Cell Diversity
• Cells are very diverse in terms of
shape, size, and internal organization
• A cell’s function influences its physical
features

13. Cell Shape
• The diversity in cell shape reflects the
different functions of cells
• A cell’s shape can be simple or complex
depending on the function of the cell
• Each cell has a shape that has evolved to allow
the cell to perform its function effectively

14. Cell Shape

15. 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/cell
s/scale/

16. 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

17. 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

18. Cell Size

19. Cube 2
Cube 1
Example 4 cm
2 cm
Cube 1 Cube 2
Surface Area of Cube 1= Length x Width x Surface Area of Cube 2= Length x Width x 6 Sides
______________
Surface Area of Cube 2= 4 cm x 4 cm x 6 =
Surface Area of Cube 1= 2 cm x 2 cm x 6 = ________ ______________
Volume of Cube 1= ______ x width x __________ Volume of Cube 2= length x width x height
Volume of Cube 2 = 4 cm x 4 cm x 4 cm
Volume of Cube 1 = 2 cm x 2 cm x 2 cm
Volume of Cube 2 = 64 cm3
Volume of Cube 1 = ____________
Surface area to Volume ratio= Surface area/volume
Surface area to Volume ratio= Surface area/volume
Surface Area to Volume ratio of Cube 2=
96 cm2/64 cm3 = ____________
Surface Area to Volume ratio of Cube 1=
24 cm2/8 cm3 = __________

20. Basic Part of a Cell
• Three basic features are common to all cell
types – an outer boundary, an interior
substance, and a control region

21. 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

22. 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

23. 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

24. Control Center
• Most prominent
structure in eukaryotic
cells
• Maintains its shape
with a protein skeleton
called a nuclear matrix

25. Two Basic Types of Cells
Eukaryotes Prokaryotes

26. 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

27. 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

28. 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

29. 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

30. 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

31. Cellular Organization