SC.912.L.14.1 THE CELL THEORY
WHAT YOU NEED TO KNOW
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You need to know the cell theory and how continuous
investigations and/or new scientific information
influenced the development of cell theory.
You need to know how scientific claims are evaluated
through scientific argumentation, critical and logical
thinking and consideration of alternative explanations,
in the context of cell theory.
You need to know the difference between theories and
laws and be able to explain how a theory is developed.
THE CELL THEORY
All living things are composed of cells. They
may be unicellular or multicellular.
 Cells are the basic units of structure and
function in living things
 Cells arise from pre-existing cells
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All living things are composed of cells.
They may be unicellular (single cell)
or multicellular (multiple cells)
The cell is the basic unit of life
Cells arise from pre-existing cells (result from
replication of pre existing cells).
Prokaryotic Cells
Eukaryotic Cells
(reproduce by binary fission)
(reproduce by mitosis and meiosis)
Cells replicate the genetic information before dividing
to form new cells.
The invention of the microscope made the
discovery of the cells possible
It was not until the mid-1600s that scientists
began to use microscopes to observe living
things
ROBERT HOOKE’S WORK
English scientists
 In 1665 he used a compound microscope he
built.
 Looked at tree bark
 Called the structures “cells”
 He observed dead cells
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ANTON VAN LEEUWENHOEK’S WORK
Dutch scientist
 Used a simple microscope
 Looked at pond water
 He saw single cells “animals” swimming in the
water and called them “animalcules” (tiny
animals)
 He observed live cells
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MATTHIAS SCHLEIDEN’S WORK
German botanist
 In 1838 used a microscope to study plants
 He concluded that plants are made up of cells
 Became the first person to propose the idea
that cells are the basic unit of life and that
plants grow by making new cells
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THEODOR SCHWANN’S WORK
German biologist
 In 1839 used a microscope to study animals
 He concluded that animals are made up of
cells
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RUDOLPH VIRCHOW’S WORK
German physician
 In 1850 proposed that cells come from preexisting cells and not spontaneously from non
living matter
 He based his ideas on his own research as well
as that done by other scientists
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Lesson Overview
Life Is Cellular
PROKARYOTES AND EUKARYOTES
Cells fall into two broad categories, depending on whether
they contain a nucleus.
The nucleus is a large membrane-enclosed structure that contains the
cell’s genetic material in the form of DNA. The nucleus controls many of the
cell’s activities.
Lesson Overview
Life Is Cellular
PROKARYOTES AND EUKARYOTES
Eukaryotes are cells that enclose their DNA in nuclei.
Prokaryotes are cells that do not enclose DNA in nuclei.
Lesson Overview
Life Is Cellular
PROKARYOTES
Prokaryotic cells are generally smaller and simpler than eukaryotic cells.
Despite their simplicity, prokaryotes grow, reproduce, and respond to the
environment, and some can even move by gliding along surfaces or
swimming through liquids.
The organisms we call bacteria are prokaryotes.
Lesson Overview
Life Is Cellular
EUKARYOTES
Eukaryotic cells are generally larger and more complex than prokaryotic
cells.
Most eukaryotic cells contain dozens of structures and internal membranes.
Many eukaryotes are highly specialized.
There are many types of eukaryotes: plants, animals, fungi, and organisms
commonly called “protists.”
PROKARYOTIC AND EUKARYOTIC CELLS
PROKARYOTIC CELL
BOTH
EUKARYOTIC CELL
No nucleus
DNA of prokaryotes floats
freely around the cell
DNA
Nucleus present
DNA is held within its
nucleus
No membrane bound
organelles
Plasma membrane
(cell membrane)
Membrane bound organelles
Smaller and simpler
Cytoplasm
Larger and more complex
Divide by binary fission
Ribosomes
Cells divide by mitosis
Usually a single circular
chromosome
DNA is replicated before Multiple linear
cell division
chromosomes
Have organelles that secrete
proteins.