Introduction to Cells
Objectives
• Students will:
–Define Spontaneous Generation
–Understand the parts of the cell
theory and the history of cells
–Differentiate between
prokaryotic and eukaryotic cells
Recipe for Mice
• Place a dirty shirt or some rags in an
open box or barrel containing a few
grains of wheat and some soil.
• Place the box in dark corner, and in
21 days mice will appear.
• There will be adult males and females
present, and some will be capable of
mating and making more mice.
Spontaneous Generation
• Today, we know that mice actually come
from other mice, but this was not
always known.
• For centuries, people based their
beliefs on their interpretations of what
they saw without testing those
interpretations (untested observations).
• One of the best examples of this was
the theory of spontaneous generation –
that non-living objects could give rise to
living organisms.
Then, the first real experiment
• In 1668, Francesco Redi decided to find
out rotting meat actually turned into or
produced flies.
• He conducted an experiment with flies
and wide-mouth jars containing meat.
• His results showed that flies were not
produced from MEAT, but rather from
maggots that came from flies laying
eggs on the meat.
Here’s what it looked like:
Meat in jar with lid
Meat in jar with gauze
Meat in open jar
Another experiment
Pasteur’s Experiment: showed that
microorganisms in the air can spoil wine and
cause disease, but the air itself does not.
Living things come only from other living
things.
What is Cork?
The Discovery of Cells
• Mid 1600’s
– Scientists began to use microscopes to
observe living things
• 1665: Robert Hooke
– Used an early compound microscope to look
at a thin slice of cork
– Noticed it looked like thousands of tiny empty
chambers which he called “cells”
• Appeared empty because cork is dead plant
material
Cork Cells
Discovery of Cells
• Anton Van Leeuwenhoek - 1670
– Best known for his refinement of the
microscope
– Most important discovery was the
existence of single-cell organisms.
• While using a microscope to examine pond
water in 1674, he observed dozens of protists,
which he called 'animalcules,' as well as green
algae .
History of the Cell
• 1838: Matthias Schleiden
– Concluded that all plants are made of cells
• 1839: Theodor Schwann
– Stated that all animals made of cells
History of The Cell
• Rudolf Virchow - 1855
– He was the first to demonstrate that the cell theory
applies to diseased tissue as well as to healthy tissue.
– He used the cell theory to explain the effects of
disease in the organs and tissues of the body. He
emphasized that diseases arose, not in organs or
tissues in general, but primarily in their individual cells.
– Cells come only from the division of other cells
• so living things come only from other living things!
The Cell Theory
• The cell theory states that:
– All living things are made up of cells
– Cells are the basic units of structure and
function
– Cells are only produced from the
division of existing cells
Exploring the Cell
• Todays researchers use microscopes and
techniques that are more powerful than
those used by Hooke, Schwann,
Schleiden, and Virchow
• Scientists can now produce advanced
pictures such as 3D images and movies
that are used to study the cell in more
detail
Cell Commonalities
• Cells come in a vast array of shapes and
sizes (most from 5-50µm in diameter)
• All cells have a few things in common:
– A cell membrane (surrounds outside of cell)
– DNA (holds genetic info)
– Ribosomes (where proteins are assembled)
– Cytoplasm (holds organelles in place)
All Cells Share Certain
Characteristics
Where
proteins
are made
Holds
everything
inside the
cell in place
Separates cell’s contents from
environment and regulates what
moves in and out of the cell.
Cell Differences
• Cells fall into 2 broad categories based on
whether they contain a nucleus
– Nucleus: contains the cell’s genetic
information and controls the cells activities
1. Eukaryotes:
– Have a nucleus
2. Prokaryotes:
– Do not have a nucleus
Prokaryotes vs. Eukaryotes
• Prokaryotes
–
–
–
–
Small and simple
Single-celled
No nucleus
No membrane-bound
organelles
– Evolved first
– Ex.: bacteria
• Eukaryotes
–
–
–
–
Large and complex
Most Multi-cellular
Has a nucleus
Has membrane bound
organelles
– Evolved later
– Ex.: plant, animal,
fungi, and protist cells
Prokaryote or Eukaryote?
Evolution of Eukaryotes
• Theory of Endosymbiosis:
– Theory that eukaryotic cells formed from a
symbiosis among several different prokaryotic
organisms
• How it happened
– 2 billion years ago, prokaryotic cells began
evolving internal cell membranes
• The result was the ancestor of all eukaryotic cells
– Other prokaryotic organisms began to enter and
live inside the ancestral eukaryote
– Over time a symbiotic relationship evolved
• The prokaryotic organisms that lived inside the
ancestral eukaryote evolved and became specialized
organelles