Lesson Overview
7.1 Life is Cellular
Lesson Overview
Life Is Cellular
THINK ABOUT IT
What’s the smallest part of any living thing that still counts as being
“alive?”
Can we just keep dividing living things into smaller and smaller parts,
or is there a point at which what’s left is no longer alive?
As you will see, there is such a limit. The smallest living unit of any
organism is the cell.
http://youtu.be/gFuEo2ccTPA
Lesson Overview
Life Is Cellular
Early Microscopes
It was not until the mid-1600s that scientists began to use microscopes to
observe living things.
In 1665, Englishman Robert Hooke used an early compound microscope to
look at a nonliving thin slice of cork, a plant material.
Under the microscope, cork seemed to be made of thousands of tiny, empty
chambers that Hooke called “cells”. The term cell is used in biology to this
day.
Today we know that living cells are not empty chambers, but contain a huge
array of working parts, each with its own function.
Lesson Overview
Life Is Cellular
Early Microscopes
In Holland, Anton van Leeuwenhoek used
better lenses- able to examine living cells!!
Examined pond water and samples taken
from a human mouth.
He drew the organisms he saw in the
mouth—which today we call bacteria.
Lesson Overview
Life Is Cellular
The Cell Theory
Contributors of the cell theory:
Robert Hooke- examined dead cells in cork
In 1838, German botanist Matthias Schleiden concluded
that all plants are made of cells.
German biologist Theodor Schwann-all animals were
made of cells.
In 1855, German physician Rudolf Virchow- new cells
could be produced only from the division of existing cells
Lesson Overview
Life Is Cellular
The Cell Theory
These discoveries are summarized in the cell theory, a
fundamental concept of biology:
-All living things are made up of cells.
-Cells are the basic units of structure and function in
living things.
-New cells are produced from existing cells.
• The modern version of the Cell Theory includes the ideas that:
Energy flow occurs within cells.
Heredity information (DNA) is passed on from cell to cell.
All cells have the same basic chemical composition.
Lesson Overview
Life Is Cellular
Exploring the Cell
Light microscopes-visible light passed through specimen and then through
glass lenses- 1000 X actual size
lenses refract (bend) light to magnify the image
Magnification: ratio of object’s image size to real size
Lesson Overview
Life Is Cellular
Resolution: clarity of image (min distance 2 pts can be
separated & still distinguished as 2 points)
Contrast: difference between light & dark areas
Life Is Cellular
Lesson Overview
Electron
Microscopes
Electron microscopes (EM) - beams of electrons
focused through or onto surface
electron beams have shorter wavelength than
visible light so much finer resolution
Electron microscopes offer much higher resolution than
light microscopes.
Lesson Overview
Life Is Cellular
• Transmission (TEM)- study internal structure of cells
• Scanning (SEM)- detailed study of 3D image
• Disadvantage of both - specimen is nonliving
Lesson Overview
Life Is Cellular
Cell Stains
Cells- nearly transparent, making it difficult to see the
structures within them.
chemical stains & dyes- can be so specific that they
reveal only compounds or structures within the cell.
Lesson Overview
Life Is Cellular
Cell Stains
Fluorescence microscope- Fluorescent dyes attached to
specific molecules and made visible using a
Fluorescence microscope
possible to identify the locations of these molecules, and
even to watch them move about in a living cell.
Lesson Overview
Life Is Cellular
Cell Size
Most cells 1-100um
The smallest objects that the unaided human eye can
see are about 0.1 mm long
Under the right conditions, you might be able to see an
ameoba proteus, a human egg, and a paramecium
without using magnification
Lesson Overview
Life Is Cellular
Prokaryotes vs Eukaryotes
Major Difference:
Prokaryotic cells do not separate their genetic material within a
nucleus it is concentrated in nucleoid (no membrane)
In eukaryotic cells, the nucleus (with membrane) separates the
genetic material from the rest of the cell.
Lesson Overview
Life Is Cellular
Nucleus- membrane-enclosed structure containing the
cell’s genetic material in the form of DNA. The nucleus
controls many of the cell’s activities.
Nuclear envelope- encloses nucleus from cytoplasm,
double membrane with pores
Lesson Overview
Life Is Cellular
Prokaryotes
Prokaryotic cells- 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.
Bacteria are prokaryotes.
Lesson Overview
Life Is Cellular
Eukaryotes
Eukaryotic cells- larger and more complex than prokaryotic cells.
Most eukaryotic cells contain organelles & internal membranes.
Many eukaryotes are highly specialized.
There are many types of eukaryotes: plants, animals, fungi, and
organisms commonly called “protists.”