Transcript Chapter 7_The Cell

Chapter 7
Cellular Structure and
Function
Section 7.1: Cell Discovery and Theory

1665 – Robert Hooke (U.K.)
Made a simple microscope and used it to observe
cork.
 He saw small box-like structures and called them
cellulae (Latin for small rooms).
 It is from Hooke’s work that we have the term cell.

History of the Cell Theory


A cell is the basic structural and functional unit
of all living organisms.
1683 – Anton van Leeuwenhoek (Dutch)
Designed his own microscope after reviewing
Hooke’s work.
 Observed single-celled organisms in pond water,
milk, and other substances.

The Cell Theory




1838 – Scientist discovers plants are made of cells.
1839 – Scientist discovers that animal tissue also
consists of individual cells.
1855 – Scientist proposes that all cells are produced
from the division of existing cells.
The Cell Theory – includes three principles:
1. All living organisms are composed of one or more cells.
2. Cells are the basic unit of structure and organization of all
living organisms.
3. Cells arise only from previously existing cells, with parent
cells passing copies of their genetic material on to their
daughter cells.
Microscope Technology


Developments in microscope technology have
given scientists the ability to study cells in great
detail.
Compound Light Microscope –
Consists of a series of glass lenses.
 Uses visible light to magnify an image.
 Each lens magnifies the image of the previous lens.

So if we use two 10X lenses, the total magnification will
be 100X (10 x 10 = 100).
 The compound light microscope is limited in that the
properties of visible light will always limit the resolution.
 Maximum magnification without blurring is 1000X.

Microscope Technology (Continued)

Electron Microscope (1940s) –
Uses magnets to aim a beam of electrons at a thin
slice of a cell.
1. Transmission Electron Microscope (TEM) Electrons are passed through a specimen to a
fluorescent screen.


TEMs can magnify up to 500,000X but specimens must
be dead, sliced very thin, and stained with heavy metals.
2. Scanning Electron Microscope (SEM) –
Directs electrons over the surface of the specimen
to produce a 3-dimensional image.
Transmission Electron Microscope
Scanning Electron Microscope
Microscope Technology (Continued)
3. Scanning Tunneling Electron Microscope
(STM) – produces 3D images of live specimens
Warm-up Question
What are the three principles
of the cell theory?
Cells differ in many ways
however…..

All cells have a plasma membrane – a special
boundary that helps control what enters and
leaves the cell.
Two Broad Categories for Cells


Prokaryotic Cells (pro = before; kary = nucleus)
Eukaryotic Cells (eu = true; kary = nucleus)
Are 1-100 times larger that prokaryotic cells
 Contain a nucleus and other organelles that are bound
by membranes (membrane-bound organelles).
 The nucleus is a distinct central organelle that contains
the cell’s genetic material (DNA).
 Organelles are specialized structures that carry out
specific cell functions. They enable cell functions to take
place in different parts of the cell at the same time.

Prokaryotic Cells



Are defined as cells without a nucleus or other
membrane bound organelles.
Most unicellular organisms (bacteria) are
prokaryotes.
Are much simpler in structure compared to
eukaryotes. Scientists believe eukaryotic cells
evolved from prokaryotic cells and that
prokaryotes were probably the first form of life
on Earth.
The Plasma Membrane





helps a cell maintain homeostasis.
is a thin, flexible boundary that separates a cell
from its environment.
allows nutrients to enter and wastes to exit.
All prokaryotes and eukaryotes have a plasma
membrane.
Selective permeability – allows some
substances to pass through and keeps others
out. (See fig. 7.5)
Structure of the Plasma
Membrane

The plasma membrane is composed of a
phospholipid bilayer – two layers of
phospholipids are arranged tail to tail.
Other Components of the Plasma
Membrane

Transport proteins - create tunnels through
which certain substances enter and leave the cell.
Needed substances – glucose, water, oxygen
 Wastes – carbon dioxide
 Therefore, transport proteins contribute to the
selective permeability of the plasma membrane.



Cholesterols contribute to the fluidity of the
plasma membrane in that they prevent the fattyacid tails from sticking together.
Carbohydrates attached to proteins stick out
from the plasma membrane.
Fluid Mosaic Model



http://www.susanahalpine.com/anim/Life/me
mb.htm
The components of the plasma membrane are in
constant motion sliding past each other.
The phospholipids in the bilayer create a “sea”
in which other molecules can float, hence
“fluid” and “mosaic” because there are many
components which appear as a pattern or a
mosaic.