Copy into Note Packet and Return to Teacher Chapter 3 Cell Structure

Section 1: Looking at Cells Objectives

•Describe how scientists measure the length of objects. •Relate magnification and resolution in the use of microscopes. •Analyze how light microscopes function. •Compare light microscopes with electron microscopes. •Describe the scanning tunneling microscope.

Cells Under the Microscope Measuring Cell Structures

Measurements taken by scientists are expressed in metric units. The official name of the metric

system is the International System of Measurements, abbreviated SI. The table below

summarizes the SI units used to measure length.

• Magnification is the quality of making an image appear larger than its actual size.

• Resolution is a measure of the clarity of an image.

• Both high magnification and good resolution are needed to view the details of extremely

small objects clearly.

Electron microscopes have much higher magnifying and resolving powers than light microscopes.

Unit Prefix Metric equivalent Real-life equivalent Kilometer (km) Kilo- 1,000 m About two-thirds of a mile Meter (m) 1 m (SI base unit) A little more than a yard Centimeter (cm) Centi- 0.01 m About half the diameter of a penny Millimeter (mm) Milli- 0.001 m About the width of a pencil tip Micrometer ( µµµµm) Micro- 0.000001 m About the length of an average

bacterial cell Nanometer (nm) Nano- 0.000000001 m About the length of a water molecule

Parts of a Light Microscope – Refer to page 1028 in your textbook and label. Types of Microscopes

• Light microscopes form an image when light passes through one or more lenses to

produce an enlarged image of a specimen.

Electron Microscopes

• Electron microscopes form an image of a specimen using a beam of electrons rather

than light.

• The electron beam and specimen must be in a vacuum so that the electron beam will not

bounce off of gas molecules.

• Live organisms cannot be viewed with an electron microscope.

Transmission Electron Microscope • An electron beam is directed at a very thin slice of a specimen stained with metal ions.

Some structures become more heavily stained than others.

• The heavily stained parts absorb electrons, those that are lightly stained allow electrons

to pass through.

• The electrons that pass through strike a fluorescent screen, forming an image.

Eyepiece

Arm

Stage Aperture or stage opening

Fine adjustment knob

Coarse adjustment knob

Base

Body tube

Revolving nosepiece

High power objective lens Low power objective lens

Stage clips Diaphragm lever

Diaphragm

Light source

Scanning Electron Microscope

• An electron beam is focused on a specimen coated with a very thin layer of metal.

• The electrons that bounce off the specimen form an image on a fluorescent screen.

• The image shows three-dimensional details of the surface of a specimen.

Scanning Tunneling Microscope

• A needle-like probe measures differences in voltage caused by electrons that leak, or

tunnel, from the surface of the object being viewed.

• A computer tracks the movement of the probe across the surface of the object.

• The image shows three-dimensional details of the surface of a specimen.

• Live specimens and objects as small as atoms can be viewed.

Section 2: Cell Features Objectives

• List the three parts of the cell theory. • Determine why cells must be relatively small. • Compare the structure of prokaryotic cells with that of eukaryotic cells. • Describe the structure of cell membranes.

The Cell Theory The Cell Theory has three parts:

1. All living things are made of one or more cells.

2. Cells are the basic units of structure and function in organisms.

3. All cells arise from existing cells.

Cell Size

Small cells function more efficiently than large cells. If a cell’s surface area–to-volume

ratio is too low, substances cannot enter and leave the cell well enough to meet the

cell’s needs.

Common Cell Features Cells share common structural features, including:

• an outer boundary called the cell membrane,

• interior substance called cytoplasm,

• structural support called the cytoskeleton,

• genetic material in the form of DNA

• cellular structures that make proteins, called ribosomes

Prokaryotes

Prokaryotes are __________________________ organisms that _____________________

and other internal compartments. They have a ____________________, may have cilia or

flagella, and have a ________________ circular molecule of DNA.

Structure of Cilia and Flagella Cilia

Eukaryotic Cells

Eukaryotic cells have:

• A _____________________ which contains the cell’s DNA

• Other internal compartments called _________________________.

Cell membrane

Extracellular matrix

Flagellum

Microtubules

Comparing Prokaryotes and Eukaryotes

Prokaryote Eukaryote

1. No nucleus 1. True nucleus

2. Circular DNA 2. Linear DNA

3. No membrane covered organelles 3. Many membrane covered organelles

4. Relatively small 4. Relatively large

5. Reproduce quickly (20 minutes) 5. Reproduce slowly (24+ hours)

Ex: Bacteria Ex : Plants, animals, fungi & protists

Parts of an Animal Cell

(Label)

Flagellum

Eukaryotic Cells

• The cytoskeleton provides the interior framework of a cell. There are three basic kinds

of cytoskeletal fibers.

1. Microfilaments: long slender

filaments made of the protein

actin

2. Microtubules: hollow tubes

made of the protein tubulin.

3. Intermediate fibers: thick ropes

made of protein.

• The cytoskeleton’s network of protein

fibers anchors the cell’s organelles and

other components of the cytoplasm.

The Cell Membrane

• The cell membrane is a selectively permeable barrier that determines which substances

enter and leave the cell.

• The selective permeability of the cell is mainly caused by the way phospholipids

interact with water.

• A phospholipid is a lipid made of a phosphate group and two fatty acids.

• Cell membranes are made of a double layer of phospholipids, called a bilayer.

Check with another student to label these pictures.

Refer to page 61 (Label)