KEY CONCEPT Cells are the Basic unit of life.

• The cell theory grew out of the work of many scientists and improvements in the microscope.

• Many scientists contributed to the cell theory.

• The cell theory grew out of the work of many scientists and improvements in the microscope.

• Many scientists contributed to the cell theory.• More was learned about cells as microscopes

improved.

• The cell theory grew out of the work of many scientists and improvements in the microscope.

• Many scientists contributed to the cell theory.• More was learned about cells as microscopes

improved.• The cell theory is a unifying concept of biology.

• Early studies led to the development of the cell theory.• The Cell theory has three principles.

– All organisms are made of cells.

• Early studies led to the development of the cell theory.• The Cell theory has three principles.

– All organisms are made of cells.– All existing cells are produced by other living cells.

• Early studies led to the development of the cell theory.• The Cell theory has three principles.

• All organisms are made of cells.• All existing cells are produced by other living cells.• The cell is the most basic unit of life.

• Prokaryotic cells lack a nucleus and most internal structures of eukaryotic cells.

• All cells share certain characteristics.

• Prokaryotic cells lack a nucleus and most internal structures of eukaryotic cells.

• All cells share certain characteristics.• Cells tend to be microscopic.

Bacterium(colored SEM; magnification 8800x)

• Prokaryotic cells lack a nucleus and most internal structures of eukaryotic cells.

• All cells share certain characteristics.• Cells tend to be microscopic.• All cells are enclosed by a membrane.

Bacterium(colored SEM; magnification 8800x)

cell membrane

• Prokaryotic cells lack a nucleus and most internal structures of eukaryotic cells.

• All cells share certain characteristics.• Cells tend to be microscopic.• All cells are enclosed by a membrane.• All cells are filled with cytoplasm.

Bacterium(colored SEM; magnification 8800x)

cell membrane

cytoplasm

• There are two cell types: eukaryotic cells and prokaryotic cells.

• There are two cell types: eukaryotic cells and prokaryotic cells.• Eukaryotic cells have a nucleus.nucleus

cell membrane

• There are two cell types: eukaryotic cells and prokaryotic cells.• Eukaryotic cells have a nucleus.• Prokaryotic cells do not have membrane-

bound organelles.

nucleus

cell membrane

organelles

• There are two cell types: eukaryotic cells and prokaryotic cells.• Prokaryotic cells do not have a nucleus.nucleus

cell membrane

organelles

• There are two cell types: eukaryotic cells and prokaryotic cells.• Prokaryotic cells do not have a nucleus.• Prokaryotic cells do not have membrane-bound

organelles.

nucleus

cell membrane

organelles

cytoplasm

Lesson Overview Life Is Cellular

Exploring the Cell

How do microscopes work?

Most microscopes use lenses to magnify the image of an object by focusing light or electrons.

Lesson Overview Life Is Cellular

Lesson Overview Life Is Cellular

Light Microscopes and Cell Stains

A typical light microscope allows light to pass through a specimen and uses two lenses to form an image.

• Two types: Dissecting (low) and Compound (high)

The first set of lenses, located just above the specimen, produces an enlarged image of the specimen.

The second set of lenses magnifies this image still further.

Because light waves are diffracted, or scattered, as they pass through matter, light microscopes can produce clear images of objects only to a magnification of about 1000 times.

Lesson Overview Life Is Cellular

Light Microscopes and Cell Stains

Another problem with light microscopy is that most living cells are nearly transparent, making it difficult to see the structures within them.

Using chemical stains or dyes can usually solve this problem. Some of these stains are so specific that they reveal only compounds or structures within the cell.

Lesson Overview Life Is Cellular

Electron Microscopes

Light microscopes can be used to see cells and cell structures as small as 1 millionth of a meter. To study something smaller than that, scientists need to use electron microscopes.

Electron microscopes use beams of electrons, not light, that are focused by magnetic fields.

Electron microscopes offer much higher resolution than light microscopes.

There are two major types of electron microscopes: transmission and scanning.

Lesson Overview Life Is Cellular

Electron Microscopes

Transmission electron microscopes make it possible to explore cell structures and large protein molecules.

Because beams of electrons can only pass through thin samples, cells and tissues must be cut first into ultra thin slices before they can be examined under a transmission electron microscope.

Transmission electron microscopes produce flat, two-dimensional images.

Lesson Overview Life Is Cellular

Electron Microscopes

In scanning electron microscopes, a pencil-like beam of electrons is scanned over the surface of a specimen.

Because the image is of the surface, specimens viewed under a scanning electron microscope do not have to be cut into thin slices to be seen.

Scanning electron microscopes produce three-dimensional images of the specimen’s surface.

Lesson Overview Life Is Cellular

Home Work

• Copy Notes handout onto appropriate page of INB• Discuss INB

Lesson Overview Life Is Cellular

INB assignment page 22

Lesson Overview Life Is Cellular

Bell Ringer Reflection

• What was the main

Idea of today’s lesson

• Did you find the

material to be difficult?

• How would you rate

yourself on the scale

shown here

• Please include any

additional feedback