Chapter 6 A Tour of the cell
Summary from Campbel biology
+exam's questions
Microscopy and Cell Fractionation
(Concept 1)
1. Microscopy Principles
Magnification: The ratio of an object's image size to its real
size.
Resolution: The measure of image clarity. It is the minimum
distance two points can be separated and still be
distinguished as separate points.
Contrast: The difference in brightness between light and dark
areas.
2. Types of Microscopes (Textual Comparison)
Light Microscope (LM): Uses visible light and glass lenses.
Effectively magnifies up to 1,000 times. Its resolution limit is
0.2 micrometers. Key Exam Advantage: It is the only type
that allows the visualization of living cells and dynamic
biological processes.
Scanning Electron Microscope (SEM): Focuses a beam of
electrons onto the specimen's surface, which is coated with
gold. Key Exam Advantage: Provides a detailed 3D image
of the surface topography. Requires cell fixation, so
specimens are dead.
Transmission Electron Microscope (TEM): Aims an
electron beam through a very thin section of a specimen
stained with heavy metals. Key Exam Advantage: Used to
study the internal ultrastructure of cells and organelle
profiles. Specimens are dead.
3. Cell Fractionation
A laboratory technique that uses a Centrifuge to break cells apart and separate major
organelles based on size and density.
The Core Rule: Larger and heavier components pellet at
lower speeds. Smaller and lighter components remain in the
liquid (supernatant) and require higher speeds to pellet.
Pelleting Sequence (From Lowest to Highest Speed):
1. Low Speed (1,000 g): Pellets the Nuclei (largest and
heaviest).
, 2. Medium Speed (20,000 g): Pellets Mitochondria and
Chloroplasts.
3. High Speed (80,000 g): Pellets Microsomes (internal
membrane fragments, pieces of ER and Golgi).
4. Very High Speed (150,000 g): Pellets Ribosomes
(smallest complexes, protein synthesis site).
Prokaryotic vs. Eukaryotic Cells & Size
Limits (Concept 2)
1. Universal Cell Features
All cells, without exception, possess four components:
Plasma Membrane: Selective barrier enclosing the
cytoplasm.
Cytosol: Semifluid, jelly-like substance in which subcellular
components are suspended.
Chromosomes: Carry genetic information in the form of DNA.
Ribosomes: Tiny complexes that make proteins according to
instructions from the genes.
2. Structural Differences (Textual Comparison)
Prokaryotic Cells (Bacteria & Archaea): DNA is
concentrated in a non-membrane-enclosed region called the
Nucleoid. They completely lack membrane-bound organelles.
They are typically much smaller (1–5 micrometers).
Eukaryotic Cells (Protists, Fungi, Plants, Animals): DNA
is safely enclosed within a true, double-membrane-bound
Nucleus. They contain highly specialized membrane-bound
organelles suspended in the cytoplasm. They are much larger
(10–100 micrometers).
3. Surface Area-to-Volume Ratio
Cell size is limited by metabolic requirements and the physics
of diffusion.
As a cell increases in size, its volume grows cubically
(r^3), which is much faster than its surface area, which
grows quadratically (r^2).
Exam Key Concept: Smaller cells are more efficient
because they maintain a higher surface area-to-volume
ratio, allowing sufficient exchange of nutrients and wastes
across the plasma membrane relative to their metabolic
volume.
Summary from Campbel biology
+exam's questions
Microscopy and Cell Fractionation
(Concept 1)
1. Microscopy Principles
Magnification: The ratio of an object's image size to its real
size.
Resolution: The measure of image clarity. It is the minimum
distance two points can be separated and still be
distinguished as separate points.
Contrast: The difference in brightness between light and dark
areas.
2. Types of Microscopes (Textual Comparison)
Light Microscope (LM): Uses visible light and glass lenses.
Effectively magnifies up to 1,000 times. Its resolution limit is
0.2 micrometers. Key Exam Advantage: It is the only type
that allows the visualization of living cells and dynamic
biological processes.
Scanning Electron Microscope (SEM): Focuses a beam of
electrons onto the specimen's surface, which is coated with
gold. Key Exam Advantage: Provides a detailed 3D image
of the surface topography. Requires cell fixation, so
specimens are dead.
Transmission Electron Microscope (TEM): Aims an
electron beam through a very thin section of a specimen
stained with heavy metals. Key Exam Advantage: Used to
study the internal ultrastructure of cells and organelle
profiles. Specimens are dead.
3. Cell Fractionation
A laboratory technique that uses a Centrifuge to break cells apart and separate major
organelles based on size and density.
The Core Rule: Larger and heavier components pellet at
lower speeds. Smaller and lighter components remain in the
liquid (supernatant) and require higher speeds to pellet.
Pelleting Sequence (From Lowest to Highest Speed):
1. Low Speed (1,000 g): Pellets the Nuclei (largest and
heaviest).
, 2. Medium Speed (20,000 g): Pellets Mitochondria and
Chloroplasts.
3. High Speed (80,000 g): Pellets Microsomes (internal
membrane fragments, pieces of ER and Golgi).
4. Very High Speed (150,000 g): Pellets Ribosomes
(smallest complexes, protein synthesis site).
Prokaryotic vs. Eukaryotic Cells & Size
Limits (Concept 2)
1. Universal Cell Features
All cells, without exception, possess four components:
Plasma Membrane: Selective barrier enclosing the
cytoplasm.
Cytosol: Semifluid, jelly-like substance in which subcellular
components are suspended.
Chromosomes: Carry genetic information in the form of DNA.
Ribosomes: Tiny complexes that make proteins according to
instructions from the genes.
2. Structural Differences (Textual Comparison)
Prokaryotic Cells (Bacteria & Archaea): DNA is
concentrated in a non-membrane-enclosed region called the
Nucleoid. They completely lack membrane-bound organelles.
They are typically much smaller (1–5 micrometers).
Eukaryotic Cells (Protists, Fungi, Plants, Animals): DNA
is safely enclosed within a true, double-membrane-bound
Nucleus. They contain highly specialized membrane-bound
organelles suspended in the cytoplasm. They are much larger
(10–100 micrometers).
3. Surface Area-to-Volume Ratio
Cell size is limited by metabolic requirements and the physics
of diffusion.
As a cell increases in size, its volume grows cubically
(r^3), which is much faster than its surface area, which
grows quadratically (r^2).
Exam Key Concept: Smaller cells are more efficient
because they maintain a higher surface area-to-volume
ratio, allowing sufficient exchange of nutrients and wastes
across the plasma membrane relative to their metabolic
volume.
