CH 6 Pearson study guide from Lecture Outline

Cell Types and Classification

Overview of Cell Types

Cells are the basic units of life and can be classified into two major types: prokaryotic and eukaryotic cells. These types differ in their structure, organization, and complexity.

• Prokaryotic cells: Simple cells without a nucleus or membrane-bound organelles. Examples include Bacteria and Archaea.

• Eukaryotic cells: Complex cells with a nucleus and membrane-bound organelles. Examples include Plants, Animals, Fungi, and Protists.

Cell Size and Surface Area to Volume Ratio

Why Are All Cells Small?

Cells are generally small because as a cell grows, its volume increases faster than its surface area. This limits the rate at which materials can enter or leave the cell, affecting cell function and efficiency.

• Surface area to volume ratio: As cells get bigger, their surface area to volume ratio decreases, making it harder for the cell to efficiently exchange materials with its environment.

• Adaptations: Cells may develop folds, microvilli, or become elongated to increase surface area.

Formula:

Microscopy and Cell Organization

Microscope Types

• Compound Light Microscope: Uses visible light and lenses to magnify small objects, suitable for viewing living cells.

• Electron Microscope: Uses beams of electrons for much higher magnification and resolution, allowing visualization of cell ultrastructure.

Cellular Level of Organization

Organelles Found in Both Cell Types

All cells share certain structures essential for life. The following table summarizes key organelles, their structure/location, and function:

Prokaryotic Cell Structure

Main Characteristics

• Size: Generally smaller than eukaryotic cells (1-10 µm).

• Mode of cell division: Binary fission.

• Genetic recombination: Horizontal gene transfer (conjugation, transformation, transduction).

• Membrane-bound organelles: Absent.

The Cell Envelope

• Glycocalyx: Outer polysaccharide layer for protection and adhesion.

• Cell Wall: Middle layer, provides shape and protection; made of peptidoglycan in bacteria.

• Plasma (Cell) Membrane: Phospholipid bilayer controlling entry/exit of substances.

External Structures

• Flagella: Whip-like appendages for motility.

• Fimbriae: Short, bristle-like fibers for adhesion.

• Conjugation pili: Tubes for DNA transfer between cells.

Inside the Cytoplasm (Unique to Prokaryotes)

• Nucleoid: Region containing single circular DNA molecule.

• Plasmids: Small accessory rings of DNA.

Bacterial Shapes

• Coccus: Spherical

• Bacillus: Rod-shaped

• Spirillum: Spiral-shaped

Eukaryotic Cell Structure

Main Characteristics

• Size: Larger than prokaryotic cells (10-100 µm).

• Mode of cell division: Mitosis and meiosis.

• Genetic recombination: Sexual reproduction and crossing over.

• Membrane-bound organelles: Present (nucleus, mitochondria, etc.).

Major Eukaryotic Organelles and Functions

Comparing Prokaryotic and Eukaryotic Cells

Key Differences

• Nucleus: Present in eukaryotes, absent in prokaryotes.

• Organelles: Membrane-bound organelles only in eukaryotes.

• Size: Eukaryotes are generally larger.

• Cell division: Binary fission (prokaryotes) vs. mitosis/meiosis (eukaryotes).

Origin of Eukaryotic Cells

Endosymbiotic Theory

The endosymbiotic theory explains the origin of eukaryotic cells as a result of symbiosis between different species of prokaryotes. Key organelles such as mitochondria and chloroplasts are believed to have originated from free-living bacteria engulfed by ancestral eukaryotic cells.

• Mitochondria: Originated from aerobic bacteria.

• Chloroplasts: Originated from photosynthetic bacteria.

• Evidence: Double membranes, own DNA, and ribosomes similar to bacteria.

Diagram Sequence: Ancestral prokaryote → Engulfment of aerobic bacterium → Mitochondrion → Engulfment of photosynthetic bacterium → Chloroplast

Summary Table: Prokaryotic vs. Eukaryotic Cells

Key Terms and Definitions

• Plasma membrane: The semipermeable boundary of the cell.

• Cell wall: Rigid structure outside the plasma membrane in plants, fungi, and bacteria.

• Ribosome: Organelle responsible for protein synthesis.

• Nucleoid: Region in prokaryotes containing DNA.

• Mitochondria: Organelle for ATP production in eukaryotes.

• Chloroplast: Organelle for photosynthesis in plants.

• Endosymbiotic theory: Theory explaining the origin of mitochondria and chloroplasts.

Example: Escherichia coli is a prokaryotic bacterium, while Arabidopsis thaliana is a eukaryotic plant.

Additional info: Some content and definitions have been expanded for clarity and completeness.