Questions and Answers
Which type of bacterial shape is characterized by a spiral form?
What is the primary function of the bacterial capsule?
Which of these bacterial arrangements describes cells that are grouped in chains?
What structure in prokaryotic cells is primarily responsible for motility?
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Which internal feature of prokaryotes contains the cell’s genetic material?
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What motion characterizes Spirochete bacteria, allowing them to navigate through viscous environments?
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Which statement best describes the composition of the bacterial plasma membrane?
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What is the main difference between facilitated diffusion and active transport?
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Which molecules are primarily moved through simple diffusion across the bacterial plasma membrane?
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What role do aquaporins play in the bacterial plasma membrane?
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Which structure is characteristic of the Gram-positive bacterial cell wall?
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What are teichoic acids and their function in the Gram-positive bacterial cell wall?
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What is the primary function of the Golgi apparatus in a eukaryotic cell?
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Which of the following structures is primarily responsible for producing ATP in cells?
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What characterizes twitching motility in bacteria?
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Which external feature provides structural support and protection in plant cells?
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What is a key function of the cytoskeleton in eukaryotic cells?
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How do flagella facilitate bacterial motility?
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Which type of bacterial motility is characterized by a smooth, slower movement without flagella?
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What is the function of cilia in eukaryotic cells?
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Study Notes
Bacterial Classification
- Bacteria can be classified by shape: cocci (spherical), bacilli (rod-shaped), spirilla (spiral-shaped), vibrios (comma-shaped), and spirochetes (corkscrew-shaped).
- Bacterial arrangements include: diplo (pairs), strepto (chains), staphyl (clusters), tetrads (groups of four), and sarcina (cube-like groups of eight).
Internal and External Features of Bacteria
Internal Features
- Nucleoid: Contains bacterial circular DNA and genetic material.
- Plasmids: Circular DNA molecules that carry advantageous genes, such as those for antibiotic resistance.
- Ribosomes: Sites of protein synthesis, smaller than those in eukaryotes.
- Cytoplasm: Gel-like substance that supports metabolic activities and contains internal components.
External Features
- Cell wall: Composed of peptidoglycan in bacteria, providing structure and protection.
- Plasma membrane: Phospholipid bilayer that regulates substance entry and exit; involved in metabolic processes.
- Flagella: Whip-like structures for motility, enabling movement towards or away from stimuli.
- Pili/Fimbriae: Hair-like structures for attachment and conjugation.
- Capsule: Gelatinous layer for protection against desiccation and evasion from the immune system.
Eukaryotic Features
Internal Features
- Nucleus: Membrane-bound organelle housing the cell's DNA; controls gene expression and DNA replication.
- Endoplasmic Reticulum (ER):
- Rough ER synthesizes and processes proteins.
- Smooth ER synthesizes lipids and detoxifies chemicals.
- Golgi apparatus: Modifies, sorts, and packages proteins and lipids.
- Mitochondria: Powerhouse of the cell, producing ATP through cellular respiration.
- Cytoskeleton: Provides structural support, aids cell division, and facilitates movement.
External Features
- Plasma membrane: Phospholipid bilayer with proteins, cholesterol, and carbs for regulating substance movement and cell signaling.
- Cell wall: Composed of cellulose in plants or chitin in fungi for structural support.
- Cilia and flagella: Microtubule-based structures for fluid movement and cell motility.
Bacterial Motility Types
- Flagellar motility: Most common, using flagella that rotate like propellers for movement.
- Twitching motility: Short jerky movements using pili.
- Gliding motility: Smooth movements observed in non-flagellated bacteria, possibly aided by slime secretion.
- Swarming motility: Coordinated movement across surfaces, producing surfactants to reduce surface tension.
- Spirochete motility: Corkscrew motion enabling movement through viscous environments due to axial filament rotation.
Bacterial Plasma Membrane Functionality
- Plasma membrane has a phospholipid bilayer with hydrophilic heads outside and hydrophobic tails inside.
- Embedded proteins facilitate various functions, including selective permeability.
- Substance transport methods:
- Simple diffusion: Small molecules passively diffuse across the membrane.
- Facilitated diffusion: Larger or polar molecules use protein channels for membrane passage.
- Active transport: Requires energy to move substances against their concentration gradient.
- Osmosis: Water moves to balance solute concentrations, sometimes using aquaporins.
Gram-positive vs. Gram-negative Cell Walls
Gram-positive Cell Wall
- Thick peptidoglycan layer (up to 40 layers) offers strength and stability.
- Contains teichoic acids for cell wall stabilization.
- Lacks an outer membrane, making them more prone to certain antibiotics.
- Stains purple due to retention of crystal violet dye after decolorization.
Gram-negative Cell Wall
- Thin peptidoglycan layer (1-2 layers) found in the periplasmic space.
- Contains an outer membrane composed of a lipid bilayer with lipopolysaccharides (LPS) for added protection.
- Has prominent porins allowing passage of small molecules.
- Stains red or pink due to the inability to retain crystal violet after counterstaining.
Structural Differences and Properties
- Gram-positive bacteria's thick peptidoglycan allows dye retention but makes them vulnerable to antibiotics.
- Gram-negative bacteria's thin layer and outer membrane provide resistance to antibiotics and environmental threats, resulting in pink staining.
Peptidoglycan Function in Osmosis and Pressure
- Osmosis facilitates water movement across a semipermeable membrane, aiming to equalize solute concentrations.
- Osmotic pressure results when water enters cells with higher internal solute concentrations, potentially leading to cell swelling or lysis if not regulated.
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