L5a Biodiversity

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The Six Kingdoms of Life

Overview of Biological Classification

The six-kingdom system is a widely accepted method for classifying all living organisms based on cellular organization and modes of nutrition. The kingdoms include Plantae, Animalia, Fungi, Protista, Eubacteria, and Archaebacteria. Eubacteria and Archaebacteria are prokaryotic, while the other four kingdoms are eukaryotic.

Diagram of the six kingdoms of life

Importance of Prokaryotes

Harmful Effects of Prokaryotes

Pathogens: Many bacteria cause diseases in humans, animals, and plants. Examples include cholera, leprosy, typhoid fever, strep throat, salmonella poisoning, and tuberculosis.
Bacterial infections can also affect livestock and crops, impacting agriculture and food supply.
Diseases that harm one species may benefit another by altering ecological balances (e.g., weakening predators can benefit prey populations).

Beneficial Effects of Prokaryotes

Decomposers: Bacteria break down dead organic matter, recycling nutrients in ecosystems.
Nitrogen Fixation: Certain bacteria convert atmospheric nitrogen into forms usable by plants, supporting plant growth.
Photosynthetic Bacteria: Cyanobacteria and other photosynthetic bacteria are major producers of atmospheric oxygen, especially in marine environments.
Gut Flora: Bacteria in animal intestines aid digestion and produce essential vitamins such as K and B12.

Photosynthetic bacteria and cyanobacteria

Commercial and Medical Uses

Bacteria are essential in the production of foods such as vinegar, butter, cheese, yogurt, and sourdough bread.
They are used to produce antibiotics and medically valuable compounds like insulin and human growth hormone.
Bacteria play a role in sewage treatment and odor control by digesting organic matter and waste.

Examples of foods produced by bacteria Medical use of bacteria for insulin production

Bacterial Classification

Two Kingdoms of Bacteria

Bacteria are classified into two main kingdoms: Eubacteria and Archaebacteria. Eubacteria are the 'true' bacteria, while Archaebacteria are ancient bacteria with unique biochemical and genetic properties.

Six kingdoms with focus on Eubacteria and Archaebacteria

Key Features of Eubacteria

Prokaryotic: Lack a nucleus and membrane-bound organelles.
Unicellular: Each organism consists of a single cell, though some form colonies.
Cell Wall: Composed of peptidoglycan.
Genetic Material: Single circular DNA molecule (chromosome) in the nucleoid region; may also contain plasmids (small DNA loops).
Reproduction: Primarily by binary fission (asexual); some exchange genetic material via conjugation (sexual-like process).
Nutrition: Can be autotrophic (make their own food) or heterotrophic (consume organic material).

Structure of a Typical Bacterial Cell

Cell Wall: Provides shape and protection; made of peptidoglycan.
Capsule: An outer layer that protects against water loss and high temperatures.
Plasma Membrane: Regulates movement of substances in and out of the cell.
Ribosomes: Sites of protein synthesis, scattered throughout the cytoplasm.
Flagella: Long, whip-like structures for movement.
Pili: Short, hair-like structures that help in attachment to surfaces and other cells.
Plasmids: Small, circular DNA molecules carrying additional genes.

Structure of a typical bacterial cell

Bacterial Morphology

Bacterial Shapes

Cocci (singular: coccus): Spherical bacteria; resistant to drying.
Bacilli (singular: bacillus): Rod-shaped bacteria; absorb nutrients efficiently due to greater surface area.
Spirilli (singular: spirillum): Spiral-shaped bacteria; move easily through fluids.

Bacterial shapes: cocci, bacilli, spirilli

Bacterial Arrangements

Diplo-: Arranged in pairs.
Staphylo-: Arranged in clusters (like grapes).
Strepto-: Arranged in chains.

Example: Streptococcus pyogenes causes strep throat and is arranged in chains.

Streptococcus arrangement in chains Diagram of bacterial arrangements and shapes

Bacterial Cell Wall Structure and Gram Staining

Gram Stain Technique

The Gram stain, developed by Hans Christian Gram in 1884, is a differential staining technique that distinguishes bacteria based on cell wall composition. It divides bacteria into two groups:

Gram-positive: Thick peptidoglycan layer; stains purple.
Gram-negative: Thin peptidoglycan layer and an outer lipid membrane; stains pink.

Gram-negative and Gram-positive bacteria under microscope Gram-negative bacteria under microscope

Type	Peptidoglycan Layer	Outer Membrane	Stain Color
Gram-positive	Thick	Absent	Purple
Gram-negative	Thin	Present	Pink

Classification by Respiration

Aerobic and Anaerobic Bacteria

Aerobic Bacteria: Require oxygen for survival and growth. Obligate aerobes cannot survive without oxygen (e.g., most animals and plants).
Anaerobic Bacteria: Do not use oxygen for respiration. Obligate anaerobes cannot survive in the presence of oxygen. Facultative anaerobes can survive with or without oxygen, switching metabolic pathways as needed.

Some bacteria can switch between aerobic and anaerobic metabolism depending on environmental conditions.

Summary Table: Key Features of Prokaryotes

Feature	Eubacteria	Archaebacteria
Cell Type	Prokaryotic	Prokaryotic
Cell Wall	Peptidoglycan	No peptidoglycan (varied composition)
Habitat	Common (soil, water, organisms)	Extreme environments (hot springs, salt lakes)
Examples	Escherichia coli, Streptococcus	Halobacterium, Methanogens

Additional info: Archaebacteria are often called extremophiles due to their ability to survive in harsh environments such as high salinity, acidity, or temperature.