Biology Classification Systems

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Questions and Answers

What is the primary function of the field of systematic biology?

Preserving collections of organisms

Providing scientific names for organisms (correct)

Studying their environmental adaptations

Investigating their evolutionary histories

Who is credited with dividing the living world into two kingdoms, plants and animals?

Charles Darwin

Jean-Baptiste Lamarck

Aristotle (correct)

Carolus Linnaeus

What was the third kingdom established in the 19th century to accommodate single-celled organisms?

Monera

Protista (correct)

Algae

Fungi

In the three-domain system, which domain comprises all eukaryotic organisms?

Domain Eukarya Signup and view all the answers

What is the main characteristic that distinguishes prokaryotes from eukaryotes?

Absence of a nucleus Signup and view all the answers

What is the naming system devised by Carolus Linnaeus?

Binomial Nomenclature Signup and view all the answers

What is the correct sequence of the eight classification levels of living things?

Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species Signup and view all the answers

What is the scientific name for the gray wolf?

Canis lupus Signup and view all the answers

What is the approximate percentage of water in the cytoplasm of a prokaryotic cell?

80% Signup and view all the answers

What is the function of mesosomes in prokaryotic cells?

They increase plasma membrane surface area and enzymatic content Signup and view all the answers

What is the characteristic of the DNA in a prokaryotic cell?

It is double-stranded and circular Signup and view all the answers

What is the function of plasmids in prokaryotic cells?

They confer protective traits such as drug resistance or the production of toxins Signup and view all the answers

What is the name of the process by which plasmids are passed on from one bacterial cell to another?

Conjugation Signup and view all the answers

What is the role of the nucleoid in a prokaryotic cell?

It is the region where the chromosome is located Signup and view all the answers

What is the characteristic of the chromosome in a prokaryotic cell?

It is single and circular Signup and view all the answers

What is the function of some plasmids in relation to antibiotics?

They code for proteins that degrade antibiotics Signup and view all the answers

What is the primary function of plasmids in genetic engineering?

To facilitate horizontal gene transfer Signup and view all the answers

What is the composition of the 50S subunit of a 70S ribosome?

23S and 5S rRNA Signup and view all the answers

What is the function of inclusion granules in bacterial cells?

To store reserve materials Signup and view all the answers

What is the characteristic of endospores that makes them resistant to adverse conditions?

Presence of calcium dipicolinate Signup and view all the answers

What is the purpose of Bacillus stearothermophilus spores in quality control?

To test heat sterilization equipment Signup and view all the answers

What is the site of protein synthesis in all organisms?

Ribosomes Signup and view all the answers

How do mRNA and tRNA molecules interact with ribosomes during protein synthesis?

mRNA attaches to the 30S subunit and tRNA attaches to the 50S subunit Signup and view all the answers

What is the characteristic of ribosomes that distinguishes them from other cell organelles?

They are composed of rRNA and protein Signup and view all the answers

What is the purpose of calcium dipicolinate in the formation of endospores?

To stabilize the proteins and DNA in the endospore Signup and view all the answers

What is the final stage of endospore formation?

Dehydration and maturation Signup and view all the answers

What is the function of the cortex in the endospore?

To protect the endospore from UV light and harsh chemicals Signup and view all the answers

What is the process by which a single endospore forms within a bacterium?

Endosporulation Signup and view all the answers

What is the structure that forms between the DNA and the rest of the cell during endosporulation?

Spore septum Signup and view all the answers

What are the unique surface layers found in endospores that are not found in vegetative cells?

Exosporium, spore coat, cortex, and core wall Signup and view all the answers

Study Notes

Systematic Biology

Provides scientific names for organisms
Describes them
Preserves collections of them
Provides classifications for the organisms, keys for their identification
Investigates their evolutionary histories
Considers their environmental adaptations

History of Classification

Aristotle (384-322 BC) divided the living world into two kingdoms: plants and animals
This system persisted for over 2000 years
By the 19th century, the microscope revealed tiny single-celled organisms, leading to the creation of a third kingdom: Protista
In 1938, Protista was divided into two kingdoms: Monera (unicellular prokaryotic microorganisms) and Protista (eukaryotic microorganisms)

Prokaryotes and Eukaryotes

In the 1940s, biologists divided living organisms (except viruses) into two distinct groups: Prokaryotes (bacteria) and Eukaryotes (all other organisms)
Prokaryotes (bacteria) have cells that lack a nucleus and other cell organelles
Eukaryotes consist of cells that contain nuclei and other kinds of organelles

Three Domains of Life

The three-domain system is currently used, replacing the old five-kingdom system
Domain Bacteria and Domain Archaea comprise the prokaryotes
Domain Eukarya includes all eukaryotic organisms

Classification Levels

There are eight classification levels of living things:
- Domain
- Kingdom
- Phylum
- Class
- Order
- Family
- Genus
- Species

Binomial Nomenclature

Carolus Linnaeus devised a naming system for organisms: Binomial Nomenclature
Rules:
- Gray wolf (Canis lupus) is native to North America and Eurasia

Bacterial Internal Structures

Cytoplasm: a gel-like matrix composed of 80% water, containing nucleic acids (DNA and RNA), enzymes, amino acids, carbohydrates, lipids, inorganic ions, and many low molecular weight compounds.
Functions of cytoplasm: site of most bacterial metabolism, leading to growth and replication.

Mesosomes

Mesosomes: plasma membrane infoldings.
Functions of mesosomes:
- Role in the formation of cell walls.
- Replication of DNA in prokaryotes.
- Increase plasma membrane surface area and enzymatic content.
- Aid in the transfer of chromosomes to daughter cells.
- Analogous to cristae in the mitochondria of eukaryotic cells.

Nucleoid

Nucleoid: also known as chromatin body, no nuclear membrane or nucleoli.
Characteristics of nucleoid:
- Single circular chromosome of double-stranded, supercoiled DNA.
- No nuclear membrane.
- No nucleolus.
- No mitotic spindle.
- No histones.
- Size: 580,000 base pairs in Mycoplasma gallinarum to 9,140,000 bp in Myxococcus xanthus.

Plasmids

Plasmids: small, nonessential, extra-chromosomal DNA, circular (linear in a few species).
Characteristics of plasmids:
- Present in cytoplasm, but may become incorporated into chromosomal DNA.
- Often confer protective traits such as drug resistance or the production of toxins and enzymes.
- Passed on in conjugation.
- Replicate independently.
- Examples: antibiotic resistance, virulence factors, and conjugative plasmids.

Ribosomes

Ribosomes: the most abundant in the cytoplasm, up to 15,000 ribosomes.
Characteristics of ribosomes:
- 70S ribosomes in prokaryotes, composed of 50S and 30S subunits.
- 50S subunit contains 23S and 5S rRNA, and 30S subunit contains 16S rRNA.
- Chemically composed of ribosomal RNA (rRNA) and protein.
- Function as a workbench for protein synthesis – translation of mRNA into proteins.

Inclusion Granules

Inclusion granules: nonliving components, not bounded by membranes, several kinds of reserve deposits.
Examples: volutin granules, polysaccharide granules, lipid inclusions, sulfur and nitrogen granules, and gas vacuoles.

Endospores

Endospores: dormant, resistant structures, produced intracellularly upon starvation.
Characteristics of endospores:
- Resistant to adverse conditions: high temperatures, irradiation, cold, and organic solvents.
- Contain calcium dipicolinate.
- Not a mechanism of reproduction.
- Examples: Bacillus and Clostridium species.
- Formation: through endosporulation, involving DNA replication, spore septum formation, peptidoglycan cortex, and spore coat formation.
- Structure: cortex, core, and inner membrane, leading to resistance against UV light and harsh chemicals.

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Test your knowledge of biological classification systems, from systematic biology to Aristotle's early contributions.