Microorganisms: Definitions, Roles, Cell Types, and Key Scientists

What is a microorganism?

A living thing that is too small to be seen with the naked eye and requires a microscope to be visualized.

What are the essential roles of microorganisms?

Decomposers (recycling nutrients) and photosynthetic microbes (producing oxygen and forming the base of food webs).

What are the beneficial roles of microorganisms?

Food production (bread, cheese, yogurt), bioremediation (cleaning up pollutants), and biotechnology (producing insulin, antibiotics, and vaccines).

What are the harmful roles of microorganisms?

Pathogens that cause infectious diseases in humans, animals, and plants.

How do prokaryotic and eukaryotic cells compare in size?

Prokaryotic cells are very small (0.1 to 5.0 µm); eukaryotic cells are significantly larger (10 to 100 µm).

What is the difference in nuclear membranes between prokaryotic and eukaryotic cells?

Prokaryotic cells lack a nuclear membrane; eukaryotic cells possess a nuclear membrane.

What is the composition of cell walls in prokaryotic and eukaryotic cells?

Prokaryotic cell walls are composed of peptidoglycan (Bacteria) or distinct polymers (Archaea); eukaryotic cell walls are made of cellulose (plants/algae) or chitin (fungi).

What organelles are present in eukaryotic cells?

Eukaryotic cells contain membrane-bound organelles like mitochondria, the endoplasmic reticulum, and the Golgi apparatus.

What major contributions did Leeuwenhoek make?

Invented the microscope and was the first to observe microbes.

What did Snow demonstrate regarding cholera?

Demonstrated the epidemic spread of cholera through water.

What did Schleiden & Schwann propose?

Proposed that all organisms are composed of cells.

What did Tyndall verify?

Verified Pasteur's evidence against spontaneous generation.

What discovery is Griffith known for?

Discovered genetic transformation.

What did Watson, Crick, Franklin & Wilkins determine?

Determined the structure of DNA.

What did Pasteur develop?

Developed evidence against spontaneous generation (swan-neck flask experiment).

What did Koch identify?

Identified the causative agent of tuberculosis.

What did Semmelweis demonstrate?

Demonstrated that puerperal/childbed fever is a contagious disease transmitted by physicians during childbirth.

What did Lister introduce?

Introduced antiseptic surgery.

What did Ehrlich use to treat syphilis?

Used salvarsan to treat syphilis.

What was Jenner's contribution?

Developed the first vaccine.

What did Fleming discover?

Discovered penicillin.

What experiment did Redi conduct?

Conducted the meat/maggot experiment and refuted spontaneous generation.

What characteristics define Bacteria?

Single-celled prokaryotes with cell walls containing peptidoglycan, found in nearly all common environments.

What defines Archaea?

Single-celled prokaryotes with cell walls lacking peptidoglycan, frequently inhabiting extreme environments.

What is Eucarya?

Organisms made of complex eukaryotic cells containing a nucleus and membrane-bound organelles.

How do Bacteria, Archaea, and Eucarya compare in cell size?

Bacteria and Archaea are small (0.3-2 µm); Eucarya are much larger (10-100 µm).

What is the cell wall composition of Bacteria?

Bacteria contain peptidoglycan.

What is the habitat of Bacteria?

Bacteria live in common/diverse environments.

What is the habitat of Archaea?

Archaea often reside in extreme environments.

What is the habitat of Eucarya?

Eucarya inhabit wide-ranging terrestrial and aquatic environments.

What are the characteristics of Algae?

Can be unicellular or multicellular; use sunlight (photoautotrophs).

What are the characteristics of Fungi?

Can be unicellular (yeasts) or multicellular (molds); absorb organic compounds (chemoheterotrophs).

What are the characteristics of Protozoa?

Strictly unicellular; ingest or absorb organic compounds (chemoheterotrophs).

What distinguishes viruses, viroids, and prions?

Viruses are obligate intracellular parasites; viroids contain RNA only; prions contain neither DNA nor RNA.

What is present in viruses but absent in viroids?

Protein coat is present in viruses; absent in viroids.