Define the boundaries of life by examining Plantae/Animalia briefly, and exploring viruses, viroids, prions, and lichens deeply.
Very brief overview of Plants and Animals.
The green trees outside your window and your pet dog belong to the two most familiar kingdoms of life. Let's look at what defines their biological boundaries.
Kingdom Plantae includes all eukaryotic, chlorophyll-containing organisms commonly called plants. At the microscopic level, their cells are defined by prominent chloroplasts and a rigid cellulosic cell wall.
Why viruses aren't in the 5 kingdoms.
History, structure, and genetic material rules of viruses.
Ever caught a cold or the "flu"? You've experienced the power of viruses firsthand!
Biologically, viruses exist in a gray area. They aren't considered truly "living" because they completely lack a cell structure. Outside of a host, a virus is just an inert crystalline structure.
However, once they infect a living cell, they hijack the host's cellular machinery to replicate themselves, often killing the host in the process. Because they absolutely require a host to survive and multiply, they are known as obligate parasites.
Diagram of a Bacteriophage.
A bacteriophage is a virus that infects bacteria. Its complex structure includes a polyhedral head protecting genetic material, a helical sheath, and tail fibres for attaching to host cells.
Definitions of viroids, prions, and lichens.
Sometimes, the smallest biological entities cause the biggest problems. Even smaller and simpler than viruses are viroids.
Discovered in 1971 by T.O. Diener, viroids are tiny infectious agents known to cause potato spindle tuber disease.
Unlike viruses, viroids are simply free RNA of low molecular weight. They completely lack the protective protein coat (capsid) that viruses have.
MCQ differentiating viruses, viroids, and prions.
A plant pathologist isolates a new infectious agent causing stunted growth and spindle-shaped deformities in a potato crop. Biochemical analysis reveals the agent is composed entirely of free, low-molecular-weight RNA and completely lacks a protein coat. Which of the following best classifies this infectious agent?
Fill in the blanks regarding lichen symbiosis.
Lichens represent mutually useful, associations between algae and fungi. The algal component is known as the , which is autotrophic in nature. Conversely, the fungal component is referred to as the , which relies on a heterotrophic mode of nutrition. In this close relationship, the algae prepare food while the fungi provide and absorb mineral nutrients and water. Because they do not grow in affected areas, lichens are considered excellent indicators.