Viruses, Bacteria, Plants & Animals: Characteristics and Differences

Nutrition, Mobility and Cell Characteristics

Nutrition

Nutrition: Variety — plants (autotrophs), animals (heterotrophs).

Mobility

Mobility: Variety — plants (immobile), animals (mobile).

Growth

Growth: Plants (often indeterminate / unlimited), animals (typically determinate / limited).

Cellular Coverings

Cell coverings: Plants: cell wall and cell membrane; Animals: plasma membrane.

Similarities of Living Beings

Similarities: assimilation, sensitivity, autoregulation and reproduction.

Cell Composition and Organelles

Cell composition: Life composed of abundant protoplasm; cells possess a cell membrane, cytoplasm, and a nuclear membrane (karyotheca) with a nucleus.

There are a variety of structures in the cytoplasm (organelles): ribosomes, endoplasmic reticulum, etc.

Viruses: Composition, Size and Characteristics

Viral Composition and Hosts

Viruses: Agents of simple chemical composition that infect plants, animals and humans. Some viruses (or virus-like agents) also attack and can destroy pathogenic bacteria (for example, bacteriophages).

Terminology: Ponzoña

Ponzoña: term unclear in original text; sometimes used historically to refer to poisons or to viral/toxic agents. (Here it may have been intended to relate to viruses or toxins.)

Size and Shape

They measure in very small units — originally described as millimicrons — and may be long, elongated or cylindrical in shape. A millimicron was historically defined as one millionth part of a millimeter.

Viral Characteristics

• No independent nutrition.
• Do not absorb or excrete in the way cellular organisms do.
• Do not respire — there is no internal transformation of substances as in cellular life.
• Do not reproduce independently by cellular mechanisms; they are formed from living matter inside host cells and are released when the cell is affected.
• They do not have the proper cellular organization of living beings.

Diseases Caused by Viruses

Diseases provoked by viruses include: yellow fever, encephalitis, rabies, smallpox and measles.

Kingdom Monera and Bacteria

Kingdom Monera

Kingdom Monera: unicellular prokaryotic organisms (organisms without a nuclear membrane), including bacteria and blue-green algae (cyanobacteria).

Bacteria: General Characteristics

Bacteria: Prokaryotic, unicellular organisms belonging to Kingdom Monera. They may be heterotrophic, are measured in microns, and can live in water, soil, air, on dead organic matter and within cells.

They can cause diseases and contribute to the decomposition of organic matter.

Classification and Examples

Classification (by shape) and examples:

• Cocci (spherical)
• Bacilli (rod-shaped)
• Spirilla (spiral-shaped)
• Vibrios (comma-shaped)

Disease examples: pneumonia (pneumococcus), syphilis (spirochete), leprosy (Mycobacterium), cholera (Vibrio cholerae).

Bacterial Survival Mechanisms

When environmental conditions are unfavorable, bacteria can lose water and form a protective, thickened structure (for example, endospores or other resistant forms). This dry form allows survival until conditions improve and the organism can rehydrate and resume activity.

Bacteria can also become encapsulated, developing a gelatinous capsule that surrounds the cell. Encapsulation can protect bacteria from phagocytosis; in some cases white blood cells cannot easily destroy encapsulated bacteria.