Understanding Viruses, Fungi, Prokaryotes, and Protista

1. Viruses

Viruses are not living organisms but very small particles that cause infectious diseases. A virus has an outer coat of protein but no nucleus. It carries genetic information and damages cells while it reproduces.

Reproductive Cycle

• Infection: A single virus attacks a cell and breaks through the cell membrane.
• Replication: The virus reproduces its genetic information inside the host cell.
• Release: The cell bursts, releasing newly made viruses to infect other cells.

2. Three More Kingdoms: Fungi, Prokaryotes, and Protista

Prokaryotes: Bacteria

Bacteria are microorganisms—living cells capable of respiration, movement, growth, feeding, and reproduction. They are unicellular and prokaryotic.

Characteristics

They are surrounded by an outer cell wall for protection. They contain cytoplasm enclosed by a cell membrane and genetic information, but they lack a nucleus.

Reproduction

In the right conditions, bacteria can reproduce very quickly by binary fission.

Nutrition

Most prokaryotes are heterotrophs, but some are autotrophic, such as cyanobacteria that perform photosynthesis.

Protista

The Protista is a group of organisms that have nuclei and are neither plants, fungi, nor animals. They are usually unicellular, although some are multicellular without specialized tissues (e.g., algae).

Animal-like Protists: Protozoa

These are unicellular, heterotrophic eukaryotes. They feed on dead organic matter and bacteria; some are predators.

Plant-like Protists: Algae

These are unicellular, colonial, or multicellular autotrophic eukaryotes. They contain chlorophyll or other pigments.

Fungi

Characteristics

• Can be multicellular or unicellular.
• Do not have specialized tissues.
• Bodies are formed by multicellular strings called hyphae.
• The entire body of a multicellular fungus is referred to as a mycelium.
• They produce reproductive structures (mushrooms) that release spores.

Reproduction

Unicellular fungi reproduce asexually by fission or budding; multicellular fungi reproduce by spores or fragmentation.

Nutrition

Fungi feed on organic matter and are divided into:

• Parasites
• Saprophages: Organisms that feed on dead organic matter.