Structure and Reproduction of Bacteria, Viruses, Fungi and Parasites

Structure and Reproduction of Bacteria, Viruses, Fungi and Parasites


  • Bacteria are single-celled organisms.
  • Their basic structure includes a cell membrane, a cytoplasm, ribosomes, a nucleoid (DNA material), and some have a capsule for protection.
  • They replicate or multiply through a process called binary fission, an asexual process where one cell divides into two identical cells.
  • The shapes of bacteria include Cocci (round), Bacilli (rod-like), and Spiral.
  • Some bacteria are beneficial, such as those in the gut flora, while others can cause diseases.


  • Viruses are tiny infectious agents that need a host cell to replicate.
  • They contain genetic material (either DNA or RNA) surrounded by a protein coat, known as a capsid. Some have an additional layer, the envelope.
  • Viruses infect a host cell and take over its machinery to replicate, producing numerous virus particles.
  • These new virus particles release from the host cell to infect more cells.
  • Viruses cause a range of diseases across various species, from influenza to rabies.


  • Fungi are eukaryotic organisms and can be single-celled or multicellular.
  • They have a complex structure which includes a cell wall, a nucleus, cytoplasm, and organelles.
  • Fungi reproduce both asexually (through budding or spore formation) and sexually (through fusion of haploid cells, followed by meiosis).
  • Fungi include yeasts, moulds, and mushrooms. Some are helpful, like yeasts involved in bread production, others cause diseases (ringworm, athlete’s foot).


  • Parasites are organisms that live on or in another organism (the host) and benefit at the host’s expense.
  • They can be unicellular like protozoa, or multicellular like worms and arthropods.
  • Parasites exhibit a wide range of reproductive strategies, depending on their species. This includes asexual reproduction (binary fission, budding, or schizogony) or sexual reproduction.
  • Parasites cause different diseases in animals. For example, ticks can transmit Lyme disease, while fleas can transmit parasitic worms.
  • Control and prevention of parasites are of utmost importance in animal management.