Grade 11 Biology Textbook Notes (1)

The Protists

Overview

• Protists are a diverse group within the Kingdom Protista.

• They include the smallest eukaryotes and some of the largest organisms.

Importance of Protists

• Photosynthesis:

  • Key producers in the world’s oceans, along with certain prokaryotes.

• Consumers:

  • Non-photosynthetic protists play a crucial role as consumers, dominating lower levels of aquatic food pyramids.

• Habitat:

  • Highly abundant in moist terrestrial environments, especially in soil.

• Parasitic Protists:

  • Many protists act as parasites, living in or on host organisms.

    • Impact on Hosts:

      • Most parasites do not harm their hosts, yet some can cause serious diseases.

      • Examples of Diseases:

        • Malaria: caused by various species of the single-celled protist genus Plasmodium.

        • Giardia lamblia: the most common human parasite in North America.

          • Infection Process: Hosts become infected by consuming contaminated water.

          • Symptoms: Abdominal pain, diarrhea, and chronic gut inflammation.

The Origins of Eukaryotes

• Protists represent the first eukaryotes with cells containing a nucleus and membrane-bound organelles.

• Development of Internal Membranes:

  • Internal membranes likely arose from the folding of ancestral prokaryotic cell membranes.

  • Increased surface area from folding enhances the cell's ability to exchange materials effectively.