Biology and Classification of the Kingdom Protoctista
The Kingdom Protoctista
The organisms included in the Kingdom Protoctista are constituted by eukaryotic cells. Therefore, they are larger than bacteria and possess a nucleus containing genetic material and cytoplasmic organelles. They may join together to form colonies or develop into multicellular organisms. These organisms live in aquatic environments or internal liquids, such as parasites, and can be autotrophs or heterotrophs, depending on the presence of chloroplasts. This kingdom includes protozoa, algae, and slime molds.
Classification and Features of Protozoa
Protozoa are heterotrophic organisms that feed by the ingestion of bacteria or organic particles. They reproduce asexually by fission and live in soil and water. Some protozoa are resistant, forming cysts and spores. Protozoa are classified according to their type of locomotion:
- Sarcodina: They have pseudopodia, which allow them to move and ingest food via phagocytosis. Amoebas and foraminifers belong to this group.
- Flagellates: These protozoa use flagella for locomotion. They live in natural environments, and some are photosynthetic.
- Ciliates: These are protozoa with a complex cell structure. They possess cilia and two nuclei: one dealing with reproduction and the other with vegetative functions. They are usually free-living.
- Sporozoa: They lack specialized structures for locomotion. All sporozoa are parasites and reproduce through multiple division, where each cell creates 4 or 8 daughter cells.
Characteristics of Algae
Algae have no distinct organs or organizational structures similar to higher plants. Today, these organisms are included in the Kingdom Protoctista.
Unicellular and Multicellular Algae
Unicellular Algae: All present chlorophyll. Their chloroplasts contain most of the cell's components, and they possess a cellulose cell wall; some also have flagella. These aquatic algae can also be found in the soil and reproduce both sexually and asexually.
Multicellular Algae: These have a very simple structure without true tissues or defined organs. They must live in wet environments to absorb all necessary substances directly, as they lack a transport system. They contain chlorophyll and other photosynthetic pigments within a cell wall composed of cellulose.
Classification of Algae by Color
Unicellular algae are aquatic organisms living in surface waters, requiring light for photosynthesis. They reproduce both asexually and sexually. Based on their pigmentation, they are classified as:
- Green Algae: Found in shallow marine and freshwater areas, their primary pigment is chlorophyll.
- Brown Algae: Exclusively marine, they contain chlorophyll and fucoxanthin, which allows light uptake at greater depths.
- Red Algae: These marine organisms live at great depths and contain phycoerythrin. Their cell membranes are often enveloped in calcium salts.
Slime Molds and Heterotrophic Protoctists
Often referred to as fungus-like protoctists, these are all heterotrophs that breed via spores found in the soil. They possess a complex life cycle.