Kingdom Protista Notes
Introduction to Kingdom Protista
* "Junk Drawer" Kingdom: Protista is sometimes called the "junk drawer" or "left-over" kingdom because it includes diverse eukaryotes that didn't fit neatly into the plant, animal, or fungus kingdoms when initially classified. Modern systematics, using complex DNA comparisons, divides protists into potentially many separate kingdoms, highlighting the difficulty in classifying these organisms.
* General Description:
* All protists are complex eukaryotes.
* Most are unicellular, but some forms are colonial or multicellular.
* They exhibit various modes of nutrition and mobility.
* Habitat: Most are aquatic (living in water or moist soil), while some inhabit the bodies of other organisms.
* Plankton: Protists that drift or swim near the water's surface are known as plankton. Surface waters and tidal habitats are rich in protists. Phytoplankton (plant-like protists) are crucial primary producers.
* Osmoregulation: Many protists, like Paramecium, have a contractile vacuole to pump out excess water absorbed via osmosis, especially in freshwater environments.
* Protists & Human Welfare/Ecology:
* Disease: Many cause human diseases, such as Malaria (caused by Plasmodium) and African Sleeping Sickness (caused by Trypanosoma). Amoebic dysentery is caused by certain amoebas. Giardia causes severe diarrhea. Insects like mosquitoes can act as vectors, transmitting protist diseases.
* Ecological Role: Phytoplankton perform about half of the world's photosynthesis and oxygen production, forming the base of marine and freshwater food chains. Fungus-like protists act as decomposers. Diatoms are significant primary producers.
* Industrial Uses: The silica skeletons of diatoms form diatomaceous earth, used as filters and abrasives. Red algae provide substances like agar and carrageenan used as thickeners (Answer based on general knowledge, supplement to Station Lab Q8).
* Bioluminescence: Some protists, like certain dinoflagellates, are bioluminescent.
* Red Tides: Blooms of dinoflagellates can cause "red tides". While individual organisms may not be harmful, their high concentration during a bloom produces toxins that accumulate in shellfish, making them dangerous to eat, and can harm marine life. Eutrophication (excess nutrients from runoff) can trigger these blooms.
Classification of Protists
Protists are broadly grouped based on how they obtain nutrition:
1. Animal-like Protists (Protozoa): Heterotrophs.
2. Plant-like Protists (Algae): Autotrophs (photosynthetic).
3. Fungus-like Protists: Heterotrophs, decomposers, or parasites.
1. Animal-like Protists (Protozoa)
* General: Heterotrophs that must hunt or absorb food. Many are motile. Four main phyla (based on movement/lifestyle):
* a) Zooflagellates (Phylum Zoomastigina):
* Move using flagella.
* Obtain food by absorbing it through the cell membrane or phagocytosis (general heterotroph characteristic).
* Live in water or inside other organisms.
* Example: Trypanosoma (causes African Sleeping Sickness). Flagella help it move within the host. Example: Giardia (causes severe diarrhea).
* b) Sarcodines (Phylum Sarcodina):
* Move and feed using temporary cytoplasmic extensions called pseudopods ("false feet").
* Feeding process is phagocytosis. Locomotion and feeding coincide as pseudopods are used for both.
* Example: Amoeba. Some amoebas cause dysentery. (Diagram labels: pseudopods, nucleus, contractile vacuole, food vacuole, ectoplasm, endoplasm ).
* c) Ciliates (Phylum Ciliophora):
* Move and feed using numerous short, hair-like projections called cilia. Cilia sweep food towards a gullet. Locomotion and feeding coincide as cilia are used for both.
* Complex protists.
* Example: Paramecium. (Diagram labels: cilia, macronucleus, micronucleus, contractile vacuole, food vacuole, oral groove, anal pore, trichocysts ).
* Nuclei: Have two types - a large macronucleus (controls daily cell functions) and one or more small micronuclei (involved in conjugation/genetic exchange).
* Trichocysts: Structures in the pellicle, possibly used for defense or anchoring (Answer based on general knowledge, supplement to Station Lab Q4).
* d) Sporozoans (Phylum Sporozoa):
* Do not move on their own.
* Parasitic.
* Example: Plasmodium (causes Malaria, transmitted by mosquitoes).
* Matching Diseases:
* Plasmodium: Malaria
* Trypanosoma: African sleeping sickness
* Amoeba: Bleeding of the intestinal wall (Amoebic dysentery)
* Giardia: Severe diarrhea & digestive problems
2. Plant-like Protists (Algae)
* General: Photosynthetic autotrophs. Often called algae. Contain chlorophyll; many have accessory pigments allowing them to live at different depths.
* Adaptation to Depth: Utilize accessory pigments that capture light wavelengths penetrating deeper water. Red algae, with phycoerythrin, can live deepest.
* Types:
* I. Unicellular Algae:
* Euglenophytes (Phylum Euglenophyta):
* Example: Euglena.
* Straddle animal/plant border: Photosynthetic (plant-like), but can absorb nutrients heterotrophically in low light; motile using flagella (animal-like).
* Eyespot: Detects light, enabling movement towards it for photosynthesis.
* Dinoflagellates (Phylum Pyrrophyta):
* Special Feature: Often have two flagella; many are bioluminescent; cell walls like armor plates; cause red tides.
* Chrysophytes (Phylum Chrysophyta - "Golden Algae"):
* Distinguishing features: Store food as oil; possess gold-colored carotenoid pigments. (Further differences not detailed in text).
* Diatoms (Phylum Bacillariophyta):
* Single-celled, found in salt and fresh water.
* Walls: Constructed of silicon dioxide (silica), forming intricate patterns.
* Ecological Role: Major component of phytoplankton, important primary producers.
* Diatomaceous Earth: Accumulations of fossilized diatom shells; used in filters, abrasives.
* II. "Other" Algae (Often Multicellular or Colonial):
* Green Algae (Phylum Chlorophyta):
* Most diverse algae group. Green due to chlorophyll being the main pigment.
* Similar chloroplasts to land plants; considered ancestors of land plants.
* Forms: Unicellular (Chlamydomonas), Colonial (Volvox - spheres of attached, independent cells), Multicellular (Ulva - sea lettuce, Chara).
* Chlamydomonas Uses: Research in photosynthesis, biofuels, cell motility (Answer based on general knowledge, supplement to Station Lab Q7).
* Brown Algae (Phylum Phaeophyta):
* Largest and most complex algae.
* Mostly marine seaweeds found in cool climates.
* Structure: Typically includes a holdfast (anchor), stipe (stem-like), and blades (leaf-like) (Structure based on general knowledge, related to Q20).
* Red Algae (Phylum Rhodophyta):
* Most of the world's seaweeds.
* Pigments: Contain phycobilins (red pigments) allowing them to absorb blue/green light and live deeper than other algae.
* No flagella at any life stage.
* Uses: Source of agar (used in labs) and carrageenan (thickener in foods); some are edible (e.g., nori) (Answer based on general knowledge, supplement to Station Lab Q8).
3. Fungus-like Protists
* General: Heterotrophs that absorb nutrients, often decomposers or parasites. Resemble fungi but differ (e.g., typically lack chitin cell walls - difference from Q23 based on general knowledge).
* Types:
* Water Molds (Phylum Oomycota):
* Live in water, moist soil, or as parasites on organisms.
* Some decompose dead matter, many are parasites.
* Slime Molds:
* Heterotrophic, amoeboid movement during certain life stages. Look like thin, colorful, shapeless slime masses.
* Ecological Role: Important decomposers, recycling nutrients.
* Cellular Slime Molds (Phylum Acrasiomycota): Spend most of life as separate amoeboid cells, aggregate into a multicellular "slug" when stressed (e.g., low food) to reproduce.
* Acellular (Plasmodial) Slime Molds (Phylum Myxomycota): Exist as a plasmodium - a single, multinucleated mass of cytoplasm without distinct cell membranes during the feeding stage.
Reproduction in Protists
* Cell Types:
* Haploid (N): One set of chromosomes (e.g., gametes, some adult protists).
* Diploid (2N): Two sets of chromosomes (e.g., zygotes, some adult protists).
* Modes of Reproduction:
* 1. Asexual Reproduction (Common in Favorable Conditions):
1. Method: Binary Fission - cell divides by mitosis to produce identical offspring (clones). Can be N -> N or 2N -> 2N.
2. Advantages: Rapid, no partner needed.
3. Disadvantages: No genetic variation.
4. Example: Paramecium, Amoeba (represented by diagram A in Q72 ).
5. Consequences of Rapid Growth (Eutrophication): Can lead to harmful algal blooms (e.g., red tides) causing toxic conditions or anoxia (oxygen depletion) harmful to aquatic life.
* 2. Sexual Reproduction (Common in Unfavorable Conditions):
1. Advantages: Increases genetic variation, potentially enhancing survival in changing environments.
2. Disadvantages: Slower, requires a partner (or compatible mating type).
3. Methods:
1. Conjugation: Genetic material (e.g., micronuclei in Paramecium) is exchanged between two individuals, but no new offspring are directly formed. It's followed by asexual reproduction (binary fission). It's like sexual reproduction because genetic material is exchanged, but unlike it because the number of individuals doesn't increase directly. Induced by environmental stress (e.g., preparing for drought).
2. Gamete Fusion: Haploid (N) gametes fuse (fertilization) to form a diploid (2N) zygote. The zygote may develop or undergo meiosis to return to the haploid state.
4. Conjugation in Spirogyra (Green Alga):
1. Two filaments align.
2. Conjugation tubes form between adjacent cells.
3. The protoplast of one cell (male gamete) moves through the tube to fuse with the stationary protoplast (female gamete) of the other cell.
4. Nuclei fuse, forming a diploid (2N) zygote. One filament is left empty, the other contains zygotes.
5. The zygote develops a thick wall, becoming a dormant zygospore to survive harsh conditions.
6. Zygospores are released.
7. In favorable conditions, the zygospore germinates via meiosis, producing haploid cells that grow into new filaments.
* Cysts: Many protists form resistant cysts to survive harsh conditions (e.g., drying, cold).
* Alternation of Generations: A life cycle pattern where organisms alternate between a multicellular haploid (N) stage (gametophyte - produces gametes) and a multicellular diploid (2N) stage (sporophyte - produces spores via meiosis).
1. There are two distinct adult forms (haploid and diploid). Represented by diagram C in Q72.
2. Examples: Ulva (sea lettuce), Plasmodium (malaria parasite - alternates between human and mosquito hosts). Humans are represented by diagram B (dominant diploid adult).
3. Comparing Chlamydomonas and Ulva: Chlamydomonas is primarily haploid, with only the zygote being diploid. Ulva exhibits true alternation of generations with distinct multicellular haploid and diploid forms.
* Plasmodium Life Cycle (Malaria): Complex cycle involving two hosts:
1. Infected mosquito bites human, injects Plasmodium sporozoites.
2. Sporozoites infect liver cells, reproduce asexually (new form: merozoites).
3. Merozoites enter the bloodstream, infect red blood cells, multiply rapidly.
4. Red blood cells burst, releasing more merozoites and causing malaria symptoms. Some develop into gametocytes.
5. Another mosquito bites an infected human, ingests gametocytes.
6. Fertilization occurs in mosquito gut, forming zygotes which develop and migrate to salivary glands. Cycle repeats.
Evolution of Multicellularity
* Protists demonstrate steps towards multicellularity:
* Single cell: Like Chlamydomonas. Cells reproduce and separate.
* Colony: Like Volvox. Cells reproduce and remain attached but are mostly independent, with little specialization. Not the same as true multicellularity.
* Multicellular: Like Ulva (sea lettuce). Cells reproduce, remain attached, and specialize for different functions (e.g., holdfast). Green algae (Chlorophyta) are considered the ancestors of multicellular plants.
* * Distinction: The key difference between colonial life and multicellularity is the specialization of cells for different functions in multicellular organisms.
Miscellaneous Q&A from Worksheets/Labs
* Protist vs. Bacteria: Protists are eukaryotes (have a nucleus and organelles), while bacteria are prokaryotes (no nucleus). Bacteria are generally smaller than protists. Bacterial shapes include spiral, coccus, bacillus. Antibiotics primarily target bacteria, though some protist infections are treated with specific antimicrobial drugs.
* Viruses: Are not considered alive, cannot reproduce without a host cell, and are the smallest infectious agents mentioned. HIV is an example.
* Lichen: A unique organism formed by a symbiotic relationship between a fungus and an alga (or cyanobacterium) (Answer based on general knowledge, supplement to Station Lab Q13).
* Myoneme: Contractile fibers found in some protists (like Vorticella) used for movement or changing shape (Answer based on general knowledge, supplement to Station Lab Q1).
Phyla Matching
* Pyrrophyta: dinoflagellates
* Sporozoans: sporozoans
* Myxomycota: acellular slime molds
* Phaeophyta: brown algae
* Chrysophyta: "golden plants"
* Chlorophyta: green algae
* Euglenophyta: euglenophytes
* Acrasiomycota: cellular slime molds
* Zoomastigina: zooflagellates
* Oomycota: water molds
* Bacillariophyta: diatoms
* Sarcodina: amoebas
* Rhodophyta: red algae
* Ciliophora: ciliates