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Characteristics of Unicellular Eukaryotes
- Unicellular eukaryotes
- Primarily aquatic
- Link between plants (Algae), fungi, and animals
- Well defined nucleus & membrane-bound organelle
- Mode of Nutrition – Photosynthetic (holophytic); holozoic
- Euglena – Mixotrophic
- Reproduction
- Asexual or vegetative – Budding, binary fission, multiple fission
- Sexual reproduction by cell fusion
- e.g. conjugation in paramecium
| Characteristics | Diatoms | Dinoflagellates | Euglena | Slime Moulds |
|---|---|---|---|---|
| Division | Chrysophyta | Pyrrhophyta | Euglenophyta | – |
| Producer | Major Chief Producer | 2nd Chief Producer | – | – |
| Characteristics | Pearls of the ocean | Protists with 2 flagella | Do not have cell wall, they have a protein rich layer called pellicle which makes their body flexible | Saprophytic protists |
| Habitat | Freshwater as well as marine | Mainly marine | Majority of them found in fresh water, in stagnant water | The body moves along decaying twigs and leaves engulfing organic material. |
| Mode of Nutrition | Holophytic | Holophytic (producer) | Mixotrophic: Holophytic (photosynthetic) & Heterotrophs (saprobic), they are photosynthetic in the presence of sunlight,(Stigma-Photoreceptive part) when deprived of sunlight they behave like heterotrophs by predating on other smaller organisms. | Saprophytic |
| Cell Wall | Cell wall is made up of cellulose, silica particles are embedded at many places, the cell walls form two thin overlapping shells, which fit together as in a soap box.The walls are embedded with silica and thus the walls are indestructible.Silicated cell wall is called frustule,have Epitheca and Hypotheca | Cell wall has stiff cellulose plates,also have Epitheca and Hypotheca, known as armoured algae | Cell wall absent, pellicle – protein-rich layer | The spores possess true walls, Cellulose in the cell walls of their spores. |
| Ecdysis | Shedding of theca | Shedding of theca | – | – |
| Flagella | They are immobile because flagella are absent, they float passively on the surface of water (plankton) | One flagella is transverse & other is longitudinal, special type of movement (whirling whips) | One large functional flagella, a short and a long one | – |
| Pigments | Chl a, Chl c, Xanthophyll (Fucoxanthin) | Chl a, Chl c, Xanthophyll (Dinoxanthin) | Chl a, Chl b, xanthophyll – pigments identical to higher plants | – |
| Stored Food | Leucosin (chrysolaminarin) & fats (oil) | Starch | – | – |
| Appearance | Golden algae | Yellow-green, brown, blue or red | – | Under suitable conditions, they form an aggregation called plasmodium |
| Special Characters | Oil-filled vacuole | Bioluminescence – Luciferin + O2 —– Luciferase —–> Light + Oxyluciferin, Histone absent in chromosome of dinoflagellates | – | – |
| Reproduction | Binary fission, Reduction in size due to asexual reproduction To restore size, sexual reproduction occurs |
Binary fission, Gonyaulax – Shows rapid multiplication due to which sea appears red. This is called RED TIDE. Blooms of dinoflagellates happen when conditions are right, meaning there are plenty of nutrients | – | During unfavourable conditions, plasmodium forms fruiting bodies which bear spores at their tip |
| Environmental Impact/Special Character/Importance | Diatoms have left behind large amount of cell wall deposits in their habitat; this accumulation over billions of years is referred to as ‘diatomaceous earth’. Being gritty this soil is used in polishing, filtration of oils and syrups. | Toxins released by large numbers can kill marine animals | Photosynthetic in sunlight, heterotrophic in absence of sunlight | Extremely resistant spores survive for many years. The spores are dispersed by air currents. |
Kingdom Protista
The Fascinating World of Unicellular Eukaryotes
2.2 Kingdom Protista: General Characteristics
Kingdom Protista comprises all single-celled eukaryotes. While their boundaries are not always strictly defined, they play a crucial role as a link between the more complex kingdoms of plants, fungi, and animals.
Key Features of Protists:
- Unicellular eukaryotes.
- Primarily aquatic habitats.
- Possess a well-defined nucleus and various membrane-bound organelles.
- Mode of Nutrition: Highly diverse, including photosynthetic (holophytic), holozoic (by ingestion), and mixotrophic (like *Euglena*).
- Reproduction: Asexual or vegetative (e.g., budding, binary fission, multiple fission) and sexual reproduction via cell fusion (e.g., conjugation in *Paramecium*).
Major Protist Groups: A Comparative Deep Dive
Explore the unique features of different Protista subgroups. Each card highlights key characteristics for easy comparison and understanding.
Diatoms (Chrysophyta)
Division
Chrysophyta
Producer Status
Major Chief Producer in oceans.
Characteristics
“Pearls of the ocean”.
Habitat
Freshwater as well as marine environments.
Mode of Nutrition
Holophytic (photosynthetic).
Cell Wall
Made of cellulose with embedded silica particles; forms two thin, overlapping shells (frustule) like a soapbox. Indestructible. Has Epitheca and Hypotheca.
Ecdysis
Not applicable.
Flagella
Absent; they are immobile and float passively as plankton.
Pigments
Chlorophyll ‘a’, Chlorophyll ‘c’, Xanthophyll (Fucoxanthin).
Stored Food
Leucosin (chrysolaminarin) & fats (oil).
Appearance
Often referred to as Golden Algae.
Special Characters
Contain oil-filled vacuoles for buoyancy.
Reproduction
Binary fission (asexual), leading to size reduction over generations. Sexual reproduction occurs to restore original size.
Environmental Impact/Importance
Accumulation of indestructible silica cell walls forms ‘diatomaceous earth’, used in polishing, and filtration of oils and syrups.
Dinoflagellates (Pyrrhophyta)
Division
Pyrrhophyta
Producer Status
Second Chief Producer in marine environments.
Characteristics
Protists characterized by two flagella; often called “armoured algae”.
Habitat
Mainly marine.
Mode of Nutrition
Holophytic (photosynthetic).
Cell Wall
Has stiff cellulose plates on the outer surface, forming an “armour”. Also has Epitheca and Hypotheca.
Ecdysis
Can undergo shedding of their cellulose plates (theca).
Flagella
One flagellum is transverse (in a furrow) & the other is longitudinal, facilitating a unique “whirling whips” movement.
Pigments
Chlorophyll ‘a’, Chlorophyll ‘c’, Xanthophyll (Dinoxanthin).
Stored Food
Starch.
Appearance
Can appear yellow-green, brown, blue, or red depending on dominant pigments.
Special Characters
Exhibit bioluminescence (Luciferin + O₂ –Luciferase–> Light + Oxyluciferin). Histones are absent in their chromosomes.
Reproduction
Binary fission. Rapid multiplication of *Gonyaulax* causes ‘RED TIDE’ blooms, especially with nutrient abundance.
Environmental Impact/Importance
Toxins released by large blooms can kill marine animals.
Euglena (Euglenophyta)
Division
Euglenophyta
Producer Status
Producer (photosynthetic) when light is available.
Characteristics
Lack a rigid cell wall; possess a flexible, protein-rich layer called **pellicle**.
Habitat
Majority found in freshwater, particularly stagnant water.
Mode of Nutrition
Mixotrophic: Holophytic (photosynthetic) in sunlight. Heterotrophic (saprobic or predating on smaller organisms) when deprived of sunlight.
Cell Wall
Absent. Has a pellicle instead.
Ecdysis
Not applicable.
Flagella
One large functional flagellum, and a shorter one.
Pigments
Chlorophyll ‘a’, Chlorophyll ‘b’, xanthophyll – pigments are identical to those found in higher plants.
Stored Food
Paramylon (a polysaccharide).
Appearance
Typically green due to chloroplasts.
Special Characters
Possesses a stigma (eyespot), a photoreceptive part.
Reproduction
Mainly asexual (e.g., longitudinal binary fission).
Environmental Importance
Its mixotrophic nature allows it to adapt to varying light conditions.
Slime Moulds
Division
Not formally classified under traditional divisions like the algal protists.
Producer Status
Not producers.
Characteristics
Saprophytic protists.
Habitat
Their body moves along decaying twigs and leaves, engulfing organic material.
Mode of Nutrition
Saprophytic (heterotrophic).
Cell Wall
The spores possess true walls (containing cellulose), but the vegetative body (plasmodium) lacks a cell wall.
Ecdysis
Not applicable.
Flagella
Present in reproductive stages (e.g., swarm cells), but not in main plasmodium.
Pigments
Absent.
Stored Food
Glycogen.
Appearance
Under suitable conditions, they form a large, spreading aggregation called **plasmodium**.
Special Characters
Plasmodium can grow and spread over several feet.
Reproduction
During unfavorable conditions, the plasmodium differentiates to form fruiting bodies which bear extremely resistant spores at their tips.
Environmental Impact/Importance
Extremely resistant spores can survive for many years and are dispersed by air currents, aiding survival and dispersal.
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