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Questions and Answers
What is a key characteristic that distinguishes prokaryotic cells from eukaryotic cells?
What is a key characteristic that distinguishes prokaryotic cells from eukaryotic cells?
Which type of ribosomes is found in prokaryotic cells?
Which type of ribosomes is found in prokaryotic cells?
What type of cellular structures do prokaryotes lack?
What type of cellular structures do prokaryotes lack?
Which of the following statements is true regarding the chromosomes of prokaryotic cells?
Which of the following statements is true regarding the chromosomes of prokaryotic cells?
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Which process is primarily associated with some prokaryotic cells and not eukaryotic cells?
Which process is primarily associated with some prokaryotic cells and not eukaryotic cells?
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Eukaryotic cells are characterized by Which feature?
Eukaryotic cells are characterized by Which feature?
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What type of membrane-bound organelles are typically found in eukaryotic cells but absent in prokaryotic cells?
What type of membrane-bound organelles are typically found in eukaryotic cells but absent in prokaryotic cells?
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Which of the following best describes ribosomal differences between prokaryotic and eukaryotic cells?
Which of the following best describes ribosomal differences between prokaryotic and eukaryotic cells?
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What type of photosynthesis is believed to have first developed in ancient organisms?
What type of photosynthesis is believed to have first developed in ancient organisms?
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What key evolutionary event allowed for the emergence of more complex organisms?
What key evolutionary event allowed for the emergence of more complex organisms?
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Which process is described as the ingestion and incorporation of a cyanobacterium into a eukaryotic cell?
Which process is described as the ingestion and incorporation of a cyanobacterium into a eukaryotic cell?
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Which groups of photosynthetic eukaryotes are included in the Archaeplastida?
Which groups of photosynthetic eukaryotes are included in the Archaeplastida?
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Which event is thought to have followed the origin of Archaeplastida?
Which event is thought to have followed the origin of Archaeplastida?
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What is the main function of the developed cyanobacterium in the eukaryotic cell after primary endosymbiosis?
What is the main function of the developed cyanobacterium in the eukaryotic cell after primary endosymbiosis?
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Which of the following statements is incorrect regarding the transition from prokaryotic to eukaryotic life forms?
Which of the following statements is incorrect regarding the transition from prokaryotic to eukaryotic life forms?
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Which is not considered a common trait of photosynthetic eukaryotes?
Which is not considered a common trait of photosynthetic eukaryotes?
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What is a significant structural difference between prokaryotic and eukaryotic cells?
What is a significant structural difference between prokaryotic and eukaryotic cells?
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Which statement correctly describes the cell wall of prokaryotic cells?
Which statement correctly describes the cell wall of prokaryotic cells?
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What process do eukaryotic cells typically use for nuclear division?
What process do eukaryotic cells typically use for nuclear division?
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Which of the following best describes the reproductive strategy of prokaryotic cells?
Which of the following best describes the reproductive strategy of prokaryotic cells?
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Which type of organism can perform nitrogen fixation?
Which type of organism can perform nitrogen fixation?
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What structural feature is typical of the flagella in eukaryotic cells?
What structural feature is typical of the flagella in eukaryotic cells?
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Why are eukaryotic cells, unlike prokaryotic ones, able to undergo sexual reproduction?
Why are eukaryotic cells, unlike prokaryotic ones, able to undergo sexual reproduction?
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What is the main difference regarding the type of nitrogen fixation capabilities between prokaryotes and eukaryotes?
What is the main difference regarding the type of nitrogen fixation capabilities between prokaryotes and eukaryotes?
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Which of the following characterizes the ribosomes found in eukaryotic cells?
Which of the following characterizes the ribosomes found in eukaryotic cells?
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Study Notes
Evolution of Algae
- Algae evolved from a common photosynthetic ancestor.
- Estimates and models from fossil records place this event around 2 billion years ago (Tor).
- Oxygen became gradually available as a potent electron acceptor.
- This enabled aerobic organisms to evolve, have more productive ecosystems, and form complex ones.
- Photosynthesis is essential for algae, and the equation for this process is 2 H₂O + CO₂ ⇒ O₂ + CH₂O + H₂O
Origin of Plastids: Primary Endosymbiosis
- Debate exists about the exact mechanisms and order of events in the creation of the first eukaryotic cell.
- A prevailing hypothesis is that photosynthetic eukaryotes developed from a heterotrophic eukaryote engulfing a cyanobacterium.
- The cyanobacterium gradually became integrated into the cellular machinery as a plastid.
- This process is known as primary endosymbiosis.
- Photosynthetic eukaryotes have three main groups: green plants, red algae, and glaucophytes. These groups make up Archaeplastida.
Cyanobacteria (Blue-Green Algae)
- Cyanobacteria are photosynthetic prokaryotes.
- They are ancient life forms classified as bacteria.
- Prokaryotes lack a nucleus, chloroplasts, and mitochondria.
Prokaryotes vs. Eukaryotes
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Prokaryotes:
- Nuclear materials are not contained within a nucleus.
- Lack chromosomes or nuclear membranes.
- Typically lack mitochondria and plastids.
- Ribosomes are smaller (70S type).
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Eukaryotes:
- Nuclear materials are contained within a nucleus.
- Chromosomes are enclosed within a nuclear membrane.
- Often contain mitochondria and plastids (e.g., in plant cells).
- Ribosomes are larger (80S type).
Common Characteristic Features of Algae
- Algae range in size from tiny unicellular microalgae to large multicellular seaweeds over 50 meters.
- They are defined as photosynthetic organisms.
- Algae lack specialized root, stem, or vascular bundles.
- They do not have a diploid embryo stage.
- They lack sterile tissue surrounding their reproductive structures.
- Zygote development occurs via mitosis or meiosis, not embryo formation.
Rhodophyta (Red Algae)
- Abundant in warm tropical and subtropical areas, also in temperate and polar seas.
- Some are unicellular, others are complex.
- Critical to coral reef development (encrusting, calcified corallines), vital for consolidation.
- Carbohydrate deposits, sometimes containing calcium carbonate, in cell walls – important globally for carbon storage.
- Among the deepest photosynthetic eukaryotes, exceeding 210 meters deep.
- Recognized by their pink color, due to phycoerythrin and phycocyanin pigments.
- Phycoerythrin efficiently harvests blue and green light, often obscuring chlorophyll a.
- Freshwater red algae may exhibit more phycocyanin, appearing bluish.
- Rhodophyta species in high light conditions display coloration variability from yellow to brown.
Batrachospermum sp.
- Found in cold, clear, running fresh water streams.
- Deep water species are a reddish violet color.
- Shallow water species are olive green.
Thallus of Red Algae
- Thallus is more delicate than brown algae.
- Algae of this class lack motile forms.
- Reproductive cells are non-flagellated.
Multicellular Macroscopic Thallus in Algae
- Most red algae species have multicellular macroscopic thallus formations having various forms.
- Uni-axial forms with an axis formed from a single row of filaments.
- Multi-axial forms with multiple filaments forming an axis.
- Important for structural diversity.
Cell Wall Structure in Algae
- Cell walls consist of cellulose fibers (rigid) and gels of sugar polymers or polysaccharides (flexible).
- Cellulose fibrils, a structural component of plant cell walls, are composed of glucose polymers.
Rhodophyta Plastid Morphologies
- Two common types of plastid morphologies exist in Rhodophyta:
- Axial/stellate plastids (e.g., Porphyridium): Large plastids with a central paranoid.
- Parietal/discoidal plastids (e.g., Audouinella): Multiple smaller plastids lacking paranoids.
Storage Products in Algae
- Floridean starch, lacking amylose but containing highly branched amylopectin, is a storage product typically found in Floridean algae.
- This is an example of a storage polysaccharide.
- The chemical structure and properties distinguish Floridean starch from starch found in other plants.
Pit Connections in Algae
- In many algal cells, 90% do not completely divide but have open regions eventually filled with proteins.
- Ordinal level taxonomic features in the cells are displayed by the core morphology of the cap.
- Primary and secondary pit connections lend strength and provide connections between the cells.
Reproduction in Algae
- Reproduction occurs vegetatively (cell division, fragmentation), asexually (monospores), and sexually (gametes).
- Gametes are formed within gametangia.
- Most taxa use vegetative or asexual reproductive methods, which can vary vastly by species.
- Sexual reproduction occurs in gametangia.
- Male gametes are spermatia produced in spermatangia
- Female gametes are carpogonia (sessile, borne on carpogonial branches), composed of trichogyne + base
Class-Bangiophyceae
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Subclasses Bangioideae and Florideae are significant classifications.
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Sub-class Bangioideae mostly feature freshwater/terrestrial environments; multicellular and unicellular forms occur in their species; they typically have only one nucleus per cell; and they have steallate chromatophores. They also commonly have one pyreniod and no pit connections
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Sub-class Florideae predominantly occupy marine environments; they are relatively complex, uniaxial or polyaxial; they often have more than one nucleus per cell; discoid chromatophores are common; they usually have pyranoid and pit connections
Life Cycle of Rhodophyta
- A variety of life cycle patterns are observed in Rhodophyte algae.
- Biphasic life history (2 phases) - common in Bangiophycidae.
- Triphasic life history (3 phases) - more common in Florideophycidae.
- Life cycles vary, but a common theme is distinct morphological and reproductive phases.
Phaeophyta (Brown Algae)
- Found in equatorial to subpolar regions, but they have their greatest diversity in cold and temperate areas.
- Their bodies typically have holdfast, stipe, and blade segments.
- The color and the texture of the algae can determine their location and general characteristic features.
- They contain fucoxanthin (golden brown xanthophyll pigment), which causes the color variation in the algae.
- Pigment coloration and cell structure are closely related.
- They have uninucleate cells.
- Mannitol and laminarin are reserve food source.
- They have a tough, leathery, or rubbery texture.
Cell Structure of Brown Algae
- Brown algae cell walls consist of cellulose, pectin substances, and algin/fucoidin compounds, leading to a gelatinous texture.
Cell Structure of Brown Algae
- Brown algae cells have mitochondria, ribosomes, endoplasmic reticulum, and Golgi bodies.
- Food reserves (e.g., laminarin) are stored within these cells.
- Mannitol is another photosynthesis product, serving as an alcohol.
- Chromatophores are plastids that store chlorophylls a and c, and fucoxanthin.
Reproduction in Brown Algae
- Brown algae exhibit various reproduction methods, including vegetative, asexual, and sexual reproduction.
- Vegetative reproduction involves fragmentation and propagules.
- Asexual reproduction involves zoospores.
- Sexual reproduction includes isogamy, anisogamy, and oogamy. Notably isogamy ranges from simple forms to more complex anisogamy.
Chlorophyta (Green Algae)
- Eukaryotic organisms with membrane-bound organelles.
- Thallus is typically green due to chlorophyll pigments.
- Chloroplasts are plastids containing chlorophylls a and b (typical of plants, not just algae).
- Pyrenoids are structures associated with starch formation.
- Starch is the major storage product; starch is stored within the cells.
- Motile forms possess eyespot (stigma) and other organelles.
- Unicellular, colonial, and multicellular filamentous forms occur.
Classification of Green Algae
- Unicellular thallus (e.g., Chlamydomonas, Chlorella, Chlorococcum).
- Colonial thallus (e.g., Gonium, Pandorina, Volvox, Chlorococcales, Pediastrum, Hydrodictyon).
- Multicellular filamentous thallus (e.g., Spirogyra, Ulothrix, Oedogonium, Chaetophora, Bulbochataete, Cladophora, Ulva, Stigeoclonium, Fristschiella).
- Siphonaceous/coenocytic thallus (e.g., Acetabularia, Characium).
Diatoms (Bacillariophyceae)
- Diatoms are eukaryotic algae with a unique, two-part silica cell wall called the frustule.
- They are mostly planktonic and occur in a variety of marine and freshwater environments.
- The frustule is composed of two overlapping parts (e.g., like petri dish halves).
- Two major orders: Centrales and Pennales are the chief divisions in Diatom morphology.
- Important as a primary food source.
- They have a biphasic life cycle that is important for understanding the algae’s genetic and reproductive patterns.
- They also have auxospores and different pigments (chlorophyll a, c, and fucoxanthin).
- Storage products are important for metabolic functions.
Differences between Bangioideae and Florideae
- Bangioideae: Primarily freshwater or terrestrial; simple cells; one nucleus per cell; and characteristic features of green algae
- Florideae (e.g., Gracilaria): Primarily marine; complexity of cell structure; many nuclei per cell, and the characteristic features of red algae.
General Differences in Algal Types (Summary)
- Pigments: Red algae (phycoerythrin/phycocyanin), brown algae (fucoxanthin), green algae (chlorophyll a&b), and diatoms (chlorophyll a, c, and fucoxanthin).
- Storage Carbohydrates: Red algae (floridean starch), brown algae (laminarin), green algae (starch), and diatoms (chrysolaminarin).
- Cell Wall Composition: Red algae (cellulose), brown algae (pectin & algin), green algae (cellulose and pectin), diatoms (hydrated silica).
Additional notes provided by the pages
- Organelles are present in all of the cells described (mitichondria, ribosomes, endoplasmic reticulum, Golgi).
- Differences in algal reproduction and life cycles are also important features to consider when making distinctions between the types.
- Various algae exhibit motile forms.
- Algae are ubiquitous in their general distribution to water sources, cold water to hot springs.
- Algae can cause significant economic loss to crops like tea and coffee.
- Detailed explanation and diagrams of algal thallus and types are also presented.
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