Algae .pdf

# Introduction to Algae ## Introduction - The scientific study of algae is called **phycology**. - *Phycos* means algae and *logy* means science in Latin. - Algae are collectively known as **chlorophyll-bearing organisms** with a **thalloid form**. - This means they lack roots, stems, and leav...

# Introduction to Algae ## Introduction - The scientific study of algae is called **phycology**. - *Phycos* means algae and *logy* means science in Latin. - Algae are collectively known as **chlorophyll-bearing organisms** with a **thalloid form**. - This means they lack roots, stems, and leaves. - Algae also lack a sterile covering of cells around their reproductive cells. - Algae and fungi were once grouped together in the **Thallophyta** group. - However, some algologists and mycologists believe that the similarities between the two are due to parallel development and not a close evolutionary relationship. - Algae show a variety of traits: - size ranging from **0.2-2.0 µm in diameter** for **picoplankton** to **60 m in length** for **giant kelps**. - They have a wide range of **ecological niches** - They have **varying levels of cellular structure**. - They have different **pigments for photosynthesis**. - They have different **reserve and structural polysaccharides**. - They have a **range of life history types**. - Algae include both **macroalgae** and **microalgae**. - The number of algal species has been estimated to be **one to ten million**. - Most of these are **microalgae**. - Algae with massive thalli are primarily **marine** for the following reasons: - Marine water provides minerals at the rate at which a large thallus needs them. - Marine water is more permanent in geological time than inland water. ## Occurrence: Habit and Habitat - Algae have a wide range of habitats: - **Moist soils** - **Freshwater** (ponds, lakes, rivers, etc.) - **Brackish water** - **Marine water** (sea and ocean) - Algae can exist in almost any environment on earth: - **Snow** on mountains - **Lichens** on rocks - **Desert soils** - **Hot springs** - Algae can tolerate a wide range of conditions: - **pH** - **Temperature** - **Turbidity** - **O2 concentration** - **CO2 concentration** - Algae can be: - **Planktonic** - **Benthic** ### Classification by Habitat - **Aquatic algae** - **Terrestrial algae** - **Aerophytes** (absorb moisture from air) - **Cryophytes** (live in ice or snow) - **Thermophytes** - **Algae of unusual habitats** ## General Characters of Algae - They are **thalloid organisms** with chlorophyll (autotrophic nutrition). - They have different types of pigments, such as: - Chlorophyll a - Chlorophyll b - Carotene - Their **sex organs** are mainly **unicellular** (except for a few species). - Sex organs are not surrounded by a sterile jacket. - **Embryo formation** does not occur. - The zygote remains inside the female sex organs. ## Classification of Algae - The classification of algae is based on the same rules as those used for land plants. - However, above the order level, classification has changed substantially since 1960. - **Electron microscopy** revealed differences in features, for example: - **Flagellar apparatus** - **Cell division process** - **Organelle structure and function** - **Molecular studies** have suggested additional changes as well. Since 1960, the number of classes has nearly doubled. - The apparent evolutionary scatter of some algae among protozoan and fungal groups makes a natural classification of algae is not feasible. ### Kingdom: Plantae - **Subkingdom: Protophyta** (primitive, no true nucleus) - Examples: Bacteria, viruses,Cyanophyta - **Subkingdom: Thallophyta** (undifferentiated thallus) - Examples: Algae (autotrophic), fungi (heterotrophic), lower plants with no vascular system - **Subkingdom: Embryophyta** (embryo present) - Examples: Higher plants ### Autotrophic vs. Heterotrophic - **Autotrophic**: The organism uses sunlight and carbon dioxide to produce carbohydrates via chlorophyll. - **Heterotrophic**: The organism relies on external sources to acquire organic carbon. - **Saprophytic**: The organism acquires nutrients from dead organic matter. - **Parasitic**: The organism acquires nutrients from a living host. - **Symbiotic**: The organism acquires nutrients from a mutually beneficial relationship with another organism. ### Division: Phylum-phyta - **Class:** -phyceae - **Order:** -ales - **Family:** -aceae - **Genus** - **Species** ## The Basics of Algal Classification - The primary classification of algae is based on the following features: - Presence or absence of a nucleus - Pigment constitution of the cell - Chemical nature of food storage - Flagella - type, number, and point of insertion - Cell wall composition ## Pigmentation: Differences Between Algal Divisions | Algal Division | Cyanophyta (Blue-green algae) | Chlorophyta (Green algae) | Bacillariophyta (Diatoms) | Phaeophyta (Brown algae) | |---|---|---|---|---| | **Nucleus** | Prokaryotic | Eukaryotic | Eukaryotic | Eukaryotic | | **Cell wall** | Pectin hemicellulose and mucopeptide | Cellulose, pectin, hemicellulose | Silicified C.W. | Cellulose, aliginic acid and fucocinic acid | | **Pigment** | Chl a (green) and carotene (yellow) | Chl a, b and carotene | Chl a, c, carotene, fucoxanthin and diatothanthin | Chl a, carotene, xanthophyll and fucoxanthin (yellow) | | **Plastids** | No plastids | Chloroplast | Chromatophores | Chromatophores | | **Pyrenoid** | Absent | Pyrenoid with a starch sheath | Naked pyrenoid | Naked pyrenoid | | **Food storage** | Cyanophycean starch found in chromoplasm | True Starch | Oil, chrysolaminarin, leucosin | Laminarin, mannitol, oil | | **Flagella (N°. and Type)** | Absent | 2 or 4 - Equal, anterior, Whiplash | One, anterior (only in male gamete of some), Tinsel | Only in reproductive cells 2, unequal, lateral whiplash, and Tinsel | | **Sexual Reproduction** | Absent | Isogamy, aniso-, and oogamy | Present (all types) | Present (all types) | ## Types of Nutrition in Algae - Most algal groups are **photoautotrophs**. - They require light energy and carbon dioxide to produce carbohydrates and ATP. - Some algae are **heterotrophs**. - **Osmotrophic**: The organism acquires nutrients from dissolved substances in the surrounding environment. - **Phagotrophic**: The organism acquires nutrients by engulfing bacteria or other cells. ### Types of Nutrition | Type of Nutrition | Principle Source of Energy | Principle Source of Carbon | |---|---|---| | **Autotrophic:** | | | | Photoautotrophic | Light | Carbon dioxide | | Chemoautotrophic | Oxidation of organic compounds | Carbon dioxide | | **Heterotrophic:** | | | | Photoheterotrophic | Light | Organic compounds | | Chemoheterotrophic | Oxidation of organic compounds | Organic compounds | ### Auxotrophy & Mixotrophy - **Auxotrophic**: The organism can't synthesize essential components and must acquire them via external sources, such as B12 complex or fatty acids. - **Mixotrophic**: The organism uses both autotrophic and heterotrophic strategies to acquire nutrients. ## Food Reserves in Algae - Algae store food primarily as **polysaccharides** (starch) and **fats**. - **True starch** is found in: - **Chlorophyta** - **Charophyta** - **Cyanophycean starch** is found in: - **Cyanophyta** - **Floridean starch** is found in: - **Rhodophyta** - Other important polysaccharides: - **Laminarin:** Phaeophyta - **Paramylon:** Euglenoids - **Leucosin:** Bacillariophyta, Xanthophyta, and Chrysophyta - A proteinaceous compound called **cyanophycin** is found in **Cyanophyta**. - **Mannitol** is found in brown algae and a few **Rhodophyta**. - **Fats** are commonly found in: - **Xanthophyta** - **Bacillariophyta** - **Chrysophyta** ## Occurrence and Distribution of Cyanophycophyta - Cyanophycophyta can be found in a wide range of habitats. - **Chamaesiphonales** are primarily **marine**. - **Chroococcales** and **Hormogonales** are mostly **freshwater**. ### Forms of Cyanophycophyta - **Unicellular individuals** - **Non-filamentous colonies** - **Filamentous forms** #### (A) Unicellular Forms - Examples: **Chroococcus** and **Gloeocapsa** #### (B) Non-Filamentous Colonial Forms - Colonies form from the confluence of gelatinous envelopes surrounding individual cells. - Examples: **Aphanocapsa** and **Aphanothece** - Colony shape depends on the plane of cell division. - **Single-plane division:** produces a **plate-like colony** (example: **Merismopedia**) - **Multiple-plane division:** produces **cubical or three-dimensional colonies** - **Irregular division:** produces **irregular colonies** (example: **Microcystis**) #### (C) Filamentous Forms - A filament forms from the continuous division of a single cell in one plane. - Examples: **Oscillatoria**. - A **trichome** is a filament that may or may not be surrounded by a sheath. - **Calothrix ** has multiple trichomes surrounded by a common sheath. ## Division: Chlorophycophyta ## Class: Chlorophyceae (Green Algae) ### General Characters of Chlorophyceae - **Chlorophyll a** and **chlorophyll b** are the primary pigments. - Other pigments include **carotene** and **xanthophylls**. - Chlorophyll masks the presence of the other pigments, resulting in the green color. - **Starch** is the primary food storage structure. - **Eukaryotic** cells. - **Vacuoles** are present in the cytoplasm. - **Eye spots (stigmas)** are present in motile forms. - Cell walls are composed of **cellulose** and **pectin**. - Reproduction occurs by **asexual** or **sexual** means. - Motile forms have **zoospores or gametes** with 2 or 4 flagella inserted anteriorly. - Some species have **multiflagellated zoospores** (example: *Oedogonium*). ### Occurrence of Chlorophyceae - Primarily **aquatic**, either freshwater or marine. - Some species are **subterranean**. - A few are **epiphytic**, living on filamentous algae. ### Organization of the Thallus - **Unicellular thallus:** - **Motile unicellular thallus:** example: *Chlamydomonas* - **Non-motile unicellular thallus:** example: *Chlorella* - **Colonial thallus:** - **Motile colonial thallus:** example: *Volvox, Gonium, Pandorina* - **Non-motile colonial thallus:** example: *Pediastrum, Hydrodictyon* - **Siphonaceous or coenocytic thallus:** example: *Enteromorpha* - **Multicellular filamentous thallus:** - **Simple filament:** - *Spirogyra*: Cells are independent. - *Ulothrix*: Has a rhizoidal cell for attachment. - *Oedogonium*: Has a branched or unbranched thallus with rhizoidal cells, cap cells for cell division, and vegetative cells for nutrition and reproduction. - **Branched filament:** example: *Cladophora, Bulbochaete* - **Foliaceous thallus:** Cells divide in three planes, resulting in thin plates. example: *Ulva* - **Massive parenchymatous:** Cells divide in a parallel fashion, forming multiple layers. - **Heterotrichous filament:** Has both a prostrate and an erect system. Example: *Stigoclonium, Fristchiella* ## Motility (Locomotion) of Algae - **Coccoid algae**: Lack flagella and are non-motile. - **Monoid algae**: Have flagella and are motile. - **Blue-green algae** and **red algae** lack flagella. - **Blue-green algae** move by **gliding** or **oscillation**. - **Oscillation**: A jerky type of movement. - **Gliding**: The cell moves within a mucilage sheath, which adheres to the substrate. - Filamentous extensions of protoplasm may propel the cell. - **Swimming**: Some marine species of *Synechococcus* are capable of swimming at speeds of 5 to 25 μm. - *Synechococcus* lacks flagella or other organs of motility. - **Chemotaxis**: movement of an organism in response to a chemical concentration gradient. - **Phototaxis**: Movement towards or away from light. ## Algal Flagellar System - **Number:** 1, 2, 3, 4, or multiple flagella - **Type:** - **Whiplash (Acronematic):** Thread-like form with a smooth surface and pointed ends. - **Tinsel (Pleuronematic):** Pinna-like form with a hairy surface. - **Length:** Can be equal or unequal. - **Insertion:** - **Terminal**: Flagella at the end of the cell. - **Sub-terminal**: Flagella near the end of the cell. - **All over the cell surface**: Example: zoospores of *Vaucheria* ## Structure of the Flagellum - **Blepharoplast**: Granule at the base of the flagellum. - **Axoneme**: Central core of the flagellum which is surrounded by a plasma membrane. - **End piece**: The terminal portion of the axoneme which may be blunt or pointed. - **Microtubules**: - **Two central microtubules** surrounded by **nine peripheral microtubules**. - The microtubules are enclosed by a **sheath** which is an extension of the plasma membrane. - The "**nine plus two**" (9+2) pattern is the basic structure of the flagellum in eukaryotes. ## Reproduction in Algae - **Reproduction** involves the production of offspring that resemble the parent. - The purpose of reproduction is to **perpetuate the species** and increase the number of individuals. - **Three main types of reproduction**: - **Vegetative reproduction** - **Asexual reproduction** - **Sexual reproduction** ### Vegetative Reproduction - Occurs primarily in **Cyanophyta**. - **Fission**: The cell divides into two daughter cells. - **Hormogonia**: Short segments of a filament break off and form new filaments. - **Heterocysts**: specialized cells that form between hormogonia. - **Separation discs**: dead cells that form between hormogonia. - **Fragmentation**: Non-filamentous and filamentous colonies break into smaller pieces. #### Fragmentation in Filamentous Forms - Fragmentation is triggered by: - Animals feeding on the trichome - Water currents - Death of certain cells ### Asexual Reproduction - It is uniparental. - Asexual reproduction produces a large number of offspring that inherit the parent's traits. - New individuals develop from specialized cells called **spores**. #### Types of Asexual Reproduction - **Spore formation** - **Fission** - **Fragmentation** - **Adventitious branches** - **Tubers** - **Budding** #### Spore Formation - **Zoospores**: Motile spores with flagella. - **Aplanospores**: Non-motile spores. ##### Types of Spores - **Zoospores**: - Flagella type: Typically whiplash. - Number: 2 or 4 flagella (example: *Chlamydomonas*), or multiple flagella (example: *Oedogonium*). - Insertion: Usually anterior, but can be posterior or all over the cell surface. - **Aplanospores**: - **Hypnospores**: Thick-walled aplanospores that are resistant to unfavorable conditions. They are commonly found in Chlorophyta. - **Autospores**: Small aplanospores that are similar to hypnospores but smaller in size. They are commonly found in Chroococcales (example: *Chlorella*). - **Endospores**: Formed from the contents of a cell. - **Exospores:** Formed when the protoplast of a cell divides, presses against the cell wall, and ruptures. - **Nanospores:** Special aplanospores with a nucleus that divides multiple times without increasing in size. - **Auxospores:** Formed in Bacillariophyta and develop into new plants. - **Carpospores:** Found in Rhodophyceae. - **Neutral spores**: Found in Rhodophyceae and not formed within sporangia. - **Monospores:** Develop within monosporangia and give rise to a new plant. - **Akinetes**: Thick-walled resistant spores that are formed under unfavorable conditions and germinate under favorable conditions. ### Sexual Reproduction - Involves the fusion of two **specialized reproductive cells** called **sex cells** or **gametes**. - **Monoecious**: Gametes are produced on the same plant. - **Dioecious**: Gametes are produced on different plants. - The fusion of gametes is called **fertilization**. - The product of fertilization is a **zygote**. - Sexual reproduction is absent in **Cyanophyta**. #### Types of Sexual Reproduction - **Isogamy**: Fusion of morphologically similar gametes. - **Heterogamy**: Fusion of dissimilar gametes. ##### Heterogamy - **Anisogamy**: Gametes differ in size, but are otherwise similar. - **Oogamy**: Gametes differ greatly in size and are produced in separate sex organs: - **Oogonium:** Female sex organ that produces a large **ovum**. - **Antheridium:** Male sex organ that produces small **sperms**. - **Trichogene**: A filament that connects the oogonium and the antheridium in Rhodophyceae. - **Spermatia**: Non-motile male gametes in Rhodophyceae. ## Life Cycles of Algae - **Haplontic:** The dominant stage is haploid. The zygote undergoes **zygotic meiosis**, producing haploid spores. - **Diplontic:** The dominant stage is diploid. The sporophyte produces haploid spores via **meiosis**. - **Diplohaplontic:** Both a haploid (gametophyte) and a diploid (sporophyte) stage are present. ## The Volvocine Line - Volvocales are a group of **green algae** that show evolutionary trends in the development of **coenobia** (non-motile colonies). - The **volvocine line** represents a series of related organisms with increasing complexity. - The line starts with **Chlamydomonas**, a unicellular organism, and progresses through **Oltmansiella, Gonium, Pandorina, Eudorina, ** and ends with **Volvox**, a highly complex colony. - These trends in development include: - Increase in the number of cells - Changes in colony shape - Morphological differentiation of cells - Specialization of reproductive cells - Evolution of sexual reproduction from isogamy toward oogamy. ### The Volvocine Line: Evolutionary Summary - **Gonium**: Has **16-32 cells** arranged in a flat plate. - **Pandorina**: Has **8-16-32 cells** arranged in a spherical colony. - **Eudorina**: Has **32-64 cells** connected by cytoplasmic strands. - **Pleodorina**: Has **128 cells** with two distinct types: - **Vegetative cells:** Small in size and located in the anterior end. - **Reproductive cells:** Large in size and located in the posterior end. - **Volvox**: - **Highly developed colony** with **500-50,000 cells**. - More specialized cells: - **Somatic cells** - **Gonidial cells** - **Antheridia** - **Oogonia** ## Algal Plastids - Algal plastids are either **chloroplasts** or **chromatophores**. - **Chloroplasts** contain both **chlorophyll a** and **chlorophyll b**. - **Chromatophores** only contain **chlorophyll a**. - The chloroplast is enclosed by a double membrane (envelope) and has an enclosed matrix called the **stroma**. - The membrane units are called **lamellae** or **thylakoids**. - **Lamellae** are responsible for the synthesis and capture of light energy. - **Thylakoids** are arranged into **stacks** or **bands** called **grana**. - Light-dependent reactions take place in **thylakoids**. - The Calvin cycle takes place in the **stroma**. ### Types of Chloroplasts - **Cup-shaped:** *Chlamydomonas* - **Girdle (collar) shape:** *Ulothrix* - **Discoid:** Diatoms - **Reticulate:** *Oedogonium* - **Ribbon (band):** *Debarya* - **Spiral:** *Spirogyra* - **Star-shape:** *Zygnema* - **Axile plate:** *Mougeotia*