Algae and Their Classes
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Questions and Answers

What are the three types of sexual reproduction observed in algae, based on gamete morphology?

Isogamous (similar gametes), anisogamous (dissimilar gametes), oogamous (large non-motile female and small motile male gamete).

Name two commercial products derived from algae and their algal sources?

Agar (from Gelidium) and carrageenan (from Chondrus).

Describe the cell wall composition of Chlorophyceae (green algae).

The cell wall consists of an outer layer of pectin and an inner layer of cellulose.

What pigments are characteristic of Phaeophyceae (brown algae), and what is one adaptation they have for marine environments?

<p>Xanthophylls, fucoxanthin, chlorophyll a and c, and carotenoids. Many species possess a holdfast that anchors them to a substratum.</p> Signup and view all the answers

What is the primary pigment responsible for the red color in Rhodophyceae (red algae), and what is their stored food reserve?

<p>Phycoerythrin is the primary pigment, and floridean starch is their stored food reserve.</p> Signup and view all the answers

Why are bryophytes called 'amphibians of the plant kingdom'?

<p>They require water for fertilization as the antherozoids need water to reach the archegonia.</p> Signup and view all the answers

What are gemmae in liverworts, and what is their function?

<p>Gemmae are specialized structures for asexual reproduction. They are green, multicellular, asexual buds, which develop in small receptacles called gemma cups.</p> Signup and view all the answers

Describe the two sub-stages of the gametophyte phase in mosses.

<p>Protonema (a creeping, branched, filamentous stage) and leafy stage (upright, slender axes with spirally arranged leaves).</p> Signup and view all the answers

Name two ecological or economic uses of bryophytes.

<p>Fuel (peat), soil binders, prevent soil erosion, pioneers in colonizing rocks.</p> Signup and view all the answers

What is a prothallus in pteridophytes, and what structures does it bear?

<p>The prothallus is the gametophyte stage in pteridophytes. It bears antheridia (male) and archegonia (female).</p> Signup and view all the answers

Differentiate between homosporous and heterosporous pteridophytes.

<p>Homosporous pteridophytes produce only one type of spore. Heterosporous pteridophytes produce two types of spores (megaspores and microspores).</p> Signup and view all the answers

What is a strobilus (cone) in gymnosperms, and what is the difference between male and female cones?

<p>A strobilus (or cone) is a reproductive structure in gymnosperms. Male cones bear microsporophylls, which produce pollen. Female cones bear megasporophylls, which contain ovules.</p> Signup and view all the answers

Describe the process of double fertilization in angiosperms.

<p>One male gamete fuses with the egg cell to form a zygote, and the other fuses with the secondary nucleus to form the triploid primary endosperm nucleus.</p> Signup and view all the answers

What is the fate of the ovule and ovary after fertilization in angiosperms?

<p>The ovule develops into the seed, and the ovary develops into the fruit.</p> Signup and view all the answers

Explain the key difference between a haplontic and a diplontic life cycle.

<p>In a haplontic life cycle, the dominant phase is the haploid gametophyte; in a diplontic life cycle, the dominant phase is the diploid sporophyte.</p> Signup and view all the answers

Flashcards

Algae

Simple, chlorophyll-bearing, autotrophic organisms found in moist environments.

Chlorophyceae

Green algae characterized by chlorophyll a and b, found in diverse forms.

Phaeophyceae

Brown algae found in seawater, notable for their size and unique pigments.

Rhodophyceae

Red algae containing phycoerythrin pigment, found mostly in warm waters.

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Bryophytes

Non-vascular plants like mosses and liverworts, thriving in moist areas.

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Gametophyte

The haploid (n) phase in bryophytes that produces gametes.

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Sporophyte

The diploid (2n) phase in plants that produces spores through meiosis.

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Pteridophytes

Vascular plants like ferns, occupying damp habitats.

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Gymnosperms

Seed plants with exposed ovules, including conifers and cycads.

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Angiosperms

Plants with seeds enclosed in fruits, divided into monocots and dicots.

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Double Fertilization

A process in angiosperms where one sperm fertilizes the egg, and another forms the endosperm.

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Alternation of Generations

Life cycle pattern that alternates between haploid gametophyte and diploid sporophyte.

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Haplodiplontic Life Cycle

Both sporophyte and gametophyte phases are multicellular in this cycle.

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Isogamous Reproduction

In algae, when gametes of similar size fuse during sexual reproduction.

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Oogamous Reproduction

In algae, when a large non-motile female gamete fuses with a small motile male gamete.

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Study Notes

Algae

  • Simple, chlorophyll-bearing, autotrophic organisms
  • Found in moist rocks, fresh water, and wood
  • Vary in size and form (unicellular, colonial, filamentous, massive plant bodies)
  • Reproduction: vegetative, asexual, sexual
    • Vegetative: fragmentation (each fragment develops into a thallus)
    • Asexual: spores (zoospores germinate into new plants)
    • Sexual: fusion of gametes to form a new organism
      • Isogamous: fusion of two similar-sized gametes (can be flagellated or non-flagellated)
      • Anisogamous: fusion of two dissimilar-sized gametes
      • Oogamous: fusion of a large, non-motile female gamete and a small, motile male gamete
  • Functions: carbon dioxide fixation, increase dissolved oxygen, food source for aquatic organisms
  • Commercial uses: agar (from Gelidium), carrageenan (from Chondrus)

Classes of Algae

Chlorophyceae (Green Algae)

  • Unicellular, colonial, or filamentous
  • Cell wall: outer layer of pectin, inner layer of cellulose
  • Chloroplasts: contain pyrenoids (starch and protein)
  • Pigments: chlorophyll a and b
  • Reproduction: vegetative (fragmentation), asexual (flagellated zoospores), sexual

Phaeophyceae (Brown Algae)

  • Found in brackish or saltwater
  • Vary in form and size (filamentous, branched, up to 100 meters tall)
  • Pigments: xanthophylls, fucoxanthin, chlorophyll a and c, carotenoids
  • Body structure: frond (leaf-like), stipe (stalk), holdfast (attaches to substratum)
  • Cell wall: cellulosic with outer gelatinous coating of algin
  • Reproduction: vegetative (fragmentation), asexual (flagellated zoospores), sexual (gametes unite in water or within oogonium)

Rhodophyceae (Red Algae)

  • Found in brackish and saltwater, mostly in warmer areas
  • Red color due to high concentration of phycoerythrin pigment
  • Thallus: multicellular
  • Food storage: floridean starch
  • Reproduction: vegetative, asexual (non-motile spores), sexual (motile spores)

Bryophytes (Mosses and Liverworts)

  • Amphibians of the plant kingdom
  • Grow in damp, humid, and shaded localities
  • Plant body: thallus-like, prostrate or erect, attached to substratum by rhizoids
  • No true roots, stems, or leaves
  • Main plant body is haploid (gametophyte)
  • Gametophyte produces gametes (male and female)
    • Male: antheridia (produce flagellated antherozoids)
    • Female: archegonia (flask-shaped, produce a single egg)
  • Fertilization: antherozoids released in water, fuse with egg to form a zygote
  • Zygote develops into a sporophyte (multicellular body, gets nutrition from gametophyte)
  • Sporophyte produces haploid spores by meiosis
  • Spores germinate to produce a gametophyte

Liverworts

  • Found in moist, shady environments (e.g., bark of trees)
  • Thallus is dorsiventral and appressed to the substrate
  • Leafy liverworts have tiny leaf-like appendages in two rows on stem-like structures
  • Reproduction: asexual (fragmentation, gemmae) and sexual

Mosses

  • Common species: Funaria, Sphagnum
  • Dominant phase: gametophyte (two sub-stages: protonema and leafy stage)
    • Protonema: thread-like chain of cells, creeping, branched, filamentous
    • Leafy stage: upright, slender axes, spirally arranged leaves, attached to soil by branched rhizoids
  • Reproduction: vegetative (fragmentation, budding) and sexual (male and female sex organs at the apex of leafy shoots)

Uses of Bryophytes

  • Peat (fuel)
  • Soil binder
  • Prevents soil erosion
  • Pioneers in colonizing rocks
  • Decomposition of rocks

Pteridophytes (Ferns)

  • Occupy damp, cool, and shady habitats
  • First terrestrial plants with vascular tissues, true roots, stems, and leaves
  • Used as ornamental plants, soil binders, and for medicinal purposes
  • Classified based on leaf organization, sporangia location (e.g., Sphenopsida, Lycopsida, Pteropsida)

Life Cycle of a Pteridophyte

  • Sporophyte bears sporangia (subtended by sporophylls)
  • Sporangia produce spores by meiosis
  • Spores germinate into gametophyte (prothallus)
  • Prothallus is small, multicellular, free-living, photosynthetic
  • Prothallus bears antheridia (produce male gametes - antherozoids) and archegonia (produce egg)
  • Antherozoids travel through water to archegonia, fuse with egg to form zygote
  • Zygote develops into a young embryo, then a sporophyte
  • Life cycle alternates between gametophyte and sporophyte phases

Types of Pteridophytes

  • Homosporous: produce spores of similar kind
  • Heterosporous: produce two types of spores (megaspores: female gametophyte, microspores: male gametophyte)

Gymnosperms (Conifers, Cycads, Ginkgoes)

  • Ovules are not enclosed by an ovary wall, remain exposed
  • Seeds develop after fertilization
  • Roots: taproots, mycorrhizae (fungal association), coralloid roots (cyanobacteria association)
  • Stems: branched or unbranched, simple or compound
  • Leaves: adapted to extreme climatic conditions (e.g., needle-like leaves in conifers)

Reproductive Structures of Gymnosperms

  • Strobili (cones): male and female cones
    • Male cone: microsporophylls bear microsporangia (produce haploid microspores)
      • Microspores develop into pollen grains (male gametophytes)
    • Female cone: megasporophylls bear ovules (megasporangium or nucellus)
      • Megasporangium produces haploid megaspores (one develops into female gametophyte)
      • Female gametophyte bears archegonia (produce egg)

Fertilization in Gymnosperms

  • Pollen grains are released by microsporangium and carried by wind
  • Pollen grain reaches ovule, pollen tube grows towards archegonium
  • Male gametes fuse with egg to form zygote
  • Zygote develops into an embryo, ovule becomes a seed

Importance of Gymnosperms

  • Source of lumber, varnish, cosmetics

Angiosperms (Flowering Plants)

  • Ovules develop inside flowers, seeds enclosed in fruits
  • Monocotyledonous or dicotyledonous

Parts of a Flower

  • Stamen (male sex organ): filament and anther
    • Anther contains microsporangia (produce pollen grains - male gametophytes)
  • Pistil (female sex organ): stigma, style, ovary
    • Ovary contains ovules (megasporangium)
    • Ovule contains megaspore mother cell (undergoes meiosis to produce haploid female gametophyte - embryo sac)

Embryo Sac

  • Contains egg cell, synergids, antipodals, and two polar nuclei
  • Polar nuclei fuse to form a diploid secondary nucleus

Fertilization in Angiosperms

  • Pollination: pollen grains dispersed by wind or insects, deposited on stigma
  • Pollen grain germinates, produces pollen tube
  • Pollen tube penetrates stigma and style, reaches embryo sac
  • Two male gametes released: one fuses with egg cell (forms zygote), the other fuses with secondary nucleus (forms triploid primary endosperm nucleus)
  • This is called double fertilization

Development of Seed and Fruit

  • Zygote develops into embryo
  • Primary endosperm nucleus develops into endosperm (nourishes embryo)
  • Ovule develops into seed
  • Ovary develops into fruit

Importance of Angiosperms

  • Source of food, fuel, fodder, medicine
  • Integral part of ecosystem, daily lives

Alternation of Generations

  • Life cycle alternates between sporophyte (diploid) and gametophyte (haploid) generations
  • Dominant phase varies in different plant groups

Haplontic Life Cycle

  • Dominant phase: gametophyte (e.g., algae like Chlamydomonas, Spirogyra, Volvox)
  • Sporophyte phase: represented by a single-celled zygote

Diplontic Life Cycle

  • Dominant phase: sporophyte (e.g., gymnosperms, angiosperms)
  • Gametophyte phase: single or few-celled

Haplodiplontic Life Cycle

  • Both sporophyte and gametophyte phases are multicellular
  • Dominant phase differs in bryophytes and pteridophytes
    • Bryophytes: dominant phase is gametophyte
    • Pteridophytes: dominant phase is sporophyte
  • Some algae (e.g., Fucus, Polysiphonia) also exhibit haplodiplontic life cycle

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Explore the fascinating world of algae, including their characteristics, reproduction methods, and commercial uses. This quiz covers specific types of algae, such as Chlorophyceae, and their ecological significance. Test your knowledge on these essential autotrophic organisms found in various environments.

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