Q1. What is the basis of classification of algae?

A1: The primary basis for the classification of algae into its main classes (like Chlorophyceae, Phaeophyceae, and Rhodophyceae) is based on the following key characteristics:

  1. Major Photosynthetic Pigments: This is the most significant factor. The type and proportion of pigments determine the characteristic colour of the algae.

    • Chlorophyceae (Green Algae): Have Chlorophyll a and b as dominant pigments.
    • Phaeophyceae (Brown Algae): Have Chlorophyll a, c, and Fucoxanthin (a xanthophyll, giving the brown colour).
    • Rhodophyceae (Red Algae): Have Chlorophyll a, d, and r-Phycoerythrin (a phycobilin, giving the red colour).

  2. Form of Stored Food: The chemical nature of the reserve food material is distinct in each class.

    • Chlorophyceae: Store food as starch.
    • Phaeophyceae: Store food as laminarin and mannitol.
    • Rhodophyceae: Store food as floridean starch.

  3. Cell Wall Composition: The cell wall is made of cellulose, but it is often combined with other substances.

    • Chlorophyceae: Cell wall of cellulose.
    • Phaeophyceae: Cell wall of cellulose and algin (a hydrocolloid).
    • Rhodophyceae: Cell wall of cellulose, pectin, and carrageenan (a hydrocolloid).

  4. Flagellar Number and Position: The presence, number, and insertion point of flagella on motile cells (zoospores and gametes) are key identifiers.

    • Chlorophyceae: Have 2-8 equal, apical (at the tip) flagella.
    • Phaeophyceae: Have 2 unequal, lateral (on the side) flagella.
    • Rhodophyceae: Completely lack flagella at all stages.

Q2. When and where does reduction division (meiosis) take place in the life cycle of a liverwort, a moss, a fern, a gymnosperm and an angiosperm?

A2: Reduction division (meiosis) is the process that converts a diploid (2n) cell into haploid (n) cells. In all these plants, it occurs in the sporophyte generation to produce haploid spores.

  • Liverwort & Moss (Bryophytes): Meiosis occurs within the spore mother cells (2n) located inside the capsule of the dependent sporophyte.
  • Fern (Pteridophyte): Meiosis occurs within the spore mother cells (2n) located inside the sporangia. These sporangia are typically found on the undersurface of specialized leaves called sporophylls on the dominant sporophyte.
  • Gymnosperm: Meiosis occurs in two places on the dominant sporophyte:
    1. Inside the microsporangia (pollen sacs) of the male cones, where microspore mother cells (2n) divide to form haploid microspores (n).
    2. Inside the megasporangia (ovules) of the female cones, where the megaspore mother cell (2n) divides to form haploid megaspores (n).
  • Angiosperm: Meiosis occurs in two places within the flower of the dominant sporophyte:
    1. Inside the microsporangia (anthers), where microspore mother cells (2n) divide to form haploid microspores (n).
    2. Inside the megasporangia (ovules), where the megaspore mother cell (2n) divides to form haploid megaspores (n).

Q3. Name three groups of plants that bear archegonia. Briefly describe the life cycle of any one of them.

A3: The three groups of plants that bear archegonia (the multicellular, flask-shaped female sex organ) are:

  1. Bryophytes (e.g., mosses, liverworts)
  2. Pteridophytes (e.g., ferns, Selaginella)
  3. Gymnosperms (e.g., Pinus, Cycas)

(Note: Archegonia are absent in Angiosperms).

Life Cycle of a Moss (a Bryophyte):

  1. Start (Spore): The life cycle begins with a haploid (n) spore landing on a suitable substrate.
  2. Gametophyte Development: The spore germinates (by mitosis) to form the protonema, a creeping, green, filamentous stage. The protonema develops buds that grow into the upright, leafy gametophyte (n), which is the dominant, photosynthetic "plant."
  3. Gamete Production: The mature gametophyte bears multicellular sex organs at its apex.
    • Antheridia (male) produce biflagellate antherozoids (n) (sperm) by mitosis.
    • Archegonia (female) produce a single egg (n) by mitosis.
  4. Fertilization: Antherozoids are released and require a film of water to swim to an archegonium and fertilize the egg.
  5. Sporophyte Development: Fertilization results in a diploid (2n) zygote. The zygote remains within the archegonium and develops (by mitosis) into the sporophyte (2n). The sporophyte consists of a foot, seta (stalk), and capsule.
  6. Dependency: The sporophyte remains attached to and is nutritionally dependent on the female gametophyte throughout its life.
  7. Spore Production: Inside the capsule, spore mother cells (2n) undergo meiosis to produce numerous haploid (n) spores.
  8. Dispersal: The capsule releases the spores, which are dispersed by wind. If a spore lands on a suitable substrate, the cycle begins again. This life cycle is haplo-diplontic, with a dominant gametophyte.

Q4. Mention the ploidy of the following: protonemal cell of a moss; primary endosperm nucleus in dicot, leaf cell of a moss; prothallus cell of a fern; gemma cell in Marchantia; meristem cell of monocot, ovum of a liverwort, and zygote of a fern.

A4: The ploidy levels of the specified structures are as follows:

  • Protonemal cell of a moss: Haploid (n) - It is the initial stage of the gametophyte, which develops from a haploid spore.
  • Primary endosperm nucleus (PEN) in dicot: Triploid (3n) - It is the product of triple fusion (one male gamete (n) + two polar nuclei (n+n)).
  • Leaf cell of a moss: Haploid (n) - The "leaf" of a moss is part of the dominant gametophyte body.
  • Prothallus cell of a fern: Haploid (n) - The prothallus is the gametophyte of a fern, which develops from a haploid spore.
  • Gemma cell in Marchantia: Haploid (n) - Gemmae are asexual reproductive structures produced by the haploid gametophyte body.
  • Meristem cell of monocot: Diploid (2n) - The meristem is part of the main plant body, which is the sporophyte.
  • Ovum (egg) of a liverwort: Haploid (n) - It is the female gamete, produced by the gametophyte within the archegonium.
  • Zygote of a fern: Diploid (2n) - It is the result of fertilization (fusion of haploid male and female gametes).

Q5. Write a note on the economic importance of algae and gymnosperms.

A5:

Economic Importance of Algae

  • Primary Producers: As photosynthetic organisms, they form the base of all aquatic food webs and are responsible for fixing at least half of the total carbon dioxide on Earth, releasing large amounts of oxygen.
  • Human Food Source: Many species of marine algae are consumed as food, such as Porphyra (used to make nori for sushi), Laminaria, and Sargassum.
  • Hydrocolloids: Algae produce water-holding substances called hydrocolloids, which are used commercially.
    • Algin is obtained from brown algae (e.g., Laminaria) and used as a thickener in foods (ice cream, sauces), cosmetics, and paints.
    • Carrageenan is obtained from red algae (e.g., Chondrus crispus) and used as an emulsifier and stabilizer in dairy products and toothpaste.
  • Agar: This gel-forming substance is obtained from red algae like Gelidium and Gracilaria. It is essential for making microbiological culture media and is also used in jellies and ice cream.
  • Protein Supplements: Unicellular algae like Chlorella and Spirullina are exceptionally rich in protein and are used as food supplements, even by space travellers.

Economic Importance of Gymnosperms

  • Timber: Many gymnosperms, especially conifers like Pinus (pine), Cedrus (deodar), and Picea (spruce), are a major source of softwood for construction, furniture, particleboard, and paper production.
  • Resins: Conifers produce resins, which are harvested to produce turpentine (a solvent) and rosin (used in waterproofing, sealing, and for treating violin bows).
  • Edible Seeds: The seeds of some species are eaten, most notably Pinus gerardiana (Chilgoza pine) seeds, which are a popular dry fruit.
  • Medicinal Uses: The drug Taxol, a highly effective anti-cancer drug, is extracted from the bark of Taxus (yew tree). Ephedrine, a drug used for respiratory ailments, is obtained from Ephedra.
  • Ornamental Plants: Many gymnosperms like Cycas, Thuja (morpankhi), Ginkgo, and Araucaria (Christmas tree) are widely used in landscaping and as ornamental garden plants.

Q6. Both gymnosperms and angiosperms bear seeds, then why are they classified separately?

A6: Although both gymnosperms and angiosperms are seed-bearing plants (Spermatophytes), they are classified separately due to several fundamental differences in their reproductive structures and life cycles.

The key differences are as follows:

Feature Gymnosperms Angiosperms
Ovules/Seeds Ovules are naked (not enclosed by an ovary wall). Seeds are exposed, often on the scales of cones. Ovules are enclosed within a specialized structure called the ovary. Seeds develop inside a fruit (which is the mature ovary).
Reproductive Structure The main reproductive structures are cones (strobili). The main reproductive structure is the flower, which may contain male parts (stamens) and/or female parts (carpels).
Fertilization Involves single fertilization (one male gamete + egg -> zygote). Involves double fertilization (Syngamy: male gamete + egg -> zygote; and Triple Fusion: male gamete + polar nuclei -> endosperm).
Endosperm Formation The nutritive endosperm is haploid (n) and develops before fertilization from the female gametophyte. The nutritive endosperm is typically triploid (3n) and develops after fertilization from the Primary Endosperm Nucleus.
Vascular Tissue Xylem typically lacks vessels (except in Gnetophytes). Phloem lacks companion cells. Xylem contains vessels. Phloem contains companion cells, which support the sieve tubes.

Q7. What is heterospory? Briefly comment on its significance. Give two examples.

A7:

  • Definition: Heterospory is a condition found in certain plants where two distinct types of spores are produced, differing in size and developmental fate:

    1. Microspores: These are small spores that germinate to form the male gametophyte (which produces sperm).
    2. Megaspores: These are large spores, containing more food reserves, that germinate to form the female gametophyte (which produces eggs).

  • Significance: Heterospory is considered a crucial evolutionary step and a precursor to the seed habit. This is because:

    1. It leads to the development of unisexual gametophytes, increasing the chances of cross-fertilization and genetic variation.
    2. The megaspore is often retained within the megasporangium on the parent sporophyte. This provides protection and a reliable source of nutrition from the sporophyte to the developing female gametophyte.
    3. Fertilization and the development of the zygote into a young embryo also occur within the female gametophyte while it is still attached to the parent plant. This retention and in-situ embryo development is the foundation of the seed.

  • Examples: Heterospory is seen in some pteridophytes (e.g., Selaginella and Salvinia) and in all seed plants (all Gymnosperms and Angiosperms).

Q8. Explain briefly the following terms with suitable examples: (i) protonema (ii) antheridium (iii) archegonium (iv) diplontic (v) sporophyll (vi) isogamy

A8:

  • (i) Protonema: This is the juvenile, filamentous, creeping stage of the gametophyte in mosses (e.g., Funaria). It develops directly from the germination of a haploid spore and resembles a green alga. It later gives rise to the upright, leafy gametophyte "plant" as lateral buds.

  • (ii) Antheridium: This is the multicellular male sex organ found in bryophytes and pteridophytes. It is a globular or club-shaped structure that produces biflagellate male gametes (antherozoids) by mitosis (e.g., found in Marchantia, Ferns).

  • (iii) Archegonium: This is the multicellular, flask-shaped female sex organ found in bryophytes, pteridophytes, and gymnosperms. It consists of a swollen base (venter) containing a single, non-motile egg cell and a long neck (e.g., found in Mosses, Ferns, Cycas).

  • (iv) Diplontic: This describes a life cycle pattern where the diploid (2n) sporophyte is the dominant, photosynthetic, and independent generation. The haploid (n) gametophyte generation is highly reduced and nutritionally dependent on the sporophyte (e.g., all Gymnosperms and Angiosperms, or the alga Fucus).

  • (v) Sporophyll: This is a modified leaf or leaf-like structure that bears sporangia (spore-producing sacs). In ferns, the "fronds" are often sporophylls. In gymnosperms and some pteridophytes (Equisetum), sporophylls are aggregated into compact structures called cones or strobili (e.g., Fern fronds, Selaginella, Pine cone scales).

  • (vi) Isogamy: This is a type of sexual reproduction where the two fusing gametes (male and female) are morphologically identical. They are similar in size and structure and are often both motile (e.g., some species of Chlamydomonas) or both non-motile (e.g., Spirogyra).

Q9. Differentiate between: (i) red algae and brown algae (ii) liverworts and moss (iii) homosporous and heterosporous pteridophyte (iv) syngamy and triple fusion

A9:

(i) Red Algae vs. Brown Algae

Feature Red Algae (Rhodophyceae) Brown Algae (Phaeophyceae)
Dominant Pigment r-Phycoerythrin (red pigment) Fucoxanthin (brown pigment)
Stored Food Floridean starch Laminarin and Mannitol
Flagella Absent in all life stages 2, unequal, lateral flagella on motile cells
Cell Wall Hydrocolloid Carrageenan Algin

(ii) Liverworts vs. Mosses

Feature Liverworts Mosses
Gametophyte Thalloid (flat and undifferentiated) or simple leafy. Differentiated into two stages: Protonema (filamentous) and a leafy stage.
Rhizoids Unicellular Multicellular and branched
Spore Dispersal Simpler mechanism (e.g., elaters). More complex and elaborate mechanism (e.g., peristome teeth).

(iii) Homosporous vs. Heterosporous Pteridophytes

Feature Homosporous Heterosporous
Spores Produced Produces only one type of spore. Produces two types of spores (small microspores and large megaspores).
Gametophyte Typically bisexual (monoecious), bearing both antheridia and archegonia. Unisexual (dioecious). Microspore forms male gametophyte; megaspore forms female.
Significance Standard pteridophyte life cycle. Seen as an evolutionary precursor to the seed habit.
Example Dryopteris (Fern), Lycopodium Selaginella, Salvinia

(iv) Syngamy vs. Triple Fusion (in Angiosperms)

Feature Syngamy Triple Fusion
Fusion (1st) Male gamete (n) + Egg cell (n) (2nd) Male gamete (n) + Secondary Nucleus (2n) (fused polar nuclei)
Product Zygote (2n) Primary Endosperm Nucleus (PEN) (3n)
Develops into The Embryo The Endosperm (nutritive tissue)

Q10. Describe the life cycle of an angiosperm.

A10: The life cycle of an angiosperm (flowering plant) is diplontic and involves the following steps:

  1. The main plant body is the dominant sporophyte (2n), which is differentiated into true roots, stem, and leaves.
  2. The sporophyte develops flowers, which are the reproductive structures.
  3. Male Gametophyte: Inside the anther (part of the stamen), microspore mother cells (2n) undergo meiosis to produce many haploid microspores (n). Each microspore develops (by mitosis) into a pollen grain (n), which is the immature male gametophyte.
  4. Female Gametophyte: Inside the ovule (within the ovary of the carpel), a single megaspore mother cell (2n) undergoes meiosis to produce four haploid megaspores (n). Usually, one megaspore survives and develops (by mitosis) into the embryo sac (n), which is the female gametophyte. A typical embryo sac is 7-celled and 8-nucleate, containing the egg cell (n) and the central cell (with two polar nuclei (n+n)).
  5. Pollination: Pollen grains are transferred from the anther to the stigma of a carpel, typically by agents like wind, water, or animals (insects, birds).
  6. Pollen Tube Growth: The pollen grain germinates on the stigma, forming a pollen tube that grows down the style, enters the ovule, and carries two male gametes (n) to the embryo sac.
  7. Double Fertilization: This is a unique event in angiosperms:
    • Syngamy: One male gamete (n) fuses with the egg cell (n) to form the diploid (2n) zygote.
    • Triple Fusion: The second male gamete (n) fuses with the central cell's two polar nuclei (n+n) to form the triploid (3n) Primary Endosperm Nucleus (PEN).
  8. Post-Fertilization Development:
    • The Zygote (2n) develops into the embryo (2n).
    • The PEN (3n) develops into the endosperm, which provides nutrition to the developing embryo.
    • The ovule matures and develops into the seed (containing the embryo and endosperm).
    • The ovary matures and develops into the fruit, which encloses and protects the seed(s).
  9. Germination: The seed is dispersed and, under favourable conditions, germinates to grow into a new sporophyte (2n) plant, completing the cycle.

Q11. Why is the endosperm in gymnosperms haploid, while in angiosperms it is triploid?

A11: The difference in ploidy is due to a fundamental difference in how and when the nutritive endosperm tissue is formed in these two groups.

  • In Gymnosperms: The nutritive tissue (endosperm) is simply the female gametophyte (n). This tissue develops from the haploid megaspore before fertilization even occurs, as a pre-prepared food source for a potential embryo. Since it is the gametophyte tissue itself, it is haploid (n).

  • In Angiosperms: The endosperm is a new structure formed only after fertilization, via a specific process called Triple Fusion. This is the second fertilization event in 'double fertilization'. It involves the fusion of one male gamete (n) with the two polar nuclei (n+n) of the central cell. This fusion results in the Primary Endosperm Nucleus (PEN), which is triploid (3n) and subsequently develops into the endosperm. This process ensures that the plant only invests energy in creating a food source if fertilization has successfully occurred.

Q12. What adaptations do gymnosperms show for surviving extreme conditions?

A12: Gymnosperms, particularly conifers (like pines and firs), are highly adapted to survive extreme environmental conditions, especially cold and drought. These are known as xerophytic adaptations.

Their key adaptations include:

  1. Needle-like Leaves: These leaves have a very small, reduced surface area. This significantly reduces the area available for water loss through transpiration.
  2. Thick Cuticle: The leaves are covered by a thick, waxy cuticle, which acts as a waterproof barrier to prevent water evaporation from the leaf surface.
  3. Sunken Stomata: The stomata (pores used for gas exchange) are positioned in pits or grooves below the leaf surface. This creates a pocket of humid air (a still boundary layer) and reduces the drying effect of wind, further decreasing water loss during transpiration.

Q13. List the three classes of algae and give one distinguishing pigment for each.

A13: The three main classes of algae and their primary distinguishing pigments are:

  1. Chlorophyceae (Green Algae): Have Chlorophyll a and b as the dominant pigments, giving them their characteristic grass-green colour.
  2. Phaeophyceae (Brown Algae): Have Chlorophyll a, c, and Fucoxanthin (a xanthophyll). Fucoxanthin masks the green colour, giving them their olive-green to brown shade.
  3. Rhodophyceae (Red Algae): Have Chlorophyll a, d, and r-Phycoerythrin (a phycobilin). The red phycoerythrin masks the other pigments and allows them to absorb blue-green light, enabling them to live at great depths.

Q14. How does the sporophyte generation differ between bryophytes and pteridophytes?

A14: The sporophyte generation differs significantly between these two groups in terms of its dominance, independence, and complexity:

  • In Bryophytes (e.g., Mosses): The sporophyte (diploid, 2n) is a simple, unbranched structure (typically a foot, seta, and capsule) that is not free-living. It remains physically attached to the dominant, photosynthetic gametophyte (haploid, n) and is nutritionally dependent on it for its entire life. It is the recessive generation.

  • In Pteridophytes (e.g., Ferns): The sporophyte (diploid, 2n) is the dominant, independent, and photosynthetic plant body. It is large, complex, and differentiated into true roots, stems, and leaves that contain vascular tissue (xylem and phloem). The gametophyte, while also independent, is small and short-lived.

Q15. What are coralloid roots?

A15: Coralloid roots are specialized roots found in the gymnosperm Cycas. They are apogeotropic, meaning they grow upwards, near the soil surface, rather than downwards. They are irregularly branched and appear coral-like, hence the name.

Their primary function and importance come from a symbiotic association with nitrogen-fixing cyanobacteria (blue-green algae), such as Anabaena or Nostoc, which live inside the root tissues. These bacteria are able to convert atmospheric nitrogen (N₂) into usable nitrogen compounds (like ammonia), providing a vital nutrient source for the Cycas plant, allowing it to thrive in nitrogen-poor soils.

Q16. Describe the three types of sexual reproduction found in algae.

A16:

  1. Isogamy: Fusion of gametes that are identical in size and morphology. They can be flagellated (motile, e.g., Chlamydomonas) or non-flagellated (non-motile, e.g., Spirogyra).
  2. Anisogamy: Fusion of two gametes that are dissimilar in size. (e.g., some species of Chlamydomonas).
  3. Oogamy: Fusion of a large, non-motile female gamete (egg) with a smaller, motile male gamete. (e.g., Volvox, Fucus).

Q17. What is double fertilization and where does it occur?

A17: Double fertilization is a unique characteristic feature of angiosperms. It involves two fusion events occurring simultaneously within the embryo sac:

  1. Syngamy: One male gamete fuses with the egg cell to form the diploid zygote (2n).
  2. Triple Fusion: The second male gamete fuses with the diploid secondary nucleus (formed from two polar nuclei) in the central cell to form the triploid primary endosperm nucleus (PEN) (3n). This process occurs inside the ovule after pollination and pollen tube growth.

Q18. Which major plant groups exhibit predominantly haplontic, diplontic, and haplo-diplontic life cycles respectively?

A18:

  • Haplontic: Predominantly found in many Algae.
  • Diplontic: Predominantly found in Gymnosperms and Angiosperms (also Fucus alga).
  • Haplo-diplontic: Predominantly found in Bryophytes and Pteridophytes (also some algae like Ectocarpus, Polysiphonia, kelps).

Q19. What is meant by alternation of generations?

A19: Alternation of generations refers to a life cycle pattern found in all plants where a haploid, gamete-producing phase (the gametophyte) alternates with a diploid, spore-producing phase (the sporophyte). The relative dominance and independence of these two phases vary across different plant groups.

Q20. Explain the 'haplontic' life cycle with suitable examples.

A20: A haplontic life cycle is one where the dominant, photosynthetic, and free-living phase is the haploid gametophyte (n). The diploid sporophyte generation is represented only by the zygote (2n). The zygote undergoes meiosis immediately to produce haploid spores, which germinate into the gametophyte. There is no multicellular sporophyte.

Examples: Many algae like Volvox, Spirogyra, and some species of Chlamydomonas.