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Plant Kingdom - Biology Chapter 3

Plant Kingdom

Explore the diverse world of plants from simple algae to complex flowering plants and understand their classification and characteristics.

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Chapter Overview

Brief Introduction

The plant kingdom includes algae, bryophytes, pteridophytes, gymnosperms and angiosperms. This chapter deals with the classification within Kingdom Plantae, popularly known as the plant kingdom. Our understanding of the plant kingdom has changed over time, with fungi and members of Monera and Protista having cell walls now excluded from Plantae.

Learning Objectives

  • Understand the classification of plants into different groups
  • Learn the characteristics of algae, bryophytes, pteridophytes, gymnosperms and angiosperms
  • Study the reproductive methods of different plant groups
  • Comprehend the evolutionary trends in plant kingdom
  • Explore the economic importance of various plant groups

Key Topics Covered

  • Classification of Algae (Chlorophyceae, Phaeophyceae, Rhodophyceae)
  • Bryophytes - Amphibians of plant kingdom
  • Pteridophytes - First vascular plants
  • Gymnosperms - Naked seed plants
  • Angiosperms - Flowering plants
  • Plant life cycles and alternation of generations
  • Economic importance of plants
  • Evolutionary trends in plant kingdom

Interactive Chapter Index

Algae

Explore the simple, chlorophyll-bearing thalloid organisms that are largely aquatic and play crucial ecological roles.

Bryophytes

Learn about the amphibians of plant kingdom that live in soil but depend on water for sexual reproduction.

Pteridophytes

Understand the first terrestrial plants to possess vascular tissues and their life cycle.

Gymnosperms

Discover the naked-seeded plants that include medium-sized trees or tall trees and shrubs.

Angiosperms

Study the exceptionally large group of flowering plants with seeds enclosed in fruits.

Chapter Summary

Review the key concepts and takeaways from this chapter about the plant kingdom.

Full Chapter Notes

3.1 Algae

Algae are chlorophyll-bearing, simple, thalloid, autotrophic and largely aquatic (both fresh water and marine) organisms. They occur in a variety of other habitats: moist stones, soils and wood. Some of them also occur in association with fungi (lichen) and animals (e.g., on sloth bear).

Characteristics of Algae:

  • Form and size is highly variable, from colonial forms like Volvox to filamentous forms like Ulothrix and Spirogyra
  • Marine forms like kelps can form massive plant bodies
  • Reproduce by vegetative (fragmentation), asexual (spores) and sexual methods
  • Sexual reproduction can be isogamous, anisogamous or oogamous
  • At least half of total carbon dioxide fixation on earth is carried out by algae
  • Increase dissolved oxygen levels in their environment
  • Primary producers in aquatic food cycles
Isogamous reproduction: Fusion of two gametes that are similar in size, which may be flagellated (as in Ulothrix) or non-flagellated (as in Spirogyra).
Economic Importance of Algae:
  • Many species (like Porphyra, Laminaria, Sargassum) are used as food
  • Produce hydrocolloids like algin (brown algae) and carrageen (red algae) used commercially
  • Agar from Gelidium and Gracilaria used to grow microbes and in food preparations
  • Chlorella (unicellular alga) rich in proteins used as food supplement
Q: What is the basis of classification of algae?
Classes Common Name Major Pigments Stored Food Cell Wall Flagellar Number and Position Habitat
Chlorophyceae Green algae Chlorophyll a, b Starch Cellulose 2-8, equal, apical Fresh water, brackish water, salt water
Phaeophyceae Brown algae Chlorophyll a, c, fucoxanthin Mannitol, laminarin Cellulose and algin 2, unequal, lateral Fresh water (rare) brackish water, salt water
Rhodophyceae Red algae Chlorophyll a, d, phycoerythrin Floridean starch Cellulose, pectin and poly sulphate esters Absent Fresh water (some), brackish water, salt water (most)

3.1.1 Chlorophyceae (Green Algae)

  • Plant body may be unicellular, colonial or filamentous
  • Grass green due to dominance of pigments chlorophyll a and b
  • Pigments localized in definite chloroplasts of various shapes
  • Most have storage bodies called pyrenoids in chloroplasts
  • Cell wall has inner layer of cellulose and outer layer of pectose
  • Vegetative reproduction by fragmentation or spores
  • Asexual reproduction by flagellated zoospores
  • Sexual reproduction may be isogamous, anisogamous or oogamous
  • Examples: Chlamydomonas, Volvox, Ulothrix, Spirogyra, Chara

3.1.2 Phaeophyceae (Brown Algae)

  • Primarily marine, show great variation in size and form
  • Range from simple branched filamentous forms to massive kelps (up to 100m)
  • Possess chlorophyll a, c, carotenoids and xanthophylls
  • Color varies from olive green to brown depending on fucoxanthin pigment
  • Store food as laminarin or mannitol
  • Cellulosic wall covered by gelatinous coating of algin
  • Plant body has holdfast, stipe and frond
  • Asexual reproduction by biflagellate zoospores
  • Sexual reproduction may be isogamous, anisogamous or oogamous
  • Examples: Ectocarpus, Dictyota, Laminaria, Sargassum, Fucus

3.1.3 Rhodophyceae (Red Algae)

  • Predominance of red pigment r-phycoerythrin
  • Mostly marine, found in both well-lighted regions and deep oceans
  • Red thalli are mostly multicellular with complex body organization
  • Store food as floridean starch (similar to amylopectin and glycogen)
  • Reproduce vegetatively by fragmentation
  • Asexual reproduction by non-motile spores
  • Sexual reproduction by non-motile gametes (oogamous)
  • Examples: Polysiphonia, Porphyra, Gracilaria, Gelidium
Types of Algae
Figure: Different types of algae - Green, Brown and Red algae

3.2 Bryophytes

Bryophytes include various mosses and liverworts commonly found growing in moist shaded areas. They are called amphibians of the plant kingdom because these plants can live in soil but are dependent on water for sexual reproduction. They usually occur in damp, humid and shaded localities and play an important role in plant succession on bare rocks/soil.

Characteristics of Bryophytes:

  • Plant body is more differentiated than algae - thallus-like, prostrate or erect
  • Attached to substratum by unicellular or multicellular rhizoids
  • Lack true roots, stem or leaves (may have root-like, leaf-like or stem-like structures)
  • Main plant body is haploid (gametophyte) which produces gametes
  • Sex organs are multicellular - male antheridium produces biflagellate antherozoids
  • Female archegonium is flask-shaped and produces a single egg
  • Zygote develops into sporophyte which is attached to gametophyte
  • Sporophyte undergoes meiosis to produce haploid spores
  • Spores germinate to produce gametophyte
Gametophyte: The haploid, gamete-producing phase in the life cycle of plants that exhibit alternation of generations. In bryophytes, it is the dominant, photosynthetic phase.
Economic Importance of Bryophytes:
  • Some mosses provide food for herbaceous mammals, birds and other animals
  • Sphagnum moss provides peat used as fuel and packing material
  • First organisms to colonize rocks (along with lichens)
  • Decompose rocks making substrate suitable for higher plants
  • Form dense mats reducing impact of rain and preventing soil erosion
Q: Why are bryophytes called amphibians of the plant kingdom?

3.2.1 Liverworts

  • Grow in moist, shady habitats like banks of streams, marshy ground, damp soil, bark of trees
  • Plant body is thalloid (e.g., Marchantia) or leafy
  • Thallus is dorsiventral and closely appressed to substrate
  • Leafy members have tiny leaf-like appendages in two rows on stem-like structures
  • Asexual reproduction by fragmentation or gemmae (green, multicellular asexual buds in gemma cups)
  • Sexual reproduction - male and female sex organs on same or different thalli
  • Sporophyte differentiated into foot, seta and capsule
  • Spores produced within capsule after meiosis

3.2.2 Mosses

  • Life cycle has two stages - protonema stage (creeping, green, branched filamentous) and leafy stage
  • Leafy stage develops from secondary protonema as lateral bud
  • Leafy stage has upright, slender axes bearing spirally arranged leaves
  • Attached to soil through multicellular, branched rhizoids
  • Vegetative reproduction by fragmentation and budding in secondary protonema
  • Sexual reproduction - antheridia and archegonia produced at apex of leafy shoots
  • After fertilization, zygote develops into sporophyte with foot, seta and capsule
  • Spores formed after meiosis in capsule
  • Elaborate mechanism of spore dispersal
  • Examples: Funaria, Polytrichum, Sphagnum
Bryophytes
Figure: Bryophytes - Liverworts and Mosses

3.3 Pteridophytes

Pteridophytes include horsetails and ferns. They are used for medicinal purposes and as soil-binders, and are frequently grown as ornamentals. Evolutionarily, they are the first terrestrial plants to possess vascular tissues - xylem and phloem. They are found in cool, damp, shady places though some may flourish well in sandy-soil conditions.

Characteristics of Pteridophytes:

  • Main plant body is sporophyte differentiated into true root, stem and leaves
  • Possess well-differentiated vascular tissues
  • Leaves may be small (microphylls) or large (macrophylls)
  • Sporophytes bear sporangia subtended by leaf-like sporophylls
  • Sporophylls may form distinct compact structures called strobili or cones
  • Spores produced by meiosis in spore mother cells
  • Spores germinate to give rise to inconspicuous, small, multicellular, free-living gametophytes called prothallus
  • Gametophytes bear male (antheridia) and female (archegonia) sex organs
  • Water required for transfer of male gametes to archegonium
  • Zygote develops into sporophyte which is dominant phase
Prothallus: The small, multicellular, free-living, mostly photosynthetic gametophyte in pteridophytes that develops from a spore and bears the sex organs.
Heterospory:

Most pteridophytes are homosporous (produce similar spores). Some like Selaginella and Salvinia are heterosporous - they produce two kinds of spores:

  • Microspores (small) - give rise to male gametophytes
  • Megaspores (large) - give rise to female gametophytes

Female gametophytes are retained on parent sporophytes for variable periods. Zygote develops into embryo within female gametophyte - a precursor to seed habit.

Q: What is the difference between homosporous and heterosporous pteridophytes?

Classification of Pteridophytes:

Pteridophytes are classified into four classes:

  1. Psilopsida: Example - Psilotum
  2. Lycopsida: Examples - Selaginella, Lycopodium
  3. Sphenopsida: Example - Equisetum
  4. Pteropsida: Examples - Dryopteris, Pteris, Adiantum
Pteridophytes
Figure: Different types of Pteridophytes

3.4 Gymnosperms

The gymnosperms (gymnos: naked, sperma: seeds) are plants in which the ovules are not enclosed by any ovary wall and remain exposed, both before and after fertilization. The seeds that develop post-fertilization are not covered (naked). Gymnosperms include medium-sized trees or tall trees and shrubs.

Characteristics of Gymnosperms:

  • Include medium-sized trees or tall trees and shrubs
  • Example: Giant redwood tree Sequoia (one of the tallest tree species)
  • Roots are generally tap roots
  • Some have fungal association (mycorrhiza in Pinus) or N2-fixing cyanobacteria (Cycas coralloid roots)
  • Stems may be unbranched (Cycas) or branched (Pinus, Cedrus)
  • Leaves may be simple or compound
  • Leaves well-adapted to withstand extremes of temperature, humidity and wind
  • In conifers, needle-like leaves reduce surface area with thick cuticle and sunken stomata to reduce water loss
Gymnosperms: Plants with naked seeds where the ovules are not enclosed by any ovary wall and remain exposed before and after fertilization. The seeds that develop are not covered.
Reproduction in Gymnosperms:
  • Heterosporous - produce haploid microspores and megaspores
  • Spores produced in sporangia on sporophylls arranged spirally to form strobili or cones
  • Microsporangiate (male) strobili bear microsporophylls and microsporangia
  • Microspores develop into highly reduced male gametophyte (pollen grain)
  • Macrosporangiate (female) strobili bear megasporophylls with ovules
  • Megaspore mother cell in nucellus divides meiotically to form four megaspores
  • One megaspore develops into multicellular female gametophyte bearing archegonia
  • Pollen grains carried by air currents to ovules
  • Pollen tube grows towards archegonia and discharges male gametes
  • After fertilization, zygote develops into embryo and ovules into seeds
Q: What are the main differences between gymnosperms and angiosperms?
Gymnosperms
Figure: Examples of Gymnosperms

3.5 Angiosperms

Unlike the gymnosperms where the ovules are naked, in the angiosperms or flowering plants, the pollen grains and ovules are developed in specialised structures called flowers. In angiosperms, the seeds are enclosed in fruits. They are an exceptionally large group of plants occurring in wide range of habitats, ranging in size from the smallest Wolffia to tall trees of Eucalyptus (over 100 metres).

Characteristics of Angiosperms:

  • Also called flowering plants
  • Ovules enclosed in ovary which develops into fruit after fertilization
  • Seeds enclosed in fruits
  • Most diverse group of plants with about 300,000 species
  • Occur in wide range of habitats
  • Range in size from tiny Wolffia to tall Eucalyptus trees
  • Provide food, fodder, fuel, medicines and other commercial products
  • Divided into two classes: dicotyledons and monocotyledons
Angiosperms: Flowering plants that produce seeds enclosed within a fruit. They are the most diverse and widespread group of plants on Earth, characterized by the presence of flowers and fruits.
Differences between Dicotyledons and Monocotyledons:
Character Dicotyledons Monocotyledons
Seed Two cotyledons One cotyledon
Leaf venation Reticulate Parallel
Root system Tap root Fibrous
Vascular bundles Arranged in a ring, open Scattered, closed
Floral parts Usually in multiples of 4 or 5 Usually in multiples of 3
Q: Both gymnosperms and angiosperms bear seeds, then why are they classified separately?
Angiosperms
Figure: Angiosperms - Dicotyledon and Monocotyledon

Chapter Summary

Key Takeaways:

  • Plant kingdom includes algae, bryophytes, pteridophytes, gymnosperms and angiosperms
  • Algae are simple, thalloid, autotrophic organisms classified into Chlorophyceae, Phaeophyceae and Rhodophyceae based on pigments and stored food
  • Algae reproduce vegetatively, asexually and sexually (isogamy, anisogamy, oogamy)
  • Bryophytes are amphibians of plant kingdom with gametophyte as dominant phase
  • Pteridophytes are first vascular plants with sporophyte as dominant phase
  • Gymnosperms have naked seeds and include medium to tall trees
  • Angiosperms are flowering plants with seeds enclosed in fruits, divided into monocots and dicots
  • Plant classification shows evolutionary progression from simple to complex forms

NCERT Solutions

Question 1: What is the basis of classification of algae?

Algae are classified based on the following characteristics:

  1. Type of pigments: Different algae contain different photosynthetic pigments which determine their color and classification.
  2. Type of stored food: The nature of reserve food material varies among different groups of algae.
  3. Cell wall composition: The chemical nature of cell wall differs among various algal groups.
  4. Flagellar number and position: Presence, number and insertion of flagella in motile forms.
  5. Habitat: Though most are aquatic, their specific habitat preferences also contribute to classification.

Based on these criteria, algae are divided into three main classes:

  • Chlorophyceae (Green algae): Chlorophyll a and b, starch as stored food, cellulose cell wall
  • Phaeophyceae (Brown algae): Chlorophyll a and c, fucoxanthin, laminarin or mannitol as food, cellulose and algin in cell wall
  • Rhodophyceae (Red algae): Chlorophyll a and d, phycoerythrin, floridean starch as food, cellulose and poly sulphate esters in cell wall

Question 2: When and where does reduction division take place in the life cycle of a liverwort, a moss, a fern, a gymnosperm and an angiosperm?

Reduction division (meiosis) occurs at the following stages in different plant groups:

Plant Group Where Meiosis Occurs
Liverwort In the capsule of sporophyte to produce spores
Moss In the capsule of sporophyte to produce spores
Fern In sporangia to produce spores (spore mother cells undergo meiosis)
Gymnosperm In microsporangia (to produce microspores) and megasporangia (to produce megaspores)
Angiosperm In anthers (to produce microspores) and ovules (to produce megaspores)

Question 3: Name three groups of plants that bear archegonia. Briefly describe the life cycle of any one of them.

Three plant groups that bear archegonia:

  1. Bryophytes (e.g., mosses, liverworts)
  2. Pteridophytes (e.g., ferns, horsetails)
  3. Gymnosperms (e.g., pine, cycas)

Life cycle of a moss (Bryophyte):

  1. The dominant phase is the gametophyte which is haploid and photosynthetic.
  2. The gametophyte bears male sex organs called antheridia (produce antherozoids) and female sex organs called archegonia (each produces one egg).
  3. Water is required for fertilization as antherozoids swim to archegonia.
  4. After fertilization, zygote is formed which develops into a diploid sporophyte attached to the gametophyte.
  5. The sporophyte is differentiated into foot, seta and capsule.
  6. In the capsule, spore mother cells undergo meiosis to produce haploid spores.
  7. Spores are released and germinate to form protonema, which develops into new gametophyte plants.

This life cycle shows alternation of generations between haploid gametophyte and diploid sporophyte phases.

Question 4: 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.

Structure Ploidy
Protonemal cell of a moss Haploid (n)
Primary endosperm nucleus in dicot Triploid (3n)
Leaf cell of a moss Haploid (n)
Prothallus cell of a fern Haploid (n)
Gemma cell in Marchantia Haploid (n)
Meristem cell of monocot Diploid (2n)
Ovum of a liverwort Haploid (n)
Zygote of a fern Diploid (2n)

Question 5: Write a note on economic importance of algae and gymnosperms.

Economic Importance of Algae:

  1. Primary producers: Algae contribute about half of global carbon fixation through photosynthesis and release oxygen.
  2. Food source: Many marine algae like Porphyra, Laminaria, Sargassum are used as food.
  3. Commercial products: Brown algae produce algin, red algae produce carrageen and agar used in food, pharmaceutical and cosmetic industries.
  4. Agar: Obtained from Gelidium and Gracilaria, used to grow microbes and in food preparations.
  5. Nutritional supplements: Chlorella is rich in proteins and used as food supplement.
  6. Water purification: Some algae help in sewage oxidation and water purification.

Economic Importance of Gymnosperms:

  1. Timber: Many gymnosperms like pine, cedar, deodar provide softwood used in construction, furniture and plywood.
  2. Resins: Used in varnishes, adhesives, waterproofing and medicinal preparations.
  3. Paper production: Coniferous wood is used for making paper pulp.
  4. Ornamental plants: Many gymnosperms like Cycas, Thuja are grown as ornamental plants.
  5. Edible products: Seeds of Pinus (chilgoza), Cycas (after proper processing) are edible.
  6. Medicinal uses: Ephedrine from Ephedra is used to treat asthma and respiratory problems.

Question 6: Both gymnosperms and angiosperms bear seeds, then why are they classified separately?

Gymnosperms and angiosperms are classified separately due to following fundamental differences:

Feature Gymnosperms Angiosperms
Seed enclosure Naked seeds (not enclosed in fruit) Seeds enclosed in fruits
Ovary Ovules not enclosed in ovary Ovules enclosed in ovary
Flowers No true flowers Have true flowers
Vessels in xylem Absent (except Gnetales) Present
Companion cells in phloem Absent Present
Double fertilization Absent Present
Diversity About 1000 species About 300,000 species

These differences in reproductive structures, anatomy and diversity justify their classification into separate groups despite both being seed-bearing plants.

Question 7: What is heterospory? Briefly comment on its significance. Give two examples.

Heterospory: It is the production of two different types of spores - microspores (small) and megaspores (large) by the sporophytes of land plants. This condition is called heterospory.

Significance of heterospory:

  1. It is considered an important step in evolution as it leads to the development of seed habit.
  2. Microspores give rise to male gametophytes while megaspores give rise to female gametophytes.
  3. The female gametophyte is retained on the parent sporophyte for variable periods, providing protection and nutrition.
  4. Zygote develops into embryo within the female gametophyte which is still attached to parent plant.
  5. This represents the beginning of the seed habit which culminates in seed plants (gymnosperms and angiosperms).

Examples of heterosporous plants:

  1. Selaginella (a pteridophyte)
  2. Salvinia (a water fern)

Note: All seed plants (gymnosperms and angiosperms) are heterosporous, but these are advanced forms where the distinction is even more pronounced.

Question 8: Explain briefly the following terms with suitable examples:

(i) Protonema: It is the first stage in the life cycle of mosses, developing directly from a spore. It is a creeping, green, branched and frequently filamentous structure. The leafy moss plant develops from the protonema as a lateral bud. Example: Protonema of Funaria.

(ii) Antheridium: It is the male sex organ in bryophytes, pteridophytes and some gymnosperms. It produces and releases male gametes called antherozoids. Example: Antheridia in mosses like Funaria or fern prothallus.

(iii) Archegonium: It is the flask-shaped female sex organ in bryophytes, pteridophytes and gymnosperms. It produces a single egg cell. Example: Archegonia in Marchantia (liverwort) or fern prothallus.

(iv) Diplontic: A life cycle where the diploid sporophyte is the dominant, photosynthetic, independent phase, while the haploid gametophyte is reduced. Example: Life cycle of gymnosperms and angiosperms.

(v) Sporophyll: It is a leaf-like structure that bears sporangia. In ferns, sporophylls bear sporangia on their undersurface. In gymnosperms, microsporophylls and megasporophylls bear microsporangia and megasporangia respectively. Example: Sporophylls in Dryopteris (fern) or microsporophylls in Cycas.

(vi) Isogamy: It is a type of sexual reproduction where the fusing gametes are morphologically similar (same size and shape) but may differ physiologically. Example: Ulothrix (green alga) where flagellated gametes of similar size fuse.

Question 9: Differentiate between the following:

(i) Red algae and brown algae:

Character Red Algae (Rhodophyceae) Brown Algae (Phaeophyceae)
Major pigments Chlorophyll a, d and phycoerythrin Chlorophyll a, c and fucoxanthin
Color Red due to phycoerythrin Olive green to brown due to fucoxanthin
Stored food Floridean starch Laminarin or mannitol
Cell wall Cellulose, pectin and poly sulphate esters Cellulose and algin
Flagella Absent Two, unequal, lateral
Habitat Mostly marine, some in fresh water Mostly marine, few in fresh water
Examples Polysiphonia, Porphyra Fucus, Sargassum

(ii) Liverworts and moss:

Character Liverworts Moss
Plant body Thalloid or leafy (if leafy, leaves in 2 rows) Leafy stage with leaves in spirals
Protonema Reduced or absent Well-developed, filamentous
Rhizoids Unicellular Multicellular and branched
Asexual reproduction By fragmentation or gemmae in gemma cups By fragmentation or secondary protonema
Sporophyte Simple, short-lived More elaborate, with foot, seta and capsule
Examples Marchantia, Riccia Funaria, Sphagnum

(iii) Homosporous and heterosporous pteridophyte:

Character Homosporous Pteridophytes Heterosporous Pteridophytes
Spores produced Only one type of spore Two types: microspores (small) and megaspores (large)
Gametophyte Bisexual (produces both male and female sex organs) Unisexual (microspores → male gametophyte; megaspores → female gametophyte)
Evolutionary significance Primitive condition Advanced condition, precursor to seed habit
Examples Most ferns like Dryopteris, Pteris Selaginella, Salvinia

Question 10: Match the following (column I with column II)

Column I Column II Answer
(a) Chlamydomonas (i) Moss (a) - (iii)
(b) Cycas (ii) Pteridophyte (b) - (iv)
(c) Selaginella (iii) Algae (c) - (ii)
(d) Sphagnum (iv) Gymnosperm (d) - (i)

Correct matching:

  • (a) Chlamydomonas - (iii) Algae (it is a green alga)
  • (b) Cycas - (iv) Gymnosperm (it is a gymnosperm)
  • (c) Selaginella - (ii) Pteridophyte (it is a heterosporous pteridophyte)
  • (d) Sphagnum - (i) Moss (it is a moss, a type of bryophyte)

Question 11: Describe the important characteristics of gymnosperms.

Important characteristics of gymnosperms:

  1. Naked seeds: The ovules are not enclosed by any ovary wall and remain exposed before and after fertilization. The seeds that develop are naked (not enclosed in fruits).
  2. Sporophyte: The dominant plant body is sporophyte which is differentiated into root, stem and leaves.
  3. Root system: Generally tap roots. Roots in some genera have fungal association (mycorrhiza) or N2-fixing cyanobacteria (coralloid roots in Cycas).
  4. Stems: May be unbranched (Cycas) or branched (Pinus, Cedrus).
  5. Leaves: May be simple or compound. Well-adapted to withstand extremes of temperature, humidity and wind. In conifers, needle-like leaves reduce surface area with thick cuticle and sunken stomata to reduce water loss.
  6. Heterosporous: Produce two types of spores - microspores (pollen grains) and megaspores.
  7. Cones: Sporophylls are arranged to form cones or strobili - male cones (microsporangiate) and female cones (macrosporangiate).
  8. Reduced gametophytes: Male gametophyte is reduced to pollen grain. Female gametophyte is retained within megasporangium.
  9. Pollination: Pollen grains are carried by wind to ovules (wind pollination).
  10. Fertilization: Pollen tube grows towards archegonia in ovules and discharges male gametes near them.
  11. Seeds: After fertilization, zygote develops into embryo and ovules into seeds which remain naked.
  12. Examples: Cycas, Pinus, Cedrus, Ginkgo, Sequoia (giant redwood tree).

Gymnosperms represent an important group of plants evolutionarily between pteridophytes and angiosperms, showing several advanced features but still retaining some primitive characteristics.

Practice Questions

1. Which of the following is not a characteristic of algae?

Correct Answer: c) Well-differentiated root, stem and leaves

Explanation: Algae are simple, thalloid organisms that do not have well-differentiated root, stem and leaves. This characteristic is seen in higher plants like pteridophytes, gymnosperms and angiosperms.

2. Bryophytes are called amphibians of plant kingdom because:

Correct Answer: b) They live in soil but need water for sexual reproduction

Explanation: Bryophytes are called amphibians because though they can live in soil (terrestrial habitat), they require water for fertilization as their male gametes (antherozoids) need water to swim to the archegonia.

3. Which of the following is heterosporous?

Correct Answer: b) Selaginella

Explanation: Selaginella is a heterosporous pteridophyte that produces two types of spores - microspores and megaspores. Funaria and Marchantia are bryophytes which are homosporous, and Spirogyra is an alga.

1. Differentiate between isogamy and oogamy with examples.

Answer:

Isogamy Oogamy
Fusion of morphologically similar gametes Fusion of dissimilar gametes (large non-motile female and small motile male)
Gametes may be flagellated (Ulothrix) or non-flagellated (Spirogyra) Male gamete is flagellated, female gamete is non-motile
Considered primitive condition Advanced condition
Examples: Ulothrix, Spirogyra Examples: Volvox, Fucus, all higher plants
2. What are gemmae? In which plant group are they found?

Answer:

Gemmae are multicellular, asexual reproductive structures found in some liverworts. They are:

  • Green, multicellular, asexual buds
  • Develop in small receptacles called gemma cups located on the thalli
  • Become detached from parent body and germinate to form new individuals
  • Help in vegetative propagation

They are found in liverworts like Marchantia. This is a method of asexual reproduction that helps in rapid multiplication.

1. Explain alternation of generations in plants with reference to bryophytes and pteridophytes.

Answer:

Alternation of generations refers to the alternation between haploid gametophyte and diploid sporophyte phases in the life cycle of plants.

In Bryophytes:

  1. The dominant phase is the haploid gametophyte which is independent and photosynthetic.
  2. Gametophyte produces male (antheridia) and female (archegonia) sex organs.
  3. Fertilization results in formation of diploid zygote which develops into sporophyte.
  4. Sporophyte is dependent on gametophyte for nutrition.
  5. Sporophyte produces haploid spores by meiosis.
  6. Spores germinate to form new gametophytes.
  7. Thus, the life cycle alternates between gametophyte (n) and sporophyte (2n) generations.

In Pteridophytes:

  1. The dominant phase is the diploid sporophyte which is independent and photosynthetic.
  2. Sporophyte produces spores by meiosis in sporangia.
  3. Spores germinate to form haploid gametophyte (prothallus) which is small but independent.
  4. Gametophyte produces antheridia and archegonia.
  5. After fertilization, zygote develops into sporophyte.
  6. Thus, the life cycle shows clear alternation between sporophyte (2n) and gametophyte (n) generations.

Key Difference: In bryophytes, gametophyte is dominant while in pteridophytes, sporophyte is dominant. This represents an evolutionary trend where sporophyte becomes more prominent in higher plants.

2. Describe the life cycle of a fern with emphasis on the independent nature of sporophyte and gametophyte generations.

Answer:

The life cycle of a fern (pteridophyte) shows alternation of generations with both sporophyte and gametophyte being independent:

1. Sporophyte Generation (2n):

  • This is the dominant, photosynthetic phase that we recognize as the fern plant.
  • It is differentiated into true roots, stem (rhizome) and leaves (fronds).
  • On the underside of mature fronds, sporangia develop in clusters called sori.
  • Spore mother cells in sporangia undergo meiosis to produce haploid spores (n).
  • Spores are released and dispersed by wind.

2. Gametophyte Generation (n):

  • Spores germinate to form heart-shaped, multicellular gametophyte called prothallus.
  • Prothallus is small (few mm) but independent and photosynthetic.
  • It bears both antheridia (male sex organs) and archegonia (female sex organs).
  • Antheridia produce flagellated antherozoids that swim in water to reach archegonia.
  • Fertilization results in formation of diploid zygote.

3. New Sporophyte:

  • Zygote develops into embryo and then mature sporophyte.
  • Initially, young sporophyte is attached to gametophyte but soon becomes independent.
  • The cycle continues with the mature sporophyte producing spores again.

Independent Nature:

  • Both sporophyte and gametophyte are free-living and photosynthetic.
  • This is different from bryophytes where gametophyte is dominant and sporophyte is dependent.
  • In ferns, sporophyte is larger and more complex while gametophyte is small but fully independent.
  • This represents an evolutionary advancement over bryophytes.

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What are the three main classes of algae?

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The three main classes of algae are:

  1. Chlorophyceae (Green algae)
  2. Phaeophyceae (Brown algae)
  3. Rhodophyceae (Red algae)

They are classified based on their pigments, stored food, and cell wall composition.

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