Class 11 Biology NCERT Notes- Chapter 3: Plant Kingdom

Detailed Study Notes – Chapter 3: Plant Kingdom ( Class 11 Biology, Notes, PDFs, Quizzes, MCQs)

1. Introduction to Plant Classification

The classification of the Plant Kingdom has evolved significantly over time. While Whittaker’s (1969) Five Kingdom system established Plantae as a distinct kingdom, its boundaries have been refined. Organisms like fungi, and members of Monera and Protista with cell walls, were once included but are now excluded. Consequently, cyanobacteria, also known as blue-green algae, are no longer classified as ‘algae’. This guide focuses on the modern understanding of Kingdom Plantae, covering Algae, Bryophytes, Pteridophytes, Gymnosperms, and Angiosperms.

Systems of Classification

• Artificial Systems: These were the earliest systems, based on superficial morphological characters like habit, color, and leaf shape, or on a single character like the androecium structure (Linnaeus’s system). A major drawback was giving equal weight to vegetative and sexual characteristics, even though vegetative traits are more susceptible to environmental changes. This often resulted in the separation of closely related species.
• Natural Classification Systems: Developed to address the shortcomings of artificial systems, these are based on natural affinities among organisms. They consider not only external features but also internal ones, such as ultrastructure, anatomy, embryology, and phytochemistry. A notable example is the system for flowering plants developed by George Bentham and Joseph Dalton Hooker.
• Phylogenetic Classification Systems: These modern systems are based on the evolutionary relationships between organisms and are widely accepted today. They operate on the assumption that organisms within the same taxa share a common ancestor. This approach becomes crucial when fossil evidence is unavailable.
• Modern Taxonomic Aids:
  • Numerical Taxonomy: Utilizes computers to process data from all observable characteristics. Each character is assigned a number and code, given equal importance, and hundreds of characters can be analyzed simultaneously.
  • Cytotaxonomy: Relies on cytological information, including chromosome number, structure, and behavior.
  • Chemotaxonomy: Uses the chemical constituents of plants to resolve classification ambiguities.

2. Algae

Algae are simple, autotrophic organisms characterized by being chlorophyll-bearing and having a thalloid (undifferentiated) body. They are predominantly aquatic, found in both freshwater and marine environments, but also inhabit moist stones, soils, and wood. Some form symbiotic relationships with fungi (as lichens) or animals (e.g., on sloth bears).

• Form and Size: Highly variable, from microscopic unicellular forms, colonial forms like Volvox, and filamentous forms like Ulothrix and Spirogyra, to massive marine kelps.
• Reproduction:
  • Vegetative: Through fragmentation, where each fragment develops into a new thallus.
  • Asexual: By producing various types of spores, most commonly motile, flagellated zoospores.
  • Sexual: Through the fusion of two gametes. This can be:
    • Isogamous: Fusion of gametes that are similar in size. They can be flagellated (Ulothrix) or non-flagellated (Spirogyra).
    • Anisogamous: Fusion of two gametes that are dissimilar in size (e.g., Eudorina).
    • Oogamous: Fusion of a large, non-motile (static) female gamete with a smaller, motile male gamete (e.g., Volvox, Fucus).
• Economic Importance:
  • Photosynthesis: Carry out at least half of the total carbon dioxide fixation on Earth, increasing dissolved oxygen levels.
  • Primary Producers: Form the base of aquatic food cycles.
  • Food: Many species, including Porphyra, Laminaria, and Sargassum, are used as food.
  • Commercial Products:
    • Hydrocolloids (water-holding substances): Algin from brown algae and carrageen from red algae.
    • Agar: Obtained from Gelidium and Gracilaria, used to grow microbes and in making ice creams and jellies.
    • Food Supplement: The protein-rich unicellular alga Chlorella is used by space travelers.

Algal Classes

Algae are divided into three main classes based on pigmentation and stored food type.

Feature	Chlorophyceae (Green Algae)	Phaeophyceae (Brown Algae)	Rhodophyceae (Red Algae)
Common Name	Green algae	Brown algae	Red algae
Major Pigments	Chlorophyll a, b	Chlorophyll a, c, Fucoxanthin	Chlorophyll a, d, Phycoerythrin
Stored Food	Starch	Mannitol, Laminarin	Floridean starch
Cell Wall	Cellulose, Pectose	Cellulose and Algin	Cellulose, Pectin, and Poly sulphate esters
Flagellar Insertions	2-8, equal, apical	2, unequal, lateral	Absent
Habitat	Fresh water, brackish, salt	Fresh water (rare), brackish, salt	Fresh water (some), brackish, salt (most)
Examples	Chlamydomonas, Volvox, Spirogyra	Ectocarpus, Laminaria, Fucus	Polysiphonia, Porphyra, Gelidium

• Chlorophyceae (Green Algae): Usually grass green with diverse chloroplast shapes. Store food in pyrenoids (protein and starch) or as oil droplets.
• Phaeophyceae (Brown Algae): Found primarily in marine habitats. Their color varies from olive green to brown due to the pigment fucoxanthin. The plant body is often differentiated into a holdfast (attachment), a stipe (stalk), and a frond (leaf-like photosynthetic organ).
• Rhodophyceae (Red Algae): The red color is due to the pigment r-phycoerythrin. Most are marine and can live at great depths where little light penetrates. They lack flagella at any stage. Sexual reproduction is oogamous and involves complex post-fertilization developments.

3. Bryophytes

Bryophytes, which include mosses and liverworts, are often called the amphibians of the plant kingdom. They live in soil but require water for sexual reproduction. Typically found in damp, humid, and shaded areas, they play a key ecological role in plant succession on bare rocks.

• Plant Body: More differentiated than algae. The body is thallus-like and can be prostrate or erect, attached to the substratum by unicellular or multicellular rhizoids. They lack true roots, stems, or leaves but may possess analogous structures.
• Life Cycle: The dominant phase is the haploid gametophyte, which produces gametes. The multicellular sporophyte is not free-living and remains attached to the gametophyte, from which it derives nourishment.
• Reproduction:
  • Sex organs are multicellular: the male antheridium produces biflagellate antherozoids, and the female archegonium is flask-shaped and produces a single egg.
  • Fertilization is water-dependent. The resulting zygote develops into a sporophyte.
  • The sporophyte undergoes meiosis to produce haploid spores, which germinate into a new gametophyte.
• Economic Importance:
  • Some mosses provide food for animals.
  • Sphagnum moss provides peat, used as fuel and as packing material for its high water-holding capacity.
  • They are important pioneer species, colonizing rocks and decomposing them to create soil.
  • Dense mats of moss help prevent soil erosion.

Divisions of Bryophytes

• Liverworts:
  • Grow in moist, shady habitats. The plant body is a thalloid (e.g., Marchantia).
  • Asexual reproduction occurs via fragmentation or through specialized structures called gemmae (asexual buds) formed in gemma cups.
  • The sporophyte is differentiated into a foot, seta, and capsule.
• Mosses:
  • The gametophyte life stage has two phases:
    1. Protonema Stage: A creeping, green, filamentous stage that develops from a spore.
    2. Leafy Stage: Develops from the protonema and consists of an upright axis with spirally arranged leaves. It bears the sex organs.
  • Vegetative reproduction occurs by fragmentation and budding in the secondary protonema.
  • The sporophyte is more elaborate than in liverworts and has a sophisticated mechanism for spore dispersal. Examples include Funaria and Sphagnum.

4. Pteridophytes

Pteridophytes, which include horsetails and ferns, are significant as the first terrestrial plants to possess vascular tissues (xylem and phloem). They are found in cool, damp, shady places and are used for medicinal purposes, as soil-binders, and as ornamentals.

• Plant Body: The main plant body is the diploid sporophyte (the dominant phase), which is differentiated into true roots, stems, and leaves.
• Leaves: Can be small (microphylls, as in Selaginella) or large (macrophylls, as in ferns).
• Reproduction:
  • The sporophyte bears sporangia on leaf-like appendages called sporophylls. In some species (Selaginella, Equisetum), these form compact structures called strobili or cones.
  • Spores are produced by meiosis and germinate into a small, free-living, photosynthetic gametophyte called a prothallus.
  • The prothallus requires cool, damp conditions and water for fertilization, which limits the geographical distribution of pteridophytes.
  • The zygote develops into a new sporophyte.
• Spore Types:
  • Homosporous: Most pteridophytes produce spores of a single kind.
  • Heterosporous: Some genera like Selaginella and Salvinia produce two types of spores: large megaspores (which develop into female gametophytes) and small microspores (which develop into male gametophytes).
• Evolutionary Significance: Heterospory is a precursor to the seed habit. In heterosporous species, the female gametophyte is retained on the parent sporophyte, and the development of the zygote into an embryo occurs within it, a critical step in evolution.

5. Gymnosperms

Gymnosperms are plants with “naked seeds” (gymnos – naked, sperma – seeds) because their ovules are not enclosed by an ovary wall and remain exposed both before and after fertilization.

• Plant Body: Includes medium-sized to tall trees (like the giant redwood Sequoia) and shrubs.
• Anatomy:
  • Roots: Generally tap roots. Some have symbiotic associations like mycorrhiza (Pinus) or coralloid roots with nitrogen-fixing cyanobacteria (Cycas).
  • Stems: May be unbranched (Cycas) or branched (Pinus).
  • Leaves: Are well-adapted to extreme conditions with features like needle-like shapes, thick cuticles, and sunken stomata to reduce water loss.
• Reproduction:
  • All gymnosperms are heterosporous.
  • Sporophylls are arranged spirally on an axis to form male and female strobili (cones).
  • The male gametophyte is highly reduced and is known as a pollen grain.
  • The female gametophyte is also reduced and retained within the megasporangium (ovule).
  • Unlike bryophytes and pteridophytes, the gametophytes do not have an independent, free-living existence.
  • Pollination occurs via air currents. The pollen tube delivers male gametes to the archegonium within the ovule for fertilization.
  • The resulting zygote develops into an embryo, and the ovule develops into an uncovered seed.

6. Angiosperms

Angiosperms, or flowering plants, are characterized by having ovules enclosed within a specialized structure, leading to seeds enclosed within fruits. They are an exceptionally large and diverse group found in a wide range of habitats.

• Key Features: Pollen grains and ovules are developed in specialized structures called flowers. Seeds are enclosed in fruits.
• Size: Range from the tiny Wolffia to massive Eucalyptus trees over 100 meters tall.
• Importance: Provide food, fodder, fuel, medicines, and numerous other commercial products.
• Classes: Divided into two classes: dicotyledons and monocotyledons.

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Knowledge Review Quiz

Short-Answer Questions

(Answer in 2-3 sentences.)

1. Describe the key differences between artificial and natural classification systems.
2. Explain the three types of sexual reproduction found in algae, providing an example for each.
3. Why are bryophytes called “amphibians of the plant kingdom”?
4. What are gemmae and what is their function in liverworts?
5. What is a prothallus and what are its requirements for growth?
6. Explain the concept of heterospory and its evolutionary significance.
7. Describe two adaptations of gymnosperm leaves to withstand extreme environmental conditions.
8. How do the gametophytes of gymnosperms differ from those of bryophytes and pteridophytes in terms of their existence?
9. What is the primary difference between gymnosperms and angiosperms regarding their ovules and seeds?
10. List three key economic or ecological contributions of algae.

Multiple-Choice Questions (MCQs)

1. The Five Kingdom classification system was proposed by: a) Linnaeus b) Bentham and Hooker c) Whittaker d) Darwin
2. Which classification system is based on evolutionary relationships between organisms? a) Artificial system b) Natural system c) Phylogenetic system d) Numerical taxonomy
3. Algin, a hydrocolloid used commercially, is obtained from: a) Red algae b) Brown algae c) Green algae d) Cyanobacteria
4. Floridean starch is the stored food in which class of algae? a) Chlorophyceae b) Phaeophyceae c) Rhodophyceae d) Xanthophyceae
5. The members of Chlorophyceae (green algae) are typically grass green due to the dominance of: a) Chlorophyll a and c b) Fucoxanthin c) r-phycoerythrin d) Chlorophyll a and b
6. Which of the following is an example of a colonial alga? a) Spirogyra b) Ulothrix c) Volvox d) Chara
7. Fusion of a large, non-motile female gamete and a smaller, motile male gamete is termed: a) Isogamous b) Anisogamous c) Oogamous d) Fragmentation
8. In the life cycle of a bryophyte, the dominant plant body is the: a) Sporophyte b) Gametophyte c) Zygote d) Spore
9. The multicellular male sex organ in bryophytes that produces biflagellate antherozoids is called the: a) Archegonium b) Oogonium c) Antheridium d) Sporangium
10. Peat, a substance long used as fuel, is derived from a moss known as: a) Funaria b) Marchantia c) Polytrichum d) Sphagnum
11. Evolutionarily, the first terrestrial plants to possess vascular tissues like xylem and phloem were the: a) Algae b) Bryophytes c) Pteridophytes d) Gymnosperms
12. In pteridophytes, the main, dominant plant body is a: a) Gametophyte b) Prothallus c) Sporophyte d) Haploid thallus
13. Compact structures called strobili or cones, which bear sporangia, are found in which pair of pteridophytes? a) Fern and Salvinia b) Selaginella and Equisetum c) Dryopteris and Pteris d) Lycopodium and Adiantum
14. The production of two kinds of spores, macro (large) and micro (small), is known as: a) Homospory b) Isogamy c) Asexual reproduction d) Heterospory
15. Coralloid roots, which are associated with N2-fixing cyanobacteria, are a characteristic feature of: a) Pinus b) Sequoia c) Cycas d) Ginkgo
16. In gymnosperms, the highly reduced male gametophyte is known as the: a) Antherozoid b) Pollen grain c) Microspore d) Embryo
17. The giant redwood tree Sequoia, one of the tallest tree species, belongs to which group? a) Angiosperms b) Pteridophytes c) Bryophytes d) Gymnosperms
18. Which statement best describes the seeds of gymnosperms? a) They are enclosed within a fruit. b) They are not covered and remain exposed. c) They develop from the gametophyte. d) They are absent; reproduction is by spores only.
19. Unlike gymnosperms, the ovules and pollen grains of angiosperms are developed in specialized structures called: a) Cones b) Strobili c) Flowers d) Fronds
20. Angiosperms are divided into two classes: a) Mosses and Liverworts b) Homosporous and Heterosporous c) Dicotyledons and Monocotyledons d) Ferns and Horsetails

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Answer Keys

Short-Answer Questions Answer Key

1. Artificial systems used a few superficial morphological characters and gave equal weightage to vegetative and sexual traits, often separating related species. Natural systems are based on natural affinities and consider both external and internal features (like anatomy and embryology) to establish relationships.
2. The three types are isogamous (fusion of similar-sized gametes, e.g., Spirogyra), anisogamous (fusion of dissimilar-sized gametes, e.g., Eudorina), and oogamous (fusion of a large, non-motile female gamete and a small, motile male gamete, e.g., Volvox).
3. Bryophytes are called amphibians of the plant kingdom because they live in soil but are dependent on water for sexual reproduction. The male gametes (antherozoids) must swim through water to reach the egg in the archegonium for fertilization to occur.
4. Gemmae are green, multicellular, asexual buds that develop in small receptacles called gemma cups on the thalli of liverworts. Their function is asexual reproduction; when detached from the parent body, they germinate to form new individuals.
5. A prothallus is the inconspicuous, small, multicellular, free-living, and mostly photosynthetic gametophyte of a pteridophyte that develops from a spore. To grow, it requires cool, damp, and shady places, as well as water for fertilization.
6. Heterospory is the production of two different kinds of spores: large megaspores and small microspores. This is evolutionarily significant because it is a precursor to the seed habit, as the female gametophyte develops and is retained on the parent sporophyte.
7. Gymnosperm leaves are adapted to extreme conditions with features like needle-like shapes that reduce surface area. They also possess a thick cuticle and sunken stomata, which help to reduce water loss.
8. In bryophytes and pteridophytes, the gametophytes have a free-living existence (though the bryophyte sporophyte is dependent). In gymnosperms, the male and female gametophytes do not have an independent, free-living existence; they remain within the sporangia retained on the sporophyte.
9. In gymnosperms, the ovules are not enclosed by any ovary wall, and the resulting seeds remain exposed or “naked.” In angiosperms, the ovules are developed within a flower, and the seeds are enclosed within a fruit.
10. Algae carry out at least half of the earth’s carbon dioxide fixation, are the primary producers in aquatic food webs, and are sources of commercial products like agar, algin, and carrageen.

Multiple-Choice Questions Answer Key

1. c) Whittaker
2. c) Phylogenetic system
3. b) Brown algae
4. c) Rhodophyceae
5. d) Chlorophyll a and b
6. c) Volvox
7. c) Oogamous
8. b) Gametophyte
9. c) Antheridium
10. d) Sphagnum
11. c) Pteridophytes
12. c) Sporophyte
13. b) Selaginella and Equisetum
14. d) Heterospory
15. c) Cycas
16. b) Pollen grain
17. d) Gymnosperms
18. b) They are not covered and remain exposed.
19. c) Flowers
20. c) Dicotyledons and Monocotyledons

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Suggested Essay Questions

1. Compare and contrast the life cycles of a moss (bryophyte) and a fern (pteridophyte), focusing on the dominant generation, plant body structure, dependency of sporophyte/gametophyte, and reproductive processes.
2. Discuss the evolution of plant classification systems, from artificial to natural to phylogenetic systems. Include the role and importance of modern taxonomic tools like numerical taxonomy, cytotaxonomy, and chemotaxonomy.
3. Describe the economic and ecological significance of algae, providing specific examples from the text for their roles as primary producers, food sources, and sources of commercial products.
4. Trace the evolutionary trend from homospory to heterospory and the development of the seed habit. Explain how the reproductive strategy in heterosporous pteridophytes is considered a precursor to the seed habit seen in gymnosperms.
5. Detail the characteristics of the three main classes of algae: Chlorophyceae, Phaeophyceae, and Rhodophyceae. Base your comparison on their major pigments, stored food, cell wall composition, flagellar arrangement, and typical habitats.

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Glossary of Key Terms

• Agar: A commercial product obtained from red algae (Gelidium, Gracilaria), used to grow microbes and in foods.
• Algin: A hydrocolloid (water-holding substance) produced by brown algae.
• Amphibians of the plant kingdom: A term for bryophytes, reflecting their dependence on water for sexual reproduction despite living on soil.
• Androecium: The male part of a flower; its structure was used by Linnaeus in an artificial classification system.
• Anisogamous: A type of sexual reproduction involving the fusion of two gametes that are dissimilar in size.
• Antheridium: The multicellular male sex organ in bryophytes and pteridophytes that produces male gametes (antherozoids).
• Antherozoids: The motile male gametes produced by the antheridium, typically biflagellate in bryophytes.
• Archegonium: The multicellular, flask-shaped female sex organ in bryophytes, pteridophytes, and gymnosperms that contains a single egg.
• Artificial system: An early classification system based on a few superficial morphological characteristics.
• Autotrophic: An organism that can produce its own food, typically through photosynthesis.
• Bryophytes: A division of plants including mosses and liverworts, characterized by a dominant gametophyte generation.
• Carrageen: A hydrocolloid (water-holding substance) produced by red algae.
• Chemotaxonomy: A method of classification that uses the chemical constituents of a plant.
• Chlorophyceae: The class of green algae.
• Coralloid roots: Specialized roots in some gymnosperms (Cycas) that are associated with nitrogen-fixing cyanobacteria.
• Cytotaxonomy: A method of classification based on cytological information like chromosome number, structure, and behavior.
• Dicotyledons: One of the two classes of angiosperms.
• Floridean starch: The form of stored food in red algae (Rhodophyceae), structurally similar to amylopectin and glycogen.
• Frond: The leaf-like photosynthetic organ of a kelp (brown alga) or a fern.
• Fucoxanthin: A xanthophyll pigment present in brown algae (Phaeophyceae) that gives them their characteristic color.
• Gametophyte: The haploid, gamete-producing phase in the life cycle of a plant.
• Gemmae: Green, multicellular, asexual buds used for vegetative reproduction in liverworts.
• Gymnosperms: A group of seed-producing plants with “naked” seeds, meaning the ovules are not enclosed in an ovary.
• Heterosporous: Producing two different types of spores (microspores and megaspores). Found in some pteridophytes and all seed plants.
• Holdfast: A root-like structure that attaches the thallus of an alga to a substratum.
• Homosporous: Producing only one type of spore, which develops into a gametophyte that typically bears both male and female sex organs.
• Hydrocolloids: Water-holding substances, such as algin and carrageen, produced by algae.
• Isogamous: A type of sexual reproduction involving the fusion of two gametes that are similar in size and form.
• Kelps: Massive marine brown algae that can form large underwater forests.
• Laminarin: A complex carbohydrate stored as food in brown algae.
• Macrophylls: Large leaves, as seen in ferns.
• Mannitol: A complex carbohydrate stored as food in brown algae.
• Megaspores: The larger of the two types of spores in heterosporous plants, which typically develops into the female gametophyte.
• Microphylls: Small leaves, as seen in Selaginella.
• Microspores: The smaller of the two types of spores in heterosporous plants, which typically develops into the male gametophyte.
• Monocotyledons: One of the two classes of angiosperms.
• Mycorrhiza: A symbiotic association between a fungus and the roots of a plant (e.g., in Pinus).
• Natural classification systems: Systems based on natural affinities among organisms, considering multiple internal and external features.
• Numerical Taxonomy: A computer-based classification method where all observable characters are coded and given equal importance.
• Oogamous: A type of sexual reproduction involving the fusion of a large, non-motile female gamete and a smaller, motile male gamete.
• Pectose: A substance forming the outer layer of the cell wall in green algae.
• Phaeophyceae: The class of brown algae.
• Phylogenetic classification systems: Systems based on the evolutionary relationships between organisms.
• Prothallus: The free-living, photosynthetic gametophyte of a pteridophyte.
• Protonema: The first, creeping, filamentous stage of a moss gametophyte that develops from a spore.
• Pteridophytes: A division of vascular plants, including ferns and horsetails, with a dominant sporophyte generation.
• Pyrenoids: Storage bodies located in the chloroplasts of most green algae, containing protein besides starch.
• r-phycoerythrin: The red pigment that gives red algae (Rhodophyceae) their characteristic color.
• Rhizoids: Unicellular or multicellular hair-like structures that anchor bryophytes to a substrate.
• Rhodophyceae: The class of red algae.
• Sporophyll: A modified leaf that bears sporangia.
• Sporophyte: The diploid, spore-producing phase in the life cycle of a plant.
• Stipe: The stalk-like structure in a kelp (brown alga) that supports the fronds.
• Strobili (or Cones): Compact structures formed by sporophylls arranged spirally along an axis, found in some pteridophytes and gymnosperms.
• Thalloid: A plant body that is not differentiated into true roots, stem, and leaves.
• Vascular tissues: Tissues (xylem and phloem) that conduct water, minerals, and nutrients within the plant.
• Zoospores: Motile, flagellated spores used for asexual reproduction in algae.