Plant Kingdom Class 11 Notes

Plants are classified into four groups based on key structural features: Bryophytes (no vascular tissue, no seeds), Pteridophytes (vascular tissue present, no seeds), Gymnosperms (vascular tissue and naked seeds) and Angiosperms (vascular tissue, seeds enclosed in fruit/ovary). A unifying concept across all plant groups is the alternation of generations.

• Haplontic — the gametophyte (n) is dominant; the sporophyte (2n) is short-lived and dependent on the gametophyte. Example: fern prothallus.
• Diplontic — the sporophyte (2n) is dominant; the gametophyte (n) is highly reduced. Examples: gymnosperms and angiosperms (seed plants).
• Haplodiplontic — both gametophyte and sporophyte are independent and photosynthetic. Examples: Bryophytes and Pteridophytes.

Bryophytes are non-vascular plants (no xylem or phloem). They are called 'amphibians of the plant kingdom' because they live on land but require water for reproduction (sperm must swim to the egg). The gametophyte is the dominant, photosynthetic and independent phase.

• Liverworts (e.g. Marchantia) — the plant body is thalloid (flat, ribbon-like) with dichotomous branching. They reproduce by fragmentation or gemmae (cup-like structures on the thallus that produce new plants).
• Mosses (e.g. Funaria, Sphagnum) — have a leafy gametophyte with a central axis (seta) and simple leaf-like structures. The sporophyte consists of a foot, seta and capsule. Spores are released from the capsule.
• Bryophytes lack true roots, stems and leaves — they have rhizoids (root-like), stems and leaf-like structures instead.
• Sphagnum (peat moss) is commercially important: it is used as packing material for transshipping living plants and in peat formation.

Pteridophytes are seedless vascular plants — they have true vascular tissue (xylem and phloem) but reproduce by spores rather than seeds. The sporophyte is the dominant phase, but the gametophyte is still independent and photosynthetic (prothallus).

• Examples: ferns (Dryopteris, Pteris), horsetails (Equisetum) and club mosses (Lycopodium, Selaginella).
• The sporophyte has true roots, stems and leaves — the first plant group to evolve these structures.
• Spores are produced in sporangia, often grouped in clusters called sori (singular: sorus) on the underside of leaves.
• The gametophyte (prothallus) is small, heart-shaped and free-living. It produces antheridia (male) and archegonia (female).
• Water is needed for fertilisation — sperm swim from antheridia to archegonia.

Gymnosperms are vascular plants that produce 'naked' seeds — seeds that are not enclosed within an ovary or fruit. The seed is borne on the surface of scales or leaves, often arranged in cones (strobili). The sporophyte is the dominant phase.

• Examples: Cycas (cycad), Pinus (pine), Ginkgo (maidenhair tree), Ephedra.
• They are woody, perennial plants — most gymnosperms are trees or shrubs.
• The ovule is not enclosed in an ovary; it lies naked on the megasporophyll (modified leaf).
• Pinus shows a unique association: its seeds lack endosperm at maturity. Nutrition is provided by mycorrhizal fungi that colonise the roots.
• The wood of gymnosperms is softwood (no vessels in xylem of Pinus; Cycas has no vessels at all).

Angiosperms are the most diverse and dominant group of land plants. They are called flowering plants because their reproductive organs are flowers. The seeds are enclosed within the ovary, which develops into a fruit after fertilisation.

• Angiosperms are divided into two groups: Monocotyledons (monocots) and Dicotyledons (dicots).
• Monocots: one cotyledon in seed, parallel leaf venation, fibrous root system, scattered vascular bundles, trimerous flowers (parts in 3s). Examples: grass, wheat, maize, rice, banana.
• Dicots: two cotyledons in seed, reticulate venation, tap root system, ring-arranged vascular bundles, tetramerous or pentamerous flowers (parts in 4s or 5s). Examples: mango, neem, pea, rose.
• Angiosperms show remarkable diversity: from tiny Wolffia (a few mm) to tall trees like Eucalyptus, from herbs to shrubs.
• The double fertilisation unique to angiosperms involves one sperm fertilising the egg (forming zygote) and the other fertilising the polar nuclei (forming endosperm — triploid).

Plants are indispensable for human survival: they provide food (cereals, fruits, vegetables), medicine, timber, fibres, rubber, dyes and ornamental products. A summary of plant groups and their key features is useful for quick revision.

• Bryophytes — non-vascular, no seeds, gametophyte dominant, need water for reproduction.
• Pteridophytes — vascular, no seeds, sporophyte dominant, gametophyte (prothallus) free-living.
• Gymnosperms — vascular, naked seeds, sporophyte dominant, seeds not in fruit.
• Angiosperms — vascular, seeds enclosed in fruit, sporophyte dominant, flowers for reproduction.

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

Solution: Bryophytes live on land (terrestrial habitat) like reptiles and amphibians, but they require water for reproduction — their flagellated sperm must swim through water to reach the egg for fertilisation. This dependence on water for sexual reproduction, despite being terrestrial, earns them the title 'amphibians of the plant kingdom'.

Example: Distinguish between homosporous and heterosporous pteridophytes. Give one example of each.

Solution: Homosporous pteridophytes produce only one type of spore, which germinates into a bisexual (bisexual) gametophyte. Example: Pteris, Lycopodium. Heterosporous pteridophytes produce two types of spores — megaspores (female) and microspores (male) — which develop into unisexual gametophytes. This is an important evolutionary step towards the seed habit. Example: Selaginella, Salvinia.

Exercises (NCERT Q1–Q11)

• 1) What is the basis of classification of algae?
• 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?
• 3) Name three groups of plants that bear archegonia. Briefly describe the life cycle of any one of them.
• 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.
• 5) Write a note on economic importance of algae and gymnosperms.
• 6) Both gymnosperms and angiosperms bear seeds, then why are they classified separately?
• 7) What is heterospory? Briefly comment on its significance. Give two examples.
• 8) Explain briefly the following terms with suitable examples:- (i) protonema (ii) antheridium (iii) archegonium (iv) diplontic (v) sporophyll (vi) isogamy
• 9) Differentiate between the following:- (i) red algae and brown algae (ii) liverworts and moss (iii) homosporous and heterosporous pteridophyte
• 10) Match the following (column I with column II) Column I Column II (a) Chlamydomonas (i) Moss (b) Cycas (ii) Pteridophyte (c) Selaginella (iii) Algae (d) Sphagnum (iv) Gymnosperm
• 11) Describe the important characteristics of gymnosperms.

Answers at a glance

1. 1
   Q1 → Algae are classified on the basis of the pigment possessed and the type of stored food, and on these two characters they are divided into three classes. Chlorophyceae, the green algae, are grass green because of chlorophyll a and b, store starch, have a cell wall of cellulose with an outer layer of pectose, and bear 2 to 8 equal flagella apically inserted. Phaeophyceae, the brown algae, have chlorophyll a and c with carotenoids and xanthophylls, their colour depending on the amount of the xanthophyll fucoxanthin, store laminarin and mannitol, have a cellulosic wall covered outside by a gelatinous coating of algin, and their motile zoospores and gametes carry two unequal laterally attached flagella. Rhodophyceae, the red algae, owe their colour to the predominance of r-phycoerythrin, store floridean starch which is very similar to amylopectin and glycogen in structure, have a wall of cellulose with pectin and poly sulphate esters, and have no flagella at all.
2. 2
   Q2 → Reduction division is meiosis and it always takes place in the spore mother cells of the sporophyte generation, the time and place differing between groups. In a liverwort it occurs in the capsule of the sporophyte, which is the small capsule borne on a seta, and produces haploid spores; the dominant plant is the gametophyte. In a moss it occurs in the capsule of the sporophyte, again with the gametophyte dominant. In a fern it occurs in the sporangia borne in sori on the underside of the fronds of the sporophyte, and both generations are independent. In a gymnosperm it occurs in the microsporangium or pollen sac and in the megasporangium or nucellus of the ovule, giving the four-celled pollen and the single megaspore. In an angiosperm it occurs in the microsporangium of the anther, giving the four-celled pollen grain, and in the megaspore mother cell of the nucellus, which gives one functional megaspore while the other three degenerate. So in every group the process is the same and occurs in the sporophyte, and only the organ concerned and its timing in the life cycle differ.
3. 3
   Q3 → The three groups bearing archegonia are the bryophytes, the pteridophytes and the gymnosperms, which together are the archegoniates or Embryophyta. Taking the fern, a pteridophyte, as the example: the familiar fern plant is the diploid sporophyte and is the dominant generation. Its sporangia are borne in sori on the undersides of the fronds, and within them the spore mother cells undergo meiosis, the reduction division, to produce haploid spores, which is the only reduction division in the fern life cycle. The spores germinate on moist soil into a small green, free-living, photosynthetic, heart-shaped prothallus, which is the haploid gametophyte and is independent of the sporophyte. The prothallus bears antheridia and archegonia on its ventral surface, and the antheridia produce biflagellate, motile antherozoids while the archegonia produce the egg. Because the antherozoids must swim through a film of water to reach the archegonium, fertilisation requires water and is oogamous, and the diploid zygote is retained in the archegonium. The zygote forms an embryo and then a sporophyte that is at first dependent on the prothallus for nourishment until it becomes independent, so the cycle is haplodiplontic with both generations free-living. The same pattern with variations runs through the other two groups, and the reduction of the gametophyte reaches its extreme in the gymnosperms, where neither the male nor the female gametophyte has an independent free-living existence and both remain within the sporangia on the sporophyte.
4. 4
   Q4 → The protonemal cell of a moss is haploid or n, since the protonema is the first phase of the gametophyte and arises from a haploid spore. The primary endosperm nucleus in a dicot is triploid or 3n, because the endosperm is formed by triple fusion of one male gamete with two polar nuclei, 1n plus 2n. The leaf cell of a moss is haploid or n, because the leafy plant is the gametophyte and the dependent capsule with seta is the sporophyte. The prothallus cell of a fern is haploid or n, since the prothallus is the fern gametophyte. The gemma cell in Marchantia is haploid or n, because Marchantia is a liverwort and its gemma cup thallus is the gametophyte. The meristem cell of a monocot is diploid or 2n, since meristem belongs to the sporophyte body. The ovum of a liverwort is haploid or n, being a gamete formed in the gametophyte. The zygote of a fern is diploid or 2n, being the product of fusion of two haploid gametes and the first diploid cell of the cycle.
5. 5
   Q5 → Algae are economically important in two main ways. As food, many species of Porphyra, Laminaria and Sargassum are among the 70 species of marine algae eaten, and Chlorella, a unicellular alga rich in proteins, is used as a food supplement even by space travellers. As industrial products, certain marine brown and red algae yield large amounts of hydrocolloids, that is water-holding substances, namely algin from the brown algae and carrageen from the red algae, which are used commercially, and agar, obtained from Gelidium and Gracilaria, is used to grow microbes and in the preparation of ice-creams and jellies. Gymnosperms are economically important for their timber, since the wood of Pinus, Cedrus and Deodar is used for construction, furniture and paper pulp, and as a source of fuel and industrial raw material, since Pinus yields turpentine oil and the resin used in making varnishes. Many gymnosperms are also grown as ornamentals, among them the cycads and conifers such as Araucaria.
6. 6
   Q6 → The two are classified separately because the seed is borne in a different position in each. In a gymnosperm the ovule and the seed are naked and exposed, borne directly on the megasporophyll and not enclosed in any fruit, which is what the name gymnosperm, naked seed, means; in an angiosperm the ovule is enclosed in an ovary that ripens into a fruit, so the seed is covered, which is what angiosperm means. The difference in the seed follows from this: a gymnosperm seed has no true endosperm, the nourishment being stored in the multicellular female gametophyte, and it has a variable number of cotyledons, from two in Pinus to many in Cycas, whereas an angiosperm seed has endosperm formed by triple fusion and a fixed number of cotyledons, two in a dicot and one in a monocot. A further difference is the degree of reduction of the gametophyte: in a gymnosperm the female gametophyte is retained within the ovule and is multicellular, while in an angiosperm it is reduced to the cells of the embryo sac. Finally the two represent successive stages, with gymnosperms the dominant vascular plants of the coal age and angiosperms the dominant ones today. So the common factor is the seed, but the position and enclosure of that seed is a fundamental difference and warrants separate classification.
7. 7
   Q7 → Heterospory is the condition in which a single sporophyte produces spores of two distinct kinds, small microspores in a small microsporangium and large megaspores in a large megasporangium, so that the plant is dimorphic in its spores; the opposite condition, of one kind of spore only, is isospory, and the general condition in most ferns. Its significance is threefold. First, heterospory is a precursor of the seed habit, because the megaspore and the female gametophyte arising from it anticipate the seed. Second, it is the forerunner of the embryo, since the megaspore and the female gametophyte are retained on the parent sporophyte within a protective jacket. Third, and most importantly, heterospory alone makes the sexual reproduction of seed plants possible, because only when the megaspore is retained on the parent sporophyte can the female gametophyte develop, be fertilised and be nourished on the parent before it is dispersed; in a homosporous plant all spores are alike and dispersed together, so the female gametophyte must grow outside the sporophyte. The two examples are Selaginella and Salvinia, and it should be added that all seed plants are also heterosporous, which is why the condition is regarded as such an important step in evolution.
8. 8
   Q8 → (i) Protonema is the early free-living, green, thread-like, haploid gametophytic stage of a moss, which develops on germination of a spore and later bears buds of leafy gametophores that grow into the plants, as in Funaria and Polytrichum. (ii) Antheridium is the male sex organ, a multicellular, jacketed, club-shaped structure that produces the male gametes, which are flagellated and motile antherozoids, as in the antheridium of Funaria. (iii) Archegonium is the female sex organ, a multicellular, jacketed, flask-shaped structure with a swollen venter that contains a single egg and a venter canal, and a neck that bears a canal of neck canal cells, and its presence makes a plant an archegoniate or Embryophyta, as in Marchantia and in ferns. (iv) Diplontic describes a life cycle in which the diploid sporophyte is the dominant independent generation, the haploid gametophyte is reduced and dependent, and the gamete is the only free haploid stage, as in all gymnosperms and angiosperms. (v) Sporophyll is a leaf-like structure of the sporophyte that bears sporangia, such as the sporophyll of a fern with its sori, the microsporophyll or stamen and the megasporophyll or carpel of a flower, and the cone scale of Cycas. (vi) Isogamy is sexual reproduction in which the male and female gametes are morphologically similar in size and shape and so are indistinguishable, and their fusion is called isogamy, as in the fusion of two alike flagellated gametes in Chlamydomonas and Volvox and of alike non-motile gametes in Spirogyra and Ulothrix.
9. 9
   Q9 → (i) Red algae differ from brown algae in pigment, red algae having chlorophyll a and d with r-phycoerythrin against brown algae with chlorophyll a and c plus fucoxanthin; in stored food, floridean starch against mannitol and laminarin; in flagella, the red algal cells being wholly non-flagellate against the two unequal laterally attached flagella, which are rare, borne by the motile zoospores and gametes of the brown algae; in cell wall, cellulose with pectin and poly sulphate esters against a cellulosic wall covered outside by a gelatinous coating of algin; in habitat, the red algae being mostly in deeper marine water against the brown algae in shallow and intertidal water, with the Fucus and Sargassum; and in reproduction, the red algae reproducing by non-motile spores and non-motile gametes, their sexual reproduction being oogamous, against the brown algae reproducing asexually by biflagellate zoospores and having sexual reproduction that may be isogamous, anisogamous or oogamous with motile gametes. (ii) Liverworts differ from mosses in body form, the liverwort being thalloid, dorsiventral and closely appressed to the substrate with tiny leaf-like appendages in two rows, against the moss with upright slender axes bearing spirally arranged leaves and attached by multicellular branched rhizoids; in the life cycle, the liverwort spore germinating straight into the free-living gametophyte, against the moss passing through a creeping, green, branched and frequently filamentous protonema stage before the leafy stage; in the sporophyte, which in both is differentiated into foot, seta and capsule but is more elaborate in the mosses, which also have an elaborate mechanism of spore dispersal; and in vegetative reproduction, the liverwort forming gemmae in gemma cups on the thallus while the moss reproduces by fragmentation and budding in the secondary protonema. (iii) A homosporous pteridophyte such as Pteris produces spores of one kind in one kind of sporangium, whereas a heterosporous pteridophyte such as Selaginella and Salvinia produces two kinds, small microspores in a microsporangium and large megaspores in a megasporangium. Heterospory is a precursor of the seed habit and is significant because only there is the megaspore retained on the parent sporophyte, which lets the female gametophyte be formed, fertilised and nourished on the parent before dispersal.
10. 10
    Q10 → (a) Chlamydomonas — (iii) Algae, because it is a unicellular flagellated green alga. (b) Cycas — (iv) Gymnosperm, because it is a cycad with naked ovules and seeds borne exposed on megasporophylls. (c) Selaginella — (ii) Pteridophyte, because it is a lycopsid with microphylls that produces both micro- and megaspores. (d) Sphagnum — (i) Moss, because it is the peat moss that accumulates as peat in bogs.
11. 11
    Q11 → The gymnosperms, from gymnos meaning naked and sperma meaning seed, are plants in which the ovules are not enclosed by any ovary wall and remain exposed both before and after fertilisation, so the seeds are naked. They are medium-sized trees, tall trees or shrubs, and the giant redwood Sequoia is one of the tallest tree species. The plant body is the sporophyte, differentiated into root, stem and leaves. The roots are generally tap roots, with a mycorrhizal fungal association in Pinus and coralloid roots associated with nitrogen-fixing cyanobacteria in Cycas. The stem is unbranched in Cycas and branched in Pinus and Cedrus, and the leaves may be simple or compound, the pinnate leaves of Cycas persisting for a few years, while in conifers the needle-like leaves reduce the surface area and a thick cuticle with sunken stomata further reduces water loss. The plants are heterosporous, producing haploid microspores and megaspores within sporangia borne on sporophylls that are arranged spirally along an axis to form lax or compact strobili or cones, the microsporophyll bearing the microsporangia in the male strobili and the megasporophyll bearing the ovules or megasporangia in the female strobili. The microspores develop into the highly reduced male gametophyte confined to a limited number of cells, which is the pollen grain, and the pollen is released from the microsporangium, carried in air currents and brought to the opening of the ovules, so pollination is by wind. The megaspore mother cell in the nucellus divides meiotically to form four megaspores, one of which develops into the multicellular female gametophyte retained within the megasporangium and bearing two or more archegonia, into which the pollen tube discharges the male gametes. Unlike the bryophytes and pteridophytes, neither gametophyte has an independent free-living existence, both remaining within the sporangia on the sporophyte. Following fertilisation the zygote develops into an embryo and the ovule into a seed, and since there is no ovary there is no true fruit, which is the character that separates the group from the angiosperms. The male and female cones may be on the same tree, as in Pinus, or on different trees, as in Cycas, and the life cycle is sporophytic with the sporophyte dominant.

MCQ Questions

1 Mark Questions

1. 1
   Define the haplontic life cycle. (Ans: a life cycle in which the dominant phase is haploid and only the zygote is diploid)
2. 2
   Name one example each of a green alga and a red alga. (Ans: Chlamydomonas/Ulva; Porphyra/Gracilaria)
3. 3
   Give one economic importance of algae. (Ans: food, agar, algin, biofertilizer, oxygen release)
4. 4
   Write the name of the male gamete of a flowering plant. (Ans: pollen grain / male gamete formed in the pollen grain)

2 Mark Questions

1. 1
   Differentiate between algae and bryophytes on any two points.
2. 2
   Mention the two types of spores and the two sporophytic stages in the life cycle of a moss. (Ans: haploid spores; protonema stage and leafy stage)
3. 3
   Why do pteridophytes and gymnosperms need water for fertilisation? (Ans: motile male gametes (antherozoids) swim in water for fertilisation)

3 Mark Questions

1. 1
   Give the salient features of brown algae (Phaeophyceae). (Ans: marine, fucoxanthin, chlorophyll a+c, cellulose+algin cell wall, food laminarin; e.g. Fucus, Laminaria)
2. 2
   Describe the alternation of generations found in bryophytes. (Ans: free-living gametophyte and dependent sporophyte, with haploid gametes and spores shown in a labelled sequence)
3. 3
   Differentiate between gymnosperms and angiosperms on any three points. (Ans: naked vs enclosed ovules/seeds; no vs presence of fruit; vascular tissue mostly tracheids vs vessels, double fertilisation absent/present)

5 Mark Questions

1. 1
   Describe the different life cycle patterns observed in plants giving one example of each. (Ans: haplontic − majority algae; diplontic − most animals, seed plants (sporophytic dominant); haplo-diplontic − bryophytes and pteridophytes with alternating phases)
2. 2
   Write a comparative account of the three classes of algae — Chlorophyceae, Phaeophyceae and Rhodophyceae — covering habitat, pigments, stored food and cell wall. (Ans: green-unicellular; brown-multicellular marine with laminarin; red-marine include agar/polygalactose; wall cellulose + algin/pectin)