Plant Kingdom
Welcome to HSLC Guru! In this chapter, students of ASSEB Class 11 Biology will study the Plant Kingdom, which deals with the classification, structure, reproduction, and life cycles of plants. The chapter explores major plant groups including algae, bryophytes, pteridophytes, gymnosperms, and angiosperms, along with their alternation of generations. This complete English-medium guide includes a clear summary, exam-oriented question answers, MCQs, fill in the blanks, true or false, and a glossary table to help you score well in your ASSEB Class 11 Biology examination.
Chapter Summary
The Plant Kingdom (Plantae) consists of eukaryotic, multicellular, autotrophic organisms that contain chlorophyll and have cell walls made of cellulose. Whittaker’s five-kingdom classification placed all plants under Kingdom Plantae. Modern classification of plants is based on morphology, anatomy, mode of nutrition, habitat, reproduction, and evolutionary relationships. The kingdom is divided into major groups: Algae, Bryophytes, Pteridophytes, Gymnosperms, and Angiosperms. Each group shows progressive evolutionary advancement from simple thallophytes to highly organised flowering plants.
Algae are simple, chlorophyll-bearing, thalloid, and largely aquatic plants. They are classified into three classes. Chlorophyceae (green algae) such as Chlamydomonas, Volvox, Spirogyra, and Ulothrix possess chlorophyll a and b and store food as starch. Phaeophyceae (brown algae) like Laminaria, Fucus, and Sargassum contain chlorophyll a, c, and fucoxanthin and store food as laminarin or mannitol. Rhodophyceae (red algae) such as Polysiphonia, Porphyra, and Gracilaria contain chlorophyll a, d, and phycoerythrin and store food as floridean starch. Algae reproduce by vegetative means (fragmentation), asexual means (zoospores, aplanospores), and sexual reproduction which may be isogamous, anisogamous, or oogamous.
Bryophytes are amphibians of the plant kingdom, requiring water for sexual reproduction. They are divided into liverworts (Marchantia, Riccia) with thalloid or leafy gametophytes, and mosses (Funaria, Sphagnum, Polytrichum) with erect leafy axes. Pteridophytes are the first true vascular plants and include Psilopsida (Psilotum), Lycopsida (Lycopodium, Selaginella), Sphenopsida (Equisetum), and Pteropsida (Dryopteris, Pteris, Adiantum). They reproduce through spores produced in sporangia. Gymnosperms are seed-bearing plants with naked ovules and include Cycadales (Cycas), Ginkgoales (Ginkgo), Coniferales (Pinus, Cedrus), and Gnetales (Ephedra, Gnetum). Angiosperms (flowering plants) are the most advanced group with seeds enclosed in fruits and are divided into Monocotyledons (one cotyledon, parallel venation, fibrous roots) and Dicotyledons (two cotyledons, reticulate venation, tap roots).
Alternation of generations is a fundamental feature of plant life cycles where a haploid gametophyte alternates with a diploid sporophyte. In the haplontic life cycle (most algae like Spirogyra, Volvox), the gametophyte is dominant and the sporophyte is represented only by a zygote. In the diplontic life cycle (seed plants and Fucus), the sporophyte is dominant and the gametophyte is reduced. In the haplo-diplontic life cycle, both phases are multicellular: in bryophytes the gametophyte is dominant, while in pteridophytes the sporophyte is dominant. This evolutionary trend shows progressive dominance of the sporophyte from algae to angiosperms.
1 Mark Question Answers
Q1. What is the main pigment found in green algae?
Answer: Chlorophyll a and chlorophyll b are the main pigments found in green algae (Chlorophyceae).
Q2. Why are bryophytes called amphibians of the plant kingdom?
Answer: Bryophytes are called amphibians of the plant kingdom because they live in soil but require water for sexual reproduction.
Q3. Name the reserve food material in red algae.
Answer: The reserve food material in red algae (Rhodophyceae) is floridean starch.
Q4. What is a prothallus?
Answer: A prothallus is the small, multicellular, free-living, photosynthetic, haploid gametophyte of pteridophytes.
Q5. Give one example each of monocot and dicot plants.
Answer: Monocot example: Wheat (Triticum). Dicot example: Pea (Pisum sativum).
Q6. What are gymnosperms?
Answer: Gymnosperms are seed-bearing vascular plants in which the ovules and seeds are naked, that is, not enclosed within an ovary.
Q7. Name the pigment that gives brown algae their characteristic colour.
Answer: The pigment fucoxanthin gives brown algae (Phaeophyceae) their characteristic brown colour.
Q8. What is alternation of generations?
Answer: Alternation of generations is the phenomenon in which a haploid gametophyte phase alternates with a diploid sporophyte phase in the life cycle of plants.
Q9. Name one liverwort and one moss.
Answer: Liverwort: Marchantia. Moss: Funaria.
Q10. What is heterospory?
Answer: Heterospory is the production of two types of spores, microspores and megaspores, by the same plant, as seen in Selaginella and Salvinia.
2-3 Marks Question Answers
Q1. Differentiate between Chlorophyceae and Phaeophyceae.
Answer: Chlorophyceae (green algae) contain chlorophyll a and b, store food as starch, have cellulose cell walls, and are mostly freshwater. Examples include Chlamydomonas, Spirogyra, and Volvox. Phaeophyceae (brown algae) contain chlorophyll a, c, and fucoxanthin, store food as mannitol or laminarin, have cellulose and algin cell walls, and are mostly marine. Examples include Laminaria, Fucus, and Sargassum.
Q2. Write a short note on the economic importance of algae.
Answer: Algae are economically important in several ways. Many species like Porphyra, Laminaria, and Sargassum are used as food. Agar from Gracilaria and Gelidium is used in microbial culture and food industry. Algin from brown algae and carrageenan from red algae are used commercially. Chlorella is used as a protein-rich food supplement and was used by space travellers. Algae also play a key role in carbon dioxide fixation in oceans.
Q3. Distinguish between liverworts and mosses.
Answer: Liverworts have a thalloid or leafy gametophyte that lies flat on the substratum, with rhizoids that are unicellular. The sporophyte is small and dependent on the gametophyte. Examples include Marchantia and Riccia. Mosses have an erect leafy gametophyte (gametophore) with multicellular rhizoids. The sporophyte is more elaborate, with a foot, seta, and capsule. Examples include Funaria, Sphagnum, and Polytrichum.
Q4. What are the four classes of pteridophytes? Give one example of each.
Answer: The four classes of pteridophytes are: (i) Psilopsida — example Psilotum, (ii) Lycopsida — example Lycopodium or Selaginella, (iii) Sphenopsida — example Equisetum, and (iv) Pteropsida — example Dryopteris, Pteris, or Adiantum. These groups show progressive development of vascular tissues and leaves.
Q5. Differentiate between monocotyledons and dicotyledons.
Answer: Monocots have one cotyledon in the seed, parallel venation in leaves, fibrous root systems, and floral parts in multiples of three. Examples are wheat, rice, and maize. Dicots have two cotyledons, reticulate venation, tap root systems, and floral parts in multiples of four or five. Examples include pea, mango, and sunflower.
Q6. Briefly describe the four orders of gymnosperms with one example each.
Answer: Cycadales — palm-like plants with pinnate leaves, example Cycas. Ginkgoales — represented by a single living species, example Ginkgo biloba. Coniferales — woody trees with needle-like leaves bearing cones, example Pinus and Cedrus. Gnetales — advanced gymnosperms with vessel elements, example Ephedra and Gnetum.
5-7 Marks Question Answers
Q1. Describe the salient features and classification of algae with examples.
Answer: Algae are chlorophyll-bearing, simple, thalloid, autotrophic, and largely aquatic organisms. They lack true roots, stems, and leaves and reproduce by vegetative, asexual, and sexual methods.
Algae are classified into three main classes:
(i) Chlorophyceae (Green algae): Contain chlorophyll a and b, give a grass-green colour. Cell walls are made of cellulose with an inner layer and pectose outer layer. Reserve food is starch. Reproduction is vegetative (fragmentation), asexual (zoospores), and sexual (isogamous, anisogamous, or oogamous). Examples: Chlamydomonas, Volvox, Spirogyra, Ulothrix, and Chara.
(ii) Phaeophyceae (Brown algae): Contain chlorophyll a, c, fucoxanthin, and other carotenoids. They are mostly marine. Cell walls have cellulose and algin. Reserve food is laminarin or mannitol. Plant body is differentiated into holdfast, stipe, and frond. Examples: Laminaria, Fucus, Sargassum, Ectocarpus, and Dictyota.
(iii) Rhodophyceae (Red algae): Contain chlorophyll a, d, and phycoerythrin which gives red colour. They are mostly marine and grow in deeper waters. Reserve food is floridean starch. Sexual reproduction is oogamous, with non-flagellated gametes. Examples: Polysiphonia, Porphyra, Gracilaria, and Gelidium.
Q2. Describe the life cycle and structure of a typical bryophyte (Funaria/Marchantia).
Answer: Bryophytes are non-vascular embryophytes that grow in moist, shaded habitats. The plant body is the haploid gametophyte. In liverworts like Marchantia, the gametophyte is dorsiventral and thalloid, while in mosses like Funaria, it consists of erect leafy axes attached by multicellular rhizoids.
Sex organs are antheridia (male) producing biflagellate antherozoids, and archegonia (female) producing a single egg. After fertilisation in the presence of water, the zygote develops into the diploid sporophyte. The sporophyte (foot, seta, and capsule) is partially or fully dependent on the gametophyte for nutrition.
Inside the capsule, meiosis produces haploid spores, which germinate to form a juvenile gametophyte (protonema in mosses) that develops into a mature gametophyte. Bryophytes thus exhibit a haplo-diplontic life cycle with a dominant gametophyte. They play important roles in soil formation, prevention of erosion, and as bio-indicators.
Q3. Explain alternation of generations with reference to haplontic, diplontic, and haplo-diplontic life cycles.
Answer: Alternation of generations refers to the alternation between a haploid gametophytic phase (n) and a diploid sporophytic phase (2n) in the life cycle of plants. The gametophyte produces gametes by mitosis, while the sporophyte produces spores by meiosis.
Haplontic life cycle: The gametophyte is dominant, free-living, multicellular, and photosynthetic. The sporophyte is represented only by the diploid zygote, which undergoes meiosis to produce haploid spores. This pattern is seen in many algae such as Spirogyra, Volvox, and Chlamydomonas.
Diplontic life cycle: The sporophyte is dominant, photosynthetic, and multicellular. The gametophyte is reduced to a few cells. This pattern is seen in Fucus (a brown alga) and all seed plants (gymnosperms and angiosperms).
Haplo-diplontic life cycle: Both gametophyte and sporophyte are multicellular and often photosynthetic. In bryophytes, the gametophyte is dominant; in pteridophytes, the sporophyte is dominant while the gametophyte (prothallus) is small and short-lived. Some algae like Ectocarpus also show this pattern.
Q4. Describe the salient features of gymnosperms and their classification with examples.
Answer: Gymnosperms are seed-bearing vascular plants in which the seeds are naked (not enclosed in an ovary). They are mainly trees or shrubs with well-developed tap roots, often associated with mycorrhizae or nitrogen-fixing organisms. Leaves may be simple or compound; in conifers, needle-like leaves help reduce water loss. Vascular tissue lacks vessels in xylem (except Gnetales) and companion cells in phloem.
Gymnosperms are heterosporous, producing microspores and megaspores in male and female cones (strobili). Pollination is mostly by wind. Fertilisation is siphonogamous (through a pollen tube) and water is not required.
Classification:
(i) Cycadales: Palm-like plants with unbranched stems and pinnate leaves. Motile sperms. Example: Cycas. (ii) Ginkgoales: Living fossils with fan-shaped leaves. Example: Ginkgo biloba. (iii) Coniferales: Tall evergreen trees with needle-like leaves and woody cones. Example: Pinus, Cedrus, Picea. (iv) Gnetales: Most advanced gymnosperms with vessels in xylem and resemble angiosperms. Example: Ephedra, Gnetum, Welwitschia.
Q5. Describe the salient features of angiosperms and differentiate between monocots and dicots.
Answer: Angiosperms are flowering plants in which seeds are enclosed within fruits formed from the ovary. They are the most evolved and diverse group of plants, ranging from tiny Wolffia to giant Eucalyptus. They have well-developed roots, stems, leaves, flowers, and fruits. The vascular system is highly advanced with vessels in xylem and companion cells in phloem.
The reproductive process involves double fertilisation, a unique feature of angiosperms. One male gamete fuses with the egg to form the zygote (2n), and the other male gamete fuses with two polar nuclei to form the primary endosperm nucleus (3n). After fertilisation, the ovary develops into the fruit and the ovule into the seed.
Angiosperms are divided into two classes:
Monocotyledons: One cotyledon, parallel venation, fibrous roots, scattered vascular bundles in stem, trimerous flowers (parts in threes). Examples: rice, wheat, maize, lily.
Dicotyledons: Two cotyledons, reticulate venation, tap roots, vascular bundles arranged in a ring, tetramerous or pentamerous flowers (parts in fours or fives). Examples: pea, mango, sunflower, hibiscus.
Multiple Choice Questions (MCQs)
Q1. The reserve food material in Rhodophyceae is:
(a) Starch (b) Floridean starch (c) Mannitol (d) Laminarin
Answer: (b) Floridean starch
Q2. Bryophytes are called amphibians because:
(a) They live in water (b) They need water for fertilisation (c) They are land plants (d) They lack vascular tissue
Answer: (b) They need water for fertilisation
Q3. Which of the following is a pteridophyte?
(a) Marchantia (b) Funaria (c) Selaginella (d) Cycas
Answer: (c) Selaginella
Q4. Naked seeds are characteristic of:
(a) Algae (b) Bryophytes (c) Gymnosperms (d) Angiosperms
Answer: (c) Gymnosperms
Q5. Double fertilisation is found in:
(a) Algae (b) Bryophytes (c) Gymnosperms (d) Angiosperms
Answer: (d) Angiosperms
Q6. Which of the following is a brown alga?
(a) Spirogyra (b) Polysiphonia (c) Sargassum (d) Chlamydomonas
Answer: (c) Sargassum
Q7. Equisetum belongs to which class of pteridophytes?
(a) Psilopsida (b) Lycopsida (c) Sphenopsida (d) Pteropsida
Answer: (c) Sphenopsida
Q8. Ginkgo biloba is an example of:
(a) Cycadales (b) Ginkgoales (c) Coniferales (d) Gnetales
Answer: (b) Ginkgoales
Q9. Haplontic life cycle is found in:
(a) Spirogyra (b) Funaria (c) Pinus (d) Mango
Answer: (a) Spirogyra
Q10. Parallel venation is characteristic of:
(a) Dicots (b) Monocots (c) Gymnosperms (d) Pteridophytes
Answer: (b) Monocots
Fill in the Blanks
Q1. The pigment _________ gives brown algae their characteristic colour.
Answer: Fucoxanthin
Q2. The gametophyte of pteridophytes is called _________.
Answer: Prothallus
Q3. _________ is a living fossil among gymnosperms.
Answer: Ginkgo biloba
Q4. In angiosperms, the endosperm is _________ ploid.
Answer: Triploid (3n)
Q5. The reserve food material of Chlorophyceae is _________.
Answer: Starch
True or False
Q1. Bryophytes have well-developed vascular tissue.
Answer: False
Q2. Pteridophytes are the first true vascular plants.
Answer: True
Q3. In gymnosperms, ovules are enclosed within an ovary.
Answer: False
Q4. Double fertilisation is unique to angiosperms.
Answer: True
Q5. Spirogyra exhibits a diplontic life cycle.
Answer: False (it is haplontic)
Glossary
| Term | Meaning |
|---|---|
| Thallus | An undifferentiated plant body without true roots, stems, or leaves. |
| Gametophyte | The haploid (n), gamete-producing phase in the life cycle of plants. |
| Sporophyte | The diploid (2n), spore-producing phase in the life cycle of plants. |
| Isogamy | Fusion of two morphologically similar gametes. |
| Anisogamy | Fusion of two morphologically different gametes (size). |
| Oogamy | Fusion of a small motile male gamete with a large non-motile female gamete. |
| Heterospory | Production of two types of spores: microspores and megaspores. |
| Prothallus | The free-living haploid gametophyte of pteridophytes. |
| Antheridium | The male sex organ producing male gametes in lower plants. |
| Archegonium | The flask-shaped female sex organ producing the egg in lower plants. |
| Strobilus | A cone-like reproductive structure bearing sporophylls. |
| Double fertilisation | Fusion of two male gametes — one with egg, one with polar nuclei — unique to angiosperms. |
| Endosperm | Triploid (3n) nutritive tissue in angiosperm seeds. |
| Cotyledon | The seed leaf present in the embryo of a seed. |
| Haplontic life cycle | Life cycle with dominant haploid gametophyte; sporophyte is just zygote. |
| Diplontic life cycle | Life cycle with dominant diploid sporophyte; gametophyte is reduced. |
| Haplo-diplontic | Life cycle with both gametophyte and sporophyte multicellular. |
| Mycorrhiza | Symbiotic association of fungi with plant roots, common in gymnosperms. |
| Siphonogamy | Transfer of male gametes through a pollen tube without water. |
| Phycoerythrin | Red pigment found in red algae (Rhodophyceae). |