Plant Kingdom ISC Class 11: Algae, Bryophytes, Pteridophytes and Gymnosperms

What Plant Kingdom is about

Weightage: Plant Kingdom belongs to the unit Diversity of Living Organisms, which CISCE weights at 9 of the 70 marks in the ISC Class XI Biology Paper I (Theory). Class XI is examined by the school, so your school sets the paper within this weightage.Source: CISCE ISC Biology syllabus, examination year 2028, Class XI unit weightage

Key concepts

Algae: general features and three classes

Algae are chlorophyll-bearing, simple, thalloid, autotrophic, mostly aquatic organisms. Chlorophyceae (green algae): pigments chlorophyll a and b; food stored as starch (in pyrenoids); cell wall of cellulose; 2–8 equal, apical flagella; mostly freshwater; isogamous, anisogamous or oogamous (e.g. *Chlamydomonas*, *Volvox*, *Ulothrix*, *Spirogyra*, *Chara*). Phaeophyceae (brown algae): chlorophyll a, c and fucoxanthin; food as laminarin and mannitol; wall of cellulose with algin; two unequal, laterally attached flagella; mostly marine; thallus often has holdfast, stipe and frond (e.g. *Ectocarpus*, *Dictyota*, *Laminaria*, *Sargassum*, *Fucus*). Rhodophyceae (red algae): chlorophyll a, d and phycoerythrin; food as floridean starch; wall of cellulose, pectin and polysulphate esters; no flagella; mostly marine, many in deep water; oogamous (e.g. *Polysiphonia*, *Porphyra*, *Gracilaria*, *Gelidium*).

Worked example

Why can red algae live deeper in the sea than green algae?

Try it first, then show the solutionSolution

1. Blue-green light penetrates deepest into sea water
2. Phycoerythrin absorbs this light and passes the energy to chlorophyll

Answer: Phycoerythrin lets red algae use the light that reaches great depths

Economic importance of algae

(1) Oxygen and food chains: algae carry out a large share of the photosynthesis on Earth and are primary producers in water. (2) Food: many marine algae are eaten, e.g. *Porphyra*, *Laminaria* and *Sargassum*. (3) Agar, from red algae such as *Gelidium* and *Gracilaria*, is used to grow microbes and in jellies and ice creams. (4) Algin (brown algae) and carrageen (red algae) are used as thickeners in food and industry. (5) Single-cell protein: unicellular algae such as *Chlorella* are rich in protein and have been tried as food supplements, even for astronauts.

Worked example

Name the source of agar and two uses of it.

Try it first, then show the solutionSolution

1. Agar comes from red algae such as *Gelidium* and *Gracilaria*
2. Uses: solidifying culture media for microbes; making jellies and ice creams

Answer: Red algae; culture media and food

Bryophytes: general characteristics; liverworts and mosses

Bryophytes are small land plants of damp, shady places, called the amphibians of the plant kingdom. The plant body is a thallus or has stem-like and leaf-like parts with rhizoids, but no true roots, stems, leaves or vascular tissue. The main plant is the haploid gametophyte; it bears antheridia (producing biflagellate antherozoids) and archegonia (flask-shaped, each with one egg). Water is needed for antherozoids to reach the egg. The zygote grows into a sporophyte (foot, seta, capsule) that stays attached to and depends on the gametophyte; meiosis in the capsule produces haploid spores. Liverworts (e.g. *Marchantia*, *Riccia*) are mostly thalloid, dorsiventral and may reproduce asexually by gemmae in gemma cups. Mosses (e.g. *Funaria*, *Polytrichum*, *Sphagnum*) have a protonema stage and an upright leafy stage with multicellular, branched rhizoids.

Worked example

Why are bryophytes called the amphibians of the plant kingdom?

Try it first, then show the solutionSolution

1. They live on land (soil, rocks, bark)
2. But they need water for the antherozoids to swim to the archegonium for fertilisation

Answer: Land plants that depend on water for sexual reproduction

Life cycle of Funaria (graphic outline) and alternation of generations

Haploid spore (n) germinates into a green, branched, filamentous protonema (n) → buds on the protonema grow into leafy gametophytes (n) → apex bears antheridia and archegonia → antherozoids (n) swim in water to the egg (n) → fertilisation → zygote (2n) → sporophyte (2n) with foot, seta and capsule, growing on the gametophyte → meiosis in spore mother cells of the capsule → haploid spores, dispersed when the capsule opens (peristome teeth). The regular change from the haploid, gamete-producing generation to the diploid, spore-producing generation is alternation of generations; in bryophytes the gametophyte is dominant. Economic importance: *Sphagnum* forms peat, used as fuel and, because it holds water, as packing material and in gardening; mosses with lichens are pioneers on bare rock and their mats prevent soil erosion.

Worked example

Suppose a moss has 2n = 20. How many chromosomes are in (i) a protonema cell (ii) a cell of the capsule wall (iii) a spore?

Try it first, then show the solutionSolution

1. (i) Protonema is gametophytic: n = 10
2. (ii) Capsule is part of the sporophyte: 2n = 20
3. (iii) Spores are produced by meiosis: n = 10

Answer: 10; 20; 10

Pteridophytes: characteristics and four classes

Pteridophytes are the first terrestrial plants with vascular tissue (xylem and phloem), found in cool, damp, shady places. The main plant body is the diploid sporophyte, with true roots, stem and leaves (small microphylls in Selaginella; large macrophylls in ferns). Sporangia are borne on leaf-like sporophylls, sometimes grouped into strobili (cones). Meiosis in sporangia gives spores, which grow into a small, independent, multicellular, photosynthetic gametophyte (prothallus) needing damp conditions; water is still needed for fertilisation. Classes: Psilopsida (*Psilotum*), Lycopsida (*Selaginella*, *Lycopodium*), Sphenopsida (*Equisetum*, horsetail) and Pteropsida (*Dryopteris*, *Pteris*, *Adiantum*: ferns).

Worked example

Place *Equisetum*, *Selaginella*, *Adiantum* and *Psilotum* in their classes.

Try it first, then show the solutionSolution

1. *Equisetum*: Sphenopsida; *Selaginella*: Lycopsida
2. *Adiantum*: Pteropsida; *Psilotum*: Psilopsida

Answer: Sphenopsida; Lycopsida; Pteropsida; Psilopsida

Fern life cycle, homospory and heterospory

Fern life cycle (outline): the sporophyte (2n) bears sori of sporangia on the underside of leaves → meiosis → haploid spores → each spore germinates into a heart-shaped prothallus (n) → prothallus bears antheridia and archegonia → antherozoids swim to the egg in a film of water → zygote (2n) → young sporophyte grows out of the prothallus, which then dies. Homospory: all spores alike (most ferns, *Lycopodium*, *Equisetum*). Heterospory: two kinds of spores, small microspores (forming male gametophytes) and large megaspores (forming female gametophytes), as in *Selaginella* and *Salvinia*. The female gametophyte developing while the megaspore is retained in the parent sporophyte is a precursor to the seed habit. Economic importance: ornamental ferns; soil binding; *Azolla* (water fern) as a nitrogen-rich green manure in rice fields; some used medicinally.

Worked example

Classify *Lycopodium*, *Selaginella*, *Dryopteris* and *Salvinia* as homosporous or heterosporous, and say what the gametophytes of a heterosporous plant are like.

Try it first, then show the solutionSolution

1. Homosporous (one kind of spore): *Lycopodium*, *Dryopteris*
2. Heterosporous (microspores and megaspores): *Selaginella*, *Salvinia*
3. In heterosporous plants the gametophytes are unisexual: microspores give male and megaspores give female gametophytes

Answer: Homosporous: Lycopodium, Dryopteris; heterosporous: Selaginella, Salvinia, with separate male and female gametophytes

Gymnosperms and the life cycle of Pinus

Gymnosperms have naked ovules (not enclosed in an ovary), so their seeds are exposed. The sporophyte is a tall tree or shrub with a tap root (coralloid roots with nitrogen-fixing cyanobacteria in *Cycas*; mycorrhizal roots in *Pinus*), and needle-like leaves with thick cuticle and sunken stomata to reduce water loss. They are heterosporous: male cones (microsporangiate strobili) produce pollen grains (male gametophytes); female cones (megasporangiate strobili) bear ovules. Pinus life cycle (outline): sporophyte (2n) → male and female cones → meiosis → microspores and megaspores (n) → pollen grains (winged, wind-dispersed) and, in the ovule, a female gametophyte with archegonia → pollination → pollen tube carries male gametes to the archegonium (no water needed) → fertilisation → zygote (2n) → embryo inside a seed, surrounded by haploid endosperm (female gametophyte tissue). Economic importance: timber and paper pulp (pines, firs), resin and turpentine (*Pinus*), edible seeds (chilgoza, *Pinus gerardiana*), ornamental plants (*Cycas*, *Thuja*), and the drug ephedrine (*Ephedra*).

Worked example

Give three adaptations of *Pinus* leaves to dry or cold conditions.

Try it first, then show the solutionSolution

1. Needle shape: small surface area
2. Thick cuticle
3. Sunken stomata reduce water loss

Answer: Needles, thick cuticle, sunken stomata

Plant Kingdom in real life

Each concept, met in an everyday situation. Read the situation, answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Topics in this chapter

• Algae, Bryophytes and Alternation of Generations
• Pteridophytes and Gymnosperms

Plant Kingdom: key facts

Alternation of generations

$\text{sporophyte }(2n)\stackrel{\text{meiosis}}{\to }\text{spores }(n)\to \text{gametophyte }(n)\to \text{gametes }(n)\to \text{zygote }(2n)$

Gametophyte dominant in bryophytes; sporophyte dominant in pteridophytes and gymnosperms.

Pigments of algae

$\text{green: chl }a,b;\text{brown: chl }a,c,\text{fucoxanthin};\text{red: chl }a,d,\text{phycoerythrin}$

Stored food: starch, laminarin/mannitol, floridean starch.

Funaria outline

$\text{spore}\to \text{protonema}\to \text{leafy gametophyte}\to \text{zygote}\to \text{capsule}\to \text{spores}$

Sporophyte depends on the gametophyte.

Heterospory

$\text{microspore}\to \text{male gametophyte};\text{megaspore}\to \text{female gametophyte}$

Selaginella, Salvinia; precursor of seeds.

Plant Kingdom: diagrams to practise

Practise each one on paper: draw it from the checklist, then tick off every label.

How the school exam asks Plant Kingdom

The question patterns to expect, and the method that works for each.

Tricks to remember Plant Kingdom

Short memory aids. Say each one aloud once, then use it on a question the same day.

• Green ab, Brown ac-fuco, Red ad-phyco

  Chlorophylls: green a+b, brown a+c (+fucoxanthin), red a+d (+phycoerythrin).

  Use it when: Algal pigments.

• Red has no ride

  Red algae have no flagella.

  Use it when: Flagella in algae.

• Bryo: G big; Pterido and Gymno: S big

  Gametophyte dominant in bryophytes; sporophyte dominant later.

  Use it when: Alternation of generations.

• Please Let Sam Pass

  Psilopsida, Lycopsida, Sphenopsida, Pteropsida.

  Use it when: Classes of pteridophytes.

• Naked seed, haploid food

  Gymnosperm seeds are naked and their endosperm is n.

  Use it when: Gymnosperm features.

Plant Kingdom: exam-level solved questions

Ordered from exam level to HOTS. Cover the solution, write your own, then compare step by step.

Case-study practice (Section D style)

Read the situation, then answer every part. In a school exam set on the board pattern this is a 5-mark question split into 1 + 1 + 1 + 2 marks.

Where the marks are

How a typical answer is split into step marks. Show every step: a right final answer alone rarely earns full marks.

Where students lose marks in Plant Kingdom

The slips examiners see most often, and what to write instead.

• ✗Mistake: Mixing up algal pigments

  The three classes have similar-looking lists.

  Wrong working

  Red algae: chlorophyll a and c.

  Right working

  Red: chlorophyll a and d with phycoerythrin; brown: a and c with fucoxanthin.

  ✓Do this: Use the 'ab, ac, ad' pattern.

  Usually costs: 1 mark.

• ✗Mistake: Calling the moss plant a sporophyte

  The leafy plant is large and conspicuous.

  Wrong working

  The leafy moss plant is diploid.

  Right working

  It is the haploid gametophyte; the capsule is the sporophyte.

  ✓Do this: In bryophytes the gametophyte is dominant.

  Usually costs: 1 mark.

• ✗Mistake: Writing angiosperm endosperm for Pinus

  Students apply 3n endosperm everywhere.

  Wrong working

  Endosperm of Pinus is triploid.

  Right working

  It is haploid (female gametophyte tissue).

  ✓Do this: No double fertilisation in gymnosperms.

  Usually costs: 1 mark.

• ✗Mistake: Life cycles without ploidy

  Students draw arrows but omit n and 2n.

  Wrong working

  Spore → prothallus → zygote → fern.

  Right working

  Mark each stage n or 2n, and mark meiosis and fertilisation.

  ✓Do this: The syllabus asks for alternation of generations; show it.

  Usually costs: 1-2 marks.

• ✗Mistake: Wrong class for Selaginella

  All pteridophytes are thought of as ferns.

  Wrong working

  *Selaginella* is a fern (Pteropsida).

  Right working

  *Selaginella* is in Lycopsida.

  ✓Do this: Learn one example per class.

  Usually costs: 1 mark.

Practice questions on Plant Kingdom

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

1. Q1 · 1 mark · MCQExam level

   Phycoerythrin is found in:
   (a) green algae
   (b) brown algae
   (c) red algae
   (d) mosses

   Hint

   Red pigment.

   Answer

   (c)

2. Q2 · 1 mark · MCQExam level

   The dominant phase in the life cycle of a fern is:
   (a) gametophyte
   (b) sporophyte
   (c) protonema
   (d) prothallus

   Hint

   The fern plant itself.

   Answer

   (b)

3. Q3 · 1 mark · Very short answerExam level

   Name a heterosporous pteridophyte.

   Hint

   Lycopsida.

   Answer

   *Selaginella* (or *Salvinia*)

4. Q4 · 1 mark · Very short answerExam level

   What is the ploidy of the endosperm in *Pinus*?

   Hint

   Female gametophyte.

   Answer

   Haploid (n)

5. Q5 · 2 marks · Short answerExam level

   What are pyrenoids? In which class of algae are they characteristic, and what do they store?

   Hint

   Inside the chloroplast.

   Answer

   Pyrenoids are small food-storing bodies inside the chloroplasts of green algae (Chlorophyceae); each has a protein core with starch stored around it.

6. Q6 · 2 marks · Short answerHarder exam level

   What is a protonema? In which group is it found?

   Hint

   First stage after spore.

   Answer

   A green, branched, filamentous juvenile gametophyte that develops from a spore and bears buds that become leafy shoots; found in mosses.

7. Q7 · 2 marks · Short answerHarder exam level

   Give two economic uses of bryophytes.

   Hint

   Sphagnum.

   Answer

   *Sphagnum* peat as fuel and as packing/gardening material (holds water); mosses prevent soil erosion and colonise bare rock.

8. Q8 · 3 marks · Short answerHarder exam level

   Distinguish between homospory and heterospory with examples.

   Hint

   One or two kinds of spores.

   Answer

   Homospory: one kind of spore (*Dryopteris*, *Lycopodium*). Heterospory: small microspores giving male gametophytes and large megaspores giving female gametophytes (*Selaginella*, *Salvinia*).

9. Q9 · 3 marks · Short answerHarder exam level

   Give three differences between bryophytes and pteridophytes.

   Hint

   Dominant phase, vascular tissue, organs.

   Answer

   Bryophytes: gametophyte dominant, no vascular tissue, no true roots/stems/leaves. Pteridophytes: sporophyte dominant, xylem and phloem present, true roots, stem and leaves.

10. Q10 · 3 marks · Short answerHarder exam level

    Name the class and one example of: (i) horsetail (ii) maidenhair fern (iii) club moss.

    Hint

    Common names.

    Answer

    (i) Sphenopsida, *Equisetum* (ii) Pteropsida, *Adiantum* (iii) Lycopsida, *Lycopodium*

11. Q11 · 3 marks · Short answerHarder exam level

    Give three features of gymnosperms.

    Hint

    Seeds, cones, leaves.

    Answer

    Naked ovules and seeds; male and female cones (heterosporous); needle-like leaves with thick cuticle and sunken stomata (in conifers).

12. Q12 · 2 marks · Short answerHarder exam level

    Give one example each of a green alga, a brown alga and a red alga used as food.

    Hint

    Edible seaweeds.

    Answer

    Green: *Ulva* (sea lettuce); brown: *Laminaria*; red: *Porphyra*

13. Q13 · 5 marks · Long answerHarder exam level

    (a) Give a graphic outline of the life cycle of *Pinus*. [3]
    (b) State two economic uses of gymnosperms. [2]

    Hint

    Cones, pollen, archegonia.

    Answer

    (a) Sporophyte (2n) → male and female cones → meiosis → pollen grains and megaspore (n) → female gametophyte with archegonia → pollination by wind → pollen tube → fertilisation → zygote (2n) → embryo in seed with haploid endosperm → new tree. (b) Timber/paper pulp; resin and turpentine (or chilgoza seeds, ephedrine).

14. Q14 · 3 marks · Short answerHOTS / competency

    *Pinus* has 2n = 24. Give the chromosome number in (i) a needle cell (ii) a pollen grain (iii) the endosperm (iv) the embryo, and explain why the endosperm differs from that of a flowering plant.

    Hint

    Which tissues belong to the gametophyte?

    Answer

    (i) 24 (sporophyte) (ii) 12 (male gametophyte) (iii) 12 (iv) 24 (from the zygote). The *Pinus* endosperm is the female gametophyte tissue, formed from the haploid megaspore before fertilisation, so it is haploid; a flowering plant's endosperm forms after double fertilisation (triple fusion) and is triploid.

15. Q15 · 3 marks · Short answerHOTS / competency

    Why do bryophytes remain small, while pteridophytes can grow much taller?

    Hint

    Transport and support.

    Answer

    Bryophytes lack xylem and phloem and true roots, so water moves only by diffusion and capillarity over short distances and there is no lignified support. Pteridophytes have vascular tissue for long-distance transport and support, and roots to absorb water.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1. 1.Stored food of red algae?Show answer

   Floridean starch.

2. 2.Flagella of brown algae?Show answer

   Two, unequal, lateral.

3. 3.Dominant phase in bryophytes?Show answer

   Gametophyte.

4. 4.Asexual structures of Marchantia?Show answer

   Gemmae in gemma cups.

5. 5.Example of Sphenopsida?Show answer

   *Equisetum*.

6. 6.Fern gametophyte?Show answer

   Prothallus.

7. 7.Ploidy of Pinus endosperm?Show answer

   Haploid.

8. 8.Source of turpentine?Show answer

   *Pinus* resin.

Quick revision checklist

The night before the exam: can you do each of these without looking?

• ☐Can you write the pigments, stored food, wall and flagella of all three algal classes?
• ☐Can you list five economic uses of algae?
• ☐Can you explain why bryophytes are amphibians of the plant kingdom?
• ☐Can you draw the Funaria life cycle with n and 2n?
• ☐Can you name one example of each pteridophyte class?
• ☐Can you outline a fern life cycle?
• ☐Can you explain heterospory and its importance?
• ☐Can you outline the Pinus life cycle and give uses of gymnosperms?

Plant Kingdom: frequently asked questions