BiologyCBSE Class 11 · Plant Kingdom

Life Cycle Patterns and Alternation of Generations in Plants

Updated 17 October 2026 · Fact-checked

Sexually reproducing plants alternate a haploid gametophyte with a diploid sporophyte. There are three patterns: haplontic (dominant haploid gametophyte, zygote the only diploid stage), diplontic (dominant diploid sporophyte, gametophyte reduced) and haplo-diplontic (both haploid and diploid phases multicellular). From bryophytes to angiosperms the sporophyte becomes dominant and the gametophyte reduced.

Notice which box is biggest: haplontic is mostly haploid, diplontic mostly diploid, and haplo-diplontic has both phases as large multicellular bodies.

Illustration drawn for QuestionBuddy.

Understand Alternation of Generations in Plants

Haploid and diploid phases. Plants produce gametes (n) in a gametophyte and spores through meiosis in a sporophyte (2n). Fusion of gametes gives the diploid zygote; meiosis restores haploidy. Plants show alternation of generations, but the dominant phase differs.

Three life cycle patterns.

Haplontic: dominant, photosynthetic phase is the haploid gametophyte; the diploid stage is only the zygote, which divides by meiosis to form haploid spores. Examples: *Volvox*, *Spirogyra* and some species of *Chlamydomonas*.
Diplontic: the diploid sporophyte is the dominant, photosynthetic, independent phase; the gametophyte is a few-celled haploid structure. Seen in all gymnosperms and angiosperms; also in the alga *Fucus*.
Haplo-diplontic: both the haploid and diploid phases are multicellular. The phases are free-living in pteridophytes and in algae such as *Ectocarpus*, *Polysiphonia* and kelps, whereas in bryophytes the sporophyte is dependent on the gametophyte.

Bryophytes (amphibians of the plant kingdom): live in moist shaded places; no true roots, stem or leaves (root-like rhizoids, stem-like and leaf-like structures); no vascular tissue. The main plant body is the haploid gametophyte. Sex organs antheridium (produces biflagellate antherozoids) and archegonium (flask-shaped, produces a single egg). Water is needed for fertilisation. The zygote develops into a sporophyte that is not free-living but attached to and dependent on the gametophyte for nutrition. Spores formed by meiosis germinate into gametophytes. Classes: liverworts (*Marchantia*, thalloid, gemmae for vegetative reproduction) and mosses (*Funaria*, *Polytrichum*, *Sphagnum*; protonema stage, leafy gametophyte). Economic uses: *Sphagnum* gives peat as fuel and packing; mosses and lichens are the first colonisers of rocks, and mosses form dense mats that reduce soil erosion.

Pteridophytes (first terrestrial plants with vascular tissue, xylem and phloem): found in damp, cool places; the main plant is a sporophyte differentiated into true root, stem and leaves (small leaves in *Selaginella*, large in ferns). Sporangia on leaf-like sporophylls, which may form compact strobili (*Selaginella*, *Equisetum*). Spores germinate into small, multicellular, free-living, mostly photosynthetic prothallus (gametophyte), which needs cool damp conditions and water for fertilisation. Most are homosporous; *Selaginella* and *Salvinia* are heterosporous (macrospores and microspores). In heterosporous forms the female gametophyte is retained on the parent sporophyte, an event considered a precursor to the seed habit. Examples: *Selaginella*, *Equisetum*, *Pteris*, *Dryopteris*, *Adiantum*.

Gymnosperms: seeds are naked (ovules not enclosed in an ovary). Roots: tap (*Pinus* with fungal mycorrhiza; *Cycas* with coralloid roots associated with nitrogen-fixing cyanobacteria). Heterosporous; microspores in microsporophylls form male cones, megaspores in megasporophylls form female cones. Pollen is carried by wind; the male gametophyte is highly reduced. Sporophyte dominant. Examples: *Cycas*, *Pinus*, *Cedrus*, *Ginkgo*.

Angiosperms: seeds are enclosed in fruits. Flowers are the reproductive organs; double fertilisation (syngamy plus triple fusion) gives the diploid zygote and the triploid primary endosperm nucleus (PEN). Dicots and monocots. Male gametophyte is the pollen grain; female gametophyte is the 7-celled, 8-nucleate embryo sac.

Trend. Bryophyte: gametophyte dominant and sporophyte dependent. Pteridophyte: sporophyte dominant with free-living gametophyte. Gymnosperm and angiosperm: sporophyte dominant; gametophyte reduced and dependent on the sporophyte; fertilisation independent of external water in seed plants.

Alternation of Generations in Plants: key facts

Haplontic: Gametophyte (n) dominant
zygote only 2n
meiosis in zygote; Volvox, Spirogyra
Diplontic: Sporophyte (2n) dominant | gametophyte few-celled; Gymnosperms, angiosperms, Fucus
Haplo-diplontic: Both haploid and diploid phases multicellular; Free-living in pteridophytes, kelps; bryophyte sporophyte is dependent on gametophyte
Endosperm: $P E N = 3 n ∣ f or m e d b y t r i pl e f u s i o n$; Angiosperms

How to answer Alternation of Generations in Plants questions

Questions ask for the dominant phase, the cycle pattern, or compare groups.

1Identify the dominant phase: gametophyte (bryophyte) or sporophyte (others).
2Write the pattern: haplontic, diplontic or haplo-diplontic.
3State whether the other phase is free-living or dependent.
4For comparisons, use a table with plant body, vascular tissue, fertilisation and seeds.
5Use chromosome numbers where given: gametophyte n, sporophyte 2n, endosperm 3n.

Alternation of Generations in Plants in real life

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

Garden moss and fern

Suppose a student scrapes a green cushion from a damp wall and also notes a large fern in a pot.

Which phase is the visible green body in each, and which is dependent?

Try it first, then show the solutionSolution

The moss cushion is the haploid gametophyte; its sporophyte is attached to it.
The fern plant is the diploid sporophyte; its gametophyte (prothallus) is tiny and free-living.
The moss sporophyte depends on the gametophyte; the fern prothallus lives independently.

Answer: Moss: gametophyte dominant; fern: sporophyte dominant.

Memory hook: Moss = n; fern = 2n.

Tricks to remember Alternation of Generations in Plants

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

Hapl-on-ly
Haplontic: only the zygote is diploid.
Use it when: Haplontic
BP-G, rest-S
Bryophytes: Gametophyte dominant; all others: Sporophyte dominant.
Use it when: Dominant phase
Naked seed Gym
Gymnosperm = naked ovule.
Use it when: Gymnosperm vs angiosperm

Alternation of Generations in Plants: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Define patterns · 3 marks · Short answerBoard level

Name the three life cycle patterns in plants with one example each.

Try it first, then show the solutionSolution

Haplontic: Spirogyra (1 mark).
Diplontic: Pinus or Fucus (1 mark).
Haplo-diplontic: moss or fern (1 mark).

Answer: Haplontic Spirogyra; diplontic Pinus; haplo-diplontic moss.

Example 2: Bryophytes · 2 marks · Very short answerBoard level

Bryophytes need a film of water for fertilisation yet live on land. Explain this with reference to their sex organs, and name the dominant phase.

Try it first, then show the solutionSolution

Antherozoids are biflagellate and swim to the archegonium, so water is needed though the plant lives on land (1 mark).
Haploid gametophyte is the dominant phase (1 mark).

Answer: Water needed for fertilisation; gametophyte dominant.

Example 3: Seed habit · 3 marks · Short answerHarder board level

Explain how heterospory in pteridophytes is a precursor to the seed habit.

Try it first, then show the solutionSolution

Selaginella and Salvinia produce macrospores and microspores (1 mark).
The female gametophyte develops inside the macrospore which is retained on the parent sporophyte (1 mark).
Zygote develops into an embryo within the parent, a feature seen in seed plants (1 mark).

Answer: Retention of the female gametophyte and embryo on the parent.

Example 4: Comparison · 4 marks · Short answerHarder board level

Compare gymnosperms and angiosperms on ovule protection, endosperm and fertilisation.

Try it first, then show the solutionSolution

Gymnosperm ovules are naked; angiosperm ovules are inside an ovary (1 mark).
Gymnosperm food tissue is haploid female gametophyte; angiosperm endosperm is triploid (1 mark).
Angiosperms show double fertilisation (1 mark).
Both depend on pollen tubes, not external water (1 mark).

Answer: Naked versus enclosed; haploid versus triploid food tissue.

Example 5: Chromosome tracing · 5 marks · Long answerHOTS / competency

A moss has n = 10. Give the chromosome number in (a) spore (b) gamete (c) zygote (d) a cell of the capsule wall, and say which meiotic event gives the spores.

Try it first, then show the solutionSolution

Spore: n = 10 (1 mark).
Gamete: n = 10 (1 mark).
Zygote: 2n = 20 (1 mark).
Capsule wall cell is sporophytic: 2n = 20 (1 mark).
Spores form by meiosis of spore mother cells in the sporangium (capsule) (1 mark).

Answer: 10, 10, 20, 20; meiosis in sporophyte.

Where students lose marks in Alternation of Generations in Plants

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

Mistake: Dominant phase in ferns
Prothallus mixed with the plant.
Wrong working
Fern gametophyte is dominant.
Right working
Fern sporophyte is dominant.
Do this: Leafy fern = 2n.
Usually costs: 1 mark.
Mistake: Triploid in gymnosperms
Endosperm confusion.
Wrong working
Gymnosperm endosperm is triploid.
Right working
Gymnosperm food tissue is haploid.
Do this: 3n only in angiosperms.
Usually costs: 1 mark.
Mistake: Gametophyte as 2n
Phase mix.
Wrong working
Gametophyte is diploid.
Right working
Gametophyte is haploid.
Do this: G = n.
Usually costs: 1 mark.

Exam tips

Always give n or 2n.
Use the words free-living or dependent.
Quote Marchantia and Funaria for bryophytes.
Link heterospory to seed habit.

Practice questions on Alternation of Generations in Plants

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

Q1 · 1 mark · MCQBoard level
In which group is the sporophyte dependent on the gametophyte?
(a) pteridophytes (b) bryophytes (c) gymnosperms (d) angiosperms
Hint
Moss capsule.
Answer
(b).
Q2 · 1 mark · Assertion-reasonHarder board level
Assertion (A): In gymnosperms the male gametophyte is highly reduced.
Reason (R): Pollen grains are carried by wind and not by water.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Hint
Reduction is not caused by wind.
Answer
(b).
Q3 · 2 marks · Very short answerHarder board level
A fern prothallus has n = 12. What is the chromosome number of the fern sporophyte leaf cell? Of the spores?
Hint
Sporophyte 2n.
Answer
Leaf cell 2n = 24; spores n = 12.
Q4 · 4 marks · Case-basedHarder board level
Read and answer.
Suppose an algal flora has Species 1, with the only diploid cell the zygote, and Species 2, where free-living diploid and haploid thalli look alike.
(a) Name the life cycle of each. (1)
(b) Name one example of each. (1)
(c) Which is common in bryophytes? (1)
(d) Where does meiosis occur in Species 1? (1)
Hint
Haplontic and haplo-diplontic.
Answer
(a) Haplontic; haplo-diplontic. (b) Spirogyra; Ectocarpus. (c) Haplo-diplontic. (d) In the zygote.
Q5 · 3 marks · Short answerHOTS / competency
Suppose a plant group needs liquid water for fertilisation but has vascular tissue and a dominant sporophyte. Identify it and justify, and state which later innovations remove the water requirement.
Hint
Pteridophytes.
Answer
Pteridophytes: sporophyte with vascular tissue is dominant, but the free-living prothallus needs water for the swimming sperm. Heterospory leading to seeds and pollen tubes in gymnosperms and angiosperms removes the water requirement.

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.What is the dominant phase in bryophytes?Show answer
Haploid gametophyte.
2.Name a heterosporous pteridophyte.Show answer
Selaginella or Salvinia.
3.What is a prothallus?Show answer
The gametophyte of pteridophytes.
4.What are rhizoids?Show answer
Root-like structures of bryophytes.
5.What is PEN?Show answer
Primary endosperm nucleus (3n).
6.Which plants have naked seeds?Show answer
Gymnosperms.

Alternation of Generations in Plants: frequently asked questions

What is alternation of generations?

The alternation of haploid gametophyte and diploid sporophyte in the life cycle.

What is haplo-diplontic?

A cycle where both the haploid and diploid phases are multicellular. The phases are free-living in pteridophytes and in algae like Ectocarpus and kelps, but in bryophytes the sporophyte depends on the gametophyte.

Why do bryophytes need water?

Their antherozoids swim to the egg.

What is double fertilisation?

Syngamy plus triple fusion in angiosperms.

What is heterospory?

Production of two kinds of spores, micro and macro.