BiologyISC Class 11 · Plant Kingdom

Algae and Bryophytes: Classes, Uses and Alternation of Generations

Updated 17 October 2026 · Fact-checked

Algae are simple, chlorophyll-bearing, thalloid, mostly aquatic plants, grouped as Chlorophyceae (green), Phaeophyceae (brown) and Rhodophyceae (red) by pigments and stored food. Bryophytes are amphibious, with a dominant gametophyte and a dependent sporophyte. Plant life cycles may be haplontic, diplontic or haplodiplontic.

In bryophytes the green gametophyte (n) is dominant; the sporophyte (2n) grows on it and its meiosis makes spores that start the next gametophyte.

Illustration drawn for QuestionBuddy.

Understand Algae, Bryophytes and Alternation of Generations

Algae. Autotrophic, thalloid, mostly aquatic; found also on moist stones, soil and as symbionts. Reproduction: vegetative (fragmentation), asexual (zoospores) and sexual (isogamous, anisogamous or oogamous).

Class	Colour and pigments	Reserve food	Cell wall	Examples
Chlorophyceae	green; chlorophyll a, b	starch (pyrenoids)	cellulose	Chlamydomonas, Volvox, Ulothrix, Spirogyra, Chara
Phaeophyceae	brown; chlorophyll a, c and fucoxanthin	mannitol, laminarin	cellulose with algin	Ectocarpus, Dictyota, Laminaria, Sargassum, Fucus
Rhodophyceae	red; chlorophyll a, d and phycoerythrin	floridean starch	cellulose	Polysiphonia, Porphyra, Gracilaria, Gelidium

Economic importance. Photosynthetic algae fix a large share of carbon dioxide and add oxygen to water. Several are food (Porphyra, Laminaria, Sargassum). Gelidium and Gracilaria give agar, used for culture media and ice creams; algin and carrageen are hydrocolloids; Chlorella and Spirulina are protein-rich supplements for space travellers.

Bryophytes. Liverworts and mosses live in moist, shaded places and need water for fertilisation because the male gametes are flagellated. The plant body is a gametophyte (haploid), a thallus (Marchantia) or a leafy stem with rhizoids (mosses). Male sex organs are antheridia and female sex organs are archegonia. The zygote develops into a sporophyte (diploid) made of foot, seta and capsule, which is attached to and nourished by the gametophyte; spores formed in the capsule by meiosis germinate into the gametophyte. Marchantia reproduces vegetatively by gemmae in gemma cups; in mosses (Funaria) the spore gives a creeping protonema and then a leafy gametophyte. Sphagnum provides peat, and mosses also help in soil formation.

Life cycles. *Haplontic*: the haploid gametophyte is dominant, and the sporophyte is only the zygote (Volvox, Spirogyra, some Chlamydomonas). *Diplontic*: the diploid sporophyte is dominant and the gametophyte is a few-celled structure (gymnosperms, angiosperms, Fucus). *Haplodiplontic*: both phases are multicellular and free-living or dependent (bryophytes, pteridophytes, Ectocarpus, kelps).

Algae, Bryophytes and Alternation of Generations: key facts

Algae classes: $C h l or o p h y ce a e : g r ee n ∣ P ha eo p h y ce a e : b r o w n ∣ R h o d o p h y ce a e : r e d$; Pigments chlorophyll a,b | a,c + fucoxanthin | a,d + phycoerythrin.
Reserve food: Starch green
Mannitol and laminarin brown
Floridean starch red; Matches the class.
Bryophyte life cycle: Dominant gametophyte (n) | dependent sporophyte (2n): foot, seta, capsule; Water is needed for fertilisation.
Types of life cycle: $H a pl o n t i c ∣ D i pl o n t i c ∣ H a pl o d i pl o n t i c$; Defined by which phase is dominant.

Starch	green
Mannitol and laminarin	brown
Floridean starch	red

Algae, Bryophytes and Alternation of Generations 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.

Agar for the laboratory

Suppose a microbiology lab prepares nutrient jelly for bacterial cultures and a food factory uses a jelly ingredient from seaweeds.

Name the algae and the product, and state their class.

Try it first, then show the solutionSolution

Gelidium and Gracilaria are red algae (Rhodophyceae).
They give agar, a jelly-forming hydrocolloid used in culture media and in foods such as ice cream.
Brown algae give algin, another hydrocolloid.

Answer: Agar from the red algae Gelidium and Gracilaria.

Memory hook: Red algae mean agar and carrageen; brown algae mean algin.

Tricks to remember Algae, Bryophytes and Alternation of Generations

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

Green starch, brown mannitol, red floridean
Match the reserve food to the colour.
Use it when: Algae classification.
Moss: water for the sperm
Bryophytes are the "amphibians of the plant kingdom" because they need water to fertilise.
Use it when: Why bryophytes remain small and moist.

Algae, Bryophytes and Alternation of Generations: solved examples

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

Example 1: Pigments of algae · 1 mark · MCQBoard level

Fucoxanthin is the characteristic pigment of the algae belonging to:
(a) Chlorophyceae
(b) Phaeophyceae
(c) Rhodophyceae
(d) Cyanophyceae

Try it first, then show the solutionSolution

Phaeophyceae (brown algae) have fucoxanthin along with chlorophyll a and c.

Answer: (b) Phaeophyceae

Example 2: Classes of algae · 3 marks · Short answerBoard level

Differentiate between the three classes of algae on the basis of pigments, reserve food and one example each.

Try it first, then show the solutionSolution

Chlorophyceae: chlorophyll a, b; starch; Spirogyra. (1 mark)
Phaeophyceae: chlorophyll a, c, fucoxanthin; mannitol and laminarin; Laminaria. (1 mark)
Rhodophyceae: chlorophyll a, d, phycoerythrin; floridean starch; Gelidium. (1 mark)

Answer: Green, brown and red algae differ in pigments and reserve food.

Example 3: Bryophyte life cycle · 4 marks · Short answerHarder board level

Describe the life cycle of a moss such as Funaria in outline, giving the ploidy of each stage.

Try it first, then show the solutionSolution

Haploid spore (n) germinates into a creeping protonema and then a leafy gametophyte (n). (1 mark)
The gametophyte bears antheridia and archegonia; the biflagellate sperm swim in water to the egg (n). (1 mark)
The zygote (2n) develops into the sporophyte, with foot, seta and capsule, attached to the gametophyte. (1 mark)
In the capsule meiosis produces haploid spores (n), completing the cycle. (1 mark)

Answer: Spore → protonema → gametophyte → gametes → zygote (2n) → sporophyte → meiosis → spores.

Example 4: Alternation of generations · 4 marks · Short answerHarder board level

In a plant the gametophyte has n = 10 chromosomes. Give the number of chromosomes in (i) the egg, (ii) the zygote, (iii) the sporophyte cells and (iv) the spores. Classify the life cycles of Spirogyra, Funaria and Fucus.

Try it first, then show the solutionSolution

(i) Egg: n = 10; (ii) zygote: 2n = 20; (iii) sporophyte cells: 2n = 20; (iv) spores: n = 10, formed by meiosis. (2 marks)
Spirogyra: haplontic (haploid dominant, zygote is the only diploid cell). (0.75 mark)
Funaria: haplodiplontic (both phases multicellular). (0.5 mark)
Fucus: diplontic (diploid dominant). (0.75 mark)

Answer: 10; 20; 20; 10; Spirogyra haplontic, Funaria haplodiplontic, Fucus diplontic.

Example 5: Algae in the economy · 5 marks · Long answerHOTS / competency

A food technology student is asked to explain how algae are useful. Give five uses with the algae involved, and explain why Gelidium and Gracilaria are called "hydrocolloid" producers and why Chlorella is used on space missions.

Try it first, then show the solutionSolution

Food: Porphyra, Laminaria and Sargassum are eaten. (1 mark)
Agar from Gelidium and Gracilaria; algin from brown algae; carrageen. They form gels in water. (1.5 marks)
Algae fix carbon dioxide in photosynthesis and add oxygen to the aquatic environment. (1 mark)
Chlorella and Spirulina are rich in protein; Chlorella is used as a food supplement by space travellers. (1 mark)
Hydrocolloids form a colloidal gel with water, useful in culture media, ice creams and jellies. (0.5 mark)

Answer: Food, agar, algin, oxygen production, protein supplements.

Where students lose marks in Algae, Bryophytes and Alternation of Generations

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

Mistake: Mixing up the pigments of algae
Writing chlorophyll c for red algae.
Do this: Green: a, b; brown: a, c and fucoxanthin; red: a, d and phycoerythrin.
Usually costs: 1 mark.
Mistake: Saying bryophyte sporophyte is independent
Treating the capsule as free-living.
Do this: The sporophyte is attached to and dependent on the gametophyte.
Usually costs: 1 to 2 marks.
Mistake: Wrong ploidy in life cycles
Calling spores diploid.
Do this: Spores are formed by meiosis, so they are haploid.
Usually costs: 1 mark.

Exam tips

Present the three algal classes as a small table.
Write the ploidy of each stage in life cycles.
Name the pigments and the reserve food for each class.
Give two uses of algae with the correct algae.

Practice questions on Algae, Bryophytes and Alternation of Generations

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
The male gametes of bryophytes are:
(a) non-motile
(b) biflagellate
(c) amoeboid
(d) multiflagellate
Hint
They swim in water to reach the egg.
Answer
(b) biflagellate
Q2 · 2 marks · Short answerBoard level
Name the reproductive structures formed by gemma cups in Marchantia.
Hint
It is a vegetative method.
Answer
Gemmae, green multicellular buds that detach and grow into new thalli; the method is vegetative reproduction.
Q3 · 3 marks · Short answerHarder board level
Distinguish between liverworts and mosses with an example of each.
Hint
One is thalloid, the other leafy.
Answer
Liverworts have a flat, dorsiventral thallus (Marchantia). Mosses have an upright leafy stem with rhizoids and a creeping protonema stage (Funaria, Sphagnum).
Q4 · 3 marks · Short answerHarder board level
What is meant by haplodiplontic life cycle? Give two plant groups showing it.
Hint
Both phases are multicellular.
Answer
In a haplodiplontic life cycle both the haploid gametophyte and the diploid sporophyte are multicellular and independent or dependent; bryophytes and pteridophytes show it.
Q5 · 3 marks · Assertion-reasonHarder board level
Assertion (A): Mosses grow best in moist, shaded places. Reason (R): The male gametes of mosses require water to swim to the egg. Choose: (a) both true and R explains A (b) both true, R does not explain A (c) A true, R false (d) A false, R true.
Hint
Water is essential for fertilisation.
Answer
(a) Both are true and R explains A.
Q6 · 4 marks · Case-basedHOTS / competency
Case study: Suppose a student studies a sample of Sphagnum from a bog.
(i) To which group does Sphagnum belong? (1 mark)
(ii) Name the dominant phase of its life cycle. (1 mark)
(iii) State one commercial use. (1 mark)
(iv) Name the sex organs. (1 mark)
Hint
Think about peat.
Answer
(i) Bryophytes (mosses). (ii) The haploid gametophyte. (iii) Peat, used as fuel and as packing material for plants. (iv) Antheridia and archegonia.

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.Pigment specific to brown algae?Show answer
Fucoxanthin.
2.Source of agar?Show answer
Gelidium and Gracilaria.
3.Dominant phase in bryophytes?Show answer
Gametophyte.
4.Female sex organ of bryophytes?Show answer
Archegonium.

Algae, Bryophytes and Alternation of Generations: frequently asked questions

Why do mosses and liverworts need a damp habitat even though they grow on land?

Their male gametes are flagellated and must swim through water to reach the egg, so fertilisation cannot take place on dry ground; this is why they are often called the amphibians of the plant kingdom.

Why do bryophytes not grow tall?

They lack true vascular tissue (xylem and phloem) and true roots, so water and food transport over long distances is limited.

What is isogamy, anisogamy and oogamy?

In isogamy the two fusing gametes are similar in size, and may be flagellated (Chlamydomonas) or non-flagellated (Spirogyra). In anisogamy the gametes are dissimilar in size. In oogamy a large, non-motile female gamete fuses with a small, motile male gamete.