Class 11 Biology · NCERT chapter 3 · 7 topics · free to read
Algae — The photosynthetic aquatic organisms that produce half the world's oxygen
Algae are simple, chlorophyll-bearing, thalloid, autotrophic organisms — mostly aquatic. NCERT classifies them into three classes based on pigment: Chlorophyceae (green), Phaeophyceae (brown), and Rhodophyceae (red). They reproduce by vegetative, asexual, and sexual methods.
General Characters of Algae
Algae range from microscopic unicellular forms (Chlamydomonas) to massive kelp forests (60 m long). They lack roots, stems, and leaves — the plant body is a thallus.
Algae are chlorophyll-bearing, autotrophic, thalloid organisms. They can be found in fresh water, marine water, moist stones, soil, and even wood. Some live inside other plants (endophytes) or on other plants (epiphytes). The relationship between algae and fungi in lichens is a classic symbiosis.
Plant body — thallus (no true roots, stems, or leaves)
Reproduction — vegetative (fragmentation), asexual (zoospores), sexual (isogamy, anisogamy, oogamy)
Economic importance — food (Laminaria, Porphyra), agar from Gelidium/Gracilaria, algin from brown algae, carrageenan from red algae
Ecological role — primary producers in aquatic ecosystems, fix CO2, produce O2
Chlorophyceae (Green Algae)
Green algae are the most plant-like algae — same pigments (chlorophyll a and b), same food storage (starch), same cell wall (cellulose). They are considered ancestors of land plants.
Green algae are grass-green due to dominance of chlorophyll a and b. They store food as starch and have a cell wall made of cellulose — exactly like land plants. Most are freshwater, some marine. Their plant body ranges from unicellular (Chlamydomonas) to colonial (Volvox) to filamentous (Ulothrix, Spirogyra).
Pigments — chlorophyll a, chlorophyll b, carotenoids
Cell wall — cellulose (inner layer), sometimes pectose
Stored food — starch
Flagella — 2-8, equal, apical (whiplash type)
Habitat — mostly freshwater, some marine, some terrestrial
Key NCERT genera to remember: - Chlamydomonas — unicellular, biflagellate, freshwater - Volvox — colonial, hollow spherical colony - Ulothrix — unbranched filamentous, attached to rocks - Spirogyra — unbranched filamentous, spiral/ribbon-shaped chloroplast (that's where the name comes from!) - Chara — multicellular, advanced, resembles a plant
Phaeophyceae (Brown Algae)
Brown algae are primarily marine, often massive (kelps). The brown color comes from the pigment fucoxanthin. They include the largest algae on Earth.
Brown algae range from simple filaments to giant kelps (Macrocystis — up to 60 m long!). They are almost exclusively marine. The brown color is due to fucoxanthin pigment, which masks the green of chlorophyll. Their body often has holdfast (anchor), stipe (stem-like), and frond (leaf-like) — resembling a plant but NOT a true plant.
Pigments — chlorophyll a, chlorophyll c, fucoxanthin (gives brown color)
Stored food — laminarin (a polysaccharide) + mannitol
Flagella — 2, unequal, lateral (one smooth, one tinsel-type)
Habitat — almost all marine; colder oceans have kelp forests
Key NCERT genera: - Ectocarpus — simple, branched filamentous - Dictyota — flattened, dichotomously branched thallus - Laminaria — large kelp, source of laminarin - Sargassum — has berry-like floats (pneumatocysts) - Fucus — rockweed, found in intertidal zones
Rhodophyceae (Red Algae)
Red algae are predominantly marine and can grow at the greatest depths among all algae because phycoerythrin absorbs blue-green light that penetrates deep water.
Red algae get their color from phycoerythrin (r-phycoerythrin), a red pigment that absorbs blue-green wavelengths. This allows red algae to photosynthesize at greater depths (up to 200+ m) than any other algae — blue light penetrates deepest in the ocean, and phycoerythrin captures it.
Pigments — chlorophyll a, chlorophyll d, phycoerythrin (red), phycocyanin (blue)
Which class of algae stores food as floridean starch?
Rhodophyceae (red algae). Floridean starch is structurally similar to amylopectin. Green algae store starch (like land plants), and brown algae store laminarin + mannitol.
Bryophytes — The amphibians of the plant kingdom
Bryophytes are non-vascular, seedless plants that depend on water for reproduction. The gametophyte is the dominant phase. They include liverworts (Marchantia), hornworts, and mosses (Funaria). NCERT calls them 'amphibians of the plant kingdom' because they need water for fertilization but live on land.
General Characters
Bryophytes bridge the gap between aquatic algae and fully terrestrial vascular plants. They have multicellular sex organs but lack true vascular tissue.
Bryophytes are the simplest land plants. They have a plant body that may be thalloid (flat, ribbon-like) or leafy, but they lack true roots, stems, and leaves. Instead, they have root-like rhizoids that anchor them and absorb water. The critical limitation: sperm are flagellated and need a film of water to swim to the egg.
Habitat — moist, shaded places (rocks, tree bark, damp soil)
Vascular tissue — absent (no xylem or phloem). Transport by diffusion/osmosis only
Dominant phase — gametophyte (n) is the main plant body you see
Sporophyte — dependent on gametophyte for nutrition (partially or fully parasitic on it)
Sex organs — multicellular and jacketed: male = antheridium, female = archegonium
Fertilization — requires water (zooidogamy — motile sperm swim to egg)
Liverworts
Liverworts have a flat, green, thalloid body with dorsiventral symmetry. Marchantia is the most important genus for NEET.
Liverworts grow in moist, shady habitats — on rocks, bark, and soil. The thallus is dorsiventral (distinct upper and lower surface) and lobed — it was thought to resemble a liver in medieval times, hence the name 'liverwort.' Marchantia is the NCERT representative genus.
Thallus — flat, dorsiventral, dichotomously branched, closely appressed to the ground
Rhizoids — unicellular, on the ventral surface
Vegetative reproduction — by fragmentation or specialized structures called gemmae (singular: gemma)
Gemmae cups — cup-shaped structures on the thallus surface containing small green gemmae that detach and grow into new plants
Sporophyte — has foot, seta (stalk), and capsule. Capsule produces spores by meiosis
Mosses
Mosses are the most familiar bryophytes. Their life cycle has two distinct stages: a creeping filamentous protonema and an upright leafy gametophore. Funaria is the NCERT example.
Mosses have a two-stage gametophytic development. A spore germinates to form the protonema — a creeping, branched, filamentous structure. The protonema then develops buds that grow into the upright leafy gametophore — the familiar green moss plant you see. This gametophore has a stem-like axis with spirally arranged leaf-like appendages.
Leafy gametophore (stage 2) — upright, with 'stem,' 'leaves,' and multicellular rhizoids
Rhizoids — multicellular with oblique septa (vs. unicellular in liverworts)
Sex organs — antheridia and archegonia at the apex of the leafy gametophore
Sporophyte — more elaborate than liverworts: foot + seta + capsule with peristome teeth for spore dispersal
Funaria — the common moss, NCERT representative genus
Thalloid (flat body)
Leafy (upright with 'leaves')
Unicellular rhizoids
Multicellular rhizoids (oblique septa)
No protonema stage
Protonema stage present
Example: Marchantia
Example: Funaria, Sphagnum
Asexual by gemmae
Asexual by fragmentation, budding
Bryophyte Life Cycle
The bryophyte life cycle is haplo-diplontic with the haploid gametophyte as the dominant, independent phase. The diploid sporophyte is short-lived and nutritionally dependent on the gametophyte.
The gametophyte (n) is the main plant body — it's what you see growing on rocks and soil. It produces antheridia (male) and archegonia (female). Flagellated sperm swim through water to the archegonium and fertilize the egg. The resulting zygote develops into the sporophyte (2n) — which remains attached to and nutritionally dependent on the gametophyte.
What is the dominant phase in the bryophyte life cycle?
The gametophyte (haploid, n) is dominant and independent. The sporophyte (diploid, 2n) is dependent on it. This is the reverse of pteridophytes/gymnosperms/angiosperms where the sporophyte dominates.
Pteridophytes — First vascular plants, sporophyte takes charge
Pteridophytes are the first plants with vascular tissue (xylem and phloem). The sporophyte is the dominant phase — a major evolutionary shift from bryophytes. They include ferns, horsetails (Equisetum), and clubmosses (Selaginella). They still need water for fertilization but are otherwise well-adapted to land life.
General Characters
Pteridophytes solved a big evolutionary problem — long-distance water and nutrient transport — by evolving xylem and phloem. This allowed them to grow much taller than bryophytes.
Pteridophytes are the first plants with true vascular tissue — xylem for water transport and phloem for food transport. This is a game-changer: bryophytes are limited to moist, low-growing habitats because they rely on diffusion. Pteridophytes can grow tall because vascular tissue acts like a plumbing system, moving water against gravity.
First vascular plants — possess xylem and phloem (true vascular tissue)
Plant body — differentiated into true root, stem, and leaves
Dominant phase — sporophyte (2n) is the main plant body
Gametophyte — small, inconspicuous, independent, called prothallus
Fertilization — still requires water (flagellated sperm swim to archegonium)
Seeds — absent (reproduce by spores)
Habitat — moist, shady places (forest floors, near waterfalls)
Classes of Pteridophytes
NCERT classifies pteridophytes into four classes based on sporangia position, leaf type, and stem structure.
Pteridophytes are classified into four classes. For NEET, you need to know the representative genera and key distinguishing features of each.
Psilopsida — most primitive, rootless, leafless. Example: Psilotum (whisk fern)
Lycopsida — small leaves called microphylls. Example: Selaginella (spike moss), Lycopodium (club moss)
Sphenopsida — jointed stem with whorled leaves. Example: Equisetum (horsetail)
Pteropsida — large leaves called megaphylls (fronds). Example: Dryopteris (fern), Pteris, Adiantum (maidenhair fern)
Heterospory & Seed Habit
Some pteridophytes produce two types of spores (heterospory) — a critical evolutionary step toward seed formation seen in gymnosperms and angiosperms.
Most pteridophytes are homosporous — they produce spores of one kind only. But some, like Selaginella and Salvinia, are heterosporous — they produce two types of spores: large megaspores (female) and small microspores (male).
Homospory — one type of spore, one type of gametophyte (bisexual). Example: Dryopteris, Pteris
Heterospory — two types of spores: megaspores (large, female) + microspores (small, male)
Megaspore → female gametophyte (archegonia) — retained on parent plant in seed plants
Microspore → male gametophyte (antheridia) — becomes pollen grain in seed plants
Selaginella and Salvinia — the NCERT examples of heterosporous pteridophytes
Quick recall
Name two heterosporous pteridophytes mentioned in NCERT.
Selaginella and Salvinia. They produce megaspores (large, female) and microspores (small, male). This is evolutionarily significant as the precursor to the seed habit in gymnosperms and angiosperms.
Gymnosperms — Naked seeds, cones, and ancient survivors
Gymnosperms are seed-bearing plants where seeds are NOT enclosed in a fruit — they lie exposed ('naked') on the surface of cone scales. They include Pinus (pine), Cycas, Ginkgo, and Sequoia. Wind-pollinated, with the sporophyte as the dominant phase. They were the dominant land plants before angiosperms took over.
General Characters
Gymnosperms ('gymnos' = naked, 'sperma' = seed) produce seeds that are not enclosed within a fruit. They bear cone-like structures (strobili) instead of flowers.
Gymnosperms are the first seed-bearing plants in the evolutionary timeline. The word literally means 'naked seed' — the ovules (and later seeds) are not enclosed in an ovary wall. Instead, they sit exposed on the surface of megasporophylls which are often arranged into cones (strobili). Think of a pine cone — the seeds are right there between the scales, not inside a fruit.
Seeds — present but NOT enclosed in fruit (naked seeds)
Plant body — sporophyte (2n) is dominant — large, woody trees/shrubs
Vascular tissue — well-developed xylem (tracheids only, NO vessels) and phloem (NO companion cells)
Leaves — needle-like (Pinus) or pinnately compound (Cycas) with thick cuticle (xerophytic adaptation)
Roots — tap root system. Pinus has mycorrhizal association (fungal roots). Cycas has coralloid roots with nitrogen-fixing cyanobacteria
Pollination — by wind (anemophily). Pollen grains often have air sacs/wings for wind dispersal
Flowers and fruits — completely absent
Reproduction in Gymnosperms
Gymnosperms are heterosporous and bear male and female cones (strobili). Pollination is by wind. The female gametophyte is retained within the ovule on the cone scale.
Gymnosperms are heterosporous — they produce microspores (in male cones) and megaspores (in female cones). The cones are typically on the same plant (monoecious in Pinus) or on different plants (dioecious in Cycas).
Male cone (microsporangiate strobilus) — bears microsporophylls with microsporangia → produce microspores → develop into pollen grains (male gametophyte)
Female cone (megasporangiate strobilus) — bears megasporophylls with ovules → megaspore develops into female gametophyte (endosperm) inside the ovule
Pollen grains — develop into winged pollen (in Pinus) for wind dispersal
Pollination — wind-borne (anemophily). Pollen lands on the ovule directly (no stigma, no style!)
Pollen tube — grows through the micropyle to deliver male gametes to the archegonium
Fertilization — male gamete + egg → zygote → embryo. NO double fertilization (that's only angiosperms)
Seeds — develop from ovules, remain naked on the cone scale (no fruit wall)
Compact, smaller
Larger, looser
Bears microsporophylls
Bears megasporophylls
Produces microspores → pollen
Contains ovules → megaspore → female gametophyte
Many per tree (at branch tips)
Fewer per tree
Short-lived
Persists until seed maturity
Important Gymnosperm Genera
NCERT highlights four key genera that NEET tests repeatedly. Each has distinctive features worth memorizing.
NCERT mentions several gymnosperm genera. Here are the must-know ones with their unique features.
Pinus — needle-like leaves in fascicles, monoecious, resinous, mycorrhizal roots, winged pollen grains, economically important (timber, resin, turpentine)
Ginkgo — fan-shaped leaves, deciduous (unusual for gymnosperms), dioecious, called 'living fossil,' only surviving species is G. biloba
Sequoia — tallest trees on Earth (coast redwood ~115 m), extremely long-lived, found in California
Cedrus (deodar) — large coniferous tree, timber tree of Himalayas
Quick recall
Which gymnosperm has coralloid roots, and what is their significance?
Cycas has coralloid roots — specialized coral-like roots that house nitrogen-fixing cyanobacteria (Anabaena). This symbiotic association allows Cycas to fix atmospheric nitrogen, similar to the Rhizobium-legume relationship.
Angiosperms — Flowers, fruits, double fertilization, world domination
Angiosperms are flowering plants with seeds enclosed within a fruit. They dominate the current plant world (~300,000 species). Their unique features include flowers, double fertilization (producing endosperm), and fruit formation. They are classified into monocots and dicots based on seed, root, leaf, and flower characters.
General Characters
Angiosperms ('angeion' = vessel/container, 'sperma' = seed) have seeds enclosed within fruits. They are the most diverse and successful group of land plants.
Angiosperms are the most evolved and dominant group of plants on Earth, with over 300,000 species. The name means 'enclosed seed' — unlike gymnosperms, angiosperm seeds develop inside an ovary which matures into a fruit. They range from tiny Wolffia (0.1 mm — smallest plant) to giant Eucalyptus trees (100 m).
Seeds — enclosed within fruits (ovary wall becomes fruit wall/pericarp)
Flowers — reproductive organs containing male (stamens) and female (carpels) parts
Double fertilization — unique to angiosperms: one sperm + egg → zygote, other sperm + 2 polar nuclei → triploid endosperm (3n)
Vascular tissue — xylem has vessels (more efficient than tracheids), phloem has companion cells
Angiosperms are divided into monocotyledons (one cotyledon) and dicotyledons (two cotyledons). They differ in seed structure, root system, leaf venation, and flower parts.
The two major classes of angiosperms are Dicotyledons (dicots) and Monocotyledons (monocots). The primary difference is the number of cotyledons (seed leaves) in the embryo — but this single difference correlates with a whole suite of other features.
Two cotyledons in seed
One cotyledon in seed
Tap root system
Fibrous (adventitious) root system
Reticulate (net) venation
Parallel venation
Flower parts in 4s or 5s (tetramerous/pentamerous)
Flower parts in 3s (trimerous)
Vascular bundles — open (with cambium), arranged in ring
Open vascular bundles (dicots) = cambium present → secondary growth possible → trees and woody plants
Closed vascular bundles (monocots) = no cambium → no secondary growth → mostly herbaceous
Exception: Some monocots show anomalous secondary growth (e.g., Dracaena, palm trees increase girth differently)
Economic importance: Monocots provide most cereals (rice, wheat, maize). Dicots provide most fruits, vegetables, and timber
Economic Importance of Angiosperms
Angiosperms are the most economically important group of plants, providing virtually all our food crops, most medicines, timber, fibers, and ornamental plants.
Nearly everything humans eat, wear, build with, and use for medicine comes from angiosperms. They're not just the dominant plants ecologically — they dominate human civilization too.
Plant Life Cycles — Alternation of generations across the plant kingdom
All plants show alternation of generations — alternating between a haploid gametophyte (n) and a diploid sporophyte (2n). The three patterns are haplontic (gametophyte dominant, e.g., most algae), diplontic (sporophyte dominant, e.g., Fucus, all seed plants), and haplo-diplontic (both phases prominent, e.g., bryophytes, pteridophytes).
Alternation of Generations
The fundamental life cycle pattern of all plants: a multicellular haploid gametophyte alternates with a multicellular diploid sporophyte. Meiosis and fertilization are the switching points.
In all plants, the life cycle alternates between two multicellular phases: the gametophyte (n) which produces gametes by mitosis, and the sporophyte (2n) which produces spores by meiosis. Fertilization (gamete fusion) switches from n → 2n. Meiosis (spore formation) switches from 2n → n. This is called alternation of generations.
Meiosis — spore mother cells in sporophyte → haploid spores → develop into gametophyte
Key insight: gametes are made by mitosis (in the gametophyte), NOT meiosis. Meiosis makes spores, not gametes
Haplontic Life Cycle
In the haplontic pattern, the free-living plant body is the haploid gametophyte. The diploid phase is reduced to just the zygote, which immediately undergoes meiosis.
In haplontic organisms, the dominant, free-living, photosynthetic plant body is the gametophyte (n). The only diploid cell is the zygote (2n) — it undergoes meiosis immediately (called zygotic meiosis) to produce haploid spores that grow back into the gametophyte. There is no multicellular sporophyte.
In the diplontic pattern, the free-living plant body is the diploid sporophyte. The gametophyte is reduced to a few cells. This is the pattern seen in all seed plants.
In diplontic organisms, the dominant, free-living plant body is the sporophyte (2n). The gametophyte is extremely reduced — in angiosperms, the male gametophyte is just the pollen grain (2-3 cells) and the female gametophyte is the embryo sac (7 cells). Meiosis is gametic in animals but sporic in plants.
Dominant phase — sporophyte (2n) — the tree/plant you see
In the haplo-diplontic pattern, BOTH the gametophyte and sporophyte are multicellular. One phase may be more prominent than the other. Bryophytes and pteridophytes follow this pattern.
This is the 'classic' alternation of generations where both phases are multicellular and visible. In bryophytes, the gametophyte dominates and the sporophyte is attached to it. In pteridophytes, the roles reverse — the sporophyte dominates and the gametophyte (prothallus) is a small, independent structure.
Both gametophyte and sporophyte are multicellular, free-living (or at least well-developed)
Bryophytes — gametophyte dominant, sporophyte dependent (attached to gametophyte)
Pteridophytes — sporophyte dominant, gametophyte independent but small (prothallus)
Some algae — Ectocarpus, Polysiphonia, kelps show haplo-diplontic cycles
Classification Summary — All five plant groups compared at a glance
A comprehensive comparison of the five major plant groups: Algae, Bryophytes, Pteridophytes, Gymnosperms, and Angiosperms — across body type, vascular tissue, seeds, dominant phase, and reproductive features. This is the ultimate revision table for Plant Kingdom.
The Five-Group Comparison Table
Every feature that NEET can test about plant groups, organized into one comparison table.
The plant kingdom shows clear evolutionary trends: increasing sporophyte dominance, vascular tissue development, seed evolution, and reduced dependence on water.
The evolution of plants shows a clear progressive trend from simple aquatic forms to complex terrestrial forms. Each new group added a critical adaptation that made land life more successful.
Plants are broadly classified into Cryptogams (without seeds — algae, bryophytes, pteridophytes) and Phanerogams (with seeds — gymnosperms, angiosperms).
An older but still NEET-relevant classification divides plants into Cryptogams ('hidden reproduction' — they reproduce by spores, no seeds) and Phanerogams ('visible reproduction' — they reproduce by seeds).