Plant Kingdom – Complete Notes | Biology

Classification of Plant Kingdom

2 Major Divisions — Cryptogamae & Phanerogamae

Cryptogamae — "hidden sex" — reproductive organs NOT visible to naked eye; includes Algae, Bryophytes, Pteridophytes
Phanerogamae — "visible sex/seeds" — reproductive organs visible; seeds present; includes Gymnosperms and Angiosperms
Phanerogamae also called Spermatophyta (seed-bearing plants)
Algae, Bryophytes, Pteridophytes have NO seeds

Division	Sub-division	Sex Organs	Seeds	Examples
Cryptogamae	Thallophyta (Algae)	Hidden/microscopic	Absent	Spirogyra, Ulva, Chara, Sargassum, Polysiphonia
	Bryophyta	Jacketed sex organs	Absent	Marchantia, Funaria, Polytrichum
	Pteridophyta	Jacketed sex organs	Absent	Pteris, Lycopodium, Selaginella, Equisetum
Phanerogamae	Gymnospermae	Visible — Cones	Naked seed (no fruit)	Pinus, Cycas, Cedrus, Sequoia, Ginkgo
	Angiospermae	Flowers	Enclosed in fruit	Mango, Neem, Wheat, Rice, all flowering plants

Tracheophyta (Vascular Bundle Present)

Tracheophyta = plants with vascular bundles (xylem + phloem) — Pteridophytes, Gymnosperms, Angiosperms
All Tracheophytes are NOT necessarily Spermatophytes (Pteridophytes are Tracheophytes but no seeds)
Algae and Bryophytes = NO vascular bundle (Non-tracheophytes)

Algae — General Features

General Features of Algae

Chlorophyll-bearing, simple, thalloid (no true root, stem, leaf)
Mainly aquatic (fresh water or marine); some on moist soil, tree bark
Nutrition: Oxygenic photosynthesis
Mostly haploid organisms — main plant body is haploid (gametophyte dominant)
No jacketed sex organs (sex organs are single-celled)
Life cycle = Haplontic — zygote is only diploid stage; undergoes meiosis (zygotic meiosis) to give haploid spores
Holdfast — basal attachment structure (present in marine algae like Kelp, Ectocarpus, Polysiphonia; absent in Spirogyra)

3 Types of Algae — Comparison

Feature	Green Algae (Chlorophyceae)	Brown Algae (Phaeophyceae)	Red Algae (Rhodophyceae)
Pigments	Chl a, Chl b	Chl a, Chl c, Fucoxanthin (brown)	Chl a, Chl d, Phycoerythrin (red), Phycocyanin
Stored food	Starch (true starch)	Mannitol, Laminarin	Floridean starch (similar to amylopectin)
Cell wall	Cellulose	Cellulose + Algin	Cellulose + Pectin
Flagella	2 equal (isokont)	2 unequal (heterokont)	Absent (non-motile)
Habitat	Mostly fresh water; some marine	Mainly marine (ocean)	Mainly marine (deep sea)
Examples	Chlamydomonas, Spirogyra, Ulva, Volvox, Chara, Cladophora, Chlorella	Ectocarpus, Dictyota, Kelp, Laminaria, Sargassum, Fucus	Polysiphonia, Porphyra, Gelidium, Gracilaria
Economic uses	Food (Chlorella), fertilizer (Chara)	Algin (food industry), Kelp (iodine source)	Agar-agar (Gelidium, Gracilaria for culture media); Carrageenan

Q. Which algae is used to prepare agar-agar and what is it used for?

✅ Answer: Gelidium and Gracilaria (Red algae) — Agar is used as culture medium in microbiology labs, as food thickener

Explanation

Agar-agar is extracted from the cell walls of red algae, primarily Gelidium and Gracilaria. It is a complex polysaccharide (agarose + agaropectin) that forms a gel when dissolved in hot water and cooled. Its most important use is as a solidifying agent in microbiological culture media — bacteria and fungi grow on agar plates. It is also used in food industry as a thickener, gelling agent in desserts, and as a growth medium for plant tissue culture. Gelidium and Gracilaria store Floridean starch (not true starch) — similar to amylopectin in structure. Red algae are predominantly marine and found in deeper water because their phycoerythrin pigment can absorb the blue-green light that penetrates deepest into the ocean.

Bryophytes — Amphibians of Plant Kingdom

General Features

Called "Amphibians of Plant Kingdom" — can live on land but need water for sexual reproduction (fertilization)
No true root, stem, leaf — have rhizoids (root-like), axis (stem-like), leaf-like structures
NO vascular tissue (no xylem, no phloem) — non-tracheophytes
Main plant body is gametophyte (haploid, green, independent)
Sporophyte is dependent on gametophyte for nutrition
Life cycle = Haplodiplontic — both gametophyte and sporophyte are multicellular
Dominant stage = Gametophyte (haploid)
Jacketed sex organs: Male = Antheridium; Female = Archegonium
Fertilization requires water (motile male gametes = antherozoids)
First land plants — Pioneer species in succession

Feature	Liverworts (Hepaticopsida)	Mosses (Bryopsida)
Body	Flat, thalloid, dorsiventral	Differentiated into stem and leaf-like structures
Examples	Marchantia, Riccia	Funaria, Polytrichum, Sphagnum
Vegetative reproduction	Gemmae (in gemma cups)	Fragmentation, protonema
Uses	—	Sphagnum = peat moss (fuel, packaging); moisture retention

Q. Why are Bryophytes called amphibians of the plant kingdom?

✅ Answer: They can live on land but require water for fertilization — male gametes swim to egg in presence of water

Explanation

Bryophytes are terrestrial plants — they can grow on land, rocks, moist soil, and even tree bark. However, they cannot complete their sexual reproduction without water. The male gametes (antherozoids) are flagellated and must swim through a film of water to reach the archegonium (female sex organ) to fertilize the egg. This dependence on water for fertilization, combined with their terrestrial habitat, earns them the title "amphibians of the plant kingdom" — just as amphibians can live on land but must return to water to reproduce. This is also why bryophytes are typically found in moist, shaded habitats. They were among the first plants to colonize land, but remained limited to moist environments due to this reproductive constraint.

Pteridophytes — First Vascular Land Plants

General Features

First plants with vascular tissue (xylem + phloem) — Tracheophytes
No seeds — seedless vascular plants
Main plant body = sporophyte (diploid, green, dominant, independent)
Gametophyte = small, prothallus (independent, green, needs shade and moisture)
Life cycle = Haplodiplontic — both generations multicellular
Dominant stage = Sporophyte (diploid)
Sex organs: Male = Antheridium; Female = Archegonium (jacketed)
Still require water for fertilization
Spores produced in sporangia on sporophylls (leaf-like structures bearing sporangia)

Class	Examples	Features
Psilopsida	Psilotum	Most primitive; no leaves, no roots
Lycopsida	Lycopodium, Selaginella	Leaves small (microphylls); Selaginella = heterosporous
Sphenopsida	Equisetum (Horsetail)	Jointed hollow stem; whorled leaves at nodes
Pteropsida	Pteris, Dryopteris, Adiantum	Large leaves (megaphylls); most familiar ferns

Homosporous vs Heterosporous Pteridophytes

Homosporous — all spores of same size and type → single type of gametophyte; e.g. Lycopodium, Equisetum, Pteris
Heterosporous — two types of spores: Microspores (small → male gametophyte) + Megaspores (large → female gametophyte); e.g. Selaginella, Salvinia
Heterospory is a precursor (evolutionary step) toward seed habit
In heterosporous pteridophytes: female gametophyte remains inside megasporangium = very close to seed condition!

Gymnosperms

General Features

Naked seed plants — ovules (megasporangia) are NOT enclosed in ovary; seeds exposed on megasporophylls
Dominant stage = Sporophyte (diploid)
Gametophyte = highly reduced, dependent on sporophyte
Life cycle = Diplontic — sporophyte dominant; gametophyte few cells
Heterosporous — Microsporophylls (male) + Megasporophylls (female) arranged in cones
Male cone (smaller) + Female cone (larger) often on same plant
Pollination = Wind (anemophily) — pollen grains carried by wind to female cone
NO double fertilization (unlike Angiosperms)
Endosperm is haploid (formed before fertilization)
Archegonium present (except Gnetum)

Feature	Cycas	Pinus
Type	Dioecious (separate male & female plants)	Monoecious (both cones on same plant)
Roots	Coralloid roots (with Cyanobacteria for N₂ fixation) + Mycorrhizal roots	Tap roots + Mycorrhizal roots
Leaves	Pinnate compound (like palm)	Needle-shaped (reduced, to minimize water loss)
Female cone	Megasporophylls (loosely arranged, not tight cone)	True woody female cone
Archegonium	Present	Present
Double fertilization	Absent	Absent

Gymnosperms — Seed Structure

Seed coat = old sporophyte (integument becomes seed coat)
Endosperm = female gametophyte (haploid) — already present before fertilization
Embryo = new sporophyte (diploid) — formed after fertilization
Seed = 3 generations: old sporophyte (seed coat) + gametophyte (endosperm) + new sporophyte (embryo)

Angiosperms

General Features

Enclosed seed plants — ovules enclosed in ovary → ovary becomes fruit after fertilization
Most evolved plant group; dominant flora on Earth
Reproductive organ = Flower
Double fertilization — unique to Angiosperms:
- 1st: Male gamete + Egg cell → Zygote (2n)
- 2nd: Male gamete + 2 Polar nuclei → Primary Endosperm Nucleus (3n) → Endosperm (triploid)
Endosperm = triploid (3n) — formed AFTER fertilization (unlike gymnosperm haploid endosperm)
Pollination: Wind, Water, Insects, Animals
2 classes: Monocots (1 cotyledon) + Dicots (2 cotyledons)

Feature	Monocots	Dicots
Cotyledons	1	2
Venation	Parallel	Reticulate (net-like)
Root system	Fibrous roots	Tap root
Flowers	Trimerous (3 or multiple of 3)	Tetramerous/Pentamerous (4 or 5)
Vascular bundles	Scattered in stem	Ring arrangement in stem
Examples	Wheat, Maize, Rice, Sugarcane, Onion, Banana	Mango, Neem, Pea, Mustard, Sunflower

Sex Organs in Plant Kingdom

Group	Male Sex Organ	Female Sex Organ	Jacketed?
Algae	Antheridium	Oogonium	Not jacketed (single-celled)
Bryophytes	Antheridium	Archegonium	Jacketed ✔
Pteridophytes	Antheridium	Archegonium	Jacketed ✔
Gymnosperms	Male cone (Microsporophyll → Pollen grains)	Archegonium (inside female cone)	Archegonium present (except Gnetum)
Angiosperms	Stamen (Microsporangia → Pollen)	Pistil (Megasporangia → Embryo sac)	No archegonium — most advanced

Jacketed Sex Organs — Definition

Jacketed sex organs = Sex organs surrounded by a protective layer (jacket) of sterile cells. Present in Bryophytes and Pteridophytes. Algae do NOT have jacketed sex organs. Angiosperms also lack archegonia.

Life Cycles — Types

Life Cycle Type	Dominant Stage	Meiosis Type	Groups
Haplontic	Gametophyte (n) dominant; sporophyte = only zygote (single-celled, 2n)	Zygotic meiosis (zygote undergoes meiosis immediately)	Most Algae (Spirogyra, Ulva)
Haplodiplontic	Both gametophyte and sporophyte are multicellular	Sporic meiosis (meiosis during spore formation)	Bryophytes (gametophyte dominant), Pteridophytes (sporophyte dominant)
Diplontic	Sporophyte (2n) dominant; gametophyte = few cells only	Gametic meiosis (meiosis during gamete formation)	Gymnosperms, Angiosperms; also some algae (Fucus)

Key Points on Life Cycles

Bryophytes — haplodiplontic; gametophyte = multicellular green, long-lived, independent; sporophyte = multicellular, short-lived, dependent on gametophyte
Pteridophytes — haplodiplontic; sporophyte = multicellular green, long-lived, independent; gametophyte (prothallus) = multicellular, short-lived, independent
Gymnosperms & Angiosperms — diplontic; sporophyte dominant; gametophyte = few cells, dependent on sporophyte, non-green
Ectocarpus (Brown alga) — exception among algae; shows haplodiplontic cycle
Polysiphonia (Red alga) — shows diplontic cycle (exception)
Most algae = haplontic; ALL algae are NOT haplontic

Q. What is the dominant phase in Bryophytes vs Pteridophytes?

✅ Answer: Bryophytes — Gametophyte (n) is dominant; Pteridophytes — Sporophyte (2n) is dominant

Explanation

Both Bryophytes and Pteridophytes show haplodiplontic life cycles — meaning both gametophyte and sporophyte generations are multicellular. However, they differ in which generation is dominant (larger, green, nutritionally independent). In Bryophytes (mosses, liverworts), the gametophyte is the main green plant you see — it is long-lived, large, and photosynthetically independent. The sporophyte is small, short-lived, and depends on the gametophyte for nutrition. In Pteridophytes (ferns), the opposite is true — the sporophyte is the large, green, dominant plant (the fern frond you recognize). The gametophyte (prothallus) is tiny, heart-shaped, short-lived, but independent. This shows an evolutionary trend: as plants evolved from Bryophytes to Pteridophytes to Gymnosperms/Angiosperms, the sporophyte became increasingly dominant and the gametophyte increasingly reduced and dependent.

Complete Comparison Table — All Plant Groups

Feature	Algae	Bryophytes	Pteridophytes	Gymnosperms	Angiosperms
Plant body	Thallus	Thallus/differentiated	Root, stem, leaf	Root, stem, leaf	Root, stem, leaf, flower
Vascular bundle	Absent	Absent	Present	Present	Present
Seeds	Absent	Absent	Absent	Present (naked)	Present (enclosed in fruit)
Dominant stage	Gametophyte (n)	Gametophyte (n)	Sporophyte (2n)	Sporophyte (2n)	Sporophyte (2n)
Gametophyte	Multicellular, green, independent	Multicellular, green, independent	Prothallus — multicellular, green, independent	Few cells, non-green, dependent	Few cells, non-green, dependent
Life cycle	Haplontic	Haplodiplontic	Haplodiplontic	Diplontic	Diplontic
Double fertilization	Absent	Absent	Absent	Absent	Present ✔
Endosperm ploidy	—	—	—	Haploid (n)	Triploid (3n)
Archegonium	Absent	Present	Present	Present (except Gnetum)	Absent

Quick Revision — Must-Know Points

Brown algae pigment → Fucoxanthin

Red algae food → Floridean starch

Agar source → Gelidium, Gracilaria (Red)

Algae flagella → Green=2 equal; Brown=2 unequal; Red=absent

Bryophytes = Amphibians of plant kingdom

Bryophyte dominant = Gametophyte

Pteridophyte dominant = Sporophyte

First vascular plants → Pteridophytes

Heterosporous pteridophyte → Selaginella, Salvinia

Precursor of seed habit → Heterospory

Naked seed → Gymnosperms

Gymnosperm endosperm → Haploid (n)

Angiosperm endosperm → Triploid (3n)

Double fertilization → Angiosperms only

Cycas root with Cyanobacteria → Coralloid roots

Life cycle Algae → Haplontic

Life cycle Bryophyte+Pterido → Haplodiplontic

Life cycle Gymno+Angio → Diplontic