NEET BiologyNCERT Class 11Chapter 3

Plant Kingdom: NEET notes

This chapter takes Whittaker's Kingdom Plantae apart group by group. It opens with how plant classification moved from artificial systems to natural and then phylogenetic ones, helped today by numerical taxonomy, cytotaxonomy and chemotaxonomy. It then describes the algae and their three classes, the bryophytes (liverworts and mosses), the pteridophytes, the gymnosperms and, briefly, the angiosperms, following one thread throughout: which phase of the life cycle is the main plant, and how much each group still needs water to reproduce.

What NEET asks

NEET usually takes a couple of questions from this chapter. The favourites are Table 3.1 (pigments, stored food, wall and flagella of green, brown and red algae), isogamy, anisogamy and oogamy with their examples, the commercial products of algae (algin, carrageen, agar, Chlorella), the dominant haploid gametophyte of bryophytes, gemmae and protonema, the dominant sporophyte and prothallus of pteridophytes, heterospory in Selaginella and Salvinia as a precursor to the seed habit, the four pteridophyte classes with examples, and gymnosperm features such as coralloid roots of Cycas, mycorrhiza of Pinus, and pollen grains and ovules on cones.

1. How plant classification changed

NCERT §3 (introduction)

Kingdom Plantae today holds algae, bryophytes, pteridophytes, gymnosperms and angiosperms. Fungi, and the walled members of Monera and Protista, were once counted as plants but have now been removed from the kingdom.
So cyanobacteria, still often called blue-green algae, are no longer treated as algae at all; they are prokaryotes in Monera.
The earliest schemes used only gross external features such as habit, colour, and the number and shape of leaves. They leaned mainly on vegetative characters, or on the structure of the androecium, which was the basis of Linnaeus's system.
Such systems were artificial. Because they rested on a handful of characters, they could split species that are closely related. They also weighted vegetative and sexual characters equally, although vegetative characters are the ones the environment changes most easily.
Natural systems followed. They grouped plants by natural affinities, using internal features such as ultrastructure, anatomy, embryology and phytochemistry as well as external form. George Bentham and Joseph Dalton Hooker gave such a system for flowering plants.
Phylogenetic systems, built on evolutionary relationships, are the ones accepted now. They assume that members of one taxon descend from a common ancestor.
Numerical taxonomy, easily run on computers, uses every observable character. Each character is given a number or code and the data are processed, so all characters count equally and hundreds can be handled at once.
Cytotaxonomy uses cell information such as chromosome number, structure and behaviour. Chemotaxonomy uses the chemical constituents of a plant to settle confusing cases. Both are especially useful where fossil evidence is missing.

2. Algae: body and reproduction

NCERT §3.1

Algae are simple, thalloid, autotrophic organisms that carry chlorophyll. Most live in water, fresh or marine, but some grow on moist stones, soil and wood, some live with fungi in lichens, and some live on animals such as the sloth bear.
Their size and form vary a lot: colonial Volvox, filamentous Ulothrix and Spirogyra, and marine kelps with very large plant bodies.
Vegetative reproduction is by fragmentation; every fragment grows into a new thallus.
Asexual reproduction is by spores of several kinds. Zoospores are the commonest; they carry flagella, swim, and germinate into new plants.
Sexual reproduction is the fusion of two gametes. When the two are of similar size it is isogamy: the gametes may both be flagellated (Ulothrix) or both lack flagella (Spirogyra).
When two gametes of unlike size fuse it is anisogamy, as in species of Eudorina.
When a large, non-motile female gamete fuses with a smaller, motile male gamete it is oogamy, as in Volvox and Fucus.

3. Why algae matter

NCERT §3.1

Algae carry out at least half of all carbon dioxide fixation on earth through photosynthesis.
Because they photosynthesise, they raise the dissolved oxygen in the water around them.
As primary producers of energy-rich compounds, they form the base of the food cycles of all aquatic animals.
About 70 species of marine algae are eaten as food, among them many species of Porphyra, Laminaria and Sargassum.
Some marine brown and red algae make large amounts of hydrocolloids, substances that hold water. Algin comes from brown algae and carrageen from red algae; both are used commercially.
Agar is obtained from Gelidium and Gracilaria. It is used to grow microbes in the laboratory and in making ice-creams and jellies.
Chlorella is a single-celled, protein-rich alga used as a food supplement, even by people travelling in space.
Algae fall into three main classes: Chlorophyceae, Phaeophyceae and Rhodophyceae.

4. Green, brown and red algae

NCERT §3.1.1–3.1.3, Table 3.1

Chlorophyceae (green algae) may be unicellular, colonial or filamentous. They are grass green because chlorophyll a and b dominate, held in definite chloroplasts whose shape varies: discoid, plate-like, reticulate, cup-shaped, spiral or ribbon-like.
Most green algae have one or more pyrenoids in their chloroplasts; these storage bodies hold protein as well as starch. Some store oil droplets. The rigid wall has cellulose inside and pectose outside.
Green algae reproduce vegetatively by fragmentation, asexually by flagellated zoospores formed in zoosporangia, and sexually by isogamy, anisogamy or oogamy. Examples: Chlamydomonas, Volvox, Ulothrix, Spirogyra, Chara.
Phaeophyceae (brown algae) are mostly marine and range from simple branched filaments (Ectocarpus) to heavily branched kelps that can grow to 100 metres. Their pigments are chlorophyll a and c, carotenoids and xanthophylls; the amount of fucoxanthin sets the colour, from olive green to shades of brown.
Brown algae store food as laminarin or mannitol. The cellulose wall usually has a gelatinous algin coat outside. The body is anchored by a holdfast and has a stalk (stipe) and a leaf-like photosynthetic frond.
Brown algae make pear-shaped (pyriform) zoospores and gametes with two unequal flagella attached at the side. Sexual reproduction may be isogamous, anisogamous or oogamous; in oogamous species the gametes unite inside the oogonium. Examples: Ectocarpus, Dictyota, Laminaria, Sargassum, Fucus.
Rhodophyceae (red algae) owe their colour to r-phycoerythrin. Most are marine, more common in warmer seas, and grow both near the lit surface and at great depths where little light reaches.
Red algae store floridean starch, which resembles amylopectin and glycogen in structure. They reproduce vegetatively by fragmentation, asexually by non-motile spores, and sexually by oogamy with non-motile gametes and elaborate changes after fertilisation. Examples: Polysiphonia, Porphyra, Gracilaria, Gelidium.
Table 3.1 in brief. Green: chlorophyll a, b; starch; cellulose wall; 2–8 equal apical flagella; fresh, brackish and salt water. Brown: chlorophyll a, c and fucoxanthin; mannitol and laminarin; cellulose and algin; 2 unequal lateral flagella; mostly salt water, rarely fresh. Red: chlorophyll a, d and phycoerythrin; floridean starch; cellulose, pectin and polysulphate esters; no flagella; mostly salt water, some fresh.

5. Bryophytes: amphibians of the plant kingdom

NCERT §3.2

Bryophytes are the mosses and liverworts, common in moist, shaded places in the hills.
They are called the amphibians of the plant kingdom: they live on land, in soil, but need water for sexual reproduction. They matter in plant succession on bare rock and soil.
The body is more differentiated than an alga's. It is thallus-like, lying flat or standing erect, and is fixed by unicellular or multicellular rhizoids. There are no true roots, stems or leaves, only root-like, stem-like and leaf-like parts.
The main plant body is haploid and makes gametes, so it is the gametophyte. The sex organs are multicellular.
The male sex organ, the antheridium, makes biflagellate antherozoids. The female sex organ, the archegonium, is flask-shaped and makes a single egg.
Antherozoids are released into water, reach the archegonium, and one fuses with the egg to form a zygote. The zygote does not undergo meiosis at once; it grows into a multicellular sporophyte.
The sporophyte is not free-living. It stays attached to the photosynthetic gametophyte and draws food from it. Some of its cells undergo meiosis to form haploid spores, which germinate into new gametophytes.
Economic importance is small overall. Some mosses feed herbivorous mammals and birds. Sphagnum gives peat, long used as fuel, and is used as packing for sending living material because it holds water.
Mosses and lichens are the first organisms to colonise rock. They break the rock down so higher plants can grow later. Dense moss mats soften falling rain and prevent soil erosion.
Bryophytes are divided into liverworts and mosses.

6. Liverworts and mosses

NCERT §3.2.1–3.2.2

Liverworts grow in moist, shady spots: stream banks, marshy ground, damp soil, tree bark and deep in woods.
A thalloid liverwort such as Marchantia has a dorsiventral thallus pressed flat against the ground. Leafy liverworts carry tiny leaf-like appendages in two rows on stem-like parts.
Liverworts reproduce asexually by fragmentation of the thallus, or by gemmae (singular gemma): green, multicellular asexual buds formed in small cups, the gemma cups, on the thallus. Gemmae break off and grow into new plants.
Male and female sex organs may be on one thallus or on separate thalli. The sporophyte has a foot, a seta and a capsule; spores form in the capsule after meiosis and grow into free-living gametophytes.
In mosses the gametophyte is the main stage, and it has two parts. The protonema grows straight from a spore and is creeping, green, branched and often filamentous.
The leafy stage grows as a lateral bud from the secondary protonema. It has upright, slender axes with spirally arranged leaves, held in the soil by multicellular, branched rhizoids, and it carries the sex organs.
Mosses reproduce vegetatively by fragmentation and by budding in the secondary protonema. Antheridia and archegonia form at the tips of the leafy shoots.
After fertilisation the zygote forms a sporophyte of foot, seta and capsule, more elaborate than a liverwort's. Spores form in the capsule after meiosis, and mosses have an elaborate way of dispersing them. Examples: Funaria, Polytrichum, Sphagnum.

7. Pteridophytes

NCERT §3.3

Pteridophytes include horsetails and ferns. They are used in medicine and as soil-binders, and many are grown as ornamentals.
In evolution they are the first land plants with vascular tissues, xylem and phloem. They grow in cool, damp, shady places, though some do well in sandy soil.
In bryophytes the gametophyte dominates; in pteridophytes the main plant is the sporophyte, with a true root, stem and leaves, each with well-developed vascular tissue.
Selaginella has small leaves (microphylls); ferns have large ones (macrophylls).
Sporangia sit on leaf-like sporophylls. In some plants the sporophylls are packed into compact strobili or cones, as in Selaginella and Equisetum. Spore mother cells in the sporangia divide by meiosis to make spores.
A spore grows into a small, inconspicuous but multicellular, free-living and mostly photosynthetic thalloid gametophyte, the prothallus. It needs cool, damp, shady conditions.
The prothallus bears antheridia and archegonia. Water carries the antherozoids from the antheridia to the mouth of the archegonium, where one fuses with the egg to give a zygote that grows into the dominant sporophyte.
Because the gametophyte needs such particular conditions, and fertilisation needs water, living pteridophytes are confined to narrow geographical areas.
The group has four classes. Psilopsida: Psilotum. Lycopsida: Selaginella and Lycopodium. Sphenopsida: Equisetum. Pteropsida: Dryopteris, Pteris and Adiantum.

8. Homospory, heterospory and the seed habit

NCERT §3.3

Most pteridophytes make spores of only one kind; they are homosporous.
Selaginella and Salvinia make two kinds: large megaspores (macrospores) and small microspores. They are heterosporous.
Megaspores grow into female gametophytes and microspores into male gametophytes.
In heterosporous plants the female gametophyte stays on the parent sporophyte for a variable time, and the zygote grows into a young embryo inside that female gametophyte.
This is a forerunner of the seed habit, which is regarded as an important step in evolution.

9. Gymnosperms: naked seeds

NCERT §3.4

Gymnosperm means naked seed (gymnos: naked, sperma: seed). The ovules have no ovary wall around them and stay exposed before and after fertilisation, so the seeds that follow are uncovered.
Gymnosperms are medium or tall trees and shrubs. The giant redwood Sequoia is among the tallest tree species.
Roots are usually tap roots. In Pinus the roots associate with fungi as mycorrhiza. In Cycas, small specialised coralloid roots house nitrogen-fixing cyanobacteria.
Stems may be unbranched (Cycas) or branched (Pinus, Cedrus). Leaves may be simple or compound; the pinnate leaves of Cycas last a few years.
Leaves are built to withstand extremes of temperature, humidity and wind. Conifer needles cut the surface area, and a thick cuticle and sunken stomata cut water loss further.

10. Gymnosperm cones, pollen and ovules

NCERT §3.4

Gymnosperms are heterosporous and make haploid microspores and megaspores, inside sporangia borne on sporophylls. The sporophylls spiral along an axis to form loose or compact strobili (cones).
Cones with microsporophylls and microsporangia are male (microsporangiate) strobili. Each microspore becomes a male gametophyte reduced to a few cells, the pollen grain, which develops inside the microsporangium.
Cones with megasporophylls carrying ovules (megasporangia) are female (macrosporangiate) strobili. Pinus bears male and female cones on the same tree; in Cycas, male cones and megasporophylls are on separate trees.
One cell of the nucellus becomes the megaspore mother cell. The nucellus wrapped in its protective envelopes is the ovule.
The megaspore mother cell divides by meiosis into four megaspores. One of them, still inside the megasporangium, grows into a multicellular female gametophyte bearing two or more archegonia, and this gametophyte too stays inside the megasporangium.
Unlike bryophytes and pteridophytes, neither gametophyte of a gymnosperm lives independently; both stay within sporangia on the sporophyte.
Pollen grains released from the microsporangium are carried by air currents to the opening of the ovules. A pollen tube carrying male gametes grows towards the archegonia and releases them near the archegonium's mouth.
After fertilisation the zygote becomes an embryo and the ovule becomes a seed, which stays uncovered.

11. Angiosperms

NCERT §3.5

In angiosperms, the flowering plants, pollen grains and ovules develop in specialised structures called flowers. The ovules are not naked as in gymnosperms.
The seeds of angiosperms are enclosed in fruits.
Angiosperms form an exceptionally large group that lives in a wide range of habitats.
They range in size from the tiny Wolffia to Eucalyptus trees taller than 100 metres.
They give us food, fodder, fuel, medicines and many other commercially important products.
The group splits into two classes: monocotyledons and dicotyledons.

Must-know facts

Plantae now excludes fungi and the walled members of Monera and Protista; cyanobacteria are not algae.
Artificial systems (e.g. Linnaeus, androecium-based) used few, mostly vegetative characters; natural systems (Bentham and Hooker) added anatomy, embryology and phytochemistry; phylogenetic systems use evolutionary relationships.
Numerical taxonomy gives every character equal weight; cytotaxonomy uses chromosomes; chemotaxonomy uses chemical constituents.
Algae: chlorophyll-bearing, simple, thalloid, autotrophic, mostly aquatic.
Isogamy: Ulothrix (flagellated gametes), Spirogyra (non-flagellated). Anisogamy: Eudorina. Oogamy: Volvox, Fucus.
Algae do at least half of earth's CO₂ fixation.
Algin: brown algae. Carrageen: red algae. Agar: Gelidium and Gracilaria. Chlorella: protein-rich food supplement.
Green algae: chlorophyll a, b; starch; pyrenoids; wall of cellulose inside, pectose outside.
Brown algae: chlorophyll a, c, fucoxanthin; laminarin or mannitol; algin coat; holdfast, stipe, frond; pear-shaped gametes with two unequal lateral flagella.
Red algae: r-phycoerythrin; floridean starch; no flagella; oogamous; can live at great depths.
Bryophytes: amphibians of the plant kingdom; haploid gametophyte is the main plant; no true roots, stems or leaves.
Bryophyte sporophyte stays attached to and fed by the gametophyte.
Antheridium: biflagellate antherozoids. Archegonium: flask-shaped, one egg.
Sphagnum gives peat (fuel, packing material). Mosses and lichens colonise bare rock first.
Marchantia: thalloid, dorsiventral liverwort; gemmae in gemma cups.
Moss gametophyte: protonema (from spore) then leafy stage (lateral bud on secondary protonema).
Sporophyte of bryophytes: foot, seta, capsule; mosses' is more elaborate than liverworts'.
Pteridophytes: first land plants with xylem and phloem; main plant is the sporophyte with true root, stem, leaves.
Microphylls in Selaginella, macrophylls in ferns; strobili in Selaginella and Equisetum.
Pteridophyte gametophyte = prothallus: small, free-living, mostly photosynthetic; water needed for fertilisation.
Four pteridophyte classes: Psilopsida (Psilotum), Lycopsida (Selaginella, Lycopodium), Sphenopsida (Equisetum), Pteropsida (Dryopteris, Pteris, Adiantum).
Heterospory in Selaginella and Salvinia; embryo develops inside retained female gametophyte, a precursor to the seed habit.
Gymnosperms: naked ovules and seeds; Pinus mycorrhiza; Cycas coralloid roots with N₂-fixing cyanobacteria.
Pollen grain = reduced male gametophyte; ovule = nucellus plus envelopes; female gametophyte bears two or more archegonia.
Angiosperms: pollen and ovules in flowers, seeds in fruits; Wolffia to Eucalyptus; dicots and monocots.

Common traps

Calling cyanobacteria (blue-green algae) algae.

They are prokaryotes in Monera; the chapter says they are no longer algae.

Giving Spirogyra as an example of anisogamy because its gametes do not swim.

Spirogyra's gametes are similar in size, so it is isogamous; non-flagellated does not mean unequal.

Linking algin with red algae and carrageen with brown algae.

Algin comes from brown algae, carrageen from red algae.

Saying red algae have flagellated gametes.

Rhodophyceae have no flagella; their spores and gametes are non-motile.

Giving brown algae chlorophyll a and b.

Brown algae have chlorophyll a and c with fucoxanthin; green algae have a and b; red algae have a and d.

Thinking the bryophyte sporophyte is free-living.

It stays attached to the gametophyte and depends on it for food.

Calling the leafy moss plant diploid.

The leafy stage is part of the haploid gametophyte; only the sporophyte (foot, seta, capsule) is diploid.

Saying the pteridophyte gametophyte is dependent on the sporophyte.

The prothallus is free-living and mostly photosynthetic; dependence of the female gametophyte appears only in heterosporous forms and seed plants.

Listing Equisetum under Lycopsida.

Equisetum is Sphenopsida; Selaginella and Lycopodium are Lycopsida.

Saying Pinus bears male and female cones on different trees.

Pinus bears both on the same tree; Cycas has male cones and megasporophylls on separate trees.

Swapping the root partners of Pinus and Cycas.

Pinus: mycorrhizal fungi. Cycas: coralloid roots with nitrogen-fixing cyanobacteria.

Key terms

Artificial system: A classification based on a few, mostly vegetative, external characters.
Natural system: A classification based on natural affinities, using external and internal features.
Phylogenetic system: A classification based on evolutionary relationships and common ancestry.
Numerical taxonomy: Computer-based classification giving equal weight to every coded character.
Cytotaxonomy: Classification using chromosome number, structure and behaviour.
Chemotaxonomy: Classification using a plant's chemical constituents.
Thallus: A plant body not divided into true root, stem and leaves.
Zoospore: A flagellated, motile asexual spore.
Isogamy: Fusion of two gametes of similar size.
Anisogamy: Fusion of two gametes of unlike size.
Oogamy: Fusion of a large non-motile female gamete with a small motile male gamete.
Pyrenoid: A storage body in green algal chloroplasts holding protein and starch.
Hydrocolloid: A water-holding substance such as algin or carrageen.
Holdfast: The part that anchors a brown alga to the substratum.
Gametophyte: The haploid, gamete-making phase of a plant.
Sporophyte: The diploid phase that makes spores by meiosis.
Antheridium: Male sex organ; in bryophytes it makes biflagellate antherozoids.
Archegonium: Flask-shaped female sex organ holding a single egg.
Gemma: A green, multicellular asexual bud formed in a gemma cup of a liverwort.
Protonema: The creeping, green, filamentous first stage of a moss gametophyte.
Sporophyll: A leaf-like structure that bears sporangia.
Strobilus: A compact cone of sporophylls.
Prothallus: The small, free-living gametophyte of a pteridophyte.
Heterospory: Production of two kinds of spores, megaspores and microspores.
Coralloid roots: Specialised Cycas roots housing nitrogen-fixing cyanobacteria.
Pollen grain: The reduced male gametophyte of a seed plant.
Ovule: The nucellus (megasporangium) with its protective envelopes.

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