Science: Biology — Plant Kingdom

Plant Kingdom (Plantae) is a regularly tested topic in Kerala PSC Science sections. Questions cover classification, photosynthesis, plant hormones, economic importance, and diseases. These notes are based on NCERT Biology (Class 11-12).

Classification of Plant Kingdom

Plants are classified based on body structure, vascular tissue, seed formation, and flower production.

Group	Features	Examples
Thallophyta (Algae)	No true roots, stems, leaves; aquatic mostly; autotrophic	Spirogyra, Ulothrix, Chlamydomonas, Ulva
Bryophyta	”Amphibians of plant kingdom”; no vascular tissue; need water for reproduction	Mosses (Funaria), Liverworts (Marchantia), Hornworts
Pteridophyta	First vascular plants (xylem, phloem); no seeds; spore reproduction	Ferns (Dryopteris), Horsetails (Equisetum), Club mosses (Selaginella)
Gymnosperms	”Naked seeds” (not enclosed in fruit); vascular; mostly evergreen	Pine (Pinus), Cycas, Deodar (Cedrus), Ginkgo
Angiosperms	”Enclosed seeds” (in fruit); flowering plants; most diverse group	All flowering plants — rice, mango, rose, wheat

Angiosperms: Monocots vs Dicots

Feature	Monocotyledons	Dicotyledons
Cotyledons	One	Two
Leaf venation	Parallel	Reticulate (net-like)
Root system	Fibrous	Tap root
Flower parts	In multiples of 3	In multiples of 4 or 5
Vascular bundles	Scattered	In a ring
Secondary growth	Absent (usually)	Present
Examples	Rice, wheat, maize, coconut, banana, bamboo	Mango, pea, sunflower, rose, neem

Photosynthesis

The process by which green plants convert light energy into chemical energy (glucose).

Aspect	Detail
Equation	6CO2 + 6H2O + light energy → C6H12O6 + 6O2
Site	Chloroplasts (in mesophyll cells of leaves)
Pigment	Chlorophyll (absorbs red and blue light; reflects green)
Two phases	Light reaction (in thylakoid membranes) and Dark reaction (in stroma)

Light Reaction vs Dark Reaction (Calvin Cycle)

Feature	Light Reaction	Dark Reaction (Calvin Cycle)
Location	Thylakoid membranes	Stroma of chloroplast
Light required?	Yes	No (but occurs in daytime too)
Products	ATP, NADPH, O2	Glucose (C6H12O6)
Water split?	Yes (photolysis — source of O2)	No
CO2 fixed?	No	Yes (CO2 fixation)
Discovered by	Hill (Hill reaction)	Melvin Calvin (Nobel Prize 1961)

Types of Photosynthesis

Type	CO2 Fixation	First Product	Plants
C3 (Calvin cycle)	RuBisCO enzyme	3-PGA (3-carbon)	Rice, wheat, most plants
C4 (Hatch-Slack)	PEP carboxylase	OAA (4-carbon)	Maize, sugarcane, sorghum
CAM	Stomata open at night	Malic acid stored	Cactus, pineapple, succulents

Plant Hormones (Phytohormones)

Hormone	Function	Discovery/Notes
Auxin (IAA)	Cell elongation; apical dominance; phototropism; root initiation	Discovered by F.W. Went; produced in shoot tips
Gibberellin (GA)	Stem elongation; breaking seed dormancy; induces flowering; parthenocarpy	Discovered from Gibberella fungus (rice disease)
Cytokinin	Cell division; delays senescence (aging); promotes lateral bud growth	Kinetin first discovered; works opposite to auxin in dominance
Abscisic Acid (ABA)	“Stress hormone”; causes stomatal closure; promotes dormancy; leaf abscission	Inhibits growth; increases during drought
Ethylene	Fruit ripening; leaf fall; flower wilting; senescence	Only gaseous hormone; used commercially for ripening

Practical Applications of Plant Hormones

Application	Hormone Used
Rooting powder for cuttings	Auxin (IBA, NAA)
Seedless fruits (parthenocarpy)	Gibberellin, Auxin
Weedkiller (synthetic)	2,4-D (synthetic auxin)
Fruit ripening acceleration	Ethylene (Ethephon spray)
Delaying fruit ripening	Cytokinin
Breaking potato dormancy	Gibberellin

Plant Nutrition

Essential Elements

Category	Elements
Macronutrients	C, H, O, N, P, K, Ca, Mg, S (9 elements needed in large quantities)
Micronutrients	Fe, Mn, Zn, Cu, Mo, B, Cl, Ni (8 elements needed in trace amounts)

Deficiency Symptoms

Nutrient	Deficiency Symptom
Nitrogen (N)	Yellowing of older leaves (chlorosis); stunted growth
Phosphorus (P)	Purple/dark green leaves; poor root development
Potassium (K)	Leaf margin scorching; weak stems
Iron (Fe)	Interveinal chlorosis in young leaves
Magnesium (Mg)	Interveinal chlorosis in older leaves (Mg is part of chlorophyll)
Calcium (Ca)	Death of growing tips; blossom end rot

Economic Botany — Important Plants

Plant	Family	Economic Use
Rice (Oryza sativa)	Poaceae (Gramineae)	Staple cereal; paddy cultivation
Wheat (Triticum aestivum)	Poaceae	Major food grain
Cotton (Gossypium)	Malvaceae	Textile fibre
Rubber (Hevea brasiliensis)	Euphorbiaceae	Natural rubber (latex); major crop in Kerala
Tea (Camellia sinensis)	Theaceae	Beverage; grown in Assam, Darjeeling, Nilgiris
Coffee (Coffea arabica)	Rubiaceae	Beverage; Karnataka, Kerala (Wayanad)
Coconut (Cocos nucifera)	Arecaceae (Palmae)	Oil, coir, copra; “Tree of Life”; Kerala state tree
Pepper (Piper nigrum)	Piperaceae	”Black Gold” / “King of Spices”; native to Kerala
Cardamom (Elettaria cardamomum)	Zingiberaceae	”Queen of Spices”; Idukki district, Kerala
Turmeric (Curcuma longa)	Zingiberaceae	Spice and medicine; curcumin is active compound
Jute (Corchorus)	Tiliaceae	”Golden fibre”; West Bengal, Bihar
Sugarcane (Saccharum officinarum)	Poaceae	Sugar production; UP largest producer

Medicinal Plants

Plant	Medicinal Use
Neem (Azadirachta indica)	Antibacterial, antifungal; pesticide (azadirachtin)
Tulsi (Ocimum sanctum)	Respiratory ailments, immunity booster
Turmeric (Curcuma longa)	Anti-inflammatory (curcumin); wound healing
Cinchona	Source of quinine (antimalarial drug)
Rauwolfia serpentina	Source of reserpine (treats hypertension)
Aloe vera	Skin healing, digestive health
Ashwagandha (Withania somnifera)	Adaptogen; stress relief; used in Ayurveda
Vinca rosea (Catharanthus roseus)	Vincristine, vinblastine — anti-cancer drugs

Plant Diseases

Disease	Causative Agent	Crop Affected
Blast of Rice	Magnaporthe grisea (fungus)	Rice
Rust of Wheat	Puccinia graminis (fungus)	Wheat
Late Blight of Potato	Phytophthora infestans (oomycete)	Potato (caused Irish Famine 1845)
Citrus Canker	Xanthomonas citri (bacterium)	Citrus fruits
Tobacco Mosaic	TMV (Tobacco Mosaic Virus)	Tobacco; first virus discovered (Ivanovsky, 1892)
Wilt of Cotton	Fusarium oxysporum (fungus)	Cotton
Black Rot of Crucifers	Xanthomonas campestris (bacterium)	Cabbage, cauliflower
Tungro Disease	Virus (transmitted by green leafhopper)	Rice

Plant Reproduction

Type	Method	Examples
Vegetative (Asexual)	Stem cutting	Rose, sugarcane
	Layering	Jasmine, bougainvillea
	Grafting	Mango, citrus
	Budding	Rose
	Tuber	Potato (eyes are buds)
	Rhizome	Ginger, turmeric
	Bulb	Onion, garlic
Sexual	Seed formation (pollination + fertilisation)	Most flowering plants

Pollination Types

Type	Agent	Examples
Anemophily	Wind	Grasses, wheat, rice, maize
Entomophily	Insects	Sunflower, mustard, apple
Hydrophily	Water	Vallisneria, Hydrilla
Ornithophily	Birds	Bombax (red silk cotton)
Chiropterophily	Bats	Bauhinia, Kigelia

Quick Revision — PSC Frequently Asked

Question	Answer
Amphibians of plant kingdom?	Bryophyta
First vascular plants?	Pteridophyta
Photosynthesis pigment?	Chlorophyll
Gas released in photosynthesis?	Oxygen (O2)
Only gaseous plant hormone?	Ethylene
Stress hormone of plants?	Abscisic Acid (ABA)
Fruit ripening hormone?	Ethylene
Largest flower in the world?	Rafflesia arnoldii
Smallest flowering plant?	Wolffia (duckweed)
Rubber plant family?	Euphorbiaceae
Coconut family?	Arecaceae (Palmae)
“Black Gold” spice?	Pepper (Piper nigrum)
Anti-cancer drug from plant?	Vincristine from Vinca rosea
Quinine source?	Cinchona bark
First virus discovered?	TMV (Tobacco Mosaic Virus), by Ivanovsky (1892)
Irish Famine caused by?	Late blight of potato (Phytophthora infestans)