Plant Life and Reproduction

Plant Kingdom

Plants are multicellular, eukaryotic organisms that perform photosynthesis (autotrophic). They are classified broadly as:

Group	Features	Examples
Thallophyta (Algae)	Simplest, no roots/stems/leaves	Spirogyra, Ulva
Bryophyta	First land plants, no vascular tissue, need water for reproduction	Moss, Marchantia
Pteridophyta	First vascular plants, no seeds (spores)	Fern, Horsetails
Gymnosperms	Vascular, naked seeds (no fruit)	Pinus, Cycas
Angiosperms	Vascular, seeds in fruit, flowers	All flowering plants

Angiosperms (flowering plants) are further divided:

• Monocots: 1 seed leaf (cotyledon), parallel leaf veins, fibrous roots — e.g., wheat, rice, maize, onion
• Dicots: 2 seed leaves, net-like leaf veins, tap root system — e.g., mango, pea, sunflower

Plant Morphology: Structure of a Flower

A typical flower has four whorls (parts) attached to the receptacle:

1. Calyx (sepals): Outermost, green, protective — collectively called the calyx
2. Corolla (petals): Colored, attracts pollinators — collectively called the corolla
3. Androecium (male reproductive organ): Multiple stamens
   • Anther: Produces pollen grains (contains male gametes)
   • Filament: Stalk supporting the anther
4. Gynoecium (female reproductive organ): One or more pistils/carpels
   • Stigma: Upper sticky surface — receives pollen
   • Style: Tube connecting stigma to ovary
   • Ovary: Contains ovules (each ovule contains an embryo sac with female gamete)
   • Ovule → after fertilization → becomes seed
   • Ovary → after fertilization → becomes fruit

Pollination

Pollination is the transfer of pollen grains from anther to stigma.

Types of Pollination

Self-pollination (Autogamy): Pollen from the same flower lands on its own stigma. Occurs in wheat, rice, oats, barley.

Cross-pollination (Xenogamy): Pollen from one flower lands on stigma of another flower of the same species. More common in nature, ensures genetic variation.

Agents of Pollination (Pollinators)

Agent	How it Works	Examples
Insects (Entomophily)	Bees, butterflies, moths are attracted to color and scent of flowers; pollen sticks to their body	Sunflower, mango
Wind (Anemophily)	Light, dry pollen; feathery stigmas to catch pollen	Wheat, rice, maize, grass
Water (Hydrophily)	Pollen floats on water to reach other flowers	Vallisneria, Hydrilla
Birds (Ornithophily)	Nectar-feeding birds carry pollen	Flame of the forest, Bombax
Bats (Chiropterophily)	Nocturnal pollinators	Night-flowering plants

Honey bee pollination is economically very important — about 75% of cultivated crops depend on bee pollination.

Adaptations for Pollination

In flowers:

• Bright colors and nectar to attract insects
• Scent (sometimes foul to attract flies)
• Nectar guides (markings on petals directing pollinators)
• Banner-like structures in legumes

In wind-pollinated flowers:

• Large feathery stigmas (to catch pollen)
• Light, dry pollen (easily carried by wind)
• Often inconspicuous (no bright petals)

Fertilization

After pollen lands on stigma:

1. Pollen grain germinates → forms pollen tube → grows down the style toward the ovary
2. Two male gametes travel down the pollen tube
3. Double fertilization (unique to angiosperms):
   • First male gamete + Egg cell (female gamete) → Zygote (→ embryo)
   • Second male gamete + Polar nuclei (2 polar nuclei fuse) → Endosperm (nutritive tissue for embryo)
4. Zygote develops inside the ovule → becomes seed (contains embryo, food, seed coat)
5. Ovary develops into fruit (protect seeds, aid dispersal)

Double fertilization is a defining characteristic of angiosperms and ensures efficient use of resources — only one pollen grain is needed to produce both embryo and food supply.

Seed Dispersal

Seeds need to be dispersed away from the parent plant to reduce competition and colonize new areas.

Method	Mechanism	Examples
Wind (Anemochory)	Light, small seeds; wings or hairs for buoyancy	Dandelion, sunflower, maple
Water (Hydrochory)	Seeds float, often in fibrous coat	Coconut, water lily
Animals (Zoochory)	Seeds in fruit, eaten and excreted; hooks/stick to fur	Mango, Custard apple, Xanthium
Explosion (Autochory)	Fruits burst open when ripe, scattering seeds	Pea, Balsam, Viola
Human agency	Involuntary transport by humans	Many crop weeds spread this way

Germination

Seed germination is the process by which a seed develops into a seedling.

Conditions required:

1. Water: Activates enzymes, softens seed coat, starts growth
2. Suitable temperature: For most temperate plants, 15–30°C; tropical plants need higher
3. Oxygen: For aerobic respiration during early growth

Process of germination:

1. Seed absorbs water (imbibition) → seed coat swells
2. Enzymes become active → convert stored food (starch) to sugars
3. Radicle (embryonic root) emerges first → grows downward
4. Plumule (embryonic shoot) emerges → grows upward
5. Cotyledons (seed leaves) provide food until photosynthesis begins

Types of Germination

Epigeal germination (cotyledons come above soil):

• Groundnut, castor, onion — cotyledons are pushed above soil
• Hypocotyl elongates, pulling cotyledons up

Hypogeal germination (cotyledons remain below soil):

• Maize, wheat, pea — cotyledons stay below ground
• Epicotyl (portion above cotyledon) grows up

Asexual Reproduction in Plants

Asexual reproduction (vegetative propagation) produces new plants that are genetically identical to the parent (clones).

Methods

1. Vegetative propagation from stems:

• Runners/Stolons: Horizontal stems that produce new plantlets at nodes — e.g., strawberry, grass
• Tubers: Modified underground stems — e.g., potato (eyes of potato are nodes that sprout)
• Bulbs: Underground storage organs — e.g., onion, garlic — parent plant produces new bulbs from axillary buds
• Corms: Solid, swollen underground stems — e.g., colocasia, gladiolus
• Rhizomes: Horizontal underground stems — e.g., ginger, turmeric

2. Vegetative propagation from leaves:

• Leaf buds: Begonia, Bryophyllum — new plant can grow from a leaf placed on moist soil

3. Vegetative propagation from roots:

• Root tubers: Sweet potato, Dahlia — new plants grow from root tubers

4. Artificial methods:

• Cuttings: A piece of stem with nodes is planted — e.g., rose, sugarcane
• Layering: Stem is bent and covered with soil while still attached to parent — e.g., jasmine
• Grafting: Shoot of one plant (scion) is attached to root system of another (stock) — e.g., apple, mango
• Tissue culture: Plant cells are cultured on artificial media to produce many clones — used for orchids, bananas

Natural Vegetative Propagation

Method	Plant Examples
Runners ( Stolons)	Strawberry, grass
Suckers	Banana, pineapple
Bulbs	Onion, garlic, tulip
Tubers	Potato, sweet potato
Rhizomes	Ginger, turmeric
Corms	Colocasia, crocus

Sexual Reproduction in Plants

Sexual reproduction involves:

• Gametes (male and female sex cells) — formed by meiosis
• Pollination (transfer of pollen)
• Fertilization (fusion of gametes)
• Seed formation

Gamete formation:

• Microsporogenesis: Pollen mother cell → 4 microspores → each becomes a pollen grain (male gametophyte)
• Megasporogenesis: One cell in ovule → meiosis → 4 megaspores → 3 degenerate → 1 functional → embryo sac (female gametophyte) → contains 7 cells including egg cell

Alternation of generations: Plants show alternation between:

• Sporophyte (diploid, produces spores via meiosis) — the visible plant body
• Gametophyte (haploid, produces gametes via mitosis) — reduced in angiosperms

CTET Exam Focus

• Plant classification: Thallophyta, Bryophyta, Pteridophyta, Gymnosperms, Angiosperms (monocots vs dicots)
• Flower structure: Calyx, corolla, androecium (stamen: anther + filament), gynoecium (pistil: stigma, style, ovary)
• Types of pollination: Self vs cross; agents (insect, wind, water, bird, bat)
• Double fertilization: Unique to angiosperms — one male gamete + egg = zygote; second male gamete + polar nuclei = endosperm
• Seed dispersal: Wind (dandelion), animals (mango), water (coconut), explosion (balsam)
• Germination: Epigeal vs hypogeal — conditions needed (water, temperature, oxygen)
• Asexual propagation: Runners, tubers (potato), bulbs (onion), rhizomes (ginger), cuttings, grafting, tissue culture

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