Science and Technology Class 9 Notes Chapter 6 Maharashtra Board

Classification of Plants

Introduction to Kingdom Plantae

What is Kingdom Plantae? Kingdom Plantae includes autotrophic living organisms with eukaryotic cells and cell walls, capable of making their own food through photosynthesis using chlorophyll.

Importance:

• Plants are the main source of food for all other living organisms.
• They give our surroundings a green, fresh look due to chlorophyll.

Difference from Animal Cells:

• Plant cells have special organelles like chloroplasts (for photosynthesis) and a cell wall (for support), which animal cells lack.

Background:

• Robert Whittaker’s Five Kingdom classification (1969) includes Monera, Protista, Fungi, Plantae, and Animalia.
• Kingdom Plantae is further divided based on specific features.

Basis for Classification

Criteria for Classification:

1. Presence or Absence of Organs: Whether plants have roots, stems, leaves, etc.
2. Conducting Tissues: Presence of separate tissues for water and food conduction.
3. Seed Production: Whether plants produce seeds and if they are enclosed in fruits.
4. Number of Cotyledons: Number of seed leaves (one for monocots, two for dicots).

Higher Classification Levels:

• Plants are grouped as cryptogams (no flowers, fruits, or seeds) or phanerogams (with seeds).
• Phanerogams are divided into gymnosperms (naked seeds) and angiosperms (seeds in fruits).
• Angiosperms are further split into monocots and dicots based on cotyledon number.

Historical Contribution:

• In 1883, botanist Eichler classified Kingdom Plantae into two subkingdoms: cryptogams and phanerogams.

Subkingdom: Cryptogams

Definition:

• Cryptogams are plants with hidden reproductive organs, reproducing via spores (cryptos: hidden, gams: reproductive organs).

Divisions:

Division I – Thallophyta:

• Features: Grow mainly in water, lack specific roots, stems, or leaves, but have chlorophyll for photosynthesis.
• Body: Soft, fibre-like, can be unicellular (e.g., Chlamydomonas) or multicellular (e.g., Ulva).
• Examples: Spirogyra, Ulothrix, Sargassum.
• Observation: Spirogyra shows spiral chloroplasts when observed under a microscope.
• Note: Some fungi (e.g., yeasts) without chlorophyll are included here.

Division II – Bryophyta:

• Features: Called “amphibians” of the plant kingdom; grow in moist soil but need water for reproduction.
• Body: Thalloid, multicellular, autotrophic, with ribbon-like structure and rhizoids (root-like parts) instead of true roots.
• Reproduction: Via spore formation.
• Examples: Funaria (moss), Marchantia, Riccia.
• Observation: Seen as green carpets on wet walls or rocks during rains.

Division III – Pteridophyta:

• Features: Have well-developed roots, stems, leaves, and conducting tissues, but no flowers or fruits.
• Reproduction: Asexual via spores (on leaf backs) and sexual via zygote formation.
• Examples: Ferns (Nephrolepis), Marsilea, Selaginella.
• Observation: Fern leaves have sporangia (spore cases) on the underside.

Similarity:

• All cryptogams (Thallophyta, Bryophyta, Pteridophyta) reproduce by spore formation, despite differences in body structure.

Subkingdom: Phanerogams

Definition:

• Phanerogams are plants with visible reproductive structures that produce seeds containing embryos and stored food.

Divisions:

Division I – Gymnosperms:

• Features: Mostly evergreen, woody, perennial plants with unbranched stems and a crown of leaves.
• Reproduction: Bear male and female flowers on different sporophylls of the same plant; seeds are naked (not in fruits).
• Examples: Cycas, Picea (Christmas tree), Pinus (Deodar).
• Observation: Compare with angiosperms to note the lack of fruit covering seeds.

Division II – Angiosperms:

• Features: Have flowers as reproductive organs; flowers develop into fruits enclosing seeds.
• Subdivision:
  • Monocotyledons (Monocots): Seeds with one cotyledon (e.g., maize, wheat).
  • Dicotyledons (Dicots): Seeds with two cotyledons (e.g., beans, mustard).
• Observation: Soak seeds (e.g., corn, groundnut) for 8-10 hours to check cotyledon number.

Examples: Mango (dicot), rice (monocot).

Key Characteristics

Cryptogams:

• No flowers, fruits, or seeds; reproduce via spores; include Thallophyta, Bryophyta, and Pteridophyta.

Phanerogams:

• Have seeds; divided into gymnosperms (naked seeds) and angiosperms (seeds in fruits).
• Angiosperms further split into monocots and dicots based on cotyledon number.