Class 11 Biology Notes Chapter 3 (Chapter 3) – Lab Manual (English) Book

Detailed Notes with MCQs of Chapter 3 from your Lab Manual, which primarily deals with the practical study of Morphology of Flowering Plants. Understanding these structures and their modifications is crucial, not just for your practical exams but also forms a basis for many questions in competitive government exams.

Chapter 3: Morphology of Flowering Plants - Key Concepts & Observations

This chapter involves observing and identifying different parts of flowering plants, focusing on variations or modifications in roots, stems, and leaves, as well as understanding the structure of flowers, inflorescences, fruits, and seeds.

1. Root Modifications

• Function: Primary functions are anchorage and absorption of water and minerals. Modifications arise for storage, support, and respiration.
• Observations & Examples:
  • For Storage:
    • Tap Roots: Get swollen and fleshy.
      • Conical: Broad at the base, tapering towards the apex (e.g., Carrot - Daucus carota).
      • Fusiform: Swollen in the middle, tapering at both ends (e.g., Radish - Raphanus sativus).
      • Napiform: Spherical at the base, abruptly tapering towards the apex (e.g., Turnip - Brassica rapa, Beetroot - Beta vulgaris).
    • Adventitious Roots: Arise from parts other than the radicle.
      • Tuberous Roots: Swollen without definite shape (e.g., Sweet Potato - Ipomoea batatas).
      • Fasciculated Roots: Tuberous roots occurring in clusters (e.g., Dahlia, Asparagus).
  • For Support:
    • Prop Roots: Arise from horizontal branches, grow downwards into the soil (e.g., Banyan tree - Ficus benghalensis).
    • Stilt Roots: Arise from lower nodes of the stem, grow obliquely downwards (e.g., Maize - Zea mays, Sugarcane - Saccharum officinarum, Pandanus).
  • For Respiration:
    • Pneumatophores: Negatively geotropic (upward growing) roots with pores (pneumathodes) for gaseous exchange. Found in marshy/saline environments (e.g., Rhizophora, Avicennia - Mangroves).

2. Stem Modifications

• Function: Primary functions are support, conduction, bearing leaves, flowers, fruits. Modifications arise for storage, perennation, protection, support, vegetative propagation.
• Observations & Examples:
  • Underground Stems (for Storage & Perennation):
    • Rhizome: Thickened, horizontal/prostrate stem with nodes, internodes, scale leaves, buds (e.g., Ginger - Zingiber officinale, Turmeric - Curcuma longa).
    • Tuber: Swollen terminal portion of an underground stem branch, possesses 'eyes' (nodes with buds) (e.g., Potato - Solanum tuberosum).
    • Bulb: Condensed stem disc with fleshy scale leaves storing food (e.g., Onion - Allium cepa, Garlic - Allium sativum).
    • Corm: Condensed, vertically growing underground stem, usually unbranched, with nodes, internodes, buds (e.g., Colocasia, Crocus, Gladiolus).
  • Sub-aerial Stems (for Vegetative Propagation):
    • Runner: Slender, prostrate branch with long internodes, rooting at nodes (e.g., Grasses - Cynodon, Strawberry).
    • Stolon: Arches down from the base of the stem to touch the ground and root (e.g., Mint - Mentha, Jasmine - Jasminum).
    • Offset: Like a runner but shorter and thicker, found in aquatic plants (e.g., Water hyacinth - Eichhornia, Water lettuce - Pistia).
    • Sucker: Arises from the basal underground part of the main stem, grows obliquely upwards (e.g., Chrysanthemum, Banana, Pineapple).
  • Aerial Stems (for Protection, Support, Photosynthesis):
    • Stem Tendrils: Thread-like, sensitive structures for climbing; modification of axillary or terminal buds (e.g., Gourds - Cucumber, Pumpkin; Grapevine - Vitis).
    • Thorns: Hard, pointed structures for protection; modification of axillary buds (e.g., Citrus, Bougainvillea, Duranta).
    • Phylloclade: Flattened or cylindrical green stem performing photosynthesis, leaves reduced to spines/scales (e.g., Opuntia - flattened, Euphorbia - cylindrical). Found in xerophytes.
    • Cladode: Phylloclade usually of one or two internodes only (e.g., Asparagus, Ruscus).

3. Leaf Modifications

• Function: Primary function is photosynthesis. Modifications for support, protection, storage, trapping insects.
• Observations & Examples:
  • Leaf Tendrils: For climbing (e.g., Pea - Pisum sativum - entire leaf or leaflets modified).
  • Spines: For protection, reduce transpiration (e.g., Cacti - Opuntia).
  • Storage Leaves: Fleshy leaves store food (e.g., Onion, Garlic).
  • Phyllode: Petiole becomes flattened, green, and leaf-like to perform photosynthesis when the lamina is reduced (e.g., Australian Acacia).
  • Insectivorous Leaves: Modified to trap insects in nitrogen-deficient soils (e.g., Pitcher plant - Nepenthes, Venus flytrap - Dionaea, Bladderwort - Utricularia).

4. Inflorescence

• Definition: The arrangement of flowers on the floral axis (peduncle).
• Types & Observations:
  • Racemose: Main axis continues to grow indefinitely. Flowers are borne laterally in acropetal succession (older flowers at the base, younger at the apex). (e.g., Mustard - Brassica, Radish - Raphanus).
  • Cymose: Main axis terminates in a flower, limiting its growth. Flowers are borne in basipetal succession (older flowers at the apex, younger at the base). (e.g., Jasmine - Jasminum, Bougainvillea, Teak).

5. Flower

• Definition: Reproductive unit of angiosperms.
• Parts: A typical flower has four whorls arranged on the thalamus.
  • Calyx: Outermost whorl, units called sepals (usually green, protective).
  • Corolla: Next whorl, units called petals (usually brightly coloured, attract pollinators).
  • Androecium: Male reproductive whorl, units called stamens (each has filament and anther).
  • Gynoecium (Pistil): Female reproductive whorl, units called carpels (each has stigma, style, ovary).
• Observation: Study of a typical flower like Hibiscus or Mustard involves identifying these parts.

6. Fruit

• Definition: A mature or ripened ovary, developed after fertilization. May include accessory parts (false fruit).
• Parts:
  • Pericarp (Fruit wall): Develops from the ovary wall. Differentiated into outer Epicarp, middle Mesocarp, inner Endocarp.
  • Seeds: Develop from ovules.
• Types & Observations:
  • Simple Fruits: Develop from a single carpel or syncarpous ovary of a single flower.
    • Drupe: Fleshy fruit with stony endocarp (e.g., Mango - Mangifera indica, Coconut - Cocos nucifera, Peach, Plum).
    • Berry: Fleshy fruit, endocarp not stony, seeds embedded in pulp (e.g., Tomato, Brinjal, Guava, Grapes).
  • (Other types like Legume, Capsule, etc., exist but Drupe and Berry are common examples).

7. Seed

• Definition: Fertilized, mature ovule containing the embryo and stored food, covered by a seed coat.
• Structure & Observations:
  • Dicot Seed (e.g., Bean, Gram, Pea):
    • Seed Coat: Outer testa, inner tegmen. Hilum, Micropyle visible.
    • Embryo: Consists of an Embryonal axis and two fleshy Cotyledons (store food).
    • Embryonal Axis: Has Plumule (future shoot) and Radicle (future root).
    • Endosperm: Generally absent in mature seeds (non-endospermic/exalbuminous) as food is stored in cotyledons (Exception: Castor is endospermic).
  • Monocot Seed (e.g., Maize, Wheat, Rice):
    • Seed Coat: Fused with the fruit wall (pericarp).
    • Endosperm: Bulky, stores food (endospermic/albuminous). Separated from the embryo by the Aleurone layer (proteinaceous).
    • Embryo: Small, situated in a groove at one end of the endosperm. Consists of one large, shield-shaped Cotyledon (Scutellum) and a short Embryonal axis.
    • Embryonal Axis: Has Plumule covered by Coleoptile and Radicle covered by Coleorhiza.

Multiple Choice Questions (MCQs) for Practice:

1. Pneumatophores are modifications of roots primarily found in plants growing in:
   a) Desert areas
   b) Marshy, saline areas
   c) Cold, tundra regions
   d) Temperate grasslands

2. In Potato (Solanum tuberosum), the edible part is a modified underground stem called a:
   a) Rhizome
   b) Corm
   c) Bulb
   d) Tuber

3. Phylloclades, like those found in Opuntia, are modifications of:
   a) Roots for photosynthesis
   b) Stems for photosynthesis
   c) Leaves for storage
   d) Petioles for climbing

4. Which of the following represents a Racemose inflorescence?
   a) Main axis terminates in a flower, limiting growth.
   b) Flowers are arranged in basipetal succession.
   c) Main axis shows indefinite growth, flowers are acropetal.
   d) Found typically in Jasmine and Bougainvillea.

5. The 'eye' of a potato represents:
   a) A scale leaf
   b) The terminal bud
   c) A node with axillary buds
   d) A root scar

6. In a Maize grain (monocot seed), the protein-rich layer separating the embryo from the endosperm is called:
   a) Scutellum
   b) Coleoptile
   c) Coleorhiza
   d) Aleurone layer

7. Prop roots in Banyan tree and Stilt roots in Maize are modifications for:
   a) Respiration
   b) Storage
   c) Support
   d) Vegetative propagation

8. Mango fruit is classified as a:
   a) Berry
   b) Drupe
   c) Pome
   d) Legume

9. In Australian Acacia, the function of photosynthesis is taken over by a modified petiole called a:
   a) Phylloclade
   b) Cladode
   c) Phyllode
   d) Tendril

10. Which of the following pairs represents stem modifications for protection and climbing respectively?
    a) Thorns (Citrus) and Tendrils (Pea)
    b) Spines (Cactus) and Tendrils (Grapevine)
    c) Thorns (Bougainvillea) and Tendrils (Gourds)
    d) Phylloclade (Opuntia) and Offset (Pistia)

Answer Key:

1. b
2. d
3. b
4. c
5. c
6. d
7. c
8. b
9. c
10. c

Study these modifications carefully, paying attention to the examples and their specific functions. Visualizing these structures as described in your lab manual will be very helpful. Good luck with your preparation!