NCERT Solutions for Class 11 Biology Chapter 5: Morphology of Flowering Plants

Modification of root refers to the change in the structure and function of roots to perform specialized roles other than their primary functions of absorption and anchorage. These modifications help plants survive in different environments.

(a) Banyan tree (Ficus benghalensis):

• Modification: Prop roots.
• Description: These are massive, pillar-like adventitious roots that grow down from the large horizontal branches of the banyan tree. They penetrate the soil, providing extra support to the heavy branches, much like pillars supporting a roof.

(b) Turnip (Brassica rapa):

• Modification: Tap root for food storage.
• Description: The tap root of the turnip becomes swollen and fleshy to store food. This specific shape is called napiform, where the root is spherical at the base and tapers sharply towards the end.

(c) Mangrove trees (e.g., Rhizophora):

• Modification: Pneumatophores or respiratory roots.
• Description: Mangroves grow in swampy areas where the soil lacks oxygen. To overcome this, some roots grow vertically upwards into the air. These roots, called pneumatophores, have small pores (lenticels) to facilitate gas exchange.

(i) Underground parts of a plant are not always roots.

This statement is true because some underground parts are modified stems, distinguished by:

1. Presence of Nodes and Internodes: Underground stems like potato (tuber) and ginger (rhizome) have nodes and internodes, which roots lack.
2. Presence of Buds: The 'eyes' of a potato are axillary buds. Roots do not have buds.
3. Presence of Scale Leaves: Underground stems possess non-green, papery scale leaves.

(ii) Flower is a modified shoot.

This is justified by the following points:

1. Condensed Axis: The thalamus (receptacle) of a flower is a condensed shoot axis with highly compressed internodes.
2. Homology of Floral Parts: Floral parts (sepals, petals, stamens, carpels) are considered modified leaves arranged on the thalamus.
3. Apical Meristem: The floral meristem gives rise to floral appendages, similar to how a shoot apical meristem gives rise to leaves.

Phyllotaxy is the pattern of arrangement of leaves on the stem. The three main types are:

1. Alternate Phyllotaxy: A single leaf arises at each node in an alternate manner. This ensures all leaves get adequate sunlight.
   • Examples: China rose (Hibiscus), Mustard, Sunflower.
2. Opposite Phyllotaxy: A pair of leaves arises at each node, opposite to each other.
   • Examples: Calotropis (Aak), Guava.
3. Whorled Phyllotaxy: If more than two leaves arise at a node and form a whorl or a circle.
   • Examples: Alstonia (Devil tree), Nerium (Oleander).

(a) Aestivation: The mode of arrangement of sepals or petals in a floral bud.

(b) Placentation: The arrangement of ovules within the ovary of a flower.

(c) Actinomorphic: A flower with radial symmetry, which can be divided into two equal halves in any radial plane. Example: Mustard.

(d) Zygomorphic: A flower with bilateral symmetry, which can be divided into two similar halves by only one vertical plane. Example: Pea.

(e) Superior Ovary: In a hypogynous flower, the ovary occupies the highest position, with other parts below it. Example: Brinjal.

(f) Perigynous Flower: The floral parts are located on the rim of the thalamus, almost at the same level as the ovary. The ovary is half-inferior. Example: Rose.

(g) Epipetalous Stamen: Stamens that are attached to the petals. Example: Brinjal.

(a) Racemose and Cymose Inflorescence

(b) Fibrous Root and Adventitious Root

(c) Apocarpous and Syncarpous Ovary

(i) Diagram of Gram Seed (Dicot Seed)

Key labels for a gram seed include:

• Seed Coat: Outermost protective layer.
• Hilum: Scar where the seed was attached to the fruit.
• Micropyle: Small pore above the hilum.
• Cotyledons (2): Fleshy, store food.
• Embryonal Axis: Contains the plumule (future shoot) and radicle (future root).

(ii) Diagram of V.S. of Maize Seed (Monocot Seed)

Key labels for a maize seed V.S. include:

• Seed coat & Pericarp (fused): Outer covering.
• Endosperm: Bulky part that stores food.
• Aleurone Layer: Protein-rich outer layer of the endosperm.
• Embryo: Containing the scutellum (cotyledon), coleoptile (protects plumule), and coleorhiza (protects radicle).

Stems are modified to perform various functions:

1. Underground Modifications (Food Storage):
   • Rhizome: Horizontal stem. E.g., Ginger, Turmeric.
   • Tuber: Swollen end of an underground branch. E.g., Potato.
   • Corm: Vertical, condensed stem. E.g., Colocasia, Saffron.
   • Bulb: Reduced stem with fleshy leaves. E.g., Onion, Garlic.
2. Sub-aerial Modifications (Vegetative Propagation):
   • Runner: Creeping stem rooting at nodes. E.g., Grass.
   • Stolon: Arched lateral branch. E.g., Jasmine, Mint.
   • Offset: Short, thick runner in aquatic plants. E.g., Pistia.
   • Sucker: Arises from the basal part. E.g., Banana, Pineapple.
3. Aerial Modifications:
   • Stem Tendrils (Support): Axillary buds form tendrils. E.g., Gourds, Grapevines.
   • Thorns (Protection): Axillary buds form woody thorns. E.g., Citrus, Bougainvillea.
   • Phylloclade (Photosynthesis): Flattened, green stem. E.g., Opuntia.

Family: Fabaceae (Example: Pea - Pisum sativum)

• Flower: Bisexual, Zygomorphic (%).
• Calyx: Sepals five, gamosepalous (united). (K₍₅₎)
• Corolla: Petals five, polypetalous, papilionaceous, vexillary aestivation. (C_1+2+(2))
• Androecium: Stamens ten, diadelphous. (A₍₉₎₊₁)
• Gynoecium: Ovary superior, monocarpellary, marginal placentation. (G₁)
• Floral Formula: % ⚥ K₍₅₎ C_1+2+(2) A₍₉₎₊₁ G₁

Family: Solanaceae (Example: Brinjal - Solanum)

• Flower: Bisexual, Actinomorphic (⊕).
• Calyx: Sepals five, united (gamosepalous), persistent. (K₍₅₎)
• Corolla: Petals five, united (gamopetalous). (C₍₅₎)
• Androecium: Stamens five, epipetalous. (A₅)
• Gynoecium: Bicarpellary, syncarpous, ovary superior, axile placentation. (G₍₂₎)
• Floral Formula: ⊕ ⚥ K₍₅₎ C₍₅₎ A₅ G₍₂₎ (with a line connecting C and A for epipetalous condition).

Placentation is the arrangement of ovules within the ovary.

1. Marginal: Ovules on a ridge along the ventral suture. E.g., Pea.
2. Axile: Ovules on a central axis in a multilocular ovary. E.g., Tomato, Lemon.
3. Parietal: Ovules on the inner wall of a unilocular ovary. E.g., Mustard.
4. Free Central: Ovules on a central axis, but septa are absent. E.g., Dianthus.
5. Basal: A single ovule at the base of the ovary. E.g., Sunflower, Marigold.

A flower is the reproductive unit in angiosperms, essentially a modified shoot for sexual reproduction. A typical flower has four whorls on the thalamus:

1. Calyx: Outermost whorl of sepals, which protects the bud.
2. Corolla: Whorl of petals, usually colorful to attract pollinators.
3. Androecium (Male part): Composed of stamens (filament and anther). The anther produces pollen grains.
4. Gynoecium (Female part): Innermost whorl of one or more carpels (stigma, style, and ovary). The ovary contains ovules.

Leaf modifications are adaptations that help plants survive:

• Tendrils for Support: Modified leaves help weak-stemmed plants climb. E.g., Pea.
• Spines for Defense: Reduce water loss and protect against grazing animals. E.g., Cacti.
• Fleshy Leaves for Food Storage: Store food and water. E.g., Onion, Garlic.
• Phyllode for Photosynthesis: Flattened petiole performs photosynthesis while reducing water loss. E.g., Australian Acacia.
• Insectivorous Leaves for Nutrition: Trap insects to supplement nitrogen needs. E.g., Pitcher plant, Venus-flytrap.

Inflorescence is the arrangement of a cluster of flowers on the floral axis.

The classification is based on whether the floral axis continues to grow:

1. Racemose Inflorescence: The main axis has indeterminate growth and continues to grow. Flowers are arranged in an acropetal succession (older at the base). E.g., Mustard.
2. Cymose Inflorescence: The main axis has determinate growth and terminates in a flower. Flowers are arranged in a basipetal order (older at the apex). E.g., Jasmine.

Let's derive the formula step-by-step:

• Actinomorphic: ⊕
• Bisexual: ⚥
• Five united sepals (Calyx): K₍₅₎
• Five free petals (Corolla): C₅
• Five free stamens (Androecium): A₅
• Two united carpels (Gynoecium) with superior ovary: G₍₂₎ (with a line underneath G)

The final floral formula is: ⊕ ⚥ K₍₅₎ C₅ A₅ G₍₂₎

Based on the position of floral parts with respect to the ovary on the thalamus, flowers are of three types:

1. Hypogynous Flower: The gynoecium is at the top, and other parts are below it. The ovary is superior. E.g., Mustard, Brinjal.
2. Perigynous Flower: The gynoecium is in the center, and other parts are on the rim of the thalamus. The ovary is half-inferior. E.g., Rose, Peach.
3. Epigynous Flower: The floral parts arise from the top of the ovary, which is enclosed by the thalamus. The ovary is inferior. E.g., Guava, Cucumber.

A phylloclade is a modified, flattened or cylindrical, green stem that carries out photosynthesis. It is found in xerophytes where leaves are reduced to spines to conserve water.

• Example: Opuntia (Cactus).
• Function: Photosynthesis and water storage.

(a) Grass: Propagates by Runners. These are slender, prostrate stems that grow along the ground, developing new roots and shoots at the nodes.

(b) Mint: Propagates by Stolons. A slender lateral branch grows aerially and then arches down to touch the ground, forming a new plant.

(c) Pistia (Water Lettuce): Propagates by Offsets. An offset is a short, thick runner that grows horizontally, bearing a rosette of leaves and a tuft of roots.

(d) Banana: Propagates by Suckers. A sucker originates from the basal, underground part of the main stem, grows horizontally, and then emerges to form a new leafy shoot.

1. What is the modification of the leaf called? The modification is called a leaf tendril.
2. Identify the type of aestivation in the flower. The aestivation is Vexillary or Papilionaceous.
3. To which family does this plant most likely belong? It belongs to the family Fabaceae.
4. What type of placentation would you expect? The placentation would be Marginal.