Definitions [2]
Define the term inflorescence.
- A flower is a modified shoot wherein the shoot apical meristem changes to a floral meristem. Internodes do not elongate and the axis gets condensed.
- The apex produces different kinds of floral appendages laterally at successive nodes instead of leaves. When a shoot tip transforms into a flower, it is always solitary. The arrangement of flowers on the floral axis is termed inflorescence.
Define the following term:
Superior ovary
- Superior ovary Flowers with a superior ovary structure have the gynoecium at the top and the remaining floral components positioned underneath it.
- This arrangement of flowers is referred to as hypogynous. Mustard and brinjal are two examples.
Key Points
Key Points: Plant Morphology
- Morphology is the study of external features of organisms, especially plants.
- Adaptation refers to structural or functional changes that help organisms survive and reproduce in their environment.
- Flowering plants (angiosperms) show great variation in size, shape, structure, and habitat.
- Basic parts of angiosperms include roots, stems, leaves, flowers, and fruits.
- Plants have two main systems: root system (underground) and shoot system (above ground), with modifications for functions like storage, protection, and climbing.
Key Points: The Root
- Root: Underground part of plant, develops from the radicle of embryo.
- Types of roots: Tap root (dicots), fibrous root (monocots), adventitious roots (from other plant parts).
- Functions: Absorption of water and minerals, anchorage, storage of food, synthesis of growth regulators.
- Root cap: Protects the tender root apex and helps in soil penetration.
- Regions of root: Meristematic (cell division), elongation (increase in length), maturation (differentiation and root hairs).
- Root hairs: Help in absorption of water and minerals from soil.
- Modifications: Support (prop, stilt), respiration (pneumatophores), storage (carrot, radish, turnip).
Key Points: The Stem
- Stem: Aerial part of the plant, develops from the plumule and bears nodes and internodes.
- Structure: Has nodes (leaf origin), internodes (between nodes) and buds (terminal and axillary).
- Functions: Supports the plant body and conducts water, minerals, and food.
- Food storage modification: Rhizome (ginger), tuber (potato), bulb (onion), corm (Colocasia).
- Support modification: Stem tendrils help in climbing (grapevine, cucumber).
- Protection & propagation: Thorns for protection (Citrus, Bougainvillaea); runners and stolons for vegetative propagation (strawberry, mint).
- Photosynthesis modification: Flattened stems (cladodes) perform photosynthesis (Opuntia).
Key Points: The Leaf
- Leaf: Lateral, green, flattened structure developing from the shoot apical meristem; the main organ for photosynthesis.
- Parts of a leaf: Leaf base, petiole, and lamina; an axillary bud is present in the axil.
- Types of leaves: Simple leaf (single blade, e.g., mango) and compound leaf (leaflets, e.g., neem, rose).
- Venation: Arrangement of veins; reticulate (dicots) and parallel (monocots).
- Phyllotaxy: Arrangement of leaves on the stem; alternate, opposite, and whorled.
- Functions: Photosynthesis, transport of water/food, and gas exchange.
- Modifications: Tendrils (climbing), spines (protection), pitcher (nutrition), hooks (support).
Key Points: The Stem
- Stem: Aerial part of the plant, develops from the plumule and bears nodes and internodes.
- Structure: Has nodes (leaf origin), internodes (between nodes) and buds (terminal and axillary).
- Functions: Supports the plant body and conducts water, minerals, and food.
- Food storage modification: Rhizome (ginger), tuber (potato), bulb (onion), corm (Colocasia).
- Support modification: Stem tendrils help in climbing (grapevine, cucumber).
- Protection & propagation: Thorns for protection (Citrus, Bougainvillaea); runners and stolons for vegetative propagation (strawberry, mint).
- Photosynthesis modification: Flattened stems (cladodes) perform photosynthesis (Opuntia).
Key Points: The Inflorescence
- Inflorescence = Arrangement of flowers on the floral axis.
- Racemose — Main axis continues to grow; flowers in acropetal order (bottom → top). Ex: Amaranthus, Mustard, Snapdragon.
- Cymose — Main axis terminates in a flower; limited growth; flowers in basipetal order (top → bottom). Ex: Calotropis, Cotton, Jasmine, Solanum.
- Flower = Modified shoot where the shoot apical meristem turns into a floral meristem; internodes do not elongate.
- Alternate phyllotaxy — One leaf per node, arranged alternately. Ex: China rose, Mustard.
- Opposite phyllotaxy — Two leaves per node, facing each other. Ex: Calotropis, Guava.
- Whorled phyllotaxy — More than two leaves per node, forming a circle. Ex: Alstonia.
Key Points: Structure of a Dicotyledonous Seed
- Seed coat: Consists of two layers—testa (outer) and tegmen (inner).
- Hilum: A scar on the seed coat showing the point of attachment to the fruit.
- Micropyle: A small pore present above the hilum helps in water absorption.
- Cotyledons: Two fleshy cotyledons present, storing reserve food material.
- Embryo: Contains an embryonal axis with radicle and plumule at opposite ends.
- Endosperm: May be present (e.g., castor) or absent (e.g., bean, gram, pea) in mature seeds.
Key Points: Structure of Monocotyledonous Seed
- Monocot seed: Usually endospermic, with endosperm storing food (except orchids).
- Endosperm: Large and bulky, separated from the embryo by a protein-rich aleurone layer.
- Embryo: Consists of a single cotyledon called the scutellum and a short embryonal axis.
- Cotyledon: Only one large, shield-shaped cotyledon present.
- Radicle and plumule: Radicle is enclosed in the coleorhiza, and plumule in the coleoptile.
- Seed structure: The seed coat is often fused with the fruit wall, and the embryo lies at one side of the endosperm.
Key Points: Semi-technical Description of a Typical Flowering Plant
- A semi-technical description is a systematic way of describing plants based on morphological features.
- The description follows an order: habit → vegetative parts (root, stem, leaves) → floral parts.
- Floral formula uses symbols like Br (bract), K (calyx), C (corolla), P (perianth), A (androecium), G (gynoecium).
- Symbols also indicate symmetry (⊕ actinomorphic, % zygomorphic) and sex of flower (male, female, bisexual).
- Fusion is shown by brackets and adhesion by a line above symbols in the floral formula.
- A floral diagram shows the number, arrangement, and relationship of floral parts.
