Plant Roots and Their Types

Roots

• Plants absorb water and minerals through roots
• Roots develop from new cells formed in the growing tip
• Fibrous root systems grow from a central stem, and many small roots are diffused
• Taproot systems have a main root that is larger and dominates the root system

Root Types

• Fibrous Roots: The primary root withers, and subsequent roots sprout; the plant has a fibrous root system.
• Taproots: The primary root becomes dominant, and the plant has a taproot system.

Specialized Roots

• Storage Roots: The taproot thickens to store energy, especially starch.
• Adventitious Roots: Roots growing from an unexpected area other than the radicle.
• Aerial Roots: Roots of epiphytic plants, typically from tropical monocot families, like orchids.
• Haustoria: Parasitic plants' specialized structures that penetrate host plants' tissues for nutrients.
• Prop Roots: Roots growing from the stem base to support the plant.
• Pneumatophores: Roots of swamp or marsh plants that grow upward from the soil to absorb air for oxygen.
• Buttress Roots: Enlarged horizontally spreading tree roots, typically found in tropical rainforests/swamps, providing mechanical support.

External Anatomy of Roots

• Root Hairs: Tiny structures on the root surface that increase water absorption.
• Root Cap: Protects the root tip as it grows through soil.
• Region of Cell Division: The area where cells rapidly divide.
• Region of Elongation: The area where cells grow larger.
• Region of Maturation: The area where cells differentiate into specific tissues.

Internal Structure of Roots

• Epidermis: Outer layer of cells.
• Cortex: Layer of cells beneath the epidermis involved in storing nutrients.
• Vascular Cylinder: Central region containing xylem and phloem for transporting water and nutrients.
• Endodermis: Layer of cells surrounding the vascular cylinder that regulates water and mineral uptake.
• Pericycle: Layer of cells from which lateral roots originate.
• Xylem: Transports water and minerals upward from the roots.
• Phloem: Transports nutrients from the leaves.

Monocot Roots vs Dicot Roots

• Monocot roots have scattered vascular bundles, while dicot roots have vascular bundles in a ring.
• Monocot roots have a central pith, while dicot roots usually lack a prominent pith.

Stems

• Stems are the main support structure for the plant, allowing the leaves, flowers, and other parts to grow upward
• Stems absorb light and nutrients
• External features vary depending on the plant type

External Morphology of Stems

• Nodes: The points where leaves attach.
• Internodes: The regions between nodes.
• Terminal buds: located at the tip of a stem
• Axillary buds: located at the junction of a leaf and stem.
• Terminal Bud: located at the apex/top of the stem; maintains terminal growth.
• Lateral Buds: located in the axils of leaves; if they grow, they create branches.

Modified Stems

• Runner: A special, narrow, prostrate branch growing from the base of erect plant stems, bearing new crowns at intervals.
• Rhizomes: Horizontal underground stems that allow for asexual reproduction
• Tubers: Swollen ends or tips of underground stems, that store food. They develop from the eyes or axillary buds.
• Bulbs: Disc-like underground stems that do not store food, but produce adventitious roots.
• Corms: Short, thick underground stems, similar to bulbs but more fleshy and upright.

Leaf

• Leaves are the primary photosynthetic organs of most plants.
• Leaves are responsible for collecting sunlight and carbon dioxide to produce energy, and typically have a petiole, a blade, and veins.
• External features of leaves vary from plant to plant (shape, size, texture)

Leaf Venation

• Pinnate: Main vein with secondary veins branching out from it.
• Palmate: Secondary veins branching out from a central point.
• Reticulate: Complex network of veins throughout the leaf.
• Parallel: Veins running parallel to each other.
• Dichotomous: Veins branch out repeatedly in two directions.

Internal Structure of Leaves

• Cuticle: A waxy, waterproof outer layer that prevents water loss.
• Upper Epidermis: A layer of cells that protects the upper surface of the leaf.
• Palisade Mesophyll: A densely packed layer of cells with chloroplasts for photosynthesis.
• Spongy Mesophyll: A loosely arranged layer of cells with air spaces.
• Lower Epidermis: A layer of cells that protects the lower surface of the leaf.
• Stomata: Tiny pores on the lower epidermis that regulate gas exchange.
• Guard Cells: Surround the stomata and regulate their opening and closing.

Leaf Arrangement on Stems

• Alternate: One leaf per node, with subsequent leaves appearing above the first on the opposite side.
• Opposite: Two leaves at a node, on opposite sides of the stem.
• Whorled: Three or more leaves at a node.

Flowers

• Flowers are the reproductive organs of plants. They attract pollinators for fertilization.
• Variable features and structures exist in terms of petals, colors, odours etc.

Parts of Flowers

• Pedicel: The stalk supporting the flower.
• Receptacle: The enlarged tip of the stem where the flower parts are attached.
• Sepal: (Calyx) Leaf-like structures surrounding the flower, forming the outermost whorl.
• Petal: (Corolla ) Colorful structures typically inside the sepals.
• Stamen: Male reproductive part containing the anther and filament.
• Carpel / Pistil: Female part comprising stigma, style and ovary.
• Parts Present/Absent: Complete flowers have all four parts: petals, sepals, stamens and carpels, while incomplete flowers lack one or more parts.
• Sexuality: Perfect flowers have both male (stamen) and female (carpel) parts, while imperfect flowers only have one or the other.
• Monoecious flowers: have both male and female parts in separate flowers, within the same plant eg. Corn
• Dioecious flowers: These plants have either only male or female flowers.

Nature of flowers

• A flower can be regular if all the parts are the same size (eg. sunflower) or irregular if some parts are different (eg. pea plant).

Flower Fusion

• Connation: When similar parts are fused together eg. fused petals forming a cone (morning glory)
• Adnation: When unlike parts are fused together. eg. stamen adnate to petals (angels trumpet)

Flower Symmetry

• Actinomorphic (Radial): Any plane through the central axis will divide the flower in two equal halves.
• Zygomorphic (Bilateral): Only one plane through the central axis will divide the flower into two equal halves.

Ovary Position

• Superior or Hypogynous: The sepals and petals are attached below the ovary.
• Half-Superior/Half-Inferior: The sepals and petals are attached at the side of the ovary.
• Inferior or Epigynous: The sepals and petals are attached above the ovary.

Fruits

• Fruits are ripened ovaries of the flower that contain one or more seeds, and they help in seed dispersal.

Parts of a Fruit

• Epicarp: Outer skin
• Mesocarp: Fleshy edible part
• Endocarp: Inner stony wall
• Seed: The developing embryo inside the fruit.

Fruit Classification

• Types: simple, aggregate, collective. The classification depends on the number of ovaries involved in forming the fruit

Seeds

• Seeds are the fertilized ovules of flowering plants, containing a miniature plant (the embryo), stored food/nutrients (endosperm), and a protective outer covering (seed coat).

Seed Structure

• Testa (seed coat): Protective outer layer
• Hilum: Scar where the seed was attached to the ovary
• Micropyle: Small opening in the seed coat.
• Embryo: The undeveloped plant within the seed
• Cotyledon: Seed leaves (store nutrients for the embryo)

Seed Dispersal

• Important for avoiding competition with parents, colonizing new areas, and avoiding pathogens and predators.
• Dispersal methods include wind, water, animals, and self-dispersal mechanisms.

Inflorescence

• Inflorescences refer to flower clusters on a branch, varying in their number, order, and sequence of flowering.
• Different inflorescence types exist to better help plants reproduce.

This quiz explores the various types of plant roots, including fibrous and taproots, as well as specialized structures such as storage roots and aerial roots. Learn about how roots absorb water and minerals and their role in plant growth. Test your understanding of root systems and their functions in plants.