Life of a Flowering Plant: Structure, Growth, and Reproduction

스터디 가이드 - 스마트 노트

자료에 맞춘 맞춤형 노트, 핵심 정의, 예시, 맥락을 확장해 제공합니다.

Flowering Plant Structure

Main Systems of a Flowering Plant

Flowering plants are composed of two main systems: the root system (below ground) and the shoot system (above ground). Each system is specialized for distinct functions essential to plant survival and reproduction.

Shoot system: Collects light, performs photosynthesis, enables reproduction, and transports nutrients between leaves and roots.
Root system: Acquires water and nutrients, anchors the plant, and stores starch.

Diagram of shoot system showing apical meristem, terminal bud, flower, petiole, stem, lateral bud, internode, node, leaf, and branch.

Key Structures in the Shoot System

Apical meristems: Regions at the tips of roots and shoots where growth occurs.
Petiole: Stalk attaching the leaf blade to the stem.
Blade: The broad, flat part of the leaf (not labeled in image).
Flower: Non-photosynthetic structure containing reproductive organs.
Internode: Space between adjacent leaves.
Bud: Growth area for stems, leaves, and flowers; terminal (top) or lateral (side).
Stem: Supports the plant upright.

Plant Growth and Meristems

Types of Growth

Plant growth occurs at specialized regions called meristems, which contain undifferentiated cells capable of division. These cells divide by mitosis, and as they mature, they differentiate to perform specific functions.

Primary growth: Increases plant height and develops specialized structures; occurs at apical meristems.
Secondary growth: Increases girth of stems and roots; occurs at lateral meristems.
Herbaceous plants: Only primary growth; flexible stems; annuals (live one year).
Woody plants: Both primary and secondary growth; perennials (live many years).

Plant hormones regulate growth, fruit ripening, and flower scent production, and are transported in the phloem.

Secondary Growth and Annual Rings

Woody plants exhibit secondary growth, producing annual rings that record each year of growth. The structure of a woody stem includes:

Heartwood: Older xylem, no longer conducts water, stores metabolic wastes.
Sapwood: Younger xylem, still conducts water.
Bark: Tough outer layer protecting inner tissues.

Light-colored rings form in spring/early summer (abundant water), dark rings in late summer/fall (less water). One light and one dark ring represent one year.

Cross-section of woody stem showing heartwood, sapwood, bark, and annual rings.

Plant Tissue Types

Three Major Tissue Types

Dermal tissue: Covers the plant's surface; includes the epidermis (outer layer) and peridermis (replaces dead epidermal cells). The epidermis is covered by a waxy cuticle to prevent water loss.
Ground tissue: Makes up most of the plant body; involved in photosynthesis, support, and storage.
Vascular tissue: Pipeline system for transporting water, minerals, and nutrients throughout the plant.

Ground Tissue Cell Types

Parenchyma cells: Thin-walled, alive, involved in photosynthesis, hormone secretion, support, and food storage.
Collenchyma cells: Elongated, alive, provide support for young and herbaceous plants.
Sclerenchyma cells: Thick-walled, dead, provide support for adult plants and fruit structures.

Vascular Tissue: Xylem and Phloem

Xylem: Conducts water and minerals upward from roots; composed of sclerenchyma fibers, tracheids, and vessel elements.
Phloem: Conducts water, sugars, amino acids, and hormones throughout the plant; composed of sieve-tube elements and companion cells.

Xylem Structure

Sclerenchyma fibers: Dead cells with lignin for support.
Tracheids: Needle-like, dead cells forming tubes for water movement.
Vessel elements: Wide, dead cells forming continuous tubes for water transport.

Diagram of xylem showing sclerenchyma fibers, vessel elements, and tracheids.

Phloem Structure

Sieve-tube elements: Pass sugars and organic molecules; separated by sieve plates; alive but not metabolically active.
Companion cells: Regulate and nourish sieve-tube elements.

Diagram of phloem showing sieve-tube elements, companion cells, and sclerenchyma fibers.

Leaf Structure and Function

Leaf Anatomy

Leaves are specialized for photosynthesis and gas exchange. Key structures include:

Cuticle: Waxy, waterproof layer preventing water loss.
Stoma (stomata): Pores for gas exchange; CO2 in, O2 and H2O vapor out.
Guard cells: Open and close stomata by changing turgor pressure.
Bundle-sheath cell: Surrounds vascular bundles (veins).
Mesophyll: Interior leaf tissue; palisade layer (photosynthesis) and spongy layer (gas exchange).

Cross-section of a leaf showing cuticle, upper and lower epidermis, palisade and spongy mesophyll, vascular bundle, guard cells, and stomata.

Stem and Root Anatomy

Stem Structure

Pith: Central part; supports, stores food, may photosynthesize; made of parenchyma cells.
Cortex: Between pith and epidermis; similar function to pith.
Epidermis: Outer protective layer.
Vascular bundle: Contains xylem and phloem.
Vascular cambium: Meristematic tissue forming new xylem and phloem.

Root System and Anatomy

Taproot: Main root for anchorage and storage.
Branch roots and root hairs: Increase surface area for absorption.
Root cap: Protects growing root tip and secretes lubricant.
Fibrous roots: Found in grasses and palms; all roots similar in size.

Diagram of root system showing taproot, branch roots, root hairs, and root cap. Photograph of root hairs on a young root.

Root Anatomy

Epidermis: Outer protective layer.
Cortex: Stores starch; loosely packed cells.
Endodermis: Closely packed cells surrounding the vascular cylinder.
Vascular cylinder: Contains xylem and phloem; pericycle is the layer closest to endodermis, conducting water and nutrients inward.
Casparian strip: Waxy layer in endodermal cells, forcing water into the vascular cylinder.

Diagram of root cross-section showing epidermis, cortex, endodermis, vascular cylinder, and Casparian strip. Diagram showing water and mineral movement through root tissues. Diagram of root tip showing apical meristem, root cap, and vascular cylinder.

Plant Root Symbioses

Mutualistic Relationships

Fungal mycorrhizae: Fungi that help plants acquire nutrients by releasing enzymes to weather rocks and make minerals available.
Nitrogen-fixing bacteria: Bacteria in root nodules convert atmospheric nitrogen into ammonium or nitrate ions usable by plants (e.g., legumes such as peas and beans).

Photograph of mycorrhizal fungi associated with plant roots. Photograph of root nodules containing nitrogen-fixing bacteria.

Monocots vs. Dicots (Eudicots)

Key Differences

Feature	Monocots	Dicots (Eudicots)
Vascular bundles	Scattered	In a ring
Root type	Fibrous	Taproot
Cotyledons	1	2
Leaf veins	Parallel	Netted
Flower parts	Multiples of 3	Multiples of 4 or 5

In angiosperms, the sporophyte is the dominant form, while the gametophyte is small and grows within the sporophyte.

Flower Anatomy and Reproduction

Flower Structure

Stamen: Male reproductive structure (anther and filament).
Anther: Produces pollen.
Filament: Supports the anther.
Carpel: Female reproductive structure (stigma, style, ovary).
Ovary: Produces ovules.
Stigma: Receives pollen.
Sepal: Supports the flower bud.
Petal: Pigmented, attracts pollinators.

Diagram of flower showing stamen, anther, filament, carpel, stigma, style, ovary, sepal, and petal.

Complete vs. Incomplete Flowers

Complete flowers: Contain all four parts (sepals, petals, stamens, carpels).
Incomplete flowers: Lack one or more parts; can be perfect (both stamens and carpels) or imperfect (only stamens or only carpels).

Photograph of zucchini flowers, which are imperfect and incomplete.

Male Gametophyte: Pollen Formation

Microspore mother cell (MMC) develops in pollen sacs.
MMC undergoes meiosis to form four haploid microspores.
Each microspore divides mitotically to form an immature pollen grain.
The generative cell divides to form two sperm cells, creating a mature pollen grain.

Diagram of pollen development from microspore mother cell to mature pollen grain.

Female Gametophyte: Embryo Sac Formation

Megaspore mother cell (MMC) develops in the ovule.
MMC undergoes meiosis to form four haploid megaspores; three degenerate.
The remaining megaspore divides mitotically three times to form eight nuclei in one cell.
Cytokinesis forms seven cells (embryo sac); one is the egg cell.

Diagram of embryo sac development from megaspore mother cell to mature embryo sac.

Pollination and Double Fertilization

Pollination occurs when a pollen grain lands on the stigma and grows a pollen tube to the ovary. Double fertilization involves:

One sperm fertilizes the egg, forming the zygote.
The other sperm fuses with two polar nuclei, forming the triploid endosperm (nutrient tissue for the embryo).

Diagram of pollination and double fertilization in flowering plants.

Fruit and Seed Development

After fertilization, the ovary develops into a fruit, which protects the seeds and aids in their dispersal. Fruits can be fleshy (eaten by animals) or dry (dispersed by wind or attachment to animals).

Diagram showing development from flower to fruit, with labeled endosperm, seed coat, and embryo.

Seed Dispersal Mechanisms

Wind: Seeds adapted for wind dispersal are lightweight or have structures for floating in the air.
Water: Some seeds float and are dispersed by water.
Animals: Seeds may be eaten and excreted, or attach to animal fur for transport.

Photograph of dandelion and maple seeds dispersed by wind. Photograph of coconut seedling dispersed by water. Photograph of seeds attached to a dog's fur, showing animal dispersal.

Seed Germination

Requirements and Process

Requires moisture and appropriate temperature.
Some seeds need to be dried, exposed to cold, or have their seed coat broken to germinate.
Many seeds undergo dormancy (reduced metabolic activity) before germination.
In monocots, the shoot is protected by a sheath called the coleoptile.
In dicots, the shoot lacks a coleoptile; the region above the cotyledons is the epicotyl, below is the hypocotyl.
In dicots, the endosperm is used up by the growing cotyledons.