Plant Form and Function

Roots

Organs that anchor the plant, absorb water and minerals, and often store carbohydrates.

Stems

Organs consisting of nodes (points of leaf attachment) and internodes; they provide structural support and transport.

Leaves

The main photosynthetic organs of most vascular plants; they exchange gases with the atmosphere.

Flowers/Fruits

Reproductive organs found in angiosperms (flowering plants).

Dermal Tissue System

The outer protective covering (epidermis in non-woody plants). Functions in defense and water regulation (stomata).

Vascular Tissue System

Facilitates the transport of materials through the plant.

Xylem

Conducts water and dissolved minerals upward from roots to shoots.

Phloem

Transports sugars from where they are made (leaves) to where they are needed (roots/sites of growth).

Ground Tissue System

Tissues that are neither dermal nor vascular. Functions include photosynthesis, storage, and support.

Parenchyma Cells

Versatile cells with thin primary walls; perform most metabolic functions (e.g., photosynthesis in leaves, starch storage in roots).

Collenchyma Cells

Grouped in strands; provide flexible support to young parts of the plant shoot without restraining growth.

Sclerenchyma Cells

Rigid cells with thick secondary walls containing lignin; provide firm structural support (often dead at functional maturity).

High SA V

Essential for organs involved in absorption or exchange (e.g., thin, flat leaves for light/gas exchange; root hairs for water uptake).

Low SA V

Ideal for storage organs (e.g., thick tubers) to minimize water loss and maximize volume for nutrient storage.

Modified Roots

Prop roots (support), Storage roots (carrots/beets), Pneumatophores (air roots for oxygen).

Modified Stems

Rhizomes (horizontal underground stems), Stolons (runners like strawberries), Tubers (potatoes).

Modified Leaves

Tendrils (climbing), Spines (protection on cacti), Storage leaves (succulents/onions).

Phenotypic Plasticity

The ability of organisms of the same species to produce different phenotypes depending on environmental conditions.

Monocot Stem

Vascular bundles are scattered throughout the ground tissue.

Eudicot Stem

Vascular bundles are arranged in a ring near the perimeter.

Monocot Root

Vascular tissue is arranged in a ring around a central core of parenchyma called the pith.

Eudicot Root

Vascular tissue is located in the center. The xylem often forms a star-like or "X" shape, with phloem wedged between the arms.

Indeterminate Growth

Growth that occurs throughout the plant's life because it possesses perpetually dividing, unspecialized tissues (meristems). Most plants grow this way.

Determinate Growth

Growth that stops after an organ reaches a certain size. Examples include leaves, thorns, and flowers.

Apical Meristems

Located at the tips of roots and the buds of shoots. They provide the additional cells that enable the plant to grow in length (Primary Growth).

Primary Meristems

Behind apical, during embryogenesis, the apical meristems give rise to protoderm, ground meristem, or procambium

Protoderm

Becomes Dermal Tissue, then epidermis

Procambium

Becomes Vascular Tissue, then xylem and pholem

Ground Meristem

Becomes Ground Tissue, then paren, scleren, and collenchyma

Epidermal Cells

General flattened cells that secrete the cuticle (a waxy coating) to prevent water loss.

Guard Cells

Specialized cells that flank stomata (pores); they open and close to regulate gas exchange and water loss.

Trichomes

Hair-like outgrowths that can reduce evaporation, reflect excess light, or secrete sticky/toxic substances to deter herbivores.

Root Hairs

Extensions of root epidermal cells that vastly increase surface area for water and mineral absorption.

Epidermis

Outermost layer responsible for absorption and protection (with root hairs).

Cortex

Thick layer of ground tissue (parenchyma) used for storage.

Endodermis

The innermost layer of the cortex; it acts as a selective barrier for water entering the vascular cylinder.

Stele (Vascular Cylinder)

The central core containing the Xylem and Phloem.

Vascular Bundles

Strands of xylem and phloem. In eudicots, they form a ring; in monocots, they are scattered.

Pith

Ground tissue internal to the vascular tissue (in eudicots).

Cortex

Ground tissue external to the vascular tissue.

Mesophyll

The "middle leaf" ground tissue where most photosynthesis happens.

Palisade Mesophyll

Tightly packed, elongated cells (usually on the top of the leaf).

Spongy Mesophyll

Loosely arranged cells with air spaces for gas exchange (usually on the bottom).

Veins

The vascular bundles of the leaf (Xylem on top, Phloem on bottom).

Tracheids & Vessel Elements

Xylem tissue, Conducts water and minerals. These cells are dead at maturity and have lignified walls for structural support.

Sieve-tube Elements & Companion Cells

Phloem tissue, Transports sugars (photosynthates). Sieve-tubes lack organelles to allow flow; Companion cells "load" the sugar and keep sieve-tubes alive.

Meristem Hierarchy

apical → primary → tissue systems

Monocot

monophyletic group/clade that have one embryonic seed leaf. Other characteristics: fibrous root system, veins parallel, floral organs in multiples of 3.

Eudicot

Consists of most of the angiosperms, have two embryonic seed leaves (cotyledons). Other characteristics: taproot, leaf veins branched, floral organs in multiples of 4 or 5

Root Cap

A protective, cap-like structure at the very tip of the root that covers the apical meristem and aids in sensing gravity (gravitropism).

Zone of cell division

apical meristem, The region where new cells are constantly produced.

Zone of elongation

The area where newly produced cells grow in size, driving the root through the soil.

Zone of maturation

Where cells differentiate into specific tissue types.

Primary Cell Wall

The relatively thin and flexible layer secreted by a young plant cell.

Secondary Cell Wall

A strong and durable matrix often deposited in several laminated layers for plant protection and support. (in xylem and sclerenchyma)

Middle Lamella

A thin layer rich in sticky polysaccharides called pectins that glues adjacent plant cells together.

Cellulose

The primary structural carbohydrate that makes up the fibers of the cell wall.

Lignin

A complex organic polymer that hardens the secondary cell walls of "woody" plants.

Vascular Cambium

thin cylinder of meristematic cells located between the primary xylem and primary phloem. divides to produce Secondary Xylem (inward, wood) and Secondary Phloem (outward, bark).

Growth Rings

In temperate regions, the vascular cambium produces large xylem cells in the spring (early wood) and smaller cells in the summer (late wood)