Stern's Introductory Plant Biology: Ch. 3-7

cell theory

a foundational principle in biology that states all plants are composed of one or more cells, the cell is the basic unit of structure, function, and organization in plants, and all cells arise only from pre-existing cells through the process of cell division.

prokaryotic cell

a simple cell type without a true nucleus or membrane-bound organelles, with DNA floating freely in the cytoplasm (example: bacteria).

eukaryotic cell

a complex cell with a true nucleus enclosed by a nuclear membrane and numerous membrane-bound organelles.

cell wall

a rigid outer layer surrounding plant cells, composed primarily of cellulose microfibrils along with pectin and lignin in some cases.

primary cell wall

thin, flexible wall formed first during cell growth, consisting mainly of cellulose and pectin.

secondary cell wall

is a thicker, stronger wall deposited inside the primary cell wall in mature cells, often containing lignin for added rigidity.

middle lamella

a pectin-rich layer that cements adjacent plant cell walls together.

plasma membrane

a semi-permeable phospholipid bilayer located just inside the cell wall that controls the movement of substances into and out of the cell.

cytoplasm

the jelly-like fluid inside the plasma membrane (excluding the nucleus) where most cellular organelles are suspended.

nucleus

the control center of the eukaryotic cell, a membrane-bound organelle containing the cell's DNA.

nucleolus

a dense, non-membrane-bound region inside the nucleus where ribosomal RNA is synthesized.

chromatin

this consists of DNA and associated proteins that make up chromosomes within the nucleus.

chromosome

a condensed structure of DNA and proteins that carries genetic information.

chloroplast

a green, membrane-bound organelle containing chlorophyll and its own DNA, serving as the site of photosynthesis.

thylakoid

flattened, membrane-bound sacs inside chloroplasts stacked into grana where the light-dependent reactions of photosynthesis occur.

granum

a stack of thylakoids within the chloroplast that increases surface area for light absorption.

stroma

the fluid-filled space surrounding the thylakoids inside the chloroplast where the light-independent reactions take place.

central vacuole

a large, fluid-filled sac that stores water, ions, wastes, pigments, and maintains turgor pressure.

tonoplast

the membrane surrounding the central vacuole that actively transports ions and molecules into or out of the vacuole.

turgor pressure

the outward pressure exerted by water against the cell wall due to water filling the central vacuole.

plasmodesmata

tiny cytoplasmic channels through adjacent cell walls that connect the cytoplasm of neighboring plant cells.

endoplasmic reticulum (ER)

an extensive network of interconnected membranes throughout the cytoplasm involved in the synthesis, folding, and transport of proteins and lipids.

rough ER(endoplasmic reticulum)

the portion of the ER(endoplasmic reticulum) studded with ribosomes on its surface, specializing in the synthesis and modification of proteins.

smooth ER(endoplasmic reticulum)

this organelle lacks ribosomes and functions in the synthesis of lipids, detoxification of harmful substances, and calcium ion storage.

Golgi apparatus

a stack of flattened membrane sacs that modifies, sorts, and packages proteins and lipids received from the ER.

vesicle

a small, membrane-bound sac that buds off from the ER or Golgi apparatus to transport proteins, lipids, or other materials.

mitochondrion

a double-membrane organelle that produces ATP through cellular respiration by breaking down glucose.

ribosome

a small organelle composed of RNA and proteins that serves as the site of protein synthesis.

cytoskeleton

an internal framework of microtubules, microfilaments, and intermediate filaments that provides structural support.

microtubule

a hollow, tube-like protein filament in the cytoskeleton that helps maintain cell shape and moves organelles.

microfilament

a thin, solid protein fiber in the cytoskeleton responsible for cell movement and changes in cell shape.

cytoplasmic streaming (cyclosis)

the continuous flowing movement of cytoplasm and organelles within the cell.

Functions of roots

The functions of roots include anchoring the plant in soil, absorbing water and dissolved minerals, storing food and water, conducting materials upward, and forming symbiotic relationships.

Root development

Root development begins when the embryo's radicle emerges from the seed during germination and grows downward to form the first root.

Taproot

A taproot is a single thick, tapered main root with smaller lateral branches, typical of dicots (e.g., carrots, dandelions).

Adventitious roots

Adventitious roots develop from stems or leaves rather than the primary root and form the fibrous root system in monocots (e.g., grasses).

Four regions of root structure

The four regions of a root (from tip outward) are the root cap, region of cell division, region of cell elongation, and region of maturation.

Root cap

The root cap is a thimble-shaped mass of parenchyma cells covering the root tip that protects the delicate meristem from soil abrasion.

Region of cell division

The region of cell division is the apical meristem area at the root tip where rapid mitosis produces new cells.

Protoderm

The protoderm is the outermost primary meristem that gives rise to the epidermis of the root and stem.

Ground meristem

The ground meristem is the primary meristem that develops into the cortex and pith (ground tissues) for storage and support.

Procambium

The procambium is the primary meristem that differentiates into the primary xylem and primary phloem of the vascular cylinder.

Region of cell elongation

The region of cell elongation is where newly produced cells rapidly increase in length by vacuole expansion and water uptake.

Region of maturation

The region of maturation (or differentiation) is where cells specialize into mature types such as root hairs, cortex, endodermis, and vascular tissues.

Root hairs

Root hairs are tubular extensions of epidermal cells in the maturation zone that dramatically increase the surface area for water and mineral absorption.

Cortex

The cortex is the ground tissue layer between epidermis and endodermis, composed mainly of parenchyma cells for storage of starch and transport of water and ions.

Endodermis

The endodermis is the innermost layer of the cortex with cells tightly joined by a waxy Casparian strip that regulates the passage of water and minerals.

Casparian strip

a band of suberin and lignin in the radial and transverse walls of endodermal cells that blocks apoplastic flow.

Pericycle

The pericycle is a layer of parenchyma cells just inside the endodermis that can initiate lateral root formation.

Vascular cylinder (stele)

The vascular cylinder (stele) is the central core of the root containing primary xylem and phloem arranged in a star-shaped pattern.

Mycorrhizae

Mycorrhizae are mutualistic symbiotic associations between fungi and plant roots that enhance the absorption of water and minerals.

Root nodules

swellings on the roots of legumes containing nitrogen-fixing bacteria (Rhizobium) that convert atmospheric N₂ into usable forms.

Specialized roots

Specialized roots include storage roots (e.g., sweet potato), prop roots, pneumatophores, and buttress roots.

Soil texture

Soil texture refers to the relative proportions of sand, silt, and clay particles that determine water-holding capacity.

Soil structure

Soil structure is the arrangement of soil particles into aggregates or clumps that influence pore space and water movement.

Soil horizons

Soil horizons are distinct horizontal layers in a soil profile formed by weathering, organic matter accumulation, and leaching.

Leaves

Leaves originate as primordia (small outgrowths) in buds and are the primary photosynthetic organs of the plant, optimized for light capture and gas exchange.

Petiole

The petiole is the stalk connecting the leaf blade to the stem; leaves lacking a petiole are called sessile (common in many monocots).

Vascular bundles

Vascular bundles in leaves form a network of veins (xylem and phloem) that deliver water/minerals and export sugars while providing structural support.

Stipules

Stipules are outgrowths at the base of the petiole that may protect young leaves or perform photosynthesis.

Simple leaf

A simple leaf has a single, undivided blade attached to the petiole.

Compound leaf

A compound leaf has a blade divided into multiple leaflets attached to a central rachis.

Pinnately compound leaf

A pinnately compound leaf has leaflets arranged in pairs along both sides of a central rachis (like a feather).

Bipinnately compound leaf

A bipinnately compound leaf has leaflets that are themselves pinnately divided, creating a twice-compound structure.

Palmately compound leaf

A palmately compound leaf has all leaflets radiating from a single point at the end of the petiole (like fingers on a hand).

Photosynthesis

Photosynthesis is the process by which green leaves capture light energy using chlorophyll and convert water plus carbon dioxide into glucose and oxygen, powering plant growth and sustaining life on Earth.

Stomata

Stomata are microscopic pores (mostly on the lower leaf surface) flanked by guard cells that regulate gas exchange (CO₂ intake, O₂ and water vapor release) and transpiration.

Guard cells

Guard cells are specialized epidermal cells surrounding each stoma that change shape via turgor pressure to open or close the pore in response to light, CO₂ levels, and water availability.

Functions of leaves

The primary functions of leaves are photosynthesis (energy capture), transpiration (water movement and cooling), guttation (liquid water excretion), waste disposal, and sometimes storage or defense.

Transpiration

Transpiration is the evaporation of water vapor from leaf surfaces (mainly through stomata) that creates a pull drawing water upward from roots through the xylem.

Guttation

Guttation is the exudation of liquid water droplets from leaf margins (via hydathodes) under high humidity when transpiration is low, often seen in the morning.

Mesophyll

The mesophyll is the photosynthetic ground tissue located between the upper and lower epidermis of the leaf, divided into palisade and spongy layers in dicots.

Palisade mesophyll

Palisade mesophyll consists of elongated, columnar cells packed tightly with chloroplasts in the upper leaf half, maximizing light absorption for photosynthesis.

Spongy mesophyll

Spongy mesophyll consists of loosely arranged cells with large intercellular air spaces in the lower leaf half, facilitating gas diffusion and exchange with stomata.

Cuticle

The cuticle is a waxy, waterproof layer secreted by the epidermis that reduces water loss and protects against pathogens and UV radiation.

Abscission

Abscission is the programmed shedding of leaves (or other organs) at a specialized abscission zone where enzymes dissolve cell walls, allowing nutrient resorption before drop.

Sun leaf

A sun leaf is typically small, thick, with a thick cuticle and high chloroplast density, adapted for intense direct sunlight with higher photosynthetic rates.

Shade leaf

A shade leaf is usually larger, thinner, with thinner cuticle and more chlorophyll to capture diffuse light efficiently in low-light environments.

Xerophyte leaf adaptations

Xerophyte leaf adaptations for dry habitats include thick cuticle, sunken stomata, reduced leaf size or spines, and sometimes CAM photosynthesis to minimize water loss.

Hydrophyte leaf adaptations

Hydrophyte leaf adaptations for wet or aquatic habitats include thin or absent cuticle, large air spaces (aerenchyma) for buoyancy and oxygen diffusion, and stomata on both surfaces.

external form of a woody twig

The external form of a woody twig is the axis produced by the stem apical meristem, bearing leaves, buds, and scars that reveal growth history and structure.

node

A node is the region of the stem where one or more leaves are attached, serving as a point of attachment for vascular bundles and buds.

opposite nodes

Opposite nodes have two leaves attached at the same level on opposite sides of the stem.

whorled nodes

Whorled nodes have three or more leaves attached at the same node in a circular arrangement.

internode

An internode is the segment of stem between two successive nodes, where elongation primarily occurs.

leaf

A leaf is a flattened, photosynthetic organ attached to the stem at a node via a petiole or directly (sessile).

petiole

A petiole is the stalk that attaches the leaf blade to the stem, containing vascular bundles for transport.

axil

The axil is the upper angle formed between a leaf petiole and the stem where an axillary bud develops.

axillary bud

An axillary bud is a bud located in the leaf axil that can develop into a branch shoot or flower.

bud scales

Bud scales are protective, modified leaves that cover and insulate dormant buds against cold and desiccation.

terminal bud

A terminal bud is the bud at the tip of the stem or twig responsible for continued apical growth in length.

bud scale scars

Bud scale scars are ring-like marks left on the twig after bud scales fall off, used to determine the age of annual growth increments.

stipules

Stipules are small, paired appendages at the base of a leaf petiole that may protect the young leaf or aid in photosynthesis.

deciduous trees/shrubs

Deciduous trees and shrubs lose all leaves annually at the end of the growing season, leaving dormant buds with visible leaf scars.

bundle scars

Bundle scars are small marks visible on leaf scars where vascular bundles (xylem and phloem) were connected between stem and leaf.

herbaceous dicot stem

A herbaceous dicot stem has vascular bundles arranged in a ring around a central pith, with distinct cortex and epidermis.

monocot stem

A monocot stem has vascular bundles scattered throughout the ground tissue, lacking a distinct pith-cortex boundary and usually no secondary growth.

woody stem

A woody stem undergoes secondary growth via vascular cambium, producing annual rings of xylem (wood) for support and conduction, with heartwood and sapwood regions.

bark

Bark includes all tissues outside the vascular cambium (secondary phloem plus periderm) and provides protection, transport of sugars, and gas exchange.

lenticels

Lenticels are small, spongy pores in the bark that allow gas exchange (oxygen in, CO₂ out) between internal tissues and the atmosphere.