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Plant Structure and Function

A Meridian© Biology AP Study Guide by John Ho and Tim Qi

Plant Terms Growth:

Growth TypesType Location Description

Primary PrimaryMeristem

Vertical growth (up-down), dominant direction in most plants.

Secondary LateralMeristem

Horizontal growth (left-right), adds layers to the plantthickening stems and roots.

• Meristem: Unspecialized embryonic plant tissue found in areas of growth Apical Meristem: Type of primary meristem located at the tip of stems or roots

where cell division occurs. Vascular Cambium: Lateral meristem found in stems that develops into secondary

xylem (inwards) and secondary phloem (outwards).

© Copyright© 2006 (March 2nd) All rights reserved. Study Guide v1.6 by Meridian notes. Do not distribute orreproduce without replicating this copyright

Plant Growth

Primary Growth Secondary Growth

Lateral MeristemPrimary Meristem

Vascular Cambium

Ground Tissue

Procambium VascularTi u

Secondary Xylem (wood)

Secondary Phloem (bark)

Periderm

Cork Cambium

Apical Meristem



Plant Tissue:Primary Growth Types

Type Region DescriptionDermal Outer Outer region made up of dead cells that act as a protective

covering aginst the environment and water loss.

Ground Contains parenchyma, collenchyma, and sclerenchyma.Performs photosynthesis and adds to structural support.

Parenchyma(Youngest)

Thin-walled cells found in mostly in younger sections of plants. Most of photosynthesis occurs in these cells

Collenchyma(Mid-aged)

Supporting cells with thicker walls that make up much of thestem.

Sclerenchyma(Oldest)

Mid

Rigid dead support cells with a secondary cell wall. The pithand bark are made up of these cells

Vascular Inner Center tissue responsible for transporting water and otherminerals.

Transportation Structures

• Water Potential: Determines direction of osmosis (high to low)

Water Potential (ΨΨΨΨ)

Value (ΨΨΨΨ)))) Solute Level Description

(-) Negative Higher Water is absorbed from surrounding environment

(0) Zero Same Potential of pure water, no amount is lost or gained

(+) Positive Lower Water is lost to surrounding environment

• Transpiration Pull: Accounts for water movement up the xylem. Water lost fromevaporation causes extremely low (negative) water potential towards the top of the plant.Water diffuses upwards, providing the necessary reactant for photosynthesis withoutexpending energy.

• Translocation: (Pressure Flow Hypothesis) Movement of sugar from “sources” to “sinks”during the build-up of pressure when a high concentration of sugar draws in water.

3. Osmosis of water intothe phloem

4. Build-up

of pressure

1. Build-up

of sugar

2. Activetransport

into phloem

5. Movementtowardslower

pressure



Sources and Sinks

Plant PartType

Spring Winter

Description

Source Leaves Root Leaves undergo photosynthesis, producing sugar which isstored in the roots.

Sink Root Leaves Roots send stored sugar into the upper portions of the plant,which now act as the sink.

• Xylem and Phloem:Xylem and Phloem

Type Transports DescriptionXylem Hollow, dead cells that act as a funnel through which water

is transported via transpiration pull.

Tracheids Found in gymnosperms, long thin tubes for water transport.

VesselElements

Water

Found in angiosperms, thicker tubes than tracheids andmore efficient at transporting material.

Phloem Living tissue that carries organic nutrients

Sieve tubeelements

Forms a tube of cells joined end to end, lack manyorganelles and rely upon companion cells for survival.

Companioncells

Sugar

Linked to sieve tube element (through plasmodesmata),metabolically active and provided sieve tube cells withnutrients.

• Tracheophytes: All vascular plants with specialized tissue for transporting water (xylemand phloem). Includes ferns, gymnosperms and angiosperms.

Plant Miscellaneous ComponentsPlant Cell Organelles

Tonoplasts Large membrane bound compartments that maintain turgor pressure(stiffness).

Leucoplasts Plant organelle for bulk storage (such as sugar), found in roots.

Ligin A polymer that binds cellulose together to form cell walls.

Suberin Waxy, water-resistant substance found in the Casparian Strip and thecork.

Vascular

Tissue

Xylem:

Water

Phloem:

Sugar

Sieve Tube

ElementsCompanion CellsTracheids Vessel Elements



Root Structure and Types Root Systems:

Root TypesTaproot One main, vertical root from which thinner, horizontal roots (lateral

roots) grow from.

Fibrous Root Dense mat of thin roots that are typically shallow.Adventitious Root System where the stem lays horizontal, allowing roots to grow from

the stem downwards.

Root Function: 1) Anchor plant, 2) Absorb nutrients, and 3)Store nutrients Root Growth :

Root Transportation:Transportation Routes

Apoplastic route Pathway in between cells (through gaps in between cell walls) watermolecules diffuse through to reach the vascular cylinder

Symplastic route Pathway within cells (through the cytoplasm) water molecules diffusethrough to reach the vascular cylinder

Root Structure:

• Stele: Also “vascular cylinder”, it is the innermost vascular tissue, located in the center inroots and around the pith (if present) in the stem.

• Casparian Strip: Waterproof strip between the cortex and stele (within endodermis) whichcontrols water entry in the vascular tissue.

Root (ground level to root cap)

Zone of Maturation

Zone of Elongation

Zone of Cell Division



Leaf Structure and Functions Leaf Structure:

• Cross-Section:

• Blade: A fully mature plant leaf, including all parts up to the stem.

• Petiole: Stalk attaching the blade to the plant’s stem.

• Stoma and Guard Cells: Located in the underside of the leaf, responsible for gasexchange.

Regulation of StomaType Turgor

PressureK+ Ion

AmountDescription

Closed Low Low Loss of K+ ions from the guard cells causes water to flow out,relaxing the pressure and causing the stoma to close.

Open High High Influx of K+ ions into the guard cells causes water to flow in,raising the pressure and opening the stoma.

meridian] plant structure and function1

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