angiosperm

1. Four Major Organs of Angiosperms

Angiosperms (flowering plants) have four primary organs:

  • Roots

  • Stems

  • Leaves

  • Flowers

These organs work together for support, transport, photosynthesis, and reproduction.

Roots

Function

  • Anchor the plant in the soil

  • Absorb water and minerals

  • Store nutrients in some plants

Types of Root Systems

Taproot System

  • One main root grows downward from the radicle

  • Smaller lateral roots branch from it

  • Found in most dicots

  • Can store carbohydrates (carrot, beet)

  • Often grows deep to access water

Fibrous Root System

  • Many thin roots of similar size form a network

  • Radicle dies early and is replaced by adventitious roots

  • Common in monocots

  • Helps prevent soil erosion

Stem

Function

  • Supports the plant body above ground

  • Holds leaves and flowers

  • Transports water, minerals, and sugars

Stem Structure

Node

  • Location where leaves or branches grow

Internode

  • Stem segment between nodes

Stem Tissue Types

Vascular tissue

  • Transports materials

Dermal tissue

  • Protects plant and regulates water/gas exchange

Meristematic tissue

  • Produces new cells for growth

Monocots vs Dicots

Difference lies mainly in vascular bundle arrangement.

Leaves

Function

Primary site of photosynthesis

Leaves capture light energy and convert it into chemical energy.

Basic Leaf Structure

Leaf blade

  • Flat surface where photosynthesis occurs

Petiole

  • Stalk attaching leaf to stem

Stipules

  • Small appendages at leaf base

Leaf Types

Simple leaf

  • Single undivided blade

Compound leaf

  • Blade divided into leaflets

Leaf Venation

Reticulate Venation (Dicots)

  • Branching network from a central midrib

Parallel Venation (Monocots)

  • Veins run parallel along leaf length

Flowers

Function

Reproduction in angiosperms.

Flowers produce gametes and form seeds after fertilization.

Four Floral Whorls

Calyx

  • Sepals that protect the flower bud

Corolla

  • Petals that attract pollinators

Androecium

  • Male reproductive part

  • Contains anthers producing pollen

Gynoecium

  • Female reproductive part

  • Contains carpel

  • Ovary holds ovules

Fertilization leads to seed formation.

Plant Tissue Systems

Plant organs contain three main tissue systems:

  1. Dermal tissue

  2. Vascular tissue

  3. Ground tissue

These tissues coordinate plant functions.

Dermal Tissue System

Function

  • Outer protective layer

  • Reduces water loss

  • Controls gas exchange

  • Absorbs water in roots

Major Cells

Epidermal cells

  • Protective outer layer

Guard cells

  • Control opening of stomata

Trichomes

  • Hair-like structures (e.g., root hairs)

Organ-Specific Features

Roots

  • Root hairs increase surface area for absorption

  • No waxy coating

Stems

  • Protective epidermis

  • May contain stomata

Leaves

  • Epidermis contains stomata

  • Covered with waxy cuticle

Cuticle

  • Waxy coating that reduces water loss.

Vascular Tissue

Transport system of the plant.

Two main tissues:

Xylem

Functions:

  • Transport water and minerals upward

  • Provide structural support

Cells:

  • Tracheids

  • Vessel elements

Wood is primarily xylem tissue.

Phloem

Functions:

  • Transport sugars produced during photosynthesis

  • Moves nutrients to roots, fruits, and growing tissues

Cells:

  • Sieve-tube elements

  • Companion cells

Vascular Arrangement

Seed plants

  • Xylem and phloem arranged in vascular bundles

Roots

  • Dicots: xylem center

  • Monocots: xylem surrounds pith

Ground Tissue

Fills space between dermal and vascular tissues.

Functions:

  • Photosynthesis

  • Storage

  • Support

  • Regeneration

Three Ground Tissue Cell Types

Parenchyma

  • Most common plant cell

  • Performs photosynthesis and storage

  • Totipotent (can become other cell types)

Collenchyma

  • Flexible support for growing regions

  • Thick primary cell walls

Sclerenchyma

  • Dead cells with lignin

  • Provide strong support and protection

Meristem Tissue and Plant Growth

Meristems are regions of actively dividing cells responsible for growth.

Plants have indeterminate growth because meristems continually produce new cells.

Types of Meristems

Apical Meristems
Location:

  • Tips of roots

  • Tips of shoots

Function:

  • Responsible for primary growth

Primary Growth

  • Increase in plant length

  • Produces new tissues in stems and roots

Secondary Growth

  • Increase in plant thickness

Occurs mainly in woody plants.

Caused by lateral meristems:

Vascular cambium

  • Produces secondary xylem (wood)

  • Produces secondary phloem

Cork cambium

  • Produces cork

  • Forms part of bark

AP Biology Core Idea

Plant structure reflects function. Roots absorb resources, stems transport and support, leaves perform photosynthesis, and flowers enable reproduction. Tissue systems coordinate these functions while meristems allow continuous plant growth.