NOT ON AP: NEEDED FOR BACKGROUND

• Plant Structure and Growth

The Diversity of Angiosperms

• Angiosperms (flowering plants) can be divided into 2 major categories:– Monocots –

• have one seed leaf (cotyledon)

– Dicots – • have 2 seed leaves

(cotyledons)

Monocots

• Monocots have only 1 cotyledon (seed leaf)• Examples of monocots:

– Corn, wheat, lilies, orchids, palms

Dicots

• Dicots have 2 cotyledons (seed leaves)• Examples of dicots:

– Roses, clover, tomatoes, oaks, daisies

Woody vs. Herbaceous Plants

• Angiosperms can also be subdivided into the groups of woody and herbaceous plants

– Woody plants are made of cells with thick cell walls that support the cell body

• Examples: trees, shrubs, vines

– Herbaceous plants do not produce wood as they grow, and instead have smooth stems

• Examples: dandelions, sunflowers

Anatomy of an

angiosperm

Angiosperm structure• Three basic organs:

– Roots (root system)

• fibrous: mat of thin roots

• taproot: one large, vertical root

– Stems (shoot system)

• nodes: leave attachment

• internodes: stem segments

• axillary bud: dormant, vegetative potential

• terminal bud: apex of young shoot

– Leaves (shoot system)

– blade

– petiole

Plant Organ Systems

• Dermal (epidermis): single layer of cells for protection– Cuticle: a waxy coating on many leaves and stems

• Vascular (material transport)– xylem: water and dissolved minerals roots to shoots– phloem: food from leaves to roots and fruits

• Ground (photosynthesis, storage, support): tissues that are neither dermal or vascular– Pith: internal to the vascular tissue – Cortex: external to the vascular tissue

Plant Growth• Life Cycles

– annuals: complete their life cycle in 1 year or less (wildflowers; food crops)

– biennials: complete their life cycle in 2 years or less (beets; carrots)

– perennials: live many years (trees; shrubs)

• Meristems: have indeterminate growth cycles

– apical: tips of roots and buds; primary growth

– lateral: cylinders of dividing cells along length of roots and stems; secondary growth (wood)

The Root System

• What do roots do?– Anchor the plant in the soil– Absorb minerals and water– Store food

• Types of root systems– Fibrous root system

• Found mostly in monocots

– Taproot system • Found mostly in dicots

Primary growth• Roots

• root cap: protection of meristem and pushes through soil

• zone of cell division: primary (apical) meristem where new root cells are produced

• zone of elongation: cells elongate; pushes root tip into soil

• zone of maturation: complete maturation and differentiate to become tissues

The Shoot System

• The shoot system consists of:– vegetative shoots (which

bear leaves)– floral shoots (which bear

flowers)• Stems have 3 important

functions:– Producing leaves, flowers,

branches– Holding leaves up to the

sunlight– Transporting substances

between roots and leaves

Primary Tissues of Stems• Vascular bundles (xylem and phloem)

• Surrounded by ground tissue (xylem faces pith (central core of plant) and phloem faces cortex (tissue between the vascular tissue and the dermis). . . See diagram below)

How do stems grow?

• Primary growth– Increase in length

– Occurs by cell divisions in apical meristem (at top of shoot)

• Secondary growth– Increase in width

– Occurs by cell divisions in the lateral meristems (also known as vascular cambium)

Apical Meristems

The Shoot System: Leaves

• Leaves are attached to stems at nodes

• The area between 2 nodes is called an internode

The Shoot System: Leaves

• Leaves are the primary photosynthetic organs of most vascular plants

• Most leaves have a flattened blade and a petiole, which is the stalk that attaches the leaf to the stem

Primary Tissues of Leaves• Epidermis/cuticle (protection; desiccation)

• Stomata (tiny pores for gas exchange and transpiration): surrounded by guard cells which open and close stomata

• Mesophyll: ground tissue between upper and lower epidermis ; site where photosynthesis takes place

Secondary Growth• This type of growth produces thickness in stems and roots in

woody plants• Two lateral meristems

– vascular cambium: produces secondary xylem (wood) and secondary phloem (diameter increase; annual growth rings)

– cork cambium: produces thick covering that replaces the epidermis; produces cork cells; cork plus cork cambium make up the periderm (outer, protective coat)

– Bark: all tissues external to vascular cambium (phloem plus periderm)

The formation of

“bark”

Tissue Systems in Plants

• All 3 plant organs (root/stem/leaf) have dermal, vascular, and ground tissue systems

• Dermal Tissue System– Outer protective covering,

similar to our skin – Protects the plant from

water loss and disease– The cuticle is a waxy

coating that helps to prevent water loss

Tissue Systems in Plants

• Vascular Tissue System– Carries out long-distance

transport of materials within the plant

– Xylem and phloem are examples of vascular tissues

• Ground Tissue System– Pith (inside vascular tissue)

and cortex (outside vascular tissue) are examples of ground tissue

– Includes cells specialized for storage, photosynthesis, and support

Summary of primary & secondary growth in a woody a stem

Apicalmeristemof stem

PRIMARY PRIMARY LATERAL SECONDARYMERISTEMS TISSUES MERISTEM TISSUES

Protoderm Epidermis Secondary phloem

Primary phloem Vascular Procambium cambium Secondary

Primary xylem xylem

Groundmeristem Ground Pith &

tissue: Cortex Cork cambium Cork

Periderm

Microscope Activity

• You will be examining various slides of plants

• In your lab notebooks, I want you to draw what you see at the 100X and 400X powers and label as many parts as you can

– You may use your textbooks for aid (look at the diagrams in Ch. 35)

– pp. 721 - 726