Roots, Stems, and Leaves

Ms. Moore9/6/2012

• What part of the plant do we eat?

• Label the stems, roots, and leaves of each vegetable.

Small stem surrounded by leaves

Stem with eyes that grow into branches

Floral bud surrounded by leaves

Principal Organs of Seed Plants• Roots– Absorb water– Anchor plants into ground– Hold plants upright through weather

• Stems– Support system– Transport system– Defense against predators and disease

• Leaves– Photosynthesis– Protect against water loss

Tissue Systems• Dermal– Epidermal cells: surround outer covering of a plant– Waxy layer protects against water loss and injury (cuticle)

• Vascular– Xylem– Phloem

• Ground– Between dermal and vascular tissues

• Meristematic– Produces new cells by mitosis

Dermal Tissue

• Single layer of closely packed cells• Covers and protects the plant; acts as “skin”• Thick waxy layer, known as cuticle

Vascular Tissue

• Xylem– Tracheid– Vessel element

• Phloem– Sieve tube elements– Companion cells

Ground Tissue• Parenchyma– Packed with chloroplasts;

site of photosynthesis

• Collenchyma– Celery “strings”; flexible

walls for support

• Sclerenchyma– Rigid; strength and support

Meristematic Tissue

• Meristems: clusters of tissue responsible for continuing growth

• Meristematic tissue: undifferentialted cells produced by mitosis

• Apical meristem: group of cells near the end or top of plant that divide to produce increased length of stems and roots

Mastery

• What are the three main organs of seed plants?

• List the three tissue systems of plants.

• What two cell types make up xylem? Phloem?

• What is the function of meristematic tissue in a plant?

Types of Roots

• Taproots– Primary root grows long and thick– Mainly in dicots

• Fibrous roots– No single root grows larger than the rest– Mainly in monocots

Structure and Growth• Root hair: water enters plant at

tiny projections

• Cortex: spongy layer of ground tissue

• Endodermis: encloses vascular subsystem

• Vascular cylinder: contains xylem and phloem

• Root cap: protects root as it grows through soil

• Casparian strip: waterproofs endodermis

Uptake of NutrientsEssential Plant Nutrients

Nutrient Role in Plant Result of Deficiency

Nitrogen Proper leaf growth and color; synthesis of amino acids, proteins, nucleic acids, and chlorophyll

Stunted plant growth; pale yellow leaves

Phosphorus Synthesis of DNA; development of roots, stems, flowers, and seeds

Poor flowering; stunted growth

Potassium Synthesis of proteins and carbohydrates; development of roots, stems, and flowers; resistance to cold and disease

Weak stems and stunted roots; edges of leaves turn brown

Magnesium Synthesis of chlorophyll Thin stems; mottled, pale leaves

Calcium Cell growth and division; cell wall structure; cellular transport; enzyme action

Stunted growth; curled leaves

Mastery

• Compare a taproot and a fibrous root.

• How are tissues distributed in a plant root?

• What are the two main functions of roots?

Stem Structure and Function• Produce leaves, branches,

and flowers• Hold leaves up to sunlight• Transport substances

between roots and leaves

• Primary Growth: cell divisions in apical meristem• Secondary Growth: growth in lateral meristems in conifers and dicots

Stem Structure

• Nodes: where leaves are attached• Internodes: region between two nodes• Buds: contain undeveloped tissue that can

produce new stems, leaves, flowers• Pith: parenchyma cells inside ring of vascular

tissue (outside cells = cortex) in stem

Monocot vs. Dicot

Growth

• Primary: apical meristem; all seed plants

• Secondary: lateral meristem; dicots– Vascular cambium: increases the thickness of

stems over time– Cork cambium: produces outer covering of stems

Formation of Wood

• Heartwood: older xylem near center no longer conducts water; darker in color

• Sapwood: active in fluid transport; surrounds heartwood; lighter in color

• Bark: tissues outside the vascular cambium

Mastery

• How do the functions of a stem relate to the roots and leaves of a plant?

• Describe how the arrangement of vascular bundles differs between monocot and dicot stems.

• What is primary and secondary growth?• How do heartwood and sapwood differ?

Leaf Structure

• Structure is optimized for absorbing light and carrying out photosynthesis and gas exchange.– Blades: collect sunlight– Petiole: attachment

• Vascular tissues are connected directly to stem’s vascular tissues.

• Xylem and phloem tissues are gathered together into bundles that run from the stem into the petiole to the leaf blade.

• In the leaf blade, vascular bundles are surrounded by parenchyma and sclerenchyma cells.

Leaf Function: Photosynthesis

• Photosynthesis: 6CO2 + 6H2O C6H12O6 + 6O2

• Mesophyll: specialized ground tissue where most photosynthesis occurs– Palisade mesophyll: closely packed cells that absorb light; located

under the epidermis– Spongy mesophyll: loose tissue with many air spaces (gas

exchange) • Stomata: porelike openings in the underside of the leaf that

allow CO2 and O2 to diffuse in and out of leaf• Guard cells: specialized cells in the epidermis that control

the opening and closing of stomata (due to changes in water pressure)

• Why is photosynthesis important to all life?

Leaf Function: Transpiration

• The surfaces of spongy mesophyll are kept moist so that gases can enter and leave the cells easily.

• Transpiration: the loss of water through the leaves

Leaf Functions: Gas Exchange• Leaves take in CO2 and give off O2 during

photosynthesis. – Do leaves ever take in O2?

• Gas exchange takes place in the stomata.• Plants keep stomata open just long enough to

allow photosynthesis to occur. – Why don’t they keep stomata open at all times?– What cells regulate the opening and closing of

stomata?

Mastery

• How is the structure of a leaf optimized for light absorption?

• What factors regulate the opening and closing of guard cells?

• Are stomata more likely to be open or closed on a hot day?

• Describe transport of water and nutrients in a leaf.

Transport in Plants• Combination of root pressure, capillary action,

and transpiration (loss of water through leaves) provides enough force to move water through the xylem tissue.

Up next…Transpiration Lab!

Water Transport

• How is water transported throughout the plant?

• Water molecules are attracted to one another by a force called cohesion; they are attracted to other molecules by adhesion.

• The tendency of water to rise in a thin tube (xylem) is called capillary action.– Water is attracted to the walls of the tube and they

are also attracted to one another.

Nutrient Transport

• Phloem carries out the seasonal movement of sugars within a plant.

• Pressure-flow hypothesis: When nutrients are pumped into or removed from the phloem system, the change in concentration causes a movement of fluid in that same direction. – Source: an area rich in nutrients– Sink: an area that needs nutrients

Review

• Vocabulary

• Study Guide

• Any Questions?