PLANT STRUCTURE & DEVELOPMENT Chapter 35

Overview  Roots – Underground  Shoots – Leafs & Stems  3 Tissue types in the above Dermal, Vascular, & Ground  5 Types of Differentiated Plant Cells Parenchyma Collenchyma Sclerenchyma Xylem Phloem

Roots  Multicellular organ  Anchors plant  Absorbs water & Minerals  May store sugar & starches

Fibrous Roots vs. Taproots  Fibrous Roots – mat of thin roots that are spread just below the root’s surface  Taproots – 1 thick, vertical root with many lateral roots that emanate from it

Root Hairs  Located at the tips of roots  Dramatically increase the surface area  Efficient absorption of H2O and minerals  Mycorrhizae – Symbiotic relationship Root tips & fungus – assist in absorption Found in most plants

Mycorrhizae

Shoots  Consist of Stems & Leaves  Leaves – main photosynthetic organ in most plants  Stems Function is to display the leaves 2 types of buds Terminal (Apical) Bud – located at top end of stem  Growth usually occurs at this bud Axillary Bud – located in the “v” between leaf and stem  Can potentially form a branch

Exercise 1  Follow directions on handout

Plant Organs (Leaf, Stem, & Roots)  3 Tissue types (Ground is on the next slide) Dermal Cover entire plant Protect against water loss  Called Cuticle in the leaves Nonspecific defense mechanism Vascular Continuous throughout the plant Transports material between roots and shoots Xylem – transports water & minerals up from the roots Phloem – transports food from the leaves to rest of plant

Plant Organ Tissue Types  Ground Any tissue that is neither dermal nor vascular If the Ground tissue is located inside the vascular tissue called pith Cortex – ground tissue located outside vascular tissue

5 Types of Differentiated Cells 1. Paren(chyma) cells – Most abundant cell type -- Present throughout the plant -- perform most of the metabolic functions of the plant (Photosynthesis & Respiration) 2. Collen(chyma) cells -- Support growing parts of the plant -- Grouped into cylinders 3. Scleren(chyma) cells -- Occupy NonGrowing parts of plant -- Tough cell walls for structural support

4 th Type of Plant Cells 4. Xylem – water conducting cells -- 2 types: Tracheids & Vessels -- Both types are dead at functional maturity -- Tracheids found in ALL vascular plants -- Long thin cells with lignin -- Water moves through the pits -- Vessels found primarily in angiosperms (flowering plants) -- Have pits & perforated end walls for water movement

Vessel Elements & Tracheids

5 th & Final Type of Plant Cell 5. Phloem – Sugar & other organic compounds 2 Types: Sieve-tube elements & Companion Cells -- Both types are alive at functional maturity Sieve Tubes -- Consist of chains of cells -- Called sieve-tube element -- Highly modified for transport -- Lack nucleus, ribosomes, & vacuoles

Phloem Continued  Besides Sieve Tubes, there are also:  Companion Cells Provide for the molecular needs of the sieve-tube elements Connected to the sieve-tube elements by plasmodesmata

Plant Growth  Plant growth is indeterminant  Growth occurs throughout plant’s life  Embryonic, developing, and mature organs exist at all times during a plant’s life  Animal growth is determinant  Growth ceases after a certain size has been reached

Angiosperms (Flowering Plants)  Classified by years in life cycle (germination  death)  Annuals – 1 year life cycle  Biennials – 2 year life cycle  Perennials – multiple year life cycle

Meristems  Meristems are perpetually embryonic tissues Responsible for indeterminate growth Growth occurs only as a result of cell division in a meristem  2 Types of Meristems Lateral Meristem – Thickening of shoots or roots Thickening is called Secondary Growth Apical Meristem – tips of roots and in buds of shoots Sites of cell division Allow the plant to grow and lengthen Primary Growth – when plant grows at apical meristems Lengthening is called Primary growth

Lateral Meristems  Type of secondary growth  Growth in the thickness of the shoot or root  2 Types  Vascular Cambium Adds layers of tissue called 2ndary Xylem & phloem  Cork Cambium Replaces the epidermis with the periderm (thicker & tougher)

Primary Growth lengthens …  Root Cap – protects delicate meristem of the root tip as it pushes through the soil Secretes a polysaccharide lubricant  Root Tip – contains 3 zones of cells in various stages of growth

3 Zones in root tip  Zone of cell division Root apical meristem & derivatives New root cells are produced in this region Mitotic divisions  Zone of elongation Cells elongate, sometimes significantly  Zone of maturation Differentiation and functional maturation occurs

Roots - Primary Growth

Lateral Roots emerge from the Pericycle (lies inside the endodermis)

What about shoots?  Apical meristem – dome of dividing cells at tip of terminal bud Primary growth (Lengthening) Accomplished by cell division and elongation

Primary Growth in Stems

How does grass continue growth after mowing?  Mowing should destroy the apical meristems, so how would it continue to grow if there were no “growth areas”?

Leaves…  Stomata interrupts the underside of the leaf Flanked by guard cells – open/close the stomata  Ground tissue is in between upper & lower epidermis, in the mesophyll Ground tissue is composed of parenchyma cells Site of photosynthesis are parenchyma cells

Leaf: Cross-Section

Question  Why would there be spaces in the spongy mesophyll?  Why would there not be spaces in the palisade mesophyll?

Secondary Growth  2 lateral meristems are responsible for 2ndary growth  Vascular Cambium – produces 2ndary xylem (wood)  Cork Cambrium – produces a tough covering that replaces epidermis Early in secondary growth  Bark – all the tissues outside the vascular cambium  Includes the phloem derived from the vascular cambium, cork cambium, & tissues derived from cork cambium

Question?  Why would the diameter of the plant have to increase as the plant grows?  Which diameter grows as a higher rate, xylem or phloem? Why?