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

Questions Which root type is focused on absorption? Which root type is focused on storage? Fibrous roots are not efficient absorbers, so what structure is responsible for absorption?

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 vast majority of plants

Mycorrhizae

Shoots Consist of Stems & Leaves Plant stuff that is above ground Leaves – main photosynthetic organ in most plants Stems Function is to display the leaves 2 types of buds (growing parts) 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

Questions What is the advantage to a plant to only grow at the apical and axillary buds? A tree house was built between the stem and a branch without axillary buds. The growth rate of the apical buds is 2 feet per year, the growth rate of the axillary buds is 3 feet per year, and the tree house was built at a height of 10 feet. What will be the height of the tree house in 10 years?

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

4th 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

5th & 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

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

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 Zone of elongation 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 grass continue to grow if there were no “growth areas”?

2 other meristems Intercalary Floral Primarily in monocots (grasses) Response to grazing pressure Floral Flower growth Determinate growth

Lateral Meristems Secondary growth 2 Types 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)

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?

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

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

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