1. PLANT STRUCTURE & DEVELOPMENT Chapter 35

2. 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

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

5. 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

6. 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

7. Mycorrhizae

8. 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

10. Exercise 1  Follow directions on handout

11. 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

12. 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

14. 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

16. 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

17. Vessel Elements & Tracheids

18. 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

19. 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

21. 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

22. 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

23. 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

24. 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)

26. 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

27. 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

28. Roots - Primary Growth

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

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

32. Primary Growth in Stems

33. 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”?

34. 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

35. Leaf: Cross-Section

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

37. 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

41. 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?