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Ch. 31 – Plant Structure, Growth and Differentiation.

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Presentation on theme: "Ch. 31 – Plant Structure, Growth and Differentiation."— Presentation transcript:

1 Ch. 31 – Plant Structure, Growth and Differentiation

2 Plant Body Root system – Underground – Anchor and absorb Shoot system – Vertical stem, leaves (flowers, fruits w/seeds) – photosynthesis

3 Fig. 35-2 Reproductive shoot (flower) Apical bud Node Internode Apical bud Shoot system Vegetative shoot Leaf Blade Petiole Axillary bud Stem Taproot Lateral branch roots Root system

4 Plant Cells and Tissues Ground tissue system – majority – Photosynthesis, storage, support Vascular tissue system – Conduction, strength, support Dermal tissue system – Covering, protection All 3 are Interconnected throughout the plant

5 Fig. 35-8 Dermal tissue Ground tissue Vascular tissue

6 Ground Tissue System Parenchyma, collenchyma, sclerenchyma tissue Primary cell wall – secreted by growing cell; stretches and expands as cell grows Secondary cell wall – secreted when cell stops growing; thick and strong (inside primary)

7 Parenchyma Living, metabolizing Most common Soft parts Function – Photosynthesis – green chloroplasts – Storage – starch, oil, water, salt – Secretion – resins, tannins, hormones, enzymes, nectar Can differentiate if plant injured (i.e. xylem cells)

8 Fig. 35-10a Parenchyma cells in Elodea leaf, with chloroplasts (LM) 60 µm

9 Parenchyma

10 Collenchyma Flexible, structural support (nonwoody parts) Elongated cells Alive at maturity Primary CW – unevenly thick, thicker in corners Near stem surface, leaf veins

11 Fig. 35-10b Collenchyma cells (in Helianthus stem) (LM) 5 µm

12 Collenchyma

13 Sclerenchyma Structural support Primary and secondary CW (strong and hard, extreme thickening, so can’t stretch, elongate) Cells dead at maturity 2 types: – Sclereids – variable shape, nut shells, pits of stone fruits, pears gritty (clusters of sclereids) – Fibers – long, tapered – patches, clumps; wood, inner bark, leaf veins

14 Sclerenchyma

15 Fig. 35-10c 5 µm 25 µm Sclereid cells in pear (LM) Fiber cells (cross section from ash tree) (LM) Cell wall

16 Vascular tissue Embedded in ground tissue Transport Xylem and phloem

17 Xylem Conducts water, dissolved nutrient minerals roots  stems, leaves Support Angiosperms – – tracheids, vessel elements - conduct – parenchyma cells - storage – fibers - support

18 Tracheids and vessel elements Dead at maturity  hollow, CW remain Tracheids – long, tapering, patches/clumps; water passes from 1 tracheid to another by pits (thin areas where sec. wall did not form) Vessel elements – larger in diameter than tracheid; end walls have perforations; stacked  water goes between; stack = vessel; pits in side walls for lateral water transport

19 Fig. 35-10d Perforation plate Vessel element Vessel elements, with perforated end walls Tracheids Pits Tracheids and vessels (colorized SEM) Vessel Tracheids 100 µm

20 Phloem Conducts food Support Angiosperms – Sieve tube members, companion cells – conduct – Fibers – support – Parenchyma cells

21 Sieve tube members Conduct food in solution Joined end-to-end  long tubes CW ends = sieve plates; cytoplasm extends between cells Living at maturity – many organelles shrink/disintegrate Can function w/o nuclei

22 Companion cells Adjacent to each sieve tube member (stm) Assists stm Living w/ nucleus – directs activities of both cells Plasmodesmata between stm and companion Helps move sugar into stm

23 Fig. 35-10e Sieve-tube element (left) and companion cell: cross section (TEM) 3 µm Sieve-tube elements: longitudinal view (LM) Sieve plate Companion cells Sieve-tube elements Plasmodesma Sieve plate Nucleus of companion cells Sieve-tube elements: longitudinal view Sieve plate with pores (SEM) 10 µm 30 µm

24 Food conducting

25 Dermal tissue system Epidermis and periderm Protective covering Herbaceous – single layer = epidermis Woody – epidermis splits w/ growth – Periderm – layers thick, under epidermis; replaces epidermis in stems, roots, composing outer bark

26 Epidermis Unspecialized dermal cells Special guard cells + trichomes Single layer, flat cells Usually no chloroplasts  transparent – Allow light through

27 Fig. 35-18a Key to labels Dermal Ground Vascular Cuticle Sclerenchyma fibers Stoma Bundle- sheath cell Xylem Phloem (a) Cutaway drawing of leaf tissues Guard cells Vein Cuticle Lower epidermis Spongy mesophyll Palisade mesophyll Upper epidermis

28 Fig. 35-18b Guard cells Stomata pore Surface view of a spiderwort (Tradescantia) leaf (LM) Epidermal cell (b) 50 µm

29 Fig. 35-18c Upper epidermis Palisade mesophyll Key to labels Dermal Ground Vascular Spongy mesophyll Lower epidermis Vein Air spacesGuard cells Cross section of a lilac (Syringa) leaf (LM) (c) 100 µm

30 Cuticle Aerial parts Secreted by epidermal cells Waxy – water loss Slows diffusion of CO2 – stomata help Stomata – Open – day – photosynthesis, evaporative cooling – Closed – night – Closed in day if drought

31 Trichomes Outgrowths or hairs Many shape, sizes, functions Ex: – Roots hairs – increase SA – Salty env. – remove excess salt – Aerial parts – increase light reflection, cooler – Protections – stinging nettles

32 Growth at Meristems Cell division – Increase # cells Cell elongation – Vacuole fills, increase pressure on CW, expands Cell differentiation – Specialize into cell types Meristems = where plant cells divide, mitosis – No differentiation

33 2 kinds of Growth Primary growth – Increase stem, root length – All plants, soft tissues Secondary growth – Increase width – Gymnosperms, woody dicots – Wood + bark

34 Fig. 35-11 Shoot tip (shoot apical meristem and young leaves) Lateral meristems: Axillary bud meristem Vascular cambium Cork cambium Root apical meristems Primary growth in stems Epidermis Cortex Primary phloem Primary xylem Pith Secondary growth in stems Periderm Cork cambium Cortex Primary phloem Secondary phloem Pith Primary xylem Secondary xylem Vascular cambium

35 Primary growth Increase in length Apical meristem – tips of roots + shoots (buds) Buds = dormant embryonic shoot (develop into branches next spring Root tip – Root cap – protective layer of cells, covers root tip – Root apical meristem – directly behind root cap – Cell elongation – behind meristem, push tip ahead, some differentiation

36 Fig. 35-13 Ground Dermal Key to labels Vascular Root hair Epidermis Cortex Vascular cylinder Zone of differentiation Zone of elongation Zone of cell division Apical meristem Root cap 100 µm


38 Fig. 35-14a1 Root with xylem and phloem in the center (typical of eudicots) (a) 100 µm Epidermis Cortex Endodermis Vascular cylinder Pericycle Xylem Phloem Dermal Ground Vascular Key to labels

39 Fig. 35-14a2 Vascular Ground Dermal Key to labels Root with xylem and phloem in the center (typical of eudicots) (a) Endodermis Pericycle Xylem Phloem 50 µm

40 Fig. 35-14b Epidermis Cortex Endodermis Vascular cylinder Pericycle Core of parenchyma cells Key to labels Dermal Ground Vascular Xylem Phloem Root with parenchyma in the center (typical of monocots) (b) 100 µm

41 Shoot apex = terminal bud – Shoot meristem – Give rise to leaf primordia and bud primordia

42 Fig. 35-16 Shoot apical meristem Leaf primordia Young leaf Developing vascular strand Axillary bud meristems 0.25 mm

43 Fig. 35-17a Sclerenchyma (fiber cells) PhloemXylem Ground tissue connecting pith to cortex Pith Cortex Epidermis Vascular bundle 1 mm Cross section of stem with vascular bundles forming a ring (typical of eudicots) (a) Dermal Ground Vascular Key to labels

44 Fig. 35-17b Ground tissue Epidermis Key to labels Cross section of stem with scattered vascular bundles (typical of monocots) Dermal Ground Vascular (b) Vascular bundles 1 mm

45 Secondary Growth Increase in width Make secondary tissues: sec. xylem, sec. phloem, periderm Lateral meristem – cells divide, not elongate 2 types: – Vascular cambium Between wood and bark Make sec. xylem (wood) + sec. phloem (inner bark)

46 Fig. 35-20 Vascular cambium Growth Secondary xylem After one year of growth After two years of growth Secondary phloem Vascular cambium XX X X X X P P P P C C C C C C C C C C C C C

47 Fig. 35-22 Growth ring Vascular ray Secondary xylem Heartwood Sapwood Bark Vascular cambium Secondary phloem Layers of periderm


49 – Cork cambium In outer bark Form cork to outside +parenchyma (storage) Periderm = cork, parenchyma, cork cambium

50 Bark – outermost covering of woody stems – Everything outside of vascular cambium – 2 regions: Living inner bark of secondary phloem Mostly dead outer bark of periderm

51 Fig. 35-19a3 Epidermis Cortex Primary phloem Vascular cambium Primary xylem Pith Primary and secondary growth in a two-year-old stem (a) Periderm (mainly cork cambia and cork) Secondary phloem Secondary xylem Epidermis Cortex Primary phloem Vascular cambium Primary xylem Pith Vascular ray Secondary xylem Secondary phloem First cork cambium Cork Growth Cork Bark Most recent cork cambium Layers of periderm

52 Fig. 35-19b Secondary phloem Vascular cambium Secondary xylem Bark Early wood Late wood Cork cambium Cork Periderm 0.5 mm Vascular ray Growth ring Cross section of a three-year- old Tilia (linden) stem (LM) (b) 0.5 mm

53 You should now be able to: 1.Compare the following structures or cells: – Dermal, vascular, and ground tissues – Parenchyma, collenchyma, sclerenchyma, water- conducting cells of the xylem, and sugar- conducting cells of the phloem – Sieve-tube element and companion cell 2.Describe in detail the primary and secondary growth of the tissues of roots and shoots 3.Describe the composition of wood and bark

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