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Lecture 9 Outline (Ch. 35) Overview of plant systems

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1 Lecture 9 Outline (Ch. 35) Overview of plant systems
Major plant cell types Three plant tissues Three plant organs Plant growth Meristems Primary vs secondary Cell elongation & division VI. Summary

2 Plant Structure, Growth, Development
Plants are notably different from animals: SA:V ratio Mobility Growth Response to environment Cell structure

3 Cells  Tissues  Organs  Systems
Setting the scene - animal bodies Cells  Tissues  Organs  Systems

4 Plant Cell Types Plant cell structure recap Cell wall, plasmodesmata
Primary wall (some have secondary wall), middle lamella

5 Plant Cell Types 1) Parenchyma (most abundant):
Flexible, thin-walled cells; living plant metabolism: Photosynthesis; hormone secretion; sugar storage Parenchyma cells in Elodea leaf,(w/chloroplasts) thin wall permeable to gasses large central vacuole able to divide and differentiate

6 Plant Cell Types 2) Collenchyma: Able to elongate
Thick-walled (uneven); living Offers support (flexible & strong) Able to elongate Grouped in strands, lack secondary wall Collenchyma cells sunflower

7 Plant Cell Types 3) Sclerenchyma: Thick, hard-walled; Dead
Offer support (e.g. hemp fibers; nut shells) Thick secondary walls with lignin Rigid (cannot elongate) Two types – sclereids and fibers Sclereid cells in pear (LM) Fiber cells in ash tree Cell wall

8 Plant Tissue Systems 1) Dermal Tissues Outer covering Protection
2) Vascular Tissues “Vessels” throughout plant Transport materials 3) Ground Tissues “Body” of plant Photosynthesis; storage; support Made mostly of basic cell types: Parenchyma Collenchyma Sclerenchyma

9 Three Basic Plant Organs: Roots, Stems, and Leaves
Plant “bodies” Dermal tissue Ground Vascular Plants, like multicellular animals, have organs composed of different tissues, which in turn are composed of cells Each plant organ has dermal, vascular, and ground tissue systems Three Basic Plant Organs: Roots, Stems, and Leaves

10 Think about plant “bodies” in comparison to animal bodies:
For humans list example: CELL TYPES TISSUES ORGANS B. For plants list: 3 CELL TYPES 3 TISSUE SYSTEMS 3 ORGANS

11 Plant Tissues - Dermis Dermal Tissue System (Covering of Plant):
1) Epidermal Tissue (epidermis): Outer layer Cuticle: Waxy covering - reduces evaporation/ predation Root Hairs: extended root surface - Increase absorption 2) Peridermal Tissue (periderm): Only in woody plants (“bark = dead cells”) Protection; support

12 Plant Tissues - Dermis Special Dermal Cells – Trichomes & Root hairs
Hair-like outgrowths of epidermis Keep leaf surfaces cool and reduce evaporation Roots hairs Tube extensions from epidermal cells Greatly increase the root’s surface area for absorption

13 Plant Tissues - Dermis Special Dermal Cells – Guard Cells
Stomata Stomata Guard cells Guard cells Epidermal cell Epidermal cell a. c. 4 µm 200 µm Paired sausage-shaped cells Flank a stoma – epidermal opening Passageway for oxygen, carbon dioxide, and water vapor Stoma Stoma Epidermal cell Epidermal cell Guard cells Guard cells b. 71 µm

14 Plant Tissues - Vascular
Vascular tissues made up of multiple cell types: Arranged in multiple bundles or central cylinder Xylem – water and nutrients Phloem – dissolved sugars and metabolites

15 Plant Tissues - Vascular
1) Xylem (dead at maturity): water and minerals roots to shoots Tracheids: Narrow, tube-like cells Vessel Elements: Wide, tube-like cells Fibers

16 Plant Tissues - Vascular
1) Xylem: Tracheids: - Most vascular plants - Long, thin, tapered ends, lignified secondary walls - Water moves cell to cell through pits Vessel elements: - Wider and shorter - Perforation plates ends of vessel elements - water flows freely though perforation plates

17 Plant Tissues - Vascular
Sieve Tubes: Wide, tube-like cells B) Companion Cells: support and regulate sieve tubes 2) Phloem (living at maturity) cells:

18 Plant Tissues - Vascular
2) Phloem (living at maturity) - Moves water, sugar, amino acids & hormones Sieve tube elements/members • Long narrow cells stack end to end • Pores in end walls (sieve plates) • Lack most cellular structures including: distinct vacuole, Some cytoskeletal elements, Nucleus, Ribosomes Companion Cells: • Adjacent to every sieve tube element • Non-conducting. • Regulate both cells • Connected by numerous plasmodesmata

19 Plant Tissues – Ground Tissue
Tissues that are neither dermal nor vascular are ground tissue Ground tissue internal to the vascular tissue is pith; ground tissue external to the vascular tissue is cortex Ground tissue includes cells specialized for storage, photosynthesis, and support Includes parenchyma, collenchyma, sclerenchyma

20 Plant Organs: Roots - Overview
Roots need sugars from photosynthesis; Shoots rely on water and minerals absorbed by the root system Root Roles: - Anchoring the plant - Absorbing minerals and water - Storing organic nutrients

21 Plant Organs: Roots - Comparisons
Taproots: Fibrous roots: Typical of dicots, primary root forms and small branch roots grow from it In monocots mostly, primary root dies, replaced by new roots from stem

22 Plant Organs: Roots – Structure and Development
Four regions: Root cap Protection, gravity detection Zone of cell division Mitotic divisions Zone of elongation Cells lengthen, no division Zone of maturation Cells differentiate, outer layer becomes dermis

23 Plant Organs: Roots – Vasculature
Epidermis Cortex Endodermis Vascular cylinder Pericycle Core of parenchyma cells Xylem Phloem Dermal Ground Vascular Key to labels 50 m 100 m (a) (b) Root with parenchyma in the center Root with xylem and phloem in the center Dicot Monocot

24 Roots – Many Plants Have Modified Roots
Prop roots “Strangling” aerial roots Storage roots Buttress roots Pneumatophores Roots – Many Plants Have Modified Roots Figure 35.4 Modified roots Water storage

25 Plant Organs: Stems - Overview
Apical bud Node Internode Apical bud Shoot system Vegetative shoot Axillary Stem Stem: an organ made of Alternating nodes, points of leaf attachment Internodes, stem length between nodes Axillary bud - can form a lateral shoot/branch Apical (terminal) bud - near the shoot tip, lengthens a shoot Apical dominance maintains dormancy in most non-apical buds

26 Vasculature - Stems In most monocot stems, the vascular bundles are scattered throughout the ground tissue, rather than forming a ring Phloem Xylem Sclerenchyma (fiber cells) Ground tissue connecting pith to cortex Pith Cortex 1 mm Epidermis Vascular bundle Cross section of stem with vascular bundles forming a ring (typical of eudicots) (a) Key to labels Dermal Ground Cross section of stem with scattered vascular bundles (typical of monocots) (b) bundles tissue Dicot Monocot

27 Stems – Many Plants Have Modified Stems
Rhizomes Bulbs Storage leaves Stem Stolons Stolon Tubers

28 So far we have covered the organs stems and roots:
Match each term number with a letter for the image: A. B. Monocot stem Monocot root Dicot stem Dicot root C. D.

29 Plant Organs: Leaves - Overview
Shoot system Leaf Blade Petiole The leaf is the main photosynthetic organ of most vascular plants Leaves generally have a flattened blade and a stalk called the petiole - joins the leaf to node of the stem

30 Leaves – Structure Leaves are several layers thick – different cell types Key to labels Dermal Ground Vascular Cuticle Xylem Phloem Sclerenchyma fibers Stoma Upper epidermis Palisade mesophyll Spongy mesophyll Lower epidermis Vein Guard cells

31 Plant Organs: Leaves Leaf epidermis contains stomata - allow CO2 exchange Stomata flanked by two guard cells, control open vs. closed

32 Plant Organs: Leaves - Comparisons
Monocots and dicots differ in the arrangement of veins, the vascular tissue of leaves Most dicots have branch-like veins and palmate leaf shape Monocots have parallel leaf veins and longer, slender blades

33 Leaves – Plants have modified leaves for various functions
Tendrils Spines Storage leaves Reproductive leaves Bracts

34 Plant Classification – Monocots vs. Dicots
Basic categories of plants based on structure and function

35 Plant Growth Plant Growth: 1) Indeterminate: Grow throughout life
2) Growth at “tips” (length) and at “hips” (girth) Growth patterns in plant: 1) Meristem Cells: Dividing Cells 2) Differentiated Cells: Cells specialized in structure & role Form stable, permanent part of plant

36 Plant Growth 1) Primary Growth: Apical Meristems:
girth length 1) Primary Growth: Apical Meristems: Mitotic cells at “tips” of roots / stems 1) Increased length 2) Specialized structures (e.g. fruits) 2) Secondary Growth: Lateral Meristems: Mitotic cells “hips” of plant Responsible for increases in stem/root diameter

37 Plant Growth – primary growth

38 Plant Growth in woody plants (secondary growth)
Two lateral meristems: vascular cambium and cork cambium Pith Primary xylem Vascular cambium Primary phloem Cortex Epidermis thicker, stronger stems Vascular Cambium: between primary xylem and phloem

39 Plant Growth Stem – Secondary Growth: Produces inside stem:
Pith Primary xylem Vascular cambium Primary phloem Cortex Epidermis Vascular ray Growth Secondary xylem Secondary phloem First cork cambium Cork Produces inside stem: A) Secondary xylem moves H2O, inward B) Secondary phloem moves sugars, outward

40 Plant Growth Vascular Cambium: Pith Primary xylem Vascular cambium
Primary phloem Cortex Epidermis Vascular ray Growth Secondary xylem Secondary phloem First cork cambium Cork Bark Most recent cork cambium Layers of periderm

41 A hammock is hung between two trees in his backyard by a young man who is 15 years old.
If he returns 20 years later to find his hammock, how will the position of the hammock have changed?

42 Plant Growth – cell growth
Plant cells have cellulose microfibrils in the cell wall These can be enzymatically loosened, and the cell expanded by storing water in the central vacuole. Later the fibrils reattach.

43 Plant Growth – asymmetric divisions
Often plant cells divide unequally in specifying cell types. For example, to form guard cells of stomata, the first division is toward one end of the cell. The second division is rotated 90 degrees. Two guard cells Unspecialized epidermal cell

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