Chapter 35.1:

1. Chapter 35.1: The Plant Body Has a Hierarchy of Organs, Tissues And Cells Raganya Ponmanadiyil, Ivon Vassileva, Amy Csete

2. Plants draw resources from above and below ground due to three basic organs: ROOTS, STEMS and LEAVES • Roots form the root system • - non photosynthetic, therefore relies on shoot system • Stems and leaves form the shoot system • - depends on root system for water & minerals

3. ROOT: a multi-cellular organ that ANCHORS a vascular plant in the soil, ABSORBS minerals and water, and often STORES carbohydrates.

4. Root System: Taproot System • TAPROOT: • main vertical root that develops from an embryonic root • - gives rise to lateral roots (branch roots) • - stores sugars and starches • - penetrates deeplyand are well-adaptedto deep soils

5. Root System: Fibrous Root System • FIBROUS: • a mat of thin roots spreading out below the soil surface, no root functioning as the main one • - do not penetrate deeply • - best adapted to shallow soils where rainfall is light

6. Root System: Fibrous Root System • ADVENTITIOUS: roots that grow in an unusual location (ex. roots arising from stems/leaves) • - In seedless vascular plants (for example: grass), the embryonic root dies and does not give rise to a main root, instead it has small roots from the stem

7. Root Hairs: thin, tubular extensions of a root epidermal cell • vast number of tiny hairs that increase the surface area of the root enormously • they absorb water and minerals • grow at the tip of the roots • main function = absorption

8. Modified Roots: Prop Roots/Ariel Roots Supports tall, top heavy plants Example: CORN

9. Modified Roots: “Strangling” Aerial Roots Wraps around the host tree or such objects; eventually causing shading to the tree resulting in it to die. Example: STRANGLER FIG

10. Modified Roots: Buttress Roots Aerial roots that look like buttresses support the tall trunks of some tropical trees Example: CEIBA TREE

11. Modified Roots: Pneumatophores aka: air roots Produced by trees that inhabit tidal swamps. They project above the water’s surface and enable the root system to obtain oxygen. Example: MANGROVES

12. Modified Roots: Storage Roots Stores food and water for future use Example: COMMON BEET

13. QUIZ TIME! State three modified roots. • Prop roots (Aerial) • Strangling aerial roots • Buttress roots • Storage roots • Air roots (Pneumatophores)

14. STEM: an organ consisting of an alternating system of NODES and INTERNODES

15. Nodes & Internodes • NODES: the area of a plant’s stem where the leaves grow • INTERNODES: the stem segments between the nodes

16. Axillary & Apical Bud • located in the upper angle (axil) formed by each leaf and stem • it is a structure that can form a lateral shoot (ie. a branch) • most axillary buds are dormant in young shoots • elongation of a young shoot is concentrated near the shoot tip; which consists of an APICAL BUD/TERMINAL BUD

17. Axillary & Apical Bud • the proximity of the axillary buds to the apical buds is partly responsible for their dormancy • APICAL DOMINANCE:the inhibition of axillary buds by an apical bud • -the evolutionary adaptation of apical dominance increases the plant’s exposure to light • if shading results in the light being more intense to theside of a plant than directly above, axillary buds break dormancy, which give rise to a lateral root • removing apical buds usually stimulates the growth of axillary buds, resulting in more lateral shoots

18. Modified Stems: Rhizomes A horizontal shoot that grows just below the surface. Example: BASE OF IRIS PLANT

19. Modified Stems: Bulbs Vertical underground shoots consisting mostly of the enlarged bases of leaves that store food. Example: ONION BULBS

20. Modified Stems: Stolons Horizontal shoots that grow along the surface (“runners”). They enable a plant to reproduce asexually. Example: STRAWBERRIES

21. Modified Stems: Tubers Enlarged ends of stolons or rhizomes specialized for storing food. Example: RED POTATOES

22. QUIZ TIME! Define bulbs and stem tubers and name their function. Bulbs - Vertical underground shoots consisting mostly of the enlarged bases of leaves Function: store food Stem Tubers - Enlarged ends of stolons or rhizomes specialized Function: storing food

23. LEAVES: generally consists of a flattened blade and the petiole (a stalk), which joins the leaf to the stem at a node The main photosynthetic organ.

24. Monocots & Eudicots • MONOCOTS: has a single cotyledonor embryonic seed leaf • - lack petioles (ie. grass), instead the base of the leaf forms a sheath that envelops the stem • - parallel major veins that run the length of the blade • EUDICOTS:has two cotyledons or embryonic seed leaves • - branched network of major veins

25. Leaf Shapes: • SIMPLE:a simple leaf has a single, undivided blade • COMPOUND: the blade consists of multiple leaflets • DOUBLY COMPOUND:each leaflet is divided into smaller leaflets • LEAFLETS have no axillary bud at the base, LEAVES have axillary buds

26. Modified Leaves: Tendrils Sometimes also modified stems. Forms a coil that brings it closer to a support. Example: GRAPEVINES

27. Modified Leaves: Spines The spines of cacti are actually leaves. Photosynthesis is carried out by the fleshy green stems. Example: PRICKLY PEAR

28. Modified Leaves: Storage Leaves Modified for storing water. Example: ICE PLANT

29. Modified Leaves: Reproductive Leaves Produce adventitious plantlets, which fall off the leaf and take root in the soil.

30. Modified Leaves: Bracts Often mistaken for petals; they surround a group of flowers. Such brightly coloured leaves attract pollinators. Example: POINSETTIA

31. Quiz time! State two modified leaves and name their function. • Tendrils: support • Spines: Photosynthesis • Storage leaves: storing water • Reproductive leaves: Produce adventitious plantlets for reproduction • Bracts: attract pollinators

32. Dermal, Vascular and Ground Tissues AS. 9.2.4 and 9.2.6

33. Each organ of a plant has three tissue systems: • Dermal • Vascular • Ground • Each system is continuous throughout the plant body

34. Dermal Tissue System: plant’s outer protective covering • Non-Woody plants: usually a single cell tissue called an epidermis • Epidermis not only protects cell, but has special characteristics in each organ • Eg. Root hairs on epidermal cell near root tip reduce water loss and reflect excess light • Provide protection against insects and toxic compounds

35. Vascular Tissue System: Transports materials from root to shoot • 2 types of vascular tissues: • xylem and phloem • Xylem: Moves water and dissolved minerals from roots to shoots • Phloem: transports sugars from leaves to roots and sites of growth

36. Ground Tissue System: Tissues that are neither dermal nor vascular • Pith: Ground tissue internal to the vascular system • Cortex: Ground tissue external to the vascular system • Ground tissue system • is a filter • includes specialized cells for functions like storage, photosynthesis and support

37. Quiz time! Label the diagram below:

38. Common Types of Plant Cells • Plants characterized by cellular differentiation • Major types of plant cells • parenchyma cells • collenchyma cells • sclerenchyma cells • water-conducting cells of the xylem • sugar-conducting cells of the phloem

39. Parenchyma Cells (“Typical” Plant Cells) • Characteristics • Have thin and flexible primary cell walls • Large central vacuole • Perform • Most metabolic functions of plant • Synthesize and store various organic products • Photosynthesis occurs in chloroplasts of these cells in the leaf • Most of these cells are able to divide and differentiate into other types of plant cells under particular conditions • During wound repair • Possible to grow entire plant from single parenchyma cell

40. CollenchymaCells (Flexible Support Cells) • Characteristics • Are grouped in strands • Help support young parts of plant shoot • Have thicker primary cell walls • Lack hardening agent lignin in primary walls • Due to this they provide flexible support without restraining growth • At maturity they are: • Living and flexible • Elongating with the stems and leaves they support

42. SclerenchymaCells (Supporting Cells) • Characteristics • Have thick cell walls • Supported by lignin • Occur only in places where plant has stopped growing in length • They produce a secondary wall before the living part of the cell dies • Rigid walls remain as a skeleton that supports plant • Cell Turgor: Cells absorb water and high pressure develops in cell • Makes cell rigid • Thickened cellulose walls also strengthen plant

43. Turgor Cell Animation • http://www.kscience.co.uk/animations/turgor.swf

44. 2 types of Sclerenchyma Cells • Sclereids and Fibers • Fibers: specialized entirely for support and strengthening Sclereids • Sclereides: Shorter than fibres, irregular shape, with thick lignified secondary walls

45. Water-Conducting Cells of Xylem • 2 types: • Tracheids and vessel elements • Die at functional maturity • Cells thickened walls remain after they disintegrate • This forms a non-living conduit through which water flows • Tracheids: • Long, thin cells • Cell walls are hardened with lignin • Prevents collapse under water tensions and provides support • Vessel Elements: • Generally wider, shorter, thinner walled, less tapered • Form long vessels • Ends enable water to flow freely through vessels

47. Sugar-Conducting Cells in the Phloem • Are alive at functional maturity • Sieve Tube Elements: • A chain of sieve cells that transport sugars in angiosperms • Although alive, lack nucleus, ribosomes, a distinct vacuole and cytoskeleton • Companion Cell • Alongside each sieve tube element- connected by channels • Nucleus and ribosomes from companion serve both it and the adjacent sieve tube element

49. Quiz time! 1. Which of the following help(s) in supporting a terrestrial woody plant? I. Xylem tissue II. Turgor pressure III. Phloem tissue A. I only B. I and II only C. II and III only D. I, II and III Answer B

50. 35.2 Meristems generate cells for new organs AS 9.1.5 and 9.1.6