Plant Structure and Function

1. Plant Structure and Function

2. Types of Plant CellsParenchyma • Thin flexible cell walls. • 2 main functions – storage and food production. • Large vacuole stores water, starch and oils. • Can contain many chloroplasts.

3. Types of Plant CellsCollenchyma • Typically long cells. • Unevenly thickened cell walls. • Thin parts can stretch and grow. • Provide support for surrounding tissue. • ie. – tough strands in celery.

4. Types of Plant CellsSclerenchyma • Thick and rigid. • Used for support • Two types: fibers and stone cells. • Fibers – long thin strands, support, strength, vascular tissue. • Stone cells – circular cells • Gritty texture of pears • Fruit pits

5. Plant TissuesDermal or Epidermis • Flattened parenchyma cells cover and protect plant like skin • Produce a waxy cuticle – prevents water loss.

6. Plant TissuesDermal or Epidermis • Contain stomata: openings that control gas exchange. • Guard cells control opening and closing.

7. Plant TissuesDermal or Epidermis • Root hairs: extensions of cell that help absorb water and minerals.

8. Plant TissuesDermal or Epidermis • Trichomes: hair like – give fuzzy texture • Reduce evaporation. • Some protect by secreting toxic substances.

9. Plant TissuesVascular Tissues • Transport food minerals and water through the plant. • Two types: • Xylem – Moves water and minerals from roots to rest of plant. • Phloem – Transport sugars and organic compounds from leaves to rest of plant.

10. Plant TissuesXylem • Two types • Tracheids: In conifers. • Tubular, tapered ends, dead at maturity. • Cell walls have pits for water flow across cells. • Vessel elements: In Anthopytes. • Wider and shorter. • Openings in end walls for water flow through cells.

11. Plant TissuesXylem

12. Plant TissuePhloem • Transport sugars and organic compounds. • Living, tubular cells. • Phloem cells are called sieve tube members. • Have cytoplasm but no nucleus or ribosomes. • Companion cells – next to each sieve tube member. Help manage transport.

13. Plant TissuesGround Tissue • All other tissues • Mostly parenchyma • Functions: photosynthesis, storage, support. • In stems and roots: have large vacuoles to store starch and water.

14. Plant TissuesMeristematic Tissues • Region of actively dividing cells. • Small, round, with large nuclei. • Apical meristems: • At tips of roots and stems. • Increase length. • Lateral meristems: • Cylinders of dividing cells in roots and stems. • Increase diameter. • Vascular cambium: produce xylem and phloem. • Cork cambium: produces tough covering for root and stems.

15. Meristems

16. Roots • Anchor, absorb water and minerals from soil. • Some used for food storage (carrots) • Two types • Taproots: central fleshy with small branch roots. (carrots, beets) • Fibrous roots: numerous branches from central point.

17. Root Variations • Adventitious roots: • Prop roots above ground to support tall plants. • Aerial roots: • Cling to objects to provide support.

18. Root Structure • Epidermis: outer layer. • Root hair: extension of single epidermal cell. • Absorbs water, oxygen and minerals.

19. Root Structure • Cortex: next layer. • Transports water and ions into vascular core. • Made of parenchyma cells • sometimes used for storage

20. Root Structure • Endodermis: forms waterproof seal around vascular tissue. • All water and minerals must pass through endodermis cells.

21. Root Structure • Pericycle: just within endodermis. • Gives rise to lateral roots (offshoots of older roots).

22. Root Structure • Xylem and phloem: center of root. • Transport of water, minerals and organic materials through plant.

23. Dicot vs. Monocot Root

24. Dicot vs. Monocot Root

25. Root Growth • Apical meristem • Lengthens root • Vascular cambium • Increase diameter • Found between xylem and phloem • Root cap • Layer of cells at root tip. • Protection

26. Stems • Transport, support and storage. • Some are Underground • Corm: short, thick, surrounded by leaf scales. (gladiolus) • Tuber: swollen underground stem with buds that sprout new plants. (potato) • Rhizomes: (iris)

27. Stem: Internal Structure • Vascular tissue arranged in bundles. Dicot Monocot

28. Woody Stems • Secondary Growth: thickness from vascular cambium. • Xylem: wood – causes growth rings. • Bark: old phloem and cork cambium.

29. Stems – Material Transport • Xylem: transports water from roots to leaves. • Phloem: transports sugars, minerals, and hormones. • Source: photosynthetic tissue – mostly leaves. • Sink: storage area (cortex of roots) • Translocation: movement from source to sink.

30. Leaf Variation • Simple: blade no divided • Compound: divided into leaflets • Alternate: only one leaf from a single point on stem • Opposite: leaves in pairs along stem • Whorled: three or more leaves occurring at same place on stem

31. Leaf Structure • Vascular tissue in veins. • Epidermis: outer layer of cells. • Two layers of Mesophyll. • Palisade mesophyll: • Most photosynthesis. • Spongy mesophyll: • Loosely packed with irregular shaped cells. • Air spaces for gas exchange: O2, CO2, H2O. • Gases move in and out of stomata.

33. Transpiration • Loss of water vapor through the stomata.

34. Leaf Venation Patterns • Parallel – monocots Netlike – dicots

35. Leaf Modifications • Cactus spines: leaves that reduce water loss and protect plant. • Bulb: short stem covered by large fleshy leaves, modified for food storage. • Pitcher plant: modified to trap insects. • Aloe vera: adapted to store water.

38. Plant Responses Hormones Tropisms Nastic Responses

39. Plant Hormones • Chemicals produced in one part of an organism and transported to another to cause a change in growth or development.

40. Auxins: Hormone • Promote cell elongation. • (IAA) Indoleacetic acid. • Produced in apical meristem. • Increases cell division and promotes cell elongation. • Weakens connections between cellulose fibers in the cell wall allowing cells to stretch.

41. Auxin • Auxins produced in apical meristem inhibits growth of side branches. • Remove stem tip – branches form

42. Gibberellins: Hormone • Growth hormone. • Stimulates cell elongation. • Also increases rate of seed germination and bud development.

43. Cytokinins: Hormone • Stimulate cell division or cytokinesis. • Stimulate production of proteins needed for mitosis. • Produced in meristem of roots and travel up xylem to rest of plant.

44. Ethylene: Hormone • A gas that speeds ripening of fruits.

45. Tropism • Response to an external stimulus from a particular direction. • Positive tropism: plant grows toward stimulus. • Negative tropism: plant grows away from stimulus.

46. Types of Tropism • Phototropism: growth toward light. • More auxin on side of stem away from light. • Cell elongation on one side – dark side. • Gravitropism: direction of plant growth in response to gravity. • Stems up and roots down. • Thigmotropism: response to touch. • Tendrils of vine coil around objects.

47. Nastic Responses • Response movement that is not dependent on direction of stimulus. • Mimosa Venus Flytrap