Plant Science Exam 2 Lecture 9: Plant tissues and Organs ● Plant Structure ○ Plants began living on land 420 million years ago. ○ Challenges of terrestrial life led to evolution of distinct, specialized tissues and organs. ○ All flowering plants have leaves, stems, and roots. ■ These parts can be modified and may not be easily recognizable. ■ No species exists for which roots, stems, or leaves have been completely lost evolutionarily. ■ Organs – roots, stems, flowers, fruits ● Plants: ○ Herbaceous or Woody ■ Herbaceous - Do not develop persistent woody parts of the plant ■ Woody – Develop woody tissue – trees and shrubs ○ Annuals: Herbaceous plants that grow, reproduce and die in 1 year or season ○ Biennials: Herbaceous plants that 2 years to complete their life cycle ○ Perennials: Woody or Herbaceous. Live for more than 2 years. ● Cells and Tissues of Plants: ○ Plant cells are organized into tissues ○ Tissue: Group of cells that form a structural and functional unit. ■ Ground tissue system: All tissue of the plant body other than the vascular tissues and the dermal tissue ● Various functions – storage, photosynthesis and plant support. ■ Vascular tissue system: The tissue system that conducts materials through the plant body ● Extends throughout the plant body and can also function in supporting the plant ■ Dermal tissue system: The tissue system that provides an outer covering for the plant body ● The Ground Tissue System: ○ Composed of three simple tissues ■ Parenchyma ■ Collenchyma ■ Sclerenchyma ○ The cell wall of each tissue distinguishes them ○ Cell wall is the structural support that surrounds each plant cell. ○ Primary cell wall: Expands with cell as it grows ○ Secondary cell wall: After cell stops growing cell wall is secreted inside the primary cell wall between the primary cell wall and cell membrane ● Parenchyma cells ○ Have thin primary cell walls ○ Found throughout the plant body and is the common type of cells and tissue. ○ Active metabolically ○ Most remain alive after they mature. ○ Functions: ■ Photosynthesis: Chloroplasts ■ Storage: Starch grains, oil droplets, salts, water ■ Secretion: Nectar, hormones, enzymes ○ Differentiate: Less specialized cell becomes a more specialized cell type. 1
● Collenchyma cells ○ Collenchyma cells have a thin primary wall that becomes thickened in other areas. ○ This allows plasticity ○ Not uniformly distributed. Found as long strands near stem surfaces and along leaf vein ■ Celery – “strings” ● Sclerenchyma cells ○ Composed of cells with rigid cell walls ■ Both primary and secondary cell walls ■ Secondary cell wall makes cells hard and strong – thickened cells ○ Provide structural support ○ Two type of sclerenchyma cells ■ Sclereids ■ Short cells. Common in shells of nuts and stones of fruits ■ Fibers ■ Long tapered cells found in groups ■ Abundant in wood, bark and leaf veins ● Vascular tissue system: ○
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- Spring '18
- Nrupali Patel
- cells, phloem, Xylem, Plant anatomy