PLANT TISSUES
Page 1
PHARMACOGNOSY I LAB MICROSCOPY-PLANT TISSUES
Page 2
Plant Tissues
Plants are multicellular eukaryotes with various specialized tissue systems.
Plant tissues comprise cells that perform specific functions, which are organized into organs.
Each organ is designated for a particular function.
Page 3
Types of Plant Tissues
Meristematic Tissue:
Found in regions of continuous cell division.
Cells are undifferentiated or incompletely differentiated.
Contributes to plant growth.
Permanent Tissue:
Composed of cells that have ceased dividing.
Page 4
Types of Meristematic Tissue
Types Based on Location:
Apical Meristems: Located at the tips of stems and roots, enabling elongation.
Lateral Meristems: Facilitate growth in thickness.
Intercalary Meristems: Found at the bases of leaf blades and nodes in monocots allowing blade elongation after mowing.
Page 5
Differentiation of Meristematic Tissue
Meristems produce cells that differentiate quickly into permanent tissue.
Types of Permanent Tissue:
Dermal Tissue: Covers and protects the plant.
Vascular Tissue: Transports water, minerals, and sugars.
Ground Tissue: Involved in photosynthesis, support, and storage.
Simple vs. Complex Tissues:
Ground tissue is simple, consisting of one cell type.
Dermal and vascular are complex with multiple cell types.
Page 6
Dermal Tissues
Dermal tissue is the outer protective layer of roots, stems, and leaves.
Functions include:
Transpiration
Gas Exchange
Defense
Composed of a single layer of epidermis cells.
May contain stomata, guard cells, root hairs, and a waxy cuticle.
Page 7
Stomata Functionality
Stomata allow CO2 uptake and O2/water vapor release.
Each stoma is regulated by two guard cells.
The curvature of guard cells changes based on whether the stoma is open or closed.
Page 8
Structure of Stomata
Components include:
Epidermal cells
Subsidiary cells
Stomatal pore
Guard cells
Page 9
Periderm in Woody Plants
In woody plants, the epidermis develops into a thick periderm due to secondary growth.
Components of Periderm:
Cork cambium: Produces cork cells.
Cork cells (dead at maturity).
Phelloderm: Parenchyma cells inside the cork cambium.
Functions as a protective barrier against various environmental factors.
Page 10
Development of Periderm
Structure includes:
Cuticle
Epidermis
Cork cells
Cork cambium
Phelloderm
Cortex
Page 11
Ground Tissues
Non-dermal and non-vascular tissues categorized as ground tissue.
Functions include storage, photosynthesis, and support.
Types of ground tissue:
Collenchyma
Sclerenchyma
Parenchyma
Page 12
Collenchyma
Living support tissue with elongated cells and unevenly thickened cell walls.
Main function: mechanical support of young stems and leaves through turgor pressure.
Page 13
Collenchyma (Visual Reference)
Page 14
Sclerenchyma
Dead supportive tissue consisting of either fibers or sclereids.
Fibers occur in bundles, while sclereids can be individual and are characterized by thick, lignin-rich secondary walls.
Provides support, hardens parts of the plant, and limits access to fruit until seeds are ready for dispersal.
Page 15
Structure of Sclerenchyma
Illustrates the arrangement of pits, lumen, and cell walls in sclerenchyma cells.
Page 16
Parenchyma
Composed of spherical or elongated cells with thin primary walls.
Main components in young plant organs, performing photosynthesis and storage.
Noted for totipotency, allowing differentiation into various cell types.
Page 17
Diagram of Parenchyma
Visual depiction of parenchyma structure, including cell wall, nucleus, vacuole, and cytoplasm.
Page 18
Vascular Tissues
Acts as the plant's plumbing system for transporting water, minerals, and sugars.
Composed of:
Xylem: Transports water and minerals.
Phloem: Distributes organic compounds.
Vascular bundles/connectivity within the plant structure.
Page 19
Vascular Bundle Structure
Visual of dicot stem showing sclerenchyma, vascular bundles, and ground tissue.
Page 20
Xylem Functionality
Xylem transports water and minerals via conducting cells called tracheary elements.
Composition includes parenchyma and sometimes sclerenchyma.
Page 21
Tracheary Elements of Xylem
Transport occurs through dead vessel elements and tracheids which have thickened cell walls and function at maturity.
Structure includes pits that allow lateral flow of water.
Page 22
Vessel Elements vs. Tracheids
Vessel elements are wider and have perforation plates for vertical water flow.
Tracheids have pits for lateral water flow.
Differences in functionality between the two types regarding air bubble susceptibility.
Page 23
Impact of Air Bubbles in Vascular Systems
Vessel elements can be drastically affected by air bubbles disrupting the water column, while tracheids limit this impact.
Vessel elements are exclusive to angiosperms; tracheids are present in both angiosperms and gymnosperms.
Page 24
Phloem Functionality
Phloem transports sugars and organic compounds via sieve elements.
Sieve-tube elements are specific to angiosperms; sieve cells are found in gymnosperms.
Page 25
Phloem Structure
Composition includes sieve-tube elements surrounded by various support cells.
Highlighting the role of companion cells in angiosperms and albuminous cells in gymnosperms.
Page 26
Support Cells in Phloem
Sieve elements rely on companion and albuminous cells for functionality and support.
Also contains parenchyma and sclerenchyma cells.
Page 27
Comparison of Xylem and Phloem
Feature | Xylem | Phloem |
|---|---|---|
Contains | Mostly dead cells | Living cells |
Transports | Water & Minerals | Sugars |
Direction | Up | Up and Down |
Biomass | Big | Small |
Page 28
Summary of Meristematic Functions
Meristems produce cells that quickly differentiate into permanent tissues: dermal, vascular, and ground tissue.
Each type serves essential plant functions such as protection, transport, photosynthesis, support, and storage.