Plant and Animal Tissues

Lesson Introduction

• Focus is on the second level of organismal organization: tissues.
• Chapter covers plant and animal tissues.
• Plant and animal tissues differ due to structural and functional differences between plants and animals.
• The lesson begins with an activity to observe tissues in plant materials.

Plant Tissue Observation Activity

• Uses three plant parts: beetle leaf, potato tuber, balsam stem.
• Goal is to observe tissue appearance in living materials.
• Temporary slides are prepared from each part.
• Thin peels are taken from the lower epidermis of the beetle leaf.
• Thin peels are cut from the potato tuber.
• A thin cross section is cut from the balsam stem.
• Temporary slides are prepared and observed under a light microscope, starting with low power.
• The aim is to identify tissues based on cell arrangement.

Detailed Procedure

• Thin peels from the plant parts are placed in a watch glass with water.
• A clean glass slide is prepared with a drop of water.
• The thinnest peel is transferred to the slide using a paintbrush.
• A coverslip is applied, avoiding air bubbles.
• Slides are observed under a light microscope, first at low power, then at higher power.
• The procedure is repeated for potato tuber and balsam plant stem specimens.

Initial Observations

• Beetle Leaf Lower Epidermis: Dark, oval stomata surrounded by bean-shaped guard cells.
• Other epidermal cells with varied shapes and greenish color.
• Potato Tuber: Mostly spherical cells, similar in size.
• Cells appear uniform in shape.
• Notable intercellular spaces are present.
• Balsam Stem: Cells are reddish-brown due to stem color.
• Smaller cells in the stem's middle part, larger cells towards the outside.
• Oval, dark regions at the periphery indicate transport tissue.
• Size and shape differences among cells exist.

Conclusions from Activity

• Different plant parts contain different types of cells.
• Similar cells are arranged together to form tissues.
• Tissues are groups of cells with a common origin, adapted for specific functions.

Tissue Definition

• Tissues are groups of cells with a common origin.
• Tissues are adapted or modified to perform specific functions.
• Plant and animal differences lead to main tissue types: plant and animal.

Activity: Observing Plant Root Growing Tips

• Banyan (stilt root)
• Pandanus (prop root), or Rampay (prop root) can be used.
• Focus is on observing external views of growing root tips.
• Root grows to secure itself and absorb water/minerals.
• Observation is enhanced with a hand lens.
• Color and shape variations depend on tissue types and cell maturity.
• Younger, dividing cells are lighter; mature cells are darker.

Observation Analysis

• The root tip is soft and light in color.
• The mature part of the root is rough and darker.
• The growing part has different tissues than the mature part.

Microscopic Root View

• Longitudinal sections of rampay prop root tips are observed.
• Thin longitudinal layers are cut from the root tip.
• Sections are placed on a glass slide and observed.
• Color, size, and arrangement of cells are noted.

Microscopic Observations

• Cells at the base of the root are larger and lighter in color.
• Cells toward the tip are smaller and darker.
• Reveals different tissue types within a single plant part.

Tissue Types in Root

• Smaller, darker cells at the tip are meristematic tissue.
• Larger, lighter cells in the base are permanent tissues.

Tissue Classification

• Plant tissues are classified based on cell division ability.
• Two main categories: meristematic and permanent tissue.

Meristematic Tissue

• Cells actively divide by mitosis.
• Produces new cells for growth.
• Cells are undifferentiated.
• The shoot apex contains meristematic tissues, increasing plant height.
• Root apex meristematic tissue leads to root elongation and growth.
• Increase in stem diameter is due to meristematic tissue division.

Features of Meristematic Tissue

• Living tissue.
• Cells are small in size.
• Contains a distinct nucleus.
• Cells are not differentiated.
• Large numbers of mitochondria are present.
• Intercellular space may be absent or not prominent.
• Large central vacuole is absent (small vacuoles may be present).
• Chloroplasts are absent.

Types of Meristematic Tissue

• Apical meristem
• Lateral meristem
• Intercalary meristem

Apical Meristem

• Present in shoot apex, root apex, and axillary buds.
• Increases plant height and root length.
• Present in axillary buds for branch and leaf growth.

Intercalary Meristem

• Primarily found at the nodes in plants of the grass family.
• Increases length of internodes.

Lateral Meristem

• Found laterally in stems and roots (parallel to longitudinal axis).
• Increases plant diameter.
• Cambium tissue in dicots.

Permanent Tissue Observation

• Thin cross sections of pumpkin stem are made.
• Sections are placed in water.
• Slides are prepared and viewed under a microscope.
• Objective is to identify different tissue types present.

Slide Observations

• Different cell layers exist.
• Cells vary in size and shape.
• Darker regions indicate vascular bundles.
• Higher magnification differentiates cells more clearly.
• Tiny cells in the middle region with polygonal-shaped cells towards the outer circumference of the stem can be seen.

Identification

• Cambium between xylem and phloem contains meristematic tissue.
• Rest of the cells are permanent tissues.

Permanent Tissue Defined

• Specialized tissue that has lost ability to divide.
• Performs a specific function.

Types of Permanent Tissues

Two main groups:

• Simple permanent tissue
• Complex permanent tissue

Simple Permanent Tissue

• Composed of only one type of cell
• Classified by cell shape and cell wall nature.

Types of Simple Permanent Tissue

• Parenchyma
• Collenchyma
• Sclerenchyma

Tissue Characteristics

• Parenchyma: Spherical cells with thin walls.
• Collenchyma: Polygonal cells with thick corners.
• Sclerenchyma: Polygonal cells with evenly thick walls.

Parenchyma Tissue

• Forms soft parts of the plant body
• The most abundant tissue in plants
• Iso-diametric or spherical cells
• Thin primary cellulose cell wall
• Large central vacuole present
• Cytoplasm pushed to the periphery
• Intercellular space
• Elongated cells are present.

Permanent Slide Observation

• Iso-diametric shape
• Similar, almost identical cells
• Clear intercellular spaces

Locations

• Located in cortex and pith of stem/roots
• Fleshy parts of fruits (e.g. papaya)
• Endosperm of seeds
• Leaves (palisade and spongy mesophyll)

Functions

• In palisade and spongy mesophyll cells.
• Food is stored.
• In storage tissues
• Supports herbaceous plants

Collenchyma Tissue

• Provides support to the plant body
• Contains modified parenchyma cells
• In cross-section, polygonal shaped cells.
• In longitudinal section, elongated cells.

Features

• Cell division cannot occur.
• Living cells
• Elongated cells
• Thickened corner.
• The prominent intercellular space.

Permanent Slide Observation

• Clear polygonal-shaped cells
• Thickened corners

Locations

• Cylindrical tissue inner to the epidermis of herbaceous stems
• Veins of dicot leaves.

Functions

• Provides mechanical support to dicot plant stem before wood formation.
• Tissue carries out photosynthesis due to the presence of chloroplasts in cells.
• Provides support to the plant leaves.

Sclerenchyma Tissue

• Provides mechanical strength
• Support to the plant body

Types of cells:

• Sclerenchyma fibers
• Sclereids

Fibers:

• Elongated long cells can be seen in longitudinal section
• In the cross section can see polygonal shape.

Sclereids:

• Sclereids-short cells

Features:

• Lignin deposit in the cell wall makes it dead
• Even Cell wall is evenly thickened.
• A lumen is present.
• The cells are tightly packed.

Permanent Slide Observation

• See clear polygonal-shaped cells
• Thick unevenly thickened walls with lignin
• A lumen in the middle is observed.

Locations

• Fibers are present in xylem and phloem
• Endocarp in coconut
• Camphor & mango fruits
• Seed coat of coffee
• Dattes

Functions

Provides support to the plant body due to lignin in the cell wall.

Complex Permanent tissues.

• This is a specialized tissue that has lost its ability to divide.
• Complex permanent tissue can be divided into xylem tissue and pholem tissue.

Xylem:

• Composed of small cells joined together to form tubular structures.

1.Xylem vessel

• Vessels are a component that makes up xylem tissue to help transport materials.

2.Tracheids

• Tracheids make up the xylem, also part of the transport of water.

3.Xylem parenchyma

• The parenchyma in the xylem helps support and provide storage to the plant.

4.Xylem fiber

• Helps as mechanical support.
• There are four different types of cells present in xylem, confirming it as a complex permanent tissue.

Xylem Vessel Elements

• Cylindrical, elongated cells that are arranged one on top of each other.
• The cross walls between elements are dissolved, creating a continuous tube-like structure.
• Xylem vessels are continuous tubes, while xylem vessel elements are individual cells
• This tubular structure facilitates water transportation in plants.

Tracheids

• Elongated, spindle-shaped cells that also help in water transportation.
• Some herbaceous plants rely solely on tracheids for water transport.

Xylem Fibers

• Narrower and shorter than tracheids.
• They provide support to the xylem tissue.

Xylem Parenchyma

• Living cells with thin cell walls.
• These cells are involved in food storage, and xylem vessels and tracheids transport water from the roots to the rest of the plant.
• Water has to be transported up very tall plants against gravity, and under high pressure.
• Xylem vessel, tracheid, and fiber cells must be strong to withstand the high pressure needed for water transport.
• Lignin deposits in the cell walls of xylem vessel elements, tracheids, and xylem fibers provide strength through lignification.
• Lignification makes xylem vessel elements, tracheids, and fibers dead cells.
• Xylem consists of three types of dead cells (vessels, tracheids, fibers) and one type of living cell (parenchyma).
• Xylem is a complex permanent tissue with four cell types: xylem vessel, tracheids, xylem fibers, and xylem parenchyma.

Functions of Xylem

• Transports water and minerals absorbed by roots throughout the plant.
• Provides mechanical support to the plant body due to lignified cells.

Phloem Tissue

• Complex permanent tissue made up of more than one type of cell
• It is the second type of complex permanent tissue.

Sieve Tube Elements

• Long, elongated cells connected together.
• Cross walls dissolve incompletely, forming sieve plates with pores (similar to a sieve).
• Sieve plates facilitate food translocation.
• Cytoplasm, nuclei, and organelles disappear in sieve tube elements, but remain living cells/tissue.

Companion Cells

• Have a prominent nucleus.
• A nucleus that controls the function of the sieve tube element, because the sieve tube element cannot function on its own.

Phloem Parenchyma

• These cells act as food storage.

Phloem Fibers

• These are used to provide support to the pholem.
• The sieve tube elements fuse end to end, cross walls are incompletely dissolved, forming sieve tubes, and the cross walls are called sieve plates with pores.
• Sieve tubes transport food (mainly sucrose) throughout the plant in solution form.
• Sucrose in phloem is known as phloem sap.
• Companion cells are elongated cells associated with sieve tube elements.
• The companion cell's nucleus controls the activities of the sieve tube element, because sieve tube elements lack a nucleus of their own
• Phloem parenchyma is for food storage.
• Phloem fibers are scattered in the phloem tissue.
• Three types of living cells exist in pholem: sieve tube element, companion cell, and parenchyma plus one dead cell type.
• The three living pholem cells have cellulose cell walls
• There is only one type of dead cells in pholem: phloem fibers are dead due to lignin deposits in their cell walls (sclerenchyma tissue).
• Phloem contains four cell types: sieve tube element, companion cell, phloem parenchyma (living), and phloem fiber (dead).
• This contrasts with xylem, which has three dead cells and one living cell.

Functions of Phloem Tissue

• Synthesized food in leaves is transported throughout the plant body.
• The transport process is known as translocation.
• Glucose (from photosynthesis) is temporarily stored as starch, then converted to sucrose, and translocated by the phloem.
• The sucrose substance is called phloem sap.

Classification of Plant Tissues

• Plant tissues are classified as meristematic or permanent.
• Meristematic tissues are further classified by location: apical, intercalary, and lateral meristems.
• Permanent tissues have differentiated cells.
• Permanent tissues are either simple (one cell type) or complex (more than one cell type).
• Simple permanent tissues include parenchyma, collenchyma, and sclerenchyma.
• Complex permanent tissues are usually vascular tissues: xylem and phloem which have more than one type of cell.