Unit 4: Plant Anatomy

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Basic Plant Cell

Cell is smallest unit which exhibits life characteristics

Features unique to plant cells are cell wall, chloroplasts, plasmodesmata, large central vacuole

Cell wall surrounds cell on outside of the plasma membrane

Made of cellulose which gives shape, protection, strength

Porous, containing channels called plasmodesmata that enable transport and communication between neighboring cells

Plasma membrane regulates specialized movement of substances in and out of cells

Cytoplasmic membrane surrounding a large central vacuole is called a tonoplast

Vacuoles are membrane-ground sacs involved in plant cell growth and storage of water, enzymes, pigments, ions, and waste proucts

Plastids are membrane-bound organelles responsible for photosynthesis, storage of products like starch, and molecule synthesis

Chloroplasts are site of phosynthesis, absorbing sunlight using green pigment, chlorophyll, and converting it into chemical energy or glucose

Sometimes convert to chromoplasts (such as when fruit ripens) which synthesize and store other pigments giving plants distinctive colors

Amyloplasts are responsible for storing glucose molecules produced during photosynthesis by linking them together in long chains of starch

Nucleus is genetic control center of cell that contains chromosomes and is surrounded by nuclear envelope

Mitochondria generate most of cell's chemical energy ATP

Osmosis and Turgor Pressure

Diffusion is movement of particles from high to low concentration

Osmosis - water molecules cross semi-permeaeble membranes moving from more dilute to more concentrated

Hypotonic solutions have lower concentration of solutes relative to cell

Hypertonic solutions have higher concentration of solutes compared to cell

Isotonic solutions contain the same relative solute concentration as the cell

Turgor pressure enables plant to hold itself upright against gravity

Allows plants to swell instead of burst with water intake

Plant cells with correct internal water pressure are said to be turgid

Plants with too little internal water are said to be flaccid or plasmolysed

Loss of water from a plant cell is called plasmolysis

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Plant Organ Anatomy

Tissue systems

Meristematic & permanent tissue

Primary growth (length) and secondary growth (width) occur from addition of new tissue via mitotic cell division

All plants have primary cell walls which are flexible and can expand as the cell grows

Some plants have secondary cell walls which contain lignin, are inflexible, and provide structural support

Meristematic tissue cells are totipotent (are able to differentiate into the entire variety of mature cell types) and are undifferentiated or incompletely differentiated

Miotic cell division occurs here

Apical, lateral, or intercalary

Once formed, continue as meristematic or become permanent tissue

Small cells with thin walls and dense cytoplasm with small vacuoles

Large, dense nuclei contain chromatin and is located centrally

Meristems can form from other injured cells & aid wound healing

Apical meristems or primary meristems give rise to primary plant body

located at tips of stems and roots enabling plant to extend in length

plant shoot system originates here as leaf and bud primordia, more complex than SAM

Lateral meristems are secondary meristems because they're responsible for secondary growth or increase in girth and thickness in a maturing plant

Not all plants exhibit secondary growth

Intercalary meristems occur at base of leaf blades and at nodes

Enables a leaf blade to increase in length from the base

Permanent tissue cells are no longer actively dividing but are differentiated into cells with distinct functions

ground, epidermal, and vascular

May be living or dead, thin or thick-walled

Meristems produce cells that differentiate or specialize and become permanent to take on specific roles and can no longer divide

Dermal tissues cover and protect plant

Outermost covering

Water regulation, protection, gas exchange

Epidermis is a single layer of cells covering and protecting underlying tissue

Bark is a tough, waterproof outer layer of cork cells that protect woody plants from damage

Epidermal cells are the most numerous and least differentiated of the cells in the epidermis with thin walls, no chloroplasts, and alive at maturity. They secrete a waxy cuticle

The following features have specialized guard cells

Stomata are openings through which the uptake of carbon dioxide and release of oxygen and water vapor can occur on the epidermis of aerial ports of plant

the guard cells on each stoma or pore shrink and swell to control exchange and water loss

They have chloroplasts, are the only epidermal cells capable of photosynthesis

Trichomes are hair-like structures on surface of leaves and stems that develop from epidermal cells

reduce loss of water from shoot system by decreasing flow of air over plant surface

Can increase solar reflectance to protect against UV & overheating

Glandular trichomes can store & exude compounds that defend against herbivory

Root hairs are tiny hair-like extensions of root epidermis that absorb water and mineral nutrients in the soil

Increase root surface to access most amount of soil

Vascular tissue transports water, minerals, sugars to different parts

Consists of xylem and phloem - long distance transport

Lie adjacent to each other and are arranged in distinct strands called vascular bundles which run up and down the stem

The vascular bundle includes the phloem and xylem strands, meristematic tissue called vascular cambium sandwiched in between that creates new vascular tissue allowing secondary growth

Xylem conducts water and minerals from roots to leaves via transpiration (loss of water from stomata of plant)

Composed of tracheids, vessel elements, xylem parenchyma, and xylem fibers

Tracheids and vessel elements are dead at maturity & have thick cell wells of lignin, joined end to end to form hollow tube for water flow

pits in side of walls allow water to move from one cell to another

In growing tissue, lignified part of cell wall is in rings or helix allowing extension

In nonexpanding parts, cell wall forms as netlike or pitted structure for mechanical support

Xylem parenchyma are the only living cells in xylem involved in storage

Xylem fibers are sclerenchyma cells in between vessels and tracheids for mechanical support

Phloem tissue are composed of companion cells, sieve tube elements, phloem parenchyma, phloem slerenchyma

Living at maturity

Conduct dissolved sugars and organic molecules in process called translocation that transports products of photosynthesis to parts where energy is needed or stores

Sieve tubes are main conducting channels of phloem and contain cytoplasm but no nucleus

Companion cells are special type of parenchyma cell found alongside sieve tubes that provide energy used during translocation

Sieve tubes & companion cells not lignified

Pholem Parenchyma - storage

Phloem Sclerenchyma - mechanical support

Ground tissue serves as site for photosynthesis, provides a supporting matrix for vascular tissue, and helps store water and sugars

Derived from ground meristem tissue and makes up most of plant body

Metabolism, support and defense

Three types mainly differing on wall structure

Ground Parenchyma cells are living cells making up bulk of soft internal tissue, commonly called pith

Thin, flexible cell walls

Large water filled vacuoles

Storage and metabolism

May contain sugars, organic acids, defense compounds, and starch

Ground Collenchyma are living cells that are long and narrow with unevenly thick extensible cell walls composed of cellulose and pectin

Found in strands or sheets beneath epidermis (young stems, petioles, leaf veins)

Provide flexible support to actively growing regions

Sclerenchyma cells take over role of mechanical support when growth is complete

Ground Sclerenchyma cells are typically dead, providing structural support and protection to non-growing regions

Cell walls are hard and rigid due to deposition of lignin

Classified as sclereids or fibers based on shape

Fibers are elongated with tapering ends and often occur in bundles

contribute more than half the volume of woody tissue and are found in all stems & leaves that are hard and tough

Sclereids are shorter with more abundant and elaborate pitting

Found in structures like seed coats, walnut shells, peach pits

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Tissue Arrangements

Stems

Epidermis of stem has distinct cuticle exuded by aerial dermal cells

Vascular bundles arranged throughout

Monocots have scattered vascular bundles without meristematic vascular cambium

Dicots have vascular bundles arranged in a ring with distinct line of vascular cambium seperating xylem from phloem

Outer ground tissue of dicot stem is the cortex, inner tissue is pith

Roots

Epidermis of a root will vary from epidermis of shoots because it won't have cuticle since it needs to absorb soil water

Cortex is composed of parenchyma cells loosely packed for aeration

Storage of extra sugar as starch

Endodermis is innermost layer of cortex with tightly packed cells with waterproof band known as Casparian strip that regulates flow of water into xylem

Pericycle is a layer of cells just within the endodermis containing meristematic cells where lateral roots emerge from

Stele is the cluster of vascular tissue at the center of the root

In dicots, will appear as an X

In monocots, will form a ring around pith (parenchyma cells similar to the cortex)

Leaves

Epidermis of leaves will have distinct cuticle as well as an upper and lower epidermal layer

Stomata mostly on underside of the leaf to protect from dust and debris and keep sheltered from direct light so water loss is limited

Dicot leaves appear different from monocots in that they have distinct palisade and spongy mesophyll (middle leaf) cells

Palisade cells will be rectangular, filled with chloroplasts, occur just below the upper epidermis

Main photosynthesizers in leaf

Spongy cells are smaller and irregular occuring closest to lower epidermis, large air pockets ensure space for gas exchange

Monocot leaves have regularly occurring vascular bundles that can be seen in cross section due to parallel venation

Reticulate venation of dicots means a cross section will only capture a few veins perfectly across so their vascular bundles will appear more irregular and scattered