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What order did the “-trophs” evolve in, and why? How old is the photosynthetic process?
Autotrophs developed after heterotrophs because heterotrophs had consumed the majority of the free-floating organic molecules. Photosynthetic process is 3.4 billion years old.
How did autotrophs contribute to the earth’s evolution?
Earth’s atmosphere was altered as O2 accumulated. Initially O2 collected in the oceans. Around 700 million years ago it began to reach the levels we are accustomed to. This created the ozone layer (O3) and allowed for aerobic respiration.
Where did plants evolve? Why?
When the ocean was nearly exhausted of its nutrients development began to occur along nutrient rich shores. Plants began to move to land after developing ways to deal with the lack of water (roots, stems, leaves, stomata).
The living and nonliving components characteristic of an area.
Give an overview of plant’s importance (agriculturally).
- Plants provide macronutrients, essential amino acids (9), and phytochemicals.
- The major antioxidants (carotenoids and flavanoids) are phytochemicals.
What is taxol? How is it generated?
Harvested from the Pacific Yew, taxol inhibits the growth of cancer cells.
Explain basic cell theory, and describe the two major types of cells.
- Cell theory: All organisms are composed of one or more cells, and all cells come from existing cells.
- Eukaryotic cells: (non bacteria) Contain membrane-bound organelles, and have DNA packed into a nucleus.
- Prokaryotic cells: (bacteria) Have no organelles and DNA is found free-floating in an area called the nucleoid.
What are the two main areas of a plant cell, and what do they encompass?
- Cell wall: Middle lamella, primary wall, secondary wall, plasmodesmata
- Protoplast: cell membrane, nucleus, and cytoplasm (everything internal to cell wall)
Describe Primary Cell Wall composition.
- Cellulose: the most abundant organic compound on earth
- Hemicullulose: functions to glue cellulose fibers together
- Pectin: helps make wall flexible because of its water loving properties
- Glycoproteins and enzymes
What is the middle lamella?
Secreted by primary cell walls it is mostly pectin and acts as a region of union between adjacent cell walls.
Describe secondary walls
- Found in some plants as a second layer internal to primary walls.
- Chemically different from primary walls due to presence of lignin and higher proportion of cellulose
- Extremely thick compared to primary walls
- Contains thinner spots called primary pits which have a high distribution of plasmodesmata
What properties does lignin have? What chemical is derived from lignin and what are its functions?
- Imparts toughness (rigidity) to the cell
- Protects against pathogenic invasion
- Gives plants resistance to decay (although specialized fungi may still cause death of tree)
- DMSO (dimethyl sulfoxide) alleviates pain, but has been banned due to studies revealing it could result in eye damage.
What are the three major functions of cell walls?
The cell won’t pop under pressure, determines overall shape and provides rigidity, and has many enzymes that help with secretion and absorption
What are the types of plant plastids with a structural and functional description of each type.
- Chloroplasts: green due to chlorophyll pigment. Functions include photosynthesis, amino acid synthesis, and fatty acid synthesis.
- Chromoplasts: red/orange/yellow due to carotenoids. Give fruits and vegetables their characteristic colors, functionally not well understood other than to attract insects to plant through coloration.
- Leucoplasts: colorless due to lack of pigment. Act as a warehouse, storing starch, oils, or proteins. Includes amyloplasts (for starch).
Define thykaloids, stroma, and grana.
- thykaloids: system of membranes in a plastid.
- stroma: homogenous matrix in a plastid.
- Grana: stacks of thylakoids in chloroplasts
Describe how various plastids can evolve.
- The proplastid is the “stem cell” of plastids, with the ability to turn into a chromoplast, leucoplast, or develop (through a process) into a chloroplast.
- The three plastids share an interesting ability to alter themselves and become a different plastid: mature chloroplast <-> chromoplast <-> leucoplast
Describe vacuoles w/ function
- Large membrane enclosed region filled with fluid containing salts, proteins, etc
- Tonoplast: membrane surrounding vacuoles
- Contains anthocyanins (soluble pigments) that contribute to flower color
- Waste crystals may be deposited here and enzymes help recycle old organelles
- Helps to maintain the rigidity of the plant cell.
What are the characteristics that make a plant cell unique?
Cell wall, plastids, and a vacuole
What tissue allows for plant growth? How is this different than animals?
- Meristem tissue: permanent regions that allow for continuous growth throughout the lifespan of the plant. (similar to a stem cell) (apical meristem tissue found on the tips of roots and stems).
- In animals the majority of all cells are able to reproduce, but are mostly done growing early in the lifespan.
Describe the meristem cell specialization pattern to primary meristems and primary tissues.
- Apical meristem -> Protoderm -> dermal tissue system (epidermis)
- Apical meristem -> Ground meristem -> ground tissue system (ground tissues) (parenchyma, collenchyma, and schlerenchyma)
- Apical meristem -> procambium -> vascular tissue system (primary xylem and primary phloem)
What are the two anatomical categories and 3 general-types of tissue classification?
- Anatomical: simple – tissue built from one cell type. Complex – tissue built from more than one cell type
- General: dermal, vascular, and ground
Describe the ground tissue system in complete detail (major tissues, cell types w/ function, etc)
- Three major tissues are parenchyma, collenchyma, and sclerenchyma.
- Parenchyma: living protoplasm, most common, have primary cell walls that are flexible (rarely have secondary walls), function to synthesize and store various organic products and to regenerate damaged tissue.
- Parenchyma cell examples include cells that store starch (via leucoplasts) in the stems and roots, the fleshy tissue of most fruit, and photosynthesizing cells in the leaf.
- Collenchyma: living protoplasm, have unevenly thickened primary walls (no secondary walls) which allow for enhanced structure in the young growing parts of the plant (herbaceous, not bark), found just interior to the epidermis in these areas and bordering the veins of leaves, typically grouped into long strands for expanded support.
- Sclerenchyma: non-living protoplasm, rigid cells which have thickened secondary walls, commonly found in regions of the plant that are no longer elongating, walls are used as a skeleton for support. Two types of sclerenchyma cells exist…
- Fiber cells – long, tapered, and in groups; have a lumen in the center (include hemp in rope and flax fibers in linen). These appear red after a stain with only a small lumen in the center.
- Sclereids – very irregular shapes, impart hardness to nutshells and seeds coats and are gritty texture of fruits, appear red after a stain due to secondary wall.
Describe the vascular tissue system in complete detail (major tissues, cell types w/ functions, etc)
- Two major tissues are xylem and phloem, has as a transport and support role
- Xylem: non-living protoplasm, water and ion transport and support that runs throughout all organs, the protoplast disintegrates leaving only the thickened cell walls behind forming a nonliving tube for water and ion transport, the secondary walls have pits (thinner regions where only primary walls are present) which allow for the horizontal transfer of water.
- Cell types include tracheids, vessel elements, parenchyma cells, and fibers. Tracheids and vessel elements both have secondary walls (used for water transfer). Vessel elements are long tubes linked end-to-end which have perforations (no primary OR secondary walls) to allow for easy fluid transports as well as pits. Tracheids are spindle-shaped cells with pits that allow water to flow from cell to cell (they do not have perforations), they are common to gymnosperms and seedless vascular plants. Both tracheids and vessel elements secondary walls are often deposited as rings or spirals due to organ growth.
- Phloem: living protoplasm. Sucrose, organic compounds, and certain ion transport. Do not have secondary walls. Cell types include sieve elements, sclerenchyma, and parenchyma. Two major transport cells are sieve tube members (elements), and sieve cells which are less specialized food transport cells found in the gymnosperms.
- Sieve tube members are alive at maturity, but lack many organelles (remaining organelles are found pushed up against the wall – smooth ER, some plastids, mitochondria), the end walls between sieve tube members (sieve plates) help the flow of nutrients from cell to cell. All sieve tube members are associated with a companion cell which contains normal living protoplasm and the two are connected by numerous plasmodesmata. The nucleus and ribosomes of the companion cell govern the action of the sieve tube member.
- P-protein (phloem protein) along with callose polysaccharide work together to plug the sieve plates and sieve areas (pores that connect adjacent protoplasts) in response to injury, preventing leakage of nutrients.
Describe the dermal tissue system in complete detail (major tissues, cell types, w/ functions, etc)
- Single layer of tightly packed cells that covers and protects all young parts of the plant. Anatomically and functionally variable. Epidermal cells secrete cutin which forms the cuticle (waxy layer to prevent water loss).
- Guard cells – regulate the opening/closing of stomata (control movement of gas in/out of the plant)
- Trichomes – projections of the epidermis which have many roles (gives fuzzy leaf feeling, facilitates absorption, insulators, counter-insect defense, etc)
- The periderm exists in plants that grow wide (have secondary growth). The epidermis is replaced with a collection of cells called the periderm which is localized to stems and roots (part of bark). Essentially as the epidermis is sloughed off (like human skin) the periderm replaces it. The outer layer of cells are protective cork cells that have walls filled with suberin (lipid compound which creates a waxy outer coating). Lenticels are openings in the periderm that allow for air to pass through the periderm and into the internal tissues.
- The anatomy of the periderm from outside to inside is… 1. Dead epidermis, 2. Cork (phellem) – dead cells with walls filled with suberin, 3. Cork cambium – produces cork to the outside and phelloderm to the inside, 4. Phelloderm – made of living parenchyma cells.
What are the functions of roots?
Anchorage, absorption & conduction (minerals/water), storage (energy/nutrients), synthesis of hormones
Describe the various root systems in depth.
- Taproot system: system established by the primary root and its lateral branches of roots. Tend to penetrate deep into the soil. In gymnosperms and eudicots the primary root grows downward giving rise to many lateral roots (not monocots). Penetrate deeper than fibrous roots.
- Fibrous root system: have a short-lived primary root. Instead, many adventitious roots branch off of the stem. This system does not have any one prominent root, but is a tangled mass of roots. Better ground cover than taproots.
- Certain root systems can be a blend of both.
What factors affect root system depth?
Soil composition, temperature, and moisture.
Where does most absorption of water/ions occur in the soil, and by what?
Feeder roots absorb most water/ions for the root system in the upper 15cm of soil. (~6 in)
What is the average ratio between the spread of the roots and the spread of the tree crown?
The spread of the roots is typically 4-7 times greater than the spread of the tree crown.
Describe the root cap and its functions in detail.
Special area of living cells (parenchyma) at the distal tip of the root that functions to physically protect the apical meristem (like a helmet). Also secretes mucigel (a polysaccharide slime) which lubricates the soil around the grown root tip and gives shelter to helpful bacteria.
Describe and give the functions of the various zones that function in the primary growth of roots in detail.
- Zone of cell division: apical meristem and its derivatives. New cells are added in this area. Just above the apical meristem the products of cell division form the three cylinders of primary meristems (protoderm, ground meristem, and procambium). If you can see mitotic cells the tissue MUST BE meristematic.
- Zone of elongation: Cells enlarge (elongate) in this area, which is the driving force behind pushing the root tip through the soil.
- Zone of maturation: The three primary meristems differentiate into their respective tissues in this zone. It can be easily recognized by the appearance of root hairs.
Describe the functions and anatomy of root hairs in detail.
- Literal extensions of the epidermis, root hairs begin to form in the zone of maturation. They are extremely compact and dramatically increase the surface area for water absorption by the plant.
- Their appearance can be used to identify the zone of maturation.
Trace the sequence of water/ions making it from soil to the xylem of the root.
Root hairs -> epidermis -> exodermis -> endodermis -> vascular cylinder -> vessel elements
Describe the endodermis and exodermis in detail.
- Endodermis: innermost layer of cells of the cortex. Cells contain a casparian strip (wall thickening made of suberin and lignin) which creates a impermeable layer for water. This helps to regulate the passage of materials into the vascular cylinder (like a filter) by forcing the material to go THROUGH the cells, and not between them.
- Exodermis: outermost layer of cells of the cortex. Anatomically similar to the endodermis, but functions to retain water within the root.
- Both the endodermis and exodermis are layers of the cortex because they are formed from the ground meristem.
What is the vascular cylinder?
The vascular cylinder is an area of the root during primary growth that contains the vascular tissues xylem and phloem and a special single layered group of cells called the pericycle.
Describe the pericycle in detail.
- The outer-most layer of cells in the vascular cylinder, located just interior of the endodermis. This group of cells is meristematic and is the source of lateral roots (roots that branch from the primary root).
- The pericycle is critical to the process of secondary growth (horizontal growth).
What is the difference between monocots and dicots? How do their root cross-sections differ during primary growth?
- Monocot: smaller grass-like plants (wheat, barley, etc). These roots have a pith in the middle. Tend to undergo very little secondary growth in roots.
- Dicots: all other plants. These roots lack a pith, and have a small vascular bundle in the center which houses the xylem, phloem, and pericycle. Tend to undergo secondary growth in roots.
What is the difference between angiosperms and gymnosperms?
- angiosperms are woody and cone-bearing.
- gymnosperms have sex organs in flowers and seeds in fruit.
Describe secondary root growth in detail (cells, root changes, etc).
- Vascular cambium and cork cambium are the main constituents of secondary growth and both ultimately came from the procambium.
- Vascular cambium: produces secondary xylem toward the inside and secondary phloem toward the outside.
- Cork cambium: produces the periderm. Phelloderm (parenchyma cells) toward the inside and cork toward the outside.
- Gain of width is due to an accumulation of secondary xylem (hard secondary walls don’t shrink under pressure, causing expansion).
- Primary phloem (except fibers) gets crushed as secondary phloem is added (soft/squishy primary wall only).
- Secondary growth causes both the epidermis and cortex (including endodermis) to be sloughed off.
Describe the various root modifications in detail.
- Aerial roots: adventitious roots that can serve a variety of functions (aerial roots of orchid can photosynthesize, prop roots of corn act as a supporter of the plant).
- Pneumatophores: exhibit negative gravitropism (grow against gravity)
- Fleshy roots: storage parenchyma permeate the vascular tissue for storage of nutrients (carrot, potato, etc)
- Water storage root: Storage of water in roots (manroot)
- Adventitious buds: Some roots can produce aerial stems (suckers) which can become separated from the roots and develop new plants.
- Parasitic roots: (dodders) develop haustoria (projections) that invade the phloem and xylem of a different plant. These plants are not green and cannot carry out photosynthesis on their own, they are true parasites.
What are the functions of the stem?
- Support (leaves) and transport
- Xylem: moves water and ions (inorganic) from roots to leaves
- Phloem: moves organic compounds from leaves to roots
Describe the basic development of a nonwoody stem, and what is responsible for its growth. What are the units of this development?
- Apical meristem adds cells that become the primary meristems (which further differentiate into the tissues). Apical meristem adds leaf primordia (will become leaves) and bud primordia (will become axillary buds then lateral stems and leaves)
- Phytomeres: repeated units added by the Apical Mersitem that consist of a node and its leaf, the internode below the node, and the inferior bud
Define node, internode
- Node: plane of leaf attachment on a stem
- Internode: the distance between nodes (stem height increase is due to enlargement of cells within internodes)
Describe the arrangements of stem (cross section) in detail w/ visual descriptions and examples. +bundle types
- Dicots: Vascular bundles arranged in a ring around a pith with pith rays (elderberry, medicago)
- Monocots: Scattered vascular bundles within ground tissue with no discernable cortex or pith
- Herbaceous dicots have further variability in that they can have room for a small amount of secondary growth (medicago) or be completely unable to have secondary growth.
- Vascular bundles of dicots that cannot perform secondary growth look like the “curious George face” with a bundle sheath – a layer of sclerenchyma cells – surrounding them (closed bundle)
- Vascular bundles of dicots that can perform little secondary growth do not contain a bundle sheath, and have a layer of vascular cambium separating the xylem and phloem (open bundle)
Briefly describe the characteristics of monocot and dicot roots and stems.
- Monocot root: vascular cylinder contains a pith, vascular bundles encircle the outer perimeter of the vascular bundle.
- Monocot stem: vascular bundles are located sporadically throughout the cross-section
- Dicot root: vascular cylinder is small and in the center, has xylem in the middle and phloem toward the outside
- Dicot stem: (medicago) vascular bundles encircle a pith, pith rays connect to the outer cortex.
Describe the leaf and stem vascular tissue connection points.
- Vascular tissue connects the leaves to the stem very early on as the procambial strands develop.
- Leaf traces: near the node, vascular tissue from the stem diverges toward the leaf (just the point of divergence)
- Leaf trace gaps: Above these diverging points there are wide gaps of ground tissue
Describe the basic anatomy of the leaf including exceptions, and the different categories of leaves.
- Commonly has lamina (blade) and petiole (stalk). May contain a stipule; a spiky structure at the base of the petiole.
- Sessile leaves: leave without a petiole. The base of the leaf expands into a sheath that encircles the stem. Common in grasses.
- Simple leaf: one large blade connected to a petiole.
- Compound leaf: rather than a large blade there are several leaflets with their own petioles. An axillary bud Is located at the base of the entire blade allowing you to discern between a single leaf or stem. (Also important for determining simple vs compound leaf).
- Pinnately Compound leaf: leaves arise from either side of central rachis (an extension of the petiole) and look similar to a feather
- Palmately compound leaf: no rachis; leaflets branch out from the petiole (like a hand at the end of an arm).
Describe the general leaf internal anatomy.
- Upper epidermis:
- Mesophyll: tissue that makes up the most of a leaf, and is made up of ground tissue specialized for photosynthesis. Found between the upper and lower epidermis it has large intercellular spaces which communicate with the stomata and numerous chloroplasts. The mesophyll tissue has two layers…
- Palisade parenchyma – tightly packed elongated cells usually perform the majority of photosynthesis (usually located at the top of the mesophyll layer)
- Spongy parenchyma – loosely packed cells that perform SOME photosynthesis (usually located beneath the palisade parenchyma)
- Lower epidermis:
- Note: typically no stomata are found in the upper epidermis
Describe the vascular tissue of a leaf, its various patterns, and what plants are associated with those patterns.
- Phloem lies beneath the xylem. The vascular bundles of the leaf are often called veins. Bundle sheaths often wrap around the outside of a vein, which are bordered by collenchyma. Two types of venation…
- Netted: (common to dicots) veins have tributaries (side veins) that branch from a larger midvein.
- Parallel: (common to monocots) veins run parallel to each other like a blade of grass
- Note – midvein + associated ground tissue = midrib. A midvein is JUST the vascular tissue.
Why do leaf structural adaptations occur? Describe the general types in detail.
- Leaf adaptation exists due to different environment conditions, with water availability being the most important factor.
- Hydrophytes: (water environment) leaves beneath the water have no stomata, leaves resting on water contain stomata only on the upper epidermis (can’t breathe water). Have reduced vascular tissue (especially xylem) because it resides in H2O. Epidermis is covered with a cuticle to keep water from escaping. Large intercellular space allows for buoyancy. Large sclereids keep the plant semi-rigid even with the large amount of intercellular space.
- Xerophytes: (arid environment) contain stomatal crypts (invaginations of lower epidermis) for trichomes and stomata. Upper epidermis is thick and multilayered to keep water in the plant. Have greater number of stomata than other leaves so that photosynthesis can occur rapidly when water conditions are favorable. Trichomes can be on either/both surfaces of the leaf (retards water loss). Palisade parenchyma often occurs on both sides of the leaf (maximizing photosynthetic potential).
- Mesophytes: (normal environment) as described in “general internal leaf anatomy.” Palisade parenchyma packed tightly near top of mesophyll with spongy parenchyma found below. Stomata and trichomes on bottom of leaf.
- Note – actual leaves could be a blend of these three types.
What is secondary stem growth (moderate detail) and what types of plants does it occur? Give information about secondary growth.
- In most herbaceous dicots and the monocots growth in a given region of a plant ends after the maturation of the primary tissues. (primary growth)
- In others, including woody magnoliids, woody dicots, and the gymnosperms growth in wide begins in regions that are no longer elongating. (secondary growth)
- Note - Primary and secondary growth occur simultaneously but in different regions of the plant.
- Secondary growth: lateral meristems (vascular cambium [from procambium] and cork cambium [from ground meristem]) add girth by producing secondary vascular tissues and periderm.
- Secondary growth is found in roots and stems and occurs in all gymnosperms and most angiosperms (except monocots)
- Stem elongation is due to activity with the apical meristem.
Describe the alternating regions of cambium cells found in the vascular cambium in detail.
- Ray initials: produce radial (like the spokes of a bicycle tire) files of parenchyma cells known as xylem rays and phloem rays. These xylem and phloem rays are living highways of cells for horizontal transport of water and nutrients AND storage of starch and other reserves.
- Fusiform initials: (occur inside a vascular bundle) produce new secondary vascular tissues (usually more xylem), over the years secondary growth produces the wood of a stem (secondary xylem = wood). Anatomically, wood = tracheids, vessel elements, and fibers in angiosperms (cell walls are lignified, dead, at maturity).
- Note - during fusiform/ray initial mitosis one cell stays an initial for future growth and the other differentiates.
Describe the creation of annual rings.
- In temperate climates the cambium is dormant in winter, but reactivated at the beginning of the growing season by Auxin secreted from the shoot tip.
- Spring wood (early wood): 1st xylem to be produced after cambium interruption. The tracheids and vessel elements have a wider diameter and thinner cell walls. This means better water and ion conduction which is needed during the start of the growing season.
- Summer wood (late wood): tracheids and vessel elements have smaller diameter.
Sapwood vs. Heartwood.
- Heartwood: (appears darker) older and no longer functions in water and ion transport (toward center of trunk). Resin material clogs the inside of these tubes and together with the lignified walls provides a central support column for the tree. Resin also helps protect the tree from fungi, bacteria, and wood-boring insects.
- Sapwood: (appears lighter) functions in the upward transport of water and ions.
When is periderm formed? What are the layers of the periderm w/ alt name? Describe the structure of the outermost cells and why they develop this way.
- Periderm replaces the epidermis in plants with secondary growth, begins to form by the end of the first year following the initiation of secondary growth.
- Periderm includes cork cells (phellem), cork cambium (phellogen), parenchyma cells (phelloderm)
- Cork cambium (derived from cells in the cortex) produces cork cells toward the exterior of the cork cambium and phelloderm (living parenchyma cells) to toward the interior.
- Cork cells walls accumulate suberin, wax, and lignin which help protect the stem from physical damage, pathogens, and water loss.
- Note – Multiple periderm layers can exist and may slough off.
What are lenticels? Describe their function, how they are formed, and their affect on growth.
- Areas where the activity of the cork cambium is higher than elsewhere and creates a tear or split.
- They allow for living cells within the trunk to exchange gases with the outside air.
- As the stem increases in size due to the vascular cambium activity, it splits the outer periderm. New cork cambium kicks in and produces a new periderm. The first periderm may keep up with the initial increase in girth for several years by periodic activity of cork cambium which doesn’t necessarily correspond to vascular cambium activity.
Describe “bark” “inner bark” and “outer bark.”
- Bark: all phloem plus periderm (everything to the outside of the vascular cambium)
- Inner bark: secondary phloem
- Outer bark: periderm (cork, cork cambium, living parenchyma)
Which areas of phloem function in a secondary stem? Why?
Only the most recent secondary phloem functions in sugar transport because the rest are destroyed (squished). Older secondary phloem dies and sloughs off as part of the bark as stem diameter increases. Thus, increase in girth is mostly due to secondary xylem accumulation.
Identify and list the function of terminal bud, axillary buds, terminal bud scale scars, bundle scars, leaf scars, lenticels, dilated rays.
- Terminal bud: meristematic area of the shoot, keeps axillary buds in check
- Axillary (lateral) buds: meristematic tissue usually kept inactive by presense of terminal bud
- Terminal bud scale scars: mark the location of previous terminal buds
- Bundle scars: severed ends of vascular bundles (leaf traces) after leaf fall
- Leaf scars: mark where the leaf falls off
- Lenticels: allow gas exchange for living cells in the trunk
- Dilated rays: dilated phloem rays sometimes occur in an attempt to compensate for the rapid girth increase caused by secondary xylem production.
Describe mutualistic symbiosis of the roots in detail for vascular plants and legumes.
- Vascular plants: Mycorrhizae are needed for the proper health of many plants. They aid in the absorption of essential nutrients such as phosphorus and water. There is a lteral invasion of the plant by fungal hyphae which moves through the epidermis, cortex, and stops at the endodermis. Up to 90% of plants rely on mycorrhizae to get proper amounts of P and other nutrients.
- Legumes: develops partnership with rhizobium bacteria which forms small swellings called nodules within the roots to house itsself. Rhizobium bacteria have specia enzymes for nitrogen fixation (converting N2 to NO3-). In order to establish this relationship the bacteria release enzymes that allow them to create the nodules by hijacking the nucleus and ribosomes in the legumes.
pit fields vs pits, collateral vs bicollateral
- Pit field: thin area of primary cell wall with many plasmodesmata
- Pits: Thinner areas of secondary walls with plasmodesmata (usually correspond to pit fields)
- Collateral: one layer of xylem and one layer of phloem
- Bicollateral: xylem is sandwiched between two layers of phloem
What are common underground stems?
- Rhizomes: horizontal stems that grow at or below soil surface (irish potato, ferns, iris)
- Tubers: tips of rhizomes which become enlarged with food storage (irish potato)
- Bulbs: large buds, consisting of small stem and numerous fleshy storage leaves (onion, lily)
- Corms: stems that superficially resemble bulbs but ocnsists mostly of stem tissue, leaves usually smaller/thinner than bulbs (gladioulus, crocus, and cyclamen)
Give information about various modified stems
- Tendrils: modified areial organs for climbing (grape, boston ivy, virginia creeper)
- Runners/stolons: creeping stems that grow horizontally on soil surface often giving rise to new plants at nodes (strawberry, spider plant)
- Thorns: modified twigs that grow in the axils of leaves; sometimes branched (hawthorn)
- Cladophylls: branches that assume the form and closely resemble foliage leaves (asparagus)
Give information about various modified leaves (not the 3 environment adaptations)
- Bud scales: of woody plants protect/envelop delicate parts of the developing bud (buds without bud scales are said to be naked buds)
- Spines: of plants such as cacti defend against herbavores
- Tendris: that are foliar in origins, such as the tendrils of the garden pea aid in support (col around a supporting structure), and constitute the terminal portion of a compound leaf.
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