Botany Chapter: Stems and Twigs
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Botany Chapter: Stems and Twigs

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Questions and Answers

What is the primary function of stems in plants?

Support and transport nutrients and water.

What type of growth do some plants exhibit?

  • Determinative growth
  • Yearly growth
  • Limited growth
  • Indeterminate growth (correct)

    • What are the two types of cambium mentioned?

    Vascular cambium and cork cambium.

    The area of the stem where leaves are attached is called a ______.

    <p>node</p> Signup and view all the answers

    Heartwood can conduct materials.

    <p>False</p> Signup and view all the answers

    Which type of stem stores food?

    <p>Tubers</p> Signup and view all the answers

    What do cotyledons provide for seedlings?

    <p>They store food needed by young seedlings.</p> Signup and view all the answers

    What are annual rings comprised of?

    <p>Spring and summer wood</p> Signup and view all the answers

    What is the role of vascular rays in a tree?

    <p>They function in lateral conduction of nutrients and water.</p> Signup and view all the answers

    What is a characteristic of hardwood?

    <p>Contains fibers and vessels</p> Signup and view all the answers

    Softwood comes from hardwood trees.

    <p>False</p> Signup and view all the answers

    What is the function of cork cambium?

    <p>To produce cork cells that reduce water loss.</p> Signup and view all the answers

    What is the term for the area of the stem where leaves are attached?

    <p>Node</p> Signup and view all the answers

    Which of the following describes a terminal bud?

    <p>Found at the tip of a twig</p> Signup and view all the answers

    What is the primary growth characteristic of stems with indeterminate growth?

    <p>They grow indefinitely.</p> Signup and view all the answers

    Which structure protects the buds on a woody twig?

    <p>Bud scales</p> Signup and view all the answers

    What term describes the angle between the petiole and the stem?

    <p>Axil</p> Signup and view all the answers

    Which of the following stem structures is distinguished by its ability to grow horizontally underground?

    <p>Rhizome</p> Signup and view all the answers

    What type of leaves are stipules commonly associated with?

    <p>Opposite leaves</p> Signup and view all the answers

    What do groups of bud scale scars on a twig indicate?

    <p>Age of the twig</p> Signup and view all the answers

    What is the main difference between monocotyledons and dicotyledons?

    <p>Monocots are typically annuals, while dicots can be annuals or perennials.</p> Signup and view all the answers

    Which type of stele features a solid core with phloem surrounding the xylem?

    <p>Protostele</p> Signup and view all the answers

    What is the primary function of lenticels in plant stems?

    <p>To facilitate gas exchange</p> Signup and view all the answers

    What types of plants primarily feature siphonosteles?

    <p>Ferns</p> Signup and view all the answers

    How does the vascular cambium function in herbaceous dicots?

    <p>It adds secondary xylem and secondary phloem.</p> Signup and view all the answers

    What occurs during the spring in terms of wood production in trees?

    <p>Larger vessel elements of secondary xylem are produced.</p> Signup and view all the answers

    What characterizes woody dicotyledonous stems compared to herbaceous stems?

    <p>They are primarily composed of secondary xylem.</p> Signup and view all the answers

    Which statement about annuals is correct?

    <p>They die after going from seed to maturity in one growing season.</p> Signup and view all the answers

    What is the role of the apical meristem in plant growth?

    <p>Increases stem length</p> Signup and view all the answers

    Which primary meristem is responsible for producing the epidermis?

    <p>Protoderm</p> Signup and view all the answers

    Which structure marks the food and water conducting tissue within leaf scars?

    <p>Bundle scars</p> Signup and view all the answers

    What do leaf and bud primordia develop into?

    <p>Mature leaves and buds</p> Signup and view all the answers

    What does the vascular cambium produce toward the surface of the plant?

    <p>Secondary phloem</p> Signup and view all the answers

    What type of cells does cork cambium primarily produce?

    <p>Cork cells with suberin</p> Signup and view all the answers

    Which part of the plant is protected by bud scales?

    <p>Apical meristem</p> Signup and view all the answers

    What type of cells are produced by the ground meristem?

    <p>Pith and cortex</p> Signup and view all the answers

    What primarily characterizes spring wood in conifers?

    <p>Larger tracheids than later in the season</p> Signup and view all the answers

    How do annual rings of wood indicate a tree's age?

    <p>Rings correspond to annual xylem production</p> Signup and view all the answers

    What is heartwood characterized by?

    <p>It consists of older, darker wood at the center</p> Signup and view all the answers

    What is the difference between sapwood and heartwood?

    <p>Sapwood contains living cells; heartwood does not</p> Signup and view all the answers

    What impact does environment have on the formation of annual rings in trees?

    <p>It influences the size of the rings produced</p> Signup and view all the answers

    What is primarily produced by the vascular cambium?

    <p>More secondary xylem than phloem</p> Signup and view all the answers

    Which element is absent in conifer wood?

    <p>Vessels</p> Signup and view all the answers

    What function do vascular rays serve in trees?

    <p>They facilitate lateral transport of nutrients and water</p> Signup and view all the answers

    What is the primary characteristic of hardwood compared to softwood?

    <p>It contains fibers and vessel elements.</p> Signup and view all the answers

    Which statement about heartwood is true?

    <p>A tree may still function after heartwood is removed.</p> Signup and view all the answers

    What distinguishes the vascular bundles of monocot stems from those of dicot stems?

    <p>Monocot stems contain no secondary vascular tissues.</p> Signup and view all the answers

    Which feature describes the bark of a tree?

    <p>It consists of alternating layers of crushed phloem and cork.</p> Signup and view all the answers

    What are laticifers in plants primarily involved in?

    <p>Secreting latex.</p> Signup and view all the answers

    Which statement accurately describes the structure of typical monocot vascular bundles?

    <p>They include two large vessels and several small vessels.</p> Signup and view all the answers

    Which of the following types of trees does not produce resin canals?

    <p>Monocot trees.</p> Signup and view all the answers

    What happens to xylem cells in monocots during their development?

    <p>They stretch and collapse, leaving air spaces.</p> Signup and view all the answers

    Study Notes

    Introduction to Stems

    • Most wood in household items comes from stems.
    • Grafting involves uniting parts of stems from different plants.
    • Some plants can grow indefinitely.

    External Form of A Woody Twig

    • Stems produce branches and leaves.
    • A woody twig has an axis with attached leaves.
    • Nodes are where leaves attach to the stem.
      • Alternate or spiral arrangement.
      • Opposite arrangement.
      • Whorled arrangement.
    • Internodes are the regions between nodes.
    • Leaves have flattened blades and are attached by petioles.

    Anatomy of A Woody Twig

    • Axil is the angle between petiole and stem.
    • Axillary buds are located in the axil.
      • Will develop into branches or flowers.
      • Bud scales protect buds.
    • Terminal buds are at the twig tip.
    • The growth makes the twig longer.
    • Bud scale scars indicate the age of the twig.
    • Stipules are leaf-like structures at the base of a leaf.

    Deciduous Tree and Shrubs

    • Deciduous trees lose all leaves annually.
    • Dormant axillary buds have leaf scars below.
    • Bundle scars mark food and water conducting tissue within leaf scars.

    Origin and Development of Stems

    • Apical meristem at the stem tip increases stem length.
    • It is dormant before the growing season begins.
    • Protected by bud scales and leaf primordia.
    • Leaf primordia are embryonic leaves.

    Primary Meristems

    • Apical meristem cells form three primary meristems:
      • Protoderm: Gives rise to the epidermis.
      • Procambium: Produces primary xylem and phloem.
      • Ground Meristem: Produces pith and cortex.

    Leaf Primordia and Bud Primordia

    • Leaf primordia and bud primordia develop into mature structures.
    • Traces branch off from xylem and phloem and enter leaves or buds.

    Vascular Cambium

    • Arises between primary xylem and primary phloem.
    • Produces secondary xylem towards the center and secondary phloem toward the surface.

    Cork Cambium

    • Produces cork cells with suberin and phelloderm cells.
    • Functions to reduce water loss and protect against injury.
    • Lenticels are parenchyma cells in cork for gas exchange.

    Tissue Patterns in Stems: Steles

    • Stele is the central cylinder of primary xylem, phloem, and pith.
    • Protostele: Solid core with phloem surrounding xylem.
      • Common in primitive plants.
    • Siphonosteles: Tubular with pith in the center.
      • Typical in ferns.
    • Eusteles: Discrete vascular bundles.
      • Found in flowering plants and conifers.

    Seed Leaves

    • Cotyledons are seed leaves.
    • Dicotyledons (dicots) have two cotyledons.
    • Monocotyledons (monocots) have a single cotyledon.

    Herbaceous Dicotyledonous Stems

    • Annuals die after completing their life cycle within one season.
    • Most monocots and many dicots are annuals.

    Tissue Patterns in Herbaceous Dicotyledonous Stems

    • Herbaceous dicots have vascular bundles arranged in a cylinder.
    • Vascular cambium adds secondary xylem and phloem.

    Woody Dicotyledonous Stems

    • Secondary xylem is wood.
    • Vascular and cork cambium active all year:
      • Produces ungrained, uniform wood.
    • Some tropical trees produce uniform wood.

    Seasonal Production of Wood

    • Spring wood has large vessel elements.
    • Summer wood has fewer, smaller vessel elements.
    • Alternating spring and summer wood creates rings.
    • Annual ring reflects the xylem growth in one year.

    Conifers

    • Conifers lack vessels and fibers.
    • Tracheids are larger in the spring.

    Annual Rings and Vascular Rays

    • One year of xylem growth forms an annual ring.
    • Annual rings indicate the tree's age and climate changes.
    • Vascular rays are parenchyma cells for lateral nutrient and water transport.
      • Xylem ray is within the xylem.
      • Phloem ray is in the phloem.

    Cross Section of a Young Stem

    • Diagram highlighting secondary growth in a young stem.

    A Block of a Woody Dicotyledonous Stem

    • 3D view of dicot wood.

    Heartwood and Sapwood

    • Heartwood is the older, darker, non-functioning wood in the center.
    • Sapwood is the lighter, active wood in the outer layers.

    Removal of Wood

    • Heartwood supports the tree but doesn't conduct materials.
    • It is possible to remove portions of sapwood without destroying the tree.

    Softwood and Hardwood

    • Softwood is wood from conifers.
    • Hardwood is wood from dicot trees.
    • Resin canals are tubes in the wood, typically present in softwoods.

    Bark and Laticifers

    • Bark consists of tissues outside the vascular cambium, including secondary phloem.
    • Mature bark alternates between crushed phloem and cork layers.
    • Laticifers are ducts in phloem that contain latex.
      • Latex can be used to produce rubber, chicle, or morphine.

    Monocotyledonous Stems

    • Monocots lack vascular and cork cambium.
    • They do not produce secondary vascular tissues or cork.
    • Vascular bundles are scattered throughout the stem.

    Typical Monocot Vascular Bundle

    • Contains large and small vessels.
    • Phloem consists of sieve tubes and companion cells.
    • Vascular bundles are surrounded by sclerenchyma cells.

    Specialized Stems

    • Rhizomes are horizontal underground stems.
    • Runners are horizontal stems that grow above ground.
    • Stolons are produced beneath the ground and grow in different directions.

    Tubers and Bulbs

    • Tubers are swollen underground stems that store food.
    • Bulbs are buds surrounded by fleshy storage leaves with a small stem at the base.

    Corms and Cladophylls

    • Corms resemble bulbs but are mostly stem tissue.
    • Cladophylls are flattened, leaf-like stems.

    Wood and Its Uses

    • Half of the wood's weight is water content.
    • The dry part is mainly composed of cellulose and lignin.
    • Density is the weight per unit volume.
    • Durability is the resistance to decay.

    Types of Sawing

    • Boards cut radially show annual rings in side view.
    • Boards cut tangentially show annual rings as irregular bands.

    Knots

    • Knots are the bases of lost branches covered by annual rings.
    • They are more common in older parts of a log.

    Wood Products

    • Lumber is used primarily for construction.
    • Sawdust and waste is used for particleboard and pulp.
    • Veneer is a thin layer of wood glued to cheaper lumber.
    • Pulp is used for paper, synthetic fibers, and plastics.
    • Wood is also used as fuel in developing countries.

    Introduction to Stems

    • Stems provide the structural support for plants and are the source of most wood used in daily life.
    • Grafting, a technique involving the joining of stems from different plant varieties, has been practiced for centuries.
    • Some plants possess indeterminate growth, allowing them to continue growing indefinitely.

    External Form of a Woody Twig

    • Stems develop a shoot system with branches and leaves.
    • A woody twig consists of an axis with attached leaves.
    • Nodes represent areas where leaves attach to the stem, exhibiting various arrangements: alternate, opposite, or whorled.
    • Internodes are the sections of stem between nodes.
    • Leaves typically have a flattened blade and are attached to the twig via a petiole.

    Anatomy of a Woody Twig

    • The axil is the angle formed between the petiole and the stem where an axillary bud is located.
    • Axillary buds develop into branches or flowers in flowering plants and are protected by bud scales.
    • The terminal bud is situated at the tip of the twig and contributes to stem elongation.
    • Stem age can be determined by counting groups of bud scale scars.
    • Stipules are paired structures, often leaf-like, located at the base of a leaf.

    Deciduous Trees and Shrubs

    • Deciduous plants shed all their leaves annually.
    • After leaf fall, dormant axillary buds remain with leaf scars below.
    • Bundle scars mark the location of food and water conducting tissue within leaf scars.

    Origin and Development of Stems

    • The apical meristem, located at the stem tip, contributes to stem length and is protected by bud scales and leaf primordia.
    • Leaf primordia are tiny embryonic leaves that develop into mature leaves.

    Primary Meristems

    • Apical meristem cells differentiate into three primary meristems: protoderm, procambium, and ground meristem.
    • Protoderm gives rise to the epidermis.
    • Procambium produces primary xylem and phloem.
    • Ground meristem forms pith and cortex, both composed of parenchyma cells.

    Leaf Primordia and Bud Primordia

    • Leaf primordia and bud primordia develop into mature leaves and buds, respectively.
    • Traces, strands of xylem and phloem, branch off from the vascular cylinder and extend into leaves or buds.

    Vascular Cambium

    • The vascular cambium, a meristematic band, arises between primary xylem and primary phloem.
    • The vascular cambium produces secondary xylem towards the center and secondary phloem towards the surface.

    Cork Cambium

    • Cork cambium (phellogen) produces cork cells containing suberin and phelloderm cells.
    • Cork cells contribute to water loss reduction and stem protection against injury.
    • Lenticels are parenchyma cells within cork that facilitate gas exchange.

    Tissue Patterns in Stems: Steles

    • The stele, the central cylinder of the stem, comprises primary xylem, primary phloem, and pith (if present).
    • Protostele, a solid core with phloem surrounding xylem, is found in primitive seed plants, whisk ferns, club mosses, and ferns.
    • Siphonosteles have a tubular structure with pith in the center, common in ferns.
    • Eusteles, with discrete vascular bundles, are characteristic of flowering plants and conifers.

    Seed Leaves

    • Cotyledons are seed leaves attached to the embryonic stem, serving as food storage for the developing seedling.
    • Dicotyledons (dicots) are flowering plants with two cotyledons in their seeds.
    • Monocotyledons (monocots) are flowering plants with a single cotyledon in their seeds.

    Herbaceous Dicotyledonous Stems

    • Annuals are plants that complete their life cycle from seed to maturity within a single growing season.
    • They are typically green and herbaceous and rely primarily on primary tissues.
    • Though many dicots are annuals, most monocots belong to this category.

    Tissue Patterns in Herbaceous Dicotyledonous Stems

    • Herbaceous dicots possess discrete vascular bundles arranged in a cylinder.
    • The vascular cambium arises between primary xylem and primary phloem, generating secondary xylem and phloem growth.

    Woody Dicotyledonous Stems

    • Wood is synonymous with secondary xylem.
    • Variations in wood development are influenced by the continuous activity of vascular cambium and cork cambium throughout the year.
    • Tropical trees often produce ungrained, uniform wood due to consistent growth.

    Seasonal Production of Wood

    • In spring, the vascular cambium produces relatively large vessel elements of secondary xylem, forming spring wood.
    • Later in the season, fewer and smaller vessel elements are produced, leading to the formation of summer wood.
    • The alternating pattern of spring and summer wood creates light and dark rings, known as annual rings.
    • Environmental factors impact the size of these rings.
    • Xylem growth within a year constitutes an annual ring.

    Conifers

    • Conifers lack vessels and fibers, but their tracheids are larger in spring than later in the season.

    Annual Rings and Vascular Rays

    • An annual ring represents a year's worth of xylem growth.
    • The vascular cambium produces more secondary xylem than phloem, forming the bulk of the tree trunk.
    • Annual rings provide insights into a tree's age and the climate during its lifetime.
    • Vascular rays, composed of parenchyma cells, function in lateral conduction of water and nutrients.
    • Vascular rays extend through both xylem and phloem, forming xylem rays and phloem rays, respectively.

    Cross Section of a Young Stem

    • A cross section of a young stem with secondary growth reveals distinct tissue layers.

    A Block of a Woody Dicotyledonous Stem

    • A 3-D view of dicot wood showcases the arrangement of vascular bundles, annual rings, and vascular rays.

    Heartwood and Sapwood

    • Heartwood, the older, darker wood at the center of the stem, accumulates resins, gums, and tannins.
    • Sapwood, the lighter-colored, functional xylem closest to the cambium, actively conducts water and nutrients.

    Removal of Wood

    • Heartwood primarily provides structural support and is no longer involved in material transport.
    • Removal of heartwood does not affect the tree's functionality.
    • Portions of sapwood can also be removed without harming the tree.

    Softwood and Hardwood

    • Softwood refers to the wood of conifers, lacking fibers or vessel elements.
    • Hardwood, derived from dicot trees, contains fibers and vessel elements.
    • Resin canals, tube-like structures scattered throughout xylem and other tissues, are typically found in conifers.

    Bark and Laticifers

    • Bark denotes tissues external to the vascular cambium, including secondary phloem.
    • Mature bark consists of alternating layers of crushed phloem and cork.
    • Laticifers, ducts primarily located in phloem, contain latex-secreting cells which are used in the production of rubber, chicle, and morphine.

    Monocotyledonous Stems

    • Monocot stems lack a vascular cambium and a cork cambium, resulting in the absence of secondary vascular tissues or cork.
    • Primary xylem and phloem are organized in scattered vascular bundles throughout the stem.

    Typical Monocot Vascular Bundle

    • Monocot vascular bundles typically contain two large vessels and several small vessels.
    • Early formed xylem cells elongate and collapse, leaving irregularly shaped air spaces.
    • Phloem comprises sieve tubes and companion cells.
    • The vascular bundle is surrounded by a sheath of sclerenchyma cells.

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    This quiz covers essential concepts related to the anatomy and external form of woody stems and twigs. Explore topics such as grafting, leaf arrangements, and the characteristics of deciduous trees. Test your understanding of how stems contribute to plant growth and structure.

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