Kingdom Plantae: Roots, Stems, and Leaves

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Kingdom Plantae Roots, Stems, and Leaves
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Roots

• Function is primarily absorption of water and
  minerals and anchorage of the plant in the ground
• Also store excess sugar (glucose) produced during
  photosynthesis as starch, the storage form of
  carbohydrates in plants

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Roots (continued)

• The following structures can be identified in a
  longitudinal section (l.s.) of a root tip
• Root cap a mass of cells at the tip of a root
  protects the delicate meristematic tissue just
  behind the cap
• Zone of cell division region of a root tip that
  consists of cells that are dividing and producing
  new cells
• Zone of elongation region of a root tip that
  consists of cells that are not dividing, but are
  growing/elongating
• Zone of maturation region of a root tip that
  consists of mature, specialized cells root
  hairs, which increase the surface area of roots,
  originate in this area and allow for most of the
  water and mineral absorption

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Roots (continued)

• The following structures can be identified in a
  cross section (c.s.) of a root tip
• Epidermis single layer of cells which covers the
  exterior of the root functions in protection
  does not have a cuticle, as does the epidermis of
  a leaf
• Cortex consists of parenchyma cells (ground
  tissue) which store starch located interior to
  the epidermis
• Vascular cylinder/stele consists of xylem and
  phloem (vascular tissue)

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Roots (continued)

• Monocots tend to have multiple fibrous roots of
  similar size dicots tend to have taproots
• In cross-sectional view, monocots have xylem and
  phloem arranged in a circle within the stele
  dicots have the xylem arranged in a cross shape/
  x shape in the center of the stele, with the
  phloem in between

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Stems

• Function is primarily transportation of water,
  dissolved minerals, and food also support leaves
  and flowers some stems (herbaceous stems) carry
  out photosynthesis
• The structure of stems is similar to that of
  roots, in that stems consist of many of the same
  parts (ex. epidermis, cortex, xylem, and phloem)

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Stems (continued)

• In monocot herbaceous stems, the xylem and phloem
  is clustered together as vascular bundles these
  bundles are scattered
• In dicot herbaceous stems, the xylem and phloem
  is clustered together as vascular bundles
  arranged in a circle within a bundle, the xylem
  is interior to the phloem between the xylem and
  phloem is vascular cambium, which produces new
  vascular tissue

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Stems (continued)

• In dicot woody stems, the xylem is interior to
  the phloem, with vascular cambium between bark
  consists of all tissue exterior to the vascular
  cambium, including cork, cortex, and phloem
• Phloem makes up the inner bark xylem makes up
  the wood

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Stems (continued)

• Heartwood older, darker wood near the center of
  a tree trunk
• Sapwood younger, lighter-colored wood exterior
  to the heartwood
• Hardwood wood from angiosperms
• Softwood wood from gymnosperms

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Stems (continued)

• Annual rings rings of xylem vessels in a tree
  trunk can be counted to determine the age of a
  tree the ring appearance is due to the variation
  in size of xylem in the spring, summer, fall, and
  winter xylem vessels are large when there has
  been much rainfall and small when there has been
  little rainfall

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Leaves

• Function is to carry out photosynthesis
• Most leaves are composed of 2 parts
• Blade the broad, expanded part
• Petiole the stalk that attaches the blade to the
  stem

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Leaves (continued)

• Simple leaves consist of one blade
• Compound leaves consist of many blades, or
  leaflets

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Leaves (continued)

• Leaves attach to the stem at nodes the portion
  of the stem between nodes is called an internode
• The veins of a leaf are vascular bundles of xylem
  and phloem
• Venation is the pattern of veins in a leaf
  monocot leaves have parallel venation, and dicot
  leaves have netted venation
• Netted venation can be either pinnate (veins
  branch off one main vein) or palmate (all veins
  radiate out from one point)

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Leaves (continued)

• The upper and lower surfaces of a leaf, the upper
  epidermis and the lower epidermis, are made up of
  epidermal cells which protect the innermost part
  of the leaf
• To prevent water loss from a leaf, the epidermis
  secretes a waxy cuticle, composed of a substance
  called cutin the upper epidermis usually has a
  thicker cuticle than the lower epidermis

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Leaves (continued)

• Many leaves are covered with hair-like structures
  called trichomes, which further help to prevent
  water loss
• The epidermis of leaves contain tiny pores called
  stomata, which allow for gas exchange the lower
  epidermis generally has more stomata than the
  upper epidermis
• Guard cells are paired cells that surround
  stomata and control the size of the openings
  they are the only epidermal cells that contain
  chloroplasts

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Leaves (continued)

• Oxygen and water vapor move out of stomata, and
  carbon dioxide moves in photosynthesis requires
  CO2 and results in the production of O2
  transpiration is the release of water vapor from
  a leaf

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Leaves (continued)

• The tissue between the upper and lower epidermis
  is called mesophyll and consists of parenchyma
  cells that contain chlorophyll within
  chloroplasts photosynthesis occurs in the
  mesophyll
• The upper portion of the mesophyll, the palisade
  mesophyll, contains cells that are column-shaped
  and closely packed next to one another
• The lower portion of the mesophyll, the spongy
  mesophyll, contains cells that are spread apart,
  with air spaces in between