Structures and Functions in Plants

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Structures and Functions in Plants

• Roots, Stems, and Leaves

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Specialized Plant Cells

• There are three types of cell found in plants
  that are arranged differently in roots, stems,
  and leaves.
• Parenchyma
• Collenchyma
• Sclerenchyma

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Parenchyma

• Loosely packed, cube-shaped or elongated cells
  with large central vacuoles
• Involved with many metabolic functions including
  photosynthesis
• Usually form the bulk of nonwoody plants
• Alive at maturity

4
Collenchyma

• Thicker cell walls
• Provide support for the plant
• Usually in founds in strands
• Celery has a lot of collenchyma cells
• Alive at maturity

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Sclerenchyma

• Thick,even,rigid cell walls
• Support and strengthen in areas of plant no
  longer growing
• Dead at maturity
• This is FIBER!

The gritty texture of the pear fruit is due to
sclerenchyma cells!
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Plants Also Have Tissue Systems

• Plants cells work together to form three tissue
  systems dermal, ground, and vascular.
• These tissue systems organize to produce the
  three organs of a plant roots, stems and leaves.

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• Dermal Tissue
• Primary function is absorption and protection.
• Parenchyma cells.
• Forms the outside covering of plants
• Epidermis and cuticle
• Ground Tissue
• This consists of all three types of cells.
• Mostly parenchyma, some collenchyma and few
• sclerenchyma
• Primary function is storage and support.
• Vascular Tissue
• Primary function is transport and support.
• Xylem and phloem

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Growth Occurs in Meristem

• Apical
• Tips of roots and shoots
• Growth in length
• Lateral
• Occurs in gymnosperms and most dicots
• Growth in diameter
• Intercalary
• Located above the bases of leaves and stems

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Roots

• Tap
• Fibrous
• Adventitious

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Primary Growth in Roots
Roots increase in length through cell division,
elongation, and maturation in the root tip. A
root cap covers the apical meristem. It produces
a slimy substance allowing the root to move
easily through the soil. Root hairs are
extensions of the epidermis that increase surface
area.
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Secondary Growth in Roots

• This occurs in gymnosperms and dicots.
• The vascular core of a primary root is surrounded
  by the pericycle.
• The pericycle produces lateral roots.

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Root Functions

• Anchor the plant in the soil
• Absorb water and minerals
• 13 minerals are required for normal growth
• Adapted to store carbohydrates
• Usually stored as starch and stored in parenchyma
  cells
• Potatoes, sweet potatoes,
• carrots, turnips

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Modified Roots
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Monocot vs Dicots Roots
Vascular tissue matures to form the innermost
cylinder of the root. In the dicot, the xylem
forms an X and the monocot has a prominent
endodermis. The cortex is between the epidermis
and endodermis. The cortex and the endodermis
compose the GROUND TISSUE.
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Stems

• There are many differences in stem shape and
  growth that are the results of adaptations to the
  environment.
• Stems have a more complex structure than roots.
• Stems grow in length at the tips and grow in
  circumference through lateral meristem.

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Stem Structures
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• Stems are divided into segments called
  internodes.
• A node is at the end of each internode.
• At the point of attachment, each leaf has bud.
• A bud is capable of developing into a new shoot.
  The bud has apical meristem enclosed in special
  leaves called bud scales.
• At the tip of each stem there is usually a
  terminal bud. Each spring when growth resumes,
  the terminal bud opens.

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Primary Growth in Stems

• Apical meristem gives rise to all three types of
  tissue.
• In gymnosperms and dicots, ground tissue forms
  the cortex and pith. Pith is located in the
  center of the stem. In monocots, the ground
  tissue does not separate into pith and cortex.

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Monocot / Dicot Stems
Monkey faces
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Secondary Growth in Stems is Called Wood
Summerwood
Sapwood (light)
Springwood
Annual ring
Heartwood
Bark-protective outer covering composed of cork,
cork cambium and phloem
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Functions of Stems

• Function in transport and storage of nutrients.
• Translocation is the movement of food in the
  phloem.
• Pressure-flow hypothesis (carbohydrates are
  actively transported and water moves by osmosis)
• Transpiration is water loss (cohesion-tension
  theory)

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Storage of Water and Nutrients

• Abundant parenchyma cells in the cortex provide
  plants with ample storage.
• Cactus stems are specialized for storing water.
• Sugar-cane stores large amounts of sucrose.
• Potatoes store starch.

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Leaves

• Most leaves are thin and flat, an adaptation that
  helps a plant capture sunlight for
  photosynthesis.
• Leaves exist in many variations that reflect
  adaptations to environmental conditions.

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Leaf Adaptations

• Tendrils coiled specialized leaves to aid a
  climbing vine ( some may be modified stems
  grapes)
• Carnivorous plants pitcher plant and venus fly
  trap leaves function as food traps
• Spines- modified leaves that protect the plant.
  Spines are small and nonphotosynthetic. In a
  cactus, spines reduce transpiration.

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Leaf Structures

• blade
• stipules
• petiole
• vein
• midrib

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Leaves are Either Simple or Compound
Simple leaves
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A compound leaf consists of several, separated
segments called leaflets. The leaflets are
usually grouped in pairs around the elongated
rhachis that corresponds to the midrib of a
normal leaf.
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Leaf Arrangement
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Vein Patterns

• In parallel - veined leaves, the veins run
  parallel to each other. This condition is
  characteristic of the monocotyledoneae.
• Pinnately netted - veined leaves have a single
  primary vein or midrib, from which smaller veins
  branch off, like the divisions of a feather.
• Palmately netted- veined leaves have several
  principal veins radiating from the base of the
  leaf blade, as in Acer rubrum (red maple).

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Parts of a leaf
Stomata palisade layer spongy layer veins chloropl
ast thylakoids grana stroma
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Leaf Functions

• Photosynthesis
• Limitations insufficient water due to
  transpiration. A corn plant losses 98 of water
  absorbed by roots through transpiration.

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Benefits of Photosynthesis

• 1. The oxygen in the air comes from
• photosynthesis. The plants continue to
• replenish the oxygen in the air.
• 2. All of our food comes directly or
• indirectly from photosynthesis.