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Plants. Plant Evolution and Classification. Preventing Water Loss Reproducing by Spores and Seeds Transporting materials throughout the plant. Classifying Plants. 2 groups based on the presence of vascular tissue Nonvascular Plants Vascular Plants Seedless-fern like

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Plant Evolution and Classification

  • Preventing Water Loss

  • Reproducing by Spores and Seeds

  • Transporting materials throughout the plant.

Classifying Plants

  • 2 groups based on the presence of vascular tissue

    • Nonvascular Plants

    • Vascular Plants

      • Seedless-fern like

      • Seeded- Maples, and Pine


  • Nonvascular Plants

    • Phylum Bryophyta

    • Phyla Haptophyta and Anthocerophyta

Seedless Vascular Plants

  • Phylum Psilotophyta

  • Phylum Lycophyta

  • Phylum Sphenophyta

  • Phylum Pterophyta

Vascular Seed Plants

  • Gymnosperms

    • Phylum Cycadophyta

    • Phylum Ginkgophyta

    • Phylum Gnetophyta

    • Phylum Coniferophyta

  • Angiosperms

    • Phylum Anthophyta


On cotyledon

Parallele Venation


Flower parts in 3’s



2 cotyledons

Net venation

Radially arranged vascular bundles

Flower parts in 4 and 5


Classes of Angiosperms

Plant Structure and Function

  • Plant Cells

    • 3 types

      • Parenchyma

      • Collenchyma

      • Sclerenchyma


  • Loosely packed cube-shaped or elongated cells that contain large central vacuole.

  • Metabolic functions, photosynthesis and storage of water and nutrients.

  • Example~ Fleshy part of an apple

Collenchyma Cells

  • Thicker cell walls, irregular shape

  • Usually grouped in strands and are specialized for supporting regions that are still growing.

  • Celery

Sclerenchyma Cells

  • Thick rigid cell walls.

  • Support and strengthen the plant in areas where growth is no longer occurring.

  • Gritty texture of a pear fruit.

Tissue Systems

  • Dermal Tissue

  • Ground Tissue

  • Vascular Tissue

Dermal Tissue

  • Forms the outer coverings in plants

  • Consists of the epidermis, the outer layer made of parenchyma cells.

    • Roots~ absorption, protection

    • Stems~ gas exchange, protection

    • Leaves, gas exchange, protections.

Ground Tissue

  • All 3 cell types

  • Storage, metabolism and support.

Vascular Tissue

  • Functions in transport and support

  • Xylem-dead

  • Phloem-living

  • 2 major components for xylem

    • Tracheid

    • Vessel Element


  • Long thick walled sclerenchyma cell with tapering ends.

  • Water moves from on tracheid to another through piths

Vessel Element

  • A sclerenchyma cell that has either large holes in the top and bottom or no end wall at all.

  • Stacked to form long tubes called vessels.

Sieve Tube Member

  • Conducting parenchyma cells of angiosperm phloem.

  • Compounds move from one to another through sieve plats.

  • Each cell has a companion cells, specialized parenchyma cell.

Growth in Meristems (Primary Growth)

  • Meristem- regions where cells continuously divide for plant growth.

  • Apical Meristem- located in the tips of stems and roots.

  • Intercalary meristems- growth between the nodes of plants.

Root Structures

Root Structures

  • Root Cap

    • Covering of cells that protects the apical meristem.

    • Produces a slimy lubricant.

  • Root Hairs

    • Extensions of the epidermal cells.

    • Increase the surface area.

Primary Growth in Roots

  • Roots increase in length

    • cell division

    • elongation

    • maturation in the root tip

  • Dermal tissue matures to form the epidermis

  • Ground tissue matures into 2 regions

    • Cortex and Endodermis


  • Located just inside the endodermis.

  • Largest region of the primary root.

  • Parenchyma cells


  • Inner cylinder of the cortex.

  • Vascular tissue in roots matures to form the innermost cylinder

  • Dicots and gymnosperms~ xylem makes of the central core of the root.

Monocot Root Cross Section

Dicot Stem


Primary Growth in Stems

  • Apical meristems give rise to the dermal, ground and vascular tissue.

    • Dermal- epidermis

    • Ground- cortex and pith

      • Cortex- just inside the epidermis

      • Pith- located in the center of the stem.

    • Vascular- xylem and phloem

Monocot Stem

Vascular Bundle of Monocot

Dicot Stem

Secondary Growth

  • Conifers and Woody dicots

  • Increases in girth or lateral dimension

  • Occurs at lateral meristems

    • Vascular cambium

      • Gives rise to secondary xylem and phloem

    • Cork cambium

      • Gives rise to bark

Vascular Cambium

  • Cells on the outside differentiate into phloem

  • Cells on the inside differentiate into xylem

    • Only new xylem transports water.

    • Older xylem located at the center is only for support.

Annual Rings


Monocot Leaf

Upper Epidermis


Lower Epidermis



Dicot Leaf

Upper Epidermis







Lower Epidermis

Guard Cells with Somata

Leaf Structures

  • Epidermis

  • Palisade Mesophyll

  • Spongy Mesophyll

  • Guard Cells

  • Vascular Bundles


  • A protective covering of one or more layers of cells.

  • Covered by the cuticle

    • Cutin

    • Transpiration

Palisade Mesophyll

  • Parenchyma cells

  • Numerous chloroplasts

Spongy Mesophyll

  • Parenchyma cells

  • Loosely arranged

    • Air spaces allow for gas exchange

Guard Cells

  • Specialized epidermal cells that control the opening and closing of stomata.

  • Controls gas exchanges with the environment.

Vascular Bundles

  • Consists of xylem and phloem tissues

    • Contains bundle sheath cells that prevent gas from entering the vascular bundle.

Transport of Water

  • Water and dissolved minerals enter the roots through root hairs by osmosis.

    • 2 Possible Pathways

      • Apoplast

      • Symplast


  • Water moves through cell walls from one cell to another without every entering the cells.


  • Water moves from one cell to another through the symplast.

  • Water moves from the cytoplasm of one cell to the cytoplasm of the next through plasmodesmata.

    • Small tubes that connect the cytoplasm of adjacent cells.

When water reaches the endodermis…

  • Water can continue into the vascular cylinder only through the symplast pathway.

  • Water that is moving via the apoplast pathway is blocked by the suberin that permeates the casparian strip.

  • Water can enter through the endodermal cells along with K+, but Na+ is blocked.

  • Water then reaches the vasuclar cylinder where xylem tissue (tracheids and vessels) conduct the water up the plant.

Water Movement Up the Plant

  • 3 Mechanisms

    • Osmosis

    • Capillary Action

    • Cohesion-tension theory

Cohesion-tension Theory

  • 3 Major Concepts

    • Transpiration

    • Cohesion

    • Bulk Flow


  • The evaporation of water from plants.

  • Water evaporates through the leaves creating negative pressure to develop in the column.


  • The molecular attraction between like substances.

  • The water molecules “stick” together creating a single column of water molecules.

Bulk Flow

  • When a water molecule is lost from a leaf by transpiration it pulls up behind it an entire column of water molecules.

Transport of Sugars

  • 4 Step process

    • Sugars enter the sieve-tube members via active transport.

    • Water enters the sieve-tube members.

    • Pressure in sieve-tube members at the source moves water and sugars to sieve-tube members at the sink through sieve tubes. As a result pressure builds causing the water and sugars to move.

    • Pressure is reduced in sieve-tube members at

Plant Movements

  • Tropisms

    • A plant movement that is determined by the direction of an environmental stimulus.

      • Positive

      • Negative

  • Nastic Movements

    • Plant movements that occur in response to environmental stimuli but are independent of the direction of the stimuli.


  • Phototropism

  • Thigmostropism

  • Gravitropism


  • Stimulus

    • Light

  • Hormone

    • Auxin

  • Function

    • Light causes the production of auxin to move to the shaded side.

    • As a result the cells on the shaded side are elongated faster then the lighted side.

    • The plant bends towards the light.


  • Stimulus

    • Contact with an object

  • Function

    • Allows for vines to “climb” walls.

    • Tendrils will coil around objects.


  • Stimulus

    • Gravity

  • Hormone

    • Auxins, Gibberellins

  • Function

    • Allows for roots to grow down.

    • Allows for shoots (stems) to grow up at the apical meristem.


  • Is the response of plants to changes in the photoperiod, or the relative length of daylight and night.

  • Plants maintain a circadian rhythm

  • External clues such as dawn and dusk reset the clock.


  • The protein involved used in maintaining the circadian rhythm.

    • 2 Forms depending on the wavelength of light that the phytochrome absorbs.

      • Pr: Phytochrome red (wavelength of 660nm)

        • Accumulates at night

      • Pfr: Phytochrome far-red (730nm)

        • Resets the circadian-rhythm clock

  • Reversible relationship between Pr and Pfr

    • When Pr is exposed to red light it is converted to Pfr

    • When Pfr is exposed to far-red light it is converted to Pr

Critical Night Length

  • CNL is responsible for resetting the circadian-rhythm clock.

  • Brief dark periods during the day have no effect on the clock.

  • Flashes of red light at night cause the clock to be reset.

Flowering in Plants

  • Regulated by the photoperiod.

    • 3 types of plants

      • Long-day

        • Plants flower in the spring and early summer when day light is increasing.

      • Short-day

        • Plants flower in late summer and early fall when daylight is decreasing.

        • Flower when daylight is less than a critical length.

      • Day-neutral

        • Do not flower in response to daylight changes.

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