Plants
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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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Plants

Plants


Plant evolution and classification

Plant Evolution and Classification

  • Preventing Water Loss

  • Reproducing by Spores and Seeds

  • Transporting materials throughout the plant.


Classifying plants

Classifying Plants

  • 2 groups based on the presence of vascular tissue

    • Nonvascular Plants

    • Vascular Plants

      • Seedless-fern like

      • Seeded- Maples, and Pine


Classification

Classification

  • Nonvascular Plants

    • Phylum Bryophyta

    • Phyla Haptophyta and Anthocerophyta


Seedless vascular plants

Seedless Vascular Plants

  • Phylum Psilotophyta

  • Phylum Lycophyta

  • Phylum Sphenophyta

  • Phylum Pterophyta


Vascular seed plants

Vascular Seed Plants

  • Gymnosperms

    • Phylum Cycadophyta

    • Phylum Ginkgophyta

    • Phylum Gnetophyta

    • Phylum Coniferophyta

  • Angiosperms

    • Phylum Anthophyta


Classes of angiosperms

Monocot

On cotyledon

Parallele Venation

Scattered

Flower parts in 3’s

Fibrous

Dicot

2 cotyledons

Net venation

Radially arranged vascular bundles

Flower parts in 4 and 5

Taproot

Classes of Angiosperms


Plant structure and function

Plant Structure and Function

  • Plant Cells

    • 3 types

      • Parenchyma

      • Collenchyma

      • Sclerenchyma


Parenchyma

Parenchyma

  • 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

Collenchyma Cells

  • Thicker cell walls, irregular shape

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

  • Celery


Sclerenchyma cells

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

Tissue Systems

  • Dermal Tissue

  • Ground Tissue

  • Vascular Tissue


Dermal 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

Ground Tissue

  • All 3 cell types

  • Storage, metabolism and support.


Vascular tissue

Vascular Tissue

  • Functions in transport and support

  • Xylem-dead

  • Phloem-living

  • 2 major components for xylem

    • Tracheid

    • Vessel Element


Tracheid

Tracheid

  • Long thick walled sclerenchyma cell with tapering ends.

  • Water moves from on tracheid to another through piths


Vessel element

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

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

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 structures1

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

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


Cortex

Cortex

  • Located just inside the endodermis.

  • Largest region of the primary root.

  • Parenchyma cells


Endodermis

Endodermis

  • 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

Monocot Root Cross Section


Dicot stem

Dicot Stem


Stems

Stems


Primary growth in stems

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

Monocot Stem


Vascular bundle of monocot

Vascular Bundle of Monocot


Dicot stem1

Dicot Stem


Secondary growth

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

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

Annual Rings


Leaves

Leaves


Monocot leaf

Monocot Leaf

Upper Epidermis

Mesophyll

Lower Epidermis

Xylem

Phloem


Dicot leaf

Dicot Leaf

Upper Epidermis

Xylem

Palisade

Mesophyll

Spongy

Mesophyll

Phloem

Lower Epidermis

Guard Cells with Somata


Leaf structures

Leaf Structures

  • Epidermis

  • Palisade Mesophyll

  • Spongy Mesophyll

  • Guard Cells

  • Vascular Bundles


Epidermis

Epidermis

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

  • Covered by the cuticle

    • Cutin

    • Transpiration


Palisade mesophyll

Palisade Mesophyll

  • Parenchyma cells

  • Numerous chloroplasts


Spongy mesophyll

Spongy Mesophyll

  • Parenchyma cells

  • Loosely arranged

    • Air spaces allow for gas exchange


Guard cells

Guard Cells

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

  • Controls gas exchanges with the environment.


Vascular bundles

Vascular Bundles

  • Consists of xylem and phloem tissues

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


Transport of water

Transport of Water

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

    • 2 Possible Pathways

      • Apoplast

      • Symplast


Apoplast

Apoplast

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


Symplast

Symplast

  • 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

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

Water Movement Up the Plant

  • 3 Mechanisms

    • Osmosis

    • Capillary Action

    • Cohesion-tension theory


Cohesion tension theory

Cohesion-tension Theory

  • 3 Major Concepts

    • Transpiration

    • Cohesion

    • Bulk Flow


Transpiration

Transpiration

  • The evaporation of water from plants.

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


Cohesion

Cohesion

  • The molecular attraction between like substances.

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


Bulk flow

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

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

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.


Tropisms

Tropisms

  • Phototropism

  • Thigmostropism

  • Gravitropism


Phototropism

Phototropism

  • 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.


Thigmotropism

Thigmotropism

  • Stimulus

    • Contact with an object

  • Function

    • Allows for vines to “climb” walls.

    • Tendrils will coil around objects.


Gravitropism

Gravitropism

  • Stimulus

    • Gravity

  • Hormone

    • Auxins, Gibberellins

  • Function

    • Allows for roots to grow down.

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


Photoperiodism

Photoperiodism

  • 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.


Phytochrome

Phytochrome

  • 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

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

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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