Plant Structure

and Growth

ObjectivesObjectives

9.1.2 – Outline three differences between the struc- tures of dicotyledonous and monocotyle- donous plants.

9.1.1 – Draw and label plan diagrams to show the distribution of tissues in the stem and leaf of a dicotyledonous plant.

9.1.3 – Explain the relationship between the distribu- tion of tissues in the leaf and the functions of these tissues. 9.1.4 – Identify modifications of roots, stems, and leaves for different functions: bulbs, stem tubers, storage roots, and tendrils.

Plant cell structure (Review)Plant cell structure (Review)Differences between plant and animal

cells? Unlike animal cells, plant cells have . . .

chloroplasts.a central vacuole.a cell wall of cellulose (angular cells not rounded).

Plant taxonomy (Review)Plant taxonomy (Review)Of ~19 plant phyla,

4 or 5 are wide- spread.

Know a dichot- omous key to separate the plant phyla!

Plant taxonomyPlant taxonomy Phylum Angiospermophyta – Flowering plants

1. non-swimming sperm 2. vascular tissues 3. seeds covered by fruit 4. flowers Class Liliopsida (monocots) - germinate with 1 leaf * Class Magnoliopsida (dicots) - germinate with 2 leaves

* Cotyledon = the leaf within the seed

Grassmonocotyledon Bean

dicotyledon

Monocots vs. DicotsMonocots vs. Dicots

Note three differences.

Monocots vs. DicotsMonocots vs. Dicots

Compare flowers. Which is a monocot, and which is a dicot?

Monocots vs. DicotsMonocots vs. Dicots

Compare leaves. Which is a monocot, and which is a dicot?

Note the 5 sepals

Monocots vs. DicotsMonocots vs. Dicots

Compare. Which are these?

Ferns have spores, not seeds:

Conifers have seedsbut no flowers:Gymnosperm

Cycads have seedsbut no flowers:Gymnosperm

None of the above

Plant structure (Dicotyledonous angiosperms)

Plant structure (Dicotyledonous angiosperms)

ShootAbove-ground

RootBelow-ground

Note the ring of vascular tissue.

Plan diagram of a dicot plant stemPlan diagram of a dicot plant stem

Plan diagrams show tissue distribution, and not individual cells.

As the dicot plant ages, the vascular tissues form a ring.

Young

Older

Don’t draw these ones!

Plan diagram of a dicot plant stemPlan diagram of a dicot plant stemAs the dicot plant ages, the vascular

tissues form a ring called the vascular cambium.

Draw this. (functions of tissues later)

The vascular cambium gives riseto the xylem & phloem tissues.

Vascularcambium

Plan diagram of a dicot plant leafPlan diagram of a dicot plant leaf

Note the distribution of the leaf tissues.(click)

Be able to draw this.

Functions of leaf tissuesFunctions of leaf tissuesCuticle: a waxy covering to prevent loss of moistureEpidermis: a layer of protective cells (no chloroplasts)

Functions of leaf tissuesFunctions of leaf tissuesMesophyll: 2 layers, both contain chloroplasts for photosynthesis

Spongy parenchyma: contains air spaces for gas exchange

Functions of leaf tissuesFunctions of leaf tissuesVascular tissue: xylem moves water from roots; phloem moves photosynthate away from the leaf.

Functions of leaf tissuesFunctions of leaf tissuesStoma (pl. stomata): an opening in the epidermis through which H2O, O2 and CO2 may pass.

Guard cells: regulate gas exchange by expanding and contract- ing using ion pumps and osmosis to open and close the stoma.

Modifications of plant organsModifications of plant organs

Modified rootsStorage roots – store food for future use

Sweet potato (not the white potato, however)Carrots, turnips, & beets

Modifications of plant organsModifications of plant organs

Modified stemsStolons – above-ground horizontal stems: strawberryRhizomes – underground horizontal stems: ginger

Tubers – for storage: white potato (eyes produce branches)

Bulbs – underground vertical stems for storage: onion (concentric layers are “leaves”)

Whitepotato

Strawberry

Modifications of plant organsModifications of plant organs

Modified leavesTendrils - support: ivySpines - protect: cactiSucculents - leaves store water

Plant Structure

and Growth

ObjectivesObjectives

9.1.5 - State that dicotyledonous plants have apical and lateral meristems.

9.1.6 - Compare growth due to apical and lateral meristems in dicotyledonous plants.

9.1.7 - Explain the role of auxin in phototropism as an example of the control of plant growth.

Plant meristemsPlant meristemsDicotyledonous plants

have apical and lateral meristems.

Apical = at tipLateral = at side

Plant meristemsPlant meristems

Growth due to apical and lateral meristems

Apical meristems increase plant height & depth.Undifferentiated cells

bud

Buds will also develop their own apical meristems

Plant meristemsPlant meristems

Growth due to apical and lateral meristems

Lateral meristems increase plant girth.

Vascular cambiumXylem and phloem

Cork cambiumBark (constantly replaced)

Vascularcambium

Control of plant growthControl of plant growth

Plants are rooted in the ground, yet they can still move. They bend one way or the other.

Geotropism – movement due to gravityPhototropism – movement due to light

PositivePhototropism

NegativeGeotropism

Control of plant growthControl of plant growth

Phototropism results from stimulation of plant cells by the hormone auxin. Hormones (click)are made in one place but act

elsewhere.Auxin (indoleacetic acid - IAA) is made in shoot meristems.

It stimulates growth (elongation) of cells.Cells on the shaded side grow larger,causing a bending of the plant shoot.

Control of plant growthControl of plant growth

Phototropism results from stimulation of plant cells by the hormone auxin.

Auxin, made in shoot meristems, causes cells to elongate by loosening their cell walls;

internal water pressure then causes cells to expand.

Note: there is no evidence for differential concentrations of auxin due to light. There is more evidence that light pro-duces growth inhibitors.