Plant Structure and Growth

ObjectivesObjectives – Outline three differences between the struc- tures of dicotyledonous and monocotyle- donous plants – Draw and label plan diagrams to show the distribution of tissues in the stem and leaf of a dicotyledonous plant – Explain the relationship between the distribu- tion of tissues in the leaf and the functions of these tissues – Identify modifications of roots, stems, and leaves for different functions: bulbs, stem tubers, storage roots, and tendrils.

Plant cell structure (Review) Differences between plant and animal cells? Unlike animal cells, plant cells have... Unlike animal cells, plant cells have...chloroplasts. a central vacuole. a cell wall of cellulose (angular cells not rounded).

Plant taxonomy (Review) Of ~19 plant phyla, 4 or 5 are wide- spread. Know a dichot- omous key to separate the plant phyla! Know a dichot- omous key to separate the plant phyla!

Plant taxonomy Phylum Angiospermophyta – Flowering plants 1. non-swimming sperm 2. vascular tissues 3. seeds covered by fruit 4. flowers 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 Class Liliopsida (monocots) - germinate with 1 leaf * Class Magnoliopsida (dicots) - germinate with 2 leaves * Cotyledon = the leaf within the seed * Cotyledon = the leaf within the seed Grass monocotyledon Bean dicotyledon

Monocots vs. Dicots Note three differences.

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

Monocots vs. Dicots Compare leaves. Which is a monocot, and which is a dicot? Note the 5 sepals

Monocots vs. Dicots Compare. Which are these? Ferns have spores, not seeds: Conifers have seeds but no flowers: Gymnosperm Cycads have seeds but no flowers: Gymnosperm None of the above

Plant structure (Dicotyledonous angiosperms) ShootAbove-groundRootBelow-ground Note the ring of vascular tissue.

Plan 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. vascular tissues form a ring. Young Older Don’t draw these ones!

Plan diagram of a dicot plant stem As the dicot plant ages, the vascular tissues form a ring called the vascular cambium. Draw this. (functions of tissues later) Draw this. (functions of tissues later) The vascular cambium gives rise to the xylem & phloem tissues. Vascular cambium

Plan diagram of a dicot plant leaf Note the distribution of the leaf tissues.(click) leaf tissuesleaf tissues Be able to draw this.

Functions of leaf tissues Cuticle: a waxy covering to prevent loss of moisture Epidermis: a layer of protective cells (no chloroplasts)

Functions of leaf tissues Mesophyll: 2 layers, both contain chloroplasts for photosynthesis Spongy parenchyma: contains air spaces for gas exchange

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

Functions of leaf tissues Stoma (pl. stomata): an opening in the epidermis through which H 2 O, O 2 and CO 2 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 organs Modified roots Storage roots – store food for future use Sweet potato (not the white potato, however) Carrots, turnips, & beets

Modifications of plant organs Modified stems Stolons – above-ground horizontal stems: strawberry Rhizomes – underground horizontal stems: ginger Tubers – for storage: white potato (eyes produce branches) Bulbs – underground vertical stems for storage: onion (concentric layers are “leaves”) White potato Strawberry

Modifications of plant organs Modified leaves Tendrils - support: ivy Spines - protect: cacti Succulents - leaves store water

Plant Structure and Growth

ObjectivesObjectives State that dicotyledonous plants have apical and lateral meristems Compare growth due to apical and lateral meristems in dicotyledonous plants Explain the role of auxin in phototropism as an example of the control of plant growth.

Plant meristems Dicotyledonous plants have apical and lateral meristems. Apical = at tip Lateral = at side

Plant 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 meristems Growth due to apical and lateral meristems Lateral meristems increase plant girth. Vascular cambium Xylem and phloem Cork cambium Bark (constantly replaced) Vascular cambium

Control 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 gravity Phototropism – movement due to light Positive Phototropism Negative Geotropism

Control of plant growth Phototropism results from stimulation of plant cells by the hormone auxin. Hormones (click)are made in one place but act elsewhere. Hormones (click)are made in one place but act elsewhere.Hormones 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. Cells on the shaded side grow larger, causing a bending of the plant shoot.

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