Plant Structure
and Growth
Objectives
9.1.2 – Outline three differences between the structures of dicotyledonous and monocotyledonous 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 distribution 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)
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)
Of ~19 plant phyla,
4 or 5 are widespread.
Know a dichotomous 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
Class Liliopsida (monocots) - germinate with 1 leaf *
Class Magnoliopsida (dicots) - germinate with 2 leaves
* 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:
None of the above
Conifers have seeds
but no flowers:
Gymnosperm
Cycads have seeds
but no flowers:
Gymnosperm
Plant structure
(Dicotyledonous
angiosperms)
Shoot
Above-ground
Root
Below-ground
Note the ring of vascular tissue.
Plan diagram of a dicot plant stem
Plan diagrams show tissue distribution, and
not individual cells. Young
Don’t draw these ones!
Older
As the dicot plant ages, the
vascular tissues form a ring.
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)
Vascular
cambium
The vascular cambium gives rise
to the xylem & phloem tissues.
Plan diagram of a dicot plant leaf
Note the distribution of the leaf tissues.(click)
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 H2O, O2 and CO2 may pass.
Guard cells: regulate gas exchange by expanding and contracting 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
Objectives
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 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
Vascular
cambium
Cork cambium
Bark (constantly replaced)
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.
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 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 produces growth inhibitors.