Chapter 17
Plant Form and
Function
With
emphasis on Angiosperms, the flowering plants
Plants are
Multicellular eukaryotes that have cellulose rich cell walls and
use starch as an energy reserve.
Most are
photosynthetic autotrophs
Have alternation
of generations
Sporophyte
gametophyte
Plants are classified by
Presence or
absence of vessels and seeds
Lack vessels (and
seeds): Bryophytes
Have vessels:
Vascular plants
Vascular plants
Without seeds:
Ferns and fern allies
With seeds:
gymnosperms (naked
seeded)
angiosperms (covered seeds, the flowering plants)
Plant Evolution
Plants have a
long evolutionary history
Evolutionary trends
Characteristics
shared with green algae:
· Chlorophyll a is the primary photosynthetic pigment,
chlorophyll b and carotenoids are accessory pigments.
· Starch is the reserve food, deposited in chloroplasts.
· Cellulose cell walls in all plants
(& some green algae).
· In cell division, form phragoplast
and cell plate in all plants (& some green algae)
This evidence
suggests that green plants arose from some green algae.
Plants are important for
Food
Wood -fuel,
building, furniture, etc
Fiber - clothing,
paper, etc.
Drugs (25% of
prescription drugs)
Oxygen production
Success of the Angiosperms
The angiosperms
are seed-bearing vascular plants
In terms of
distribution and diversity, they are the most successful plants on Earth
The structure and
function of this plant group help explain its success
Flowering Plants Can Be
divided into two Groups: Monocots and Dicots
How Are Plant Bodies Organized?
Flowering Plants
Have a Root System and a Shoot System
Shoots and Roots
Shoots
Produce food by
photosynthesis
Carry out
reproductive functions
Transport
materials
Roots
Anchor the plant
Penetrate the
soil and absorb water and dissolved minerals
Store food
Different Processes Are Responsible for
Growth in Length and Width
Meristems are region where cell divisions produce plant growth
Apical meristems
Lengthen stems
and roots
Responsible for primary
growth
Lateral meristems
Increase width of
stems
Responsible for secondary
growth
Apical Meristems
Lengthen shoots
and roots from tips
During growth, meristem cells give rise to differentiated cells
Lateral Meristems
Increases girth
of older roots and stems
Cylindrical
arrays of cells
Three Tissue Types
What Are the Tissues and Cell Types of Plants?
Dermal Tissue
Covers the Plant Body
Epidermis:
Covers and
protects plant surfaces
Secretes a waxy,
waterproof cuticle
What Are the Tissues and Cell Types of Plants?
Ground Tissue
Makes Up Most of the Young Plant Body
Carry out most function
Photosynthesis
Store sugars, starches
Secrete hormones
Provide support
What Are the Tissues and Cell Types of Plants?
Vascular Tissue
Consists of Xylem and Phloem
Xylem Conducts
Water and Dissolved Nutrients from the Roots to the Rest of the Plant
Phloem Conducts
Substances throughout the Plant
Xylem
Phloem:
A Complex Vascular Tissue
Transports
sugars
Main conducting
cells are sieve-tube members
Companion cells
assist in the loading of sugars
Root Structure
Root cap covers
tip
Apical meristem produces the cap
Cell divisions at
the apical meristem cause the root to lengthen
Farther up, cells
differentiate and mature
Internal Structure of a Root
Outermost layer
is epidermis
Root cortex is
beneath the epidermis
Endodermis
surrounds the vascular cylinder
In some plants,
there is a central pith
How Do Roots Grow and What Do They Do?
The Epidermis of
the Root Is Very Permeable to Water
How Do Roots Grow and What Do They Do?
The Cortex
Controls the Absorption of Water and Nutrients
Outer layer is
loose cells
Inner layer is
endodermis
Function of Endodermis
Ring of cells
surrounds vascular cylinder
Cell walls are
waterproof
Water can only
enter vascular cylinder by moving through endodermal
cells
Allows plant to
control inward flow
Internal Structure of a
Dicot Stem
Outermost layer
is epidermis
Cortex lies
beneath epidermis
Ring of vascular
bundles separates the cortex from the pith
The pith lies in
the center of the stem
Internal Structure of a Monocot Stem
How Do Stems Grow and What Do They Do?
The Epidermis of
the Stem Retards Water Loss While Allowing Carbon Dioxide to Enter
The Cortex and
Pith Support the Stem, Store Food, and Photosynthesize
Vascular Tissues
in Stems Transport Water, Dissolved Nutrients, and Hormones
Herbaceous vs. Woody
Herbaceous have
primary growth, live a single year grass, beans
Woody- have
secondary growth, can live multiple years trees and shrubs
Secondary Growth
Produces Thicker, Stronger Stems
Secondary Growth
Occurs in all
gymnosperms, some monocots, and many dicots
A ring of
vascular cambium produces secondary xylem and phloem
Wood is the
accumulation of these secondary tissues, especially xylem
Secondary Growth
Lateral meristem
One or two cells
thick
Divides in two
directions
Cells formed to
the outside become secondary phloem
Cells formed to
the inside become secondary xylem
Woody Stem
Annual Rings
Concentric rings
of secondary xylem
Alternating bands
of early and late wood
Early wood
Xylem cells with
large diameter, thin walls
Late wood
Xylem cells with
smaller diameter, thicker walls
How Do Stems Grow and What Do They Do?
Secondary Growth Causes the Epidermis to Be
Replaced by Woody Cork
Some Specialized Stems Produce New Plants or
Store Water or Food
What Is the Structure of Leaves and What Do
They Do?
Leaves Have Two
Major Parts:
Stalk
Blade
Photosynthesis,
gas exchange, transport
Gross Leaf Structure
Adapted for Photosynthesis
Leaves are
usually thin
High surface
area-to-volume ratio
Promotes
diffusion of carbon dioxide in, oxygen out
Leaves are
arranged to capture sunlight
Are held
perpendicular to rays of sun
Arrange so they
dont shade one another
Leaf Veins: Vascular Bundles
Xylem and phloem;
often strengthened with fibers
In dicots, veins are netlike
In monocots, they
are parallel
Specialized
Leaves May Provide Support, Store Food, or Even Capture Insects
How Do Plants Acquire Nutrients?
Roots Take Up
Minerals Dissolved in Water
Fungi and
Bacteria Help Plants Acquire Nutrients
Fungal Mycorrhizae Help Plants Acquire Minerals
Bacteria-Filled
Nodules on Their Roots Help Legumes Acquire Nitrogen
How Do Plants Acquire Water and Transport
Water and Minerals?
Water Enters
Roots Mainly by Pressure Differences Created by Transpiration
Adjustable
Stomata Control the Rate of Transpiration
Transpiration
Provides the Force for Water Movement in Xylem
Plant diversity
Even plants that
are weeds may contain drugs or genes that might be useful
We need to
preserve habitats as well as fund seed banks and other conservation efforts.
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