Plant Science
Structure, Transport, and
Reproduction
PLANT EVOLUTION AND DIVERSITY
The following 24 slides are for general reference and not required material
Do not take notes, just listen and ask questions.
Kingdom Plantae
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Eukaryotes
Possess cellulose-rich cell walls
Store energy in the form of starch
Photosynthesize
Multi-cellular
Life cycles display both haploid and diploid
multi-cellular forms (alternation of generations)
Origin of Plants
 ‘Plants’ are believed have evolved
from green algae
 Charophyceans, a group of green
algae, are the ancestors of plants
 Algae are…
 single-celled
 colonial
 multi-cellular
…and do not possess…
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leaves
vascular tissue
roots
flowers
seeds
A multi-cellular Charophycean,
the nearest living relative to plants
Alternation of Generations
 All plants undergo a life cycle that takes them through
both haploid and diploid generations.
 The multicellular diploid plant structure is called the
sporophyte, which produces spores through meiotic
(asexual) division.
 The multicellular haploid plant structure is called the
gametophyte, which is formed from the spore and give
rise to the haploid gametes.
 The fluctuation between these diploid and haploid stages
that occurs in plants is called the alternation of
generations.
Alternation of
Generations
Plant Diversity
 There are four main groups of plants
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Bryophytes : mosses and allies
Filicinophytes: ferns and allies
Coniferophytes: conifers
Angiospermophytes: flowering plants
 The groups can be distinguished by
morphology and methods of reproduction
Plant Diversity
Bryophytes
 Most primitive of land plants
 Includes mosses, liverworts, and
hornworts
 Do not have roots
 Do not have vascular tissues (do not
circulate internal liquids)
 Do not flower or produce seeds
 Reproduce via spores
Mosses
Moss Reproduction
 Spores, haploid cells, are produced in a capsule.
 Capsule develops at end of stalk
Moss Facts
 Max. height – 0.5 m
 Number of known species ~ 10,000
 Moss will grow wherever there is an adequate amount of
moisture and sunlight. (not just the north side of a tree)
 Mosses prefer deciduous trees instead of conifers
because conifers have more acidic bark. (that’s why you
don’t see mosses on redwoods very often)
 Mosses cannot survive in polluted air. Like the lichens,
they need a healthy atmosphere to survive
Filicinophytes
 Commonly known as ferns
 Have roots, leaves, and short, nonwoody stems
 Have vascular tissues to circulate water
and nutrients
 Do not flower or produce seeds
 Reproduce via spores
Fern sorus, sporangia (2n),
and spores (n)
Fern gametophyte (n)
Pinnate Leaves:
Resembling a feather; having parts or branches
arranged on each side of a common axis
Simple
Bi-pinnate
Pinnate
Tri-pinnate
Ferns
Fern Facts
 The fern was one of the first plants on
Earth.
 Fossil fern remains, dating back 450
million years, have been found in coal
beds.
 There are about 12,000 species in the
world today.
Conifers
Coniferophytes: conifers
 Also known as gymnosperms
 Produce naked seeds in cones
 Have leaves, stems, roots, and
vascular tissue
 Most are trees, some shrubs
 All are woody
 Leaves are reduced and waxy
Conifer
Life
Cycle:
sporophyte
phase
dominant
Naked Seeds (no flesh like
fruit) are produced in Cones
Cones can be male (produce pollen) or
female (contain ovules), these are all
female
Conifer facts
 Typical examples of conifers include cedars, douglasfirs, cypresses, firs, junipers, kauris, larches, pines,
redwoods, spruces, and yews.
 Conifers are of immense economic value, primarily for
timber and paper production.
 The division contains approximately 700 living species.
 The world's tallest, largest, thickest and oldest living
things are all conifers.
Phylogeny of Plants
Angiosperms
Angiosperms
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Flowering Plants
Plant group with the most recent origin
Have roots, leaves, vascular tissue
Produce seeds within endosperm (fruit)
Two main types – monocots and dicots
Can be shrubs, vines, trees, grasses,
cacti, etc.
Monocot vs. Dicot
 Angiosperms typically belong to two general
groups monocots and dicots
 Monocots have 1 embryonic leaf (cotyledon)
 include all grasses (rice, corn, wheat), palms, and
many ornamentals (orchids,lilies, tulips)
 Dicots have 2 embryonic leaves
 Include beans, apples, roses, and oaks
Flower Facts
 There are an estimated 350,000 species of
angiosperms, over ¾ of the worlds plants
 Fossil evidence of first flowering plants dates back to
125 mya
 Many plants have co-evolved with insects in mutual
symbiosis,
 ex. bees pollinate
 The value of angiosperms to humans are priceless, they
are the source of nearly all terrestrial based food
production,
 ex. Fruits, veggies, grains, grass for livestock
Xerophytes:
plants adapted to grow in dry environments
 Spines instead of leaves, to reduce
transpiration
 Thick stems store water
 Very thick cuticle prevents water loss
 Wide, shallow root network absorbs
occasional rain fall
Xerophytes:
cacti
Plant Structure
Plant Structure
 Angiosperms may take on a wide variety of
morphologies and adaptations
 Species are distinguished primarily by flower
characteristics
 Areas of focus:
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Basic Features
Leaf Characteristics
Vascular system (stem and root)
Generalized Flower
Basic Features
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Flower:
 reproduction
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Fruit:
 seed dispersal
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Leaf:
 energy absorption
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Bud:
 growth site
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Vascular tissue:
 water and nutrient transport
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Ground tissue:
 basic support
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Root system:
 water and mineral absorption
 acts as anchor
The Leaf
 Site of photosynthesis, highest concentration of
chloroplast in plant
 CO2 enters, and H2O exits, through stomata
 Stoma – opening in epidermis
 Guard cell – swells or shrinks to close or open
stoma
 Vessels bring water to cells, and transport
sugar away to rest of plant
Leaf Parts
 Mesophyll – ground tissue
 Spongy – bottom part of leaf, air pocket
allow for gas exchange
 Palisade – top layers of cells, tightly packed
to absorb maximum amount of sunlight
 Cuticle –
 waxy coating prevents water loss, thicker on
upper epidermis
Vascular Tissue
 Specialized cells form
tubes to allow
movement of solution
 Xylem:
 Transports water and
minerals up from the
roots
 Phloem:
 Transports sugar down
from the leaves where it
was made
Xylem
 Technically ‘dead’: no nucleus, cell
membrane, organelles, cytoplasm, etc.
 Modified cell wall containing lignin for
increased strength
 Tracheids:
 Long, thin cells with high surface area to
volume ratio; highly porous
 Vessel Elements:
 Larger diameter and shorter, lower surface
to area ratio than tracheids; highly porous
Phloem
 Composed of cells known as
sieve tube cells and companion
cells
 Sieve tubes lacked nucleus,
ribosomes, and vacuole
 Companion cells maintain
functioning of sieve cells and
transport carbohydrates into
tubes
Vascular Cells
Dicot Stem Cross Section
 Ground Tissue:
 Pith – interior to cambium
 Cortex – exterior to cambium
 Epidermis
 Prevents water loss, can be specialized to become root hairs
or create cuticle
Vascular Bundle
 Cambium:
 actively dividing tissue, gives rise to both
xylem and phloem
Dicot Root
Roots
 Absorb minerals (nitrogen, phosphorous) by
active transport
 Water follows by osmosis because root has high
solute concentration
 Roots can be used to store energy in tubers
 Stele: the vascular tissue of the root
 Pericycle: the tissue immediately surrounding
stele, gives rise to lateral branch roots
Dicot Root Cross Section
Root Hairs:
extensions of epidermis,
function in water and mineral absorption by
significantly increasing surface area
Water Absorption
 Water moves toward
vascular tissue by
osmosis
 Apoplastic
 Water moves through cell
walls, but not through cells
 Symplastic
 Water moves directly
through cells
Casparian Strip
A band of modified
cell wall that
separates the outer
cortex from the stele
Prevents passive
flow of water and
materials into stele
Forces water and
materials to exit
apoplast (cell wall)
and enter symplast
(cellular cytoplasm)
The shape of root systems vary
between species
Special Modifications
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Bulbs
Stem Tubers
Storage Roots
Tendrils
Plant Growth
 Plants exhibit two primary methods of
growth
 Primary – elongation from terminal or
auxiliary shoot or root tips
 Secondary – lateral growth of cambium
 Tissue capable of active cell division is
termed ‘meristematic’
Primary Growth of Shoot
 Meristem
 Terminal bud
 Auxiliary bud
A Root Branch:
note apical meristem
Secondary Growth:
division in the cambium
Secondary Growth
causes thickening of
plant girth
Meristems
 The actively dividing tissue of plants
 Apical: located at end of branch or root
 Elongating
 Includes auxiliary bud
 Lateral: located within existing stems,
branches, or roots.
 Widening
 Tissue known as the cambium
Phototropism
 The growth of the
shoot toward a light
source
 Increased elongation
of specific ground
tissue caused by
plant hormone auxin
Phototropism and Auxin
 Auxin is released from
apical meristem
 Auxin is released
asymmetrically
 In higher concentrations
on side of plant away from
light source
Auxin
 Polar Transport:
 auxins carrier found
only on lower
membranes of cells
 unidirectional
hormone movement
 Acid Growth
Hypothesis:
 Auxin increases cell
wall acidity, causing
cell to expand
Auxin and Cell Elongation
- Acid Growth Hypothesis
1. Auxin increases the activity of proton pumps
2. The cell wall becomes more acidic
3. Expansin proteins (activated by low pH) cause
cell wall fibers to loosen.
4. Turgor pressure causes cell to expand
Acid Growth Hypothesis