Botany (the Study of Plants)€¦ · Plant Hormones REVIEW: Hormones are chemical signals that...
Transcript of Botany (the Study of Plants)€¦ · Plant Hormones REVIEW: Hormones are chemical signals that...
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Botany
(the Study of Plants)
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General Plant Review All plants are:
Eukaryotic
Autotrophic
Multicellular
Cell Walls with cellulose
Chloroplasts w/ chlorophyll a, b, and carotenoids
May have waxy cuticle to prevent water loss.
Stomata allow gas exchange.
Plants probably evolved from green algae (charophytes) Chloroplast similarity
Biochemical similarities
Cell Wall similarities
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Plant Reproduction
Alternation of Generations – plants grow a separate,
haploid organism to produce gametes; the same plant
exists in two different forms during its life, although
sometimes it’s hard to differentiate between the forms
Multicellular
Sporophyte – (2N)
Meiosis
Multicellular
Gametophyte (N)
Zygote (2N)
Unicellular
Spores (N)
Unicellular
Gametes (egg
& sperm)
fertilization
Mitosis
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Evolutionary Trend – early plants displayed the gametophyte
(n) as the dominant structure, modern plants show the
sporophyte as dominant (2n) (Ex: Moss is HAPLOID, but Oak
Trees are DIPLOID)
zygote
GREEN ALGA BRYOPHYTE FERN GYMNOSPERM ANGIOSPERM
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Classifying Plants
Plants can be divided into 2 major categories based on their characteristics: Nonvascular Plants
Do NOT have specialized tissues to transport water and nutrients
Instead, these plants transport water from cell-to-cell by osmosis
Vascular Plants Have specialized tissues to transport water and nutrients in
plants
Xylem – carries water upward from roots
Phloem – carries nutrients and carbohydrates produced by
photosynthesis
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Nonvascular Plants (Bryophytes)
Short with no specialized tissues to transport water
Major types:
Mosses
Liverworts
Hornworts
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Nonvascular Plants/
Bryophytes
Mosses
Have rhizoids that anchor
them to the ground
(instead of roots)
Depend on water for
fertilization
The sperm must swim to the
egg
Therefore, nonvascular
plants must live in MOIST
environments
Gametophyte is the dominant
phase of the life cycle
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Moss/ Bryophyte Life Cycle
Zygote grows, develops into a sporophyte while still attached to gametophyte.
Fertilization
zygote
sperm-producing structure
egg-producing structure
Diploid Stage
Haploid Stage
mature sporophyte
Meiosis
Spores germinate.
male gametophyte
female gametophyte
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Vascular Plants/Tracheophytes
Have specialized tissues to transport water
and nutrients in plants called Xylem & phloem
Vascular plants (tracheophytes) can be
divided into 2 categories:
Seedless vascular plants (spores)
Seed (vascular) plants
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Seedless Vascular Plants
Ferns – A Close Up
Diploid sporophyte is the
dominant stage
Have rhizomes, which are
underground stems
Fronds: large “leaves”
where spores develop
Develop spores in
sporangia on underside
of fronds
Reproduce using spores
A sorus (plural: sori) is a
cluster of sporangia
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Fern Life Cycle
Spores
are
released
Sporophyte still attached to gametophyte
zygote
fertilization Diploid Stage
Haploid Stage
egg
sperm
mature gametophyte
Spores develop
meiosis
Spore germinates
rhizome
sorus
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Seed (Vascular) Plants
Have true roots, leaves, and stems
Have the ability to form seeds, which are used for reproduction
Seed plants are the most dominant group of photosynthetic organisms on land
There are 2 types of seed (vascular) plants:
1. gymnosperms (cones)
2. angiosperms (flowers)
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Seed (Vascular) Plants Gymnosperms =
“cone bearers” “naked seeds” – not
enclosed in ovaries
Bear seeds directly on the surfaces of cones
Cones = sporophyte structures that produce
gametophytes (seeds)
Coniferous trees are the major example
Pines, junipers, spruces, etc.
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section through one ovule
ovule
surface view of one cone scale (houses two ovules)
section through a pollen-producing sac
surface view of one cone scale (houses a pollen-producing sac)
meiosis fertilization
seed coat
embryo
zygote
mature sporophyte
seeding
pollen tube
sperm-producing cell
eggs
female gametophyte
pollination
microspores form
megaspores form
seed Diploid
Haploid
Pine Life Cycle
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Seed (Vascular) Plants
Angiosperms = flowering plants
Seeds are enclosed by an ovary
Flowers are reproductive organs
Evolutionary advantage
attract pollinators
Flowering plants contain ovaries
Ovaries surround and protect
seeds
Ovary develops into a fruit after
pollination & helps with seed
dispersal when eaten
Examples:
Maple trees, tulips, grass
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Flowering
Plant Life
Cycle Double fertilization Meiosis Meiosis
microspores
female gametophyte
pollination
mitosis
without
cytoplasmic
division
two
sperm
enter
ovule
Diploid
Haploid
sporophyte
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Evolutionary Tree for Plants
green
algae zygophytes,
related
groups
charophytes bryophytes lycophytes horsetails cycads conifers
flowering
plants
seed plants
euphyllophytes
vascular plants
embryophytes (land plants)
(closely related groups)
ferns ginkgos gnetophytes
Nested monophyletic groups
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Transport in Vascular
Plants
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Transport Within Plants
Water and minerals
absorbed by roots are
drawn upward in the
xylem to the shoots
Sugar produced by
photosynthesis is
exported from leaves
to other organs via the
phloem
Transport can be
passive or active
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Short- and Long-Distance
Transport in Plants
Water and sugars move differently in
plants, depending on whether they’re
going a short or a long distance
Ie. – walking down the street or taking an
airplane across the world
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Short-Distance Transport 1. Simple diffusion/osmosis
substances in one cell move out of one cell, across the cell wall, and into another cell
2. Plasmodesmata
Plasmodesmata are connections between the cytoplasm of adjacent plant cells
Substances move between cells through these openings
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Long-Distance Transport
Over long distances, these 3 processes
(simple diffusion, apoplast,& symplast) take
too long
Water and solutes move through xylem and
phloem by bulk flow, the movement of a fluid
driven by pressure
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Transpiration
Transpiration is the evaporation of water from
leaves and other parts of the plant; it causes a pull
that brings more water up through the xylem
An average maple tree loses more than 200L of
water per hour during the summer!
Unless this water is replaced by water absorbed by
the roots, leaves will wilt and die
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(Cohesion-Tension Theory) Transpiration works through a
combination of evaporation, water potential, adhesion, and cohesion to pull water up the xylem
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The Photosynthesis-
Transpiration Compromise
Exposing leaves to the sun and opening stomata (cellular “holes” in the underside of the leaf) to allow for gas exchange helps photosynthesis, but causes transpiration to occur at a faster rate. Plants balance the loss by controlling when stomata are open.
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Mechanism for Stomatal
Opening & Closing
Guard cells open and close
stomata by changing shape
using ion and hormone
signals based on plant
stress.
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Plant Structure, Growth, &
Development
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The Diversity of Angiosperms
Angiosperms
(flowering plants) can
be divided into 2
major categories:
Monocots –
have one seed leaf
(cotyledon)
Dicots –
have 2 seed leaves
(cotyledons)
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Monocots
Monocots have only 1 cotyledon (seed leaf)
Examples of monocots:
Corn, wheat, lilies, orchids, palms
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Dicots
Dicots have 2 cotyledons (seed leaves)
Examples of dicots:
Roses, clover, tomatoes, oaks, daisies
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Woody vs. Herbaceous Plants
Angiosperms can also be subdivided into
woody (produce wood) and herbaceous (do
not produce wood) plants
Woody plants are made of cells with thick cell
walls that support the cell body
Examples: trees, shrubs, vines
Herbaceous plants do not produce wood as they
grow, and instead have smooth stems
Examples: dandelions, sunflowers
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Plant Life Spans The lifespan of plants, however, is genetically
determined Annuals – complete their life cycle in 1 year
Examples: marigolds, cucumbers (lots of garden plants)
Biennials - complete their life cycle in 2 years
Year 1: germinate & grow roots
Year 2: grow stems & leaves, produce flowers & seeds
Examples: evening primrose, celery
Perennials – live for more than 2 years
Examples: Maple trees, grasses, palm trees
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Plant Structure
Plants are made up of
a root system and a
shoot system
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The Root System
What do roots do?
Anchor the plant in the soil
Absorb minerals and water
Store food
Types of root systems
Fibrous root system
Found mostly in monocots
Taproot system
Found mostly in dicots
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How do roots grow?
Roots grow down from the tip in a region called the apical meristem, where the cells are dividing quickly
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The Shoot System
The shoot system consists of: vegetative shoots (which
bear leaves)
floral shoots (which bear flowers)
Stems have 3 important functions: Producing leaves, flowers
(reproduction), branches
Holding leaves up to the sunlight for photosynthesis
Transporting substances between roots and leaves
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How do stems grow? Primary growth
Increase in length
Occurs by cell divisions in
apical meristem (at top
of shoot)
Secondary growth
Increase in width
Occurs by cell divisions in
the lateral meristems
(outward growth)
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The Shoot System: Leaves
Leaves are the primary
photosynthetic organs of
most vascular plants
Most leaves have a
flattened blade and a
petiole, which is the
stalk that attaches the
leaf to the stem
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Tissues in Plants
All 3 plant organs (root/stem/leaf) have dermal, vascular, and ground tissue systems
Dermal Tissue System
Outer protective covering, similar to our skin
Protects the plant from water loss and disease
The cuticle is a waxy coating that helps to prevent water loss
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Tissue Systems in Plants
Vascular Tissue System
Carries out long-distance transport of materials within the plant
Xylem and phloem are examples of vascular tissues
Ground Tissue System
Pith (inside vascular tissue) and cortex (outside vascular tissue) are examples of ground tissue
Inner cells specialized for storage, photosynthesis, and support
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Flower Structure
Flowers are the reproductive structure of angiosperms
Sepals: Enclose the bud before
it opens
Protect flower while it’s developing
Petals: Usually brightly colored
to attract pollinators
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Flower Structure
Stamens:
The male portion of a
flower
Made up of an anther
and a filament
The anther produces
haploid pollen grains by
meiosis
Most flowers have
multiple stamens
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Flower Structure
Carpels/Pistils: The female portion of a
flower
Stigma:
Sticky – to trap pollen
Style:
Hollow tube which connects stigma and ovary
Ovary:
Produces female gametes (ovules)
Fruit grows from an expanded ovary
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Seed Dormancy
Seed dormancy means that a seed will not
germinate, even if sown in a favorable place,
until a specific environmental cue causes
them to break dormancy
Seed dormancy increases the chances that
germination will occur at a time and place
most advantageous to the seedling
How did we break dormancy in our lab??
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Stages of Seed Germination
(1) The seed absorbs water, causing it to expand and rupture its seed coat
(2) The embryo resumes growth, digesting the storage materials of the endosperm
(3) The radicle (embryonic root) emerges from the germinating seed
(4) The shoot tip breaks through the soil surface
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Stages of Seed Germination
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Plant Asexual Reproduction
When plant species clone
themselves by asexual
reproduction, it’s known
as vegetative
reproduction
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Asexual Reproduction
Fragmentation is the
separation of a parent
plant into parts that re-
form whole plants
This type of asexual
reproduction is used to
produce clones from
cuttings (common with
houseplants)
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Plant Responses to
Internal & External
Signals
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Plant Hormones
REVIEW: Hormones are chemical signals
that coordinate the various parts of an
organism
A hormone is a compound produced in one part
of the body which is then transported to other
parts of the body, where it triggers responses in
target cells and tissues
Examples of human hormones:
Adrenaline, testosterone, estrogen, epinephrine…
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Plant Hormones
There are 5 major classes of plant hormones:
Auxin -
Cytokinins
Gibberellins
Abscisic acid
Ethylene
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Auxin
Stimulates stem elongation
Stimulates fruit development
Involved in phototropism (bending to light)
and gravitropism (growing UP)
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Cytokinins
Stimulate cell division and growth
Stimulate cytokinesis
Stimulate germination and flowering
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Gibberellins
Trigger seed and
bud germination
Promote stem
elongation and leaf
growth
Important in fruit
growth
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Ethylene
Promotes fruit ripening
Senescence (aging) is a progression of irreversible change that eventually leads to death Caused, at least in part,
by ethylene
“One bad apple spoils the whole bunch”
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Abscisic Acid
Induces seed dormancy
Anti-gibberellin
Inhibits cell growth
Anti-cytokinin
Inhibits fruit ripening
Anti-ethylene
Closes stomata during
water stress, allowing
many plants to survive
droughts
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Tropisms
Tropisms are growth responses that result in curvatures of whole plant organs toward or away from a stimuli
There are three major stimuli that induce tropisms
Light (Phototropism)
Gravity (Gravitropism/Geotropism)
Touch (Thigmotropism)
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Phototropism
Phototropism is the
growth of a shoot
towards light
This is primarily due to
the action of auxin
Auxin elongates the
cells on the non-light
side
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Plant Defenses
Plants defend themselves against herbivores
in several ways
Physical defenses, such as thorns
Chemical defenses, such as
producing distasteful/toxic
compounds