1
Plants
Plant Classification
Aquatic Plants
- Green algae
- Similarities to land plants:
o Have chlorophylls a + b
o Cellulose cell walls
o Store food energy in form of starch
Terrestrial Plants (400MYA)
- Adaptations needed before moving to
land:
o Protection from drying out
o System of transport from outside
environment to cells in plant body
o System to support plant body
- 3 organs developed to adapt:
o Roots: penetrate soil to anchor plant;
reach water source
o Leaves: greater SA for
photosynthesis
o Stems: rigid tissue to raise & support
leaves
Land Plants: Non-Vascular
- Called bryophytes
- Have root-like, stem-like, leaf-like
structures
o Poorly developed
- Grow short, small
- Ex. Mosses, liver/hornworts
Land Plants: Vascular
- Appeared 360MYA
- Called tracheophytes
- Vascular tissue: a system of tubes that
carry water & dissolved nutrients
through plant
- Have true roots, stems, leaves
- Grow tall, large
- Seedless (spore producing)
o Ex. Ferns
o Grow in marshes & shores
o Requires water for spores to swim in
water to female organ
- Seed producing
o Ex. Flowering plants
- Advantages:
o Can live in drier environment
o Can grow larger (water/nutrients
reach farther)
Advantages of Having Seeds:
- Food storage
-
Tough waterproof coat
Protection to harsh conditions
- Remain dormant
o Survive harsh exposure
- Sexual reproduction sans water
Seeds: Gymnosperms
- “Naked seed”
o Ex. Ginkgoes, conifers
o Produce cones (male=clustered,
female=scattered/hidden)
- Seeds exposed to environment
- Thin cover of protection
- Environments with long, cold winters
& low nutrients in soil
o Canada, Europe, Asia
- Less species: about 1000
Seeds: Angiosperms
- “Seed in vessel”
- Seed = embryo + nutrient storage +
coat
- Flowering plants
- Grass & herbs
- Seeds not exposed to environment
- Seed protected by body of fruit
- All over the world
- More species: about 250k
Angiosperms: Cotyledons
- Structure in a plant’s seed that stores
carbs for the seedling
o Also known as “seed leaf” because
first leaf develops from it
- Monocotyledon: single leaf
o Flowers: multiples of 3
o Fewer species
o Ex. Tulip, corn, onion, grass, rice
- Dicotyledon: two leaves
o Flowers: multiples of 4/5
o More species
o Ex. Rose, maple, carrot, beans
Monocotyledons: Leaves
- Parallel veins
- Long strips
- 1 cotyledon
- Spongy mesophyll
Monocotyledons: Roots + Stem
- Vascular bundles in a ring (roots);
scattered (stem)
- Fibrous roots
- Herbaceous, soft, fleshy stems
o
2
Plants
o Only 10% are woody
Dicotyledons: Leaves
- Network veins
- Broad leaf
- 2 cotyledons
- Palisade + spongy mesophyll
Dicotyledons: Roots + Stem
- Xylem in center in X-shape with
phloem around (roots); ring (stem)
- Tap roots
- Woody, tough, rigid steams
Reproduction
- Stamen: male
o Filament & anther
o Anther releases pollen
- Pistil: female
o Stigma, style, & ovary
Double Fertilization
- 1) Between sperm (n) & egg (n)
o Becomes zygote (2n) & develops
into embryo
- 2) Between sperm & two polar nuclei
(n+n)
o Becomes endosperm (3n)
o Provides nutrients for embryo
- Each ovule forms a seed
- Ovary develops into a fruit
Gametes
- Inside anther, microspores are
produced via meiosis (n)
- Ovary contains ovules, producing
megaspores via meiosis (n)
o Only 1 survives & develops
- When pollen reaches stigma, it grows
a pollen tube extending down
Plant Structures & Function
Meristematic Tissue (Growth)
- Embryonic: can develop into different
cells
- Apical meristem:
o At root tips & buds of shoots
o Found in herbaceous, young plants
o Unspecialized from which all
primary tissues (dermal, vascular,
ground) are derived
o Primary growth: length
- Lateral meristem:
o
Vascular cambium: vascular &
ground tissue produced
o Cork cambium: cork produced
o Cylinders of cells along lengths of
roots & shoots
o Never in leaves
o Secondary growth: width
o Adds strength to plant
o Forms woody rings in trees
Vascular Cambium
- In vascular bundle between phloem &
xylem (divides)
- Cells divide & form secondary xylem
towards inside & secondary phloem
towards outside
- Growth rings: seasonal climates
o Cells grow faster & larger in spring
Dermal Tissue (Protection)
- Epidermis:
o Flat rectangular cells
o Layer is 1 cell thick
o Outer layer
o Surface covered with waxy layer
(cutin/cuticle)
o In leaves/herbaceous roots/stems
o Waterproofing
o Protection
o Prevent infection
- Cork:
o Dead, hollow cells
o Covers surface of roots/stems
o Replaces epidermis during secondary
growth
o In roots/stems of woody plants
o Waterproofing
Vascular Tissue (Conductive): Xylem
- 2 types: vessel elements (angiosperms)
& tracheids
- Long thin cylindrical cells
- Dead & hollow
o Allows water flow through empty
spaces & saves energy
- Perforates side & end walls
- End to end arrangement
- Transports water & dissolved minerals
from roots to leaves
o Only upwards
Vascular Tissue (Conductive): Phloem
- Long cylindrical cells
3
Plants
-
Living, but no cytoplasm/nucleus
Perforated ends
Companion cells adjacent, responsibly
for controlling activity
- Transport manufactured food for
storage & use
- Transport hormones
o Both directions
- Require energy via cellular respiration
Ground Tissue
- Cortex
o Root & stem
o Storage for starch (roots)
o Structural support (stem)
- Pith
o Only in stem
o Storage of water
- Mesophyll
o Only in leaves
o Palisade & spongy
o Photosynthesis
Roots
- 3 main roles:
o Anchor plant to ground
o Absorb water & nutrients
o Starch storage
- 3 types of tissues that make up roots
(outer layer to inner layer)
o Epidermis
o Cortex
o Vascular
- Function of roots hairs:
o Absorption of water/minerals
o More hair = more SA
- Cells in epidermis cannot do
photosynthesis: no chloroplasts
- Epidermal cells undergo cellular
respiration to obtain energy
o Glucose comes from starch
- Cellular respiration: glucose + oxygen
= water + carbon dioxide + energy
- 4 zones of the root:
o Maturation: cells differentiate
o Elongation: allows root to grow
deeper into soil
o Cell division (meristematic region):
rapid mitosis of undifferentiated
meristematic cells
o Root cap: protects above region
-
Storage of starch in:
Cortex
Vacuole of each cell
- Vascular tissues: clustered in center of
the roots
- Adventitious roots (monocot): emerge
from tissues other than root (stem/leaf)
- Endodermis (innermost layer of
cortex):
o Surrounds vascular tissue
o Thing continuous rings of cells
Root types
- Fibrous root:
o Larger SA for absorption
o Holds topsoil in place
- Tap root:
o Firm anchor
o Food storage
o Locate water far below
Stem Composition
- Epidermis:
o Protective layer
o Contains chloroplast, cuticle, stoma
o Allows photosynthesis
- Cortex:
o Layer surrounding pith
o Rigid, structural support
o Stores water & nutrients
- Pith:
o Found in center of the stem
o Contains air spaces (spongy)
o Stores water & nutrients
- 2 main roles:
o Structural support
o Water & nutrient transport
- Axillary bud: bud that has a potential
to form a new stem
- Terminal/Apical bud: located at the
time of stem (dominant)
- Apical dominance: terminal buds
inhibit axillary growth; plant grows
taller for more light exposure
o Remove terminal bud 🡪 axillary
breaks dominance & width grows
Modified Stems
- Stolon:
o Surface of ground
o Horizontal growth
o
o
4
Plants
o
Buds can develop into stems of new
plants
o Ex. Strawberry
- Rhizome:
o Underground
o Horizontal growth
o Buds can develop into stems
o Ex. Ginger
o Not roots because do not absorb;
have buds
- Tuber:
o Swollen ends of rhizomes
o Food storage
o Buds can grow into new shoots
above ground
o Ex. Potato
- Bulb (corm):
o Underground
o Small stem
o Paper-like cover
o Surrounded by layers of modified
leaves
o Ex. Onion
- Cactus
Leaves
- Main role: photosynthesis
o Converts solar energy to chemical
- Parts of leaf:
o Epidermis
o Palisade layer (mesophyll)
o Spongy layer (mesophyll)
o Vascular tissue
o Stoma & guard cells
- Cuticle:
o Function: protect; prevent water loss
o Structure: waxy coating
o Transparent (like epidermis) to allow
light to pass through
- Palisade cells:
o Function: photosynthesis
o Structure: long, thin cells packed
o Top end of cell exposed to light
o Bottom end exposed to gases in
spongy layer
o Packed cells maximize light intake
o Dicots only
- Spongy layer:
o Contain mesophyll cells for
photosynthesis
o
o
Cells are not packed
Has air space for gases
- Stoma (lower epidermis):
o Greek word for mouth
o Structure: pore-like openings
o Function: permits gas exchange
o Larger opening = faster exchange
o Controlled by two guard cells
- Guard cells:
o Structure: paired, thick inner walls,
has microfibrils
o Function: controls size of stomata
- How guard cells work:
o Water flows in cells, pushing outside
of membrane
o Rings prevent increase of cell
diameter
o Cell increases length
o Outer wall is more flexible & bulges
outwards
o Inner wall is pulled
o Stoma opens
o Closing: water flows out & guard
cells return
Water & Food Transportation
Sugars in a Plant
- Glucose:
o Leaf
o Used for energy in cellular
respiration (in spring)
- Sucrose:
o Stem
o Transportation, dissolved in water
o Ex. Maple sap
- Starch:
o Root
o Stored in cortex
o Not soluble in water
o Cannot be transported
Direction of Sugar Transport
- Spring/night time:
o No leaves, no photosynthesis
o Starch stored in root 🡪 broken down
to sucrose
o Sucrose travels up stem 🡪 broken
down to glucose for leaf growth
- Summer/day time:
5
Plants
o
Leaves produce glucose via
photosynthesis
o Starch to sucrose for transportation
in stem 🡪 starch stored in roots
o Excess glucose becomes starch in
chloroplasts
Types of Nutrient Transport
- Water & minerals:
o Roots (from soil) 🡪 leaves
o Xylem
- Newly manufactured food (glucose):
o Leaves (photosynthesis) 🡪 roots
(Storage)
o Phloem
- Stored food (starch):
o Roots 🡪 leaves
o Phloem
Water Transport/Absorption
- Absorbed at the roots
- Capillary action in xylem
- Evaporation at leaves (transpiration)
- Mineral absorption must occur before
water is absorbs in roots
Mineral Transport
- Minerals in soil enter roots via root
hairs
- Higher [minerals] absorbed in xylem
than soil
- Minerals absorbs in roots via active
transport (against c. gradient)
- Required ATP from cellular
respiration
- Endodermis prevents mineral back
flow (passive diffusion) to soil
Water Absorption in Roots
- Hypertonic = high [solute], less water
than in cell
- Hypotonic = low [solute], more water
than in cell
- Roots are in hypotonic environment
o High [minerals] inside, more water
outside
o Water flows into xylem cells via
osmosis
- Hypertonic environment: water would
flow out
Water Movement: Stem
-
Water & minerals accumulate in
xylem cells
- Root pressure increases
- Pressure pushes xylem sap up
- Adhesion: water molecules tend to
stick to hydrophilic surfaces 🡪 xylem
wall
- Cohesion: polar water molecules stick
together due to H bonds
Water Movement: Capillary Action
- Force of cohesion + adhesion
- Forms a column of water within xylem
o Water is pushed up
- The narrower the tube the higher the
water can “climb”
o Max. height = 32 feet
Water Movement: Transpiration
- As each water molecule evaporates
through stoma via transpiration:
o It pulls on the next water molecule
o More are drawn up stem & roots
- Pulling water from roots via leaves:
called transpiration pull
- Higher air temp. = more heat energy
provided for evaporation
o Rate of transpiration is height
o Xylem sap (water + nutrients) rise
faster (up to 75cm a minute)
- Pressure differences created draws
water out of roots
- Creates lower pressure in roots,
drawing in more water
Food Transport (Translocation)
- In leaves, sugar (sucrose 🡪 glucose) is
pumped into phloem sieve tube cells
by active transport
o Builds hypertonic solution inside
phloem
- Causes water to move in via osmosis
from xylem to sieve tube cells
- Creates pressure gradient: high
pressure in leaves, low in roots
- High leaf pressure pushes sap down to
roots
o Passive movement of sugar
- Sugar can end up in any plant part
where sugar pressure is low
Plant Responses to Stimuli
6
Plants
-
Growth = irreversible increase in mass
(results from cell division/expansion)
- Development = sum of all changes
that progressively elaborate an
organism’s body
- Indeterminate growth = growth as long
as organism is alive
o Ex. Plant stem
- Determinate growth = stop growing
after organism reaches certain size
o Ex. Animals
Growth Cycles
- Annuals:
o Life cycle within a year or less
o Dies after a growing season
o Seeds grow into new plants
o Ex. Impatients
- Biennial:
o Life span = approx. 2 years
o Live through winter between
vegetative growth (1st spring) &
flowering (2nd spring)
o Ex. Beets, carrots
- Perennials:
o Live many years
o Death usually from infection, trauma,
environment
o Ex. Woody/herbaceous plants
Carnivorous Plants
- Consume insects or protozoans
- Darwin wrote first account in 1875
- Live in soil with low nitrogen
- Sticky & use digestive enzymes
- Ex. Venus fly trap, sundew plant
tendrils, pitcher plant
- Active traps
- Small sensory hairs
Nastic Movement
- Stimulated response that is
non-directional
- Ex. Mimosas & Venus fly traps
o Touch stimulus
o Closes leaves, but no direction
change
Turgor Response
- Rapid movement of plants in response
to stimuli brought by turgor pressure
change
Plant cells filled with water = rigid 🡪
higher turgor pressure
- Plant cells with less water = limp 🡪
lower turgor pressure
- Touching a VFT causes a sudden loss
in turgor in special cells which become
limp
o Leaflets close quickly
Tropism
- Directional growth response to
unequal stimulation from external
environment
o Results in curvatures of whole plants
o To or away from stimuli
- Positive tropism = growth towards
- Negative tropism = growth away
- Phototropism:
o Light stimulus
o Positive response by stems, leaves
o Negative response by roots
- Gravitropism:
o Gravity stimulus
o Positive response by roots
o Negative response by leaves
- Thigmotropism:
o Touch stimulus
o Positive response by vines
o Negative response by most
Darwin & Darwin (1880)
1) Planted seedlings with light coming
from 1 direction 🡪 plant bends
towards light
2) Removed the tip 🡪 no bending
3) Covered tip with opaque cap 🡪 no
bending
4) Covered tip with transparent cap 🡪
bending
5) Conclusion: tip is responsible for
sensing light
Boysen-Jensen (1913)
1) Placed a gelatin barrier between tip &
rest of shoot (allowing chemicals to
pass) 🡪 bending
2) Placed impermeable barrier between
tip & rest of shoot🡪 no bending
3) Conclusion: chemical messages pass
to elongating region, resulting in
bending
-
7
Plants
Phototropism & Auxin
- Auxin accumulates on the shaded side
of stem 🡪 cells elongate 🡪 stem bends
towards light
- If the plant is turned around, stem
bends in other direction
o Previous curve(s) remain(s)
Gravitropism & Statoliths
- Statolith: particle containing a great
quantity & density of starch
- Accumulate in lower part of cell roots
due to gravity
- Cause auxin build up at lower part of
cells
o Too much auxin inhibits cell growth
in roots
- Slows growth on lower side but rapid
elongation of cells on upper side
o Roots curve down
Plant Growth & Hormones
- Environmental conditions optimal =
max. height growth
o Includes light, nutrients, moisture &
warmth
Hormonal Control of Plant Growth
- Darwin & his son wanted to find out
what causes grass to grow
o Seeds normally grow towards light
source, but grass has opaque capsule
preventing light in
- Experiment:
o In 1926 Frits Went found out that a
chemical enhanced plant growth
o Auxin: Means to increase in Greek
- Other observations:
o People noticed rice infected with a
fungus grew abnormally tall 🡪 had
some sort of chemical in it
o In 1935 scientists were able to isolate
the chemical & named it gibberellic
acid
o When you apply gibberellic acid
plants grow abnormally tall
- What is a hormone?
o A compound produced by one part of
the body & transported to another
o Binds to a specific receptor &
triggers responses in target cells
Auxins
- Classification:
o Promoter
- Site of production:
o Apical meristem
- Cell division/elongation/
differentiation:
o Promotes elongation, vascular tissue
development
- Fruit:
o Delays ripening
- Abscission (leaf drop):
o Inhibits before leaf ages, promotes
after
- Senescence (aging): N/A
- Application:
o Prevents ripe fruit from falling off
trees
o Gives farmers extra time to harvest
Cytokinins
- Classification:
o Promoter
- Site of production:
o Actively growing tissue
- Cell division/elongation/
differentiation:
o Promotes division & differentiation
(mitosis)
- Fruit: N/A
- Abscission (leaf drop): N/A
- Senescence (aging):
o Delays
- Application:
o Spray cut flowers
o Keeps them fresh longer
- “Cytospray”:
o Nitrozime
o High content of natural occurring
plant hormones such a cytokinins,
auxins, gibberellins
Gibberellins
- Classification:
o Promoter
- Site of production:
o Apical meristem
- Cell division/elongation/
differentiation:
o Promotes division, elongation, stem
length
8
Plants
-
Fruit:
Delays ripening in citrus
- Abscission (leaf drop): N/A
- Senescence (aging): N/A
- Application:
o Japanese rice plants with fungal
infections produced too much
gibberellin
o Grew very tall
o Fell over & badly damaged
- Promotes cell enlargement
- Promotes uptake of starch tissue by
embryos in germinating seeds
- Stimulates vascular cambium to
produce secondary phloem (woody)
- Overall taller/stronger plants
Ethylene (gas)
- Classification:
o Inhibitor
- Site of production:
o Ripened fruit, damaged tissue
- Cell division/elongation/
differentiation:
o Promotes elongation
- Fruit:
o Promotes ripening, can stimulate
other plants to ripen
o Ex. Oranges
- Abscission (leaf drop):
o Speed up
- Senescence (aging):
o Speed up
- Application:
o Pick fruits before ripening & apply
artificially
Abscisic Acid (ABA)
- Classification:
o Inhibitor
- Site of production:
o Mature green leaves, fruits, root caps
- Cell division/elongation/
differentiation:
o Promotes growth of axillary buds,
inhibit seed germination, blocks
action of growth promoting
hormones
- Fruit:
o Promotes ripening
- Abscission (leaf drop):
o
o
Promotes
Senescence (aging):
o Promotes
- Application:
o Better colour in fruit
- Stops the stomata from opening,
therefore blocking intake of carbon
dioxide
- Inhibits seed germination
Oligosaccharins
- Stimulate the plant to produce an
antibiotic in response to attacks by
fungi or bacteria
- Allows plant to grow to its full
potential
-