Plant Physiology
Chapters
Angiosperms – Flowering Plants
AP Biology
Chapter 1
Plant Form and
Function
Monocots vs. Dicots
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Grass, wheat, corn ,
rice, sugar cane
Fibrous roots
Parallel veins
Flowers in 3’s
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Most others
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Tap Roots
Net-like veins
Flowers in 4’s and 5’s
Can become woody
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Plant Organs and Tissues
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Organs: roots, stem, leaves – all organs are made out of the
same three tissues
Tissues
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Dermal Tissue – epidermis – protective
Vascular Tissue – veins – carry food and water
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Xylem – carries water and minerals – made of tracheids and vessel
elements
Phloem – carries sugar – made of sieve tubes and companion cells
Ground Tissue – everything else – used for support,
photosynthesis, storage
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Pith-ground tissue inside vascular tissue
Cortex-ground tissue outside of vascular tissue
Outside layer =
epidermis – dermal
tissue for protection
Cortex = ground
tissue – storage of
food, uptake of
minerals
Steele = xylem and
phloem – vascular
tissue
Root Hairs – increase
surface area for
increased water
absorption
Root vs. Shoot System
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Root system (roots)
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Takes water and minerals
from the soil (absorbs from the tips
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of the roots and root hairs increase
surface area from absorption)
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Anatomy:
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Tap roots (dicots) – a large
vertical root with smaller lateral
roots (store food)
Fibrous roots (monocots) –
mat-like roots that spread
Shoot system (stem, leaves,
flowers)
Takes CO2 from the air, make
sugar, plant reproduction
Transports sugar to the rest of
the plant
Anatomy
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Stems:
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Nodes – where leaves attach
Buds – create more shoots
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Terminal buds – end of stem –
cause apical dominance –
inhibits side growth
Axillary buds – side budS
Leaves: Petiole – attaches leaf to
the node (not in monocots – leaf
ensheathed in stem)
Flowers – modified leaves with
stem specialized for reproduction
Dicot Root
Roots:
Epidermis –
dermal
Cortex –
ground
Vascular vascular
Stems
Vascular
Bundle
Cortex
Epidermis
Vascular
Bundle
←Dicot – C3 Plant
Monocot – C4 Plant→
Plant Cell Types
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Parenchyma – “normal plant cells” – have large vacuoles, no
secondary cell wall, usually not mitotic, but can be stimulated
to divide in injury
Examples: Most of the cells that make up ground tissue
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Photosynthetic cells in leaf mesophyll
Cells that store starch in stems and roots
Fruit cells – store sugar
Sieve tube cells that make up phloem
Collenchyma – cells are elongated, thicker primary wall but
no secondary cell wall, provides for growth and support
Examples:
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Cells that support young stems and petioles
Some ground tissue
Sclerenchyma – rigid secondary cells walls (can’t elongate),
may be dead and used for plant support
Examples:
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The shells of nuts and outer coat of seeds
Fiber cells – used to make plant fibers that are used to make rope
Tracheids and Vessel Elements (make up xylem) – dead water conducting cells
used for support (cells disintegrate leaving empty cell with a double cell wall –
water moves from cells to cell through pits or end to end perforations
sclerenchyma
Plant Growth
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Meristems embryonic tissue (stem cells –
undifferentiated) – can divide and become any
kind of plant cell
Primary Meristems(apical) – make plant grow
longer – in root tips and at buds or new shoots
Secondary Meristems(lateral) – make plant
grow wider – in stem – adding more xylem
which becomes wood
Lateral Growth
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Lateral Meristems also called vascular cambium –
forms between xylem and phloem so there is a
continuous cylinder around xylem and interior ground
tissue
It forms 2ndary xylem on the inside and 2ndary
phloem on the outside
Lateral Growth
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Xylem (wood) Over the years, vascular cambium
makes many layers of 2ndary xylem on the inside
(made of tracheids and vessel elements with very
strong cell walls) – This is wood! Only the most
exterior xylem works to carry water. Interior xylem
dies and harden more
Phloem (part of bark) Formed outside the vascular
cambium – only newest xylem closest to interior is
alive and transports food – rest dies and sloughs off
so doesn’t become thick like wood part
Lateral Growth continued
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Cork cambium forms outside the phloem and
makes cork cells which fill with suberin – a
waxy material that protect the trunk and
branches
The epidermis cracks off and the outside
becomes the cork cells
Bark = Phloem, Cork Cambium, Cork
Heartwood = dead,
older xylem
Sapwood = new
xylem still carrying
water
Phloem – carries
food - old phloem
sloughs
Plant Transport
nd
2 Plant Chapter
Chapter 36
I. Local Transport (all review)
Facilitated Diffusion
A.
a.
b.
c.
Open channels
Shape change channels (not regulared by ATP must by solutes
moving thru)
Gated channels
Active Transport
B.
a.
b.
c.
Normal
Chemiosmosis – coupling the pumping of protons to the movement
of other solutes (ex. Pump protons to cause the movement of K+ into
guard cells)
Co-transport – pumping protons, they attach to solutes and move
them passively as they flow back thru the membrane
Examples:
1. bringing nitrogen into the roots (pump H+ out of the epidermis into
the soil and as it flows back it in brings nitrogen
2. loading sucrose into the phloem (pump H+ out of sieve tubes in
phloem into the leaf mesophyll and it flows back bring sucrose with it)
C.
Osmosis – remember in plants, water doesn’t just move
from high to low concentration, pressure also plays a role
and can override solute and water concentration
Osmosis Continued
Ψ = Ψp + Ψs
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Water potential – the tendency for water to leave one
place and go to another – the higher the Ψ the more
likely water will leave and go somewhere else
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Water moves from high to low water potential
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Water potential = pressure potential + solute potential
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Pressure potential is usually positive created by the
pressure exerted by the cell wall – the higher the
pressure potential – the higher water potential
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Solute potential is 0 in pure water and negative if there
are any solutes - the more solutes the more negative
solute potential and the lower the water potential – water
moves where there is more solute!
II. Lateral Movement – short
distance
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There are three compartments within plant cells:
Apoplast – continuum of cell walls
Symplast – continuum of cytoplasm thru
plasmodesmata
Tonoplast – vacuole compartment set apart by the
vacuole membrane – not continuous from cell to cell
and the vacuole membrane can actively transport and
do chemiosmosis
Water and solutes can move through the apoplast,
symplast, or into the tonoplast
Lateral Movement in Plants
III. Long Distance Transport
(vertical movement thru xylem and
phloem – diffusion is too slow
A. Xylem (tracheids and vessel elements with 2
set of cells walls) - schlerenchyma
↑
↑
Tracheids
↑
Vessel Element
Xylem Continued
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Water and mineral transported from roots to leaves
To get into the xylem – things pass from the
epidermis of the roots into the cortex and into the
steele which then branches into the xylem in the stem
In roots, root hairs increase surface area to absorb
more thru the epidermis
Endodermis (between cortex and steele) is selective
in what mineral can cross into the steele
Xylem continued
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Xylem has two methods of movement:
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Main method is transpiration accompanied by
cohesion and adhesion (transpiration caused by
lower water potential in air than in mesophyll of
leaf)
Second method that helps some is root pressure.
Minerals are actively transported into the xylem in
the root which decreases water potential in the
xylem cells, water flows in and pushes the water
up (only good for a few meters)
Movement of Water - Transpiration
Xylem continued
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Regulation of Transpiration controls the flow of water
thru the plant and also makes sure that the plant
doesn’t dry out and have no water for photosynthesis
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Guard cells buckle outward when full of water
Guard cells flap closed when empty (when water is lacking,
turgor pressure decreases and the cells become flaccid and
flop together
Also, guard cells use chemiosmosis to open and close
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They pump H+ out which causes a neg. charge inside that caused
K+ to be drawn into the cell
Due to the K+ in the cell – it become hypertonic and water flows in
The active pumping is stimulated by light and low CO2
For closing, K+ is transported out in response to high temp or high
CO2 (mediated by abscisic acid- a hormone)
Long Distance Transport Continued
Phloem (sieve tubes and companion cells)
B.
Sugar is transported from the leaves to storage areas of
the plant (roots and fruit)
Phloem sap is mostly sugar in water but also contains aa,
hormones, and some minerals
Sugar will diffuse thru plasmodesmata from mesophyll
cells to sieve tubes due to concentration difference
Sugar is also actively transported into the sieve tubes
making the sieve tube cells hypertonic so water rushes in
and pushes the sugar water thru the phloem to needy
areas
Once in the phloem it moves from source to sink:
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•
At the sink end (no sugar), sugar is leaving the sieve tubes to go
into storage cells by concentration differences
This causes pressure to decrease and sugar flows high to low
pressure and high to low concentration
Plant Nutrition
rd
3 Plant Chapter
Chapter 37
Plant Growth – where does the
plant’s mass come from
1. Most of the plant weight is water
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Water accumulates in vacuoles and elongates the
cells and makes them turgid and acts as a solvent
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Water also supplies hygrogen which is
incorporated into sugar in the Calvin Cycle
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90% of a plant’s water is lost in transpiration and
then replaced
Plant Growth Continued
Of the dry weight – 95% is organic
2.
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Most weight is CO2 from the air that is
incorporated into carbohydrates (remember most
of structure is cell walls, made of cellulose which
are strings of glucose)
Of the dry weight – 5% is inorganic
3.

From minerals from the soil
Macronutrients (needed in lg. amts.)
Source of macronutrients:
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C, O → air
H
→ water
N,S,P,K, Ca, Mg → soil
Purpose of macronutrients:
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C, O, H – sugar and cell wall production
N, S – make proteins
N, P, - nucleic acids, ATP, phosphorylation cascades in cell signalling
K – water balance, opening and closing stomates, cofactor for protein
synthesis enyzmes
Ca – membrane structure, formation of cell walls, cofactor
Mg – part of chlorophyll
Micronutrients (needed is small amts.)
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Fe, Cl, Cu, Mn, , B, Ni → all from soil, all used as cofactors
Soil
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Soil is eroded rock and humus (dead organic stuff) and spaces
for water
Texture of soil determines the quality for certain plants
Type of soil depends on how tightly packed - sand (loosest) →
clay (tightest packed)
A mix of soil types is the best
Soil pH affects the availability of minerals
Soil often gets acidic from acid rain – put own lime which
is basic – positve ions bind up negative ions and plants
can’t get them from the soil
Soils with a lot of clay bind up all the positive ions like K+,
Ca++, Mg++, NH4+ and it’s hard for plants to get.
Negative minerals NO3-, PO4- don’t stay in the soil very
long and wash away
Some plants secrete H+ into soil which will compete for
binding the to clay and release the postive mi nerals
Plants getting Nitrogen
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Needed for aa and nucleic acids
80% of the air is nitrogen but N N, no enzymes
in plants to break N2 bond so it’s unuseable
Plants get nitrogen from:
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Decomposition of organic material to inorganic
compounds that plants can absorb (NH4+, NO3-,
ammonium and nitrate)
Nitrogen fixation – specialized bacteria (Rhizobium)
which live free in soil or symbiotically on plant roots
(legumes like peas, beans, soy, nuts) are able to
convert N2 into useable ammonium and nitrate
Note: Some roots have leghemoglobin to bind O2 for
the bacteria to use because nitrogen fixation requires
a lot of energy and the bacteria need a lot of oxygen
for CR
Getting Nitrogen
Denitrified by bacteria to N2
– goes back into air unusable
Decomposed to
Organic Material
NH4+, NO3Absorbed by plant roots
OR
Note – many times in farming – there is no
decomposition so farmers add fertilizer –
feces containing usable nitrogen cmpds.
N2 in air
Getting Phosphorus
Mycorrhizae – fungus living symbiotically on many plant roots,
absorb PO4- and water and secrete plant root growth factors (in
turn the plant feeds the non-photosynthetic fungus
Plant Adaptations to get minerals
and water
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Parasitic plants - do some photosythesis to make
sugar but tap into other plants vascular system and
suck out water and minerals
Epiphytes – grow on other plants but are fully
photosynthetic and not parastitic
Carnivorous Plants – live in poor soil conditions –
usually nitrogen deficient – capture animals for
nitrogen and other minerals but are fully
photosythetic for sugar (venus fly trap)
Farming Practices and Plants
Crops are not Natural
Crops remove minerals from soil but don’t
decompose and return the organic or inorganic
components to the soil
1.
Must use fertilizers to replace N, P, K which then can run
off and cause too much plant growth in rivers – clogging
them and killing fish
a.
•
b.
Can use natural fertilizers which are slow release vs. commercial
fertilizers which release faster but usually don’t stay in soil as
long
Can rotate crops – rotate with legumes – add nitrogen to
soil and plow them under as fertilizer
Farming Continued
Crops remove water from the soil
2.
Ground aquifers collapse
Many farmers irrigate with water containing salts – as the
water evaporates, the soil becomes salty making the soil
hypertonic (lower water potential) so water leaves the
roots instead of entering
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3.
Crop harvesting causes the loss of top soil – soil
blows or washes away once crops are harvested.
Can combat problem by:
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Contour farming
Not plowing at the end of the season
Now planting in rows or plant plants that don’t grow in
rows
Planting crops that trap soil – rotating crops
Plant Signaling and Plant
Hormones
AP Biology
Plant Class #4
Hormone Action
The same hormone can have different effects depending on location,
concentration, developmental stage or plant, etc.
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Effect Gene Expression
Effect Enzyme Activity
Change Membrane Properties
Open Gated Channels
Change Metabolism
Stimulate Cell Division
Affect the differentiation and development of
cells
General Action of Hormones
1.
2.
3.
4.
5.
Bind to receptors
Receptors change shape in response to binding
2nd messengers are activated which activate
enzymes
OR
Directly activate or cause transcription of enzymes
(particulary kinases which phosphorylate other
enzymes)
Enzymes ultimately:
1.
2.
3.
4.
Activate gene transcription
Activate transcription factors
Deactivate transcriptional repressors
Cause chemical reactions
Example of Plant Cell Signaling
Response to a stem breaking through the ground
for the first time
Light activates Phytochromes (light receptor
connected to a kinase)
cGMP activated
Opens gated channels for Ca++ in cell membrane
Enzymes are phosphorylated
Calcium binds to Calmodulin
Turn on transcription factors
Activated kinases and turns on transcription
factors
Make Photosynthesis enzymes
Make enzymes to make chlorophyll
Make enzymes to decrease auxin production so don’t keep elongating the stems
Plant Hormones (internal signaling)
Auxin
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Produced by apical meristems, young leaves, developing seeds
and fruit – generally moves from shoot to the base
Moves through the parenchyma cells themselves – not
vascular tissue - Transported by chemiosmosis
In low conc. – causes cells to elongate faster
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Stimulates pumps to pump H+ into cell wall, ↓pH activates enzymes
that break down cell wall – allows water flowing in to expand wall
Phototropism – growing toward light – elongates cells on dark
side faster
In high concentrations - induces ethylene gas which slows cell
growth
Control apical dominance
Controls stem elongation in developing shoots
Kills dicots/not monocots = pesticide for corn or grass fields
Causes fruit to grow – if spray on plants, fruit will develop
without seeds = seedless fruit
Cytokinins
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Produced by the roots, Moves through the xylem,
modified adenine, named for cytokinesis since in
actively growing parts of plant
Stimulates cell division in roots, embryos, fruits,
retards protein breakdown and prevents aging in
leaves and fruits (florists spray on cut flowers to keep
them fresh), stimulates seed germination
Works with auxin, relative concentrations control
growth and differentiation of plant parts
Works opposite auxin to control height vs. bushiness
(more auxin – grow tall, more cytokinins – more
axillary buds – bushier)
Gibberellins
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Produced in roots and young leaves
Elongation and cell division in stems and leaves
(activates enzymes that allow cellulose digesting
enzymes to penetrate the cell wall)
Cause germination of seeds – water stimulates release
of gibberellins – stimulates production of amylase to
break down carbs
Important for pollen development, pollen tube growth
Works with auxin for fruit growth (spray to make
seedless grapes)
Abscisic Acid
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Readies the plant for winter – slow growth of
buds, inhibits growth
Causes stomates to close in a wilting plant,
opens the K+ channels so K+ leaves guard
cells, water follows
Keep seeds dormant when conditions not
suitable (light, rain, etc. inactivates abscisic
acid to cause seeds to germinate)
Ethylene
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Gas – causes fruit ripening (breakdown of starch to
sugar, breakdown of cell walls to soften, chlorophyll
breaks down)
Inhibits axillary growth in response to high auxin
Causes leaf death in winter (can’t get water from
frozen ground – don’t want to lose waterfrom leaves)
Produced also in response to stress (drought, flood,
infection)
Destroys inside of xylem to make hollow tubes
Plant growth in sprouting plant – when hits
something solid – secretes ethylene – plant grows
horizontally to escape object then turns upward again
Brassinosteriods

Cells elongation and division in stem (like
auxin)
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Prevents leaves from falling off
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Promotes root growth at low conc. and stops
root growth at high concentrations
Circadian Rhythms
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Fluctuations based on a 24 hour cycle – not
due to environmental stimuli – based on some
internal time clock
Devoid of environmental clues – it deviates
slightly from the 24 hour cycle (vary from 2127 hours)
External Signaling in Plants
Light, Gravity, Mechanical Stimuli
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Phototropism – growing toward sun (Auxin)
Gravitropism – roots grow down, stems grow up (Auxin)
Thigmotropism – change in growth due to mechanical stress
(vines grow straight until contact – wrap around due to
differential growth on opposite sides)
Rapid Leaf Movements – loss of K+ causes water loss and
leaves to fold up
Sleep movements – transport K+ from 1 side of leaf to another
– changing water flow
Rubbing or touching a plant changes gene expression – can
make plants shorter by rubbing the stem a couple of times a
day
Plant response to light

Two types of light receptors
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Blue light receivers
Phytochromes – receive red light – photoreceptor
linked to a kinase
Photoperiodism – control of flowering and leaf
growth by length of days
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Short Day/Long Night – flower when light is
shorter than a critical length (flower late summer)
Long Day/Short Night – flower when light is
longer than a critical length (flower in spring)
Controlled by phytochromes – bound to a light
absorbing molecule – light changes shape of
phytochrome which change cellular responses)
Plant Response to Stress

Lack of Water

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Lack of Oxygen (from overwatering – reduces air in
soil)

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Some form air tubes in roots (ethylene causes cell death in
ground cells in roots forming tubes, or roots are out of soil)
Too much salt (causes water deficit)

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activate abscisic acid = K+ leaves and so does water –
guard cells close
Leaf growth inhibited due to lack of turgor pressure, so less
water lost
Make internal solutes to deep water potential lower in plant
Heat (enzymes denature, water evaporates
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Transpiration for evaporative cooling
Make heat shock proteins – may help prevent denaturation
of proteins
Plant Response to Stress Continued

Cold
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Herbivores
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Plants increase amt. of unsat. Fatty acids in membrane to make them
more fluid
Change solute concentration in cells to prevent cooling with out ice
crystals forming in cells
Physical defenses – thorns, stickers
Chemical toxins (ex. Make a weird aa that when incorporated into
insect proteins – proteins are misshapen and the insects die) (ex. 2 –
plant sends chemical signal in response to damage – signal causes
wasps to come and inject eggs into catepillars eating the plant, wasp
babies eat their way out)
Infections

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Tough epidermis
Phytoalexins and PR proteins – kill bacteria by dissolving their cell
walls
Express defense genes – apoptosis of infected cells, produce antibiotics
Produce Salicylic Acid – makes cells resistant to attack