Chap 6 Plant Adaptations

All life on Earth is...

carbon based

photosyntheis

light energy from the sun dives a series of reactions that result in the fixation if CO2 and the release of O2

photosynthetic pigments

absorb light in the 400-700 nm range (same as visible right spectrum for humans

- PAR range

photosynthetic light energy

is converted to the chemical bond (potential energy) in sugar:

- 6CO2 + 12H2O → C6H12O6 + 6O2 + 6H2O

- other carbon based molecules included complex carbs, proteins, fatty acids are made in other parts of the plant

photosynthesis (light dependent)

light-dependent reactions convert light energy into chemical bond energy

chlorophyll

pigment in the chloroplasts that absorbs light energy

energy is transferred....

to electron carriers in photosynthetic electron transport

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- requires sunlight

- synthesizes ATP

- reduces NADP+ to NADPH

Light independent reactions use...

chemical bond energy in ATP and NADPH to incorporate CO2 into simple sugars

- doesn't require sunlight

- more adaptive variations

Plants and cellular respiration

plants use this to convert the energy in sugars and other molecules into ATP

C6H12O6 + 6O2 → 6CO2 + 6H2O + ATP

- both use CO2 during photosynthesis and producing it during respiration

Net photsynthesis

Photosynthesis - Respiration

- measured in moles CO2 per leaf are (or mass) per unit time

- µmmol/m2/s

how can we estimate respiration in a plant?

1) measure CO2 production rate with lights off

2) measure CO2 production from roots

Diffusion of CO2 is controlled by

the diffusion gradient or difference in CO2 concentration in the air next to the leaf and the leaf interior (ppm)

Stomatal conduction

flow rate of Co2 through the stomata µmmol/m2/s

Stomata conduction is determined by

- stomatal density

- aperture

stomatal density

# per unit leaf surface area

aperture

size of stomatal openings

why do the stomata close?

- limits water loss

- limits transpiration

- dry conditions or low energy demands

Transpiration

when the somata are open, water vapor in the leaf diffuses out (defusing down its concentration gradient)

transpiration rate depends on...

the vapor pressure gradient (VPD) and stomatal conduction of H2O vapor

- the ralative humidity inside a leaf is usually > than 99%

turgor pressure

force exerted outward on a cell wall by the liquid water inside the cell

- plants function best when their cells are fully hydrated (at maximum turgor)

what happens to the plant when the water content of its cells declines?

it dies

how do plants replace water lost through transpiration?

it draws up more water from the roots

water potential (ψ)

difference in Gibbs energy per mole between the water in the continuum and pure water

- expressed in terms of pressure (energy per volum using pascals

- Pa= 1 Newton/m^2

- ψ= zero for pure water at ATM

at field capacity

-ψ soil is at or close to negative

- water is freely avialable

as water is taken from the soil

- ψ soil becomes more negative

- water holds more tightly to the soil

clay soils

have a higher surface area meaning they have more negative ψ soil than sandy soils

What two points are made in this graph?

- when leaves get dry, stomata close to conserve water (but this stops photosynthesis because CO2 can be exchanged)

- different species have different stomatal closing threshold

Thermal performance curve is described by three values

Tmin = minimum temp (net photosynthesis near 0)

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Tmax = maximum temp (net photosynthesis near 0)

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Topt = range of temp over which net carbon uptake is highest

Leaf temperature determines

rate of these two process not the air temp

plants (leaf temperature)

- absorb both shortwave (solar) and longwave (thermal) radiation

- reflect some solar radiation and emit some longwave back to the atmosphere

How much incoming solar radiation is used for metabolism and stored in chemical bonds by a lead?

<10%

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WHY?

- Some reflected

- remainder raises the temperature of the leaves and surrounding air

terrestrial plants largely lose heat by.....

evaporation and convection

evaporation

part of transpiration

- it requires a large amount of energy to change water from a liquid to a gas

- water transpires from the leaves and thermal energy is lost

higher rate of transpiration

> the evaporative cooling

Convenction

transfer of heat energy through the circulation of fluids (air/water)

if the surface of the leaf is warmer

Thermal energy:

- adjacent molecules of air or water through conduction

- moves from the air next to the leaf

- surrounding air through convection

boundary layer

layer of still air or water next to the surface of each leaf

- reduces the transfer of heat water and CO2 between the leaf and environment

- if no convection, the boundary layer increases in thickness

size of an object can influence the boundary layer

bigger objects = bigger boundary layer (vise versa)

Leafs losing heat through convection due to their size

smaller the leaf = quicker the heat loss (vise versa)

Physical environment can affect....

- areas of high water quality

- areas of lower water quality

Areas of lower water availability

- transpiration is limited to reduce water loss

- plants tend to have smaller leaves

(=> boundary layer => incr. convective heat loss)

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How is heat lost by these plants

A) conduction

B) convection

C) Evaporation

D) radiation

E) None

Evaporation (most through transpiration)

How is most heat lost in areas of lower water availability

through convection

Solar radiation influences

-the amount of PAR

-the temperature of the leaf and surrounding air

-the temperature of the surrounding air affects the relative humidity

-relative humidity affects the rates of transpiration and evaporation of water in the soil

A sunny, dry environment has

-greater PAR

-higher air temperatures

-higher leaf temperatures

-lower humidity

-higher rate of transpiration

-higher rate of evaporation

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Plants adapted to this enviroment might have smaller leaves, more leaves, more roots, deeper root

Adaptive trade-off

adaptations for one environment may not be as effective in a different environment

- caused by multiple environmental conditions

Plants distribution of carbon is acquired through

Photosynthesis

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EX: allocating more carbon to producing leaves and stem

- increase access to light and CO2

- Reduce the carbon available to produce roots

- decrease access to water and soil nutrients

Demand for water is related to temperature

as air temp rises

- saturation vapor pressure rises

- rate of transpiration rises

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- Water availability and water requirements vary with time

Opening/closing stomata depends on

current conditions

stomata may be closed or partially closed...

- when the atmosphere is dry

- when soil is dry

- during the hottest part of the day

As water stress continues

stomata may be open only during cooler, more humid conditions such as early morning

Closing the stomata

-reduces water loss through transpiration

-reduces CO2 diffusion into the leaf

-reduces evaporative cooling

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Reduces the ability to photosynthesize

photosyntheis declines

leaf temperature can rise (get warm)

Some plants respond to moisture stress by

curling leaves or wilting

why is curling or wilting advantageous?

- reduce water loss

- reduce heat gain because the surface area of the leaf is reduced

If a plant encounters low soil water availability during development, carbon allocation is

- increased for the production of roots

- decreased for the production of leaves (Shoots)

- increases the uptake of water per unit leaf area

- reduces total amount of water lost by transpiration (in responce to dry conditions

mesophyll cells

location of light energy capture and conversion, transformation of CO2 into sugars

- products of photosyntheis move into the vascular bundles to be transported around the plant

Carboxylation (C3 pathway)

1) RuBP (5 C mol.) combines with CO2 and fixes it into a solid form

2) reaction produces 2 molecules of 3-PGA (3 C mol)

3) 3-PGA, ATP, and NADPH are used to syntheisze the energy rich G3P

4) some G3P is used to produce sugars and carbs

5) most G3P used to create

new RuBP (with ATP)

Light availability can limit the light-independent reactions

because it controls ATP and NADPH

C3 pathway drawbacks

Rubisco = oxygenase

- catalyzes the reaction between O2 and RuBP

- results in the photorespiration - the release of CO2

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Reduces the effiencey of C3 photosynttheis by 25%

photorespiraton

oxygen is being introduced into the Calvin cycle in replace of CO2

- resulting in the decrease in G3P molecules

- Hense reducing the products of Calvin cycle

plants that undergo C4 photosynthesis

have a different leaf anatomy

- contain 2 types of photosynthetic cells

- dosent react with oxygen (unlike C3)

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PHOTOSYNTHETIC CELLS (C4)

- mesophyll cells

- bundle sheath cell

bundle sheath cells

surround the vascular tissue

C4 pathway

1) mesophyll cells, CO2 reacts with PEP (3 C mol) to produce

OAA (4 C mol.)

2) OAA is transformed into a 4-C acid

3)Organic acids are transported to the bundle sheath cells

4) Enzymes break them down to form CO2

5) This CO2 then enters the Calvin Cycle

PEP

phosphoenolpyruvate

advantages of C4 photosynthesis

- PEP does not react with oxygen

photorespiration does not occur

- conversion of organic acids into CO2 within the bundle sheath cells concentrates CO2

- reaches much higher concentrations than in C3

- increases efficiency of CO2 and RuBP reaction

Spatially

seperates the steps in two different parts of the leaf

How are O2 and rubisco separated?

O2 produced in light reactions in mesophyll cells and rubisco perform carboxylation in bundle sheath cells

C4 plants have a higher..

- max rate of Photosynthesis (than C3 plants)

- > water use efffciency is an advantage in hot dry climates

- increased energy to produce PEP, bundle sheath cells , and enzymes are the cost

Most C4 plants are

- grasses in tropical or subtropical environments

- shrubs in arid or salty environments

Hot deserts have severe invironments

++ solar radiation

-- water availability

Plants in hot deserts (succulents)

have different type of photosynthesis

- CAM pathway

CAM pathway (crassulacean acid metabolism)

similar to C4 but steps are separated temporally instead of spatially

CAM plants open their stomata at night.

- take up CO2

- Convert to malic acid using PEP carboxylase

- large amounts of malic acid accumulate in mesophyll cells

close stomata during the day

-malic acid converted to CO2

-C3 pathway used to fix CO2 and produce sugars

how is this adaptive for plants living in a hot dry environment

- CAM plants dramatically reduce water loss by opening stomata only at night

Plants in dry enviroments

- have lower stomatal conductance

- few and smaller stomata

- increased water use efficency

- decreased rate of photosynthesis

greater allocation of carbon to produce roots instead of shoots and leaves

increases ares for extracting water

(volume and depth)

structural features

- can reduce the amount of energy striking the leaf

- increase loss of heat through convection

- reduce the loss of water through transpiration

leaves of plants in dry environments are

- smaller and thicker

- covered with hairs that scatter solar radiation

- have leaves coated with waxes and resins that reflect light and reduce absorption

Plants exhibit variation in thermal performance of photosynthesis due to

- genetics

- photosynthesis type

- acclimation

Periods of extreme hot or cold

can damage plant cells and tissues

frost hardening (cold tolerant plants)

genetic ability to tolerate extreme cold

- variable within and among species

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FEATURES

- can produce compounds that allow leaves to survive freezing temperatures

- has needle leaf evergreens (pine and spruce)

- some are winter deciduous

winter deciduous

shed their leaves before the beginning of the cold season

Macronutrients

nutrients needed in large amounts

C, H, O (macronutrients)

derived from CO2 and H2O

N, P, K, Ca, Mg, S (macronutrients)

- terrestrial plants acquire from the soil;

- aquatic autotrophs acquire from the substrate or water

Micronutrients (trace elements)

nutrients required in very small quantities for growth and reproduction

What adaptations are exhibited by plants in low nutrient environemnts?

- Higher ratio of roots to shoots

- lower growth rate

- increased leaf longevity

- carnivory

FACE experiments

determine plants responses to elevate levels of atmospheric CO2

Why type of photosynthesis is likely to benefit the most from elevated CO2

A) C3

B) C4

C) CAM

C3 because they're naturally less efficient at assimulating carbon