BIOL 2390 - Topic 4

organismal ecology

what environments might have little variation?

marine + aquatic are more stable - less variation as compared to terrestrial

name common stressors

• climatic stressors ex. long term weather patterns

• chemical stressors ex. pollutants, oxygen availabilty

• physical stressors ex. wind, water current

• biological stressors ex. competition, disease

explain the effects stressors can have at the different levels

• individual response: loss of productivity

• population level: alteration of gene pool

• community level: loss of vulnerable species, opening of niches that can be filled by tolerant species, negatively affect biodiversity

what is reproductive potential, and what is it determined by? 

• maximum number of potential offspring and is determined by genotype 

what affects the actual reproductive success

many environmental stressors can limit performance - physiology, morphology, behavior.

define tolerance

when stressors have lower impact on organisms

define resilience

when organisms can recover after stressor is removed

what 4 main patterns do degree of response to stress follow ?

• little tolerance - type A response 

• direct relationship - type B response 

• resistance/tolerance - type C response 

  • high tolerance - type D response 

what are the 3 responses to stress

1. developmental response

2. acclimatory responses

3. regulatory responses

describe developmental response

irreversible change lasts for the life span (could be years)

descibe acclimatory responses 

can last from days - weeks and are reversible 

describe regulatory responses

real-time changes that can last seconds - minutes

in response to changing environments, organisms can be conformers vs regulators

reversible changes allow for homeostasis

what 2 processes occur simultaneously in leaves ?

photosynthesis + cellular respiration

light reactions only occur when _ is available? what is produced ?

PAR : photosynthetically active radiation 

CO2 consumption (fixed) as sugars are produced

what happens if PAR is not present ? what is the net CO2 uptake ?

only respiration occurs; net CO2 uptake is negative 

what effects can stressors have on organisms? (3) 

• reproductive potential 

• tolerance 

• resilience 

what 2 processes does photosynthesis consist of?

Light reactions and the calvin cycle 

light reactions: where does energy come from ?

Photosynthetically active radiation (PAR) = light

where do electrons for light reactions come from ?

water

what is the carbon source for Calvin Cycle?

CO2

Calvin cycle: where does energy come from?

light reactions

what does cellular reproduction produce ?

CO2

What happens to CO2 uptake when PAR increases?

CO2 uptake increases

define light compensation point

when fixation = respiration

(no net gain or loss)

light compensation point vs low-shade plants 

have a low LCP – they can survive in low light.

light compensation point vs sun loving plants

have a higher LCP – they need more light to break even.

define light satuation point

light intensity at which the rate of photosynthesis reaches its maximum and no longer increases even if more light is provided.

explain what happens when were below the light saturation point

More light = faster photosynthesis (light is the limiting factor)

explain what happens when were above or at the light saturation point 

Photosynthesis plateaus because another factor (like CO₂, temperature, or enzyme activity) becomes limiting.

sun loving plants vs LSP

have a high LSP — they can use high light levels efficiently.

shade plants vs LSP

each LSP at lower light intensities — too much light can actually stress them.

define gross photosynthesis 

total amount of carbon dioxide (CO₂) fixed (or oxygen produced) by a plant during photosynthesis before subtracting the CO₂ lost to respiration. 

define net photosynthesis

the difference between CO2 uptake and respiration

• usable energy the plant has left over for growth, storage, and reproduction after meeting its own energy needs.

t max happens when … (graph)

where the lines cross

this graph demonstrates what? and what response ?

-population of a species can adapt to local environmental pressures

• demonstrates that Topt shifts as individuals adapt

• acclimatory response

this graph demonstrates what? what response ?

some species can adapt to seasonal environmental pressures 

• Topt shifts as individuals acclimate to seasonal change 

• acclimatory response

interpret this graph :

• shade tolerant:

  • LSP, net co2 uptake at LSP

• shade intolerant:

  • LSP, net co2 uptake at LSP

• shade tolerant:

  • LSP: (~700 mol) net co2 uptake at LSP (10 mol)

• shade intolerant:

  • LSP (~1200 mol) , net co2 uptake at LSP (19 mol)

Shade-tolerant plants:

• rubisco levels → results in what regarding LSP, growth and photosynthesis rates?

• energy demands

• rate of respiration

• LCP

• rubisco levels: Less rubisco required → results in what Lower LSP meaning organism stays small, slower growth rates and limited photosynthesis rates

• Lower energy demands

• lower rate of respiration

• smaller LCP

boundary layer

is a barrier to heat loss. the thin layer of still or slow-moving air (or fluid) that forms right next to a surface, like a leaf, skin, or building wall.

what mechanism cools leaves ?

convective heat loss: When air or water moves past a warm object, it carries heat away.
- heat lost due to movement of the fluid.

what influences thickness of boundary layer?

size and shape

thick boundary layers - who benefits ?

Slower exchange of heat, water vapor, CO₂/O₂

• Desert plants, dry environments

thin boundary layers - who benefits?

Faster exchange (cooling, transpiration, gas uptake)

• Tropical rainforest plants

simple leaves vs boundary layer

• Larger continuous surface area

• Thicker boundary layer forms across the surface

• Slower gas and heat exchange

• advantages:

  • Better water conservation

  • Useful in dry or cold environments where reducing transpiration or heat loss is key

compound leaves vs boundary layer

• Thinner boundary layer around each leaflet due to greater air flow

• Faster gas exchange and cooling

• advantages:

  • Enhanced photosynthesis and cooling

  • More efficient in hot, humid, or well-ventilated environments

Why is the Calvin cycle temperatue sensitive, but light reactions are not?

The Calvin Cycle depends on temperature-sensitive enzymes, while the light reactions rely on light energy and electron flow, which are physical/chemical processes not limited by temperature in the same way.

what does an inbalance between light reactions lead to ?

photoinhibiton

if reaction centers remain reduced what will happen?

If reaction centers remain reduced (can't pass on electrons):

• Electron flow stops in the light reactions

• ATP and NADPH are not produced

• Water splitting slows or stops → less or no O₂ released

• The Calvin cycle can't run (no energy supply)

  • Photodamage may occur due to excess light energy not being used properly

anthocynanins

 (red, purple, blue pigments)

• Common in leaves during autumn (e.g., red maple)

• Accumulate in vacuoles of leaf cells

• Act as "sunscreen" pigments

Carotenoids

(orange and yellow pigments)

photostasis

the dynamic balance of light energy absorption and utilization in photosynthetic organisms, especially plants and algae.

How Do Organisms Maintain Photostasis

Adjusting Pigment Composition

• Increase light-harvesting pigments (like chlorophyll) in low light

  • Increase protective pigments (like carotenoids or anthocyanins) in high light

Carbon allocation

the process by which plants distribute the carbon they fix through photosynthesis (mainly in the form of sugars) to different parts of the plant for growth, storage, maintenance, and defense.

if growth is directed to the shoot system, what are the rates of photosynthesis, respiration and the net C gain ?

rate of photosynthesis: increases greatly 

rate of respiration: increases a little

net C gain is: increasing 

if growth is directed to the root system, what are the rates of photosynthesis, respiration and the net C gain ?

rate of photosynthesis: is not affected

rate of respiration: increases, root tissues are respiring

net C gain is: smaller

why would a plant opt to allocate more carbon to the root system?

when it needs to improve its access to water or nutrients, or when environmental conditions make it advantageous to invest below ground rather than above.

• when water is scarce; a more extensive root system abosrbs more at the cost of reduced growth 

stomata

regulate gas exchange in leaves and control water loss

what happens to water levels when plants take in CO2?

lose water

what does a plant do to prevent water loss?

keep stomata closed, but this lowers CO2 levels, and slows calvin cycle

C4 photosynthesis 

• adaptation found in some grasses in arid climates 

  • allows more co2 to enter leaf while stomata is open, less water is lost

CAM photosynthesis

another adaptation of photosynthesis in arid environments

• stomatas are open only at night , ambient T is cooler.

• keeps CO2 cytoplasm low, allowing more diffusion

during the day, stomata stay closed to minimize evaporation w high ambient T

rate of absorption is limited by what?

root surface area

less absorption leads to _ concentration throughout the plant 

lower concentration 

nitrogen is a component of _ and _. it affects the rate of _

chlorophyll and rubsico.

photosynthesis

what is an adaptation to low nutrients ?

slower growth

explain the 3 sisters planting method 

• squash: provides shade to reduce evaporation 

• corn: grows tall and becomes support 

  • bean: legumes have rhizobia which fix nitrogen,  enriching sol