L1: Gaining light in different environments Flashcards
how do plants cope with environmental change
acclimation
what is acclimation
- a phenotypic change
- occurs over a short time (days to weeks) and within an organisms lifetime
- not genetic
- sometimes involves differences in phenotype
give two examples of acclimation in plants
- the hardening off of plants. Some plants can survive freezing temperatures if temperature gradually drops lower and lower each night over a period of days or weeks
- sun versus shade leaves
Describe sun leaves
- thicker leaf
- thicker cuticle (for greater protection)
- more chlorophyll per unit area
Describe leaves
- thinner leaf
- increased leaf area
What is adaptation
- a genetic change
- occurs over time scales covering multiple generations of populations
- evolutionary change of phenotypes
what is an example of adaptation
ecotypes of same species along environmental gradients (eg. altitudes) with different growth responses when grown together
What influences plant design and development? main way
- plants depend on light energy they gain from photosynthesis ( they must exceed the compensation point)
- solar radiation is also important for determining temperature and causing water stress
- if plants elevate light capturing structures above competitors, then must cope with gravity and wind, being more conspicuous to herbivores
- must avoid photoinhibition at high light intensities
What compensation point
- the minimum a plant needs to photosynthesize to survive
- when the rate of photosynthesis = rate of respiration
true or false, to grow, a plant must be above the compensation point.
true, so that to balance respiratory demands against photosynthetic rate; particularly important in low light environment
What is photoinhibition
- photochemical response to excessive sunlight
what are the implications of photoinhibiton
- causes degredation of photosystems and bleaching of chlorophyll of photo oxidation; thus plants in high light environment adapt to reduce light available
What are the trade offs plants need to balance to gain light in different environments
- ) Economics of gas exchange
- transpiration is an inevitable consequence of photosynthesis
- benefits of CO2 gained, against cost of H2O lost - ) Economics of thermoregulation
- a large leaf orientated for maximum light interception minimize the ability of the leaf to dissipate
- benefits of light to capture against cost of excessively raised or lowered temperature - ) Economics of support
- benefits of increased photosynthetic area against cost of mechanical support to cope with gravity and wind shape - ) Economics of herbivore interactions
- benefits of increased photosynthetic area against cost of attractiveness to herbivores
what is transpiration
the diffusion of water into the atomosphere due to stomatal opening resulting in water loss
what is the thin layer and where is located
the thin layer is located on the surface of the leaf; it moderates the diffusion of both CO2 and water ; slows own the diffusion
true or false, the thin layer changes depending on the environment the leaf developed in
true
why does water diffuse faster than CO2
this is because the concentration gradient of water vapor is 100 times that of CO2, meaning that water can diffuse out of the leaf 100 times faster than CO2 can diffuse in the stomata are open
true or false, stomata control water loss to maximise water use efficiency
true
what does WUE stand for
carbon gain for water lost
true or false, transpiration also carries heat away from the plant since a liquid is always cooled as some of it evaporates
true, thus transpiration affects leaf temperature
What is the boundary layer
is the layer of still air close to a leaf
what is the purpose of the boundary layer
impedes heat transfer and influences temperature of leaf
what does the thickness of the boundary layer depend on
the wind speed and the leaf size
true or false the transpiration increases with wind velocity and leaf temperature
true
true or false, the thickness of a boundary layer increases with length from the windward edge of the leaf
true
true or false, a large leaf will have a thicker boundary layer therefore it will be cooled much slower than a small set leaf
true
is it possible that heat and water balance are major determinants in the evolution of the leaf shape
true
true or false, the boundary layer is thinner at the edges of the leaf than in the middle of the leaf
true
if the wind speed is fast, does that cause the boundary layer to become thinner
true
what are the advantages of sunken stomata (w/ stomatal crypts)
prevents water loss
true or false, the boundary layer is thicker and more intact in larger leaves
true …..
true or false, leaves divided up into numerous sections decrease the size of the boundary layer that surrounds each part of the leaf
true
what is the trade off herbivory
trade off the ability to photosynthesize against allocations to making leaves tough and less attractive to increase leaf life span
why do plants in low nutrient ecosystems tend to have tougher leaves
this is because theyre harder to replace
What structures of leaf are architecturally engineered to optimize photosythesis
- leaf size and shape
- leaf angle and movement
- leaf rolling and folding
- phyllotaxy (the problem of self shading)
- flexible arrangement of modular structure
- foliage dispersion and crown shape
true or false, as rainfall increases, the leaf width increases
true
true or false, leaves are thicker and smaller in species occupying habitats with low moisture availability, high light, or low nutrients
true
why are toothed leaves are often thin
this is because of problems of mechanical support around secondary veins
what does entire leaf mean
no teeth
true or false, there is a positive correlation between the mean annual temperature and the percentage of tree species with entire margined leaves
true
true or false, leaf teeth commonly expand and mature faster than the bulk leaf, so in habitats with low temperature, teeth could play an important role in maximising leaf growth early in the season
true
what are the two most basic characteristics of a plant affecting the efficiency of light capture
crown shape and arrangement of leaves within the crown
what orientation do leaves present on the upper part of the plant tend to adopt
a steep leaf angle and rolled edges
what orientation of leaves in heavily shaded areas often adopt
more horizontal and planar
why do leaves in high light environment tend to have greater inclination and more rolling and folding
to reduce leaf area ( less photoinhibtion, water loss and heat stress)
what is photoinhibition
decrease in photosynthetic rate
what is diaheliotropuc
leaf blade kept perpendicular to sun’s rays
what is paraheliotropic
leaf blade kept parallel to sun’s rays
true or false, arrangement of leaves on a stem (phyllotaxis) can influence the amount of self shading a plant receives
true
true or false, leaf shades below it to 50-70 times its diameter
true
what are the characteristics of low light environments ( tropical forest understory)
- low self shading
- large amount of leaf area displayed
- high interception available light
- horizontal leaf surfaces
what are the characteristics of desert plants (high light environment)
- high self shading
- smaller amount of leaf area displayed
- foliage at higher angles
- more leaf rolling + folding
- lower interception available light
desert plant canopy shape
flat top
temperate region canopy shape of plants
conical, to be perpendicular to the sun
true or false, leaves are thinner and bigger in fertile, wet environments and vice versa
true
