Topic 7 Flashcards
Photosynthesis
process where energy from the sun is used to transform CO2 into carbohydrates and O2
Where does photosynthesis take place in plants
specialized cells (mesophyll cells) in the leaf
Process of photosynthesis
Chlorophyll (light absorbing pigment) traps light energy → synthesizes ATP → this energy drives CO2 → O2 + sugars
Photosynthesis is depend on..
enzyme called rubisco
Photosynthesis can be broken down into 2 reactions
- light reactions
- dark reactions
Light reactions
generate energy transferred by carrier molecules and produces O2
Light reaction process
light energy is funnelled into energy carriers (ATP or NADPH) via elections and H2O is the source of elections yielding waste O2 as byproduct
Dark reactions
fix carbon (CO2) into sugars. energy carriers are used to power the calvin cycle. depleted energy carriers are returned to light reactions
Dark reaction process (C3 pathways)
CO2 fixed by rubisco in a 3 carbon compound in Calcin cycle. simple sugars (glucose) eventually formed
C3 pathway drawback
rubisco can bind oxygen instead of CO2 causing photorespiration, decreased efficiency of photosynthesis because energy is lost powering calvin cycle, has no CO2 fixation and leads to reduced sugar output
Respiration
in the mitochondria of cells, carbs are broken down to generate energy (ATP) releasing CO2
Plants both use and produce ..
CO2
Difference in the rates of using and producing CO2 =
net photosynthesis = photosynthesis - respiration (aka = carbon uptake-carbon loss)
CO2 diffuses in to the leaf through..
openings in the surface of the leaf (stomata)
Transpiration
CO2 diffuses into the leaf, water diffuses out of the leaf
CO2 evers
atmosphere»_space;> leaf
Water leaves
atmosphere «_space;leaf
Plants must require what essential resources
light, CO2, water, nutrients
Leaf tissue
photosynthesis (uptake of CO2)
Stem tissue
structural support (gain access to light)
Root tissue
water and nutrient uptake from soil
Plants adapt to different environmental conditions to keep ..
- photosynthesis > respiration (+ carbon balance to grow)
- photosynthesis > transpiration (+ water balance to survive)
Individuals must tolerate environmental conditions that..
influence the acquisition of all essential resources
Adaptations that allow a plant to successfully grow, source and reproduce under on set of environmental conditions may limit its ability to..
do equally well under different environmental
Tree top (direct sunlight)
smaller, thick leaves to reduce water loss in direct sunlight
Tree bottoms (shade)
larger, thinner to increase photosynthetic rate in shade
Leaves in arid environments minimize evaporation by
angling leaves away from the sun
In shade photosynthesis is
limited by availability of light
Shade tolerant (low light)
lower production of rubisco in leaf tissue (don’t expend energy producing high amounts of rubisco) equals lower maximum photosynthetic rate
Shade tolerant plants compensate by
- higher production of chlorophyll (light absorbing pigment)
- higher leaf surface area
- higher growth of leaves than roots
Increase the photosynthetic surface area to..
offset the decrease in photosynthetic rate (due to low rubisco)
Shade tolerant grow..
similarly under sunlight and shade
Shade intolerant grow..
highly under sunlight and low under shade
Mountain Avens
flowers track movement of the sun. parabolic formation of steals concentrate light to maintain constant temp of 25C
Photosynthesis and respiration respond directly to
variations in temp
As temp rise above 0 rate of both respiration and photosynthesis
increase
Protein denature and respiration and photosynthesis ..
stop
Heat loss of leaf by convection
transfer of heat to a moving fluid body (ie. Wind)
Heat loss of leaf by conduction (radiation)
Heat moving from a warmer to a cooler body
Heat loss of leaf by evaporation (transpiration)
Evaporation causes a loss of heat energy and temperatures drop due to evaporative cooling
Transfer of heat from a plant to environment is influenced by..
the boundary layer (layer of still air adjacent to surface of leaf)
Conditions of true boundary layer are
slightly different from the environment because its modified by water and CO2 moving to/from plant surface
Boundary layer of leaf is related to
size and surface roughness (small smooth leaves lose heat faster (desert plants))
Pubescence
small light coloured hairs that line leafs surface and reflect. less heat obtained from solar radiation and creates insulted boundary layer
Skunk cabbage
Metabolically generates heat in the spring to thaw snow and attract pollinator. endothermic plant
Accumulation of compounds (sugar, amino acids, etc)
lowers the freezing point of water to prevent ice4 formation
Supercooling
Special anti freeze proteins preventing ice crystal growth allowing plants to survive up to -35C. present in floral and shoot buds
Frost hardening
Changes composition of membranes allowing cells to export water and ice to form between cells instead of within. allows survival up to -50C
Deciduous trees
adaptive loss of leaves as temp drops in fall. programmed death to survive winter when leaves would freeze
When the atmospheric humidity and soil moisture levels are low plants will
close their stomata
Mid day stomata close to..
conserve water (short term scale)
Leaf curling or wilting
reduces surface area of leaf exposed to solar radiation and water loss
Moderate time scales (acclimatory/developmental) water plant adaptions
individuals can balance leaf vs root tissue in wet and dry conditions
Wet conditions (ideal)
increase leaf tissue and lower root and shoot. increase the photosynthetic surface (maximizes CO2 uptake and photosynthetic rates → growth)
Dry conditions
increase root tissue and decrease leaf and shoot. increases the volume of tissue in soil to extract water and reduces surface area of leaf tissue to reduce water loss
Leaf morphology adaptations to dry conditions
- smaller thicker leaves (water storage)
- smaller stomata
- cover leaves in wax, resin, little hairs
C4 photosynthesis
3% of plants most common in grasses
CAM photosynthesis
7% of plants, common in epiphytes and cacti.
Alternative photosynthetic pathways
- C4 photosynthesis
- CAM photosynthesis
CAM photosynthesis adds an extra step in the conversion of
CO2 into an organic acid before entering Calvin cycle (dark reactions)
Advantages of photosynthetic adaptations to water
- Reduces O2 binding by rubisco (reduced energy loss)
- Concentrates CO2 to rubisco (faster fixation speeds)
- Much higher maximum rate of photosynthesis is possible
Due to higher photosynthetic rate a plant loses ..
less water per unit go photosynthetic product. means C4 and CAM plants have a greater water use efficiency relative to C3 plants (successful in hot dry climates)
