TOPIC 7: PLANT ADAPTATIONS Flashcards
Photosynthesis
process where energy from the sun is used to transform CO2 into
carbohydrates (simple sugars) and O2
Chlorophyll (light absorbing pigment) traps light energy → synthesizes ATP →
this energy drives CO2 → O2 + sugars
Where does photosynthesis take place?
takes place in specialized cells (mesophyll cells) in the leaf
rubisco
enzyme that catalyzes part of the photosynthetic reaction
- makes rxn happen after
- more of it= faster rxn
- Respiration:
: in the mitochondria of cells (plant & animal) - carbohydrates are broken down to generate energy (ATP), releasing CO2
Net Photosynthesis
Plants both use and produce CO2 and the difference in the rates of these two processes
is:
Net Photosynthesis = Photosynthesis – Respiration
* (= carbon uptake – carbon loss)
stomata
openings in the leaf thru which CO2 diffuses into the leaf
transpiration
- CO2 enters: atmosphere»_space; leaf
- Water leaves: atmosphere «_space;leaf
What essential resources do plants require?
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 the soil
Compare the adaptations that plants have at the tree top vs tree bottom
- Tree Top (direct sunlight)
- smaller, thicker leaves
→ reduces water loss in direct sunlight - Tree bottom (shade)
- larger, thinner
→ increases photosynthetic rate in shade
Plants are either…..
to low light (shade-tolerant) or high light (shade-intolerant)
Shade-tolerant (low light):
In shade: photosynthesis is limited by availability of light
* lower production of rubisco in leaf tissue (do not expend energy producing high amounts of rubisco)
Lower maximum photosynthetic rate
How do shade tolerant plants compensate?
- 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 lower amount of rubisco)
What happens to the plant growth if you put a shade intolerant plant in the shade vs if you put a shade tolerant plant in the sun?
- Shade-intolerant - high growth rates under sunlight, but low rates in shade
- Shade-tolerant - grow similarly under sunlight and shade
- cannot increase growth dramatically in sunlight because limited by rates of
photosynthesis (lower concentration of rubisco)
Mountain Avens
Flowers track the movement if the sun
- Parabolic formation of petals concentrate light to maintain a constant temperature of
25⁰C.
- Keeps sex organs of the plant warm and creates a microhabitat favourable for
pollinators
Mountain Avens
Flowers track the movement if the sun
- Parabolic formation of petals concentrate light to maintain a constant temperature of
25⁰C.
- Keeps sex organs of the plant warm and creates a microhabitat favourable for
pollinators
Plants vs. Temperature
Photosynthesis and respiration respond directly to variations in temperature
* As temperatures rise above 0, rates of both respiration and photosynthesis increase
* A maximum rate of photosynthesis and respiration occur at different points
* Proteins denature and both processes stop eventually
What must a leaf do to maintain optimal levels of photosynthesis?
must exchange excess heat with the
surrounding environment
Heat loss by convection
transfer of heat to a moving fluid body (ie. Wind)
Heat loss by conduction
- Heat moving from a warmer to a cooler body
Heat loss by evaporation
Evaporation causes a loss of heat energy and temperatures drop due to
evaporative cooling
Pubescence
small light-coloured hairs that line a leaf’s surface and reflect
- Less heat obtained from solar radiation
- Also creates a insulative boundary later
Skunk cabbage
- Metabolically generates heat in the spring to thaw snow and attract pollinator
- Endothermic plant
Accumulation of compounds
- Sugars, amino acids (proline) and other solutes
- Lowers the freezing point of water to prevent ice 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 the temperature drops in the fall months
- Programmed death to survive the winter when the leaves would freeze
Plants vs. Water Availability
- Plants have evolved a range of adaptations in response to the variability of precipitation
and soil moisture - When the atmospheric humidity and soil moisture levels are low plants will close their
stomata - Can also occur on a daily basis, where mid day, stomata close to conserve water
- Remain open during the mornings and later afternoon
- Short time scales:
Regulate opening and closing of stomata during different parts of the day
e.g. close stomata during hottest part of the day when highest water loss through evaporation
* Leaf curling or wilting – reduces the surface area of the leaf exposed to solar
radiation and, thus, water loss
- Moderate time scales:
- Individuals can balance leaf vs root tissue
- Wet conditions (ideal) → ↑ leaf tissue & ↓ root and shoot
- Increase the photosynthetic surface (maximizes CO2 uptake and
photosynthetic rates → growth) - No increase in other tissues (i.e. shoot, root) because this
increases the rate of respiration (CO2 loss) - Dry conditions → ↑ root tissue & ↓ leaf and shoot
- Increases the volume of tissue in the soil to extract water
Reduces the surface area of leaf tissue to reduce water loss
Long time scales:
- leaf morphology adaptations to dry conditions:
- smaller and thicker leaves (water storage)
- smaller stomata
- cover leaves in wax, resin, little hairs (e.g. cactus)
- Some species have alternative photosynthetic pathways
- C4 photosynthesis
- 3% of plants, common in grasses
- CAM photosynthesis
- 7% of plants, common in epiphytes and cacti
- Add an extra step in the conversion of CO2 into an organic acid before entering
Calvin cycle (dark reactions)
