plant Flashcards
parts of leaf from top to bottom
cuticle, upper epidermis, palisade mesophyll layer (with chloroplasts), spongy mesophyll lAyer (with vascular bundles), lower epidermis, cuticle with stomata
cuticle function
Waxy: reduce water loss by evaporation
Transparent: light reaches cells within for photosynthesis
upper epidermis function
protect leaf from physical damage
palisade mesophyll layer function
more chloroplasts in the upper palisade tissue, more light energy absorbed near leaf surface to be converted to more chemical energy in the manufacture of sugars
spongy mesophyll layer function
loosely arranged with air particles to allow rapid diffusion of CO2 and O2 in and out of mesophyll cells
petiole (leaf stalk) function
holds leaf in position to absorb maximum light energy
lamina (leaf blade) function
broadness provides large SA for maximum absorption of light
thinness provides short diffusion distance for gases, enables light to reach all mesophyll cells
stomata function
opens in presence of light, allowing carbon dioxide to diffuse in and oxygen to diffuse out of the leaf
guard cells change shape causing the stomata to close and open. adjusts plants transpiration rates to external environmental conditions. (by regulating diffusion of water vapour)
xylem and phloem function
xylem transports water and mineral salts to mesophyll cells, phloem transports sugars SUCROSE away from the leaf
cambium
wall separating xylem and phloem
what is transpiration
process which water vapour is lost from aerial parts of the plant as a result of evaporation of water
- from surface of (spongy) mesophyll cells via the air space in the leaf to the atmosphere
- then diffusion of water vapour out of the leaf thru stomata, down a water vapour conc grad
(mesophyll cells have thin water film arnd the outside the of cell)
root pressure
active transport of ions into root xylem vessel lowers its water potential resulting in accumulation of water in the roots by osmosis and flows upwards a few metres but insufficient to reach tall tree leaves.
transpiration stream
- as water leaves xylem vessels in leaf, a tension is set up on the entire water column in the xylem tissue
- as water has extremely strong adhesive and cohesive properties, results in flow of water up plant
- no energy expenditure
humidity affecting transpiration
low humidity increases water vapour conc grad between leaf and atmosphere, increasing water evaporation
temp affecting transpiration
a rise in surrounding temp will increase heat energy which in turn increases the evaporation of water from the surface of the mesophyll cells
wind affecting transpiration
the stronger the wind, the higher the rate of transpiration as wind blows away saturated air from around the leaves, maintaining a conc grad between the leaf interior and air outside stomata.
light intensity affecting transpiration
in sunlight during photosynthesis, the stomata will open and become wider due to gaseous exchange, allowing more water vapour to diffuse into the atmosphere
water supply affecting trnaspiration
ample water supply will keep leaf cells turgid. Stomata remains open.
when does wilting occur
under strong sunlight, when rate of transpiration exceeds rate of absorption of water by roots
what happens when plants wilt
-cells lose turgor, become flaccid
- reduction of exposure of leaf surface to sunlight
- closure of stomata from excessive water loss, guard cells become flaccid
- decrease in rate of photosynthesis due to decrease in uptake of carbon dioxide, water and exposure of leaf area to sunlight
transpiration is a consequence of gaseous exchange
Stomata must be open for gaseous exchange
as CO2 is needed for the light-indp stage of photosynthesis
while O2 is the by-product of light-depd photosynthesis
water vapour diffuse out thru open stomata during TRANSPIRATION
properties of pholem
Sieve tubes, companion cells.
- sieve tubes are long, narrow, elongated elements connected end-to-end with reduced cytoplasm and absence of nucleus and many other organelles to maximise space for translocation of products of photosynthesis from leaves to other parts of the plant.
- sieve tubes are living tissues maintained by companion cells.
why does rate of photosynthesis not increase even when I continue increasing the limiting factor?
As this point, light is no longer the limiting factor of photosynthesis.
CO2 concentration could be the limiting factor OF PHOTOSYNTHESIS instead.
Stages of light-depd and indp photosynthesis
6 steps
- photolysis of water molecules to hydrogen and oxygen. oxygen released as by-product.
- hydrogen accepted by NADP: it is reduced to NADPH
- CO2 diffused in stroma through stomata is fixed with ribulose biSphosphate in the presence of RuBisCo enzyme
- Energy from adenosine triphosphate and hydrogen from NADPH is used to reduce 2 molecules of glycerate 3-phosphate to triose phosphate.
- NADPH and adenosine triphosphate regenerate ribulose bisphosphate from triose phosphate so more CO2 can be fixed
- NADPH and adenosine triphosphate activate triose phosphate for synthesis of complex organic compounds like carbohydrates (sucrose, starch), lipids and amino acids.
