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EEB 162 Exam Latest Update
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EEB 162 Exam Latest Update
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EEB 162 Exam Latest Update5 typical parameters of a photosynthetic light response curve. how would these vary
between sun-adapted vs. shade adapted? - Answer 1. saturation irradiance
2. dark respiration (Yint)
3. quantum yield (slope of left hand portion)
4. light-saturated assimilation rate (Amax)
5. light compensation point (xint)
Sun-adapted: Increased everything though similar quantum yields
How are leaves specialized for internal CO2 uptake? Name two ways - Answer 1.
transparent epithelium: convex cells that act as lenses to focus light to chloroplasts
2. palisade cell layers: shaped like rods with large SA/volume ratio; guides light to
spongy mesophyll tissue
How can you tell if a leaf is adapted to shade by looking at its cross-section? Name two
features - Answer 1. Thin due to few layers of palisade cell layers
2. more spongy mesophyll tissue to capture diffuse light
3. choloroplasts are spread out in plane of leaf
Explain phloem structure and function - use: sieve elements, sieve cells, companion
cells, gridling, translocation, sieve areas, p-proteins, non-reducing sugars. - Answer
phloem transports sugar (photosynth product) from mature leaves to storage and
growing tissues. It also conducts signal molecules and redistributes water thruout plant.
it extends throughout the body parallel to xylem; in trees with secondary growth, phylem
is on the outside of vascular cambium with the outer layer dysfunctional due to xylem
(wood).
Phloem can be removed by gridling the tree (removing the bark) - this causes sugar
transport between the leaves and roots to stop.
Phloem is composed of several cell types: sieve elements (include sieve cells in
gymnosperms and sieve tube elements in angiosperms; do translocation - transport of
photosyntheetic molecules driven by positve pressure), companion cells, parenchyma
cells which store and release food, fibers and sclerids for protection and strength, and
occasionally lacticifers for protection.
COMPANION CELLS are associated with sieve tube elements via plasmodesmata and
, they assist with transport of photosynthetic produces from mesophyll cells to seive
elements and they also provide atp to sieve elemetns. THere are three types; ordinary
companion cells (few plasmodesmatal connections to cells except its own sieve
element, symplastically isplated from surrounding cells), transfer cells (similar, have
finger like ingrowths of cells walls to increase surface area for solute transfer from the
apoplast), and intermediary cells (only one involved in symplastic loading; have multiple
plasmodesmatal connections with bundle sheath cells which can take up solutes from
cytoplasm).
SIEVE ELEMENTS are living cells which lack certain organelles like nuclei but do have
other organelles like mitochondria. They are soft and deal with translocation. They have
SIEVE AREAS in their cell walls where pores can connect to other sieve elements. In
angiosperms, sieve areas can di
How fast does sap move on avg in the phloem?
What is the driving force for movement of phloem sap?
Why do phloem loading and unloading require water to flow into the phloem from the
xylem? - Answer Sap moves 1m/hr.
The driving force for movement of phloem sap is a pressure gradient via bulk flow.
The pressure gradient due to un/loading of sugar into sieve tube cells leads to osmosis
of water generating pressure. Phloem loading: sugar in sieve elements = low solute
potential = low water potential == water flows in.
Unloading in sink: unloading increases solute potential = increased water potential ==
water leaves so that total p potential falls.
What facts support the pressure-flow hypothesis for phloem translocation? - Answer
Pressure flow hypothesis is supported by the facts that the sieve pores are open, that
phloem transport in a single sieve tube always occur in one direction at a time and that
the flow does not require energy. The lack of energy requirement can be seen by the
fact that phloem transport can be maintained even in chilled leaf petioles.
What are the differences between apoplastic loading and symplastic loading? Describe
the differences in pathway and sugar molecules involved.Why does apoplastic loading
require energy? - Answer Apoplast: involves movement through the extracellular cell
wall space across membranes. It involves movign sucrose against its concentration
gradient and thus requires energy - it uses a H/ATPase to transport H+ into the apoplast
and a H+/sucrose transporter moves sucrose from apoplast into SE-CCell complex. It is
fast. It is regulated by solute potential in SE, turgor pressor of SE, sucrose
concentration in the apoplast and available number of symporters.
Bundle Sheath to phloem parenchyma cell
Bundle sheath to ordinary CC (not via plasmodesmata) to SE
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