114 total points possible

Biology 332
Spring 1997

Exam II


Distinguish xylem and phloem. (10 points)
cell type that conductsscler-enchymapar-enchyma
thickness of cell wallthick       thinthick       thin
presence of cytoplasmpresent       absentpresent       absent
primary solute being conductedmineralssugar
primary direction of flow in tree trunk (summer)up       downup       down

Name and briefly describe the components of transpiration. (9 points)
pushroot pressureendodermis pumps minerals into vascular cylinder, water follows by osmosis, pressure develops
climbcapillarityxylem sap has surface tension that helps a mensicus form to climb xylem walls
pullevaporationwater evaporates from leaf into atmosphere, water removed from xylem column is cohesive to other water molecules in column due to H bonding, lifts them up column

Name and briefly describe the components of translocation. (6 points)
pushphloem loadingleaf bundle sheath pumps sugar into phloem, water follows by osmosis, pressure develops
pullphloem unloadingpericycle in root removes sugar by active transport, water follows, pressure reduced

Compare the activities and products of the two cambia. (10 points)
vascular cambiumcork cambium
name of sclerenchyma derivativessecondary xylemcork
name of parenchyma derivativessecondary phloemphelloderm
parenchyma derivative forms oninside       outsideinside       outside
most common derivative cell typeparenchyma       sclerenchymaparenchyma       sclerenchyma
name of chemical loaded into cell walls of sclerenchyma derivativesligninsuberin


In the space below, diagram a cross section of a dicot root (no secondary growth, just primary plant body structure). Label it completely with the name and distinguishing major function of each labeled structure. (14 points)

xylem--conducts water and minerals up plant
phloem--conducts water and photosynthate from leaves to rest of plant
pericycle--forms lateral roots
endodermis--selective mineral uptake via active transport
cortex--storage of photosynthate as starch or oil
epidermis--mineral and water intake
root hair--increase surface area, cation exchange

Short Answers (6 points)
Why is there no collenchyma in the root cross section?   root is supported by soil

What is the xylem/phloem arrangement in the dicot root?   radial

What is the xylem maturation pattern in the dicot root?   exarch

What metabolic process provides the energy in all living cells in the root?   respiration

What external chemical allows the endodermis to function effectively?   suberin

What membrane chemical(s) is(are) critical to the major endodermis function?   transport proteins

In the laboratory you cut a stem and placed it in a 1% eosin y (dark red) solution. The stem and leaves became progressively red. What would you expect to happen if you repeated that project, but put a stem with a complete and intact root system in the dye for a similar duration? Explain briefly. (5 points)

There will be no red dye transported in xylem. The eosin will penetrate the root apoplastically until it reaches the endodermis. The endodermis will not have the appropriate transport protein for active eosin uptake, so the dye cannot enter that cell or the vascular cylinder. Transport is halted at the apoplastic barrier: the casparian strip.


In the space below, diagram a cross section of a woody dicot stem. Label it completely with the name and the major distinguishing function of each labeled structure. (24 points)

pith--storage of defense molecules
primary xylem--conducts water and minerals up
secondary xylem--conducts water and minerals up...supports trunk
vascular cambium--divides meristematically to make secondary xylem/phloem
secondary phloem--conducts water and photosynthate up
primary phloem--conducts water and photosynthate up
bundle cap--supports stem while in primary body
cortex--photosynthesis (some starch storage)
phelloderm--live cell of periderm-respiration
cork cambium--divides meristematically to make phelloderm and cork
cork--loaded with suberin to waterproof external "skin" or "bark"
epidermis--window for light and water barrier for primary body

How would a monocot stem be different from the diagram above? (4 points)
no secondary xylem or phloemno periderm
no pithnumerous vascular bundles-complex array

Given that a stem must grow and support itself in the air, describe how this might be accomplished during the life of the plant. A list of the sequence of the support elements would be appropriate. (5 points)
turgor pressurecollenchyma during growthfibers for primary bodyprimary xylem for old primary bodysecondary xylem for secondary body

Describe what is produced when fusiform initial cells of the vascular cambium divide by mitosis and lay down a new wall in the... (3 points)
cell produced>
tangential plane2o xylem or phloem
transverse planeray initials
radial planemore fusiform initials


What are the two major functions of leaves? (2 points):   photosynthesis       evaporative cooling

Give two examples of terrestrial leaves that each have one additional and very different unusual function. (4 points)
ExampleUnusual Function
pea tendrilanchorage and support to grow on environment structures
venus fly traptraps and digests insects for mineral supply

What is different about the metabolic functions of the mesophyll in a C-4 tropical grass compared to the mesophyll of a C-3 temperate grass? (1 point)

The mesophyll of the C-4 tropical grass does the C-4 carbon dioxide pumping rather than the C-3 Calvin cycle of the C-3 temperate grass.

What cell structure would be an unusually prominent feature of the mesophyll cells of a CAM leaf? (1 point)

The vacuole to store water and especially malate during the carbon fixation at night

How do you know that a leaf contains gas? Name/describe briefly three different ways you have demonstrated this. (3 points)
Leaf discs float on water before aspiration or heat treatment Drove gas out with high pressure Drove gas out with reduced pressure (partial vacuum)

Leaf Disk Project: (7 points)
Why don't leaf discs placed in the dark sink immediately in a bicarbonate buffer?
They contain 70% (approx) nitrogen gas that cannot be utilized to make them sink.
Why do leaf discs that have been aspirated refloat in the light in a bicarbonate buffer?
The mesophyll does photosynthesis producing oxygen gas that refills the gas space and the discs refloat.
Why won't leaf discs that have been aspirated refloat in the light in a plain buffer?
Carbon dioxide (as bicarbonate) is required to run the Calvin cycle, which is needed to recycle the NADP back to the light reactions to make oxygen via photolysis (Hill reaction). If there is no Calvin Cycle, the light reactions stop, the discs won't refloat!
Why won't aspirated white leaf discs refloat in the light in a bicarbonate buffer?
Chlorophyll is needed as the primary light receptor for the light reactions that generate the oxygen to refloat the discs.
Aspirated green leaf discs are refloated in the light in a bicarbonate buffer. The container is moved into darkness. What happens?
The leaf discs sink.
Why does that happen?
Respiration uses up the collected oxygen gas from the spaces in the leaf so they sink. (CO2 dissolves in buffer)
What gas refloats the aspirated green leaf discs in the light in a bicarbonate buffer?

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