|- ____ = ____ /||97|
|This exam was designed to test your understanding from prerequisite courses: Principles of Biology, Organismal Biology, Cell and Molecular Biology.|
A general suggestion:
Plants produce a variety of materials that are useful to humans. From this point of view, name at least 12 fundamentally-different reasons to study plants. 12 points
Other possible answers include: beautification, reduce greenhouse gas, limit erosion, provide animal habitat, provide shade, etc.
oxygen wood latex resins ozone paper fossil fuel fiber food medicine flavors/fragrances jobs
In the space below, sketch the EM view of a "typical" plant cell (that probably means a photosynthetic parenchyma cell) and label it completely. For each structure labeled, also indicate its single most-important function. You only need to show one of each type of organelle. 24 points.
middle lamella - glue holds cells together
cell wall - turgor pressure development
cell membrane - import/export
nucleus - replication/transcription
ribosome - translation
endoplasmic reticulum - internal transport
dictyosome/Golgi - sorting/packaging
vesicle - import/export containment and delivery
vacuole - waste processing
mitochondrion - Krebs cycle, electron transport, oxidative phosphorylation
chloroplast - photosynthesis
cytosol - glycolysis/sucrose synthesis
plasmodesma - intercellular communications
peroxysome - photorespiration
glyoxysome - fat metabolism
microtubules - mitosis
microfilaments - cyclosis
intercellular space - gas exchange
Scoring was 12 structures and 12 functions from the above list. Most of the class earned only 16-18 points, representing only a 9th grade understanding of cell biology.
Fill-in Story 33 points.
The cell that gives rise to a parenchyma cell is a meristematic cell, which has as its characteristic function, cell cycle/division. This kind of cell goes through the cell cycle approximately once in 24 hours. During the first few hours of this cell's life, the cell is in the portion of inter-phase called G1. During these hours, the cell is primarily involved in protein synthesis. In this process, the DNA found in the nucleus is transcribed into RNA which, in turn, is exported from the nucleus. In the cytosol, it is translated into protein. The next part of the cell's life is the S portion of inter-phase. During these next few hours, the DNA is replicated into a second complete set. The cell then enters the G2 portion of inter-phase. The activities in this portion are similar to those observed in the first few hours of this cell's life. Upon completion of this first phase of the cell's life, the cell begins the four-phase process of mitosis. The first phase is called pro-phase, in which chromosomes condense out of the chromatin and the nuclear membrane disappears. The second phase is called meta-phase, in which the spindle apparatus forms and the chromosomes are pushed to the equatorial plane. During the third phase, ana-phase, the chromosomes split at the centromere and sister chromatids are pulled to opposite poles of the cell. Finally in the fourth phase, telo-phase, the spindle apparatus breaks down and the nucleus reforms. With this four-phase process complete, the cell undergoes cytokinesis to finish its life. In plant cells this final step involves formation of a cell plate/phragmoplast.
The cell involved in the story above would look somewhat different from the one you sketched on the first page of this test. Describe the major differences. 5 points.
The meristematic cell...
Tell the story of how and where the process of respiration takes place. A reasonably-detailed flow chart might be a useful way to demonstrate your knowledge, but a sketch with suitable process labels might also work. You could also write a few paragraphs. The choice is yours! 30 points.
Glycolysis 10 best elementscytosolKrebs Cycle 10 best elementsinputs: ATP + NAD + carbohydrate
process: enzymatic, several steps
control: PFKase, ADP up-regulates, ATP/Citrate down-regulates
outputs: ATP + NADH + pyruvatemitochondrial matrixElectron Transport/Oxidative Phosphorylation 10 best elementsinputs: Pyruvate/Acetyl Co A + ADP + NAD + ubiquinone
process: enzymatic, several steps
control: pyruvate availability via PFKase see above
outputs: ATP + NADH + ubiquinol + CO2mitochondrial cristaeinputs: NADH + ubiquinol + O2 + ADP
process: electronic, several steps, proton pump
control: NADH availability via PFKase see above
outputs: ATP + H2O + NAD + ubiquinone
If your score is -12 or more deducted, then you don't have the college version of respiration in your mind yet!
Photosynthesis: a "Fantastic Voyage"
You and some biology partners devise a sort of submarine, which you board, and which your partners then shrink down to the size of a ribosome. They load the ship into a biolistic gun and shoot you into the cells of a Crassula leaf. You are left to explore for several days. You hope to make your way into a chloroplast. Your ship is equipped with fluid propulsion, light sensors, oxygen and carbon dioxide sensors, a membrane-penetrating pH sensor, and electrodes to change the surface charges of your ship. The penetrating pH sensor is interesting in that it allows you to monitor the pH on the opposite side of a membrane while your ship stays safely on the other side. You may assume that your partners will keep the leaf at a constant temperature in spite of the day/night cycles.
It turns out your ship has been delivered into the nucleus. How will you get out? You don't want to use your surface charge electrodes as this would use too much power just yet. 2 points.
Use your fluid propulsion to exit by a pore in the nuclear envelope
Maybe: use a few surface electrodes to attach to an RNA or ribosome subunit and "hitch" a ride through a pore.
Assuming all went well with your nuclear exit, you are in the cytosol. You use your propulsion unit to drive up to a large membrane that looms ahead. To test the hypothesis that this is the vacuole, how would you proceed to make a decision? 5 points.
Note: Crassula is a CAM plant!
Insert pH sensor through membrane
Use light sensor to monitor light
Monitor pH changes for at least 1 day/night cycle
If pH drops drastically at night, and
recovers when light comes back on,
then the sensor is inserted in the vacuole.
OK, so that was a vacuole. You find your way to a colorless membrane but it appears to be green inside this membrane. It is a likely prospect! How will you get inside? 5 points.
Assuming you got inside the organelle, you should be in the chloroplast. Now, how can you be sure you are not in the mitochondrion by using the sensors you have available to you? 5 points.
Use O2 and CO2 sensors to monitor changes
through day/night cycle by using light sensor to determine coordination.
As light comes on, O2 should increase and
CO2 should decrease if this is a chloroplast.
If you are indeed in a chloroplast, how can you tell that you are indeed in the stroma and not the thylakoid lumen? Again, use the sensors available to you to make your decision. 5 points.
Insert pH sensor through any nearby green membrane
Use light sensor to determine day/night cycle while monitoring pH
If pH drops just as light comes up, then probe is in the thylakoid lumen and ship is in stroma
Also monitor O2 sensor and if O2 increases suddenly when light comes on, then ship is in thylakoid lumen
Also monitor CO2 sensor and if CO2 decreases suddenly when light comes on, then ship is in the stroma
If you lost more than 5 points on this page, then you either don't understand photosynthesis completely or you have not yet developed strong creativity/analysis skills in science.
This page © Ross E. Koning 1994.
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