BOT 331 Exam 1 ACTUAL Exam
Questions and CORRECT ANSWERS
There are two types of nucleic acids: DNA and RNA. There is both DNA and RNA inside the
nucleus, mitochondria and plastids.
Is there both DNA and RNA in the cytosol? Explain your answer - CORRECT ANSWER-
✔✔No, not both. DNA remains in the nucleus. RNA copies of genes are synthesized in the
nucleus, but then moved out pores into the cytosol, where ribosomes (also containing RNA)
bind RNA and use the RNA to direct synthesis of proteins.
In the case of plastids and mitochondria, RNA copies of the organelle's genes remain in the
organelle, and are translated into protein by ribosomes in the plastid stroma or mitochondrial
matrix.
The conducting cells of the xylem experience negative water pressures that could cause the
cell's walls to collapse, but the walls typically resist collapsing.
State two properties of a conducting cell's wall that resists collapse. - CORRECT ANSWER-
✔✔The walls resist collapse because the walls are very thick. Most of the thickness is
secondary wall that is dense with cellulose microfibrils and the phenolic polymer lignin,
which is very rigid. The phenols of lignin also cross-link to microfibrils, strengthening the
wall.
the tension is what potentially could cause collapse and the thick, lignified walls resist the
collapse.
What is stress relaxation AND how does a cell cause stress relaxation? - CORRECT
ANSWER- ✔✔Stress relaxation is when microfibrils slide relative to each other, which
relieves the tension that is otherwise pulling on microfibrils. Tension in the wall is due to the
cell's turgor pressure.
A cell causes relaxation by breaking the bonds between hemicellulose and cellulose, which
allows the fibers to slide. A cell breaks the bonds by pumping protons into the wall
(acidification), which activates a protein called Expansin. Expansin catalyzes breaking of the
hemicelluose cross-links.
Be sure to answer all of the following 3 questions about water potential before moving to the
next question.
For each, explain your answer.
(a) If the water potential in the apoplast is -0.5 MPa, and the water potential inside a cell is -
0.25 MPa, then will water flow into the cell or out of the cell.
, (b) Considering the scenario in (a), at what point does net flow of water stop?
(c) If water flows into a plant cell with a rigid cell wall, will the osmotic potential or the
pressure potential change the most? - CORRECT ANSWER- ✔✔a) Water flows from a
region of high water potential (less negative) to a region of low water potential (more
negative). Because the apoplast has a lower water potential than the cell, water will flow out
of the cell.
b) Net flow stops when the water potential inside the cell is equal to the apoplast; when there
is no longer a gradient of high to low.
c)The pressure potential will change the most, because the volume of the cell will not change
much. As soon as water flowing in causes the cell's volume to push on the wall, the rigid wall
resists causing the pressure potential to increase (become more positive). Because the volume
does not change much, the concentration of solutes does not change, so the osmotic potential
(solute potential) does not change.
True/false, if false explain why
Guard cells are specialized for secreting waxes into their cell wall, so that the majority of the
plant's shoot surface is covered in a cuticle. - CORRECT ANSWER- ✔✔False, epidermal
cells cover most of a plant's shoot surface with their secretions of cutin that make up the
cuticle. Guard cells are specialized for converting changes in cell size to opening or closing
stomatal pores.
True/false, if false explain why
A meristem is a region of a plant that has stopped growing and is fully mature. - CORRECT
ANSWER- ✔✔False, a meristem is a region where many cells are going through the cell
cycle - growing and dividing. Many of the cells in a meristem have not yet fully
differentiated, so are not mature; have not taken on their final organization for specialized
functions.
True/false, if false explain why
The CSI1 protein catalyzes synthesis of cellulose microfibrils in a direction parallel to
microtubules. - CORRECT ANSWER- ✔✔False, the CSI1 protein does NOT catalyze
synthesis of cellulose. Cellulose Synthase is the enzyme that synthesizes cellulose
microfibrils. CSI1 is believed to be a protein that binds to both a Cellulose Synthase and a
microtubule, so that the Synthase, when synthesizing cellulose, moves in the direction of the
microtubule.
Questions and CORRECT ANSWERS
There are two types of nucleic acids: DNA and RNA. There is both DNA and RNA inside the
nucleus, mitochondria and plastids.
Is there both DNA and RNA in the cytosol? Explain your answer - CORRECT ANSWER-
✔✔No, not both. DNA remains in the nucleus. RNA copies of genes are synthesized in the
nucleus, but then moved out pores into the cytosol, where ribosomes (also containing RNA)
bind RNA and use the RNA to direct synthesis of proteins.
In the case of plastids and mitochondria, RNA copies of the organelle's genes remain in the
organelle, and are translated into protein by ribosomes in the plastid stroma or mitochondrial
matrix.
The conducting cells of the xylem experience negative water pressures that could cause the
cell's walls to collapse, but the walls typically resist collapsing.
State two properties of a conducting cell's wall that resists collapse. - CORRECT ANSWER-
✔✔The walls resist collapse because the walls are very thick. Most of the thickness is
secondary wall that is dense with cellulose microfibrils and the phenolic polymer lignin,
which is very rigid. The phenols of lignin also cross-link to microfibrils, strengthening the
wall.
the tension is what potentially could cause collapse and the thick, lignified walls resist the
collapse.
What is stress relaxation AND how does a cell cause stress relaxation? - CORRECT
ANSWER- ✔✔Stress relaxation is when microfibrils slide relative to each other, which
relieves the tension that is otherwise pulling on microfibrils. Tension in the wall is due to the
cell's turgor pressure.
A cell causes relaxation by breaking the bonds between hemicellulose and cellulose, which
allows the fibers to slide. A cell breaks the bonds by pumping protons into the wall
(acidification), which activates a protein called Expansin. Expansin catalyzes breaking of the
hemicelluose cross-links.
Be sure to answer all of the following 3 questions about water potential before moving to the
next question.
For each, explain your answer.
(a) If the water potential in the apoplast is -0.5 MPa, and the water potential inside a cell is -
0.25 MPa, then will water flow into the cell or out of the cell.
, (b) Considering the scenario in (a), at what point does net flow of water stop?
(c) If water flows into a plant cell with a rigid cell wall, will the osmotic potential or the
pressure potential change the most? - CORRECT ANSWER- ✔✔a) Water flows from a
region of high water potential (less negative) to a region of low water potential (more
negative). Because the apoplast has a lower water potential than the cell, water will flow out
of the cell.
b) Net flow stops when the water potential inside the cell is equal to the apoplast; when there
is no longer a gradient of high to low.
c)The pressure potential will change the most, because the volume of the cell will not change
much. As soon as water flowing in causes the cell's volume to push on the wall, the rigid wall
resists causing the pressure potential to increase (become more positive). Because the volume
does not change much, the concentration of solutes does not change, so the osmotic potential
(solute potential) does not change.
True/false, if false explain why
Guard cells are specialized for secreting waxes into their cell wall, so that the majority of the
plant's shoot surface is covered in a cuticle. - CORRECT ANSWER- ✔✔False, epidermal
cells cover most of a plant's shoot surface with their secretions of cutin that make up the
cuticle. Guard cells are specialized for converting changes in cell size to opening or closing
stomatal pores.
True/false, if false explain why
A meristem is a region of a plant that has stopped growing and is fully mature. - CORRECT
ANSWER- ✔✔False, a meristem is a region where many cells are going through the cell
cycle - growing and dividing. Many of the cells in a meristem have not yet fully
differentiated, so are not mature; have not taken on their final organization for specialized
functions.
True/false, if false explain why
The CSI1 protein catalyzes synthesis of cellulose microfibrils in a direction parallel to
microtubules. - CORRECT ANSWER- ✔✔False, the CSI1 protein does NOT catalyze
synthesis of cellulose. Cellulose Synthase is the enzyme that synthesizes cellulose
microfibrils. CSI1 is believed to be a protein that binds to both a Cellulose Synthase and a
microtubule, so that the Synthase, when synthesizing cellulose, moves in the direction of the
microtubule.
