©SIRJOEL EXAM SOLUTIONS
10/7/2024 11:03AM
BOT 331 Exam 1 Questions With 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 - 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. - 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.
, ©SIRJOEL EXAM SOLUTIONS
10/7/2024 11:03AM
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? - 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?
10/7/2024 11:03AM
BOT 331 Exam 1 Questions With 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 - 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. - 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.
, ©SIRJOEL EXAM SOLUTIONS
10/7/2024 11:03AM
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? - 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?
