BIOL 4100 Exam Study Guide –
Practice Questions with
Verified Answers with
Rationales. GRADED A+. Latest
2026/2027 Update
When the transport vesicle shown below fuses with the plasma membrane,
which monolayer will face the cell cytosol?
Choose one:
A. It depends on whether the vesicle is coming from the endoplasmic reticulum
or the Golgi apparatus.
B. The orange monolayer will face the cytosol.
C. Half the time the orange monolayer will face the cytosol, and half the time
the blue monolayer will face the cytosol.
D. The blue monolayer will face the cytosol.
E. It depends on the cargo the vesicle is carrying. - Answer✔✔-B. The orange
monolayer will face the cytosol.
EXPLANATION:
,Most cell membranes are asymmetric, as the two halves of the bilayer often
include strikingly different sets of phospholipids. This asymmetry is preserved
as membranes bud from one organelle and fuse with another, or with the
plasma membrane. This means that all cell membranes have distinct "inside"
and "outside" faces: the cytosolic monolayer always faces the cytosol, while
the noncytosolic monolayer is exposed to either the cell exterior—in the case
of the plasma membrane—or the interior space (lumen) of an organelle.
Maintaining this asymmetric organization is essential for preserving the
asymmetric distribution of phospholipids and glycolipids, which may be
confined to one or another monolayer to carry out their physiological function.
Animals exploit the phospholipid asymmetry of their plasma membrane to
distinguish between live cells and dead ones. When animal cells undergo a
form of programmed cell death called apoptosis, phosphatidylserine—a
phospholipid that is normally confined to the cytosolic monolayer of the
plasma membrane—rapidly translocates to the extracellular, outer monolayer.
The presence of phosphatidylserine on the cell surface serves as a signal that
helps direct the rapid removal of the dead cell.
How might a cell actively engineer this phospholipid redistribution?
Choose one:
A. by activating a scramblase and inactivating a flippase in the plasma
membrane
B. by inactivating a scramblase in the plasma membrane
C. by inactivating both a flippase and a scramblase in the plasma membrane
D. by inverting the existing plasma membrane
,E. by boosting the activity of a flippase in the plasma membrane - Answer✔✔-
A. by activating a scramblase and inactivating a flippase in the plasma
membrane
EXPLANATION:
All cells are separated from the extracellular environment by the plasma
membrane. This cell membrane plays a key role in cell communication,
presenting signals that relate information about the state of the cell, including
its relative health. In healthy cells, the distribution of phospholipids in the
plasma membrane is asymmetric. Some phospholipids, such as
phosphatidylcholine and sphingomyelin, are confined to the noncytosolic half
of the plasma membrane, while others such as phosphatidylserine and
phosphatidylethanolamine are present only in the membrane's cytosolic
monolayer.
When cells are no longer needed or are damaged beyond repair, they can
activate a form of programmed cell death called apoptosis. A cell undergoing
apoptosis actively destroys itself from within, digesting its proteins and
degrading its DNA. It also displays signals that direct circulating phagocytic cells
to engulf its remains.
One of these signals involves the relocation of phosphatidylserine. An
apoptotic cell displays phosphatidylserine—normally confined to the cytosolic
monolayer of the plasma membrane—on its surface.
This reversal involves manipulating the activity of both flippases and
scramblases in the plasma membrane. First, the scramblase that transfers
random phospholipids from one monolayer of the plasma membrane to the
other must be activated. This scrambling causes phosphatidylserine—initially
deposited in the cytosolic monolayer—to become distributed to both halves of
the bilayer. At the same time, the flippase that would normally transfer
phosphatidylserine from the extracellular monolayer to the cytosolic
monolayer must be inactivated. Together, these actions cause
phosphatidylserine to rapidly accumulate at the cell surface.
, Bo
Shown is a schematic diagram of a membrane phospholipid. Which segment
will always carry a negative charge?
Choose one:
A. A
B. B
C. C
D. D
E. E - Answer✔✔-B. B
EXPLANATION:
A typical membrane phospholipid molecule has a hydrophilic head and two
hydrophobic tails.
The hydrophobic tails of both phospholipids are long hydrocarbon chains,
which are uncharged. Glycerol, here outlined in green, is also uncharged. The
hydrophillic head includes a chemical group (blue) characteristic of the specific
phospholipid: serine in phosphatidylserine and choline in phosphatidylcholine.
As shown in the figure, choline contains a positively charged nitrogen atom;
serine, with its positively charged nitrogen and negatively charged carboxyl
oxygen, is overall uncharged. The remaining component of the hydrophilic
head, the phosphate group (yellow), includes oxygen atoms. One of these
oxygens always carries a negative charge.
Practice Questions with
Verified Answers with
Rationales. GRADED A+. Latest
2026/2027 Update
When the transport vesicle shown below fuses with the plasma membrane,
which monolayer will face the cell cytosol?
Choose one:
A. It depends on whether the vesicle is coming from the endoplasmic reticulum
or the Golgi apparatus.
B. The orange monolayer will face the cytosol.
C. Half the time the orange monolayer will face the cytosol, and half the time
the blue monolayer will face the cytosol.
D. The blue monolayer will face the cytosol.
E. It depends on the cargo the vesicle is carrying. - Answer✔✔-B. The orange
monolayer will face the cytosol.
EXPLANATION:
,Most cell membranes are asymmetric, as the two halves of the bilayer often
include strikingly different sets of phospholipids. This asymmetry is preserved
as membranes bud from one organelle and fuse with another, or with the
plasma membrane. This means that all cell membranes have distinct "inside"
and "outside" faces: the cytosolic monolayer always faces the cytosol, while
the noncytosolic monolayer is exposed to either the cell exterior—in the case
of the plasma membrane—or the interior space (lumen) of an organelle.
Maintaining this asymmetric organization is essential for preserving the
asymmetric distribution of phospholipids and glycolipids, which may be
confined to one or another monolayer to carry out their physiological function.
Animals exploit the phospholipid asymmetry of their plasma membrane to
distinguish between live cells and dead ones. When animal cells undergo a
form of programmed cell death called apoptosis, phosphatidylserine—a
phospholipid that is normally confined to the cytosolic monolayer of the
plasma membrane—rapidly translocates to the extracellular, outer monolayer.
The presence of phosphatidylserine on the cell surface serves as a signal that
helps direct the rapid removal of the dead cell.
How might a cell actively engineer this phospholipid redistribution?
Choose one:
A. by activating a scramblase and inactivating a flippase in the plasma
membrane
B. by inactivating a scramblase in the plasma membrane
C. by inactivating both a flippase and a scramblase in the plasma membrane
D. by inverting the existing plasma membrane
,E. by boosting the activity of a flippase in the plasma membrane - Answer✔✔-
A. by activating a scramblase and inactivating a flippase in the plasma
membrane
EXPLANATION:
All cells are separated from the extracellular environment by the plasma
membrane. This cell membrane plays a key role in cell communication,
presenting signals that relate information about the state of the cell, including
its relative health. In healthy cells, the distribution of phospholipids in the
plasma membrane is asymmetric. Some phospholipids, such as
phosphatidylcholine and sphingomyelin, are confined to the noncytosolic half
of the plasma membrane, while others such as phosphatidylserine and
phosphatidylethanolamine are present only in the membrane's cytosolic
monolayer.
When cells are no longer needed or are damaged beyond repair, they can
activate a form of programmed cell death called apoptosis. A cell undergoing
apoptosis actively destroys itself from within, digesting its proteins and
degrading its DNA. It also displays signals that direct circulating phagocytic cells
to engulf its remains.
One of these signals involves the relocation of phosphatidylserine. An
apoptotic cell displays phosphatidylserine—normally confined to the cytosolic
monolayer of the plasma membrane—on its surface.
This reversal involves manipulating the activity of both flippases and
scramblases in the plasma membrane. First, the scramblase that transfers
random phospholipids from one monolayer of the plasma membrane to the
other must be activated. This scrambling causes phosphatidylserine—initially
deposited in the cytosolic monolayer—to become distributed to both halves of
the bilayer. At the same time, the flippase that would normally transfer
phosphatidylserine from the extracellular monolayer to the cytosolic
monolayer must be inactivated. Together, these actions cause
phosphatidylserine to rapidly accumulate at the cell surface.
, Bo
Shown is a schematic diagram of a membrane phospholipid. Which segment
will always carry a negative charge?
Choose one:
A. A
B. B
C. C
D. D
E. E - Answer✔✔-B. B
EXPLANATION:
A typical membrane phospholipid molecule has a hydrophilic head and two
hydrophobic tails.
The hydrophobic tails of both phospholipids are long hydrocarbon chains,
which are uncharged. Glycerol, here outlined in green, is also uncharged. The
hydrophillic head includes a chemical group (blue) characteristic of the specific
phospholipid: serine in phosphatidylserine and choline in phosphatidylcholine.
As shown in the figure, choline contains a positively charged nitrogen atom;
serine, with its positively charged nitrogen and negatively charged carboxyl
oxygen, is overall uncharged. The remaining component of the hydrophilic
head, the phosphate group (yellow), includes oxygen atoms. One of these
oxygens always carries a negative charge.
