AP Biology Unit 2: Cells
Explore AP Biology Unit 2 questions on cell structure, size, membranes, transport, tonicity, osmoregulation, and the origins of cellular compartmentalization.
- Syllabus
- Effective Fall 2025
- Course
- AP Biology
Covered syllabus points
2 Cells question 1
Most proteins that are secreted from a cell must be transported to the endoplasmic reticulum
(ER) either during translation or after translation.
Question (a)
(a)
Describe the function of ribosomes.
For proteins transported during translation, this process begins in the cytosol and pauses
when a specific sequence of amino acids is translated. The translation complex is then
transported to the surface of the ER where translation continues. Proteins that are transported
after translation are translated entirely in the cytosol and then transported to the ER. In both
instances, the translated proteins enter the ER through a protein channel in the membrane of
the ER.
Researchers studying the two types of protein transport identified that the ER membrane
protein SR is necessary for transport during translation, while the ER membrane protein Sec62
is necessary for transport after translation. To investigate which transport mechanism is used
for different proteins, researchers first created small interfering RNAs (siRNAs) that reduce
expression of either SR or Sec62. They then treated groups of cells with either the SR siRNA or
the Sec62 siRNA and determined the relative amount of SR and Sec62 protein in each group of
cells compared with cells treated with a control siRNA (Figure 1).
Figure 1. Average relative amounts of Sec62 and SR proteins in cells treated with control siRNA, Sec62 siRNA, or SR siRNA. Error bars represent \(\pm \mathrm{SE}_{x}\)
[ 1 ]
Question (b)
(b)
B.
[ 3 ]
Question (i)
(i)
Identify the dependent variable in the experiments shown in Figure 1.
[ 1 ]
Question (ii)
(ii)
Justify why the researchers included the control of measuring the relative amounts of
both Sec62 and SR proteins in cells that were treated with Sec62 siRNA only (data shown
in Figure 1).
[ 1 ]
Question (iii)
(iii)
Based on Figure 1, describe the effect on the production of SR protein when cells are
treated with Sec62 siRNA.
The researchers then measured the amount of each of three different proteins that was
transported to the ER in cells treated with Sec62 siRNA or SR siRNA. The researchers calculated
the percent transported relative to the cells treated with control siRNA (Figure 2).
Figure 2. Average relative amounts of three proteins that were transported to the ER when treated with control siRNA, Sec62 siRNA, or SR siRNA. Error bars represent \(\pm \mathrm{SE}_{x}\)
[ 1 ]
Question (c)
(c)
C.
[ 2 ]
Question (i)
(i)
Identify the independent variable in the researchers' second experiment (data shown in
Figure 2).
[ 1 ]
Question (ii)
(ii)
Based on Figure 2, identify the protein(s) that when treated with Sec62 siRNA showed an
increase in percent transport to the ER compared with the control.
[ 1 ]
Question (d)
(d)
D.
[ 2 ]
Question (i)
(i)
Researchers claim that protein 1 is the only tested protein that is transported to the ER
following its complete translation in the cytosol. Using data from Figure 2, support the
researchers' claim.
[ 1 ]
Question (ii)
(ii)
For any protein that enters the ER, researchers claim that amino acids close to the
protein's amino terminus determine how likely the protein is to pass through the
protein channel within the ER membrane. Justify the researchers' claim based on your
understanding of factors that affect the transport of proteins across membranes.
[ 1 ]
2 Cells question 2
Students were using the formulas for the surface area and volume of a rectangular solid to model cells of different sizes and shapes. They produced the data shown in the table.
Question (a)
(a)
Identify the rectangular solid that represents the cell with the smallest amount of plasma membrane per volume of cytoplasm.
[ 1 ]
Question (b)
(b)
Describe the relationship between the dimensions of the rectangular solids and their surface area-to-volume ratios.
[ 1 ]
Question (c)
(c)
Using the data from the model, evaluate the hypothesis that cells shaped like rectangular solids 1 and 2 are better suited for slow metabolism and the long-term storage of energy-containing molecules than are cells shaped like rectangular solids 4 and 5.
[ 1 ]
Question (d)
(d)
Based on the trends shown in the data, explain why some rectangular cells include folds or projections in their plasma membranes.
PAGE FOR ANSWERING QUESTION 6
[ 1 ]
2 Cells question 3
Many insects rely on pheromones (chemical signals) that are released by the females to find
mating partners. Scientists hypothesize that, in a certain type of moth, the behavior of male
moths in response to pheromones is regulated by the extracellular signaling molecule 20E.
Many receptors are embedded in the plasma membrane. Describe the polarity of the portion
of the receptor that is inside the membrane.
To investigate whether the binding of 20E to its receptor, DopEcR, affects behavior in moths,
scientists injected male moths with saline (control solution) or with small interfering RNA
molecules (siRNAs) that inhibit the expression of the gene encoding DopEcR. The scientists then
exposed the moths to the pheromone and determined the percent of total time observed that
the moths engaged in general activity, defined as movement in any direction. The scientists also
determined the percent of the general activity time that the moths spent in oriented activity,
defined as movement toward an area of high pheromone concentration (Table 1).
Table 1. Average General and Oriented Activity in Male Moths Injected With Saline or siRNA Molecules
DopEcR is a G protein-coupled receptor. When 20E binds to DopEcR, GTP displaces the GDP
bound to the G protein, and a signaling pathway is activated. The scientists hypothesize that this
leads to the transcription of genes associated with the oriented activity observed in the male
moths (Figure 1).
Figure 1. A simplified model of a signaling pathway activated by the binding of 20E to its receptor, DopEcR
All question bank results loaded