Explore AP Biology Unit 4 questions on cell communication, signal transduction pathways, feedback mechanisms, the cell cycle, and cell-cycle regulation.
A portion of the human immune system response to an invading
pathogen is shown below.
Macrophages are white blood cells that ingest invading pathogens.
After digesting the pathogen, macrophages present the antigens from
the pathogen to helper T cells in the immune system. These helper T
cells then secrete chemical signals called cytokines. The cytokines can
travel short distances to activate nearby cytotoxic T cells, which will
kill infected cells. Some cytokines will activate the enzyme adenylyl
cyclase in nearby B cells to produce cyclic AMP (cAMP). cAMP will
then activate the production of antibodies in the B cells.
Part A
(i) Describe the characteristics of juxtacrine signaling.
(ii) Draw a square around the step (1, 2, 3, or 4) in the figure that
illustrates an example of juxtacrine signaling.
Part B
(i) Explain the role cytokines play in the cell signaling process
described above.
Part C
(i) Draw a circle around a molecule that functions as a secondary
messenger in the pathway.
Part D
(i) Explain how secondary messengers can amplify a response in a
cell.
Questions 43-48
Figure 1. Model of synapse
Researchers investigating the regulation of neurotransmitter release from presynaptic neurons proposed a model
(Figure 1) in which CDK5, a protein expressed in axon terminals, inhibits the movement of synaptic vesicles to the
presynaptic membrane.
To test their model, the researchers used a modified version of green fluorescent protein (GFP*). In slightly
alkaline conditions, GFP* exhibits a bright green fluorescence. In acidic conditions, GFP* exhibits no fluorescence.
Using standard techniques, the gene encoding GFP* is easily introduced into living cells. By engineering the
expression of GFP* in laboratory-cultured nerve cells, the researchers found that a bright green fluorescence was
exhibited only when a presynaptic neuron was given a certain stimulus.
Based on the model, which of the following
describes the most likely mechanism by which
CDK5 regulates neurotransmitter release?
CDK5 adds methyl groups to DNA, altering
expression of genes required for synthesis
of neurotransmitters.
CDK5 promotes the rearrangement of the
lipid molecules of two bilayers into a single
membrane.
CDK5 alters the activity of other proteins
involved in the movement of synaptic
vesicles to the plasma membrane.
CDK5 binds to gated ion channels in the
postsynaptic membrane, resulting in
diffusion of calcium ions.
B-cell activation model
As represented in the model above, B cells are activated by direct contact with antigens or stimulated helper T cells . Based on the model, which of the following best describes an outcome of B cell activation?
Activated B cells differentiate into plasma cells and memory cells.
Activated B cells stimulate cells to secrete antibodies.
Both B cells and cells release chemical signals that negatively regulate antigen-presenting cells.
Plasma cells produce antibodies that activate additional B cells by a positive feedback mechanism.
Questions 12-17 Certain reef-building corals contain photosynthetic, symbiotic algae that have the ability to make dimethylsulphoniopropionate (DMSP), a chemical involved in the marine sulfur cycle. DMSP is released into the surrounding water, where it is converted to the gas dimethyl sulfide (DMS) by microorganisms and enters the atmosphere. Once in the atmosphere, it triggers the formation of sulfate aerosols, which induce cloud formation and block sunlight from heating up the water. The symbiotic algae produce DMSP when they are stressed by a high water temperature. If water temperature is too high, corals will expel the symbiotic algae that produce DMSP. Researchers measured the amount of DMSP produced by juvenile and adult coral and their symbionts under normal and thermally stressed conditions. The data are shown in the graphs in Figure 1.
Figure 1: DMSP concentration in juvenile and adult corals and their symbionts in normal and thermally-stressed conditions. Error bars represent \(\pm 2 \mathrm{SE}_{x}\)
The researchers also measured the density of the symbiont as well as the photosynthetic yield in adult corals at the two temperatures. Photosynthetic yield is an index measure of energy output compared to sunlight energy input in which larger photosynthetic yield values represent photosynthetic organisms producing more energy.
Figure 2: Variation in symbiont density and photosynthetic yield in adult corals grown in normal and thermally-stressed conditions. Error bars represent \(\pm 2 \mathrm{SE}_{x}\)
Which of the following best describes the production of DMSP by coral and coral symbionts?
A negative feedback mechanism that increases the environmental change
A negative feedback mechanism that reverses the environmental change
A positive feedback mechanism that increases the environmental change
A positive feedback mechanism that reverses the environmental change
