Cell Communication Part 2
The diagram above shows a developing worm embryo at the four-cell stage. Experiments have shown that when cell 3 divides, the anterior daughter cell gives rise to muscle and gonads and the posterior daughter cell gives rise to the intestine. However, if the cells of the embryo are separated from one another early during the four-cell stage, no intestine will form. Other experiments have shown that if cell 3 and cell 4 are recombined after the initial separation, the posterior daughter cell of cell 3 will once again give rise to normal intestine. Which of the following is the most plausible explanation for these findings?
A cell surface protein on cell 4 signals cell 3 to induce formation of the worm's intestine.
The graph above shows changes in glucagon and insulin secretions at different concentrations of blood glucose. Which of the following feedback mechanisms is best supported by the data?
A low glucose level causes the release of glucagon, which stimulates the release of more glucose from tissues, which in turn lowers the amount of glucagon being released.
Which of the following diagrams best represents hormone-activated gene expression?
A) steroid hormone
The endocrine system incorporates feedback mechanisms that maintain homeostasis. Which of the following demonstrates negative feedback by the endocrine system?
After a meal, blood glucose levels become elevated, stimulating beta cells of the pancreas to release insulin into the blood. Excess glucose is then converted to glycogen in the liver, reducing blood glucose levels.
The vertebrate forelimb initially develops in the embryo as a solid mass of tissue. As development progresses, the solid mass near the end of the forelimb is remodeled into individual digits. Which of the following best explains the role of apoptosis in remodeling of the forelimb?
Apoptosis involves the regulated activation of proteins in specific cells of the developing forelimb that leads to the death of those cells.
Which of the following is a correct conclusion that can be drawn from the data in Figures 1, 2, and 3?
Most of the increase in the concentration of all gibberellins 40 to 45 days after planting is due to an increase in the concentration of GAl.
Based on the information presented, which of the following will also occur in response to steroid signaling?
Production of a specific mRNA will increase as a result of the binding of the hormone-receptor complex to the DNA .
Which of the following occurs in both meiosis and mitosis?
Separation of sister chromatids
When a stimulus is applied to a receptor in the skin, an action potential is propagated along a neuron to the brain, where another signal is sent back to the muscle for a response. Which of the following best describes what occurs when the action potential reaches a chemical synapse at the end of an axon?
The action potential causes a release of neurotransmitters that travel across the synapse.
Which of the following is a correct conclusion that can be drawn based only on the data in Figure 4?
The greater the inhibition of GAl synthesis, the lower the plant height after 80 days.
When the concentration of GAl is highest, the average height of the control seedlings is approximately
10 cm
The concentration of all gibberellins 65 days after planting is approximately
20 ng/gram
Which of the following is true of mitosis?
It maintains the same chromosome number in the daughter cells as in the parent cell.
Most cells that have become transformed into cancer cells have which of the following characteristics when compared to normal, healthy cells?
Shorter cell cycle
Transmission of an action potential across a synapse involves the release of neurotransmitters by the presynaptic neuron. The arrival of the action potential triggers a rise in the calcium concentration in the synaptic terminal (cell on the right), and the change in concentration triggers a release of neurotransmitters into the synaptic cleft. Knowing that the resting membrane potential is established by the sodium-potassium pump, which of the following representations of the movement of calcium, sodium, and potassium ions best shows how an action potential is transmitted to the postsynaptic neuron?
a) Ca++ going in Na+ going in K+ is going out
Precise regulation of specific hormone levels is required for optimal sperm production in mammals, as summarized in the figure above. Anabolic-androgenic steroids (AAS) are synthetic variants of testosterone that are sometimes abused by persons who desire to enhance their athletic performance or alter their physique. Assuming that AAS function in the same way as naturally occurring testosterone, it is most likely that long-term abuse of AAS would
reduce sperm production
A tissue culture of vertebrate muscle was provided with a constant excess supply of glucose under anaerobic conditions starting at time zero and the amounts of pyruvic acid and ATP produced were measured. The solid line in the graph above represents the pyruvic acid produced in moles per liter per minute. ATP levels were also found to be highest at points A and C, lowest at B and D. A second culture was set up under the same conditions, except that substance X was added, and the results are indicated by the dotted line. The rate of pyruvic acid formation fluctuates because
the reaction is affected by negative feedback