Destroying the cerebellum of a cat would cause significant impairment of normal:
Answer(s): C
To answer this question, you have to be familiar with the functions under the control of the cerebellum. The cerebellum is part of the hindbrain, which is the posterior part of the brain and consists of the pons and the medulla oblongata, in addition to the cerebellum. The cerebellum receives sensory information from the visual and auditory systems, as well as information about the orientation of joints and muscles. In fact, one of the cerebellum's main functions is hand-eye coordination. It also receives information about the motor signals being initiated by the cerebrum. The cerebellum takes all of this information and integrates it to produce balance and unconscious coordinated movement. Damage to the cerebellum could damage any one of these functions. Total destruction of the cerebellum would eliminate all of them. Therefore, choice C is correct because destruction of a cat's cerebellum would seriously impair coordinated movement in the cat. Let's take a look at the other choices. Urine formation, choice A, is the primary function of the kidneys, with a little bit of hormonal regulation to help things out. Choice B, sense of smell, or olfaction, is a function of the cerebrum not the cerebellum. Thermoregulation, choice D, is a function of the hypothalamus, which is a part of the cerebrum.
A cell with a high intracellular K+ concentration, whose plasma membrane is impermeable to K+, is placed in an ATP-rich medium with a low K+ concentration. After several minutes, it is determined that the extracellular concentrations of both K+ and ATP have decreased, while the intracellular K+ concentration has increased.What is the most likely explanation for this phenomenon?
Answer(s): D
This question requires knowledge of the different mechanisms of transport across a cell membrane and an application of this knowledge to the specific situation described in the question stem. A cell with a high intracellular potassium concentration is placed in a medium with a low potassium concentration and a high ATP concentration. Furthermore, we're told that the cell membrane is impermeable to potassium. If the cell were permeable to potassium, you would expect potassium to flow out of the cell, along its concentration gradient.But, this is clearly not the case. What does happen is that the extracellular concentration of both the potassium and the ATP decreases, while the intracellular concentration of potassium increases. This implies that the potassium moved into the cell, across a membrane that is impermeable to it, and against its concentration gradient. You're asked to choose the most likely explanation for this phenomenon. Choice A says that the potassium passively diffused into the cell, and choice B says that the potassium entered the cell by way of facilitated transport. Since both diffusion and facilitated transport occur ALONG a substance's concentration gradient, not against it, both choices A and B must be incorrect. Furthermore, the potassium could not possibly diffuse across the membrane, because we know that the membrane is impermeable to it. And finally, neither of these choices accounts for the decrease in extracellular ATP concentration. Choice C sounds kind of reasonable, except for two main reasons: First, ATP is not a very lipid-soluble complex with potassium to which we're told the membrane is also impermeable hereby enabling the potassium to cross the lipid cell membrane and enter the cell. Second, there is no evidence to support the theory that ATP functions as a carrier molecule, shuttling potassium across cell membranes. ATP is the energy currency used by cells. Energy is stored in its high-energy phosphate bonds; and this energy is made available to cells when ATP is hydrolyzed to ADP and AMP. Thus, choice C is also incorrect. Choice D, however, does make sense; it explains both the movement of potassium into the cell against its gradient, as well as the decreased extracellular ATP concentration. Active transport is the movement of a substance against its concentration gradient with the aid of carrier molecules and ENERGY.
Early experimentation on the single-celled organism Acetabularia led to important discoveries about the role of the nucleus in regulating cell function. Acetabularia is an enormous single cell with three distinct regions: a cap, a root-like rhizoid, and a stalk which connects the two. The following experiments were conducted to study the development of the cell:Experiment 1The stalk of an Acetabularia was cut, fragmenting the cell. The fragment which included the cap died shortly afterwards while the fragment containing the rhizoid regenerated to form a complete Acetabularia.Experiment 2The nucleus from Acetabularia mediterranea, which has a flat cap, was transplanted into Acetabularia crenulata, which has a tufted cap, following removal of the Acetabularia crenulata nucleus. The Acetabularia crenulata cap eventually assumed the flat shape.Experiment 3The nucleus of Acetabularia mediterranea was removed from the young cell before it first formed a cap. A normal cap formed several weeks later. The cell proved to be inviable and died shortly thereafter.Experiment 4A young Acetabularia was fractioned into a number of portions before it first formed a cap. Several weeks later, both the portion containing the nucleus and the portion containing the apical tip of the stalk formed caps. The other portions did not form caps.One explanation for the results of Experiment 4 is that the instructions for forming the cap are stored in the apical tip of the stalk several weeks prior to stalk formation. Which of the following pieces of evidence best supports this explanation?
The question stem asks for support of the fact that the information for forming the cap is stored in the apical tip of the stalk. This information is in the form of mRNA which is used as the template for translation of the proteins which coordinate cap formation. The other choices may be true but they do not provide evidence for the storage of information in the apical tip.Choice A is incorrect because the DNA coding for cap inducing proteins would be present at all times in the Acetabularia genome. This does not provide evidence for the storage of information in the stalk tip.Choice B is incorrect because, although exposure of the Acetabularia to ribonuclease and the consequent cleavage of RNA would temporarily block formation of the cap (until more RNA is transcribed), this does not provide evidence for the storage of information in the apical stalk segment. Rather, it provides evidence that RNA is the conveyor of information.Choice C is incorrect because although the passage describes this exchange of nuclei in Experiment 2, this does not provide evidence for the storage of information in the apical stalk.
Early experimentation on the single-celled organism Acetabularia led to important discoveries about the role of the nucleus in regulating cell function. Acetabularia is an enormous single cell with three distinct regions: a cap, a root-like rhizoid, and a stalk which connects the two. The following experiments were conducted to study the development of the cell:Experiment 1The stalk of an Acetabularia was cut, fragmenting the cell. The fragment which included the cap died shortly afterwards while the fragment containing the rhizoid regenerated to form a complete Acetabularia.Experiment 2The nucleus from Acetabularia mediterranea, which has a flat cap, was transplanted into Acetabularia crenulata, which has a tufted cap, following removal of the Acetabularia crenulata nucleus. The Acetabularia crenulata cap eventually assumed the flat shape.Experiment 3The nucleus of Acetabularia mediterranea was removed from the young cell before it first formed a cap. A normal cap formed several weeks later. The cell proved to be inviable and died shortly thereafter.Experiment 4A young Acetabularia was fractioned into a number of portions before it first formed a cap. Several weeks later, both the portion containing the nucleus and the portion containing the apical tip of the stalk formed caps. The other portions did not form caps.Acetabularia is a(n):
The passage describes Acetabularia as a single cell with a nucleus. Only eukaryotes have nuclei, and other membrane bound organelles.Choice A is incorrect because a virus does not have a cell membrane, nucleus, or many of the other components of a cell. A virus is essentially composed of DNA or RNA and a protein coat.Choice B is incorrect because prokaryotes lack a nucleus.Choice D is incorrect because the term bacteria refers to prokaryotes which, by definition, lack nuclei.
Early experimentation on the single-celled organism Acetabularia led to important discoveries about the role of the nucleus in regulating cell function. Acetabularia is an enormous single cell with three distinct regions: a cap, a root-like rhizoid, and a stalk which connects the two. The following experiments were conducted to study the development of the cell:Experiment 1The stalk of an Acetabularia was cut, fragmenting the cell. The fragment which included the cap died shortly afterwards while the fragment containing the rhizoid regenerated to form a complete Acetabularia.Experiment 2The nucleus from Acetabularia mediterranea, which has a flat cap, was transplanted into Acetabularia crenulata, which has a tufted cap, following removal of the Acetabularia crenulata nucleus. The Acetabularia crenulata cap eventually assumed the flat shape.Experiment 3The nucleus of Acetabularia mediterranea was removed from the young cell before it first formed a cap. A normal cap formed several weeks later. The cell proved to be inviable and died shortly thereafter.Experiment 4A young Acetabularia was fractioned into a number of portions before it first formed a cap. Several weeks later, both the portion containing the nucleus and the portion containing the apical tip of the stalk formed caps. The other portions did not form caps.Which of the following conclusions can be logically drawn from the fact that the Acetabularia segment containing the rhizoid regenerated a complete and viable Acetabularia in Experiment 1?
Answer(s): A
In order for a cell fragment to survive, it must contain all of the necessary machinery for maintaining life. This requires the production of proteins which are coded for by DNA. In Acetabularia, the region with the rhizoid survives, indicating that the nucleus must be located there.Choice B is incorrect because, while some prokaryotes multiply by budding, eukaryotic cells multiply by mitosis.Also, this information cannot be concluded from the fact that the rhizoid bearing fragment survives.Choice C is incorrect because while there is indication in Experiment 1 that the cap alone is not sufficient for the Acetabularia to survive, there is no indication that the cap is a vestigial (unnecessary) structure.Choice D is incorrect because although the statement may be true, it is not unambiguously proven by the experiment. The experiment demonstrates that cap-coding mRNA is present in the rhizoid region of the fragmented Acetabularia at some point during regeneration. The cap-coding mRNA may have been stored in the rhizoid region when the Acetabularia was cut or it could have been transcribed only after the cell was fragmented.
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