-
vikram4689
- Legendary Member
- Posts: 1325
- Joined: Sun Nov 01, 2009 6:24 am
- Thanked: 105 times
- Followed by:14 members
Some one and a half or two billion years ago, when the earth was still poor in oxygen, a primitive bacterium that made a precarious living from the anaerobic fermentation of organic molecules engulfed a smaller cell that had somehow evolved the ability to respire. Respiration liberates far more energy than fermentation, and the growing abundance of oxygen in the atmosphere must have been the driving force behind a symbiotic relation that developed between the two cells, with the aerobic cell generating energy in return for shelter and nutrients from its larger host.
In time the engulfed cell and others like it were to become subcellular organelles, passed on by host cells to their progeny. Eventually the host cells themselves changed, developing other subcellular structures and internal membranes and segregating their genetic material in chromosomes within a nucleus. These cells were the ancestors of all modern eukaryotic (nucleated) cells. The present-day descendants of those ancient symbiotic respiring bacteria are the mitochondria, the power plants of the eukaryotic cell.
Mitochondria are oval organelles, about half a micrometer in diameter and from two to five micrometers long. The mitochondrion has an outer membrane and an extensively folded inner membrane that encloses a fluid matrix. The organelle is the site of oxidative phosphorylation, the primary source of cellular energy. In the fluid matrix, organic molecules derived from the breakdown of foodstuffs are oxidized in a series of chemical reactions known as the citric acid cycle. Electrons removed in the course of oxidation are passed along a chain of respiratory-enzyme complexes arrayed in the inner membrane, driving the phosphorylation of adenosine diphosphate to form adenosine triphosphate (ATP), the universal energy carrier of cells. The cytoplasm (the region outside the nucleus) of eukaryotic cells contains a few mitochondria to many hundreds, depending on the energy demands placed on the cell.
1. The author of the passage would most likely agree with which one of the following statements about the "symbiotic relation" in line 10?
(A) The new cell that developed out of the symbiotic relation between anaerobic and aerobic cells has not changed over the last one-and-a-half billion years.
(B) Neither anaerobic nor aerobic cells had a specific function to perform in the new cell.
(C) Anaerobic and aerobic cells combined to create a new cell because neither type of cell was capable of surviving for long on its own.
(D) Anaerobic and aerobic cells could not have joined to form a new cell in the absence of the proper atmospheric conditions.
(E) The chromosomes of eukaryotic cells were originally located in aerobic cells before aerobic cells combined with anaerobic cells to form a new cell.
2. The passage suggests which one of the following about "anaerobic fermentation" (line 2)?
(A) It occurs in the mitochondria located in cells' cytoplasm.
(B) It causes the breakdown of organic molecules during the citric acid cycle.
(C) It is the basis of energy production in modern eukaryotic cells.
(D) It can only be carried on by primitive bacterium in an oxygen-poor environment.
(E) It is not the most efficient way for cells to produce energy.
3. According to the passage, the energy released by a eukaryotic cell is
(A) generated by the mitochondria contained in its cytoplasm
(B) dependent on the transformation of adenosine triphosphate into adenosine diphosphate
(C) caused by chemical reactions that take place outside of the mitochondrion's inner membrane
(D) related to the number of chromosomes in the cell nucleus
(E) incorporated into the mitochondrion's genetic material
4. According to the passage, which one of the following occurs during the citric acid cycle?
(A) Organic molecules that are derived from food penetrate the mitochondrion's outer membrane
(B) Electrons help to transform adenosine diphosphate into adenosine triphosphate.
(C) Mitochondria from a eukaryotic cell's cytoplasm are transported to the cell's nucleus.
(D) Eukaryotic cells develop subcellular structures, internal membranes and nuclei.
(E) The fluid matrix enclosed by the mitochondrion's inner membrane is transformed into organic molecules that are later broken down in a series of chemical reactions.
DEAB[spoiler][/spoiler]
In time the engulfed cell and others like it were to become subcellular organelles, passed on by host cells to their progeny. Eventually the host cells themselves changed, developing other subcellular structures and internal membranes and segregating their genetic material in chromosomes within a nucleus. These cells were the ancestors of all modern eukaryotic (nucleated) cells. The present-day descendants of those ancient symbiotic respiring bacteria are the mitochondria, the power plants of the eukaryotic cell.
Mitochondria are oval organelles, about half a micrometer in diameter and from two to five micrometers long. The mitochondrion has an outer membrane and an extensively folded inner membrane that encloses a fluid matrix. The organelle is the site of oxidative phosphorylation, the primary source of cellular energy. In the fluid matrix, organic molecules derived from the breakdown of foodstuffs are oxidized in a series of chemical reactions known as the citric acid cycle. Electrons removed in the course of oxidation are passed along a chain of respiratory-enzyme complexes arrayed in the inner membrane, driving the phosphorylation of adenosine diphosphate to form adenosine triphosphate (ATP), the universal energy carrier of cells. The cytoplasm (the region outside the nucleus) of eukaryotic cells contains a few mitochondria to many hundreds, depending on the energy demands placed on the cell.
1. The author of the passage would most likely agree with which one of the following statements about the "symbiotic relation" in line 10?
(A) The new cell that developed out of the symbiotic relation between anaerobic and aerobic cells has not changed over the last one-and-a-half billion years.
(B) Neither anaerobic nor aerobic cells had a specific function to perform in the new cell.
(C) Anaerobic and aerobic cells combined to create a new cell because neither type of cell was capable of surviving for long on its own.
(D) Anaerobic and aerobic cells could not have joined to form a new cell in the absence of the proper atmospheric conditions.
(E) The chromosomes of eukaryotic cells were originally located in aerobic cells before aerobic cells combined with anaerobic cells to form a new cell.
2. The passage suggests which one of the following about "anaerobic fermentation" (line 2)?
(A) It occurs in the mitochondria located in cells' cytoplasm.
(B) It causes the breakdown of organic molecules during the citric acid cycle.
(C) It is the basis of energy production in modern eukaryotic cells.
(D) It can only be carried on by primitive bacterium in an oxygen-poor environment.
(E) It is not the most efficient way for cells to produce energy.
3. According to the passage, the energy released by a eukaryotic cell is
(A) generated by the mitochondria contained in its cytoplasm
(B) dependent on the transformation of adenosine triphosphate into adenosine diphosphate
(C) caused by chemical reactions that take place outside of the mitochondrion's inner membrane
(D) related to the number of chromosomes in the cell nucleus
(E) incorporated into the mitochondrion's genetic material
4. According to the passage, which one of the following occurs during the citric acid cycle?
(A) Organic molecules that are derived from food penetrate the mitochondrion's outer membrane
(B) Electrons help to transform adenosine diphosphate into adenosine triphosphate.
(C) Mitochondria from a eukaryotic cell's cytoplasm are transported to the cell's nucleus.
(D) Eukaryotic cells develop subcellular structures, internal membranes and nuclei.
(E) The fluid matrix enclosed by the mitochondrion's inner membrane is transformed into organic molecules that are later broken down in a series of chemical reactions.
DEAB[spoiler][/spoiler]
Premise: If you like my post
Conclusion : Press the Thanks Button
Conclusion : Press the Thanks Button
