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Changing the shape or morphology of the mitochondrial inner membrane can change the efficiency of mitochondrial function.
Which of the following outcomes will most likely result from a change in the shape of the mitochondrial inner membrane from a highly folded surface to a smooth, flat surface?
(d) Mitochondria will become less efficient because the surface area of the inner mitochondrial membranes will decrease
The figure shows a process by which a cell might absorb food from its surrounding environment and break it down for use as a source of energy and matter. The process involves lysosomes, which are membrane-bound organelles that contain hydrolytic enzymes. Activation of the hydrolytic enzymes requires an acidic pH, and lysosomes maintain an internal acidic pH by using ion pumps.
(b) The internal pH of the lysosomes will increase, which will prevent the activation of hydrolytic enzymes and interfere with the intracellular digestion of food.
Which of the following statements best predicts the effect of increasing the permeability of the mitochondrial membranes to large molecules?
ATP production will decrease because of an increase in the occurrence of uncontrolled chemical reactions
Researchers propose a model to explain variation in phytoplankton cell sizes in a marine environment. They base their model on the idea that smaller cells absorb nutrients more efficiently. The researchers predict that the mean diameter of phytoplankton cells will change by 50 micrometers for every 5-kilometer increase in distance from the shore because of a gradual decrease in nutrient availability. To test their model, the researchers determine that the phytoplankton cells found closest to shore have a mean diameter of 900 micrometers.
Based on the model, what will be the mean diameter of the phytoplankton cells that are found 25 kilometers from shore?
650 micrometers
A spherical bacterial cell has a radius of 3 um. The human egg cell has a radius of 100 um.
Which statement correctly indicates the cell that is able to more efficiently exchange materials with the external environment and provides a correct explanation?
The bacterial cell, because it has the largest surface-to-volume ratio.
Two different models of a living cell are represented in the figure.
Of the two cells represented in the figure, which would likely be more efficient at exchanging substances with the surrounding environment?
Cell A, because it has the larger surface-area-to-volume ratio.
Organelles such as mitochondria and the endoplasmic reticulum have membranes that compartmentalize reactions and other metabolic processes. To function properly, the organelles must move substances across their membranes.
Which of the following statements describes a feature shared by mitochondria and the endoplasmic reticulum that increases the efficiency of their basic functions?
They have highly folded membranes.
All eukaryotic cells contain at least one Golgi complex, typically located in the cytoplasm and near the endoplasmic reticulum.
Which of the following best describes a process that occurs within the Golgi complex?
Enzymatic modification of newly synthesized integral membrane proteins
Cells contain smaller components called organelles that are necessary for a cell’s survival. Organelle functions have often been compared to components of larger systems.
Which of the following functional differences between the rough and smooth endoplasmic reticulum
is explained by the structural differences between them?
Rough ER can synthesize and package proteins for export, and smooth ER cannot.
Which of the following claims is scientifically accurate and consistent with an observation that a decrease in lysosome production within a cell leads to a decline in mitochondrial activity?
Fewer lysosomes will be available to break down macromolecules to provide the necessary nutrients for cellular respiration.
Muscle cells have high ATP demands. Which of the following is a scientific claim about how the structure of the mitochondria in muscle cells should be different than it is in other cells because of the high energy demands of mitochondria?
The inner membrane of the mitochondria in muscle cells should have more folds to increase the surface area, allowing more ATP to be synthesized
Researchers have proposed a model of the process by which a newly synthesized protein is transported to the plasma membrane and secreted into the extracellular space. The model is represented in Figure 1.
Figure 1. A model of the intracellular transport of a newly synthesized secreted protein
Based on the model, the newly synthesized protein is transported directly from the endoplasmic reticulum to which of the following?
the golgi complex
The illustration shows the active transport of hydrogen ions through a membrane protein.
Which of the following best predicts the effect of not having ATP available to supply energy to this process?
Responses
H+ ions will stop moving through the protein
Which statement best describes the effect on water transport across the cell membrane if the aquaporin in the figure ceases to function?
Water molecules will still be able to move across the cell membrane but at a slower rate
A cell’s membrane potential is maintained by the movement of ions into and out of the cell. A model showing the influence of membrane proteins on the movement of sodium (Na+) and potassium (K+) ions across the plasma membrane is presented in Figure 1.
Figure 1. Section of a cell’s plasma membrane, showing ion concentrations and membrane proteins
Based on the model presented in Figure 1, which of the following outcomes will most likely result from a loss of protein X function?
Responses
The membrane potential will be disrupted by an increase in K+ concentration inside the cell
Cholesterol is an important component of animal cell membranes. Cholesterol molecules are often delivered to body cells by the blood, which transports the molecules in the form of cholesterol-protein complexes. The complexes must be moved into the body cells before the cholesterol molecules can be incorporated into the phospholipid bilayers of cell membranes.
Based on the information presented, which of the following is the most likely explanation for a buildup of cholesterol molecules in the blood of an animal?
The animal’s body cells are defective in endocytosis
Which of the following statements best explains the processes of passive and active transport?
Passive transport is the net movement of substances down a concentration gradient that does not require metabolic energy. Active transport is the movement of substances up a concentration gradient that requires energy.
In an experiment, cells were isolated from an aquatic plant and suspended in pond water, a sucrose sugar solution, or distilled water. All of the cells were then viewed under a microscope. Compared with the cell in the pond water, the cell in the sugar solution appeared shriveled, and the cell in the distilled water appeared inflated. The results of the experiment are represented in Figure 1.
Figure 1. The results of an experiment using aquatic plant cells
Which of the following statements best explains the observations represented in Figure 1 ?
There was a net movement of water out of the cell suspended in the sugar solution and a net movement of water into the cell suspended in the distilled water.
Aquaporins are channel proteins that facilitate the transport of water across the cell membrane. One group of researchers hypothesizes that without functional aquaporins, no water will be able to enter the cell. A different group proposes an alternative hypothesis, stating that even with nonfunctional aquaporins, a small amount of water will still cross the cell membrane. An experiment is set up in which plant cells with mutated (nonfunctional) aquaporins and plant cells with normally functioning aquaporins are both placed in distilled water.
Which of the following data would support the alternative hypothesis?
Cells with mutated aquaporins exhibit moderate turgor pressure and are hypertonic.
Plant cell walls are composed of cellulose, while fungal cell walls are composed of chitin. A group of scientists hypothesize that this difference means the cell wall has largely different functions in plant cells and fungal cells. Alternatively, another group of scientists hypothesize that despite their biochemical differences, plant and fungal cell walls serve similar functions.
Which of the following observations would best support the alternative hypothesis described above?
In both plant cells and fungal cells, the cell wall surrounds the outside of the cell membrane.
A team of biologists develop a new drug, and one team member hypothesizes that the drug is incapable of freely passing across the plasma membrane and requires the help of membrane proteins to enter cells. Alternatively, another biologist on the team hypothesizes that the drug can diffuse passively across the plasma membrane like O2 and CO2 can.
Which of the following, if true about the drug, best supports the alternative hypothesis that the new drug will exhibit simple diffusion across plasma membranes?
The drug is a small nonpolar molecule.
Figure 1 shows a model of how a channel protein influences the movement of a particle across a cell’s plasma membrane.
Figure 1. A section of a cell’s plasma membrane, showing a channel protein and a concentration gradient across the membrane
An investigator wants to understand whether a newly found membrane protein is involved in membrane transport of a certain particle. Which investigation will help determine whether the new membrane protein is a channel protein involved in membrane transport?
Add more of the proteins to the plasma membrane and measure the rate of the particle movement.
Water is constantly diffusing into the cytosol of freshwater single-celled organisms. In order to maintain the proper solute concentrations in the cytosol, contractile vacuoles pump out the excess water. An experimenter placed single-celled organisms into various saline concentrations and recorded the ATP used by the contractile vacuole. The data are shown in the graph.
Of the following, which additional investigation can be used to determine when the cells are in an isotonic solution?
Increasing the salinity of the environment a little at a time until the ATP usage reaches a minimum
The transport of a substance across a plasma membrane of a specific organelle requires energy. The rate at which the transport takes place also depends on temperature. A scientist isolated the specific organelle and then used the following treatments to determine the conditions that will result in the maximal transport. All treatments contained the extracted organelle and were maintained at 25°C.
The data from this experiment indicate that maximal rate of transport of protein X at 25°C occurs at an ATP concentration of 1.0μm/mL.
Figure 1. The four ATP concentrations used in the experiment
Which procedure should be done next to gather data needed to meet the scientist’s objective?
Incubate samples containing 1.0μm/mL of ATP at four temperatures other than 25°C.
Researchers claimed that a particular organelle originated from a free-living prokaryotic cell that was engulfed by a larger cell, as shown in Figure 1.
Figure 1. A model showing a cell engulfing a smaller cell
Which of the following provides evidence to best support the researchers’ claim?
The organelle has a double membrane
Which of the following statements best supports the claim that certain organelles within eukaryotic cells evolved from free-living prokaryotic cells?
Some organelles contain their own DNA that is more similar to prokaryotic DNA in structure and function than to the eukaryotic DNA found in the cell's nucleus.
The endosymbiont theory proposes a model for the evolution of mitochondria. According to the model, an ancestral eukaryote engulfed a small, free-living prokaryotic organism. The engulfed prokaryote then formed an endosymbiotic relationship with the eukaryotic host.
Which of the following observations best supports the model?
Mitochondria and some prokaryotes share similar metabolic reactions that produce ATP.
Which of the following best describes the numbered areas?
Responses
Areas 1 and 3 are polar, since the membrane molecules are aligned with water molecules.
The model below shows the structure of a portion of a plasma membrane in an animal cell.
Which statement best explains the orientation of the phospholipid molecules in this model?
The hydrophilic phosphate groups of the phospholipid molecules are attracted to the aqueous internal and external environments.
A model of the plasma membrane showing several biological molecules, including a transmembrane protein, is shown in Figure 1.
Figure 1. Phospholipid bilayer with transmembrane protein
Which statement best explains why correct protein folding is critical in the transmembrane protein shown above?
Interactions of the hydrophobic and hydrophilic amino acids help to anchor the protein in the membrane.
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