ap study unit 2

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. The model predicts that phytoplankton cell size will decrease with increasing distance from the shore, resulting in increased efficiency of nutrient absorption. The correct value was arrived at by subtracting 250 from 900.

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. If the movement of particles is mediated by the channel protein, then an increase in proteins in the cell membrane should influence the rate of particle movement across the membrane.

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 ATPATP usage reaches a minimum If the environment is isotonic to the cell, the net flow of water due to diffusion is zero, and ATPATP is not used to pump water out of the cell.

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. 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. This procedure combines the optimal ATP concentration for transport with data for transport rates at four other temperatures.

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. Passive transport is the net movement of substances down (with) a concentration gradient that does not require metabolic energy and active transport is the movement of substances up (against) a concentration gradient that requires energy.

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. Membrane proteins and secreted proteins are synthesized by ribosomes bound to the surface of the endoplasmic reticulum. As shown in the figure, a newly synthesized secreted protein is transported by vesicles from the endoplasmic reticulum directly to the Golgi complex.

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. Small nonpolar molecules freely pass across the plasma membrane. If the drug is a small nonpolar molecule, this supports the alternative hypothesis.

Which of the following best describes the numbered areas?

Areas 1 and 3 are polar, since the membrane molecules are aligned with water molecules. As indicated in the diagram, the heads of the phospholipids in areas 1 and 3 are adjacent to water molecules, which shows that the phospholipid heads are hydrophilic.

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. Of the two cells represented in the figure, Cell A has the larger surface-area-to-volume ratio of 0.91 compared to a surface-area-to-volume ratio of 0.75 for Cell B. Cell A would likely exchange substances with the surrounding environment at a greater rate.

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. Even with mutated aquaporins, a small amount of water is able to enter and leave the cell. Thus, turgor pressure is not lost and the alternative hypothesis is supported.

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 The Golgi complex is a membrane-bound structure to which some proteins are moved from the rough endoplasmic reticulum, where they are enzymatically modified before being sent to a cellular membrane.

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. A function of the lysosomes is the breakdown and recycling of macronutrients, such as carbohydrates. Products of carbohydrate breakdown such as glucose are utilized by the mitochondria in the process of cell respiration.

Which of the following best predicts the effect of not having ATP available to supply energy to this process?

H+ ions will stop moving through the protein. Metabolic energy such as ATP is required for active transport of ions against a concentration gradient.

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. In both plants and fungi, a major function of the cell wall is to confer structural rigidity to the cell. Thus, in both cell types, the cell wall's location is similar. This is evidence supporting the alternative hypothesis proposed above.

A model of the plasma membrane showing several biological molecules, including a transmembrane protein, is shown in Figure 1. 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. Tertiary structure of the protein resulting from hydrophobic and hydrophilic interactions plays a key role in how the protein interacts with the hydrophobic tails and hydrophilic head of the membrane phospholipids.

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 (ER) is explained by the structural differences between them?

Rough ER can synthesize and package proteins for export, and smooth ER cannot. The ribosomes associated with rough ER synthesize proteins that are then exported from 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. The cholesterol-protein complexes are most likely moved into the body cells by endocytosis. A defect in endocytosis is likely to result in a buildup of cholesterol in the blood.

A spherical bacterial cell has a radius of 3μm. The human egg cell has a radius of 100μm. 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. The bacterial cell is more efficient in the exchange of materials with the external environment. While the egg cell is much larger than the bacterial cell, the egg cell has a surface-to-volume ratio that is 33 times smaller than the bacterial cell's surface-to-volume ratio.

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. The hydrophilic polar phosphate groups of the phospholipid molecules orient toward the polar internal and external aqueous environments, forming a bilayer that keeps the hydrophobic portions of the phospholipids away from the polar molecules.

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. The amount of ATP produced is related to the number of ATP synthase molecules located on the inner mitochondria membrane. Increasing the folds increases the number of ATP generation sites and results in more ATP production.

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. Based on the model presented in Figure 1, which of the following outcomes will most likely result from a loss of protein X function?

The membrane potential will be disrupted by an increase in K+ concentration inside the cell. The intracellular K+ concentration will increase because the Na+−K+ pump will continue to transport K+K+ into the cell without any diffusing out of the cell. As a result, the cell's membrane potential will be disrupted.

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. 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. The plasma membrane that surrounds a living cell is typically permeable to water but not sucrose. In the experiment represented in Figure 1, there was a net movement of water out of the cell suspended in the sugar solution, causing the cell to appear shriveled, and a net movement of water into the cell suspended in the distilled water, causing the cell to appear inflated.

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. Compared with a smooth membrane, a highly folded membrane has a greater surface area that increases the rate of material transport across the membrane and provides more support for membrane-associated processes.

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. The aquaporin facilitates water passage, but water can still move across the membrane by osmosis.