AP BIOLOGY. chapter 6: hw.

Is glucose uptake into cells affected by age? Glucose, an important energy source for animals, is transported into cells by facilitated diffusion using protein carriers. In this exercise, you will interpret a graph from an experiment in which researchers incubated guinea pig red blood cells in a 300 mM (millimolar) radioactive glucose solution at pH 7.4 at 25°C. Every 10 or 15 minutes, they removed a sample of cells from the solution and measured the concentration of radioactive glucose inside those cells. Cells came from either a 15-day-old guinea pig or a 1-month-old guinea pig.The graph at left shows the data from the experiment.

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Osmosis is the net movement of water across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration. The water will continue to move across the semipermeable membrane as the system attempts to reach equilibrium, where both solutions have the same concentration. There are three different ways a solution can be described in relation to a cell placed in the solution: isotonic, hypotonic, and hypertonic. Compared to a cell, an isotonic solution exerts the same osmotic pressure as the cellular fluids. In other words, it behaves as if it had the same solute concentration as the cell. A hypertonic solution behaves as if it had a higher solute concentration than the cell. A hypotonic solution behaves as if it had a lower solute concentration than the cell. If a cell is placed in an isotonic solution, nothing happens to the cell because water moves into the cell at the same rate that it moves out of the cell. If a cell is placed in a hypotonic solution, water will flow into the cell, causing it to swell (and possibly burst). If a cell is placed in a hypertonic solution, water will flow out of the cell, causing it to shrink.

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A red blood cell placed in a hypertonic solution will shrink in a process called crenation. A red blood cell placed in a hypotonic solution will swell and potentially burst in a process called hemolysis. To prevent crenation or hemolysis, a cell must be placed in an isotonic solution such as 0.9% (m/v) NaCl or 5.0% (m/v) glucose. This does not mean that a cell has a 5.0% (m/v) glucose concentration; it just means that 5.0% (m/v) glucose will exert the same osmotic pressure as the solution inside the cell, which contains several different solutes. A red blood cell is placed into each of the following solutions. Indicate whether crenation, hemolysis, or neither will occur.Solution A: 3.21% (m/v) NaClSolution B: 1.65% (m/v) glucoseSolution C: distilled H2OSolution D: 6.97% (m/v) glucoseSolution E: 5.0% (m/v) glucose and 0.9%(m/v) NaCl Drag each solution to the appropriate bin.

Crenation: A, D, E Hemolysis: B, C Neither: blank

All molecules have energy that causes thermal motion. One result of thermal motion is diffusion: the tendency of substances to spread out evenly in the available space. Although the motion of each individual molecule is random, there can be directional motion of an entire population of molecules. Consider a chamber containing two different types of dye molecules, purple and orange. The chamber is divided into two compartments (A and B) by a membrane that is permeable to both types of dye. Initially (left image), the concentration of the orange dye is greater on side A, and the concentration of the purple dye is greater on side B. With time, the dye molecules diffuse to a final, equilibrium state (right image) where they are evenly distributed throughout the chamber. Drag the labels onto the table to indicate when each statement is true. Labels can be used once, more than once, or not at all.

1. orange dye moves independently of purple dye: always 2. concentration gradients exist that drive diffusion of both dyes: only before equilibrium is reached. 3. there is net movement of orange dye from side a to side b: only before equilibrium is reached. 4. purple dye moves only from side b to side a: never 5. there is no net movement of purple dye: only at equilibrium.

What concentration of radioactive glucose did the researchers find in the red blood cells of a 15-day-old guinea pig after an incubation time of 30 minutes?

85 mM

Sort the phrases into the appropriate bins depending on whether they describe exocytosis, endocytosis, or both.

Exocytosis: requires fusion of vesicles with plasma membrane, secretes large molecules out of the cel, increases the surface area of the plasma membrane Endocytosis: forms vesicles from inward folding of the plasma membrane AND decreases the surface area of the plasma membrane Both: requires cellular energy AND transported substances never physically cross the plasma membrane

A red blood cell has been placed into three different solutions. One solution is isotonic to the cell, one solution is hypotonic to the cell, and one solution is hypertonic to the cell. Determine which type of solution is in each beaker based on the cell's reaction. Drag each item to the appropriate bin.

Hypertonic: smallest cell with pointy protrusions Hypotonic: Large cell with bursting hole Isotonic: normal cell

A semipermeable membrane is placed between the following solutions. Which solution will decrease in volume?

Solution A: 1.4% (m/v) starch

A semipermeable membrane is placed between the following solutions. Which solution will increase in volume?

Solution D: 12.4% (m/v) NaCl Submit

Which of the following statements correctly describe(s) the driving forces for diffusion of Na+ and K+ ions through their respective channels? Select all that apply.

The diffusion of Na+ ions into the cell is facilitated by the Na+ concentration gradient across the plasma membrane. The diffusion of K+ ions out of the cell is impeded by the electrical gradient across the plasma membrane. The electrochemical gradient is larger for Na+ than for K+. Submit

Which of the following hypotheses is a reasonable explanation for the data represented in the graph?

The red blood cells of older guinea pigs have fewer glucose transporter proteins than the red blood cells of younger guinea pigs. Submit

Extracellular fluid

A. Hydrophillic E. Hydrophilic

Identify the trend common to both the 15-day-old and 1-month-old guinea pigs' red blood cells.

Both experienced the most rapid uptake of glucose at the beginning of the experiment. Submit

Plasma membrane

C. and D. the tails face each other F. Hydrophobic

What is the main difference between the trends for the 15-day-old and 1-month-old guinea pigs' red blood cells?

The younger guinea pig's cells took up more glucose than the older guinea pig's cells at all incubation times.

In many animal cells, the uptake of glucose into the cell occurs by a cotransport mechanism, in which glucose is cotransported with Na+ ions. Complete the diagram below using the following steps. Drag the pink labels to the pink targets, indicating the relative concentration of glucose inside and outside the cell. Drag the correct white label to the white target, indicating the direction that Na+ ions and glucose move through the cotransporter. Drag the blue labels to complete the sentences on the right, indicating how Na+ ions and glucose move through the cotransporter relative to their electrochemical and concentration gradients.

a. Na+ high: glucose low outside cell b. glucose and Na+ inside cell c. Na+ low: glucose high inside cell 1. Na+ moves DOWN its electrochemical gradient. 2. Glucose moves AGAINST its electrochemical gradient.

Phospholipids vary in the small molecules attached to the phosphate group. The phospholipid shown in the figure has a ____________ attached to phosphate.

chonline group

Which variable is the dependent variable--the variable that depended on the treatment and was measured by the researchers? Is the dependent variable on the x-axis or the y-axis?

concentration of radioactive glucose; on the y-axis

A phospholipid also has two "tails" made up of two ____________ molecules, which consist of a carboxyl group with a long hydrocarbon chain attached.

fatty acid

Because the phosphate group and its attachments are either charged or polar, the phospholipid head is _____________, which means it has an affinity for water.

hydrophilic

Because the C-H bonds in the fatty acid tails are relatively nonpolar, the phospholipid tails are _____________, which means they are excluded from water.

hydrophobic

Which variable is the independent variable--the variable that was controlled by the researchers? Is the independent variable on the x-axis or the y-axis?

incubation time; on the x-axis

How does phospholipid structure relate to the selective permeability of the plasma membrane?Part complete A critical feature of the plasma membrane is that it is selectively permeable. This allows the plasma membrane to regulate transport across cellular boundaries--a function essential to any cell's existence. How does phospholipid structure prevent certain molecules from crossing the plasma membrane freely? Drag the labels to fill in the table. Use only white labels for white targets, pink labels for pink targets, and blue labels for blue targets.

nonpolar molecules- a. hydrophobic b. can cross easily c. no transport protein required polar molecules- d. hydrophillic e. have difficulty crossing the hydrophobic part f. transport protein required to cross efficiently ions- g. hydrophillic h. have difficulty crossing the hydrophobic part i. transport protein required to cross efficiently

The majority of solutes that diffuse across the plasma membrane cannot move directly through the lipid bilayer. The passive movement of such solutes (down their concentration gradients without the input of cellular energy) requires the presence of specific transport proteins, either channels or carrier proteins. Diffusion through a transport protein in the plasma membrane is called facilitated diffusion. Sort the phrases into the appropriate bins depending on whether they are true only for channels, true only for carrier proteins, or true for both channels and carriers.

only channels: allow water molecules and small ions to flow quickly across the membrane AND provide a continuous path across the membrane only carries: undergo a change in shape to transport solutes across the membrane AND transport primarily small polar organic molecules both channels and carries: are integral membrane proteins AND transport solutes down a concentration gradient or electrochemical gradient AND provide a hydrophillic path across the membrane

All cells contain ion pumps that use the energy of ATP hydrolysis to pump ions across the plasma membrane. These pumps create an electrochemical gradient across the plasma membrane that is used to power other processes at the plasma membrane, including some transport processes. In animal cells, the main ion pump is the sodium-potassium pump. Complete the diagram below using the following steps. Drag the correct white label to the white target, indicating how many ions move through the pump and in which directions. Drag the pink labels to the pink targets, indicating the relative concentrations of Na+ and K+ inside and outside the cell. Drag the blue labels to the blue targets, indicating the relative charges inside and outside the cell.

outside cell: b. NA+ high, K+ low c. excess + charge a. 3 NA+ outside cell, 2 K+ inside cell inside cell: d. NA+ low, K+ high e. excess - charge

What do the blue dots represent?

the concentration of radioactive glucose found in a 1-month-old guinea pig's red blood cells after different incubation times

What do the red dots represent?

the concentration of radioactive glucose found in a 15-day-old guinea pig's red blood cells after different incubation times Submit

Some solutes are able to pass directly through the lipid bilayer of a plasma membrane, whereas other solutes require a transport protein or other mechanism to cross between the inside and the outside of a cell. The fact that the plasma membrane is permeable to some solutes but not others is what is referred to as selective permeability. Which of the following molecules can cross the lipid bilayer of a membrane directly, without a transport protein or other mechanism? Select all that apply.

water carbon dioxide lipids oxygen