Chapter 7 Homework

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

https://docs.google.com/document/d/1UkKgW01NpcQhUKCtO5gb0qc88BOcW0n_qvoUHvEP8F8/edit?usp=sharing

If more sugar were added to the solution on the left side of the tube, what would happen to the water level on the right side of the tube?

The water level would go down.; If more solute were added on the left side, it would draw more water to cluster around the solute molecules, lowering the free water on the left compared to the right side. That would cause osmosis of water toward the left side, lowering the water level on the right side.

Which of the following factors would tend to increase membrane fluidity?

a greater proportion of unsaturated phospholipids

In this diagram of the plasma membranes of two adjoining cells, identify the protein indicated by the white arrow, including its function.

a receptor protein that binds with a signaling molecule and relays the message into the cell by activating other molecules inside the cell; Signaling proteins are part of signal transduction pathways that transmit external chemical signals into the cell.

You are working on a team that is designing a new drug. For this drug to work, it must enter the cytoplasm of specific target cells. Which of the following would be a factor that determines whether the molecule selectively enters the target cells?

the similarity of the drug molecule to other molecules that are transported into the target cells; If the target cells have transport proteins that specifically bind to certain molecules, they may bind with and transport a drug that is similar in structure.

Which of the following statements is TRUE with regard to this animation?

Both sodium and potassium ions are transported against their concentration gradients; Both ions are transported from where their concentration is low to where their concentration is high, and the cell expends energy in the form of ATP to do it.

Which of the following statements about the conditions shown in the U-shaped tube are true?

There is less free water in the right arm of the tube than in the left arm of the tube. Water is tightly clustered around the hydrophilic solute molecules on both sides of the membrane. Water molecules will cluster around hydrophilic solute molecules (shown as green dots), leaving less water "free" in the solution. There is more solute in the right arm of the tube, so there is less free water on that side.

According to the fluid mosaic model of membrane structure, proteins of the membrane are mostly

embedded in a lipid bilayer.

This figure reviews the structure of a phospholipid. Drag the terms on the left to the appropriate blanks on the right to complete the sentences.

1. A phospholipid has a "head" made up of a glycerol molecule attached to a single Phosphate Group, which is attached to another small molecule. 2. Phospholipids vary in the small molecules attached to the phosphate group. The phospholipid shown in the figure has a Choline Group attached to phosphate. 3. Because the phosphate group and its attachments are either charged or polar, the phospholipid head is Hydrophilic , which means it has an affinity for water. 4. A phospholipid also has two "tails" made up of two fatty acid molecules, which consist of a carboxyl group with a long hydrocarbon chain attached. 5. Because the C-H bonds in the fatty acid tails are relatively nonpolar, the phospholipid tails are hydrophobic , which means they are excluded from water.

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. Use targets of Group 1 to indicate the relative concentrations of Na+ and K+ inside and outside the cell. Use targets of Group 2 to indicate the relative charges inside and outside the cell. Use targets of Group 3 to indicate how many ions move through the pump and in which directions.

- 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+. The concentration gradient of Na+ ions across the membrane (higher Na+ concentration outside) facilitates the diffusion of Na+ into the cell. At the same time, the electrical gradient across the membrane (excess positive charge outside) drives Na+ into the cell. The concentration gradient of K+ ions across the membrane (higher K+ concentration inside) facilitates the diffusion of K+ out of the cell. However, the electrical gradient across the membrane (excess positive charge outside) impedes the diffusion of K+ out of the cell. The electrochemical gradient for an ion is the sum of the concentration (chemical) gradient and the electrical gradient (charge difference) across the membrane. For Na+ ions, diffusion through the Na+ channel is driven by both the concentration gradient and the electrical gradient. But for K+ ions, the electrical gradient opposes the concentration gradient. Therefore, the electrochemical gradient for Na+ is greater than the electrochemical gradient for K+.

Biologists use the fluid mosaic model to describe membrane structure. Which statements about the fluid mosaic structure of a membrane are correct? Select the three correct statements.

- The diverse proteins found in and attached to membranes perform many important functions. - Because membranes are fluid, membrane proteins and phospholipids can drift about in the membrane. - The framework of a membrane is a bilayer of phospholipids with their hydrophilic heads facing the aqueous environment inside and outside of the cell and their hydrophobic tails clustered in the center. Membranes consist of diverse proteins suspended in and attached to a phospholipid bilayer. Kinks in the unsaturated fatty acid tails of some phospholipids keep the membrane fluid, and a mosaic of proteins perform a variety of functions.

Drag the terms on the left to the appropriate blanks on the right to complete the sentence. Terms may be used more than once.

During osmosis, water diffuses across a selectively permeable membrane from the region of higher Free Water concentration and lower solute concentration to the side with lower free water concentration and higher solute concentration

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.

NONPOLAR: Hydrophobic Can cross easily No transport protein required POLAR:Hydrophilic Have difficulty in crossing the hydrophobic part Transport protein required to cross efficiently IONS:Hydrophilic Have difficulty in crossing the hydrophobic part Transport protein required to cross efficiently The structure of the plasma membrane makes it selectively permeable, enabling it to regulate the transport of substances into and out of the cell. Small, nonpolar molecules are hydrophobic, so they can easily cross the phospholipid bilayer of the plasma membrane. Polar molecules and ions are hydrophilic, so they cannot very easily cross the hydrophobic portion of the plasma membrane (formed by the phospholipid tails). Water is an unusual molecule because, despite the fact that it is polar, it is small enough to pass directly through the hydrophobic interior of the lipid bilayer, albeit slowly. Polar molecules and ions generally cross the plasma membrane with the help of transport proteins. For example, water crosses the bilayer rapidly via transport proteins called aquaporins.

Phospholipids form the main fabric of the plasma membrane. One feature of phospholipids is that when they are placed in an aqueous solution, they will self-assemble into a double layer (bilayer) that resembles the bilayer of the plasma membrane. This self-assembly occurs because phospholipids are hydrophilic at one end (the phospholipid head) and hydrophobic at the other end (the phospholipid tails). Drag the labels to their appropriate locations in the figure. First, drag labels of Group 1 to targets (a) and (b) to indicate whether these environments are hydrophilic or hydrophobic. Next, drag the phospholipid layers (Group 2) to targets (c) and (d) to indicate how they are oriented in the plasma membrane. Finally, drag labels of Group 1 to targets (e), (f), and (g) to indicate which portions of the membrane protein are hydrophilic and which are hydrophobic.

Phospholipids make up the main fabric of the plasma membrane. In the plasma membrane, the phospholipids are found in a bilayer. The hydrophilic heads are exposed to the aqueous environments of the cytoplasm and extracellular fluid, and the hydrophobic tails are sandwiched within, sheltered from these aqueous environments. Other elements of the plasma membrane conform to the hydrophilic and hydrophobic regions established by the phospholipids. For example, membrane proteins have hydrophilic and hydrophobic regions that are found among the hydrophilic and hydrophobic portions of the plasma membrane, respectively. Cholesterol is a hydrophobic molecule and is found among the hydrophobic tails, which you can see in the figure below.

If the pores in the selectively permeable membrane became larger, but still not large enough to let the sugar pass through, what would happen during osmosis in the U-shaped tube compared to what is shown in the figure?

The final water levels would be the same as shown in the figure, but the solutions would reach near equal concentrations faster; The relative concentrations of solutes and free water on either side of the membrane determines the amount of osmosis, but the size of the pores determines how fast osmosis occurs.

How do membrane phospholipids interact with water?

The polar heads interact with water; the nonpolar tails do not. If you had trouble with this question, review the following material: A phospholipid is similar to a fat molecule but has only two fatty acids attached to glycerol rather than three. The third hydroxyl group of glycerol is joined to a phosphate group, which has a negative electrical charge in the cell. The fatty acids, referred to as the "tails" of the phospholipid, are hydrocarbons that are hydrophobic and therefore do not interact with water. The phosphate group and its attachments form a hydrophilic "head" that has an affinity for water.