Mastering Bio Ch.7

Which of these can RAPIDLY pass directly through the phospholipids of the plasma membrane, without the help of a transport protein? A. Lipid solute molecule B. water C. Glucose D. Hydrogen ion

A only

Both sodium and potassium ions are transported against their concentration gradients. Active and passive transport of solutes across a membrane typically differ in which of the following ways?

Active transport always involves the utilization of cellular energy, whereas passive transport does not require cellular energy.

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.

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. The diverse proteins found in and attached to membranes perform many important functions.

When molecules move down their concentration gradient, they move from where they are more concentrated to where they are less concentrated.

Diffusion across a biological membrane is called passive transport.

Which of the following correctly describes some aspect of exocytosis or endocytosis?

Exocytosis and endocytosis temporarily change the surface area of the plasma membrane.

isotonic, hypotonic, hypertonic

For a cell in an isotonic solution, water flows into the cell to the same extent that it flows out of the cell. If a cell is in a hypotonic solution, water flows into the cell, which causes it to swell and potentially burst. For a cell in a hypertonic solution, water flows out of the cell, which causes it to shrink.

Identify Structure A.

Glycoprotein

Facilitated diffusion is a type of _______.

Passive transport

Structure A is a _____. (triangles going through the trasnport)

Solute

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

Solution A: 1.4% (m/v) starch

Which solution will increase in volume?

Solution D: 12.4% (m/v) NaCl

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+.

How do membrane phospholipids interact with water?

The polar heads interact with water; the nonpolar tails do not.

Structure A in the figure is a(n) _____.

Transport protein

Structure B is a _____.

Transport protein

In facilitated diffusion, what is the role of the transport protein?

Transport proteins provide a hydrophilic route for the solute to cross the membrane.

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

Hydrophobic substances like salad oil are

nonpolar molecules that repel water molecules.

Identify Structure D.

phospholipid bilayer of membrane

What is the function of Structure E?

stabilization of the phospholipids

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

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.

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 have a hydrophilic head and hydrophobic tails.

• The hydrophilic head includes a glycerol molecule attached to a single phosphate group, which is then attached to another small molecule. The phosphate group and its attachments are either polar or charged. Water molecules are polar and therefore are attracted to these charged regions of the phospholipid head. • The hydrophobic tails are two fatty acids attached to the glycerol molecule of the head. Water molecules are not attracted to the tails because C-H bonds are relatively nonpolar and therefore do not result in charged regions in the tails,