Membranes

A lipid bilayer is composed of ______ leaflet(s).

2

To move a substance through a membrane against a concentration gradient, which of the following are necessary?

A transport protein A source of energy

Which of the following could provide energy to fuel active transport? A concentration gradient ATP Carbohydrate Flippase

ATP

Movement of a substance from a region where its concentration is low to a region where its concentration is high with the aid of a transport protein and a source of energy

Active tranport

ATP can be used to power which of the following processes?

Active transport

Which type of transport requires a source of energy and a transport protein?

Active transport

What are functions of the selectively permeable plasma membrane?

Allows the removal of waste products from the cell Maintains a proper supply of essential molecules such as glucose and amino acids Maintains a proper balance of ions within the cell

Why is the phospholipid bilayer an effective barrier to hydrophilic or polar molecules?

Because of the hydrophobic interior of the bilayer

Movement of a substance from a region where its concentration is high to a region where its concentration is low

Diffusion

What is osmosis?

Diffusion of water from an area of low solute concentration to an area of high solute concentration

Movement of a substance from a region where its concentration is high to a region where its concentration is low through a passageway provided by a transport protein

Facilitated diffusion

What types of transport require a transport protein?

Facilitated diffusion Active transport

Which statements comparing simple and facilitated diffusion are true?

Facilitated diffusion, but not simple diffusion, requires a transport protein. Both simple and facilitated diffusion require concentration gradients.

According to the ______ model, membrane proteins and lipids are able to move relative to one another within the plasma membrane.

Fluid-mosaic

Which of the following can readily diffuse across the cell membrane?

Gases Small, uncharged molecules

Why is the phospholipid bilayer composed of two leaflets?

Hydrophobic nonpolar tails can be isolated into a hydrophobic environment between the two leaflets. Phospholipids are amphipathic and must interact with polar and nonpolar environments. Membranes must interact with two polar environments, a hydrophilic cytoplasm and a hydrophilic extracellular environment.

The solute concentration outside a cell is higher than the solute concentration inside the cell.

Hypertonic solution

The solute concentration outside the cell is lower than the solute concentration inside the cell.

Hypotonic solution

Water diffuses through a membrane from a solution that is _________ (lower concentration of dissolved particles) into a solution that is _________ (higher concentration of dissolved particles). Solutions with identical concentrations are said to be __________.

Hypotonic; hypertonic; isotonic

What changes in lipid composition would be expected to increase the fluidity of a phospholipid bilayer?

Incorporating more cholesterol at low temperatures Incorporating more unsaturated fatty acids

Which of the following changes in lipid composition would be expected to increase the fluidity of a phospholipid bilayer?

Incorporating more unsaturated fatty acids Incorporating more cholesterol at low temperatures

Which of the following statements is correct about a biological membrane that is fluid?

Individual molecules can move within the membrane.

The solute concentration outside a cell is equal to the solute concentration inside the cell.

Isotonic solution

How does cholesterol affect the plasma membrane at low temperatures?

It makes the membrane more fluid and prevents freezing.

Which of the following statements are consistent with the fluid-mosaic model?

Many membrane proteins move within the plane of the membrane. Membranes are mainly composed of proteins and phospholipids. Phospholipids can move within the plane of the membrane.

Shorter nonpolar tails make the membrane ______ fluid.

More

What is the basic structure of the plasma membrane?

Phospholipid bilayer

Why is it more appropriate to describe membranes as semifluid?

Phospholipids usually move in two dimensions. Molecules move laterally within the membrane leaflet.

The cell membrane is referred to as a mosaic because it is a mixture of what types of molecules?

Proteins Carbohydrates Lipids

The fluidity of the plasma membrane can be increased by incorporating fatty acids with ______ tails or by incorporating ______ lipids.

Shorter; unsaturated

What separates the internal contents of a cell from the extracellular environment?

The plasma membrane

The transport of a substance that requires an input of energy is called ________ transport.

active

The difference between passive transport and active transport is that active transport requires:

an input of energy.

A key similarity between simple and facilitated diffusion is that both require ______.

concentration gradients

Some molecules are known to move laterally in the plane of the membrane. As such, we can say the membrane is:

fluid

What property of biological membranes describes the ability of individual molecules to move within the membrane?

fluidity

When the concentration of a solute is higher on one side of membrane than the other, a transmembrane _______ is established.

gradient

Membrane fluidity is increased when membrane lipids:

have shorter nonpolar tails.

Movements that keep the phospholipid nonpolar tail within the __________ region of the bilayer are energetically favorable.

hydrophobic

Phospholipid bilayers are an effective barrier to many charged or polar solutes because of their ________ interior region.

hydrophobic

Movements that keep the phospholipid nonpolar tail within the ___________ region of the bilayer are energetically favorable.

hydrophobic, nonpolar, internal, interior, inside, or inner

A solution whose solute concentration is higher than the concentration of solutes inside a cell is ______.

hypertonic

When the concentration of solutes outside the cell is higher than that intra-cellularly, the solution is said to be _________ relative to the inside of the cell.

hypertonic

When the concentration of solutes outside the cell is lower than that intra-cellularly, the solution is said to be _________ relative to the inside of the cell.

hypotonic

When the solute concentration is higher inside the cell relative to outside the cell, the outside solution is said to be:

hypotonic.

When the concentrations of dissolved particles (solutes) on both sides of the plasma membrane are equal, the two solutions are said to be

isotonic

A solution in which the solute concentration on both sides of the membrane is equal is classified as:

isotonic.

Which of the following movements of a phospholipid are energetically favorable within the bilayer?

lateral movements rotational movements

Most phospholipids move freely within a semifluid membrane __________.

laterally along the plane of the membrane in two dimensions

One layer, or half of a phospholipid bilayer, is termed a(n) ________.

leaflet

At a high temperature, cholesterol makes a membrane ______ fluid.

less

Osmosis describes the movement of water from areas where the solute concentration is _________ to areas in which the solute concentration is ________.

low; high

The internal and external environments of a cell are separated by a structure known as the plasma ________.

membrane

Because the plasma membrane contains lipids, proteins, and carbohydrates, it is often described as a(n) ______.

mosaic

Small, uncharged molecules pass through the membrane via ______.

passive diffusion

The selective ____________ of the plasma membrane allows the cell to maintain a favorable internal environment.

permeability

The plasma membrane consists of a _________ bilayer.

phospholipid

The three main types of macromolecules that comprise the plasma membrane are:

phospholipids, proteins, and carbohydrates

The plasma membrane of a cell is considered to be:

selectively permeable

All cells are surrounded by __________ permeable plasma membrane, meaning that the membrane allows the passage of some molecules and ions but not others.

semi

The two leaflets of a lipid bilayer are formed because:

the polar head groups of phospholipids can interact with the polar interior and exterior of the cell.

Cellular membranes are described as fluid because ______.

their lipids and proteins can move relative to each other

A term that describes a situation in which the concentration of a solute is higher on one side of a membrane than the other is:

transmembrane gradient.