Carr Chapter 5

What are two major differences between active transport and passive transport? Please give a specific example of each that occurs within a eukaryotic cell.

Active transport moves molecules against their concentration gradient and thus requires energy, whereas passive transport requires movement with the concentration gradient and does not require energy. Oxygen moves through passive transport, whereas glucose can be moved through active transport.

Which statement below is true?

All internal cell membranes are similar in structure to the plasma membrane.

The 1985 Nobel Prize in Physiology or Medicine was awarded to Michael Brown and Joseph Goldstein for their work on cholesterol metabolism. Brown and Goldstein investigated the cause of remarkably high levels of circulating cholesterol found in certain families. Just as remarkable was the high incidence of heart disease in these families. What Brown and Goldstein found was not what might be expected-these individuals did not make too much cholesterol. Instead, most of these people had defects in receptor-mediated endocytosis (RME). What could possibly link high cholesterol levels in the blood and defective RME in these patients?

Cholesterol was not transported into cells by RME and therefore accumulated in the blood.

Which statement about diffusion is correct?

Diffusion causes movement of materials toward equilibrium.

________ is the process that a cell can use to bring very large molecules into the cell.

Endocytosis

How does glucose enter a cell if levels of blood glucose are high?

Insulin molecules bind to glucose receptors, causing cellular responses to take up glucose.

Which of the following is true of the plasma membrane?

It controls the passage of substances into and out of the cell.

Which of the following is an accurate description of the plasma membrane?

It is a phospholipid bilayer embedded with proteins.

passive transport

Movement of materials across a cell membrane that does not require energy

An accident victim lost a lot of blood and was rushed to the emergency room. In the emergency room, the first thing the doctors did was replace lost fluids by giving an IV of pure water. But this caused the patient to die. Propose a reason why the patient died.

Pure water is hypotonic to the cells in the blood. This would cause blood cells to swell and burst, which could lead to the death of the patient.

active transport

Requires the expenditure of energy to move molecules or ions across a cell membrane

You have isolated a cell that is unable to produce cholesterol for its cell membranes. Which of the following defects is this cell most likely to have?

The cell membrane will not have the correct fluidity.

The central vacuoles of some plant cells you are studying fill with water and press the cell contents against their cell walls because of osmosis. What can you predict about the concentration of solutes in the solution that bathes the turgid plant cells?

The concentration of solutes outside the cell must be significantly lower than the concentration within the cell.

For this type of transport to take place, which of the following must be true about the interior and exterior environments?

The glucose concentration must be higher outside the cell than inside the cell

It seems that bacteria and molds should grow well in jam. It's extremely high in sugar, a substance many cells can use for energy, and contains enough other nutrients to support cell growth. Yet jam can be left unrefrigerated for a very long time without contamination by microorganisms. How can this be?

The high sugar concentration causes bacterial and mold cells to shrink and die.

If you transferred a phospholipid bilayer from water to oil, what effect would this have on the membrane?

The membrane would invert its normal structure by positioning the heads on the inside of the bilayer and the fatty-acid tails outside.

If you could add a colored label to one phospholipid in the cell's plasma membrane to observe this molecule, what kind of movement of the molecule would you see?

The molecule would move rapidly back and forth across the surface of the membrane.

simple diffusion

The movement of molecules down their concentration gradient without the use of a transport protein

The plasma membrane proteins of a cell can be linked to colored marker molecules. In an experiment, you labeled the membrane proteins of one cell with a red marker and the membrane proteins of a second cell with a blue marker. Using your understanding of the fluid-mosaic model, what might you see happen if you connected the plasma membranes of the two cells so that they form one continuous membrane?

The plasma membrane is fluid, so the proteins are free to move across the membrane. Eventually, the red proteins of one cell would move to the membrane of the second cell, and the blue proteins of the second cell would move to the membrane of the first cell. Eventually you would have an even mix of red and blue proteins throughout the membrane.

A woman suffering from severe dehydration goes into the hospital. The doctor tells the woman that her blood has far too much solute in it and not enough water. Explain how this condition could affect the cells of her body and why.

This could make the cells of her body lose their water by osmosis. The water in the cells will rush out, trying to equilibrate the higher-than-normal solute level outside the cells.

What is the role of transport proteins within the plasma membrane?

Transport proteins allow movement of ions and polar molecules through the plasma membrane.

Endocytosis

Uses a transport vesicle to bring large materials into the cell

Exocytosis

Uses a transport vesicle to release materials to the exterior of a cell

facilitated diffusion

Uses transport proteins to assist the movement of materials down a concentration gradient

Red blood cells placed in pure water will swell and burst. What process is causing this to happen?

Water is diffusing across the plasma membrane from a region of high (outside the cell) to low (inside the cell) "free" water concentration.

A main function of the carbohydrates that form the glycocalyx is to:

act as binding sites for signaling molecules.

One difference between passive and active transport through a cell membrane is that:

active transport requires ATP.

Yeast cells take up glucose (a sugar) to use as their primary source of energy. Typically, glucose concentrations outside yeast cells are far lower than glucose concentrations inside the cells. Therefore, for yeast to take up glucose, the cells must use:

active transport to move glucose up its concentration gradient

The sodium-potassium pump is an example of:

active transport.

Cystic fibrosis is the result of

an abnormal chloride channel protein

The phospholipids of membranes are:

both hydrophilic and hydrophobic molecules.

Small, nonpolar molecules easily pass through the phospholipid bilayer because the molecules:

can dissolve in the hydrophobic portion of the bilayer.

A component of the plasma membrane that helps to maintain its fluidity is

cholesterol

Diffusing molecules move ________ until they are ________.

down their concentration gradients; evenly distributed

Phagocytosis is a type of ________ in which a cell engulfs another cell.

endocytosis

All of the following processes bring materials into a cell except:

exocytosis.

Insulin and many other hormones are protein molecules. Based on your knowledge of transport processes, you can say that cells that secrete these types of hormones do so through:

exocytosis.

The glycocalyx is found just inside the plasma membrane of the cell.

false

t/f A substance moving down the concentration gradient is an example of active transport

false

t/f Cholesterol is a hormone receptor in the plasma membrane

false

t/f Exocytosis is an example of active transport of a substance into the cell.

false

t/f Integral proteins always extend completely through the plasma membrane.

false

t/f Phagocytosis is an example of passive transport.

false

t/f The hydrophilic region of the phospholipid bilayer faces to the interior of the plasma membrane.

false

The plasma membrane is composed of phospholipids, which are free to move laterally, and is peppered with both stationary and mobile proteins. This view of the plasma membrane is known as the:

fluid-mosaic model.

A purpose of the plasma membrane is to: .

form the outer boundary of a cell.

The ________ functions in cell lubrication, adhesion, and signaling.

glycocalyx

Short chains of sugars attached to proteins or phospholipids in the cell membrane make up the:

glycocalyx.

Diffusion is a process by which a substance:

goes down its concentration gradient.

The ________ of a phospholipid molecule will seek water, whereas the ________ of the molecules will avoid water.

head; tail

The fatty-acid tails of a phospholipid are:

hydrophobic

Water moves from a

hypotonic environment to a hypertonic environment

Facilitated diffusion is similar to simple diffusion because:

in both, materials move down their concentration gradient.

Which type of proteins are involved in nutrient transport across the plasma membrane and why?

integral proteins, because they span the membrane and are able to carry nutrients across the membrane

You have lost a lot of blood in an accident. In the emergency room the first thing the doctors will need to do is replace lost fluids. The fluids they give you should be:

isotonic to your cells.

Membrane proteins perform all of the following functions except:

maintainance of membrane fluidity.

Active transport:

moves substances against their concentration gradient.

The term that describes the diffusion of water is:

osmosis.

The plasma membrane is a semipermeable membrane. This means that it is:

permeable to small and uncharged molecules but not to larger or charged substances.

The primary component of the plasma membrane is

phospholipid

The outer living limit of the cell is called the

plasma membrane

The huge array of capabilities of the plasma membrane are performed by its:

proteins.

A ________ plasma membrane allows water but not solutes to pass through it.

semipermeable

Oxygen moving through the plasma membrane down its concentration gradient is an example of:

simple diffusion.

Which of the following would be least likely to diffuse through a phospholipid bilayer?

sodium ions

Facilitated diffusion occurs with the help of:

transport proteins.

t/f A cell wall stops a plant cell from taking in so much water that it will burst

true

t/f Active transport moves a substance against the concentration gradient.

true

t/f Carbohydrate chains serve as the binding sites for many signaling molecules

true

t/f Cholesterol helps to maintain the correct fluidity of the plasma membrane

true

t/f Diffusion occurs because of random molecular movement

true

t/f Facilitated diffusion occurs down a concentration gradient.

true

t/f Facilitated diffusion occurs through membrane-bound transport proteins

true

t/f Having defective proteins in the cell membrane can cause disease

true

t/f Hydrophobic molecules easily pass through the fatty-acid region of the plasma membrane

true

t/f In cystic fibrosis, cells cannot pump out enough chloride ions

true

t/f Osmosis is an example of passive transport

true

t/f Signals sent between cells reach a cell at receptor proteins

true

t/f Some integral proteins can span the entire phospholipid bilayer

true

t/f The chief component of the plasma membrane is the phospholipid bilayer

true

t/f The functioning of the immune system depends on recognition proteins

true

t/f The hydrophilic heads of phospholipids in the plasma membrane face a water-based environment.

true

t/f The most up-to-date explanation of the structure of the plasma membrane is called the fluid-mosaic model

true

t/f The phospholipid bilayer forms because fatty-acid tails do not dissolve in water.

true

t/f The phospholipid bilayer forms spontaneously in water.

true

t/f To move a molecule into a cell against the concentration gradient requires energy

true

t/f Transport proteins are integral plasma membrane proteins

true

t/f Water moves freely through a semipermeable membrane

true

Peripheral proteins:

usually attach to integral proteins.

Osmosis refers to the diffusion of ________ across a membrane.

water

Plants stay standing upright because of turgor pressure caused by:

water rushing into the cells, keeping the cells tight.

Calcium ions (Ca2+) are present in the endoplasmic reticulum at concentrations 1,000 times higher than in the cytosol (the gel-like part of the cell outside organelles). One protein on the endoplasmic reticulum membrane is devoted to allowing Ca2+ to move from the endoplasmic reticulum to the cytosol, and another protein moves Ca2+ from the cytosol to the endoplasmic reticulum. These processes are not trivial-Ca2+ released into the cytosol allows, for example, for muscle contraction and communication between nerve cells. In this pair of Ca2+ transport proteins, you would predict that the protein moving Ca2+ from the endoplasmic reticulum to the cytosol ________, and the protein that moves Ca2+ from cytosol to the endoplasmic reticulum ________.

works without ATP; requires ATP