Chapter 7: Membrane Structure and Function

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Mastering Biology

Which of the following types of molecules are the major structural components of the cell membrane?

phospholipids and proteins

The presence of cholesterol in the plasma membranes of some animals

enables the membrane to stay fluid more easily when cell temperature drops.

Which of the following is one of the ways that the membranes of winter wheat are able to remain fluid when it is extremely cold?

by increasing the percentage of unsaturated phospholipids in the membrane

In order for a protein to be an integral membrane protein it would have to be which of the following?

amphipathic

When a membrane is freeze-fractured, the bilayer splits down the middle between the two layers of phospholipids. In an electron micrograph of a freeze-fractured membrane, the bumps seen on the fractured surface of the membrane are

integral proteins

Which of the following is a reasonable explanation for why unsaturated fatty acids help keep any membrane more fluid at lower temperatures?

The double bonds form kinks in the fatty acid tails, forcing adjacent lipids to be further apart.

Of the following functions, which is most important for the glycoproteins and glycolipids of animal cell membranes?

a cell's ability to distinguish one type of neighboring cell from another

An animal cell lacking oligosaccharides on the external surface of its plasma membrane would likely be impaired in which function?

cell-cell recognition

Which of these are not embedded in the lipid bilayer at all?

peripheral proteins

Which of these often serve as receptors or cell recognition molecules on cell surfaces?

glycoproteins

What kinds of molecules pass through a cell membrane most easily?

small and hydrophobic

Which of the following is a characteristic feature of a carrier protein in a plasma membrane?

It exhibits a specificity for a particular type of molecule.

Which of the following would likely move through the lipid bilayer of a plasma membrane most rapidly?

CO2

Which of the following statements is correct about diffusion?

It is a passive process in which molecules move from a region of higher concentration to a region of lower concentration.

Water passes quickly through cell membranes because

it moves through aquaporins in the membrane.

Cystic fibrosis is a genetic disease in humans in which chloride ion channels in cell membranes are missing or nonfunctional.

Chloride ion channels are membrane structures that include which of the following?

hydrophilic proteins

Which of the following factors does not affect membrane permeability?

The polarity of membrane phospholipids

How can a lipid be distinguished from a sugar?

Lipids are mostly nonpolar.

True or false? Osmosis is a type of diffusion.

True

What property of dishwashing liquid (detergent) makes it useful to wash grease from pans?

Amphipathic nature

Which of the following particles could diffuse easily through a cell membrane?

Oxygen (O2)

True or false? The water-soluble portion of a phospholipid is the polar head, which generally consists of a glycerol molecule linked to a phosphate group.

True

If a red blood cell is placed in a salt solution and bursts, what is the tonicity of the solution relative to the interior of the cell?

Hypotonic

What name is given to the process by which water crosses a selectively permeable membrane?

Osmosis

Celery stalks that are immersed in fresh water for several hours become stiff and hard. Similar stalks left in a salt solution become limp and soft. From this we can deduce that the cells of the celery stalks are

hypertonic to fresh water but hypotonic to the salt solution.

Which of the following statements correctly describes the normal tonicity conditions for typical plant and animal cells?

The animal cell is in an isotonic solution, and the plant cell is in a hypotonic solution.

Which of the following membrane activities require energy from ATP hydrolysis?

Na+ ions moving out of the cell

What are the membrane structures that function in active transport?

integral proteins

Glucose diffuses slowly through artificial phospholipid bilayers. The cells lining the small intestine, however, rapidly move large quantities of glucose from the glucose-rich food into their glucose-poor cytoplasm. Using this information, which transport mechanism is most probably functioning in the intestinal cells?

facilitated diffusion

What is the voltage across a membrane called?

membrane potential

The sodium-potassium pump is called an electrogenic pump because it

contributes to the membrane potential.

The movement of potassium into an animal cell requires

an energy source such as ATP or a proton gradient.

Endocytosis moves materials _____ a cell via _____.

into ... membranous vesicles

A white blood cell engulfing a bacterium is an example of _____.

phagocytosis

White blood cells engulf bacteria through what process?

phagocytosis

In receptor-mediated endocytosis, receptor molecules initially project to the outside of the cell. Where do they end up after endocytosis?

on the inside surface of the vesicle

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

a greater proportion of unsaturated phospholipids

The presence of cholesterol in the plasma membranes of some animals

enables the membrane to stay fluid more easily when cell temperature drops.

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