Biology 2.1

What factor would tend to increase membrane fluidity?

A greater proportion of unsaturated phospholipids

What crosses lipid bilayers the slowest?

A sodium ion

Which of the following allows water to move much faster across cell membranes?

Aquaporins

A function of cholesterol that does not harm health is its role _____.

As a component of animal cell membranes

Triglycerides vary with respect to the number of ...

C atoms in the tails & double bonds in the tails

In fat synthesis, ____ and fatty acids combine to make fats plus ____.

Glycerol; water

Phospholipids and triglycerides both ____.

Have a glycerol backbone

In the reaction that builds fat, ____ groups react with ____ groups.

Hydroxyl; carboxyl

Celery stalks that are immersed in fresh water for several hours will become stiff. Similar stalks left in a 0.15M salt solution become limp. From this we can deduce that the fresh water _____.

Is hypotonic and the salt solution is hypertonic to the cells of the celery stalks

What do fats, steroids, and waxes have in common?

Low solubility in water.

A phospholipid is a ____.

Non polar lipid molecule that is made amphipathic by the addition of a phosphate

Which is not a lipid? steroids, RNA, wax, cholesterol, phospholipid

RNA (nucleic acid)

The presence of many C-C and C-H bonds causes fats to be ___.

Rich in energy and insoluble in water

If you mechanically shook a mixture of phospholipids and water, what would you expect to see when you observe the solution using an electron microscope?

Some lipids will have formed tiny vesicles filled with water

What is a large organic molecule that is NOT assembled by polymerization of a few kinds of simple subunits?

Steroid

What region of a steroid is hydrophilic?

The terminal hydroxyl group

Why are lipids and proteins free to move laterally in membranes?

There are only weak hydrophobic interactions in the interior of the membrane.

Which aspect of phospholipids is most important to the formation of bilayers?

They are amphipathic

What do DNA, proteins, and fats have in common?

They contain carbonyl groups.

"To move in the bloodstream, fats need the help of phospholipids." What would be a good students response?

Yes. Nonpolar molecules aren't compatible with water.

Lipids _____.

are insoluble in water

The presence of cholesterol in the plasma membranes of some animal cells ____.

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

A food company hydrogenated a barrel of fat. The treatment ...

made the fat less fluid.

Lipids that form membranes have what kind of structure?

polar heads and nonpolar tails; the polar heads interact with water

The most unsaturated fats have ...

the most double bonds.

Ions diffuse across membranes through specific ion channels down ____.

their electrochemical gradients.

Under what circumstances does membrane transport require energy?

whenever a solute is moved against its electrochemical gradient