AP Biology : Understanding Lipids

Study concepts, example questions & explanations for AP Biology

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Example Questions

Example Question #121 : Ap Biology

The tails of phospholipids are __________.

Possible Answers:

lipophilic

hydrophobic

hydrophilic

polar

Correct answer:

hydrophobic

Explanation:

The tails of phospholipids consist of hydrocarbons only. Thus they are nonpolar, hydrophobic, lipophilic and fat-soluble.  

Example Question #21 : Understanding Lipids

In a cell membrane, the tails of the phospholipids point towards __________.

Possible Answers:

The exterior of the membrane, away from water

the interior of the membrane, away from water

either the interior or the exterior of the membrane, depending on the type of cell membrane

the exterior of the membrane, towards water

Correct answer:

the interior of the membrane, away from water

Explanation:

The tails of phospholipids are hydrocarbons and are thus hydrophobic so they point towards the interior of the membrane to avoid contact with the aqueous solutions of the cytoplasm and the extracellular fluid.  

Example Question #21 : Understanding Lipids

A given molecule has a structure containing a carbon skeleton of four fused rings. Which of the following is it most likely to be?

Possible Answers:

Fat

Phospholipid

Fatty acid

Cholesterol

Correct answer:

Cholesterol

Explanation:

Cholesterol is class of lipids known as steroids. All steroids have four fused carbon rings in their structures. Fats, fatty acids and phospholipid do not contain any ring structures. Fatty acids are components of both fats and phospholipids and are long chains of hydrocarbons. Phospholipids contain two fatty acids attached to a polar head and a phosphate group.

Example Question #22 : Understanding Lipids

In a cell membrane, the heads of the phospholipids point toward __________.

Possible Answers:

Cannot be determined without knowing the type of cell membrane

the interior of the membrane, away from water

None of these; it varies randomly throughout the membrane.

the exterior of the membrane, facing water

Correct answer:

the exterior of the membrane, facing water

Explanation:

The heads of phospholipids are hydrophilic and so they will face the exterior of the cell membrane in order to interact with the aqueous environments of the extracellular fluid and the cytosol. The hydrophobic tails will face the interior of the membrane to avoid water contact.

Example Question #21 : Understanding Lipids

Lipids consist mostly of __________.

Possible Answers:

amino acids

hydrocarbons

glycogen

oxygen

Correct answer:

hydrocarbons

Explanation:

Lipids are mostly made up of hydrocarbons, which makes them nonpolar and thus, hydrophobic. Glycogen is a type of carbohydrate; it is the storage form of glucose in animals. Amino acids are the monomeric units of polypeptides.  

Example Question #22 : Understanding Lipids

An important trait that all lipids share is __________.

Possible Answers:

hydrophobicity

solubility

basicity

hydrophilicity

acidity

Correct answer:

hydrophobicity

Explanation:

Because lipids are made mostly of hydrocarbons, they are nonpolar and thus hydrophobic, which means they avoid contact with water. The root "hydro" refers to water and the root "phobic" refers to fear. Hence hydrophobic means "water fearing". Hydrophilic on the other hand means "water loving" and is used to describe polar molecules.    

Example Question #24 : Understanding Lipids

Which of the following is not an example of lipid(s)?

Possible Answers:

Phospholipids

Glycogen

Fatty acids

Oils

Correct answer:

Glycogen

Explanation:

Glycogen is a carbohydrate. It is a polysaccharide that animals use to store glucose when sugars are needed by the body for fuel. All other answer choices are lipids.

Example Question #25 : Understanding Lipids

Which of the following is not an example of lipid(s)?

Possible Answers:

Triglycerides

Testosterone

Waxes

Fructose

Correct answer:

Fructose

Explanation:

Monosaccharides such as fructose are carbohydrates not lipids. Waxes, steroid hormones such as testosterone, estrogen and progesterone, and triglycerides (fats) are composed mainly of hydrocarbons and are classified as lipids.   

Example Question #101 : Macromolecules

Chitin is what class of molecule?

Possible Answers:

Wax

Nucleic acid

Lipid

Carbohydrate

Correct answer:

Carbohydrate

Explanation:

Chitin is a carbohydrate. Specifically, it is a polysaccharide used by arthopods to build exoskeletons, and is found in the cell walls of fungi. Waxes are types of lipids, and nucleic acids are DNA and RNA.   

Example Question #21 : Understanding Lipids

Starch belongs to which class of macromolecules?

Possible Answers:

Polypeptides

Lipids

Nucleic acids

Carbohydrates

Correct answer:

Carbohydrates

Explanation:

Starch is a carbohydrate. Specifically, it is a polysaccharide carbohydrate used in plants. The enzyme amylase breaks down starch in the mouth and small intestine, where it can is absorbed as monosaccharides and disaccharides.

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