Milk contains a high concentration of the carbohydrate lactose. What is the basic structure of lactose?

• two monosaccharides joined together
• a chain of amino acids in a helix shape
• two fatty acids joined to a phosphate group
• a chain of alternating sugar and phosphate groups

A cell membrane has a double layer of molecules. These molecules are made up of a phosphorus-containing “head” and two long, fatty acid “tails.”Which of the following best explains why the molecules are classified as lipids?

• They contain phosphorus.
• They form a double layer.
• They are made up of fatty acids.
• They are found in the cell membrane.

Which group of organic compounds contains fatty acids?

• carbohydrates
• lipids
• nucleic acids
• proteins

What do disaccharides, such as sucrose, and polysaccharides, such as starch, have in common?

• They are lipids made of fatty acids.
• They are proteins made of amino acids.
• They are nucleic acids made of nucleotides.
• They are carbohydrates made of simple sugars.

A student is preparing to run in a school track competition. For the quickest source of energy, the student should eat a food that contains a high percentage of

• carbohydrates
• fat
• proteins
• sodium

Which type of molecule in the yolk of a chicken egg provides the most energy for a developing chick?

• lipid
• nucleic acid
• salt
• water
• protein

Which of the following best describes the composition of a nucleotide?

• a pair of six-carbon rings attached to each other
• a carbon atom joined to hydrogen and three functional groups
• a chain of carbon atoms with a carboxyl group bonded to one end
• a five-carbon sugar attached to a phosphate group and a nitrogenous base

One category of organic compounds contains molecules composed of long hydrocarbon chains. The hydrocarbon chains may be saturated or unsaturated. Which of the following categories of organic compounds contains these molecules?

• carbohydrates
• lipids
• nucleic acids
• proteins

Some bacteria contain a substance called nitrogenase. Nitrogenase catalyzes the chemical reaction that converts atmospheric nitrogen (N2) into ammonia (NH3). Nitrogenase is an example of which of the following?

• a sugar
• an enzyme
• a nucleotide
• an amino acid

Which of the following categories of organic molecules is correctly paired with one of its functions?

• nucleic acids—digest dead cells
• lipids—give quick energy to cells
• carbohydrates—store genetic information
• proteins—provide structure in skin, hair, and nails