19) Answer is: carbohydrates (sugars and starches) contain 4 calories per gram and lipids contain 9 calories per gram, so they contain more energy than carbohydrates. Carbohydrates should provide 40 to 60 percent of calories and lipids should provide no more than 35 percent of body daily calories.
20) Answer is: yes, the order of nucleotides in DNA determines genetic information. The sequence of the DNA of a living thing encodes the information for that living thing to survive and reproduce. Determining the sequence is useful in fundamental research into why and how organisms live.
21) Answer is: b. compound B.
Branched-chain alkanes are alkanes that contain only C and H, but are not linear. Compound B contain methyl group branch. The molecule B known as 2-methylpropane. A continuous (unbranched) chain of carbon atoms is a straight chain.
22) Answer is: b. structural formula.
Structural formula of a organic chemical compound is a graphic representation of the molecular structure, represeting how the atoms in organic molecule are arranged. Structural formula shows arrangements of atoms (molecular groups) in three dimensional space.
23) Answer is: a. C₄H₁₀.
Both molecules have four carbon atoms and ten hydrogen atoms. They have same molecular formula, but different arrangement of atoms (structural formula) in the molecule and different properties. They are isomers (contain the same number of atoms of each element, but have different arrangements of their atoms).