62 exam-style questions on Biology · Biological molecules, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.
Ten Biology · Biological molecules questions with answers
Try each one, then open the answer. These ten stay the same; the test draws new ones every time.
1. Starch from a potato is a mixture of amylose and amylopectin. Which statement about them is correct?
A
Both are polymers of α-glucose, but only amylopectin is branched.
B
Both are polymers of α-glucose, but only amylose is branched.
C
Amylose is a polymer of β-glucose and amylopectin of α-glucose.
D
Both are branched polymers of β-glucose, like cellulose.
Show answer
Answer: A. Amylose is an unbranched chain of α-glucose units linked 1,4, which coils into a helix; amylopectin has similar chains with 1,6 branch points. β-glucose is the monomer of cellulose, not of starch.
2. Two α-glucose molecules join to form maltose. The bond formed and the change in water are
A
an α(1→6) glycosidic bond, with one water molecule taken up
B
a β(1→4) glycosidic bond, with one water molecule released
C
an α(1→4) glycosidic bond, with one water molecule released
D
a peptide bond, with one water molecule released
Show answer
Answer: C. Carbon 1 of one α-glucose links to carbon 4 of the other by condensation, releasing one H2O. A β(1→4) link joins β-glucose units, as in cellulose, and peptide bonds join amino acids.
3. Cholesterol and the sex hormones are steroids. Unlike triglycerides, steroids
A
are made of glycerol joined to two fatty acids and one phosphate group
B
are built on four fused carbon rings, not on glycerol and fatty acids
C
are polymers of amino acids joined together by peptide bonds
D
are made of a long-chain alcohol joined to a single fatty acid
Show answer
Answer: B. Steroids have a skeleton of four fused carbon rings and contain no fatty acids. Glycerol with two fatty acids and a phosphate is a phospholipid, and a long-chain alcohol with a fatty acid is a wax.
4. In any double-stranded DNA molecule, which ratio of bases is always equal to 1?
A
(A + T) ÷ (G + C)
B
A ÷ G
C
T ÷ C
D
(A + G) ÷ (T + C)
Show answer
Answer: D. Every purine (A or G) pairs with a pyrimidine (T or C), so the number of purines equals the number of pyrimidines (Chargaff's rule). The ratio (A + T) ÷ (G + C) varies from one species to another.
5. Weight for weight, triglycerides store more energy than carbohydrates because they contain
A
more oxygen and less hydrogen in proportion to carbon
B
nitrogen in addition to carbon, hydrogen and oxygen
C
high-energy phosphate bonds like those of ATP
D
more hydrogen and less oxygen in proportion to carbon
Show answer
Answer: D. Fats are less oxidised than carbohydrates: they are rich in C–H bonds and poor in oxygen, so their oxidation supplies more hydrogen (electrons) to the respiratory chain and releases more energy per gram.
6. Adenosine is adenine joined to the sugar ribose; adenosine monophosphate (AMP) has a phosphate group added as well. Adenosine and AMP are, respectively,
A
a nucleoside and a nucleotide
B
a nucleotide and a nucleoside
C
a nucleoside and a dinucleotide
D
a nitrogenous base and a nucleoside
Show answer
Answer: A. A nucleoside is a base plus a pentose sugar; adding a phosphate makes a nucleotide. Two nucleotides joined together, as in NAD (nicotinamide adenine dinucleotide), form a dinucleotide.
7. Disulphide bridges that help hold the tertiary structure of a protein are formed between the side chains of two
A
glycine residues
B
valine residues
C
cysteine residues
D
glutamic acid residues
Show answer
Answer: C. Cysteine has an –SH group in its R group, and two such groups can be oxidised to form an S–S (disulphide) bridge. Glycine, valine and glutamic acid have no sulphur in their R groups.
8. Evaporation of sweat cools the body effectively because water has a high
A
specific heat capacity
B
density
C
surface tension
D
heat of vaporisation
Show answer
Answer: D. Much heat is needed to break hydrogen bonds as water evaporates, so each gram of sweat that evaporates removes a lot of heat from the skin. A high specific heat capacity keeps body temperature steady but does not explain cooling by evaporation.
9. Glycogen is well suited to storing energy in animals because it is
A
highly branched, so glucose is released fast from many chain ends
B
made of β-glucose chains packed tightly into strong microfibrils
C
a straight, unbranched chain that dissolves easily in water
D
made of fructose units, which release energy faster than glucose
Show answer
Answer: A. Glycogen is a compact, highly branched polymer of α-glucose; enzymes remove glucose units from the ends of many branches at once, giving rapid release. β-glucose chains in microfibrils describe cellulose.
10. Bacteria whose DNA contains only heavy nitrogen (15N) are moved to a medium containing only light nitrogen (14N) and allowed to replicate their DNA twice. If replication is semi-conservative, the DNA molecules will then be
A
all of intermediate (hybrid) density
B
half hybrid and half light
C
one quarter heavy and three quarters light
D
half heavy and half light
Show answer
Answer: B. In each round every new molecule keeps one parent strand. After one round all molecules are hybrid (15N/14N); after the second, the two old heavy strands each sit in a hybrid molecule and the rest are light, so half are hybrid and half light. One quarter heavy and three quarters light fits conservative replication, while the dispersive model predicts a single band of intermediate density.
Biology · Biological molecules: questions students ask
How many Biology · Biological molecules MCQs are there?
62, each with the answer and a short explanation, across 3 topics: Water and carbohydrates, Proteins and lipids, Nucleic acids. Every chapter test draws ten of them, so you can take it many times.
Is the MDCAT Biology chapter 3 test free?
Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.
How is the chapter test marked?
The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.
