Free Biological Molecules MCQs with Answers
1,790 Biological Molecules MCQs from Biology, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.
The chapter covers water's polarity and biological roles, carbohydrates, lipids, proteins and nucleic acids, including their monomers, bonds, structures and functions. It also distinguishes RNA from DNA and explains conjugated molecules such as glycoproteins, glycolipids and nucleoproteins, which combine organic molecules with a non-protein component.
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- A. specific heat capacity
- B. latent heat of vaporisation
- C. surface tension
- D. density
Explanation: A large amount of energy is needed to break the hydrogen bonds holding liquid water together and convert it to vapour, and that energy is…
Correct answer: latent heat of vaporisation- A. the ice layer insulates the water below, letting aquatic organisms survive the winter
- B. it allows water to evaporate faster in cold weather
- C. it increases the amount of oxygen dissolved in the lake
- D. it lowers the freezing point of the remaining water
Explanation: Water is unusual in becoming less dense as it freezes, because the hydrogen bonds lock the molecules into an open lattice, so ice forms at…
Correct answer: the ice layer insulates the water below, letting aquatic organisms survive the winter- A. the low viscosity of water
- B. the high density of water
- C. cohesion between water molecules caused by hydrogen bonding
- D. the fact that water is a poor solvent for gases
Explanation: Hydrogen bonds make water molecules stick to one another, so a column pulled by evaporation at the leaves does not break, and adhesion to…
Correct answer: cohesion between water molecules caused by hydrogen bonding- A. isomers
- B. polymers
- C. isotopes
- D. identical sugars
Explanation: Isomers share a molecular formula but differ in the arrangement of their atoms, and here glucose carries an aldehyde group while fructose…
Correct answer: isomers- A. contains no glycosidic bonds
- B. is soluble and diffuses freely out of the cell
- C. is built from beta glucose
- D. is far more branched, so many ends can be hydrolysed at once
Explanation: Extensive branching gives a large number of terminal glucose units, so enzymes can release glucose very rapidly when an active animal…
Correct answer: is far more branched, so many ends can be hydrolysed at once- A. its peptide bonds are hydrolysed and amino acids are released
- B. its tertiary structure is destroyed but its primary structure remains intact
- C. its amino acid sequence is rearranged
- D. it becomes more soluble and more active
Explanation: Heat breaks the relatively weak hydrogen, ionic and hydrophobic interactions that hold the chain in its three dimensional shape, so the…
Correct answer: its tertiary structure is destroyed but its primary structure remains intact- A. are found in every protein
- B. cannot be synthesised by the body and must be supplied in the diet
- C. are needed only during childhood
- D. make up the active site of every enzyme
Explanation: About nine of the twenty amino acids cannot be made by the human body at a useful rate, so they have to come from food, and a protein…
Correct answer: cannot be synthesised by the body and must be supplied in the diet- A. hydrogen bonds between R groups
- B. ionic bonds between charged R groups
- C. disulphide bridges between cysteine residues
- D. peptide bonds between R groups
Explanation: Peptide bonds join the amino group of one residue to the carboxyl group of the next along the backbone, so they build the primary…
Correct answer: peptide bonds between R groups- A. contains one or more carbon to carbon double bonds in its hydrocarbon chain
- B. contains more hydrogen atoms per carbon
- C. has no carboxyl group
- D. cannot be used in respiration
Explanation: Each double bond puts a kink in the chain, so the molecules pack together less closely and the fat has a lower melting point, which is why…
Correct answer: contains one or more carbon to carbon double bonds in its hydrocarbon chain- A. is the main energy store of adipose tissue
- B. carries oxygen in the blood
- C. is the precursor of the steroid sex hormones, bile salts and vitamin D
- D. forms the walls of plant cells
Explanation: Cholesterol is a steroid and the starting material for testosterone, oestrogen, bile salts and vitamin D, and it also sits between the…
Correct answer: is the precursor of the steroid sex hormones, bile salts and vitamin D- A. hydrolysis, forming glycosidic bonds
- B. condensation, forming ester bonds and releasing three molecules of water
- C. oxidation, forming peptide bonds
- D. reduction, forming hydrogen bonds
Explanation: Each of the three hydroxyl groups of glycerol reacts with the carboxyl group of a fatty acid, so three ester bonds form and three water…
Correct answer: condensation, forming ester bonds and releasing three molecules of water- A. carry the genetic message out of the nucleus
- B. form the structural core of the ribosome
- C. unwind the DNA double helix
- D. bring the correct amino acid to the ribosome according to the codon being read
Explanation: Each tRNA carries an anticodon at one end and its matching amino acid at the other, so it acts as the adaptor that translates the language…
Correct answer: bring the correct amino acid to the ribosome according to the codon being read- A. carries a copy of the base sequence of a gene from the nucleus to the ribosome
- B. is folded into a clover leaf shape
- C. carries an anticodon at one end
- D. is the most abundant type of RNA in the cell
Explanation: Messenger RNA is transcribed from one strand of a gene and is read in triplets by the ribosome, so its length varies with the gene it…
Correct answer: carries a copy of the base sequence of a gene from the nucleus to the ribosome- A. Mendel and Morgan
- B. Griffith and Avery
- C. Watson and Crick, using the X ray diffraction data of Rosalind Franklin
- D. Sanger and Gilbert
Explanation: Watson and Crick built the model from Franklin's X ray photographs, which showed the helix and its dimensions, together with Chargaff's…
Correct answer: Watson and Crick, using the X ray diffraction data of Rosalind Franklin- A. consists of four identical polypeptide chains
- B. contains only amino acids joined by peptide bonds
- C. is made in the bone marrow rather than the liver
- D. contains a non protein haem group attached to its polypeptide chains
Explanation: A conjugated protein is a protein permanently joined to a non protein prosthetic group, and in haemoglobin each of the four chains carries…
Correct answer: contains a non protein haem group attached to its polypeptide chains- A. condensation
- B. hydrolysis
- C. oxidation
- D. photolysis
Explanation: In condensation, an OH from one molecule and an H from the other leave as water while a covalent bond forms, which is how disaccharides…
Correct answer: condensation- A. Phosphorus
- B. Nitrogen
- C. Magnesium
- D. Calcium
Explanation: Every amino acid carries an amino group, so nitrogen is a constant feature of proteins, and sulphur also appears in some.
Correct answer: Nitrogen- A. Proteins
- B. Nucleic acids
- C. Lipids
- D. Carbohydrates
Explanation: Lipids are small molecules, a triglyceride being glycerol plus three fatty acids, and they do not form long repeating chains.
Correct answer: Lipids- A. peptide bond
- B. ester bond
- C. phosphodiester bond
- D. glycosidic bond
Explanation: A glycosidic bond forms by condensation between the hydroxyl groups of two sugars.
Correct answer: glycosidic bond- A. makes water an excellent solvent for ions
- B. allows cell temperature to fluctuate rapidly with the surroundings
- C. keeps the temperature of cells and of water bodies relatively stable
- D. speeds up every enzyme controlled reaction
Explanation: A large amount of heat is needed to raise the temperature of water because much of the energy first breaks hydrogen bonds between…
Correct answer: keeps the temperature of cells and of water bodies relatively stable