Which of the following represent disaccharides?
- A.Starch and glycogen
- B.Glucose and galactose
- C.Maltose and lactose
- D.Ribose and xylose
Correct answer
Explanation
The correct answer is C, Maltose and lactose. Each of them is made of two simple sugar units joined together, which is exactly what a disaccharide is.
Carbohydrates are grouped by the number of sugar units they contain. Monosaccharides are single units such as glucose, fructose and galactose. Disaccharides are two units linked by a glycosidic bond: maltose is glucose plus glucose, lactose (milk sugar) is glucose plus galactose, and sucrose (cane sugar) is glucose plus fructose. Polysaccharides are long chains of hundreds of units, such as starch, glycogen and cellulose. During digestion, enzymes like maltase and lactase split disaccharides back into monosaccharides so that they can be absorbed.
Option A is wrong because starch and glycogen are polysaccharides. Option B is wrong because glucose and galactose are monosaccharides, the building blocks of lactose. Option D is wrong because ribose and xylose are five-carbon monosaccharides (pentoses).
Exam tip: maltose = glucose + glucose, lactose = glucose + galactose, sucrose = glucose + fructose.
Practice Questions
View allThe fact that the planets move around the Sun, not in circles but in ellipses, was first demonstrated by
- A.Galileo
- B.Martin Luther
- C.Johannes Kepler
- D.Copernicus
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In 1609 Kepler showed that the planets move around the Sun in elliptical orbits, with the Sun at one focus of the ellipse.
Read the full explanation →Which one of the following statements is correct?
- A.Urea is produced in liver.
- B.Urea is produced in blood.
- C.Urea is produced from digestion of starch.
- D.Urea is produced in lung and kidney.
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Read the full explanation →Which one of the following is the correct sequence of passage of light in a compound microscope?
- A.Condenser-Objective lens-Eyepiece-Body tube
- B.Objective lens-Condenser-Body tube-Eyepiece
- C.Condenser-Objective lens-Body tube-Eyepiece
- D.Eyepiece-Objective lens-Body tube-Mirror
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Light passes through the condenser to the specimen, is picked up by the objective lens, travels up the body tube and reaches the eye through the eyepiece.
Read the full explanation →Which one of the following statements regarding haemoglobin is correct?
- A.Haemoglobin present in RBC can carry only oxygen but not carbon dioxide.
- B.Haemoglobin of RBC can carry both oxygen and carbon dioxide.
- C.Haemoglobin of RBC can carry only carbon dioxide.
- D.Haemoglobin is only used for blood clotting and not for carrying gases.
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Read the full explanation →Which one of the following statements regarding histone proteins is correct?
- A.Histones are proteins that are present in mitochondrial membrane.
- B.Histones are proteins that are present in nucleus in association with DNA.
- C.Histones are proteins associated with lipids in the cytosol.
- D.Histones are proteins associated with carbohydrates in the cytosol.
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They are the proteins around which DNA winds to form chromatin in the nucleus of eukaryotic cells. Histones are small basic proteins, rich in the positively charged amino acids lysine and arginine, which attract the negatively charged phosphate groups of DNA.
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