The lactic acid that gets accumulated in the muscle cells during rigorous exercise causing muscle cramps is produced from
- A.ATP
- B.Pyruvate
- C.Ethanol
- D.Glucose
Correct answer
Explanation
The correct answer is B, Pyruvate. When muscles run short of oxygen, the pyruvate formed from glucose is converted into lactic acid instead of being broken down fully. Respiration begins in the cytoplasm with glycolysis, in which one molecule of glucose, a six-carbon sugar, is split into two molecules of pyruvate, a three-carbon compound. With enough oxygen, pyruvate enters the mitochondria and is broken down to carbon dioxide and water, releasing a lot of energy. During hard exercise the oxygen supply falls short, so the muscle cells reduce pyruvate to lactic acid, which gives a little energy quickly; its build-up is linked with the cramps and fatigue that follow. Option A is wrong because ATP is the energy currency produced by respiration, not the raw material for lactic acid. Option C is wrong because ethanol is formed from pyruvate by yeast during fermentation, and muscles do not make it. Option D is wrong because glucose is only the starting point; it must first become pyruvate. Exam tip: glucose → pyruvate → lactic acid in muscles, or ethanol and carbon dioxide in yeast.
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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Liver cells turn the toxic ammonia released from the breakdown of amino acids into urea through the ornithine cycle, also called the urea cycle.
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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It binds oxygen at its iron-containing haem groups and carries some carbon dioxide on its protein chains. Each haemoglobin molecule has four polypeptide chains and four haem groups, and each haem iron can hold one oxygen molecule, forming oxyhaemoglobin in the lungs.
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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