Accumulation of which one of the following in the muscles of sprinters leads to cramp?
- A.Lactic acid
- B.Ethanol
- C.Pyruvic acid
- D.Glucose
Correct answer
Explanation
The correct answer is A, Lactic acid. During a sprint the muscles need energy faster than the blood can supply oxygen, so they switch to anaerobic respiration and lactic acid builds up. In normal aerobic respiration, glucose is first broken into pyruvic acid, which is then fully oxidised to carbon dioxide and water in the mitochondria, releasing a lot of energy. When oxygen runs short, the muscle cells instead convert pyruvic acid into lactic acid, which releases a little energy quickly. The build-up of lactic acid in the muscles causes fatigue, a burning feeling and cramps. After rest, deep breathing supplies oxygen and the lactic acid is carried away and cleared, mostly by the liver. Option B is wrong because ethanol is made by yeast during anaerobic respiration, not by human muscles. Option C is wrong because pyruvic acid is only the intermediate step and does not pile up to cause cramp. Option D is wrong because glucose is the fuel that is broken down, not a waste product. Exam tip: anaerobic respiration, lactic acid in muscles, 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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