A pressure cooker cooks food faster by
- A.increasing the boiling point of water
- B.decreasing the boiling point of water
- C.increasing the melting point of water
- D.decreasing the melting point of water
Correct answer
Explanation
The correct answer is A, increasing the boiling point of water. The trapped steam raises the pressure inside the cooker, and at higher pressure water boils at a higher temperature, so food cooks faster.
The boiling point of a liquid is the temperature at which its vapour pressure equals the pressure above it. In an open pan at sea level water boils at 100 °C and cannot get hotter. A pressure cooker is sealed, so the steam cannot escape and the pressure inside rises to roughly double the atmospheric pressure. The water then boils only at about 120 °C, and food cooked in this hotter water and steam softens in much less time. The weight on the lid lets out extra steam to keep the pressure safe.
B is wrong: lowering the boiling point is what happens on high mountains, where cooking becomes slower.
C is wrong: the melting point of ice has nothing to do with cooking in boiling water.
D is wrong: the melting point plays no part in how a pressure cooker works.
Exam tip: more pressure raises the boiling point (pressure cooker); less pressure lowers it (hills).
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
Show answer
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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