Which one among the following separation techniques is used for blood tests in diagnostic laboratories ?
- A.Filtration
- B.Chromatography
- C.Centrifugation
- D.Crystallization
Correct answer
Explanation
The correct answer is C, Centrifugation. Diagnostic laboratories spin blood samples in a centrifuge to separate the plasma or serum from the blood cells.
In centrifugation a sample is rotated at high speed, so the denser particles are pushed to the bottom of the tube and the lighter liquid stays on top. In blood, red cells settle at the bottom, a thin layer of white cells and platelets forms above them, and the straw-coloured plasma remains at the top for testing. The same principle is used in dairies to separate cream from milk and in the drier of a washing machine.
A is wrong: filtration separates insoluble solids from a liquid through filter paper or a sieve, and cannot split blood cells from plasma for tests.
B is wrong: chromatography separates dissolved substances, such as the dyes in ink, by how fast they move through a medium.
D is wrong: crystallization obtains a pure solid, such as salt or alum, from its solution.
Exam tip: blood tests and cream from milk = centrifugation; dyes in ink = chromatography.
Practice Questions
View allThe speed of the wind is measured by
- A.wind vane
- B.wind rose
- C.barometer
- D.anemometer
Show answer
An anemometer measures how fast the wind is blowing; its name comes from the Greek word anemos, meaning wind.
Read the full explanation →Brilliance of diamond is due to
- A.interference of light
- B.diffraction of light
- C.polarization of light
- D.total internal reflection of light
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Light that enters a cut diamond is reflected again and again inside it before it escapes, which makes the stone sparkle.
Read the full explanation →Which one of the following is NOT an electromagnetic wave ?
- A.Light wave
- B.Radio wave
- C.Sound wave
- D.Micro wave
Show answer
Sound is a mechanical wave that needs a medium to travel, while the other three are electromagnetic waves. Sound travels as a longitudinal wave of compressions and rarefactions in air, water or solids, which is why it cannot pass through a vacuum.
Read the full explanation →Which one of the following is NOT true for an electromagnetic wave ?
- A.Electromagnetic wave transports energy and momentum
- B.Electromagnetic wave can be polarized and reflected
- C.Electromagnetic wave is longitudinal
- D.Electromagnetic wave propagation is described by the varying electric and magnetic fields
Show answer
Electromagnetic waves are transverse, not longitudinal, so this statement is false. In an electromagnetic wave the electric field and the magnetic field oscillate at right angles to each other and both at right angles to the direction in which the wave travels.
Read the full explanation →Which one of the following frequency ranges is sensitive to human ears ?
- A.0-200 Hz
- B.20-20,000 Hz
- C.200-20,000 Hz only
- D.2,000-20,000 Hz only
Show answer
The normal human ear hears sound from about 20 hertz to 20,000 hertz, the audible range. Frequency, measured in hertz, is the number of vibrations per second, and it decides the pitch of a sound: the higher the frequency, the shriller the note.
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