Photo 51 refers to an image of
- A.a crater on the Moon
- B.DNA molecules
- C.the virus responsible for COVID-19
- D.the virus responsible for common cold
Correct answer
Explanation
The correct answer is B, DNA molecules. Photo 51 is the X-ray diffraction photograph of DNA that revealed its helical shape.
The picture was taken in May 1952 at King's College London by Rosalind Franklin and her student Raymond Gosling. Its clear X-shaped pattern showed that DNA is a helix and gave measurements of its spacing. Maurice Wilkins showed the photograph to James Watson, and in 1953 Watson and Francis Crick used it, along with other data, to build their double-helix model of DNA. Watson, Crick and Wilkins received the Nobel Prize in Physiology or Medicine in 1962; Franklin had died in 1958, and the Nobel is not given after death.
A is wrong: Photo 51 has nothing to do with the Moon.
C is wrong: the COVID-19 virus, SARS-CoV-2, was identified only in 2019.
D is wrong: it is not an image of any cold virus.
Exam tip: Photo 51 = Rosalind Franklin, 1952; double-helix model = Watson and Crick, 1953.
Practice Questions
View allConsider the following animals :
1. Hedgehog
2. Marmot
3. Pangolin
To reduce the chance of being captured by predators, which of the above organisms rolls up/roll up and protects/protect its/their vulnerable parts?
- A.1 and 2
- B.2 only
- C.3 only
- D.1 and 3
Show answer
Hedgehogs and pangolins curl into a tight ball when threatened, covering the soft belly and face with spines or scales; marmots do not.
Read the full explanation →Which one of the following is used in preparing a natural mosquito repellent?
- A.Congress grass
- B.Elephant grass
- C.Lemongrass
- D.Nut grass
Show answer
Lemongrass and its close relative citronella grass yield aromatic oils that keep mosquitoes away, so they are the base of many natural repellents.
Read the full explanation →Which one of the following devices is non-ohmic ?
- A.Conducting copper coil
- B.Electric heating coil
- C.Semi conductor diode
- D.Rheostat
Show answer
A diode does not obey Ohm's law: the current through it is not proportional to the voltage across it. An ohmic conductor gives a straight-line graph of current against voltage, so its resistance stays constant at a fixed temperature.
Read the full explanation →What is the formula mass of anhydrous sodium carbonate? (Given that the atomic masses of sodium, carbon and oxygen are 23 u, 12 u and 16 u respectively)
- A.286 u
- B.106 u
- C.83 u
- D.53 u
Show answer
Anhydrous sodium carbonate is Na₂CO₃, and 2 × 23 + 12 + 3 × 16 = 106 u. Formula mass is the sum of the atomic masses of all the atoms in one formula unit of an ionic compound.
Read the full explanation →Which one of the following minerals is used as a fuel in nuclear power stations ?
- A.Bauxite
- B.Quartz
- C.Feldspar
- D.Pitchblende
Show answer
Pitchblende, or uraninite, is the chief ore of uranium, the fuel used in most nuclear power stations. Pitchblende is a heavy, black mineral made mostly of uranium oxide.
Read the full explanation →