Which one of the following statements regarding viruses is not true ?
- A.Viruses need living cells to reproduce.
- B.All viruses are parasites.
- C.Viruses can synthesize their food through photosynthesis.
- D.Viruses are similar to chemical substances outside the host.
Correct answer
Explanation
The correct answer is C, Viruses can synthesize their food through photosynthesis. This is false because viruses have no chlorophyll, no cell organelles and no metabolism of their own, so they cannot make food in any way. A virus is only a core of nucleic acid, either DNA or RNA, wrapped in a protein coat. It shows signs of life only after it enters a living host cell, where it takes over the cell's machinery to make copies of itself. For this reason viruses are often described as being on the border between living and non-living things. Option A is a true statement: viruses multiply only inside living host cells. Option B is a true statement: since they depend fully on a host, all viruses are obligate parasites of bacteria, plants or animals. Option D is a true statement: outside a host a virus is inert and can even be crystallised like a chemical, as Wendell Stanley showed with tobacco mosaic virus in 1935. Exam tip: virus = nucleic acid + protein coat; obligate parasite; crystallisable (TMV, Stanley).
Practice Questions
View allWhich one of the following is not used as fertilizer?
- A.Ammonium nitrate
- B.Ammonium sulphide
- C.Ammonium phosphate
- D.Ammonium sulphate
Show answer
Ammonium sulphide is an unstable, foul-smelling compound that breaks down to release ammonia and toxic hydrogen sulphide, so it is not used as a fertiliser.
Read the full explanation →The focal length of the objective lens of a telescope is 50 cm. If the magnification of the telescope is 25, then the focal length of the eye-piece is
- A.12.5 cm
- B.5 cm
- C.2 cm
- D.10 cm
Show answer
For an astronomical telescope in normal adjustment the magnifying power equals the focal length of the objective divided by that of the eyepiece, so the eyepiece focal length is 50 ÷ 25 = 2 cm.
Read the full explanation →The major source of vitamins and minerals for vegetarians is
- A.black gram and wheat.
- B.rice and mustard.
- C.vegetables and fruits.
- D.soya bean and milk.
Show answer
Vegetables and fruits supply most of the vitamins and minerals in a vegetarian diet, which is why they are called protective foods.
Read the full explanation →Which one of the following compounds is used in black and white photography?
- A.AgF
- B.AgBr
- C.AgCl
- D.Ag2SO4
Show answer
Silver bromide is the light-sensitive compound coated on black and white photographic film and paper, because light breaks it down into tiny grains of silver metal.
Read the full explanation →Which one of the following statements about speed and velocity is correct?
- A.Speed and velocity both are vector quantities.
- B.Speed and velocity both are scalar quantities.
- C.Speed is vector quantity and velocity is scalar quantity.
- D.Speed is scalar quantity and velocity is vector quantity.
Show answer
Speed tells only how fast a body moves, while velocity also tells the direction of motion, and a quantity with both magnitude and direction is a vector.
Read the full explanation →