Which one of the following statements about the process of photosynthesis is correct?
- A.Light energy is directly converted to kinetic energy which oxidizes carbon dioxide.
- B.Light energy is directly converted to chemical energy which causes reduction of water.
- C.Chlorophyll absorbs the chemical energy of light which causes oxidation of carbon dioxide.
- D.Chlorophyll absorbs light energy which causes splitting of water molecules and reduction of carbon dioxide.
Correct answer
Explanation
The correct answer is D. Chlorophyll absorbs light energy, which is used to split water and then to reduce carbon dioxide to sugar.
In the light reactions, energy trapped by chlorophyll splits water molecules (photolysis), releasing oxygen, hydrogen ions and electrons and producing ATP and NADPH. In the dark reactions (the Calvin cycle) these are used to reduce carbon dioxide to glucose. So water is oxidised and carbon dioxide is reduced; the oxygen we breathe comes from the water, not from the carbon dioxide.
A is wrong: light becomes chemical energy, not kinetic energy, and carbon dioxide is reduced, not oxidised.
B is wrong: water is oxidised (split) in photosynthesis, not reduced.
C is wrong: chlorophyll absorbs light energy, not chemical energy, and carbon dioxide is reduced.
Exam tip: in photosynthesis water is oxidised to oxygen and carbon dioxide is reduced to glucose.
Practice Questions
View allWhich one of the following is synthesised in human body that dilates blood vessels and increases blood flow?
- A.Nitric oxide
- B.Nitrous oxide
- C.Nitrogen dioxide
- D.Nitrogen pentoxide
Show answer
The body makes nitric oxide (NO) itself, and it relaxes the walls of blood vessels so that they widen and carry more blood.
Read the full explanation →Which of the following properties is true for a tooth paste?
- A.It is acidic
- B.It is neutral
- C.It is basic
- D.It is made up of Calcium phosphate, the material of tooth enamel
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Toothpaste is mildly basic so that it can neutralise the acid that causes tooth decay. Bacteria in the mouth break down sugar and food particles left on the teeth and produce acids.
Read the full explanation →A stainless steel chamber contains Ar gas at a temperature T and pressure P. The total number of Ar atoms in the chamber is n. Now Ar gas in the chamber is replaced by CO₂ gas and the total number of CO₂ molecules in the chamber is n/2 at the same temperature T. The pressure in the chamber now is P'. Which one of the following relations holds true? (Both the gases behave as ideal gases)
- A.P' = P
- B.P' = 2P
- C.P' = P/2
- D.P' = P/4
Show answer
For an ideal gas in a fixed volume at a fixed temperature, pressure is proportional to the number of molecules, so half the molecules give half the pressure.
Read the full explanation →In which of the following pairs are the ions isoelectronic?
- A.Mg²⁺, Ar
- B.Na⁺, O²⁻
- C.Al³⁺, Cl⁻
- D.K⁺, Ne
Show answer
Both have 10 electrons, the same number as a neon atom, so they are isoelectronic. Isoelectronic species have the same number of electrons.
Read the full explanation →A solid disc and a solid sphere have the same mass and same radius. Which one has the higher moment of inertia about its centre of mass?
- A.The disc
- B.The sphere
- C.Both have the same moment of inertia
- D.The information provided is not sufficient to answer the question
Show answer
About an axis through the centre, a solid disc has I = ½MR² while a solid sphere has I = ⅖MR², and ½ is larger than ⅖.
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