Which one of the following statements about the process of photosynthesis is correct ?
- A.Chemical energy is converted into light energy.
- B.Carbon dioxide is oxidised to form carbohydrate.
- C.Water molecule splits into hydrogen and oxygen.
- D.Light energy is directly used to split water.
Correct answer
Explanation
The correct answer is C, Water molecule splits into hydrogen and oxygen. In the light reaction of photosynthesis, water is broken up; its hydrogen is used to make food and its oxygen is given out. NCERT lists three main events of photosynthesis: absorption of light energy by chlorophyll, conversion of light energy into chemical energy together with the splitting of water into hydrogen and oxygen, and the reduction of carbon dioxide to carbohydrates. The splitting of water, called photolysis, takes place in the chloroplasts and is the source of all the oxygen that plants release. Option A is wrong because photosynthesis turns light energy into chemical energy stored in glucose, not the other way round. Option B is wrong because carbon dioxide gains hydrogen and is reduced, not oxidised, to form carbohydrate. Option D is wrong because light is first trapped by chlorophyll and passed on through the photosystems; it is not applied directly to water. Exam tip: in photosynthesis water is oxidised to oxygen and carbon dioxide is reduced to glucose.
Practice Questions
View allWhich one of the following plant tissues has dead cells ?
- A.Epidermis
- B.Parenchyma
- C.Collenchyma
- D.Sclerenchyma
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Sclerenchyma cells are dead at maturity, with thick walls hardened by lignin. Sclerenchyma is the tissue that makes plants hard and stiff.
Read the full explanation →Imagine a current-carrying straight conductor with magnetic field of lines in anti-clockwise direction. Then the direction of current is determined by
- A.the Right-Hand Thumb rule and it would be in the downward direction.
- B.the Left-Hand Thumb rule and it would be in the downward direction.
- C.the Right-Hand Thumb rule and it would be in the upward direction.
- D.the Left-Hand Thumb rule and it would be in the upward direction.
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For a straight wire, the right-hand thumb rule links the current to the circular field lines around it. Hold the wire in the right hand with the thumb along the current; the curled fingers then show the direction of the magnetic field lines, which form concentric circles around the wire.
Read the full explanation →Which one of the following statements is true for sound waves propagating in air?
- A.Sound is an electromagnetic wave and transverse in nature
- B.Sound is a mechanical wave and longitudinal in nature
- C.Sound is a mechanical wave and transverse in nature
- D.Sound is an electromagnetic wave and longitudinal in nature
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Sound needs a material medium to travel, and in air its particles vibrate back and forth along the direction the wave moves.
Read the full explanation →Which one of the following is primarily responsible for conduction of current in a metal?
- A.Bound electrons
- B.Free electrons
- C.Both bound and free electrons
- D.Ions
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In a metal, the outer electrons of the atoms are not tied to any one atom and drift through the lattice when a voltage is applied, carrying the current.
Read the full explanation →Which one of the following statements is correct about the magnification of an optical microscope?
- A.Magnification increases with the increase in focal length of eyepiece
- B.Magnification increases with the increase in focal length of objective
- C.Magnification does not depend upon the focal length of eyepiece
- D.Magnification decreases with the increase in focal length of eyepiece
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A compound microscope magnifies more when both its lenses have short focal lengths. In a compound microscope the objective forms a real, enlarged image, and the eyepiece magnifies it further like a simple magnifier.
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