This set of Biology Multiple Choice Questions & Answers (MCQs) focuses on “Higher Plants Photosynthesis – Light Reaction”.
1. The reaction center in the light-harvesting complex is formed by _____
a) Chlorophyll b
c) Chlorophyll e
d) A single chlorophyll a molecule
Explanation: The reaction center in the light-harvesting complex is formed by a single “chlorophyll a” molecule. This chlorophyll a molecule has the capability to absorb different wavelengths of light energy. It is mainly known for the process called photoionization of chlorophyll.
2. Which of the following is not related to the light reaction?
a) Also called Photochemical phase
b) Light absorption
c) Electron transport
d) Water splitting
Explanation: Electron transport is not related to light reaction. It is because light reaction is mainly based on photochemical processes like light absorption, water splitting, the formation of ATP and NADPH, etc. where electron transport is not included.
3. How many light-harvesting systems are there in light reaction?
Explanation: The photosynthetic pigments are organized into two groups of light-harvesting systems. They are mainly composed of many pigments bonded to proteins. These light-harvesting systems are present within PS I and PS II.
4. The harvesting systems are named in the order of their functioning sequence.
Explanation: It is a false statement. Light-harvesting systems are named in the sequence of their discovery time and not based on the order of their functioning sequence. PS I was found first and later PS II.
5. Which pigment is absent in each photosystem?
a) One molecule of chlorophyll a
b) Two molecules of chlorophyll b
c) One molecule of chlorophyll b
d) One molecule of xanthophyll
Explanation: One molecule of chlorophyll a is absent in each photosystem forming a light-harvesting system also known as the antenna. These pigments make photosynthesis more efficient. The reaction center is formed by this one molecule of chlorophyll a.
6. The reaction center is different in both the photosystems.
Explanation: It is true since chlorophyll a has an absorption peak at 700 nm for PS I. For PS II, it has got an absorption maximum at 680 nm. Hence, the names P700 and P680 were given for the reaction centers.
7. PS I is the photosystem present only in _______ photosynthesis.
Explanation: PS I is the only photosystem present in bacterial photosynthesis. It lacks PS II since it is having less complexity for photosynthesis, they only require one photosystem.
8. Which among the following are raw materials required for the light reaction?
a) NADPH2 and H2O
b) ADP and OH2
c) ATP only
d) ADP, H2O, and NADP
Explanation: ADP, H2O, and NADP are the main required materials for light reaction. The water undergoes photolysis i.e. it splits into hydrogen and oxygen. ADP gets converted into ATP and NADP to NADPH.
9. ______ discovered the two-pigment system theory of light reaction?
Explanation: Emerson was the scientist who proposed the two-pigment theory of light reaction. Robert Hill was the scientist who found the light reaction or photochemical phase. Arnon coined the term phosphorylation.
10. Which of the following is most sensitive to higher wavelengths of sunlight?
c) PS I
d) PS II
Explanation: Photosystem I is most sensitive to higher wavelengths of sunlight. It is because its absorption maxima are 700nm which gives it more strength to capture wavelengths of light. PS II is not as much sensitive as PS I since it has absorption peak only at 680nm.
11. How many electrons and protons are produced during the photolysis of water?
a) 4 electrons and 3 protons
b) 1 electron and 2 protons
c) 3 electrons and protons
d) 4 electrons and 4 protons
Explanation: Four electrons and four protons are produced at the end of the photolysis of water. Two molecules of water get converted into 4H+ and 4e– along with free oxygen. The ions used for this splitting is Mn2+, Ca2+, and Cl–.
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