Plants are autotrophic organisms that make their own food by the process of photosynthesis. In this process they use light energy to drive the synthesis of organic molecules. Here is a collection of all important questions related to photosynthesis in higher plants that are crucial for NEET 2023.
- Which one of the following photosystems is predominantly present in stroma lamellae?
(a) PS I
(b) PS II
(c) PS I and PS II
(d) None of the above
Answer: (a)
Explanation: The chlorophyll a and the accessory pigments form the photosystem. There are two photosystems found in the chloroplast – PS I and PS II. PS I absorbs light of wavelength 700 nm and PS II absorbs light of wavelength 680 nm. The grana lamellae have both PS I and PS II while the stromal lamellae has only PS I. Because stromal lamellae has only PS I, only cyclic photophosphorylation occurs here, no non-cyclic photophosphorylation occurs.
- Label a, b and c respectively.
(a) chlorophyll a, chlorophyll b, xanthophylls
(b) chlorophyll a , chlorophyll b, carotenoids
(c) chlorophyll a, xanthophylls, carotenoids
(d) chlorophyll a, xanthophylls, chlorophyll b
Answer: (b)
Explanation: The above graph shows the absorption spectrum of chlorophyll a, chlorophyll b and carotenoids in the range of visible light (380 nm to 700 nm). It shows the absorption of different pigments at different wavelengths.
- Water-splitting complex is associated with which of the following?
(a) PS-I and is located on the inner side of the thylakoid membrane.
(b) PS-II and is located on the inner side of the thylakoid membrane.
(c) PS-II and is located on the outer side of the thylakoid membrane.
(d) PS-I is located on the outer side of the thylakoid membrane.
Answer: (b)
Explanation: Water splitting complex is associated with PS-II which is located on the inner side of the thylakoid membrane. The process of splitting of water is known as photolysis which is denoted by the following reaction:
| 2H2O → 4H+ + 4e– + O2 |
|---|
- Which of the following statements about chloroplast is incorrect?
(a) Chloroplasts have an inner and an outer membrane.
(b) Chloroplasts contain stacks of thylakoids called grana.
(c) Chloroplasts contain pigments like chlorophyll a and chlorophyll b.
(d) Chloroplasts don’t contain any ribosomes.
Answer: (d)
Explanation: Chloroplasts are large organelles that are bound by an inner and an outer membrane. The inner membrane encloses a fluid called stroma. The stroma consists of disc-shaped structures called thylakoids. The thylakoids are stacked upon each other to form the granum.
The chloroplast consists of light-absorbing pigments such as chlorophyll a, chlorophyll b, xanthophylls and carotenoids. They have their own DNA and ribosomes, and thus, are capable of making their own proteins.
Check your knowledge : MCQs on Chloroplasts
- In a chloroplast, enzymatic reaction to synthesise sugar takes place in
(a) the lumen of the thylakoids
(b) stroma
(c) ribosome
(d) stroma lamellae
Answer: (b)
Explanation: The dark reaction uses carbon dioxide and water in the presence of ATP and NADPH to synthesise glucose, which is the food source for plants. This involves a series of enzyme-catalysed reactions. The enzymes for these dark reactions to occur are present in the stroma. Hence, we can say that the sugar synthesis takes place in stroma.
- Which of the following is correct regarding cyclic phosphorylation?
(a) It involves both PS-I and PS-II.
(b) The electrons released from PS-I are again cycled back to PS-I.
(c) It requires an external electron donor.
(d) Both ATP and NADPH are formed.
Answer: (b)
Explanation: Cyclic photophosphorylation takes place in the PS-I, where the reaction centre absorbs light at the wavelength of 700 nm and releases electrons. These electrons are cycled back to the reaction centre and hence there is no requirement for an external donor. In this process, only ATP is formed.
- Which of the following products from light-independent reactions is used as a source of energy in the light-independent reactions?
(a) NADPH
(b) Oxygen
(c) Glucose
(d) ADP
Answer: (a)
Explanation: In the light-dependent reactions, the assimilatory powers – ATP and NADPH – are formed. These energy molecules are utilised during the light-independent reactions. NADPH reduces the intermediates that form carbohydrates and gets oxidised. Oxygen is also evolved during the photolysis of water; but it is not used during light-independent reactions for the synthesis of sugars.
- Proton gradient helps in:
(a) ATP synthesis
(b) NADPH synthesis
(c) Providing electrons to PS-II
(d) Providing oxygen to PS-II
Answer: (a)
Explanation: There is proton accumulation inside the thylakoid membrane when electrons are transported across the photosystems and during splitting of water. As a result, the number of protons is high inside the lumen of thylakoids when compared to the stroma of the chloroplast. This creates a proton gradient which results in the movement of protons across the membrane into the stroma through ATP synthase. This movement of protons from a region of higher concentration (thylakoid lumen) to low concentration (stroma) activates the enzymes and helps in the synthesis of ATP.
- Which of the following is correct with respect to ATP synthase?
(a) It is an active transport pump.
(b) It is a facilitated diffusion channel.
(c) It is a passive transport channel.
(d) Both b and c are correct.
Answer: (d)
Explanation: ATP synthase is a protein that forms transmembrane channels. It allows facilitated diffusion of protons, which results in generation of ATP. Facilitated diffusion is a method of passive transport which involves movement of molecules from its higher concentration to lower concentration.
- _____ are required for the formation of one molecule of glucose in the Calvin pathway.
(a) 3CO2 + 18 ATP + 18 NADPH
(b) 6CO2 + 12 ATP
(c) 6CO2 + 18 ATP + 12 NADPH
(d) 6CO2 + 18 ATP + 24 NADPH
Answer: (c)
Explanation: The calvin cycle includes three stages – carboxylation, reduction and regeneration. ATP and NADPH are energy molecules that are formed during the light reaction of photosynthesis. They are utilised in the synthesis of glucose. In the carboxylation step of the Calvin cycle, no energy molecules are required. 12 ATP and 12 NADPH are utilised in the reduction stage. 6 ATP are also required in the regeneration phase. Thus, for the synthesis of one molecule of glucose, 6CO2, 18 ATP and 12 NADPH are required.
- The C3 cycle is so called because
(a) 3 molecules of CO2 are required for the formulation of 1 glucose
(b) 3 ATP and 3 NADPH are utilised in this cycle
(c) the cycle has to be repeated three times to generate 1 glucose molecule
(d) the first stable product of CO2 fixation is a 3-carbon compound
Answer: (d)
Explanation: The Calvin cycle is also called C3 cycle as the first stable product formed is a 3-carbon compound, 3-phosphoglyceric acid (3-PGA). In C3 plants, the primary acceptor of carbon dioxide is a five-carbon compound, RuBP (ribulose – 1,5 bisphosphate).
- In the Calvin cycle, triose phosphate is formed during
(a) carboxylation stage
(b) reduction stage
(c) regeneration stage
(d) oxidation stage
Answer: (b)
Explanation: In the reduction phase, 3 phosphoglycerate is converted into glyceraldehyde-3-phosphate at the expense of one ATP and NADPH.
| 2 (3-Phosphoglycerate) → 2 (3-Glyceraldehyde-3-phosphate) |
|---|
- Photorespiration is a wasteful process because
(a) no synthesis of sugar takes place
(b) no ATP production takes place
(c) CO2 is released during ATP
(d) all of the above
Answer: (d)
Explanation: Photorespiration is a process where enzyme RuBisCO (ribulose bisphosphate carboxylase oxygenase) takes up oxygen instead of carbon dioxide, thereby inhibiting photosynthesis. This eventually leads to a decrease in the products of photosynthesis like glucose and oxygen. There is no production of ATP; instead it is utilised to release the carbon dioxide. Thus, all the statements justify that photorespiration is a wasteful process.
- Photorespiration does not occur in C4 plants because
(a) of the enzyme RuBisCO
(b) the first primary acceptor is phosphoenolpyruvate
(c) they do not require CO2
(d) they have a mechanism that increases the concentration of CO2 at the enzyme site
Answer: (d)
Explanation: Photorespiration does not occur in C4 plants because they have a mechanism that increases the concentration of CO2 at the enzyme site. In the C4 pathway, carbon fixation ultimately results in the production of malic acid in the mesophyll cells. The malic acid is broken down in the bundle sheath to release CO2. Since the bundle sheath cells have thick walls, they do not allow CO2 to escape. This results in an increase in intracellular concentration of CO2. This ensures that the RuBisCO in the bundle sheath cells function as a carboxylase and not an oxygenase, thus preventing photorespiration.
- How many ATP molecules are utilised during the carboxylation stage of the Calvin cycle?
(a) 2
(b) 11
(c) 3
(d) none
Answer: (d)
Explanation: During carboxylation, CO2 combines with RuBP and forms 3-phosphoglycerate. This step does not require ATP.
- The CAM pathway helps the plants in ________.
(a) secondary growth
(b) primary growth
(c) transporting minerals and nutrients from the soil
(d) reducing loss of water by transpiration
Answer: (d)
Explanation: The CAM pathway is an adaptation that helps the plant to open the stomata during night and keep it closed during the day. This helps in taking in CO2 for fixation without losing water due to opening of stomata and prevents water loss by transpiration.
- Which of the following is the primary product formed during CO2 fixation in the C4 pathway?
(a) Ribulose-1,5-bisphosphate
(b) Oxaloacetic acid
(c) Phosphoglycerate
(d) Phosphoenolpyruvate
Answer: (b)
Explanation: Oxaloacetic acid is the primary CO2 fixation product in the C4 pathway. Ribulose-1,5-bisphosphate is the primary CO2 acceptor in the Calvin cycle. Phosphoglycerate is the primary fixation product in the Calvin cycle. Phosphoenolpyruvate is the primary CO2 acceptor in the C4 cycle.
- Kranz anatomy is typically seen in which of the following?
(a) C2 plants
(b) C4 plants
(c) C3 plants
(d) Both C3 and C4 plants
Answer: (b)
Explanation: C4 plants such as cacti and orchids exhibit Kranz anatomy, in which the bundle sheath cells form several layers around the vascular bundles. They have thick walls with no intercellular spaces to prevent photolysis of water and accumulation of oxygen. It also has a large number of agranal chloroplasts with unstacked thylakoids.
- The number of equivalent molecules of ATP required to produce one molecule of glucose in C4 plants is ______.
(a) 39
(b) 12
(c) 18
(d) 30
Answer: (d)
Explanation: In the C3 cycle, every carbon atom fixation produces 3 molecules of ATP. One molecule of glucose that contains six carbons will thus produce 18 ATP. Similarly in C4, two ATP per carbon fixation is produced, thereby producing 12 ATPs per glucose molecule. Therefore, the number of equivalent molecules of ATP required to produce one molecule of glucose in C4 plants is 30 ATP.
- Which of the following is not a limiting factor for photosynthesis?
(a) Carbon dioxide
(b) Oxygen
(c) Light
(d) Chlorophyll
Answer: (b)
Explanation: When several factors interact and simultaneously affect a process, anything in lower amounts that prevents it from occurring at its maximum rate is called a limiting factor. Oxygen is not a limiting factor in photosynthesis as it is not a requirement or reactant, but it is released as a byproduct.
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