NEET Biology Photosynthesis and Respiration in Plants MCQs Set 01

Answer: (d) \(\ce{6CO2 + 12H2O ->[Sunlight, Chlorophyll] C6H12O6 + 6O2 + 6H2O}\)

Explanation:
1. (a) and (b) represent respiration.
2. The correct photosynthesis equation shows that 12 water molecules are used and 6 are produced, since the oxygen comes from water.
3. (d) shows this, whereas (c) is the simplified equation that hides the source of oxygen.

Teacher's Note:
1. The balanced equation with 12 \(\ce{H2O}\) on the left tells us that all the oxygen released comes from water.
2. The simple equation is only a net summary.

Answer: (b) Chlorophyll b

Explanation:
1. On a paper chromatogram, chlorophyll a is bright or blue green, chlorophyll b is yellow green, xanthophyll is yellow and carotene is yellow to yellow-orange.
2. So chlorophyll b gives the yellow-green band.

Teacher's Note:
1. Order from the top of the chromatogram: carotene, xanthophyll, chlorophyll a, chlorophyll b.
2. Remember the colours with the pigment names.

Answer: (c) PS I

Explanation:
1. The membranes of the stroma lamellae contain only photosystem I (PS I) and the ATP synthase, and they lack PS II, the water splitting complex and NADP reductase (which lies on the stroma side of the grana).
2. So PS I is the only one present among the options.

Teacher's Note:
1. Grana thylakoids hold PS II, stroma thylakoids hold PS I.
2. This separation helps in cyclic photophosphorylation.

Answer: (c) Electron pump

Explanation:
1. Chemiosmosis needs a membrane, a proton pump, a proton gradient and ATP synthase (ATPase).
2. Electrons are carried by the electron transport chain, but there is no separate electron pump required in the chemiosmotic hypothesis, so this is the odd one.

Teacher's Note:
1. Remember that the protons are pumped, not the electrons.
2. The gradient drives ATP synthesis through the \(F_0\)-\(F_1\) particle.

Answer: (c) Pheophytin

Explanation:
1. When P680 absorbs light it loses an electron to the primary acceptor, pheophytin.
2. The electron then passes to plastoquinone, the cytochrome b6f complex and plastocyanin.

Teacher's Note:
1. The order is P680, pheophytin, plastoquinone, cytochrome b6f, plastocyanin, PS I.
2. Learn the sequence as a chain.

Answer: (a) 5

Explanation:
1. Wheat is a \(\ce{C3}\) plant, in which the primary \(\ce{CO2}\) acceptor is ribulose bisphosphate (RuBP), a 5-carbon sugar.
2. In \(\ce{C4}\) plants the primary acceptor is PEP, a 3-carbon compound.

Teacher's Note:
1. C3 plants fix carbon dioxide directly in the Calvin cycle with RuBP and Rubisco.
2. The first stable product is the 3-carbon PGA.

Answer: (b) 360 \(\mu\)L/L and 450 \(\mu\)L/L

Explanation:
1. \(\ce{C4}\) plants such as maize reach saturation at about 360 \(\mu\)L/L of \(\ce{CO2}\) and do not respond to higher levels.
2. \(\ce{C3}\) plants such as wheat respond to higher levels and the optimum is about 450 \(\mu\)L/L.
3. So maize is 360 and wheat is 450.

Teacher's Note:
1. C4 plants have a built-in carbon dioxide concentrating mechanism.
2. C3 plants benefit from enriched air in greenhouses.

Answer: (d) destruction of chlorophyll

Explanation:
1. At very high light intensity, chlorophyll is destroyed by photo-oxidation, which is called solarisation.
2. The leaf turns pale and photosynthesis falls.

Teacher's Note:
1. Too much light is as bad as too little.
2. This is one of the reasons that light saturation exists.

Answer: (c) 36 and 24

Explanation:
1. One hexose needs 6 turns of the Calvin cycle, using \(6 \times 3 = 18\) ATP and \(6 \times 2 = 12\) NADPH.
2. Sucrose contains two hexose units (glucose and fructose), so the requirement is doubled: 36 ATP and 24 NADPH.

Teacher's Note:
1. Each turn of the cycle uses 3 ATP and 2 NADPH.
2. Sucrose needs 12 turns.

Answer: (d) \(F_1\) is an intrinsic protein

Explanation:
1. \(F_0\) is the embedded part that forms the proton channel, so (a) is correct.
2. \(F_1\) is the headpiece that projects on the stroma side and has the catalytic sites, so (b) and (c) are correct.
3. \(F_1\) is a peripheral (extrinsic) protein attached to \(F_0\), not an intrinsic one, so (d) is incorrect.

Teacher's Note:
1. Intrinsic proteins are embedded in the membrane; extrinsic ones sit on the surface.
2. F0 spans the membrane and F1 does not.

Answer: (c) \(\alpha\)-ketoglutaric acid

Explanation:
1. \(\alpha\)-Ketoglutaric acid has five carbons and two carboxyl groups (OAA has four carbons).
2. It is the acceptor of ammonia in reductive amination to form glutamic acid, which links the Krebs cycle to nitrogen metabolism.

Teacher's Note:
1. OAA (4C) can also be aminated to aspartate.
2. These two acids connect respiration and amino acid synthesis.

Answer: (c) 19 ATP

Explanation:
1. One glucose gives two molecules of PGAL (glyceraldehyde 3-phosphate) in glycolysis.
2. Complete aerobic oxidation of glucose yields 38 ATP in the older convention, so one PGAL gives half of this, 19 ATP.

Teacher's Note:
1. PGAL is a three-carbon compound, half of glucose.
2. The total number depends on the convention used for NADH (2 or 3 ATP).

Answer: (c) Invertase

Explanation:
1. Invertase (sucrase) hydrolyses the glycosidic bond of sucrose to give glucose and fructose.
2. Hexokinase phosphorylates glucose, pyruvate decarboxylase acts in alcoholic fermentation and catalase breaks down hydrogen peroxide.

Teacher's Note:
1. The mixture of glucose and fructose is called invert sugar.
2. Respiration starts with glucose derived this way.

Answer: (d) Inner mitochondrial membrane

Explanation:
1. In aerobic respiration, NADH is oxidised by Complex I of the electron transport chain, located on the inner mitochondrial membrane.
2. The electrons pass finally to oxygen, and NAD+ is regenerated.

Teacher's Note:
1. In anaerobic conditions NADH is oxidised in the cytoplasm by fermentation.
2. Aerobic oxidation needs the mitochondrial electron transport chain.

Answer: (b) Acetyl CoA

Explanation:
1. Fats give fatty acids, which are broken down to acetyl CoA; carbohydrates give pyruvate, which forms acetyl CoA; and amino acids feed in as pyruvate, acetyl CoA or Krebs cycle intermediates.
2. Acetyl CoA is the common entry point to the Krebs cycle for all three.

Teacher's Note:
1. Acetyl CoA is the meeting point of the catabolic pathways.
2. It is also the starting material for fatty acid synthesis.

Answer: (b) Carbohydrate > protein > fatty acid

Explanation:
1. RQ is the ratio of volume of \(\ce{CO2}\) released to the volume of \(\ce{O2}\) consumed.
2. For carbohydrates RQ = 1, for proteins about 0.9 and for fats about 0.7.
3. The decreasing order is carbohydrate > protein > fatty acid.

Teacher's Note:
1. Fats are rich in hydrogen and need more oxygen, so RQ is low.
2. Organic acids have an RQ greater than 1.

Answer: (a) 36

Explanation:
1. Glycolysis gives a net of 2 ATP, the link reaction and Krebs cycle give 2 GTP/ATP, and the electron transport chain gives the remaining ATP from NADH and FADH2.
2. The commonly used total is 36 ATP per glucose in the aerobic oxidation in many textbooks (38 in the older count when NADH is counted as 3 ATP).

Teacher's Note:
1. The number differs by textbook (30 to 38) depending on the assumed yields.
2. Remember the value used in your course.

Answer: (b) Phosphofructokinase

Explanation:
1. Phosphofructokinase catalyses the committed step in which fructose-6-phosphate becomes fructose-1,6-bisphosphate.
2. It is regulated by ATP, citrate and AMP, so it controls the rate of glycolysis.

Teacher's Note:
1. The enzyme is inhibited by high ATP levels.
2. That makes glycolysis slow down when the cell has enough energy.

Answer: (b) 2 ATP

Explanation:
1. Succinate dehydrogenase passes two hydrogen atoms to FAD to form \(\ce{FADH2}\).
2. \(\ce{FADH2}\) enters the electron transport chain at Complex II and yields 2 ATP in the older count (1.5 in the newer one).

Teacher's Note:
1. FADH2 gives fewer ATP than NADH because it enters at Complex II.
2. Succinate dehydrogenase is the only Krebs cycle enzyme bound to the membrane.

Answer: (c) 1 \(\ce{FADH2}\), 3 NADH, 1 GTP

Explanation:
1. In one turn, three NAD+ are reduced (at isocitrate dehydrogenase, alpha-ketoglutarate dehydrogenase and malate dehydrogenase).
2. One FAD is reduced at succinate dehydrogenase, and one GTP (or ATP) is made at the succinyl-CoA step.
3. So one turn gives 3 NADH, 1 \(\ce{FADH2}\) and 1 GTP.

Teacher's Note:
1. One glucose gives two turns of the cycle.
2. Multiply by two for a whole glucose molecule.