NEET Biology Photosynthesis in Higher Plants MCQs Set 18

Answer: (b) Water

Explanation:
1. Experiments with heavy oxygen (O¹⁸) showed that the oxygen released comes from water.
2. Carbon dioxide supplies the carbon and oxygen of the sugar formed.

Teacher's Note:
1. Water is split in the light reaction (photolysis) to give O₂, protons and electrons.

Answer: (c) Photosynthesis

Explanation:
1. Photosynthesis traps light energy and stores it in the bonds of carbohydrates.
2. Respiration, digestion and fermentation release chemical energy.

Teacher's Note:
1. Photosynthesis is an endergonic, anabolic process.

Answer: (b) Carbon dioxide

Explanation:
1. The oxygen of glucose is derived from the CO₂ taken up in the Calvin cycle.
2. The oxygen released as gas is derived from water, not the glucose oxygen.

Teacher's Note:
1. Do not confuse the oxygen released (from water) with the oxygen in carbohydrate (from CO₂).

Answer: (d) Blackman

Explanation:
1. Blackman proposed in 1905 that when several factors affect a process, its rate is limited by the factor nearest its minimum value.
2. Hill, Krebs and Calvin worked on other aspects.

Teacher's Note:
1. Blackman = limiting factors. Hill = Hill reaction. Calvin = dark reaction pathway.

Answer: (d) 1 to 2 percent

Explanation:
1. Only about 1 to 2 percent of the incident light energy is converted into chemical energy by plants.
2. The rest is reflected, transmitted or lost as heat.

Teacher's Note:
1. Photosynthetic efficiency is low even though photosynthesis supports nearly all life.

Answer: (b) C¹⁴

Explanation:
1. Radioactive carbon-14 labelled CO₂ was used by Calvin to trace the path of carbon.
2. Carbon-13 is stable and the others are not used in such work.

Teacher's Note:
1. Calvin used 14CO₂ and Chlorella to find the Calvin cycle.

Answer: (d) All of the above

Explanation:
1. Ruben and Kamen's O¹⁸ experiment, Hill's experiment and van Niel's work on sulphur bacteria all point to water as the source.
2. So all three statements support the conclusion.

Teacher's Note:
1. Hill showed O₂ evolution without CO₂ in the presence of an oxidant. Van Niel proposed the general equation.

Answer: (b) C¹⁴O₂

Explanation:
1. Calvin and coworkers fed radioactive 14CO₂ to algae and followed the labelled carbon through the intermediates.
2. P³² and O¹⁸ were used for other studies.

Teacher's Note:
1. Paper chromatography and autoradiography were used with 14C.

Answer: (a) Two distinct photosystems

Explanation:
1. Emerson found that light of wavelength shorter and longer than 680 nm together gave a higher rate than the sum of each alone.
2. This enhancement led to the idea of two photosystems working together.

Teacher's Note:
1. The red drop and enhancement effect led to the concept of PS I and PS II.

Answer: (c) Joseph Priestley

Explanation:
1. Priestley showed that a mint plant in a closed jar restored air in which a candle had burnt out or an animal had died.
2. The others worked on chlorophyll, cells or CO₂ effects.

Teacher's Note:
1. Priestley in 1770; Ingenhousz in 1779 showed that sunlight and green parts are required.

Answer: (c) Less than 1 percent

Explanation:
1. Most of the water absorbed is lost in transpiration.
2. Only a very small fraction, under 1 percent, enters photosynthesis.

Teacher's Note:
1. This is why water stress affects photosynthesis mainly through stomatal closure.

Answer: (a) Carbon dioxide is essential for photosynthesis

Explanation:
1. In this experiment one half of a leaf is kept in a bottle containing KOH that absorbs CO₂ while the other half is in normal air.
2. Starch forms only in the half that has CO₂.

Teacher's Note:
1. KOH absorbs CO₂, which is why the half in the flask shows no starch.

Answer: (a) Ruben and Kamen

Explanation:
1. Ruben and Kamen used water labelled with heavy oxygen and found it in the released O₂.
2. Hill showed oxygen evolution by isolated chloroplasts with an artificial acceptor.

Teacher's Note:
1. Ruben and Kamen also traced carbon with C-11 and C-14 in early work.

Answer: (d) Engelmann

Explanation:
1. Engelmann used the filamentous alga Cladophora and aerobic bacteria placed in a prism spectrum.
2. Bacteria collected in the blue and red regions where photosynthesis was fastest.

Teacher's Note:
1. This gave the first action spectrum of photosynthesis.

Answer: (c) There is effective pumping of CO₂ into the bundle sheath cells

Explanation:
1. C₄ plants pump CO₂ from mesophyll cells into the bundle sheath cells as C₄ acids.
2. This raises the CO₂ level around RuBisCO even when atmospheric CO₂ is low.

Teacher's Note:
1. The other options describe the mechanism but the actual reason is the CO₂ concentrating effect.

Answer: (b) A redox reaction, endergonic, anabolic

Explanation:
1. Water is oxidised and CO₂ is reduced, so it is a redox reaction.
2. It needs energy input and builds large molecules, so it is endergonic and anabolic.

Teacher's Note:
1. Respiration is the reverse: catabolic and exergonic.

Answer: (d) Both longer and shorter than 680 nm given together

Explanation:
1. Emerson found that red light beyond 680 nm alone gave a low rate, but when shorter wavelength light was added, the rate was more than the sum.
2. So both ranges together are needed.

Teacher's Note:
1. This led to the two-photosystem model.

Answer: (a) Chloroplast

Explanation:
1. Photophosphorylation forms ATP using light energy on the thylakoid membranes.
2. Mitochondria carry out oxidative phosphorylation.

Teacher's Note:
1. Chloroplast = photophosphorylation; mitochondria = oxidative phosphorylation.

Answer: (d) Stroma thylakoids and non-appressed part of grana thylakoids

Explanation:
1. PS I is present in the non-appressed regions of thylakoids, that is in stroma lamellae and the grana margins.
2. PS II is found mainly in the appressed regions of the grana.

Teacher's Note:
1. PS I has no water-splitting ability, which is why it lives where it does not need PS II.

Answer: (d) Anthocyanin

Explanation:
1. Anthocyanin is a water-soluble pigment found in the cell sap of vacuoles.
2. Carotene, xanthophyll and chlorophyll are plastid pigments.

Teacher's Note:
1. Anthocyanins give red, blue and purple colours to flowers and fruits.

Answer: (b) Mg

Explanation:
1. The porphyrin head of chlorophyll has a magnesium atom at its centre.
2. Iron is needed to make chlorophyll but is not part of it.

Teacher's Note:
1. Remember that haemoglobin has Fe and chlorophyll has Mg.

Answer: (c) Anthocyanin

Explanation:
1. Anthocyanin is dissolved in vacuolar sap.
2. Chlorophyll, carotene and xanthophyll are lipid soluble.

Teacher's Note:
1. Plastid pigments dissolve in organic solvents such as acetone and ether.

Answer: (a) Stroma

Explanation:
1. The Calvin cycle enzymes are present in the stroma of the chloroplast.
2. Grana are the sites of the light reaction.

Teacher's Note:
1. Stroma = dark reaction, thylakoid = light reaction.

Answer: (a) In the grana of chloroplasts

Explanation:
1. Chlorophyll is embedded in the thylakoid membranes, which are stacked as grana.
2. It is not found freely in the stroma or on the outside of the organelle.

Teacher's Note:
1. Thylakoid membranes carry the pigments and electron carriers.

Answer: (c) Protecting chlorophyll molecules from photooxidation

Explanation:
1. Carotenoids absorb excess light energy and protect chlorophyll from photooxidation.
2. They also pass some absorbed energy to chlorophyll a.

Teacher's Note:
1. Carotenoids are accessory pigments that widen the range of absorbed light.