Photosynthesis MCQ Quiz - Objective Question with Answer for Photosynthesis - Download Free PDF

The correct answer is Statement 1 and 3 are correct

Explanation:

Statement 1: Accessory pigments protect chlorophyll a from photo-oxidation.

• This statement is correct. Accessory pigments like carotenoids play a protective role by dissipating excess light energy and preventing the formation of reactive oxygen species that can damage chlorophyll a and other cellular components.

Statement 2: The color that we see in leaves is due to a single pigment.

• This statement is incorrect. The color of leaves is usually due to a combination of pigments, including chlorophylls (which give leaves their green color), carotenoids (which contribute yellow, orange, and red colors), and anthocyanins (which can provide red, purple, and blue hues).
• The overall color of a leaf is the result of the combined absorption and reflection properties of these various pigments.

Statement 3: Leaf pigments can be separated through paper chromatography.

• This statement is correct. Paper chromatography is a common laboratory technique used to separate and identify different pigments present in leaves.
• By placing a leaf extract on chromatography paper and allowing a solvent to move through the paper, the pigments separate based on their solubility and affinity for the paper, revealing distinct bands of color

The correct answer is A is true, but R is false.

Explanation:
Assertion (A): The action spectrum of photosynthesis perfectly matches the absorption spectrum of chlorophyll a.

• The action spectrum of photosynthesis shows the relative effectiveness of different wavelengths of light in driving the process of photosynthesis.
• The absorption spectrum of chlorophyll a indicates the specific wavelengths of light that chlorophyll a can absorb.

Fig: b) Graph showing action spectrum of photosynthesis
c) Graph showing action spectrum of photosynthesis superimposed on absorption spectrum of chlorophyll a

Reason (R): Chlorophyll a is the only pigment involved in photosynthesis.

• This statement is incorrect. Although chlorophyll a is the primary pigment involved in the reaction centers of photosystems I and II, it is not the only pigment.
• Accessory pigments like chlorophyll b, carotenoids (e.g., beta-carotene, lutein), and phycobilins (in some algae and cyanobacteria) also play significant roles by capturing light energy at different wavelengths and transferring it to chlorophyll a.

The correct answer is Xanthophylls

Explanation:

• Xanthophyll: Xanthophylls are a class of oxygen-containing carotenoid pigments. They generally appear yellow in colour.
• Carotenoid: Carotenoids are pigments that range from red to yellow-orange. They specifically appear yellow to yellow-orange in chromatograms.
• Chlorophyll b: Chlorophyll b is an accessory pigment to chlorophyll a and typically absorbs light in the blue and red part of the spectrum, appearing yellow-green.
• Chlorophyll a: Chlorophyll a is the primary photosynthetic pigment in plants and appears bright or blue-green in chromatograms

The correct answer is Statement-A is incorrect but Statement-B is correct

Explanation:

• A part of a leaf is enclosed in a test tube containing some KOH soaked cotton (which absorbs CO₂), while the other half is exposed to air.
• The setup is then placed in light for some time.
• On testing for the presence of starch later in the two parts of the leaf, the exposed part of the leaf tested positive for starch while the portion that was in the tube, tested negative. This showed that CO₂ was required for photosynthesis.

The correct answer is 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ 

Explanation:

• Photosynthesis is a fundamental biological process by which plants, algae, and some bacteria convert light energy into chemical energy, storing it in the bonds of glucose (a type of sugar)
• The overall chemical equation for photosynthesis in oxygen-evolving organisms is as follows 6CO₂ + 12 H₂O → C₆H₁₂O₆ + 6 H₂O + 6O₂ 

The correct answer is autotrophic nutrition.Key Points

• Autotrophic nutrition is the mode of nutrition in which organisms make their food themselves from simple substances.
• The process of autotrophic nutrition involves the use of light energy (in photosynthesis) or chemical energy (in chemosynthesis) to produce organic compounds.
• Autotrophs are organisms that carry out autotrophic nutrition, such as plants, algae, and some bacteria.

Additional Information

• Heterotrophic nutrition is the mode of nutrition in which organisms obtain their food by consuming other organisms or organic matter.
• Saprotrophic nutrition is a type of heterotrophic nutrition in which organisms obtain their food by decomposing dead organic matter.
• Phototrophic nutrition is a subcategory of autotrophic nutrition, in which organisms use light energy to produce their own food.

The correct answer is Sugarcane and Sugarbeet.

Key Points

C3 plants

• C3 plants are those where the initial product is 3-phosphoglycerate with 3 carbon atoms. These plants also known as temperate plants. 
• These plants carry out the C3 cycle to fix carbon from carbon dioxide into 3 carbon sugars.
• It is a cycle of chemical reactions where plants, over a period of time, can transform the 3 carbon compounds into nucleotides, amino acids and complex sugars(starches).
• They are highly rich in proteins.
• Approximately 95% of the shrubs, trees, and plants are C3 plants.
• Examples of C3 plants are Sunflower, Spinach, Beans, Rice, Cotton, and Sugarbeet.

C4 plants

• C4 plants are plants which cycle carbon dioxide to 4-carbon sugar compounds in order to enter the C3 or the Calvin cycle.
• The C4 plants are very productive in climatic conditions that are hot and dry and produce a lot of energy. Some of the plants that we usually consume are C4 plants such as pineapple, corn, sugar cane, etc.
• The C4 pathway is used by only 3% of the vascular plants.
• The plants are so-called because of the 4 carbon compound oxaloacetate produced during the pathway.
• About 5% of plants on earth are C4 plants.
• Examples of C4 plants are Sugarcane, Sorghum, and Maize etc

There are also a few similarities between the C3 and C4 plants:

• Both the plants fix energy from sunlight.
• Both synthesize carbohydrates.
• They are the type of dark reactions of photosynthesis.
• The site of photosynthesis is chloroplast in both types of plants.

Concept-

• Light reactions or the ‘Photochemical’ phase include light absorption, water splitting, oxygen release, and the formation of high-energy chemical intermediates, ATP and NADPH.
• The whole scheme of transfer of electrons, starting from the PS II, uphill to the acceptor, down the electron transport chain to PS I, excitation of electrons, transfer to another acceptor, and finally downhill to NADP+ reducing it to NADPH + H+ is called the Z scheme, due to its characteristic shape.
• During the 'Z' scheme of Photosynthesis, it is the electrons from Photosystem I (PSI) which ultimately reduce NADP+ to NADPH

Explanation-

• The splitting of water in the presence of sunlight is called photolysis.
• It occurs during non-cyclic photophosphorylation.
• It results in the supply of electrons to PSII and the protons to NADP⁺.
• O₂ is liberated during this process. 
• Electrons released from water finally reach NADP⁺ through PSII and PSI. Thus NADP⁺ is reduced to NADPH + H⁺.

Important Points

• The NADP reductase enzyme is located on the stromal side of the membrane. Along with electrons that come from the acceptor of electrons of PS I, protons are necessary for the reduction of NADP+ to NADPH+ H+. These protons are also removed from the stroma. 

The correct answer is the reduction of carbon-di-oxide.

Concept:

• Photosynthesis is the process by which all green plants, some bacteria, and some protists (Euglena) use energy from sunlight to produce sugar, which through cellular respiration produces ATP, the fuel used by all living organisms.
• Photosynthesis occurs in the chloroplast of the cell.
• The reaction of Photosynthesis is commonly written as:
  • 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂.
• The process of Photosynthesis takes place in two steps:
  • Light Reaction (Photochemical phase)
  • Dark Reaction (Biosynthetic phase)

Explanation:

Light Reaction:

• Light Reaction takes place only in the presence of light.
• The light reaction takes place in the thylakoid membranes.
• Light is absorbed in the light reaction, and energy is used to drive electrons from water to generate NADPH and protons across the membrane.
• The following major events occur during the light reaction of photosynthesis:
• Photolysis of water: 
  • In this water splits into protons, electrons and oxygen and produces NADPH and ATP.
• Photophosphorylation: 
  • Photophosphorylation is the process through which, ATP is synthesized from ADP and inorganic phosphate (P) by the cell organelles (like mitochondria and chloroplast).
• Reduction of NADP:
  • NADP is a reduced in the photosynthesis light reactions that is consumed in the Calvin cycle and used in many other anabolic reactions in both plants and animals.

Additional InformationDifference between Light reaction and Dark reaction:

Correct Answer: T.W. Engelmann

Key Points

• T.W. Engelmann carried out the action spectrum experiment.
• Through this experiment, he deduced that the most photosynthetically active region will show the highest concentration of bacteria.

Additional Information

• Photosynthesis is the chemical process by which carbohydrates (organic molecules) are synthesized from inorganic materials like CO2 and H2O with the help of light energy which is trapped by pigments like chlorophyll.
• Oxygen is given out at the end of the photosynthesis process.

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• Green plants, algae, and photosynthetic bacteria carry out the process of photosynthesis.
• Chlorophyll, carotenoids, and phycobilins are some of the most important pigments involved in the photosynthetic process.
• Chlorophyll pigments efficiently capture solar energy. 
• Chlorophylls absorb light in the violet, blue and red wavelengths of the light spectrum. This part of the light spectrum is also referred to as photosynthetically active radiation (PAR). It ranges from 400nm to 700nm.

Concept:

• Calvin-Benson Cycle or Calvin Cycle or C3 Cycle: The cycle was discovered in 1950 by Melvin Calvin, James Bassham, and Andrew Benson.
• It is called C3 Cycle because the first stable compound formed is a 3 carbon molecule PGA
• The Calvin cycle can be described under three stages: carboxylation, reduction, and regeneration.

Explanation:

• Carboxylation – Carboxylation is the fixation of CO2 into a stable organic intermediate. Carboxylation is the most crucial step of the Calvin cycle where CO₂ is utilized for the carboxylation of RuBP.​
• This reaction is catalyzed by the enzyme RuBP carboxylase which results in the formation of two molecules of 3-PGA. Since this enzyme also has an oxygenation activity it would be more correct to call it RuBP carboxylase-oxygenase or RuBisCO.
• ​Reduction – These are a series of reactions that lead to the formation of glucose. The steps involve the utilization of 2 molecules of ATP for phosphorylation and two of NADPH for reduction per CO2 molecule fixed.
• The fixation of six molecules of CO₂ and 6 turns of the cycle are required for the formation of one molecule of glucose from the pathway.
• Regeneration – Regeneration of the CO2 acceptor molecule RuBP is crucial if the cycle is to continue uninterrupted. The regeneration steps require one ATP for phosphorylation to form RuBP.
• Hence for every CO2 molecule entering the Calvin cycle, 3 molecules of ATP and 2 of NADPH are required. It is probably to meet this difference in the number of ATP and NADPH used in the dark reaction that the cyclic phosphorylation takes place.
• To make one molecule of glucose 6 turns of the cycle are required.

Concept: Plants that are adapted to dry tropical regions have the C₄ pathway.  C4 plants have a special type of leaf anatomy, they tolerate higher temperatures, they show a response to high light intensities, they lack a process called photorespiration, and have greater productivity of biomass. 

Explanation:  Plants in tropical desert regions commonly follow the C₄ pathway. Here, a 4-carbon compound called oxaloacetic acid (OAA) is the first product of carbon fixation. Such plants have certain adaptations as well.

Statement I:  The primary CO₂ acceptor is a 3-carbon molecule, phosphoenol pyruvate (PEP), and is present in the mesophyll cells. The enzyme responsible for this fixation is PEP carboxylase or PEPcase. This statement is correct.

Statement II:  Mesophyll cells of C₄ plants lack the RuBisCO enzyme.  The C₄ acid OAA is formed in the mesophyll cells. This statement is correct. 

So, option 2 is correct.

Concept:

• RuBisCO stands for Ribulose-1,5-biphosphate carboxylase-oxygenase.
• It is a chief enzyme of the Calvin cycle in photosynthesis. It is present in the stroma.

Explanation: 

• RuBisCO is called the most abundant enzyme in the world because:

1. Its active site can bind with both CO2 and O2 i.e. RuBisCO can act as both carboxylase as well as oxygenase.

• It acts as carboxylase at a lower concentration of oxygen and a higher concentration of carbon dioxide. It catalyzes the process of carboxylation of 5C compound Ribulose-1,5-bisphosphate into a 6C compound 3-phosphoglycerate in the Calvin cycle
• It acts as an oxygenase at a higher concentration of oxygen and a low concentration of carbon dioxide. This causes photorespiration in C3 plants which is a wasteful process.

      2. RuBisCO comprises about 15-50% of total chloroplast proteins.

Thus it can be said that RuBisCO is the most abundant enzyme in the world.

Key Points

• Crassulacean Acid Metabolism or CAM is a pathway for carbon fixation that is found in some plants.
• It is so-called because it was first found in the Crassulaceae family plants.
• It is a special adaptation for conserving water in xeric plants (that are found in dry conditions).
• In this process, the stomata open only at night and remain closed during the day.
• At night, the CO₂ is converted into malic acid which is stored in the vacuole.
• During daytime as the atmospheric CO₂ is absent, the malic acid is transported out of the vacuole and converted to pyruvate and CO₂. This CO₂ then takes part in the Calvin-Benson cycle in the chloroplast.

Explanation:

• Phosphoenolpyruvic acid or PEP is a compound that serves as primary acceptor in the mesophyll cell cytoplasm of plants like maize, sugarcane, Sorghum etc.
• These plants are known as C4 plants that are specially adapted for CO₂ fixation at its lower concentrations, like when the stomata are closed to reduce transpiration.

Key Points

• In the C4 plants, two pathways run for CO₂ fixation - C3 Cycle or Calvin cycle & C4 Cycle or Hatch and Slack Pathway.
• The primary CO₂ acceptor is 3-carbon molecule phosphoenolpyruvate (PEP) and is present in the mesophyll cells.
• The enzyme responsible for this fixation is PEP carboxylase or PEPcase.
• It is important to register that the mesophyll cells lack the RuBisCO enzyme.
• The C4 acid Oxaloacetate (OAA) is formed in the mesophyll cells.
• It then forms other 4-carbon compounds like malic acid or aspartic acid in the mesophyll cells themselves, which are transported to the bundle sheath cells.
• In the bundle sheath cells, these C4 acids are broken down to release CO₂ and a 3-carbon molecule.
• The 3-carbon molecule is transported back to the mesophyll where it is converted to PEP again, thus, completing the cycle.
• The CO₂ released in the bundle sheath cells enters the C3 or the Calvin pathway, a pathway common to all plants.
• The bundle sheath cells are rich in the enzyme Ribulose bisphosphate carboxylase-oxygenase (RuBisCO), but lack PEPcase.
• Thus, the basic pathway that results in the formation of the sugars, the Calvin pathway, is common to the C3 and C4 plants.