Test: Photosynthetic Apparatus - ACT MCQ

Pyruvate carboxylase is a mitochondrial enzyme that catalyzes carboxylation of pyruvate into oxaloacetate. Hexokinase is an enzyme of glycolysis and is present in the cytoplasm. RUBP carboxylase catalyzes carboxylation of RuBP during photosynthetic carbon fixation. Chloroplasts is the site of photosynthesis and contain maximum quantity of RUBP carboxylase. 

The important photosynthetic pigments are chlorophyll, carotenoids, and phycobilins.
As many as 8 major types of chlorophylls are known to exist in the plant kingdom- chlorophyll a, b, c, d, e, bacteriochlorophylls a and b and chlorobium chlorophyll.
The chlorophyll a is the primary photosynthetic pigment and is found in all photosynthetic organisms except bacteria.
So, the correct answer is option A.

Chlorophyll are light harvesting cyclic tetrapyrrole compounds. The chlorophyll biosynthesis requires iron and magnesium mineral ions. The succinyl CoA, an intermediate of Krebs cycle and the amino acid glycine initiate the biosynthesis of chlorophyll 'A', leading to production of protochlorophyllide or protochlorophyll. The protochlorophyllide or protochlorophyll is converted to chlorophyll 'A' in presence of light.

Xanthophylls are yellow coloured carotenoids also called xanthols or carotenols.

Carotenoids in higher plants primarily absorb specific fractions of the visible spectrum of solar radiation. The correct answer is:

- C: Violet and blue

Explanation:
- Carotenoids are pigments that appear yellow, orange, or red and are known to primarily absorb light in the blue and violet regions of the visible spectrum.
- This absorption helps in providing protection to plants by dissipating excess light energy and in some cases transferring this energy to chlorophyll for photosynthesis.

Photosynthesis occurs most efficiently with red or blue light because the chlorophyll pigments can absorb light maximally at these wavelengths and the least at green light.

The pigment acting as a reaction center during photosynthesis is "P700." Here's a concise explanation of why this is the correct answer:

- P700 refers to a type of chlorophyll molecule found in photosystem I of plants.
- This pigment absorbs light energy during photosynthesis and is essential for the conversion of light energy into chemical energy.
- P700 plays a crucial role in the photosynthetic electron transport chain by accepting electrons and passing them along to other molecules involved in the process.
- Its specific absorption properties make it a key player in the light-dependent reactions of photosynthesis.

The correct answer is C: PS-II.
- Photosystem II (PS-II) is inactivated in red light.
- PS-II is a part of the photosynthetic process where light energy is absorbed by chlorophyll to initiate the conversion of light energy into chemical energy.
- In red light, the absorption spectrum of chlorophyll primarily affects PS-II, leading to its inactivation.

Understanding the specific pigment systems affected by different wavelengths of light is crucial in comprehending the intricacies of photosynthesis.

Photosynthesis occurs in two stages in a cell. In the first stage, light-dependent reactions capture the energy of light and use it to make the energy-storage and transport molecules ATP and NADPH. The light-independent Calvin cycle uses the energy from short-lived electronically excited carriers to convert carbon dioxide and water into organic compounds that can be used by the organism (and by animals that feed on it). This set of reactions is also called as carbon fixation. The key enzyme of the cycle is called as RuBisCO. The Calvin cycle or reductive pentose phosphate cycle or C3 cycle is a series of biochemical redox reactions that take place in the stroma of chloroplasts in photosynthetic organisms. 

The cycle was discovered by Melvin Calvin, James Bassham and Andrew Benson at the University of California, Berkeley by using the radioactive isotope carbon-14.

- Correct Answer:
- Chlorophyll molecule has magnesium (Mg) situated in the center of the porphyrin ring.

Chlorophyll is a pigment responsible for photosynthesis, containing a porphyrin ring structure with magnesium at its core. This positioning of magnesium is crucial for the molecule's ability to absorb light energy and facilitate the conversion of that energy into chemical energy through the process of photosynthesis.

Chlorophylls, the photosynthetic pigments, are soluble in organic solvent. Here's why:

- Chlorophylls are non-polar molecules due to their hydrophobic tail.
- Organic solvents have non-polar properties, making them suitable for dissolving chlorophylls.
- Water, being a polar solvent, cannot effectively dissolve non-polar chlorophylls.
- Inorganic solvents lack the appropriate properties to dissolve chlorophylls effectively.

Therefore, the correct answer is C: Organic solvent.

Half leaf experiment proves that CO₂ is essential for photosynthesis.

Chlorophyll is light harvesting pigments found in chloroplasts. The approx concentration of chlorophyll in a chloroplast is approx 30mM. The percentage of chlorophyll in a normal chloroplast is 5 to 10 percent.
So, the correct answer is option A.

In the regeneration phase of the Calvin cycle during photosynthesis, ribulose-1,5-bisphosphate (RuBP) is regenerated. To synthesize one glucose molecule, 6 molecules of RuBP need to be regenerated. The regeneration of each RuBP molecule requires 1 ATP and 1 NADPH. Therefore, the number of ATP molecules needed for the regeneration of 6 RuBP molecules is 6 ATP molecules (6 RuBP x 1 ATP/RuBP = 6 ATP). Thus, the correct answer is A: 6 ATP molecules.

The universal photosynthetic chlorophyll is Chl-'a'. Here's why:

- Chl-'a' is the primary pigment involved in photosynthesis, found in the chloroplasts of all green plants and cyanobacteria.
- It plays a crucial role in capturing light energy and converting it into chemical energy during the light reactions of photosynthesis.
- Chl-'a' absorbs light most effectively in the red and blue-violet parts of the electromagnetic spectrum, crucial for photosynthetic processes.
- Other chlorophyll types like Chl 'b', Chl 'c', and Chl 'e' have slightly different absorption spectra and roles in specific organisms, but Chl-'a' is universal.

Lumen of thylakoid sacs is the site of photolysis of water.
The photolysis of water occurs during light reaction. The site for occurrence of photolysis is thylakoid lumen. The photolysis of water releases protons, which accumulate in the lumen and contribute to the electrochemical gradient of protons. The electrons released are used up to fill the electron hole in the reaction centre of PSII and oxygen molecule is released as a by product of photosynthesis. 

The chlorophyll molecule is important for trapping of light in photosynthesis. The minerals magnesium and iron are an important requirement for their biosynthesis. The chlorophylls are synthesized as protochlorophyllide, which gets converted into chlorophyll on exposure to light. The succinyl-CoA, an intermediate of Krebs cycle and the amino acid glycine initiate the biosynthesis of chlorophyll a-first producing protochlorophyllide, then chlorophyllide A and ultimately chlorophyll A.
So, the correct answer is option B.

Photosynthesis takes place in the green leaves of plants and other green parts of plants like stem etc. The most active photosynthetic tissue in higher plants is the mesophyll of leaves. Mesophyll cells have many chloroplasts, which contain the specialized light-absorbing green pigments, the chlorophylls. When chlorophyll absorbs light, it gets excited and emits electrons. These chlorophylls are found in photosynthetic units called Photosystem I and Photosystem II. Each unit has a specific reaction centre which contains pigment molecules. These molecules absorb light of different wavelengths and emit electrons. Due to the photon of light, electrons of chlorophyll get excited. These electrons are picked up by an electron acceptor which passes them to an electron transport system of cytochromes. The excitement of electrons of chlorophyll b photon of light is the first step of photosynthesis.

The ultimate gain of the light reaction in photosynthesis is ATP and NADPH₂. This process occurs in the thylakoid membranes of chloroplasts and involves capturing light energy to convert it into chemical energy. Here's a concise explanation:

- Light energy is absorbed by chlorophyll and other pigments.
- Water molecules are split into oxygen, protons, and electrons.
- ATP and NADPH₂ are generated as carriers of energy to the Calvin cycle.
- ATP provides energy for the synthesis of carbohydrates, while NADPH₂ provides electrons needed for reducing CO₂ to sugar.