Test: Plant Physiology: Photosynthetic Apparatus - ACT MCQ

Photosynthesis is the process of converting the energy of light into the energy of chemical bonds. This occurs in the chloroplasts of cells, specifically, in the thylakoid membranes. The formation of ATP during the photosynthesis is called the photophosphorylation.
Hence, the correct answer is 'Chloroplasts'.

Chloroplasts are eukaryotic cell organelles. They are covered by the double membrane and also have an internal membrane system comprised of thylakoid membranes. The thylakoid membranes are of two types. The membranes which make grana are called granal lamellae. The other thylakoid membranes are called stromal membranes . The non-appressed membranes (stromal membranes and edges of granal membranes) are in direct contact with the stroma. The PS- I is abundant in non-appressed membrane whereas PS- II is abundant in granal membranes.

Photophosphorylation refers to the synthesis of ATP from ADP. Here's a breakdown of why this is the correct answer:

- ATP Production: Photophosphorylation occurs during the light-dependent reactions of photosynthesis.
- Energy Source: Light energy is used to drive the phosphorylation of ADP to form ATP.
- Photosystems: This process takes place in the thylakoid membranes of chloroplasts.
- Role in Photosynthesis: ATP produced is used to power the Calvin cycle, where carbon fixation occurs.

Understanding this process is crucial to grasp how plants convert light energy into chemical energy.

In chloroplasts, the pigment that does not occur is Anthocyanin. Here's why:

- Carotene: A pigment found in chloroplasts aiding in photosynthesis.
- Xanthophyll: Another pigment present in chloroplasts, helping in light absorption.
- Chlorophyll 'b': Essential pigment in chloroplasts, assisting in capturing light energy.
- Anthocyanin: Not found in chloroplasts; it's responsible for red, purple, or blue colors in plants but not involved in photosynthesis.

Chlorophyll pigment is activated by sunlight mostly chlorophyll b absorbs the sunlight which is then used to combine carbon dioxide and water into sugars in the process of photosynthesis.

Chlorophyll contains magnesium (Mg). Here's why:

- Mg is the central atom in the chlorophyll molecule.
- It plays a crucial role in capturing light energy during photosynthesis.
- This captures energy is then converted into chemical energy for the plant.
- Without Mg, chlorophyll cannot perform its function effectively.
- Hence, the correct answer is B: Mg.

Anthocyanins (literally "flower blue") are water-soluble flavonoid pigments that appear red to blue, according to pH. They occur in all tissues of higher plants, providing color in leaves, plant stem, roots, flowers, and fruits, though not always in sufficient quantities to be noticeable.

Chloroplasts perform many metabolic reactions in green leaves. In addition to carbon dioxide fixation, the synthesis of almost all amino acids, all fatty acids and carotenes, all pyrimidines and probably all purines occurs in chloroplasts. Reactions which fix carbon dioxide and convert it to hexose sugars are powered by the energy released by ATP hydrolysis and by the reducing agent NADPH. The enzymes that catalyze the calvin cycle reactions are rapidly inactivated in the dark, so that carbohydrates formation generally ceases when light is absent.

In the process of photosynthesis, the phosphorylation of ADP to form ATP using the energy of sunlight is called photophosphorylation.

The main site for the dark reaction of photosynthesis is the Stroma. This process, also known as the Calvin Cycle, occurs in the stroma of chloroplasts. Here's why:

- Stroma is the fluid-filled space surrounding the grana in chloroplasts.
- In the stroma, key enzymes like RuBisCO are present to drive the Calvin Cycle.
- During the Calvin Cycle, carbon dioxide is converted into glucose using ATP and NADPH generated in the light reaction.
- This step is crucial for the synthesis of sugars and occurs independently of light.

Therefore, option A, Stroma, is the correct answer.

When chlorophyll is burnt, what remains is magnesium. Here's why:

- Chlorophyll contains a central magnesium atom.
- When chlorophyll is burnt, the organic components are destroyed, leaving behind the inorganic residue.
- Magnesium is a key component of the chlorophyll molecule, and it remains as ash after the burning process.
- The other elements mentioned (manganese, iron, and sulfur) are not typically found in chlorophyll in significant amounts, so they do not remain after burning.

Therefore, the correct answer is A: Magnesium.

Chlorophyll is present in the grana of chloroplasts.

- Chlorophyll, the green pigment crucial for photosynthesis, is primarily located in the grana.
- Grana are stacks of thylakoids where light-dependent reactions occur.
- Chlorophyll molecules are embedded in the thylakoid membranes within the grana.
- Here, they capture light energy needed for photosynthesis.
- This strategic positioning allows efficient absorption of light for the conversion of carbon dioxide and water into glucose.

Photochemical reaction

• It is a chemical reaction that results when the reacting substance is exposed to radiation.
• According to Einstein's law of Photochemical equivalence “, Each quantum of radiation absorbed activates one molecule in the primary step of a photochemical process.”
• The law states that each molecule takes one quantum of radiation for its activation and subsequent chemical reaction.
• So, the rate of Photochemical reaction increases with increasing intensity of light and is independent of the concentration of the reactant and product.

Solar energy is converted into ATP in the Chloroplast. Here's the detailed explanation:

- Chloroplasts are organelles found in plant cells responsible for photosynthesis.
- During photosynthesis, solar energy is captured by chlorophyll in the chloroplasts.
- This energy is used to convert carbon dioxide and water into glucose, releasing oxygen as a byproduct.
- ATP, the energy currency of cells, is produced during this process through a series of reactions in the chloroplasts.
- Therefore, the correct answer is B: Chloroplast.

• Kranz anatomy is found in the leaves of C₄ plants. e.g. sorghum, maize, sugarcane, millets.
• The differences between the C₄ and C₃ plants are that the bundle sheath cells of C₃ plants do not contain chloroplast whereas the bundle sheath cells of C₄ plants do.

To explain the correct answer "All of the above" in detail:

- Light and suitable temperature: Photosynthesis requires light energy for the conversion of carbon dioxide and water into glucose. Suitable temperature ensures optimal enzyme activity.
- Chlorophyll and water: Chlorophyll is essential for capturing light energy. Water is a reactant in the light-dependent reactions of photosynthesis.
- Carbon dioxide: A crucial raw material for photosynthesis, taken in through stomata in leaves.

Therefore, all the mentioned conditions (A, B, and C) are necessary for photosynthesis to occur effectively.

Photosynthesis is maximum during Intermittent light because:
- Intermittent light allows for a balance between light-dependent reactions and light-independent reactions.
- Under continuous strong light, plants may experience photoinhibition, reducing photosynthetic efficiency.
- Continuous weak light may not provide enough energy for optimal photosynthesis.
- Intermittent light helps in maintaining a suitable balance for the light reactions to proceed efficiently.
- Therefore, the correct answer is Intermittent light (Option C).

• Chlorophyll, a member of the most important class of pigments involved in photosynthesis, the process by which light energy is converted to chemical energy through the synthesis of organic compounds.
• Chlorophyll is found in virtually all photosynthetic organisms, including green plants, cyanobacteria, and algae.
• It absorbs energy from light; this energy is then used to convert carbon dioxide to carbohydrates. 
• The chlorophyll molecule consists of a central magnesium atom surrounded by a nitrogen-containing structure called a porphyrin ring; attached to the ring is a long carbon-hydrogen side chain, known as a phytol chain. Variations are due to minor modifications of certain side groups.
• Chlorophyll is remarkably similar in structure to hemoglobin, the oxygen-carrying pigment found in the red blood cells of mammals and other vertebrates.

Chlorophylls are present in chloroplasts, which absorb light energy. Chlorophyll a is the primary photosynthetic pigment and is found in all the photosynthetic organisms except bacteria. The chlorophyll a absorbs blue, yellow and red wavelengths of the spectrum. It shows maximum absorption of blue light.

So, the correct answer is option A.

The carotenoids are unsaturated polyhydrocarbons being composed of eight isoprene (C5​H8​) units. Carotene are a type of carotenoids. These are orange coloured pigments. The carotenoids mainly absorb violet indigo and blue wavelength of the spectrum and to some extent the green wavelength too ranging between 400 - 505 nm. The maximum absorption occurs in high energy blue wavelength, thus protecting the chlorophyll molecules from photooxidation.

Thus, the correct answer is option C. 

- Rubisco is located in the Chloroplast.
- Chloroplasts are organelles found in plant cells.
- Rubisco plays a key role in photosynthesis by catalyzing the first major step of carbon fixation.
- It captures carbon dioxide from the atmosphere and converts it into organic molecules.
- This process is crucial for producing glucose and other carbohydrates essential for plant growth.
- Understanding Rubisco's location helps in comprehending how plants utilize carbon dioxide for energy production.

Cyanobacteria have both photosystems and hence, can carry out the light reaction as seen in higher plants during oxygenic photosynthesis. Oxygenic photosynthesis is a term used to denote photosynthesis in which oxygen is evolved. The oxygen gas can be evolved if both photosystems are present and noncyclic phosphorylation occurs. The oxygen gas is released during noncyclic phosphorylation as a byproduct of the photolysis process. Other photosynthetic bacteria lack PS- II and hence cannot evolve oxygen and consequently do not show oxygenic photosynthesis.

The correct answer is C: Anthocyanin.

- Anthocyanin is a water-soluble photosynthetic pigment.
- Chlorophyll a and b are the primary pigments responsible for photosynthesis.
- Xanthophylls are yellow pigments that help in light absorption and protection.
- Anthocyanins are responsible for red, purple, and blue colors in plants.
- They play a role in protecting plant tissues and attract pollinators.

The thylakoid membrane of chloroplasts contain around 250-400 particles known as quantasomes. They are present on the surface of thylakoid discs in chloroplasts.

Chlorophyll has cyclic tetrapyrrole porphyrin head and a long chain alcohol called as phytol. Chlorophyll 'a' has methyl group at carbon 3 while chlorophyll b has formyl or aldehyde group attached to this atom.

For chlorophyll formation in plants, the elements needed are:

- Iron and magnesium

Explanation:
- Iron is essential for the synthesis of chlorophyll molecules.
- Magnesium is a central component of the chlorophyll molecule, playing a crucial role in capturing sunlight for photosynthesis.
- Together, iron and magnesium work synergistically to ensure the proper formation and function of chlorophyll in plants, facilitating photosynthesis and plant growth.

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.