Test: Photosynthesis in Higher Plants - 1 - NEET MCQ

This is the correct option as statement 'b' is false. Biosynthetic phase reactions occur in stroma or matrix of chloroplasts and do not require light.

Line in NCERT: "The former set of reactions, since they are directly light driven are called light reactions (photochemical reactions). The latter are not directly light driven but are dependent on the products of light reactions (ATP and NADPH)."

ATP is synthesized by cells (in mitochondria and chloroplasts) is named phosphorylation.

Line in NCERT: "ATP is synthesised by cells (in mitochondria and chloroplasts) is named phosphorylation."

The Calvin cycle can be described under three stages: carboxylation, reduction and regeneration. Pathway operated in cyclic manner.

Line in NCERT: "For ease of understanding, the Calvin cycle can be described under three stages: carboxylation, reduction and regeneration."

• In the photorespiratory pathway, there is no synthesis of ATP or NADPH. Therefore, photorespiration is a wasteful process.
• In C₄ plants photorespiration does not occur. This is because they have a mechanism that increases the concentration of CO₂ at the enzyme site.

Line in NCERT: "In C₄ plants photorespiration does not occur."

Jan Ingenhousz's experiments with an aquatic plant showed that in bright sunlight, small bubbles containing oxygen were formed around the green parts of the plant, while in the dark, they did not. This demonstrated that sunlight is essential for the process by which plants release oxygen.

Line in NCERT: "Using a similar setup as the one used by Priestley, but by placing it once in the dark and once in the sunlight, Jan Ingenhousz showed that sunlight is essential to the plant process that somehow purifies the air fouled by burning candles or breathing animals."

The work of Melvin Calvin is the discovery that the first CO₂ fixation product was a 3-carbon organic acid. He also contributed to working out the complete biosynthetic pathway; hence it was called the Calvin cycle.

Line in NCERT: "the work of Melvin Calvin is exemplary. The use of radioactive 14C by him in algal photosynthesis studies led to the discovery that the first CO₂ fixation product was a 3-carbon organic acid. He also contributed to working out the complete biosynthetic pathway; hence it was called Calvin cycle after him."

In C₄ plants, Carbon dioxide is fixed in malic acid with the help of enzyme phosphoenel pyruvate (PEP). Malic acid is a four-carbon compound that later changes into oxaloacetic acid.

Dark reaction of Carbon dioxide fixation in CAM plants is called as ossification because it produces Malic acid. These plants open their stomata during night to prevent transpiration.

Line in NCERT: "the C acid OAA is formed in the mesophyll cells. It then forms other 4-carbon compounds like malic acid or aspartic acid in the mesophyll cells itself."

Pigments are substances that have an ability to absorb light, at specific wavelengths. The chlorophyll a pigment to absorb lights of different wavelengths.

Line in NCERT: "Pigments are substances that have an ability to absorb light, at specific wavelengths."

Electrons become excited and jump into an orbit farther from the atomic nucleus. These electrons are picked up by an electron acceptor which passes them to an electrons transport of cytochrome.

Line in NCERT: "These electrons are picked up by an electron acceptor which passes them to an electrons transport system consisting of cytochromes."

In the leaves of C4 plants such as maize, sorghum we can observe the Kranz anatomy.

Line in NCERT: "The particularly large cells around the vascular bundles of the C plants are called bundle sheath cells, and the leaves which have such anatomy are said to have ‘Kranz' anatomy."

When several factors affect any [bio] chemical process, Blackman’s (1905) Law of Limiting Factors comes into effect.

• According to this law, If a chemical process is affected by more than one factor, then its rate will be determined by the factor which is nearest to its minimal value: it is the factor that directly affects the process if its quantity is changed.

Splitting of water takes place near PS II, located in the inner side of the thylakoid membrane.

Splitting of water releases oxygen in the atmosphere and generates a proton gradient across the thylakoid membrane.

Line in NCERT: "Since splitting of the water molecule takes place on the inner side of the membrane, the protons or hydrogen ions that are produced by the splitting of water accumulate within the lumen of the thylakoids."

• Photosystems are the protein complexes involved in photosynthesis. Each photosystem is characterized by the wavelength of light to which its reaction centre is most reactive.
• Photosystem I, reaction centre pigment chlorophyll-a has absorption peak at 700nm.
• Thus Photosystem I is also known as P700​

So, the correct answer is 700 nm.

Line in NCERT: "In PS I the reaction centre chlorophyll a has an absorption peak at 700 nm, hence is called P700, while in PS II it has absorption maxima at 680 nm, and is called P680."

Light reactions or the ‘Photochemical’ phase include light absorption, water splitting, oxygen release, and the formation of high-energy chemical intermediates, ATP and NADPH. Several complexes are involved in the process.

Line in NCERT: "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 presence of the bundle sheath would help you identify the C4 plants. This pathway that has been named the Hatch and Slack Pathway, is again a cyclic process.

Line in NCERT: "The pathway that has been named the Hatch and Slack Pathway, is again a cyclic process."

• The pathway of photosynthesis was discovered by Melvin Calvin after experiment on single celled algae.
• The first stable product of C3 cycle is a three carbon compound called PGA (phosphoglyceric acid).

Line in NCERT: "The use of radioactive 14C by him in algal photosynthesis studies led to the discovery that the first CO2 fixation product was a 3-carbon organic acid."

• The other pathway, non-cyclic photophosphorylation, is a two-stage process involving two different chlorophyll photosystems. Being a light reaction, non-cyclic photophosphorylation occurs in the thylakoid membrane. First, a water molecule is broken down into 2H⁺ + 1/2 O₂ + 2e⁻ by a process called photolysis (or light-splitting).
• The two electrons from the water molecule are kept in photosystem II, while the 2H⁺and 1/2O₂ are left out for further use. Then a photon is absorbed by chlorophyll pigments surrounding the reaction core centre of the photosystem.
• The light excites the electrons of each pigment, causing a chain reaction that eventually transfers energy to the core of photosystem II, exciting the two electrons that are transferred to the primary electron acceptor, phaeophytin.

Line in NCERT: "The splitting of water molecules is associated with PS II; water is split into 2H+, [O] and electrons."

Photosynthesis occurs in two steps- light reaction and dark reaction. During light reaction ATP and NADPH molecules are formed and in dark reaction carbon dioxide is fixed.

Line in NCERT: "CO2 is combined with H2O to produce (CH₂O) or sugars."

Blackman formulated the principle of limiting factors. He studied the effect of CO₂ concentration, light intensity and temperature on the rate of photosynthesis.

Line in NCERT: "When several factors affect any [bio] chemical process, Blackman's (1905) Law of Limiting Factors comes into effect."