Photosynthesis MCQs: Process & Sample Questions

Answer: (d) A photon of light excites an electron of chlorophyll

Explanation: Photosynthesis is synthesis of organic compounds from inorganic raw materials with the help of enzymes and solar energy trapped through pigments like chlorophyll. Chlorophyll is also known as the primary photosynthetic pigment that is responsible for the primary reaction of photosynthesis or conversion of light into electrochemical energy. The function of charge separation is performed by some special chlorophyll molecules called reaction centers (P₇₀₀, P₆₈₀). Other photosynthetic pigments like chlorophyll b, c,d and e, carotenoids and phycobilins are termed as accessory pigments. The accessory pigments absorb light energy of various wavelengths, get excited and handover the energy in the form of an electron to chlorophyll a molecule through electron spin resonance.

Answer: B) Absorption of Light , oxygen release and formation of high-energy chemical compounds. 

Explanation: The process of photosynthesis is basically of two phases light-dependent and light-independent. The light dependent phase is also called the photochemical phase, which involves absorption of light, photolysis, evolution of oxygen and processing of assimilatory power like ATP and NADPH. The light-dependent reaction eventuates the existence of light inside the thylakoid of the chloroplast. It takes place in the 400-700 nm wavelength of visible light. It is highest in blue-red light and lowest in green light.

Answer. B) Reaction centres are different

Explanation: Photosystem I (PS I) and Photosystem II (PS II) are the two types of photosynthetic units. Photosynthetic units are the collection of pigment molecules which are involved in the transformation of light energy into chemical energy. Each unit comprises a reaction centre of a definite chlorophyll, a molecule that can intake light energy of longer and different wavelengths. These reaction centre are also called as photo centres. An electron is released by these centres upon absorption of energy. The reaction centre of PS I where chlorophyll a is present, has an absorption limit at 700 nm, hence is called P₇₀₀, while in PS II, reaction centre has an absorption limit at 680 nm and is called P_680.

Answer: d) H₂O

Explanation: Non-cyclic photophosphorylation, is a two-stage process containing two different chlorophyll photosystems. It is a form of light reaction that happens in the thylakoid membrane. First of all a water molecule is broken down into 2H+ + ½ O₂ + 2e− with the help of a procedure called photolysis (light-splitting). Thereafter the water molecule releases two electrons which are maintained in photosystem II, while the 2H+ and ½ O₂ are liberated out for other use. 

Then the chlorophyll pigments surrounding the reaction core centre of the photosystem absorb a photon. The light activates electrons of each pigment, resulting in a chain reaction that finally transmits energy to the centre of photosystem II, exciting the two electrons which are then received by the primary electron acceptor, pheophytin. The shortage of electrons is again fulfilled by taking electrons from another water molecule i.e H₂O.

Answer: (a) C₄ plants

Explanation: Kranz Anatomy is found in C₄ plants which have basically two features- 

1) Green bundle sheath cells(BS cells) present around the vascular bundles.

2) Dimorphic Chloroplasts are there in leaf cells. Chloroplast of B.S cells also known as Kranz cells are larger in size and are present without grana. Mesophyll chloroplast are small with grana

Answer: (a) PGA

Explanation: The Calvin Cycle which is also known as C₃ cycle is a type of dark phase or carbon Assimilation. In this stage, CO₂ is assimilated with the help of assimilatory power to produce organic compounds The C₃ cycle is studied in three stages i.e. Carboxylation, Reduction and Regeneration. In the carboxylation phase, in the presence of Mg- Activated rubisco, Co₂ combines with ribulose biphosphate(acceptor molecule) to form first a transitory 2-carboxy 3-keto 1,biphosphoribotal and then two molecules of 3- phosphoglyceric acid or PGA which also happens to be the first stable product of dark reaction in C₃ plants.

Answer: (c) Peroxisomes to mitochondria 

Explanation: There are many steps involved in the biochemical pathway of photorespiration where a constituent named glycolic acid synthesizes in chloroplasts as an early product of photosynthesis which is later transported to the perixomes. The glycolic acid reacts with O2 and oxidises to glyoxylic acid and hydrogen peroxide with the help of enzyme glycolic acid oxidase to form Glyoxylic acid. The glyoxylic acid is then converted to an amino acid glycine by transamination reaction catalyzed by enzyme glutamate glyoxylate transaminase to form glycine. The glycine is transported out of peroxisomes and into mitochondria where two molecules of glycine interact to form one molecule each of serine, CO₂ and NH^3-.

Answer: (b) stroma

Explanation: Dark reaction which is also known as biosynthetic phase occurs in the stroma of chloroplasts where the products of light reaction are used to assimilate carbon from CO2 to carbohydrate.

Answer: (d) photosystem 1

Explanation: Photosystem 1 or PS-l contains a single molecule of chlorophyll a700 or P700. Besides P₇₀₀, the PS-l consists of 200-400 Chlorophylls, 50 carotenoids, and two iron containing proteins similar to ferredoxin called Fe~ S protein. It also consists ferrodoxin and cytochrome f and cytochrome b₅₆₃.

Answer: b) Proton gradient

Explanation: According to the Chemiosmotic hypothesis, the ATP synthesis is linked to development of a Proton gradient across the thylakoid membrane in cytoplasts.