Question
Which of the following statement is incorrect? [NEET 2021]
(a) Both ATP and NADPH $+\mathrm{H}^{+}$are synthesised during non-cyclic photophosphorylation
(b) Stroma lamellae have PS-I only and lack NADP reductase
(c) Grana lamellae have both PS-I and PS-II
(d) Cyclic photophosphorylation involves both PS-I and PS-II
Answer/Explanation
Ans. (d)
Statement in option (d) is incorrect and can be corrected as
Only photosystem I is involved in cyclic photophosphorylation process. Cyclic photophosphorylation is a process in which an electron expelled by the excited photocentre is returned to it after passing through a series of electron carriers. The excited electron does not pass on to $\mathrm{NADP}^{+}$but is cycled back to the PS I complex through the electron transport chain.
Non-cyclic photophosphorylation involves both photosystems I and II. The electron follows a non-cyclic pathway in it. The representation of it is also called Zscheme.
Question
In light reaction, plastoquinone facilitates the transfer of electrons from [NEET (Sep.) 2020]
(a) Cyt-b $b_6$ complex to PS-1
(b) PS-I to NADP+
(c) PS-I to ATP synthase
(d) PS-II to Cyt- $b_6 f$ complex
Answer/Explanation
Ans. (d)
In light reaction, plastoquinone facilitates the transfer of electrons from PS II to cytochrome $b_{\mathrm{f}}$ f complex (non-cyclic photophosphorylation) process of light reaction starts with PS $11(680 \mathrm{~nm})$. When sunlight falls on the reaction center (chlorophyll, a) it abosrbs $680 \mathrm{~nm}$ wavelength of red light causing electrons to become excited and jump into an orbit farther from the atomic nucleus. These electrons are picked by the electron acceptor which passes them to an electron transport system consisting of cytochrome $b_8$ complex.
Question
Which of the following is not a product of light reaction of photosynthesis? [NEET 2018]
(a) NADPH
(b) $\mathrm{NADH}$
(c) ATP
(d) Oxygen
Answer/Explanation
Ans. (b)
During light reaction of photosynthesis NADPH, ATP and oxygen are formed. Oxygen is liberated by the photolysis of water.
The electrons released during photolysis of water are picked up by $\mathrm{P}_{60}$ photocentre of PS-II. On receiving light energy photocentre expels an electron which passes over a series of carriers. As a result assimilatory power, i.e. ATP and NADPH is produced. NADH is formed during respiration.
Question
In photosynthesis, the light-independent reactions take place at [CBSE AIPMT 2015]
(a) thylakoid lumen
(b) photosystem-I
(c) photosystem-II
(d) stromal matrix.
Answer/Explanation
Ans. (d)
The light-independent reactions(or dark reactions) take place in the stromal matrix of the chloroplasts.
In light independent reactions, carbon dioxide is reduced to glucose (carbohydrate) by the hydrogen in NADPH by using the chemical energy stored in ATP. This reaction takes place in the presence of a substance called RuDP.
Question
Anoxygenic photosynthesis is characteristic of [CBSE AIPMT 2014]
(a) Rhodospirillum
(b) Spirogyra
(c) Chlamydomonas
(d) Ulva
Answer/Explanation
Ans. (a)
Anoxygenic photosynthesis (in which $\mathrm{O}_2$ is not released) is seen in Rhodospirillum which is a purple non-sulphur bacteria. It helps an organism to trap light energy and store it as chemical energy. Other than this anoxygenic photosynthesis commonly occurs in purple non-sulphur bacteria, green sulphur/non-sulphur bacteria, and heliobacteria, etc.
Question
A process that makes important difference between $\mathrm{C}_3$ and $C_4$-plants is [CBSE AIPMT 2012]
(a)transpiration
(b) glycolysis
(c) photosynthesis
(d) photorespiration
Answer/Explanation
Ans. (d)
Photorespiration is a light dependent process which occurs in $\mathrm{C}_3$-plants. It is opposite to photosynthesis because during this process, uptake of $\mathrm{O}_2$ and release of $\mathrm{CO}_2$ take place. Due to the presence of Kranz anatomy, $\mathrm{C}_4$-plants do not show photorespiration.
Question
Oxygenic photosynthesis occurs in [CBSE AIPMT 2009]
(a) Chromatium
(b) Oscillatoria
(c) Rhodospirillum
(d) Chlorobium
Answer/Explanation
Ans. (b)
Oscillatoria is a photosynthetic cyanobacterium. In this cyanobacteria during photosynthesis water is electron donor and oxygen is a byproduct, i.e., oxygenic photosynthesis occurs. Rhodospirillum and Chlorobium are non-oxygenic photosynthetic, purple non-sulphur and green- sulphur bacteria. Chromatium is purple sulphur bacterium, also a non-oxygenic photosynthetic.
Question
Cyclic-photophosphorylation results in the formation of [CBSE AIPMT 2009]
(a) $\mathrm{NADPH}$
(b) ATP and NADPH
(c)ATP, NADPH and $\mathrm{O}_2$
(d)ATP
Answer/Explanation
Ans. (d)
Cyclic-photophosphorylation involves only pigment system-l and results in the formation of ATP only. When the photons activate PS-I, a pair of electrons are raised to a higher energy level. They are captured by primary acceptor which passes them on to ferredoxin, plastoquinone, cytochrome complex, plastocyanin and finally back to reaction centre of $\mathrm{PS}-1$, i.e., $\mathrm{P}_{700}$. At each step of electron transfer, the electrons lose potential energy. Their trip down hill is caused by the transport chain to pump $\mathrm{H}^{+}$across the thylakoid membrane. The proton gradient thus established is responsible for forming ATP ( 2 molecules). No reduction of NADP to NADPH $+\mathrm{H}^{+}$.
Question
The first acceptor of electrons from an excited chlorophyll molecule of photosystem-II is [CBSE AIPMT 2007, 08]
(a) cytochrome
(b) iron-sulphur protein
(c) ferredoxin
(d) quinone
Answer/Explanation
Ans. (d)
Plastoquinone is the first acceptor of electrons from an excited chlorophyll molecule of photosystem-1I.
Question
In photosystem-I the first electron acceptor is [CBSE AIPMT 2006]
(a) cytochrome
(b) plastocyanin
(c) an iron-sulphur protein
(d) ferredoxin
Answer/Explanation
Ans. (c)
In photosystem-1, the primary electron acceptor is probably a Fe-S protein.
The reduced primary acceptor transfers the electrons to secondary electron acceptor (most probably $\mathrm{P}_{430}$ ). The sequence of electron transfer is as follows : The reduced $P_{430}$ passes its electrons to ferredoxin (Fd) present at outer surface of thylakoid membrane.
Question
Which of the following absorb light energy for photosynthesis? [CBSE AIPMT 2002]
(a) Chlorophyll
(b) Water molecule
(c) $\mathrm{O}_2$
(d) RuBP
Answer/Explanation
Ans. (a)
Chlorophyll molecule absorbs light for photosynthesis. $\mathrm{H}_2 \mathrm{O}$ molecules provide $\mathrm{H}^{+}$ions and electrons during photosynthesis. $\mathrm{O}_2$ is liberated during photosynthesis. RuBP(Ribulose 1, 5-bisphosphate) reacts with $\mathrm{CO}_2$ during dark reaction of photosynthesis. This process takes place in the presence of enzyme RuBisC0.
Question
Which pigment system is inactivated in red drop? [CBSE AIPMT 2001]
(a) PS-l and PS-II
(b) PS-1
(c) PS-II
(d) None of these
Answer/Explanation
Ans. (c)
The fall in photosynthetic yield beyond red region of spectrum $(680 \mathrm{~nm})$ is called red drop. Reaction centre of PS-II is $\mathrm{P}_{600}$ while that of $P S-1$ is $\mathrm{P}_{70}$. So in the red drop reaction PS-ll is inactivated.
Question
Photochemical reactions in the chloroplast are directly involved in [CBSE AIPMT 2000]
(a) formation of phosphoglyceric acid
(b) fixation of carbon dioxide
(c) synthesis of glucose and starch
(d) photolysis of water and phosphorylation of ADP to ATP
Answer/Explanation
Ans. (d)
$\mathrm{CO}_2$ is fixed in the stroma of the chloroplast leading to the synthesis of PGA from which glyceraldehyde phosphate is formed. From glyceraldehyde phosphate, sugar and starch are formed. All these do not require light. However, photolysis of water and phosphorylation of ADP to ATP requires light energy.
Question
Protochlorophyll differs from chlorophyll in lacking [CBSE AIPMT 1998]
(a) 2 hydrogen atoms in one of its pyrrole rings
(b) 2 hydrogen atoms in two of its pyrrole rings
(c) 4 hydrogen atoms in one of its pyrrole rings
(d) 4 hydrogen atoms in two of its pyrrole rings
Answer/Explanation
Ans. (a)
Protochlorophyll differs from chlorophyll in lacking 2 hydrogen atoms in one of its pyrrole rings.
Question
$ \mathrm{NADPH}$ is generated through [CBSE AIPMT 1997]
(a) photosystem-1
(b) photosystem-II
(c) anaerobic respiration
(d) glycolysis
Answer/Explanation
Ans. (b)
NADPH is generated through photosystem-II. In non-cyclic photophosphorylation (which involves both PS-I and II) protons released from photolysis and electrons emitted from $\mathrm{P}_{\mathrm{To}}$ are ultimately passed on to $\mathrm{NACP}^{+}$ resulting in the formation of NADPH. In cyclic photophosphorylation (which involves only PS-1) electrons flow in a cyclic manner but there is no net formation of $\mathrm{NADPH}$ and $\mathrm{O}_2$.
Question
Which one occurs both during cyclic and non-cyclic modes of photophosphorylation? [CBSE AIPMT 1994]
(a) Involvement of both PS-l and PS-II
(b) Formation of ATP
(c) Release of $\mathrm{O}_2$
(d) Formation of NADPH
Answer/Explanation
Ans. (b)
Cyclic photophosphorylation is that type of light energised ATP synthesis in which electron expelled by excited photocentre does not return to them. It involves two Photochemical Systems (PS-l and PS-II) and produces assimilatory power (ATP and NADPH). In both, cyclic and non-cyclic photophosphorylation, formation of ATP takes place.
Question
Formation of ATP in photosynthesis and respiration is an oxidation process which utilises the energy from [CBSE AIPMT 1992]
(a) cytochromes
(b) ferredoxin
(c) electrons
(d) carbon dioxide
Answer/Explanation
Ans. (c)
Cytochromes(Keilin; 1925) are the electron transport intermediates containing heme (or related prosthetic groups) in which the iron undergoes valency changes during electron transfer and produces energy (ATP) in both photosynthesis and respiration.
Question
Photosystem-Il occurs in [CBSE AIPMT 1992]
(a) stroma
(b) cytochrome
(c) grana
(d) mitochondrial surface
Answer/Explanation
Ans. (c)
PS-II is present in appressed part of granal thylakoids. PS-l is present in stroma thylakoids and non-appressed parts of granal thylakoids.
Question
Ferredoxin is a constituent of [CBSE AIPMT 1991]
(a) PS-I
(b) PS-11
(c) Hill reaction
(d) $\mathrm{P}_{690}$
Answer/Explanation
Ans. (a)
Ferredoxin $(\mathrm{Fd})$ is a soluble protein which acts as electron carrier and forms a constituent of PS-I. Ferredoxin passes electrons to reductase complex which helps in reducing NADP ${ }^{+}$to NADPH (a strong reducing agent).
Question
$ \mathrm{NADP}^{+}$is reduced to NADPH in [CBSE AIPMT 1988]
(a) PS-I
(b) PS-II
(c) Calvin cycle
(d) Non-cyclic photophosphorylation
Answer/Explanation
Ans. (d)
In photosynthesis during non-cyclic photophosphorylation involving both PS-I and PS-II, electrons released during photolysis of water are transfered to PS-II and then PS-I via a series of electron carriers. $P_{200}$ of PS-1 releases electron after absorbing light energy. This electron passes through chlorophyll X, Fe-S, ferredoxin and finally to $\mathrm{NADP}^{+}$. $\mathrm{NADP}^{+}$combines with $\mathrm{H}^{+}$(released during photolysis) with the help of NADP reductase to form NADPH.