Pigments involved in photo synthesis Questions in English

(A) Chlorophyll '$a$' is the primary photosynthetic pigment in plants and algae,which acts as the reaction center.
Accessory pigments include chlorophyll '$b$',chlorophyll '$c$',chlorophyll '$d$',chlorophyll '$e$',carotenoids (like xanthophylls),and phycobilins (like phycocyanin).
These pigments absorb light energy and transfer it to chlorophyll '$a$'.
Therefore,chlorophyll '$a$' is a primary pigment,not an accessory pigment.

(B) Inside the chloroplast,there are flattened,membrane-bound,disc-like sacs called thylakoids.
These thylakoids are stacked like piles of coins to form structures known as grana.
The thylakoid membrane contains chlorophyll pigments,which are essential for the light-dependent reactions of photosynthesis.

(D) Quantasomes are the structural units of the thylakoid membrane in chloroplasts, which are involved in the light-dependent reactions of photosynthesis. They were first identified and named by $R.B. \text{Park}$ and $J. \text{Biggins}$ in $1964$ using electron microscopy. These structures contain chlorophyll and other pigments necessary for capturing light energy.

(C) Chlorophyll $a$ and $b$ are the primary pigments involved in photosynthesis.
Both molecules possess a porphyrin ring with a central $Mg^{2+}$ ion.
The fundamental chemical difference lies in the substituent group attached to the third carbon of the second pyrrole ring.
In chlorophyll $a$,this position is occupied by a methyl group $(-CH_3)$,whereas in chlorophyll $b$,it is replaced by an aldehyde group $(-CHO)$.

(D) Quantasomes are the structural units of the thylakoid membrane in chloroplasts,which are involved in the light-dependent reactions of photosynthesis.
Each quantasome is estimated to contain approximately $230$ chlorophyll molecules,along with other pigments and proteins,which function as a photosynthetic unit.

(A) Fret channels,also known as stroma lamellae or fret membranes,are the membranous channels that connect the thylakoids of different grana within a chloroplast.
These channels facilitate the connection between two grana,allowing for the transport of materials and maintaining the structural integrity of the thylakoid system.
Therefore,they are associated with connecting two grana of a chloroplast.

(D) The correct answer is $D$.
Anthocyanin is a water-soluble vacuolar pigment that is found in the cell sap of vacuoles,not in the chloroplasts.
Chloroplasts contain photosynthetic pigments such as Chlorophyll $a$,Chlorophyll $b$,Carotene,and Xanthophyll.

(A) The chloroplast contains a system of thylakoids,which are flattened,sac-like structures arranged in parallel stacks called grana.
This parallel layering of membranes increases the surface area significantly.
This increased surface area allows for the maximum absorption of light energy by chlorophyll pigments embedded in the thylakoid membranes.
Furthermore,it provides a large surface area for the attachment of various enzymes and electron carriers involved in the light-dependent reactions of photosynthesis,ensuring maximum enzymatic efficiency.

(A) Inside the chloroplast,thylakoids are flattened,sac-like structures that are stacked together like a pile of coins.
This stack of thylakoids is known as a $Granum$ (plural: $Grana$).
$Stroma$ is the fluid-filled space surrounding the thylakoids.
$ER$ stands for Endoplasmic Reticulum,an organelle involved in protein and lipid synthesis.
$F_1$ particles are associated with the inner mitochondrial membrane and are involved in $ATP$ synthesis.

(A) Chlorophyll $a$ is the primary photosynthetic pigment found in plants. Its molecular formula is $C_{55}H_{72}O_5N_4Mg$.
It consists of a porphyrin ring with a central magnesium atom and a long phytol tail.

(A) Chloroplasts are double-membrane organelles found in plant cells.
Inside the chloroplast,there is a system of flattened,sac-like structures called thylakoids.
These thylakoids are arranged in stacks known as grana.
The membranes of the thylakoids contain chlorophyll pigments,which are essential for capturing light energy during the process of photosynthesis.
Therefore,chlorophyll is located in the thylakoids.

(C) Chlorophyll is a magnesium-porphyrin complex. The central atom in the porphyrin ring of the chlorophyll molecule is magnesium $(Mg)$. When chlorophyll is burnt,the organic components (carbon,hydrogen,oxygen,and nitrogen) are oxidized and released as gases,leaving behind the non-volatile mineral element,which is magnesium $(Mg)$.

(D) The term 'Thylakoid' was coined by $Menke$ in $1961$.
Thylakoids are flattened,sac-like membranous structures found within the chloroplasts of plants and cyanobacteria.
They are the site of the light-dependent reactions of photosynthesis,containing chlorophyll and other pigments.

(B) Paper chromatography is a technique used for the separation of pigments based on their differential solubility in a solvent. As the solvent moves up the filter paper,the pigments move at different rates depending on their solubility and affinity for the paper,allowing for the effective separation of chlorophylls and carotenoids.

(C) Thylakoids are flattened,disc-like sacs found within the chloroplasts.
These thylakoids are arranged in stacks,similar to a stack of coins.
One such stack of thylakoids is referred to as a granum (plural: grana).

(B) The visible spectrum of light ranges from approximately $380 \ nm$ to $750 \ nm$ $(380 - 750 \ m\mu)$.
Green light typically falls within the range of $500 \ m\mu$ to $570 \ m\mu$.
Therefore,the option $500 - 550 \ m\mu$ represents the wavelength of green light.

(A) In the chloroplasts of higher plants,the thylakoids are arranged in stacks like a pile of coins. Each of these stacks is called a granum (plural: grana). These structures are the sites of the light-dependent reactions of photosynthesis.

(D) To isolate intact chloroplasts from green leaves,an isotonic or hypertonic solution is required to maintain the structural integrity of the organelle.
Acetone,ethanol,and alcohol are organic solvents that dissolve the lipid bilayer of the chloroplast membrane,causing the organelle to rupture.
$A$ sugar solution (such as sucrose) provides an osmotic environment that prevents the chloroplast from bursting,allowing for the isolation of intact organelles.

(A) Leaves appear green because chlorophyll pigments do not absorb green light efficiently.
Instead,the green light is reflected and transmitted by the leaves,which is then perceived by our eyes.

(B) Park and Biggins $(1964)$ introduced the term 'quantasome' to describe the structural units of the thylakoid membrane involved in photosynthesis. Each quantasome is estimated to contain approximately $230$ chlorophyll molecules along with other accessory pigments and electron transport components.

(D) . Chlorophyll is essential for photosynthesis.
Photosynthesis occurs primarily in the green parts of the plant,specifically within the chloroplasts of cells containing chlorophyll.
Chlorophyll $a$ acts as the primary pigment and the reaction center for the light-dependent reactions of photosynthesis.
Therefore,only cells that contain chlorophyll are capable of performing photosynthesis.

(C) The rate of photosynthesis is dependent on the wavelength of light absorbed by photosynthetic pigments like chlorophyll $a$ and $b$.
Chlorophyll pigments absorb light most efficiently in the blue and red regions of the visible spectrum.
Green light is largely reflected or transmitted by the leaves,which is why plants appear green to our eyes.
Therefore,green light is the least efficient radiation for photosynthesis in most plants.
Note: While red algae can utilize green light efficiently due to accessory pigments,in the context of general plant physiology,green light is considered the least efficient.

(D) The chlorophyll molecule consists of a porphyrin head and a phytol tail.
The porphyrin head is a cyclic tetrapyrrole structure,meaning it is composed of four pyrrole rings arranged in a square planar configuration around a central magnesium $(Mg^{2+})$ ion.
Therefore,the correct answer is $(d)$ Tetrapyrrole.

(A) The photosynthetic pigments (such as chlorophyll $a$,chlorophyll $b$,xanthophylls,and carotenoids) are fat-soluble molecules.
These pigments are embedded within the lipid bilayer of the thylakoid membranes in the chloroplast.
The thylakoid membranes are the sites where the light-dependent reactions of photosynthesis occur.

(D) . Xanthophylls are yellow-coloured carotenoid pigments,also known as xanthols or carotenols. While carotenes are generally yellow to orange,xanthophylls are specifically characterized by their distinct yellow colour due to the presence of oxygen atoms in their molecular structure.

(A) Chlorophyll consists of two main parts: a head and a tail.
$1$. The head is a porphyrin ring,which is polar and hydrophilic.
$2$. The tail is a long hydrocarbon chain known as the phytol tail,which is non-polar and hydrophobic.
Therefore,the phytol tail is the non-polar part of the chlorophyll molecule.

(C) The visible spectrum ranges from approximately $390 \, nm$ to $760 \, nm$.
Specifically,the red part of the visible spectrum corresponds to wavelengths between $650 \, nm$ and $760 \, nm$.
Among the given options,$680 \, nm$ falls within this range.
Therefore,the correct option is $C$.

(B) The correct answer is $B$.
$\beta$-carotene is the primary pigment responsible for the orange-yellow color of carrot roots.
Upon hydrolysis,$\beta$-carotene yields vitamin $A$,which is why carotenes are often referred to as provitamin $A$.

(C) Quantasomes are the structural units of the thylakoid membrane in chloroplasts,which are responsible for the light-dependent reactions of photosynthesis.
These units contain both Pigment system-$I$ $(PS-I)$ and Pigment system-$II$ $(PS-II)$ along with their associated electron transport components.
Therefore,quantasomes are present in both pigment systems.

(D) In the process of photosynthesis,the photolysis of water (splitting of water molecules) occurs at the oxygen-evolving complex associated with photosystem-$II$ $(PS-II)$.
In cyanobacteria (blue-green algae),the pigment responsible for light harvesting and associated with the $PS-II$ complex is Phycocyanin.
Phycocyanin is a phycobiliprotein that captures light energy and transfers it to the reaction center,playing a crucial role in the light-dependent reactions of these organisms.

(D) In Photosystem-$I$ $(PS-I)$,the reaction center is a special form of chlorophyll-$a$ known as $P-700$.
When this reaction center absorbs light energy,it becomes excited and releases an electron,which is then accepted by an electron acceptor.

(A) The chlorophyll molecule possesses a tadpole-like structure consisting of a porphyrin head and a phytol tail.
The porphyrin head is a cyclic tetrapyrrole structure,which is composed of four pyrrole rings linked by methine $(-CH=)$ groups.
This porphyrin ring system is central to the light-absorbing properties of chlorophyll.

(C) The colors of leaves are modified in certain plants due to the presence of a purple pigment called anthocyanins.
Anthocyanins are water-soluble pigments,which means they are found dissolved in the cell sap (the aqueous solution within the vacuoles of plant cells).

(C) Chlorophyll is the primary photosynthetic pigment that captures light energy.
This absorbed light energy is used to excite electrons,which initiates the process of photosynthesis.
The energy is further utilized for the photolysis (photochemical decomposition) of water molecules into protons,electrons,and oxygen $(2H_2O \rightarrow 4H^+ + 4e^- + O_2)$.
Therefore,chlorophyll plays a dual role in light absorption and the subsequent splitting of water.

(C) Chlorophyll is the primary photosynthetic pigment responsible for trapping light energy.
In the chloroplast,chlorophyll molecules are embedded within the thylakoid membranes.
The thylakoids are stacked together to form structures known as grana.
Therefore,chlorophyll is located in the grana of the chloroplast,where the light-dependent reactions of photosynthesis occur.

(B) The core metal of chlorophyll is $Mg$ (Magnesium).
Chlorophyll is a porphyrin derivative with a central magnesium atom coordinated to four nitrogen atoms of the porphyrin ring.
This central $Mg^{2+}$ ion is essential for the light-harvesting function of chlorophyll molecules during photosynthesis.
If the central $Mg$ atom is replaced by $Fe$ (Iron),the molecule is converted into a different pigment,such as those found in cytochromes,which are involved in electron transport rather than light absorption.

(D) The chlorophyll molecule consists of a porphyrin head and a phytol tail.
The porphyrin head is a tetrapyrrole structure with a magnesium atom at the center.
The approximate dimension of this porphyrin head is $15 \times 15 \, \mathring{A}$.
The phytol tail is a long hydrocarbon chain approximately $20 \, \mathring{A}$ in length.
Therefore,the correct option is $D$.

(A) When a chlorophyll molecule absorbs a photon,it enters an excited state. This excited state is highly unstable and extremely short-lived. The lifetime of an excited chlorophyll molecule is typically in the range of $10^{-9}$ to $10^{-7}$ seconds,which is significantly less than $0.01$ seconds. Therefore,the energy must be transferred rapidly to the reaction center to initiate photosynthesis.

(A) Chlorophyll is a lipid-soluble pigment.
It is insoluble in water but soluble in organic solvents such as alcohol,acetone,and ether.
Therefore,the correct option is $A$.

(A) Phycobilins are water-soluble accessory pigments found in cyanobacteria and red algae. Their primary role in photosynthesis is to absorb light energy at wavelengths that chlorophyll $a$ cannot efficiently capture and then transfer this energy to chlorophyll $a$ molecules in the reaction center. This process expands the range of light wavelengths that can be utilized for photosynthesis.

(B) Chlorophyll $a$ and chlorophyll $b$ are the two primary pigments involved in photosynthesis.
Both molecules share a similar porphyrin ring structure with a central magnesium atom.
The key chemical difference lies in the substituent group attached to the $3^{rd}$ carbon of the porphyrin ring.
In chlorophyll $a$,this position is occupied by a methyl group $(-CH_3)$.
In chlorophyll $b$,this position is occupied by an aldehyde group $(-CHO)$.

(C) Chlorophyll is a complex organic molecule that contains a central magnesium atom $(Mg^{2+})$ coordinated within a porphyrin ring structure.
When chlorophyll is burnt,the organic components (carbon,hydrogen,oxygen,nitrogen) are oxidized and released as gases like $CO_2$,$H_2O$,and $NO_x$.
The magnesium atom,being a metal,does not volatilize and remains in the ash as magnesium oxide $(MgO)$ or other magnesium salts.
Therefore,magnesium is the element that remains.

(C) Chloroplasts contain pigments like chlorophyll $a$,chlorophyll $b$,and carotenoids that are responsible for absorbing light energy.
These pigments primarily absorb light in the visible spectrum,which ranges from approximately $400 \, nm$ to $700 \, nm$.
This range is known as Photosynthetically Active Radiation $(PAR)$.
Light wavelengths shorter than $400 \, nm$ (ultraviolet) or longer than $700 \, nm$ (infrared) are generally not effective for the process of photosynthesis.

(C) The reaction center of Photosystem-$I$ $(PS-I)$ is $P_{700}$,which is a special form of chlorophyll $a$ that absorbs light at $700 \ nm$.
Photosystem-$I$ also contains accessory pigments including chlorophyll $a$,chlorophyll $b$,and carotenoids.
Among the given options,option $(C)$ correctly identifies the core components associated with $PS-I$ in standard textbook contexts,where $P_{700}$ is the reaction center and chlorophyll $a$ and $b$ are the primary light-harvesting pigments.

(C) quantasome is a structural unit of the thylakoid membrane involved in photosynthesis. It consists of a specific arrangement of photosynthetic pigments and electron carriers. The quantitative composition of pigments in a quantasome follows the order: Chlorophyll $a$ > Chlorophyll $b$ > Carotenoids > Quinones. Therefore,option $C$ is the correct representation of this composition.

(A) Chlorophyll is the primary photosynthetic pigment found in the chloroplasts of plants.
During the process of photosynthesis,chlorophyll molecules absorb light energy (photons).
This absorbed light energy is then used to drive the synthesis of energy-rich molecules like $ATP$ and $NADPH$.
Thus,chlorophyll effectively converts light energy into chemical energy,which is stored in the bonds of organic compounds.

(C) Photosynthetic pigments in higher plants are primarily chlorophylls and carotenoids.
Specifically,chlorophyll $a$ is the primary pigment,while chlorophyll $b$ and carotenoids (which include carotenes and xanthophylls) act as accessory pigments.
These pigments work together to absorb light energy and transfer it to the reaction center.
Therefore,the correct combination is Chl $a$ + Chl $b$ + carotenoid.

(C) The absorption spectrum of chlorophyll $a$ and chlorophyll $b$ indicates that these pigments mainly absorb light in the blue and red wavelengths of the visible spectrum.
Consequently,the action spectrum of photosynthesis shows that the maximum rate of photosynthesis occurs in the blue and red regions of the light spectrum.

(C) Chlorophyll $a$ is the primary photosynthetic pigment.
According to the absorption spectrum of chlorophyll $a$,it shows maximum absorption in the blue and red regions of the visible light spectrum.
The peak in the blue region is approximately at $430 \ nm$,and the peak in the red region is approximately at $660 \ nm$.
Therefore,the correct option is $C$.