Pigments involved in photo synthesis Questions in English

(A) Carotenoids are accessory pigments in higher plants. They primarily absorb light in the blue and violet regions of the visible spectrum. By absorbing these wavelengths,they protect the chlorophyll molecules from photo-oxidation and transfer the absorbed energy to chlorophyll-$a$ for photosynthesis.

(A) Chlorophyll is the primary photosynthetic pigment responsible for capturing light energy.
In the chloroplast,chlorophyll molecules are embedded within the thylakoid membranes.
These thylakoid membranes are stacked to form structures known as $Grana$.
Therefore,chlorophyll is specifically located in the $Grana$ of the chloroplast,where the light-dependent reactions of photosynthesis occur.

(C) The Assertion is correct because $Rhoeo$ leaves possess anthocyanin pigments in their epidermal cells,which provide a purple or reddish coloration to the leaves.
However,the Reason is incorrect. Anthocyanins are water-soluble vacuolar pigments that provide red,purple,or blue colors to plant parts like petals,fruits,and leaves. They are not involved in photosynthesis and do not act as accessory photosynthetic pigments. Accessory photosynthetic pigments include chlorophyll $b$,xanthophylls,and carotenoids,which capture light energy and transfer it to chlorophyll $a$.

(D) Chlorophyll-$a$ is the primary photosynthetic pigment and acts as the reaction center in both Photosystem-$I$ and Photosystem-$II$. It is the only pigment capable of converting light energy into chemical energy by emitting electrons during the light reaction.
Chlorophyll-$b$,carotenoids,and xanthophylls are accessory pigments. They absorb light energy at different wavelengths and transfer it to Chlorophyll-$a$,thereby increasing the efficiency of photosynthesis. Additionally,they protect the Chlorophyll-$a$ molecule from photo-oxidation.
If a plant lacks Chlorophyll-$a$,it cannot perform the primary photochemical reaction. Therefore,such a plant would not be able to carry out photosynthesis,even if it has a high concentration of Chlorophyll-$b$.

(N/A) Leaves require light to perform photosynthesis. When a leaf is kept in the dark,the production of chlorophyll,which is essential for photosynthesis,stops. Existing chlorophyll molecules gradually break down,causing the leaf to change from a dark green to a pale green shade.
As the chlorophyll content decreases,other pigments like xanthophylls and carotenoids,which were previously masked,become visible. This causes the leaf to turn yellow.
These pigments (xanthophylls and carotenoids) are more stable than chlorophyll because their production is not dependent on light. They are always present in the plant tissues.

(C) $\Rightarrow$ The pigments of plant leaves can be separated and studied using paper chromatography.
$\Rightarrow$ Chromatographic separation of leaf pigments reveals that the color observed in leaves is not due to a single pigment,but rather a combination of four distinct pigments:
$(1)$ Chlorophyll $a$ (bright or blue-green in the chromatogram),
$(2)$ Chlorophyll $b$ (yellow-green),
$(3)$ Xanthophylls (yellow),
$(4)$ Carotenoids (yellow to yellow-orange).
Therefore,there are four major pigments involved in photosynthesis.

(N/A) $ \Rightarrow $ Pigments are substances that have the ability to absorb light at specific wavelengths.
$ \Rightarrow $ The most abundant plant pigment in the world is chlorophyll-$a$.
$ \Rightarrow $ We are familiar with the wavelength of the visible spectrum of light as well as the $VIBGYOR$: $V=$ Violet,$I=$ Indigo,$B=$ Blue,$G=$ Green,$Y=$ Yellow,$O=$ Orange,$R=$ Red.
$ \Rightarrow $ Looking at figure $(a)$,we can determine the wavelengths at which chlorophyll-$a$ absorbs the most light.
$ \Rightarrow $ Figure $(b)$ shows the wavelengths at which maximum photosynthesis occurs in a plant. We can see that the wavelengths at which there is maximum absorption by chlorophyll-$a$ are in the blue and red regions.
$ \Rightarrow $ This shows a higher rate of photosynthesis. Hence,we can conclude that chlorophyll-$a$ is the chief pigment associated with photosynthesis.
$ \Rightarrow $ By observing figure $(c)$,we can say that there is a complete one-to-one overlap between the absorption spectrum of chlorophyll-$a$ and the action spectrum of photosynthesis.
$ \Rightarrow $ These graphs together show that most of the photosynthesis takes place at these wavelengths of the visible spectrum.
$ \Rightarrow $ Though chlorophyll-$a$ is the major pigment responsible for trapping light,other thylakoid pigments like chlorophyll-$b$,xanthophylls,and carotenoids,which are called accessory pigments,also absorb light and transfer the energy to chlorophyll-$a$.
$ \Rightarrow $ Indeed,they not only enable a wider range of wavelengths of incoming light to be utilized for photosynthesis but also protect chlorophyll-$a$ from photo-oxidation.

(N/A) Light harvesting complexes $(LHC)$ are clusters of pigment molecules that function to capture light energy for photosynthesis.
$1$. Composition: Each $LHC$ consists of hundreds of pigment molecules bound to proteins.
$2$. Pigments: These include chlorophyll $a$,chlorophyll $b$,carotenoids,and xanthophylls.
$3$. Function: These pigments absorb light of different wavelengths,making photosynthesis more efficient by capturing a broader spectrum of light.
$4$. Energy Transfer: The absorbed energy is passed from one pigment molecule to another through resonance energy transfer until it reaches the reaction center (chlorophyll $a$ molecule).
$5$. Role: LHCs ensure that the reaction center is constantly supplied with energy,even when light intensity is low.

- Each photosystem consists of all the pigments (except one molecule of chlorophyll-$a$) forming a light-harvesting system,also called antennae.
- These pigments help to make photosynthesis more efficient by absorbing different wavelengths of light.
- The single chlorophyll-$a$ molecule forms the reaction centre.
- In $PS-I$,the reaction centre of chlorophyll-$a$ has an absorption peak at $700 \ nm$,hence it is called $P_{700}$.
- In $PS-II$,it has an absorption maximum at $680 \ nm$,and is called $P_{680}$.

(A) Photosynthetic pigments are substances that absorb light energy for photosynthesis. They are primarily categorized into three main groups:
$1$. Chlorophylls: These are the primary pigments,including $Chlorophyll \ a$ (the reaction center) and $Chlorophyll \ b$ (an accessory pigment).
$2$. Carotenoids: These include carotenes and xanthophylls,which act as accessory pigments by absorbing light and protecting chlorophyll from photo-oxidation.
$3$. Phycobilins: These are water-soluble pigments found in cyanobacteria and red algae (e.g.,phycocyanin and phycoerythrin).

(A) $NADP$ stands for Nicotinamide Adenine Dinucleotide Phosphate.
It is a coenzyme that acts as an electron carrier in various metabolic reactions,particularly in photosynthesis.

(N/A) $(1)$ $LHC$ stands for Light Harvesting Complex. It consists of hundreds of pigment molecules bound to proteins.
$(2)$ $PS$ stands for Photosystem. It is a functional unit of photosynthesis,consisting of a reaction center surrounded by light-harvesting complexes.

(N/A) Chlorophyll $b$,xanthophylls,and carotenoids are accessory pigments.
They are also photosynthetic pigments.
They are not directly associated with the excitation of electrons in the reaction center.
However,they absorb solar energy at different wavelengths and transfer this energy towards chlorophyll $a$.
Chlorophyll $a$ absorbs the maximum radiation in the blue and red regions of the spectrum,making it the primary pigment,whereas chlorophyll $b$,xanthophylls,and carotenoids act as accessory pigments by broadening the spectrum of light absorption.

(A) The primary property of the pigment (chlorophyll) responsible for initiating photosynthesis is its ability to absorb light energy and become excited,leading to the emission of high-energy electrons $(e^-)$.
$1$. When chlorophyll molecules absorb light,they reach an excited state and lose electrons. These electrons are then transferred to an electron transport system.
$2$. The electron deficiency in chlorophyll is compensated by electrons derived from the photolysis (splitting) of water molecules.
The rate of photosynthesis is higher in the red and blue regions of the light spectrum because:
$1$. Chlorophyll pigments have peak absorption spectra in the blue ($430-450$ $nm$) and red ($640-680$ $nm$) wavelengths.
$2$. These wavelengths fall within the Photosynthetically Active Radiation $(PAR)$ range ($400-700$ $nm$),providing optimal energy to excite the electrons required for the light-dependent reactions.

(N/A) $1$. The overlap between the action spectrum and the absorption spectrum of chlorophyll $a$ indicates that chlorophyll $a$ is the primary pigment responsible for photosynthesis.
$2$. The absorption spectrum shows the light wavelengths absorbed by pigments like chlorophyll $a$,chlorophyll $b$,and carotenoids. The action spectrum shows the rate of photosynthesis at different wavelengths.
$3$. Both spectra show peaks in the blue and red regions of the visible light spectrum.
$4$. Specifically,they show peaks in the blue region (approximately $430-470 \ nm$) and the red region (approximately $660-680 \ nm$).
$5$. This confirms that light energy absorbed by chlorophyll $a$ in these specific wavelengths is most effective in driving the photosynthetic process.

(N/A) An action spectrum indicates the rate of photosynthesis at different wavelengths of light. It can be plotted by measuring the rate of photosynthesis (e.g.,oxygen evolution or $CO_2$ uptake) at various specific wavelengths of light and plotting these rates against the corresponding wavelengths.
$(b)$ An absorption spectrum for any substance is derived by measuring the amount of light of different wavelengths absorbed by that substance using a spectrophotometer and plotting the absorbance values against the wavelengths.
$(c)$ The action spectrum and absorption spectrum do not overlap perfectly because chlorophyll-$a$ is the primary pigment,but other accessory pigments like chlorophyll-$b$,xanthophylls,and carotenoids also absorb light energy at different wavelengths and transfer this energy to chlorophyll-$a$. These accessory pigments broaden the range of light absorption and also protect chlorophyll-$a$ from photo-oxidation.

(N/A) $(1)$ Chlorophyll-$a$ appears blue-green in chromatograms,whereas Chlorophyll-$b$ appears yellow-green.
$(2)$ In $PS-I$,the reaction center chlorophyll-$a$ has an absorption peak at $700 \,nm$ (known as $P_{700}$),while in $PS-II$,the reaction center chlorophyll-$a$ has an absorption peak at $680 \,nm$ (known as $P_{680}$).

(B) The statement is incorrect. Chlorophyll $a$ appears bright or blue-green in chromatograms. Chlorophyll $b$ appears yellow-green,Xanthophylls appear yellow,and Carotenoids appear yellow to yellow-orange.

(C) Grana are stacked membranous structures within the chloroplasts of plants and green algae that contain chlorophyll (green pigment).
They are the site of the light-dependent reactions of photosynthesis.
The individual sac-like membranes that make up the grana are known as thylakoids.

(D) The chlorophyll molecule consists of a porphyrin ring (a head) and a phytol tail.
The porphyrin ring is a tetrapyrrole structure with a central $Mg^{2+}$ ion coordinated to the four nitrogen atoms of the pyrrole rings.
Therefore,magnesium $(Mg)$ is the element located at the centre of the porphyrin ring in chlorophyll.

(A) Chlorophyll is the primary pigment found in chloroplasts. The structure of the chlorophyll molecule consists of a porphyrin ring (a tetrapyrrole ring) with a central magnesium $(Mg^{2+})$ ion. When a chloroplast is burnt,the organic components (carbon,hydrogen,oxygen,nitrogen) are oxidized and released as gases,while the mineral component,specifically the magnesium ion,remains as part of the ash.

(C) The Action Spectrum is the curve depicting the relative rate of photosynthesis at different wavelengths of light.
It shows that the maximum rate of photosynthesis occurs in the blue and red regions of the light spectrum.
These regions correspond to the peak absorption regions of chlorophyll-$a$.
Therefore,the action spectrum of photosynthesis is almost identical to the absorption spectrum of chlorophyll-$a$.

(D) Pigments are substances that have the ability to absorb light at specific wavelengths.
Among all pigments,$Chlorophyll-a$ absorbs the maximum amount of light in the blue and red regions of the spectrum.
In these regions,$Chlorophyll-a$ performs the maximum rate of photosynthesis.
Thus,$Chlorophyll-a$ is called the primary photosynthetic pigment.

(A) The absorption spectrum of photosynthetic pigments shows that Chlorophyll-$a$ is the primary pigment involved in photosynthesis.
Chlorophyll-$a$ shows maximum absorption in the blue and red wavelengths of the visible light spectrum.
These regions correspond to the peaks of the absorption spectrum,which drive the light-dependent reactions of photosynthesis.
Therefore,Chlorophyll-$a$ is the correct answer.

(C) The Light Harvesting Complex $(LHC)$ consists of hundreds of pigment molecules bound to proteins.
These pigments include chlorophyll-$a$,chlorophyll-$b$,and carotenoids.
They help in absorbing light energy and transferring it to the reaction center.

(D) The molecular formulas for chlorophyll-$a$ and chlorophyll-$b$ are as follows:
Chlorophyll-$a$: $C_{55}H_{72}O_{5}N_{4}Mg$
Chlorophyll-$b$: $C_{55}H_{70}O_{6}N_{4}Mg$
Chlorophyll-$b$ differs from chlorophyll-$a$ by having a formyl group $(-CHO)$ instead of a methyl group $(-CH_{3})$ at the third carbon position of the porphyrin ring. This substitution results in the loss of two hydrogen atoms and the gain of one oxygen atom compared to chlorophyll-$a$.

(B) $(I)$ $PS-I$ contains a higher proportion of chlorophyll-a compared to chlorophyll-b (approximately $2:1$ ratio).
$(II)$ $PS-II$ contains chlorophyll-a and chlorophyll-b in roughly equal amounts,or sometimes slightly more chlorophyll-a,but it does not have more chlorophyll-b than chlorophyll-a.
Therefore,statement $I$ is correct and statement $II$ is incorrect.

(A) Chlorophylls are magnesium porphyrin compounds. Chlorophyll-$a$ $(C_{55}H_{72}O_{5}N_{4}Mg)$ and chlorophyll-$b$ $(C_{55}H_{70}O_{6}N_{4}Mg)$ both consist of a magnesium porphyrin head,which is hydrophilic,and a phytol tail,which is lipophilic.
Chlorophyll-$b$ differs from chlorophyll-$a$ only in one of the functional groups bonded to the porphyrin ring.
Specifically,in chlorophyll-$b$,there is a $-CHO$ (aldehyde) group instead of a $-CH_{3}$ (methyl) group at the third carbon atom in the second pyrrole ring.

(D) $Photosystem$ $(PS)$ consists of a $Reaction$ $Centre$ surrounded by many $Light$ $Harvesting$ $Complexes$ $(LHCs)$.
These $LHCs$ are composed of hundreds of pigment molecules bound to proteins,including chlorophyll $a$,chlorophyll $b$,and accessory pigments like carotenoids and xanthophylls.
Since both the $Light$ $Harvesting$ $Complex$ and the $Reaction$ $Centre$ (which contains accessory pigments) are integral parts of the $Photosystem$,option $D$ is the correct answer.

(D) Chlorophyll-$a$ is the primary pigment and is soluble in petroleum ether. It shows maximum absorption peaks at approximately $430 \ nm$ and $662 \ nm$.
Chlorophyll-$b$ is an accessory pigment and is soluble in methyl alcohol. It shows maximum absorption peaks at approximately $453 \ nm$ and $642 \ nm$.
In the molecular structure of chlorophyll-$b$,the methyl group $(-CH_3)$ present at the $3-C$ position in chlorophyll-$a$ is replaced by an aldehyde group $(-CHO)$.
Therefore,the statement regarding the biosynthesis of chlorophyll using succinyl $CoA$ and glycine is the correct biological fact,as these are the precursors for the porphyrin ring synthesis.

(B) The Assertion is correct: Carotenoids act as accessory pigments that protect chlorophyll molecules from photooxidation by absorbing excess light energy and dissipating it as heat.
The Reason is also correct: Carotenoids absorb light in the blue-violet region and transfer this energy to chlorophyll $a$,thereby expanding the range of wavelengths that can be used for photosynthesis.
Since both statements are scientifically accurate and describe distinct functional roles of carotenoids,the Reason does not directly explain the mechanism of protection mentioned in the Assertion. Therefore,both are correct but the Reason is not the correct explanation of the Assertion.

(A) Chlorophyll is the primary photosynthetic pigment found in plants.
In eukaryotic cells,photosynthesis occurs within organelles called chloroplasts.
Inside the chloroplast,the thylakoid membranes contain the photosystems and chlorophyll pigments necessary for the light-dependent reactions of photosynthesis.
Therefore,the correct location of chlorophyll is the thylakoid membrane.

(A) Chlorophyll is a magnesium-porphyrin complex,meaning that $Mg^{2+}$ is the central metal ion in the structure of the chlorophyll molecule.
Iron $(Fe)$ is not a structural component of chlorophyll,but it is essential for the synthesis of chlorophyll because it acts as a cofactor for enzymes involved in the chlorophyll biosynthetic pathway.
Therefore,$Mg$ is required for the structure,and $Fe$ is required for its synthesis.

(B) Photosynthesis primarily utilizes the visible spectrum of light,specifically the range known as Photosynthetically Active Radiation $(PAR)$.
$PAR$ ranges from $400 \ nm$ to $700 \ nm$ in wavelength.
Chlorophyll pigments absorb light most efficiently in the blue and red regions of this visible spectrum.
$UV$ rays and infrared rays are generally not used for the light-dependent reactions of photosynthesis.

(D) In higher plants,the pigments involved in photosynthesis are primarily categorized into four types based on paper chromatography:
$1$. Chlorophyll $a$ (bright or blue-green in the chromatogram).
$2$. Chlorophyll $b$ (yellow-green).
$3$. Xanthophylls (yellow).
$4$. Carotenoids (yellow to yellow-orange).
Therefore,there are $4$ main types of pigments found in the leaves of higher plants.

(A) The molecular formulas and approximate molecular weights of these photosynthetic pigments are as follows:
$1$. Chlorophyll $a$ $(C_{55}H_{72}O_5N_4Mg)$: Molecular weight $\approx 893.5 \text{ g/mol}$.
$2$. Chlorophyll $b$ $(C_{55}H_{70}O_6N_4Mg)$: Molecular weight $\approx 907.5 \text{ g/mol}$.
$3$. Xanthophylls (e.g., Lutein, $C_{40}H_{56}O_2$): Molecular weight $\approx 568.8 \text{ g/mol}$.
$4$. Carotenoids (e.g., $\beta$-carotene, $C_{40}H_{56}$): Molecular weight $\approx 536.8 \text{ g/mol}$.
Comparing these values, the order from higher to lower molecular weight is: Chlorophyll $b$ $(907.5)$ > Chlorophyll $a$ $(893.5)$ > Xanthophylls $(568.8)$ > Carotenoids $(536.8)$.
Thus, the correct sequence is Chlorophyll $b$ > Chlorophyll $a$ > Xanthophylls > Carotenoids.

(B) The correct matches for the photosynthetic pigments and their colors are as follows:
$1$. Chlorophyll $a$: Bright or blue-green $(P-III)$
$2$. Chlorophyll $b$: Yellow-green $(Q-II)$
$3$. Carotenoids: Yellow to yellow-orange $(R-I)$
$4$. Xanthophylls: Yellow $(S-IV)$
Therefore, the correct matching is $(P-III), (Q-II), (R-I), (S-IV)$.

(A) In the light-harvesting complex of photosynthesis,various pigments (accessory pigments) absorb light energy and transfer it to the reaction center. The reaction center is composed of a specific molecule of Chlorophyll-$a$. This molecule is responsible for the primary photochemical reaction,where it loses an electron upon excitation,initiating the electron transport chain.

(D) Accessory pigments are pigments that absorb light energy and transfer it to chlorophyll-$a$,which is the primary pigment involved in photosynthesis.
Chlorophyll-$b$,carotenoids,and xanthophylls all function as accessory pigments.
They broaden the spectrum of light that can be absorbed for photosynthesis and also protect chlorophyll-$a$ from photo-oxidation.
Therefore,all the given options are correct.

(A) In a photosystem,the reaction center is formed by a single molecule of chlorophyll-$a$.
This chlorophyll-$a$ molecule acts as the primary electron donor in the light-dependent reactions of photosynthesis.
While there are hundreds of accessory pigment molecules (such as chlorophyll-$b$,carotenoids,and xanthophylls) that form the light-harvesting complex $(LHC)$,the reaction center itself consists of only one molecule of chlorophyll-$a$.

(B) The pigments involved in photosynthesis exhibit specific colors in chromatograms:
$1$. Chlorophyll $a$ appears as bright or blue-green in the chromatogram.
$2$. Chlorophyll $b$ appears as yellow-green.
$3$. Xanthophylls appear as yellow.
$4$. Carotenoids appear as yellow to yellow-orange.
Therefore,the correct matching is: $A-III, B-I, C-II, D-IV$.

(B) Chloroplasts are double-membrane organelles found in plant cells.
Inside the chloroplast,there is a system of flattened,sac-like structures called thylakoids.
The membranes of these thylakoids contain photosynthetic pigments such as chlorophyll $a$,chlorophyll $b$,and carotenoids.
These pigments are essential for capturing light energy during the light-dependent reactions of photosynthesis.
Therefore,the correct location for photosynthetic pigments is the thylakoid membrane.

(A) In paper chromatography,pigments are separated based on their solubility in the solvent system.
Chlorophyll $a$ is the primary photosynthetic pigment and appears blue-green in the chromatogram.
Chlorophyll $b$ is an accessory pigment and appears yellow-green in the chromatogram.
Therefore,the correct sequence is blue-green and yellow-green.

(B) According to the paper chromatography of leaf pigments,the colours observed are as follows:
$1$. Chlorophyll '$b$' appears as Yellow green $(t)$.
$2$. Carotenoids appear as Yellow to Yellow orange $(p)$.
$3$. Chlorophyll '$a$' appears as Blue green $(s)$.
$4$. Xanthophylls appear as Yellow $(r)$.
Therefore,the correct matching is $1-t, 2-p, 3-s, 4-r$.

(B) The correct answer is $B$.
Plastoquinone $(PQ)$ is a mobile electron carrier in the electron transport chain of photosynthesis.
It is functionally associated with the movement of electrons from Photosystem $II$ to the Cytochrome $b_6f$ complex.
Chlorophyll-$b$ is an accessory pigment that transfers energy to chlorophyll-$a$ and is primarily found in the light-harvesting complexes of Photosystem $II$,where Plastoquinone acts as the primary electron acceptor.